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Municipal Solid Waste and Leachate Characterization in the Cairo Metropolitan Area

Municipal Solid Waste and Leachate Characterization in the Cairo Metropolitan Area resources Article Municipal Solid Waste and Leachate Characterization in the Cairo Metropolitan Area 1 2 3 4 , Maged A. Hussieny , Mohamed S. Morsy , Mostafa Ahmed , Sherien Elagroudy * and Mohamed H. Abdelrazik Public Works Department, Faculty of Engineering, Ain Shams University, 1 El-Sarayat Street, Cairo 11535, Egypt Soil Mechanics & Foundation Engineering Group, Structural Engineering Department, Faculty of Engineering, Ain Shams University, 1 El-Sarayat Street, Cairo 11535, Egypt Civil Engineering Department, Faculty of Engineering, Higher Technological Institute, Tenth of Ramadan City 44629, Egypt Egypt Solid Waste Management Center of Excellence, Ain Shams University, 1 El-Sarayat Street, Cairo 11535, Egypt * Correspondence: s.elagroudy@eng.asu.edu.eg; Tel.: +20-1006070032 Abstract: The composition of municipal solid waste (MSW) in the Cairo metropolitan area is in- vestigated. The outputs of MSW sorting analysis at various locations in Cairo with different waste management schemes are presented. Organics (58–75%) and plastic waste (19–28%) are the main components of MSW in Cairo with a higher percentage of organics in landfills compared to dump- sites. The leachate quality is analyzed, and the analysis results indicate that the concentration of 4+ + 2+ 2+ 2+ macro inorganic pollutants (NH , Na , Ca , and Cl ) and heavy metals (e.g., Cd and Zn ) are exceeding the majority of values reported in the literature in various cities all over the world. There was no evidence of an effect of the recycling process on chloride concentration in leachate, while the concentration of iron was reduced. The variation of leachate quality with time for two samples collected from the same municipal solid waste landfill is presented. The first leachate sample is Citation: Hussieny, M.A.; Morsy, a two-year-old, and the second sample is a sixteen-year-old. There was a significant increase in the M.S.; Ahmed, M.; Elagroudy, S.; concentration of chloride, sodium, chromium, calcium, and magnesium. The implications of the Abdelrazik, M.H. Municipal Solid Waste and Leachate Characterization leachate quality in Cairo on the longevity of barrier systems in an MSW landfill are discussed. in the Cairo Metropolitan Area. Resources 2022, 11, 102. https:// Keywords: municipal solid waste; waste stream; landfills; municipal solid waste leachate; leachate doi.org/10.3390/resources11110102 age; barrier systems; geomembranes Academic Editors: Ben McLellan and Elena Rada Received: 9 August 2022 1. Introduction Accepted: 27 October 2022 Municipal solid waste (MSW) composition varies from one country to another, and Published: 1 November 2022 even inside the same country, due to differences in cultural background, income level, Publisher’s Note: MDPI stays neutral waste management scenarios, and social circumstances [1–3]. The municipal solid waste with regard to jurisdictional claims in leachate is formed due to the leaching of soluble salts and biodegraded organic components published maps and institutional affil- inside the waste mass by rainfall or moisture percolating through the waste. Subsequently, iations. the composition of leachate varies between different regions due to the variability of waste decomposition besides other factors such as rate of rainfall, ambient temperature, rate of waste disposal, and daily cover that contributes to the suspended solids in the waste [3,4]. Municipal solid waste leachate is a complex fluid with characteristics that varies over the Copyright: © 2022 by the authors. different phases of the leachate starting from the acetogenic phase for young leachate to Licensee MDPI, Basel, Switzerland. the methanogenic phase for older leachate [5]. The MSW leachate is composed primarily This article is an open access article of dissolved organic, inorganic, and xenobiotic compounds, inorganic ions, and heavy distributed under the terms and metals [6–8]. The concentration of various elements and compounds in the MSW varies conditions of the Creative Commons with time [9] due to several factors such as variations in a waste stream, rate of waste Attribution (CC BY) license (https:// disposal, and changes in organic loading attributed to the biodegradation of waste [10]. creativecommons.org/licenses/by/ 4.0/). Resources 2022, 11, 102. https://doi.org/10.3390/resources11110102 https://www.mdpi.com/journal/resources Resources 2022, 11, 102 2 of 21 Proper waste management is crucial since poor waste management could have an ad- verse effect on the environment and the health of living organisms. Indeed, the long-term cost associated with poor waste management could be higher than primary proper waste management [11]. Waste disposal has developed from dump sites at which the waste is in direct contact with the ground to engineered landfills that comprise base barriers that separate the waste from groundwater [12]. Landfilling is the most common waste disposal method in many countries [13–15], and landfills are the destination for waste either directly from the source (if landfilling is adopted solely as a waste management system), or the residual waste by-product from other waste management techniques [13]. This could be attributed to the relatively low construction and operation cost relative to other waste disposal methods [16]. Reduction of waste volume disposed into a landfill could be needed if the land area assigned for landfilling is limited, or to increase the landfill’s cells capacity to extend the service time of an existing landfill without the need to construct a new one. Waste volume reduction methods include (a) waste compaction, (b) landfill bioreactors, (c) recycling, (d) composting, and (e) waste incineration. Waste compaction aims to reduce the air voids entrapped inside the waste mass, subsequently reducing the total waste volume and increasing the air space in a landfill [17]. Landfill bioreactors involve air and/or liquid circulation within the waste mass to motivate the aerobic bacterial processes (in presence of oxygen) or anaerobic waste biodegradation (in absence of oxygen) [18,19]. Both processes result in accelerated waste biodegradation in less time and hence increased landfill air space is obtained. Recycling is a waste diversion process that aims to reduce the waste mass and volume disposed into a landfill through the separation of waste either at the source or at a recycling plant, followed by the collection of similar waste components, then the manufacturing of marketable products [20–22]. Another waste diversion process is composting (mechanical biological treatment) which involves the bio decomposition of organic waste under controlled aerobic conditions into a humus-like product, known as compost, which can be used in land remediation, restoration, and agriculture [23–26]. Finally, incineration of waste involves burning the waste inside an incinerator turning the waste into bottom ash, fly ash, air pollution control residues, and gaseous products principally carbon dioxide and water vapor [27,28]. This process reduces the waste volume by approximately 90% [29], with the remaining volume of waste either diverted or landfilled. Each of the foregoing waste reduction approaches has advantages and disadvantages. Recycling provides a sustainable solution that promotes the waste value and turns it into products, but the revenue of waste reduction, increasing air space in a landfill, and selling recycled materials shall overweight the cost of separation, recycling awareness campaigns, and recycling plants. Similarly, waste composting results in a 20–40% reduction in waste volume [30]. However, high heavy metal concentrations in compost applied to food crops, especially partially oxidized ones, might have an adverse effect on crop yields. Moreover, higher metal concentrations were reported for composted soil and plants [25,31–33]. The Waste Framework Directive (2008) considered waste disposal through landfilling as the least preferable scenario and favored waste reduction, reuse, recycling, and recovery, respectively. Nevertheless, this recommendation [34] was describing waste management alternatives for more developed countries. In contrast to developed countries, engineered landfills are considered a reasonable waste management development from uncontrolled dumping practices in less developed countries [35]. Therefore, Egyptian environmental authorities decided to construct several engineered modern landfills in various governorates in the country along with intermediate waste transfer stations to increase the waste collection efficiency and protect the environment. A notable number of these landfills are located in the Cairo metropolitan area, since it is the most populous region in Egypt (20 million residents), with the greatest share of the amount of waste generated in Egypt with more than six million tons of waste generated annually [36] out of the twenty-one million tons/year produced all over Egypt [37]. However, these landfills could provide a relatively cheap Resources 2022, 11, x FOR PEER REVIEW 3 of 23 annually [36] out of the twenty-one million tons/year produced all over Egypt [37]. How- Resources 2022, 11, 102 3 of 21 ever, these landfills could provide a relatively cheap waste disposal solution and protect the environment if designed properly. The first step towards a sustainable design of an MSW landfill is proper identification of the waste stream, the chemical composition of waste disposal solution and protect the environment if designed properly. The first step effluent leachate, and the variation of the leachate quality over time. Thus, the objectives towards a sustainable design of an MSW landfill is proper identification of the waste stream, of this study are (i) to analyze the composition of the waste stream for various scenarios the chemical composition of effluent leachate, and the variation of the leachate quality of waste management in the Cairo metropolitan area, (ii) to identify the leachate quality over time. Thus, the objectives of this study are (i) to analyze the composition of the waste in a dumpsite, a landfill after the recycling process, as well as a landfill that receives waste stream for various scenarios of waste management in the Cairo metropolitan area, (ii) to directly from the source, and (iii) to present and analyze the variation in the concentration identify the leachate quality in a dumpsite, a landfill after the recycling process, as well as of leachate with time in one of Cairo’s major MSW landfills. a landfill that receives waste directly from the source, and (iii) to present and analyze the variation in the concentration of leachate with time in one of Cairo’s major MSW landfills. 2. Field and Experimental Investigation 2.1. Study Scope 2. Field and Experimental Investigation 2.1. Study The geog Scope raphic scope of the study is the Cairo metropolitan area (Figure 1). This study involved three districts: (1) Southern and Western districts of Cairo (15th May land- The geographic scope of the study is the Cairo metropolitan area (Figure 1). This study fill), (2) Northern and Eastern Cairo (El-obour landfill, and El-wafaa & El-amal landfill), involved three districts: (1) Southern and Western districts of Cairo (15th May landfill), and (3) Giza (Shabramant dumpsite). The waste in the Northern and Eastern regions is (2) Northern and Eastern Cairo (El-obour landfill, and El-wafaa & El-amal landfill), and initially placed at a transfer station, then separated in an MSW recycling plant, and finally (3) Giza (Shabramant dumpsite). The waste in the Northern and Eastern regions is initially disposed of at El-Obour landfill (at the time of this study) and previously disposed of at placed at a transfer station, then separated in an MSW recycling plant, and finally disposed El-Wafaa & El-Amal landfill. In the Southern and Western regions, the waste is collected of at El-Obour landfill (at the time of this study) and previously disposed of at El-Wafaa from the source, then transferred to a waste treatment and disposal facility, where organic & El-Amal landfill. In the Southern and Western regions, the waste is collected from the waste is composted, recyclables separated, and the non-recyclable portion is disposed of source, then transferred to a waste treatment and disposal facility, where organic waste is at the May 15 landfill. In contrast, the waste was disposed of directly into the Shabramant composted, recyclables separated, and the non-recyclable portion is disposed of at the May dumpsite without intermediate processing. The composition of MSW in each region was 15 landfill. In contrast, the waste was disposed of directly into the Shabramant dumpsite without examineintermediate d at various pr diocessing. sposal locat The ions: composition the transfer of MSW station, in rec each ycl region ing plan was t, and examined landfill at. various Therefore disposal , this study locations: investigate the transfer s the eff station, ect of va recycling rious com plant, binations and landfill. of waste Ther man efor agemen e, thist study methods investigates on the com the po ef sit fect ion of of various MSW d combinations umped in a lan ofdfill, waste and management subsequenmethods tly, the leach on the ate composition composition.of MSW dumped in a landfill, and subsequently, the leachate composition. Figure 1. Municipal solid waste and leachate sampling locations in the Cairo metropolitan area. Figure 1. Municipal solid waste and leachate sampling locations in the Cairo metropolitan area. 2.2. Waste Composition Analysis 2.2. Waste Composition Analysis Waste composition analysis was performed at nine sites. These sites were selected Waste composition analysis was performed at nine sites. These sites were selected to to track the waste composition through the different regions of the Cairo metropolitan track the waste composition through the different regions of the Cairo metropolitan area area from the source to the final destination in the three aforementioned districts in Cairo. from the source to the final destination in the three aforementioned districts in Cairo. The The nine sites were selected to represent the waste composition at collection, transfer, nine sites were selected to represent the waste composition at collection, transfer, and dis- and disposal sites as follows: three sites where the waste was directly collected from the posal sites as follows: three sites where the waste was directly collected from the source source without any losses, a transfer station, two recycling plants, a dumpsite (Shabramant, without any losses, a transfer station, two recycling plants, a dumpsite (Shabramant, Giza, Giza, Egypt), and two landfills. The dumpsite (Shabramant in Giza) had neither a barrier Egypt), and two landfills. The dumpsite (Shabramant in Giza) had neither a barrier sys- system, nor a leachate collection system, while the two landfills were the 15th May landfill tem, nor a leachate collection system, while the two landfills were the 15th May landfill in in Southern & Western Cairo, and the El-Obour landfill in Northern & Eastern Cairo. The 15th May landfill was an engineered landfill with a leachate collection system and was receiving waste for three years. The El-obour landfill was a landfill with a barrier system, but without a leachate collection system, and had started receiving waste a few Resources 2022, 11, 102 4 of 21 months before the study. Therefore, the waste analysis in the Northern & Eastern region of Cairo was performed in the El-Obour landfill, while the leachate analysis (Section 2.3) was performed for samples collected from the El-wafaa & El-amal landfill that was closed in 2018. Both landfills were receiving the waste from exactly the same districts and hence the leachate samples collected from El-wafaa & El-amal landfill were considered representative of the waste composition analyzed at the El-obour landfill. The waste composition analysis was performed at the source, transfer stations, recy- cling plants, dumpsites, and landfills before the intervention of scavengers at the inlet of these sites at various times during the study’s duration (March 2020 to March 2021). The waste sorting was conducted in accordance with the American standard test method for the determination of the composition of unprocessed municipal solid waste (ASTM D34) [38]. An approximately clean levelled surface covered with tarpaulin was selected for discharg- ing the load of a random truck. The discharged truck load was moved longitudinally using a front-end loader along one side to obtain a representative waste sample. Three sorting samples were analyzed at each site, each of 91–136 kg to represent the characteristics of a collection truckload. Each sample was sorted manually, and each component of the waste was placed inside a container, then the weight of each waste component and the container was measured using a calibrated scale. The weight of each component was calculated by subtracting the empty container weight, then the fraction weight of each component was estimated as a ratio of the total weight of all waste components. The desired level of precision (e) of the waste composition analysis was estimated based on the number of samples (truck loads; n) of three, viz: t s e =p (1) n  x where, t* (unitless): t-student statistic corresponding to the desired level of confidence; s (unitless): estimated standard deviation; and x (unitless): estimated mean. The major component of the analyzed MSW in Cairo was food waste, hence s and x were assumed as 0.03 and 0.1 based on values provided by [38]. These values were estimated based on MSW analysis data at various locations in the United States of America (ASTM D34). Consequently, the confidence level was estimated using the following equation: Confidence Level = 1 e (2) The confidence level for the analysis results at each site was 71.5%, and could be increased to 80% (6 samples) and 84% (9 samples) on grouping results from various sites. 2.3. Leachate Chemical Analysis MSW leachate samples were collected from two landfills and a dumpsite in Cairo metropolitan area, namely, El-wafaa & El-amal (landfill serving Northern and Eastern Cairo; 16 years old), 15th of May City (landfill serving Southern and Western Cairo; 3 years old), and Shabramant dumpsite (Giza; 15 years old). Samples were collected from the leachate collection sump (El-wafaa & El-amal landfill), or pump station (15th May landfill), and a fresh leachate pond formed at the Shabramant dumpsite. Three samples were collected from each site and stored in polyethylene bottles in a fridge at 4 C. Then the leachate samples were analyzed in accordance with APHA (2005) [39]. The analyzed components were (abbreviation and/or analysis method is mentioned in parenthesis): chemical oxygen demand (COD), biological oxygen demand (BOD), total solids (TS; convection oven dry- ing procedure), organic nitrogen (N; Total Kjeldahl Nitrogen-TKN), ammonium nitrogen (NH ; chromatography mass spectrometry), potential of hydrogen (pH; pH meter), total alkalinity (TA; titration; expressed by % calcium carbonate), volatile fatty acids (TFA; ion- exclusion chromatography), and elements concentration (inductively coupled plasma mass spectrometer and ion chromatography). Resources 2022, 11, 102 5 of 21 3. Results & Discussion 3.1. Waste Composition This section presents the results of waste analysis at the source at the three regions investigated in Cairo, followed by an illustration of the variation of waste composition from the source to the dumpsite/landfill passing by an intermediate transfer station or a recycling plant. Three MSW samples were collected from the source before scavenging activities and their composition was analyzed. The main components of the waste (Table 1) were organics (range: 61% to 71%; confidence level = 71%) and plastics (range: 15–25%; confidence level = 71%). The one-way analysis of variance (ANOVA) between observations of organic, plastics, and textiles waste components fraction at the three zones studied in the Cairo metropolitan area (Northern and Eastern, Southern and Western, and Giza) showed that there was a statistically significant difference (at 95% confidence level) that was greater than would be expected by a chance. Yet the statistical comparison using the student t-test (at 95% confidence level) between every two groups separately had shown that the difference was statistically insignificant between the observations of organics and plastics in Southern and Western Cairo, and Giza. Thus, the source of difference was the waste composition in Eastern and Northern Cairo, and this could be attributed to the difference in socioeconomic conditions among the three studied zones. The Northern and Eastern zone is predominantly urban residential, administrative, and commercial area, whereas Giza involves urban and rural districts. Finally, the Southern and Western zone involves industrial activities. Notwithstanding this statistically significant difference between mean values of observations between the Northern and Eastern zone of Cairo, besides the obvious difference in socioeconomic activities among the three zones under study, the mean waste components fraction at the three zones was estimated to obtain the percentage of each component at 84% confidence level (Table 1) and to compare the obtained waste composition in Cairo (current study) with that reported by the Egyptian environmental affairs agency (EEAA) for the waste composition in Egypt (Figure 2). The organics were 56% [37] and 64% (current study), while the plastics were 13% (EEAA) and 21% (current study). Moreover, the fraction of paper and cardboard reported by [37] for all Egypt was 10% and in Cairo (current study) was 4%. Hence, the percentage of organics and plastics in Cairo is higher and this could indicate a significant difference in waste composition in Cairo compared to other governorates in Egypt, or a change in the socioeconomic conditions since the EEAA report publication time. Similarly, the percentage of organics in Assiut (a governorate located 400 km to the south of Cairo) was 41% [40] which is less than the values in Cairo (60–71%; current study) and [37]. In conclusion, the statistically significant difference in waste composition across various zones of Cairo, and Assiut compared to the averaged values over Egypt [37] suggests that waste composition analysis shall be presented for each region independently and cannot be generalized all over Egypt. Additionally, the waste composition shall be analyzed periodically to monitor the variation in waste composition; this would highlight the socioeconomic changes and could aid in better waste management, the design of recycling systems, and engineering design for landfills. These socioeconomic changes might involve an increase in the usage of lightweight plastic packaging instead of heavier-weight glass and steel cans packaging [41]. This phenomenon is known as an evolving ton, where the recyclable waste has declining tonnage compared to volume [42], and hence material recovery facilities shall do more recyclables processing for a proximate revenue [41]. Resources 2022, 11, x FOR PEER REVIEW 6 of 23 Resources 2022, 11, 102 6 of 21 Table 1. Municipal solid waste composition (mean ± standard deviation) at the source. Table 1. Municipal solid waste composition (mean  standard deviation) at the source. a Waste Northern a & Southern & b c Waste Composition (%) Northern & Eastern Cairo Southern & Western Cairo Giza c Average Values Giza Average Values a a b Composition (%) Eastern Cairo Western Cairo Organics Organics 71 ± 3.4 71  3.4 60± 2.9 60  2.9 61 ± 61  2.8 2.8 64 ± 64  3.0 3.0 Plastics 15 ± 1.7 25 ±2.8 25 ± 2.3 21 ± 2.3 Plastics 15  1.7 25 2.8 25  2.3 21  2.3 Textiles 2.5 ± 0.4 2.4 ± 0.4 7.4 ± 2.4 4.1 ± 1.1 Textiles 2.5  0.4 2.4  0.4 7.4  2.4 4.1  1.1 Paper & Cardboard 4.0 ± 1.4 4.9 ± 1.7 3.1 ± 0.6 4.0 ± 1.2 Paper & Cardboard 4.0  1.4 4.9  1.7 3.1  0.6 4.0  1.2 Diapers 6.1 ± 2.6 7.5 ± 3.2 2.6 ± 0.8 5.4 ± 2.2 Diapers 6.1  2.6 7.5  3.2 2.6  0.8 5.4  2.2 Wood 0.6 ± 1.1 0.0 ± 0.0 1.0 ± 1.4 0.6 ± 0.8 Wood 0.6  1.1 0.0  0.0 1.0  1.4 0.6  0.8 Metals 0.3 ± 0.4 0.4 ± 0.4 0.3 ± 0.3 0.3 ± 0.3 Metals 0.3  0.4 0.4  0.4 0.3  0.3 0.3  0.3 Glass 1.0 ± 1.0 0.0 ± 0.0 0.5 ± 0.5 0.5 ± 0.5 a b Sampling Glass dates: 10 March 2020 1.0,  20 1.0 February 2021 0.0 , and  0.0 27 February 0.5202  0.5 1; Dates of 0.5 sa mpli 0.5ng: 7 Febr a uary 2021, 15 February 2021, and 23 February 2021; Dates of b sampling: 8 February 2021, 16 Sampling dates: 10 March 2020, 20 February 2021, and 27 February 2021; Dates of sampling: 7 February 2021, Febr 15 Fe uary 2021 bruary 2021 , ,and and 2 24 3 F Febr ebrua uar ry 2 y 2021 021; D . ates of sampling: 8 February 2021, 16 February 2021, and 24 February 2021. Organics Plastics Paper & Glass Metals Others Cardboard Waste component EEAA Current study Figure 2. Comparison between the waste composition in Cairo (current study) and the generalized Figure 2. Comparison between the waste composition in Cairo (current study) and the generalized co composition mposition in in Egypt Egypt issued issuedby by the the Egyptian Egyptiaenvir n environm onmental ental affairs affai agency rs agen “Reprinted/adapted cy “Reprinted/adapte with d with permission from Ref. [17]. 2010, the Authors”. permission from Ref. [17]. 2010, the Authors”. MSW was tracked through the successive waste management stages in Northern & MSW was tracked through the successive waste management stages in Northern & Eastern Cairo, from source to El-obour landfill passing through a transfer station and a recy- Eastern Cairo, from source to El-obour landfill passing through a transfer station and a cling plant. Three samples were analyzed at each stage and the waste components fraction recycling plant. Three samples were analyzed at each stage and the waste components was obtained (Table 2). The analysis showed that the organic fraction was reduced, and fraction was obtained (Table 2). The analysis showed that the organic fraction was re- the plastic fraction increased at the transfer station compared to the source. Furthermore, duced, and the plastic fraction increased at the transfer station compared to the source. the coefficient of variation increased from 5.3% and 11.6% to 8.6% and 28.4% for organics Furthermore, the coefficient of variation increased from 5.3% and 11.6% to 8.6% and 28.4% and plastic waste, respectively, indicating greater dispersion around the mean value. Since for organics and plastic waste, respectively, indicating greater dispersion around the the waste at source samples was collected from areas covered with collection services, mean value. Since the waste at source samples was collected from areas covered with col- the results imply direct disposal of waste at the transfer station. Hence, the results imply lection services, the results imply direct disposal of waste at the transfer station. Hence, a deficiency of waste collection coverage in Northern and Eastern Cairo. Comparing the the results imply a deficiency of waste collection coverage in Northern and Eastern Cairo. transfer station samples to that at the recycling plant manifests the scavenging activities oc- Comparing the transfer station samples to that at the recycling plant manifests the scav- curring at the transfer station. For instance, the plastics fraction decreased from 23%  7% enging activities occurring at the transfer station. For instance, the plastics fraction de- to 17%  5%, and the percentage of papers and carboards decreased from 3.3%  1.2% to creased from 23% ± 7% to 17% ± 5%, and the percentage of papers and carboards decreased 1.4%  1.4%. Finally, the MSW landfilled at El-obour landfill was composed of organic from 3.3% ± 1.2% to 1.4% ± 1.4%. Finally, the MSW landfilled at El-obour landfill was waste (75%  4.4%) and plastics unsuitable for reprocessing (20%  3.6%), and textiles composed of organic waste (75% ± 4.4%) and plastics unsuitable for reprocessing (20% ± (5.2%  5.2%). The textile fraction of the landfilled waste was minor. However, the coeffi- 3.6%), and textiles (5.2% ± 5.2%). The textile fraction of the landfilled waste was minor. cient of variation for the textiles waste reaching the landfills was 100% (mean = standard However, the coefficient of variation for the textiles waste reaching the landfills was 100% deviation) because the data points were highly distant from the mean implying a significant (mean = standard deviation) because the data points were highly distant from the mean variability in the landfilled textiles waste fraction. implying a significant variability in the landfilled textiles waste fraction. Percentage (%) Resources 2022, 11, 102 7 of 21 Table 2. Municipal solid waste composition (mean  standard deviation) in the various waste management stages in Northern & Eastern Cairo; rounded to two significant digits. Waste Transfer Recycling Landfill Source Composition (%) Station Plant (El-Obour Landfill) Organics 71  3.4 63  5.4 65  3.4 75  4.4 Plastics 15  1.7 23  6.5 17  5.0 20  3.6 Textiles 2.5  0.4 3.9  2.0 6.0  7.0 5.2  5.2 Paper & Cardboard 4.0  1.4 3.3  1.2 1.4  1.4 0.0  0.0 Diapers 6.1  2.6 5.3  1.4 8.1  4.0 0.2  0.3 Wood 0.6  1.1 0.0  0.0 1.3  2.3 0.0  0.0 Metals 0.3  0.4 0.0  0.0 0.8  0.8 0.0  0.0 Glass 1.0  1.0 1.6  1.4 0.9  1.1 0.0  0.0 Sampling dates: 10 March 2020, 20 February 2021, and 27 February 2021. In Southern & Western Cairo, waste collected from the source was processed at a recycling plant before disposal at the landfill. Waste composition analyses were performed to obtain the waste component fraction at the source, recycling plant, and landfill (Table 3). Plastics, textiles, paper, and cardboard fractions decreased at the recycling plant compared to the source, and consequently, the organic waste fraction increased. The statistical comparison between the organic and plastics fraction at the recycling plant and the landfill using the student t-test (confidence level = 95%) showed that the difference in the mean values between the two groups was not great enough and it could be relevant to random variability in sampling. For instance, the p-value (probability that difference between observations occurred by chance) was 0.518 (>0.05) for organics and 1.00 (>0.05) for plastics. The higher coefficient of variation for organics in the landfill (COV = 10%) compared to the recycling plant (COV = 1%) could be attributed to the presence of a composting plant at 15th May city in the vicinity of the landfill analyzed herein. Table 3. Municipal solid waste composition (mean  standard deviation) in the various waste management stages in Southern & Western Cairo; rounded to two significant digits. a b Waste Composition (%) Source Recycling Plant Landfill (15th May Landfill) Organics 61  2.9 74  0.8 71  7.3 Plastics 25  2.8 19  1.5 19  5.9 Textiles 2.4  0.4 0.7  1.1 6.2  5.7 Paper & Cardboard 4.9  1.7 1.3  0.4 0.0  0.0 Diapers 7.5  3.2 3.4  1.4 4.1  3.9 Wood 0.0  0.0 0.5  0.7 0.0  0.0 Metals 0.4  0.4 0.0  0.0 0.0  0.0 Glass 0.0  0.0 1.1  0.1 0.0  0.0 a b Sampling dates: 7 February 2021, 15 February 2021, and 23 February 2021; Composting plant exists in the vicinity of the 15th May landfill. In Giza, the waste was transferred directly from the source to the dumpsite without intermediate waste reduction processes. Thus, the waste components were analyzed at the source and Shabramant dumpsite (Table 4). The difference in mean values of all waste components with the exception of glass was not great enough (p > 0.05) suggesting that the Resources 2022, 11, 102 8 of 21 source of this difference was random variability in sampling. Furthermore, this statistically insignificant difference could be attributed to the absence of any waste reduction processes in Giza such as recycling and composting. Additionally, most of the scavenging activities probably occur at the dumpsite in this zone. Table 4. Municipal solid waste composition (mean  standard deviation) in the various waste management stages in Giza; rounded to two significant digits. a b Waste Composition (%) Source Dumpsite Organics 61  2.8 58  7.1 Plastics 25  2.3 28  6.6 Textiles 7.4  2.4 4.2  1.4 Paper & Cardboard 3.1  0.6 3.2  1.2 Diapers 2.6  0.8 1.9  1.9 Wood 1.0  1.4 1.1  1.9 Metals 0.3  0.3 0.6  0.5 Glass 0.5  0.5 2.7  1.2 a b Sampling dates: 8 February 2021, 16 February 2021, and 24 February 2021; Composting plant exists in the vicinity of 15th May landfill. In short, the waste management processes had an obvious effect on the waste compo- nents fraction disposed of at the landfill or the dumpsite. The recycling process resulted in a reduction in plastics (25% to 19%) and an increase in organics (61% to 74%) as evident from the waste analysis in Southern and Western Cairo, and Giza (Tables 3 and 4). The waste management in the earlier zone involved the recycling process, while the latter did not involve the recycling process. Both zones had statistically insignificant differences between the mean values of organics and plastics fraction in the source. The increase in organic fraction associated with the recycling process can be reduced by composting considering environmental protection measurements. The foregoing results present the waste composition along the waste track from source to disposal at a dumpsite or a landfill. These results could not be used to assess the efficiency of waste recovery by recycling due to the scavenging activities which are common in Cairo at source, transfer stations, and recycling plants. 3.2. Leachate Composition Leachate samples were collected from two landfills and a dumpsite in Cairo metropoli- tan area and were analyzed according to the parameters indicated by [43] for leachate characterization (Table 5). ANOVA one-way analyses were performed to compare the mean values of the concentration of various elements composing the leachate. The difference between the mean values of all concentrations was statistically significant (at confidence level = 95%) and greater than would be expected by chance, except for the BOD and NH . This finding was in good agreement with the statistical comparison between the waste components fraction at these zones of Cairo metropolitan area. Similarly, the difference in the mean values of the leachate concentrations was statistically significant (confidence level = 95%) with the exception of BOD, TFA, N , and NH , while the difference in the org mean values of the waste component fraction between Giza and Southern and Western Cairo was statistically insignificant (at confidence level = 95%). This statistically significant difference in leachate quality between the two waste streams of statistically insignificant difference could be relevant to various factors. The most important is that the leachate samples were collected from the waste stream in the dumpsite (Giza), since there was no leachate collection system at that site, while in the landfill (Southern and Western Cairo) the leachate samples were collected from a leachate collection system. Although samples collected from a well within the waste mass should have higher strength than those col- Resources 2022, 11, 102 9 of 21 lected from a leachate collection system [44,45], the strength of the leachate collected from the dumpsite was mostly less than the one collected from the leachate collection system in the landfill based on the concentration of various leachate parameters (Table 5). This could be attributed to the difference in leachate age at both sites (fifteen years for the Shabramant dumpsite, and three years for the 15th May landfill). Similarly, the leachate samples collected from El-waffa & El-amal landfill (Northern & Eastern Cairo; 16-year- old; TDS = 45,800 ppm) could have lower TDS compared to the leachate collected from the 15th May landfill (Southern & Western Cairo; 3-year-old; TDS = 88,700 ppm) due to various factors such as the difference in waste composition and age, the efficiency of the leachate collection system (clogging, leachate flow rate), and the variation concentration of key contaminants in leachate with time. The range of leachate quality concentrations was estimated (Table 5) for comparison purposes with leachate quality presented in the literature in different regions/countries over the world (Tables 6 and 7). Table 5. Leachate composition (mean  standard deviation) in Cairo metropolitan area; digits are rounded to three significant digits. Southern & Western Northern & Eastern Giza (Shabramant Parameter Unit Cairo Landfill Cairo (El-Wafaa & Range Dumpsite) b c (15th May Landfill) El-amal Landfill) COD mg/L 29,500  1470 24,600  1230 23,300  1160 23,300–29,500 BOD mg/L 4530  1380 3880  660 4860  830 3880–4860 pH - 6.14  0.06 6.30  0.06 8.14  0.08 6.14–8.14 TFA mg/L 1.98  0.10 1.74  0.09 1.45  0.07 1.45–1.98 TDS mg/L 72,600  4360 88,700  5320 45,800  2750 45,800–88,700 NH mg/L 2460  120 2550  130 2250  110 2250–2550 N mg/L 390  20.0 380  20.0 340  20.0 340–390 org CaCO mg/L 26,000  1300 30,000  1500 24,000  1200 24,000–30,000 Na mg/L 18,900  380 22,000  440 12,500  250 12,500–22,000 2+ Ca mg/L 9800  490 133,00  660 2320  120 2320–13,300 2+ Mg mg/L 6620  130 5640  110 530  10.0 530–6620 2+ Mn mg/L 20.6  0.41 9.90  0.20 0.25  0.01 0.25–20.6 2+ Fe mg/L 317  6.34 129  2.58 9.50  0.19 9.50–317 Cl mg/L 14,000  700 28,000  1400 11,000  550 11,000–28,000 SO mg/L 400  10.0 980  20.0 770  20.0 400–980 PO mg/L 0.30  0.01 71.0  1.42 0.08  0.00 0.08–71.0 3+ Cr mg/L 1.00  0.02 0.21  0.00 0.89  0.02 0.21–1.00 2+ Cd mg/L 0.60  0.01 0.09  0.00 0.01  0.00 0.01–0.60 2+ Pb mg/L 0.70  0.01 0.80  0.02 0.86  0.02 0.70–0.86 2+ b Zn mg/L 37.4  0.75 0.50  0.01 <0.01 <0.01–37.4 a b c Sampling dates: 8, 16, and 24 February 2021; Sampling dates: 7, 15, and 23 February 2021; 1, 6, and 10 March 2020; based on the minimum and maximum mean values obtained in the three zones investigated in Cairo; below detection limit; COD: Chemical oxygen demand; BOD: Biological oxygen demand; TFA: + 3 trifluoroacetic acid; TDS: total dissolved solids; NH : ammonium; N organic nitrogen; PO : phosphate; org: 4 4 2 + CaCo3: Calcium carbonate and it expresses total alkalinity of leachate; Cl : chloride; SO : sulfate; Na : sodium; 2+ 2+ 2+ 2+ 2+ 2+ 3+ Mg : magnesium; Ca : calcium; Zn : zinc; Mn : manganese; Fe : iron; Cd : cadmium; Cr : chromium; 2+ Pb : lead. Resources 2022, 11, 102 10 of 21 Chemical oxygen demand (COD) ranged between 23,300 and 29,500 mg/L, while biological oxygen demand (BOD ) range was 3880–4860 mg/L. Thus, the BOD /COD 5 5 ranged between 0.15 and 0.21 indicating young leachate in the landfills and dumpsite examined [46]. The COD range in Cairo was only preceded by the leachate collected from the United Kingdom and Nova Scotia, Canada ([47,48]; Tables 6 and 7). Similarly, the BOD was higher than all leachates presented in Tables 6 and 7, except for that reported by [47] in the United Kingdom. This high BOD value might indicate relatively higher organic constituents in the leachate in Cairo, or deficiency in the leachate collection system in the landfills examined [49]. The leachate samples collected from the Shabramant dumpsite (Giza), and the 15th May landfill (Southern and Western Cairo) were slightly acidic (pH= 6.14–6.30), while the leachate samples collected from El-wafaa & El-amal landfill (Northern and Eastern Cairo) were slightly basic (pH = 8.14). These values reflected the landfill age (Shabramant dumpsite: fresh leachate collected from the waste mass; 15th May landfill: 3 years; El Wafaa & El-Amal: 16 years) with lower pH values for relative new landfills (pH = 4.5–7.5) and relative higher pH values (pH closer to 9) for relatively old landfills [50,51]. The concentration range of macro inorganic constituents (Table 5) was higher than the typical ranges for MSW landfills indicated by [43]. For instance, the concentration of am- + + monium (NH ) was 2250–2550 mg/L (typical values: 50–2200 mg/L), sodium (Na ) was 2+ 12,500–22,000 mg/L (typical values: 70–7700 mg/L), Calcium (Ca ) was 2320–13,300 mg/L (typical values: 10–7200 mg/L), and chloride was 11,000–28,000 mg/L (typical values: 2+ 150–4500 mg/L). Similar high concentrations of Ca were reported for a landfill in Riyadh, Saudi Arabia [52] and Nova Scotia, Canada [48] as presented in Tables 6 and 7. The concen- tration of chloride in the leachate samples collected in Cairo (11,000–28,000 mg/L; current study) and other samples from another Egyptian mega-city, Alexandria (11,400 mg/L; [53]) were far higher than counterparts presented in Tables 6 and 7 with the exception for the leachate collected from landfills in Germany [6,54]. The heavy metals concentrations detected in the leachate were 9.5–317 mg/L (iron; 2+ 2+ 3+ Fe ), 0.01–0.60 mg/L (cadmium; Cd ), 0.21–1.0 (chromium; Cr ), and <0.01–37.4 (zinc; 2+ Zn ). These values were higher than the typical values that could be encountered in an 3+ 2+ MSW landfill young leachate [55]. These typical values are 1 mg/L (Cr ), 0.1 mg/L (Cd ), 2+ 2+ 1 mg/L (Pb ), and 0.01 mg/L (Zn ). These findings are common in developing countries due to the uncontrolled disposal of industrial and electronic waste in MSW streams [56]. More important these findings showed the positive impact of intermediate processing of waste, either in a transfer station or a recycling plant, on the reduction of heavy metals concentration in leachate. This was obvious from the higher heavy metals concentration in leachate collected from Shabramant, Giza (waste directly disposed from source to the dumpsite) compared to leachate collected in the landfills located at Northern and Eastern Cairo; Southern and Western Cairo and was subjected to intermediate processing. For 2+ example, the concentration of Fe was 317  6.34 (Table 5) compared to 9.50  0.19 (El- Wafaa & El-Amal landfill) and 129  2.58 (15th May landfill). Similarly, the concentration 2+ of Zn was 37.4  0.75 at Shabaramant dumpsite, 0.50  0.01 (15th May landfill), and <0.01 (below detection limit; El- wafaa & El-amal landfill). Furthermore, the highest 2+ Cd concentration among the leachates presented in Tables 6 and 7, was detected in the leachate collected from Shabramant dumpsite (0.60  0.01 mg/L; current study), followed by leachates collected from two sites in Zhejiang, China (0.24–0.60 mg/L; [57]), then the leachate collected from Alexandria, Egypt (0.09  0.03 mg/L; [53]). These high values might indicate a disposal of electronic waste in the MSW stream at these locations [58]. Resources 2022, 11, 102 11 of 21 Table 6. Chemical composition of municipal solid waste leachate collected from landfills in various regions/countries; digits are rounded to three significant digits. Site 1, Site 2, Site 3, Site 1 Site 2 Site 3 Tsuen-Wan Sai-Kung Jaleeb Nova Ouled City or Region Central Central Central Sulaibiyah Zhejiang Zhejiang Zhejiang Hong Hong AlShiookh Scotia Fayet Country area of area of area of Kuwait China China China Kong Kong Kuwait Canada Algeria Taiwan Taiwan Taiwan Parameter Unit [57] [59] [60] [61] [48] [62] Study date - NA NA NA Feb. 2001–July 2003 March 1990–Jan. 1991 May–Oct.2000 NA 2006 pH - 8.01 7.75 7.66 7.03–8.50 7.30–8.40 6.82–8.37 7.20–8.00 7.20–8.40 6.90–8.20 7.82–8.06 5.10 8.27 BOD mg/L 1000 876 834 12–97 26.0–492 16.0–312 - - 30–600 210–345 - 980 COD mg/L 1490 1100 1900 320–1340 400–4300 840–4200 489–1670 147–1590 158–9440 6400–8800 11,6000 3790 CaCO mg/L NA NA NA NA NA NA NA NA NA NA NA 85.8 NH mg/L NA NA NA NA NA NA NA NA NA NA NA - N mg/L NA NA NA NA NA NA NA NA NA NA NA 58.2 org 3- PO mg/L NA NA NA NA NA NA NA NA NA NA NA NA Cl mg/L 1430 819 3150 NA NA NA 464–1340 140–1100 NA NA 3720 4570 2- SO mg/L NA NA NA NA NA NA - - NA NA - 3060 Na mg/L NA NA NA 320–1340 297–3530 431–3140 484–1190 132–743 NA NA 3800 NA 2+ Mg mg/L NA NA NA 27.8–103 23.0–163 15.7–157 35.0–63.0 9.00–26.0 5.20–20.8 86.0–268 1020 NA 2+ Ca mg/L NA NA NA 47.2–137 67.2–133.7 15.9–61.0 NA NA 5.60–67.6 52.0–122 6300 NA 2+ Zn mg/L 17.2 533 1330 0.04–1.61 0.003–0.56 0.03–0.66 0.24–2.55 0.13–0.39 0.00–0.20 0.20–4.80 13.5 NA 2+ Mn mg/L 0.54 2.39 5.98 0.18–5.27 0.02–0.74 0.02–0.75 0.05–0.24 0.05–1.30 NA NA 51.0 0.41 2+ Fe mg/L 1.94 15.5 38.6 0.26–5.44 0.26–15.3 0.39–28.0 1.14–3.25 1.26–5.00 0.30–18.1 1.40–54.6 297 8.23 2+ Cd mg/L 0.01 0.24 0.60 <0.15 <0.01 <0.01 <0.01 <0.02 NA NA 0.02 NA 3+ Cr mg/L 0.17 0.31 0.78 0.01–0.18 0.12–0.52 0.04–1.26 0.03–0.15 0.02–0.23 NA NA 0.40 0.20 2+ Pb mg/L 0.23 4.56 11.4 <0.02 <0.01–0.09 0.02–0.18 0.03–0.12 <0.10 0–0.10 NA 0.81 3.49 Resources 2022, 11, 102 12 of 21 Table 7. Chemical composition of municipal solid waste leachate collected from landfills in various regions/countries; digits are rounded to 3 significant digits. Riyadh Site 1 Site 2 City or Region Southern Thessaloniki New Alexandria Saudi USA Italy Germany UK South South Hong Kong Cairo Egypt Country Italy Greece Zealand Egypt Arabia Africa Africa Parameter Unit [52] [6] [47] [63] [64] [65] [53] Current study March Study Feb.–May Jan.–March - 1972–1979 1987 1991 NA NA 1999–2003 1990–1991 1986–1987 NA 2020–March date 2008 2000 pH - 5.94–6.32 5.10–6.90 6.00–8.50 5.70–8.10 6.70 8.20 7.90 7.50 8.20 7.80 7.00 7.00–7.80 6.14–8.14 BOD mg/L NA 13400 2130–10,400 400–45,900 18,600 2300 1050 170 550 117 737 10,824 95 3880–4860 COD mg/L 13,900–22,400 1340–18,100 7750–38,500 1630–63,700 36,800 10,500 5350 760 4560 873 1700 15,600 206 23,300–29,500 CaCO mg/L NA NA NA NA 7250 21,500 4950 2420 9650 4940 NA NA 24,000–30,000 NH mg/L NA NA NA NA 922 5210 940 435 1550 1160 NA 321  68.0 2250–2550 N mg/L NA NA NA NA NA NA NA NA NA NA NA NA 340–390 org 3- PO mg/L NA NA NA NA 5.00 32.0 8.80 1.40 13.0 22.2 NA NA 0.08–71.0 Cl mg/L NA 180–2260 1870–3650 1490–21,700 1810 4900 4120 1690 4630 821 973 11,400 119 11,000–28,000 2- SO mg/L NA NA NA NA 676 NA 210 NA NA NA 1.00 596  87 400–980 Na mg/L 4140–7770 160–1380 1300–1400 NA 1370 3970 NA 590 2830 217 429 NA 12,500–22,000 2+ Mg mg/L 693–2610 233–410 830–1470 100–270 384 24.1 140 80.0 195 18.0 160 NA 530–6620 2+ Ca mg/L 5300–8600 354–2300 70.0–290 130–4000 2240 15.7 NA 105 198 22.0 NA NA 2320–13,300 2+ Zn mg/L 0.11–0.23 18.8–67.0 5.00–10.0 NA 17.4 0.16 NA 0.17 NA 0.90 1.65 0.75  0.24 <0.01–37.4 2+ Mn mg/L 9.25–13.2 NA NA NA 32.9 0.04 NA 0.86 NA NA 6.56 0.84  0.17 0.25–20.6 2+ Fe mg/L 134–190 4.20–1190 47.0–330 8.00–870 654 2.70 16.2 18.8 9.35 7.80 0.89 6.31  1.83 9.50–317 2+ Cd mg/L <0.002 NA NA NA 0.02 NA NA NA NA NA 0.02 0.09  0.03 0.01–0.60 3+ Cr mg/L 0.21–0.34 NA NA NA 0.13 2.21 1.91 0.08 NA NA 0.07 0.06  0.04 0.21–1.00 2+ Pb mg/L <0.04 0.00–0.46 NA NA 0.28 NA NA NA 0.02 NA 0.15 0.02  0.01 0.70–0.86 + 3- NA: not available; COD: Chemical oxygen demand; BOD: Biological oxygen demand; NH : ammonium; Norg: organic nitrogen; PO : phosphate; CaCo : Calcium carbonate and it 4 4 3 2 + 2+ 2+ 2+ 2+ 2+ 2+ 3+ expresses total alkalinity of leachate; Cl : chloride; SO : sulfate; Na : sodium; Mg : magnesium; Ca : calcium; Zn : zinc; Mn : manganese; Fe : iron; Cd : cadmium; Cr : 2+ chromium; Pb : lead. Resources 2022, 11, 102 13 of 21 In short, the strength of leachate collected from three sites in Cairo was high but not exceptional compared to leachate quality in other countries (Tables 6 and 7). The high concentrations of sodium, iron, magnesium, manganese, chloride, and the organic con- stituent expressed by BOD were significant in comparison with other leachates presented in Tables 6 and 7. The practical implications of these high concentrations, their effect on the environment, and methods of mitigations will be discussed later in Section 5. 4. Variation of Leachate Quality with Time Leachate characteristics vary with time, and after passing through a leachate collection system due to the interaction between leachate and the granular soil particles of the leachate collection system. This section presents a comparison between the leachate quality from the same landfill (El-wafaa & El-amal; Northern & Eastern Cairo) in 2006 and 2020 (Table 8). The landfill understudy is located in Eastern Cairo, and it serves about four million residents with a capacity of 8.8 million tons of waste that was disposed of directly to the landfill without intermediate processing such as recycling or composting. The landfill was built in 2004 and it was one of the earlier engineered landfills in Egypt with baseliners and a leachate collection system. The landfill was closed in 2018 with clear signs of failure in the leachate collection system (Figure 3) implied by the leachate pond formed beside the landfill and side slopes failure probably caused by leachate seepage force acting on the slopes (Figure 4). Two-year-old leachate samples were collected from the end of the leachate collection system in 2006 [66], and other samples were collected in 2020 (sixteen-year-old) from the end of the leachate collection system (current study). The variations in the concentration of leachate quality among the two-year-old and sixteen-year-old specimens are presented in Figure 5. The ammonia concentration decreased from 12,100 ppm (2006) to 2250 (2020), while the chloride concentration increased extensively from 325 ppm to 11,000 pm during the same period (Table 8). Similarly, higher concentration was observed for sodium (301 ppm in 2006; 12,520 ppm in 2020), calcium (137 ppm in 2006; 2320 ppm in 2020), magnesium (104 ppm in 2006; 530 ppm in 2020), phosphate (33.5 ppm in 2006; 80.0 ppm in 2020), and chromium (2.26 ppm in 2006; 890 ppm in 2020). In contrast, the concentration of lead remained constant at 855–860 ppm. The leachate became more alkaline with pH increased from 8.10 to 8.90 mostly due to the 3200% increase in the concentration of the soluble inorganic load represented by chloride. Additionally, the remarkable increase in COD from 7350 mg/L in 2007 to 23,250 mg/L in 2020 could be attributed to the 1600% increase in the insoluble fraction of inorganic loading represented by calcium, besides a possible increase in the organic loading in the leachate. The BOD value decreased from 18,630 mg/L (two-year-old leachate; 2006) to 4860 mg/L (sixteen-year-old leachate; 2020) probably due to the biodegradation of the organic component of the waste [65]. The ratio of BOD /COD was 2.5 in 2006 indicating that the leachate was young leachate in the acetogenic phase (BOD /COD > 0.4; [10]) and decreased to 0.21 in 2020 indicating old leachate in the methanogenic phase. The changes in concentration of various leachate and key parameters mentioned earlier could be attributed to various causes; some are engineering, and others are relevant to socioeconomic changes in the surrounding districts served by this landfill. Firstly, the engineering reason was the failure of the leachate collection system at the time of collecting the sixteen-year-old sample, which subsequently resulted in the leachate mounding and formation of leachate ponds surrounding the landfill cell. Thus, the high concentration of calcium in the analyzed sixteen-year-old sample was not consumed by deposition in the leachate collection system [45]. The socioeconomic reason could be attributed to the noticeable expansion of the nearby districts accompanied by an increase in the population served by the landfill. More importantly, the increased number of commercial and administrative facilities in nearby districts could influence the waste stream disposed of at that landfill and subsequently change the leachate quality. Resources 2022, 11, 102 14 of 21 Table 8. Variation in municipal solid waste leachate quality with time in Northern and Eastern Cairo (Al Wafaa & Al Amal landfill); digits are rounded to three significant digits. a b 2006 2020 Parameter Units (LCS) (Sump) COD mg/L 7350 23,300  1160 BOD mg/L 18.6 4900  830 pH - 8.10 8.90  0.08 TFA mg/L NA 1.45 TS mg/L NA 45,800 TDS mg/L 32,900 54,000 Resources 2022, 11, x FOR PEER REVIEW 16 of 23 N mg/L NA 340  20 org NH mg/L 12,100 2300  110 TFA mg/L NA 1.45 Na mg/L 301 12,500  250 TS mg/L NA 45,800 2+ Ca mg/L 137 2300  120 TDS mg/L 329,00 54,000 2+ MgNorg mg/L mg/L NA 104 340 ± 530 20 10 NH4 mg/L 12,100 2300 ± 110 2+ Mn mg/L NA 0.25  0.01 Na mg/L 301 12,500 ± 250 2+ Fe mg/L NA 9.50  0.19 2+ Ca mg/L 137 2300 ± 120 2+ Mg mg/L 104 530 ± 10 Cl mg/L 325 11,000  550 2+ Mn mg/L NA 0.25 ± 0.01 SO mg/L NA 770 20 2+ Fe mg/L NA 9.50 ± 0.19 TA − mg/L NA 24,000  1200 Cl mg/L 325 11,000 ± 550 2− SO4 mg/L NA 770 ±20 PO mg/L 33.5 80.0  0.0 TA mg/L NA 24,000 ± 1200 3+ Cr mg/L 2.26 890  20 3− PO4 mg/L 33.5 80.0 ± 0.0 2+ 3+ Cd mg/L NA 10.0  0.00 Cr mg/L 2.26 890 ± 20 2+ Cd 2+ mg/L NA 10.0 ± 0.00 Pb mg/L 855 860  20 2+ Pb mg/L 855 860 ± 20 a b mean value cited from Eid et al., (2009); mean  standard deviation estimated in the current study. a b mean value cited from Eid et al., (2009); mean ± standard deviation estimated in the current study. Figure 3. Signs of failure of the leachate collection system in El- Wafaa & El- Amal landfill located Figure 3. Signs of failure of the leachate collection system in El- Wafaa & El- Amal landfill located in in Eastern Cairo in 2020 after landfill closure (sixteen-year-old). Eastern Cairo in 2020 after landfill closure (sixteen-year-old). Figure 4. El-wafaa & El-amal landfill (Eastern Cairo) cell side slope failure due to seepage of mound- ing leachate after leachate collection system failure. The photo was taken in 2020 after landfill clo- sure (sixteen-year-old). Resources 2022, 11, x FOR PEER REVIEW 16 of 23 TFA mg/L NA 1.45 TS mg/L NA 45,800 TDS mg/L 329,00 54,000 Norg mg/L NA 340 ± 20 NH4 mg/L 12,100 2300 ± 110 Na mg/L 301 12,500 ± 250 2+ Ca mg/L 137 2300 ± 120 2+ Mg mg/L 104 530 ± 10 2+ Mn mg/L NA 0.25 ± 0.01 2+ Fe mg/L NA 9.50 ± 0.19 Cl mg/L 325 11,000 ± 550 2− SO4 mg/L NA 770 ±20 TA mg/L NA 24,000 ± 1200 3− PO4 mg/L 33.5 80.0 ± 0.0 3+ Cr mg/L 2.26 890 ± 20 2+ Cd mg/L NA 10.0 ± 0.00 2+ Pb mg/L 855 860 ± 20 a b mean value cited from Eid et al., (2009); mean ± standard deviation estimated in the current study. Resources 2022, 11, 102 15 of 21 Figure 3. Signs of failure of the leachate collection system in El- Wafaa & El- Amal landfill located in Eastern Cairo in 2020 after landfill closure (sixteen-year-old). Figure 4. El-wafaa & El-amal landfill (Eastern Cairo) cell side slope failure due to seepage of mound- Figure 4. El-wafaa & El-amal landfill (Eastern Cairo) cell side slope failure due to seepage of Resources 2022, 11, x FOR PEER REVIEW 17 of 23 ing leachate after leachate collection system failure. The photo was taken in 2020 after landfill clo- mounding leachate after leachate collection system failure. The photo was taken in 2020 after landfill sure (sixteen-year-old). closure (sixteen-year-old). Figure 5. Variations in the concentration of leachate quality in El-wafaa & El- amal landfill (Eastern Figure 5. Variations in the concentration of leachate quality in El-wafaa & El- amal landfill (Eastern Cairo). The two-year-old leachate quality was reprinted/adapted with permission from Ref. [64]. Cairo). The two-year-old leachate quality was reprinted/adapted with permission from Ref. [64]. 2003, the Authors,while the sixteen-year-old sample was analyzed in the current study. 2003, the Authors, while the sixteen-year-old sample was analyzed in the current study. 5. Practical Implications 5. Practical Implications Th The e out outputs puts of of tthis his s study tudy revea revealed led a a ne need ed for for incre increasing asing tthe he co collection llection cov coverage erage and and building a national waste tracking information system to avoid misuse of some waste building a national waste tracking information system to avoid misuse of some waste components such as medical waste (e.g., paper masks and syringes, especially in times of components such as medical waste (e.g., paper masks and syringes, especially in times of pandemic), and hygiene waste. Further use of such items might have drastic effects on pandemic), and hygiene waste. Further use of such items might have drastic effects on public health. Moreover, developing a waste tracking database and a good identification of public health. Moreover, developing a waste tracking database and a good identification waste management scenarios in various cities in Cairo will help with proper identification of waste management scenarios in various cities in Cairo will help with proper identifica- of waste streams disposed of at a landfill that serves a certain district. Hence, a more tion of waste streams disposed of at a landfill that serves a certain district. Hence, a more sustainable design for various components of a landfill can be achieved. sustainable design for various components of a landfill can be achieved. The waste composition analysis that has been done in this study indicated that recy- The waste composition analysis that has been done in this study indicated that recy- cling had a positive impact on reducing the concentration of some key contaminants in cling had a positive impact on reducing the concentration of some key contaminants in the leachate such as iron, while the concentration of other contaminants was not reduced the leachate such as iron, while the concentration of other contaminants was not reduced such as chloride, since the chloride concentration is mainly attributed to the type of waste such as chloride, since the chloride concentration is mainly attributed to the type of waste disposed of and cannot be reduced by recycling activities [67]. For instance, the chloride disposed of and cannot be reduced by recycling activities [67]. For instance, the chloride concentration in the leachate collected from the landfill in the Southern and Western parts of concentration in the leachate collected from the landfill in the Southern and Western parts Cairo was 28,000 ppm compared to 14,000 ppm in the dumpsite in Giza (Table 5). However, of Cairo was 28,000 ppm compared to 14,000 ppm in the dumpsite in Giza (Table 5). How- the earlier landfill receives waste from a recycling plant, and the later dumpsite receives ever, the earlier landfill receives waste from a recycling plant, and the later dumpsite re- ceives landfill from the source. This variation implies that recycling the waste did not re- sult in a lower chloride concentration acknowledging the difference in the waste stream. In the meantime, the recycling had resulted in a reduction in the iron concentration in the leachate collected from the 15th May landfill (129 ppm; Table 5; Southern and Western Cairo) compared to that detected in the leachate collected from the dumpsite (317 ppm; Northern and Eastern Cairo). This reduction in iron concentration due to recycling might result in better long-term performance for a leachate collection system [68]. Moreover, the waste processing before disposal in the landfills either in a recycling plant or by scaven- 2+ gers in a transfer station resulted in the reduction of Cd concentration from 0.60 mg/L at Shabramant dumpsite (direct waste disposal from source) to 0.01–0.09 mg/L in 15th May and El-wafaa and El-amal landfills. In short, intermediate waste processing before the dis- posal of the waste directly into the landfill resulted in a reduction of the concentration of heavy metals (Table 5) such as iron and cadmium in the leachate, and subsequently better protection for the environment since these elements have an adverse effect on the envi- ronment associated with their bioaccumulation and long lifetime [69]. The leachate samples collected at the end of the leachate collection system from land- fills in Cairo had a high concentration of ammonia (2400 mg/L) which was defined as a primary source of toxicity of MSW landfill leachate [5]. Thus, the leachate treatment Concentration (mg/l) COD BOD5 pH Ammonia Sodium Calcium Magnesium Chloride Phosphate Chromium Lead Resources 2022, 11, 102 16 of 21 landfill from the source. This variation implies that recycling the waste did not result in a lower chloride concentration acknowledging the difference in the waste stream. In the meantime, the recycling had resulted in a reduction in the iron concentration in the leachate collected from the 15th May landfill (129 ppm; Table 5; Southern and Western Cairo) compared to that detected in the leachate collected from the dumpsite (317 ppm; Northern and Eastern Cairo). This reduction in iron concentration due to recycling might result in better long-term performance for a leachate collection system [68]. Moreover, the waste processing before disposal in the landfills either in a recycling plant or by scavengers 2+ in a transfer station resulted in the reduction of Cd concentration from 0.60 mg/L at Shabramant dumpsite (direct waste disposal from source) to 0.01–0.09 mg/L in 15th May and El-wafaa and El-amal landfills. In short, intermediate waste processing before the disposal of the waste directly into the landfill resulted in a reduction of the concentration of heavy metals (Table 5) such as iron and cadmium in the leachate, and subsequently better protection for the environment since these elements have an adverse effect on the environment associated with their bioaccumulation and long lifetime [69]. The leachate samples collected at the end of the leachate collection system from landfills in Cairo had a high concentration of ammonia (2400 mg/L) which was defined as a primary source of toxicity of MSW landfill leachate [5]. Thus, the leachate treatment method must reduce the ammonia to an acceptable level. Two options could be adopted, either an aerobic biological treatment with extended aeration or subsequent nitrification and denitrification of the leachate [70]. Additionally, the BOD /COD of the leachate samples analyzed in this study were mostly 0.2 indicating biologically stable leachate that is difficult to degrade [71,72]. Therefore, it is recommended to treat leachate using phsico-chemical treatment techniques that introduce chemicals to alter the physical state of the colloidal particles in the leachate [73]. The concentration of contaminants in leachate influences the selection of a landfill barrier system configuration and subsequently the design of various components of this barrier system. For instance, the thickness and hydraulic conductivity of a compacted clay liner along with the thickness of the geomembrane shall be estimated to limit the concentration of contaminants in an aquifer within the allowable limits of drinking water. The chemical analysis of MSW leachate in the Cairo metropolitan area revealed a far higher concentration of chlorides of 17,700 mg/L compared to 1000–4500 mg/L for leachates analyzed in landfills in other countries (Tables 6 and 7); this concentration is much higher than drinking water allowable values [74]. Furthermore, chloride mobility in leachate is one of the highest [75], and 100–150 years are needed before chloride in MSW leachate can be directly released without attenuation to the environment [76]). Consequently, a high- density polyethylene (HDPE) geomembrane base liner shall be implemented in MSW landfills in Cairo because the non-polar matrix of polyethylene reduces the diffusibility of inorganic salts into the geomembrane [67,77,78]. Specifically, the diffusion of chloride into the HDPE geomembrane is extremely low [75]. The service life of geomembrane (GMB) base liners is dependent on the concentra- tion of various elements in leachate [78,79] along with other factors including the GMB thickness, polymer resin, ambient temperature, antioxidant/stabilizer package, surface con- dition (white coated, smooth or textured), production residual stresses, and strains induced in the GMB [6,80–87]. The time to nominal failure of various high-density polyethylene geomembranes reported by [86] ranged between 100 and >2000 years at a temperature range of 5–20 C when exposed to municipal solid waste leachate whose fewer salt con- centrations compared to the MSW leachate in Cairo. For instance, the concentration range of calcium and magnesium ions for leachate samples in Cairo was 2300–13,300 mg/L and 530–6630 mg/L, respectively, compared to 732 mg/L (calcium) and 395 mg/L (magnesium) for the MSW leachate adopted by [86] and was simulating the leachate of Keele Valley land- fill in Ontario [88,89]. Calcium and magnesium function as catalysts for the auto-oxidative degradation of a polymer [78], therefore a geomembrane exposed to leachate with higher calcium and magnesium concentrations will most likely suffer faster chemical degradation. Resources 2022, 11, 102 17 of 21 This might imply that for two identical geomembranes, theoretically speaking, the service life for one installed in a landfill in Cairo could have a shorter service life compared to a counterpart in Ontario, assuming all other factors are the same (temperature, stresses, and barrier system configuration). The rate of accumulation of chemical precipitates and small particles (e.g., silt and sand) and buildup of a biofilm inside leachate collection system pipes are influenced by the leachate characteristics, besides the leachate flow rate and configuration of the leachate collection system [45,67]. The faster rate of the clogging of drainage gravel and a geotextile wrapped around a leachate collection system is associated with higher COD expressing volatile fatty acids, and inorganic elements especially calcium [90], besides the leachate flow rate [91]. Thus, special attention is needed for designing the leachate collection system elements in Cairo (geotextiles, drainage gravel, and pipes) because of the noticeably high concentration of calcium (2320–13,300 mg/L) in leachate compared to leachate from other regions (Tables 6 and 7), and the COD higher than the most of leachates presented in Tables 6 and 7. In summary, the high concentrations observed for inorganic and organic constituents, and heavy metals in leachate samples collected from Cairo could be mitigated by adopting the following waste management scenarios: (i) construction of recycling plant(s) along with a new landfill that serves certain districts, (ii) HDPE base liners shall be used in all landfills currently in the design phase in Cairo either alone or combined with compacted clay liner or geosynthetic clay liner to contain the MSW leachate with significantly high chloride concentration, and (iii) leachate collection system compatible with the leachate in Cairo shall be investigated and designed. 6. Conclusions The municipal solid waste composition was identified at different locations in the Cairo metropolitan area, namely, Northern and Eastern Cairo, Southern and Western Cairo, and the city of Giza. The effect of various waste disposal scenarios on waste composition was investigated by sorting the waste in the source, transfer stations, recycling plants, a dumpsite, and landfills. Furthermore, chemical analysis was performed for leachate samples collected from 3–16 year-age dumpsites or landfills covering the aforementioned regions of Cairo. The following conclusions were reached for the conditions examined at the time of the study: 1. The main components of municipal solid waste in Cairo were organics (58–75%) and plastics (19–28%). 2. The percentage of organics was higher in the waste disposed of in the landfills exam- ined compared to the dumpsite since landfilling was accompanied by the recycling process that consumes plastics and paper/cardboard components. 3. The leachate analyzed at different locations in Cairo contained ammonia concentra- tions higher than most of the values reported for MSW leachate from other countries. Hence, aerobic biological treatment of leachate with extended aeration is needed. 4. The chloride concentration detected in the MSW leachate in Cairo is high but not exceptional. HDPE geomembrane base barrier shall be mandatory in landfills planned in Cairo since it has excellent resistance to chloride diffusibility. 5. The high, but not exceptional, COD (23,250–24,570 mg/L) and BOD (3880–4860 mg/L) values of the MSW leachate examined in this study might indicate clogging in the leachate collection system of the two landfills examined. Consequently, the grain size distribution of the leachate collection system used in MSW landfills in Cairo shall be investigated. 6. The relatively high concentration of Calcium (8470 mg/L) and magnesium (4260 mg/L) suggests an expected shorter service life for HDPE geomembranes used as baseliners in MSW landfills in Cairo, assuming every other factor is kept the same, compared to values reported in the literature. Resources 2022, 11, 102 18 of 21 7. The concentration of the soluble inorganic load, alkalinity, and COD of an MSW leachate in Cairo increased with time. For instance, the concentration of chloride for the two-year-age leachate analyzed was 325 ppm compared to 11,000 ppm for the sixteen-year-old specimen. This study has shown the effect of waste management scenarios on the waste com- position and subsequently the leachate quality. A further study is needed to monitor the leachate quality effluent from various waste streams with different organic components un- der controlled conditions (e.g., bioreactors in a laboratory) to mimic various recycling levels and, hence, better understanding of the outcomes of various waste management scenarios. Author Contributions: Conceptualization, M.S.M. and S.E.; methodology, M.A.H.; investigation, M.A.H.; resources; data curation, M.A.H. and M.S.M.; writing—M.S.M., M.A.H. and M.A.; writing—review and editing, M.S.M. and S.E.; visualization, M.A.H. and M.S.M.; supervision, M.H.A., S.E. and M.S.M.; project administration, M.S.M. and M.A.H.; funding acquisition, M.S.M. and M.A.H. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded by the Science, Technology, and Innovation Funding Authority (STDF), grant number 43001. Acknowledgments: The research reported in this paper was supported by the Science, Technology, and Innovation Funding Authority (STDF) grant to Morsy for research project number 43001. Egypt’s solid waste management center of excellence generously provided the instruments needed for some experiments. Conflicts of Interest: The authors declare no conflict of interest. References 1. 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Municipal Solid Waste and Leachate Characterization in the Cairo Metropolitan Area

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resources Article Municipal Solid Waste and Leachate Characterization in the Cairo Metropolitan Area 1 2 3 4 , Maged A. Hussieny , Mohamed S. Morsy , Mostafa Ahmed , Sherien Elagroudy * and Mohamed H. Abdelrazik Public Works Department, Faculty of Engineering, Ain Shams University, 1 El-Sarayat Street, Cairo 11535, Egypt Soil Mechanics & Foundation Engineering Group, Structural Engineering Department, Faculty of Engineering, Ain Shams University, 1 El-Sarayat Street, Cairo 11535, Egypt Civil Engineering Department, Faculty of Engineering, Higher Technological Institute, Tenth of Ramadan City 44629, Egypt Egypt Solid Waste Management Center of Excellence, Ain Shams University, 1 El-Sarayat Street, Cairo 11535, Egypt * Correspondence: s.elagroudy@eng.asu.edu.eg; Tel.: +20-1006070032 Abstract: The composition of municipal solid waste (MSW) in the Cairo metropolitan area is in- vestigated. The outputs of MSW sorting analysis at various locations in Cairo with different waste management schemes are presented. Organics (58–75%) and plastic waste (19–28%) are the main components of MSW in Cairo with a higher percentage of organics in landfills compared to dump- sites. The leachate quality is analyzed, and the analysis results indicate that the concentration of 4+ + 2+ 2+ 2+ macro inorganic pollutants (NH , Na , Ca , and Cl ) and heavy metals (e.g., Cd and Zn ) are exceeding the majority of values reported in the literature in various cities all over the world. There was no evidence of an effect of the recycling process on chloride concentration in leachate, while the concentration of iron was reduced. The variation of leachate quality with time for two samples collected from the same municipal solid waste landfill is presented. The first leachate sample is Citation: Hussieny, M.A.; Morsy, a two-year-old, and the second sample is a sixteen-year-old. There was a significant increase in the M.S.; Ahmed, M.; Elagroudy, S.; concentration of chloride, sodium, chromium, calcium, and magnesium. The implications of the Abdelrazik, M.H. Municipal Solid Waste and Leachate Characterization leachate quality in Cairo on the longevity of barrier systems in an MSW landfill are discussed. in the Cairo Metropolitan Area. Resources 2022, 11, 102. https:// Keywords: municipal solid waste; waste stream; landfills; municipal solid waste leachate; leachate doi.org/10.3390/resources11110102 age; barrier systems; geomembranes Academic Editors: Ben McLellan and Elena Rada Received: 9 August 2022 1. Introduction Accepted: 27 October 2022 Municipal solid waste (MSW) composition varies from one country to another, and Published: 1 November 2022 even inside the same country, due to differences in cultural background, income level, Publisher’s Note: MDPI stays neutral waste management scenarios, and social circumstances [1–3]. The municipal solid waste with regard to jurisdictional claims in leachate is formed due to the leaching of soluble salts and biodegraded organic components published maps and institutional affil- inside the waste mass by rainfall or moisture percolating through the waste. Subsequently, iations. the composition of leachate varies between different regions due to the variability of waste decomposition besides other factors such as rate of rainfall, ambient temperature, rate of waste disposal, and daily cover that contributes to the suspended solids in the waste [3,4]. Municipal solid waste leachate is a complex fluid with characteristics that varies over the Copyright: © 2022 by the authors. different phases of the leachate starting from the acetogenic phase for young leachate to Licensee MDPI, Basel, Switzerland. the methanogenic phase for older leachate [5]. The MSW leachate is composed primarily This article is an open access article of dissolved organic, inorganic, and xenobiotic compounds, inorganic ions, and heavy distributed under the terms and metals [6–8]. The concentration of various elements and compounds in the MSW varies conditions of the Creative Commons with time [9] due to several factors such as variations in a waste stream, rate of waste Attribution (CC BY) license (https:// disposal, and changes in organic loading attributed to the biodegradation of waste [10]. creativecommons.org/licenses/by/ 4.0/). Resources 2022, 11, 102. https://doi.org/10.3390/resources11110102 https://www.mdpi.com/journal/resources Resources 2022, 11, 102 2 of 21 Proper waste management is crucial since poor waste management could have an ad- verse effect on the environment and the health of living organisms. Indeed, the long-term cost associated with poor waste management could be higher than primary proper waste management [11]. Waste disposal has developed from dump sites at which the waste is in direct contact with the ground to engineered landfills that comprise base barriers that separate the waste from groundwater [12]. Landfilling is the most common waste disposal method in many countries [13–15], and landfills are the destination for waste either directly from the source (if landfilling is adopted solely as a waste management system), or the residual waste by-product from other waste management techniques [13]. This could be attributed to the relatively low construction and operation cost relative to other waste disposal methods [16]. Reduction of waste volume disposed into a landfill could be needed if the land area assigned for landfilling is limited, or to increase the landfill’s cells capacity to extend the service time of an existing landfill without the need to construct a new one. Waste volume reduction methods include (a) waste compaction, (b) landfill bioreactors, (c) recycling, (d) composting, and (e) waste incineration. Waste compaction aims to reduce the air voids entrapped inside the waste mass, subsequently reducing the total waste volume and increasing the air space in a landfill [17]. Landfill bioreactors involve air and/or liquid circulation within the waste mass to motivate the aerobic bacterial processes (in presence of oxygen) or anaerobic waste biodegradation (in absence of oxygen) [18,19]. Both processes result in accelerated waste biodegradation in less time and hence increased landfill air space is obtained. Recycling is a waste diversion process that aims to reduce the waste mass and volume disposed into a landfill through the separation of waste either at the source or at a recycling plant, followed by the collection of similar waste components, then the manufacturing of marketable products [20–22]. Another waste diversion process is composting (mechanical biological treatment) which involves the bio decomposition of organic waste under controlled aerobic conditions into a humus-like product, known as compost, which can be used in land remediation, restoration, and agriculture [23–26]. Finally, incineration of waste involves burning the waste inside an incinerator turning the waste into bottom ash, fly ash, air pollution control residues, and gaseous products principally carbon dioxide and water vapor [27,28]. This process reduces the waste volume by approximately 90% [29], with the remaining volume of waste either diverted or landfilled. Each of the foregoing waste reduction approaches has advantages and disadvantages. Recycling provides a sustainable solution that promotes the waste value and turns it into products, but the revenue of waste reduction, increasing air space in a landfill, and selling recycled materials shall overweight the cost of separation, recycling awareness campaigns, and recycling plants. Similarly, waste composting results in a 20–40% reduction in waste volume [30]. However, high heavy metal concentrations in compost applied to food crops, especially partially oxidized ones, might have an adverse effect on crop yields. Moreover, higher metal concentrations were reported for composted soil and plants [25,31–33]. The Waste Framework Directive (2008) considered waste disposal through landfilling as the least preferable scenario and favored waste reduction, reuse, recycling, and recovery, respectively. Nevertheless, this recommendation [34] was describing waste management alternatives for more developed countries. In contrast to developed countries, engineered landfills are considered a reasonable waste management development from uncontrolled dumping practices in less developed countries [35]. Therefore, Egyptian environmental authorities decided to construct several engineered modern landfills in various governorates in the country along with intermediate waste transfer stations to increase the waste collection efficiency and protect the environment. A notable number of these landfills are located in the Cairo metropolitan area, since it is the most populous region in Egypt (20 million residents), with the greatest share of the amount of waste generated in Egypt with more than six million tons of waste generated annually [36] out of the twenty-one million tons/year produced all over Egypt [37]. However, these landfills could provide a relatively cheap Resources 2022, 11, x FOR PEER REVIEW 3 of 23 annually [36] out of the twenty-one million tons/year produced all over Egypt [37]. How- Resources 2022, 11, 102 3 of 21 ever, these landfills could provide a relatively cheap waste disposal solution and protect the environment if designed properly. The first step towards a sustainable design of an MSW landfill is proper identification of the waste stream, the chemical composition of waste disposal solution and protect the environment if designed properly. The first step effluent leachate, and the variation of the leachate quality over time. Thus, the objectives towards a sustainable design of an MSW landfill is proper identification of the waste stream, of this study are (i) to analyze the composition of the waste stream for various scenarios the chemical composition of effluent leachate, and the variation of the leachate quality of waste management in the Cairo metropolitan area, (ii) to identify the leachate quality over time. Thus, the objectives of this study are (i) to analyze the composition of the waste in a dumpsite, a landfill after the recycling process, as well as a landfill that receives waste stream for various scenarios of waste management in the Cairo metropolitan area, (ii) to directly from the source, and (iii) to present and analyze the variation in the concentration identify the leachate quality in a dumpsite, a landfill after the recycling process, as well as of leachate with time in one of Cairo’s major MSW landfills. a landfill that receives waste directly from the source, and (iii) to present and analyze the variation in the concentration of leachate with time in one of Cairo’s major MSW landfills. 2. Field and Experimental Investigation 2.1. Study Scope 2. Field and Experimental Investigation 2.1. Study The geog Scope raphic scope of the study is the Cairo metropolitan area (Figure 1). This study involved three districts: (1) Southern and Western districts of Cairo (15th May land- The geographic scope of the study is the Cairo metropolitan area (Figure 1). This study fill), (2) Northern and Eastern Cairo (El-obour landfill, and El-wafaa & El-amal landfill), involved three districts: (1) Southern and Western districts of Cairo (15th May landfill), and (3) Giza (Shabramant dumpsite). The waste in the Northern and Eastern regions is (2) Northern and Eastern Cairo (El-obour landfill, and El-wafaa & El-amal landfill), and initially placed at a transfer station, then separated in an MSW recycling plant, and finally (3) Giza (Shabramant dumpsite). The waste in the Northern and Eastern regions is initially disposed of at El-Obour landfill (at the time of this study) and previously disposed of at placed at a transfer station, then separated in an MSW recycling plant, and finally disposed El-Wafaa & El-Amal landfill. In the Southern and Western regions, the waste is collected of at El-Obour landfill (at the time of this study) and previously disposed of at El-Wafaa from the source, then transferred to a waste treatment and disposal facility, where organic & El-Amal landfill. In the Southern and Western regions, the waste is collected from the waste is composted, recyclables separated, and the non-recyclable portion is disposed of source, then transferred to a waste treatment and disposal facility, where organic waste is at the May 15 landfill. In contrast, the waste was disposed of directly into the Shabramant composted, recyclables separated, and the non-recyclable portion is disposed of at the May dumpsite without intermediate processing. The composition of MSW in each region was 15 landfill. In contrast, the waste was disposed of directly into the Shabramant dumpsite without examineintermediate d at various pr diocessing. sposal locat The ions: composition the transfer of MSW station, in rec each ycl region ing plan was t, and examined landfill at. various Therefore disposal , this study locations: investigate the transfer s the eff station, ect of va recycling rious com plant, binations and landfill. of waste Ther man efor agemen e, thist study methods investigates on the com the po ef sit fect ion of of various MSW d combinations umped in a lan ofdfill, waste and management subsequenmethods tly, the leach on the ate composition composition.of MSW dumped in a landfill, and subsequently, the leachate composition. Figure 1. Municipal solid waste and leachate sampling locations in the Cairo metropolitan area. Figure 1. Municipal solid waste and leachate sampling locations in the Cairo metropolitan area. 2.2. Waste Composition Analysis 2.2. Waste Composition Analysis Waste composition analysis was performed at nine sites. These sites were selected Waste composition analysis was performed at nine sites. These sites were selected to to track the waste composition through the different regions of the Cairo metropolitan track the waste composition through the different regions of the Cairo metropolitan area area from the source to the final destination in the three aforementioned districts in Cairo. from the source to the final destination in the three aforementioned districts in Cairo. The The nine sites were selected to represent the waste composition at collection, transfer, nine sites were selected to represent the waste composition at collection, transfer, and dis- and disposal sites as follows: three sites where the waste was directly collected from the posal sites as follows: three sites where the waste was directly collected from the source source without any losses, a transfer station, two recycling plants, a dumpsite (Shabramant, without any losses, a transfer station, two recycling plants, a dumpsite (Shabramant, Giza, Giza, Egypt), and two landfills. The dumpsite (Shabramant in Giza) had neither a barrier Egypt), and two landfills. The dumpsite (Shabramant in Giza) had neither a barrier sys- system, nor a leachate collection system, while the two landfills were the 15th May landfill tem, nor a leachate collection system, while the two landfills were the 15th May landfill in in Southern & Western Cairo, and the El-Obour landfill in Northern & Eastern Cairo. The 15th May landfill was an engineered landfill with a leachate collection system and was receiving waste for three years. The El-obour landfill was a landfill with a barrier system, but without a leachate collection system, and had started receiving waste a few Resources 2022, 11, 102 4 of 21 months before the study. Therefore, the waste analysis in the Northern & Eastern region of Cairo was performed in the El-Obour landfill, while the leachate analysis (Section 2.3) was performed for samples collected from the El-wafaa & El-amal landfill that was closed in 2018. Both landfills were receiving the waste from exactly the same districts and hence the leachate samples collected from El-wafaa & El-amal landfill were considered representative of the waste composition analyzed at the El-obour landfill. The waste composition analysis was performed at the source, transfer stations, recy- cling plants, dumpsites, and landfills before the intervention of scavengers at the inlet of these sites at various times during the study’s duration (March 2020 to March 2021). The waste sorting was conducted in accordance with the American standard test method for the determination of the composition of unprocessed municipal solid waste (ASTM D34) [38]. An approximately clean levelled surface covered with tarpaulin was selected for discharg- ing the load of a random truck. The discharged truck load was moved longitudinally using a front-end loader along one side to obtain a representative waste sample. Three sorting samples were analyzed at each site, each of 91–136 kg to represent the characteristics of a collection truckload. Each sample was sorted manually, and each component of the waste was placed inside a container, then the weight of each waste component and the container was measured using a calibrated scale. The weight of each component was calculated by subtracting the empty container weight, then the fraction weight of each component was estimated as a ratio of the total weight of all waste components. The desired level of precision (e) of the waste composition analysis was estimated based on the number of samples (truck loads; n) of three, viz: t s e =p (1) n  x where, t* (unitless): t-student statistic corresponding to the desired level of confidence; s (unitless): estimated standard deviation; and x (unitless): estimated mean. The major component of the analyzed MSW in Cairo was food waste, hence s and x were assumed as 0.03 and 0.1 based on values provided by [38]. These values were estimated based on MSW analysis data at various locations in the United States of America (ASTM D34). Consequently, the confidence level was estimated using the following equation: Confidence Level = 1 e (2) The confidence level for the analysis results at each site was 71.5%, and could be increased to 80% (6 samples) and 84% (9 samples) on grouping results from various sites. 2.3. Leachate Chemical Analysis MSW leachate samples were collected from two landfills and a dumpsite in Cairo metropolitan area, namely, El-wafaa & El-amal (landfill serving Northern and Eastern Cairo; 16 years old), 15th of May City (landfill serving Southern and Western Cairo; 3 years old), and Shabramant dumpsite (Giza; 15 years old). Samples were collected from the leachate collection sump (El-wafaa & El-amal landfill), or pump station (15th May landfill), and a fresh leachate pond formed at the Shabramant dumpsite. Three samples were collected from each site and stored in polyethylene bottles in a fridge at 4 C. Then the leachate samples were analyzed in accordance with APHA (2005) [39]. The analyzed components were (abbreviation and/or analysis method is mentioned in parenthesis): chemical oxygen demand (COD), biological oxygen demand (BOD), total solids (TS; convection oven dry- ing procedure), organic nitrogen (N; Total Kjeldahl Nitrogen-TKN), ammonium nitrogen (NH ; chromatography mass spectrometry), potential of hydrogen (pH; pH meter), total alkalinity (TA; titration; expressed by % calcium carbonate), volatile fatty acids (TFA; ion- exclusion chromatography), and elements concentration (inductively coupled plasma mass spectrometer and ion chromatography). Resources 2022, 11, 102 5 of 21 3. Results & Discussion 3.1. Waste Composition This section presents the results of waste analysis at the source at the three regions investigated in Cairo, followed by an illustration of the variation of waste composition from the source to the dumpsite/landfill passing by an intermediate transfer station or a recycling plant. Three MSW samples were collected from the source before scavenging activities and their composition was analyzed. The main components of the waste (Table 1) were organics (range: 61% to 71%; confidence level = 71%) and plastics (range: 15–25%; confidence level = 71%). The one-way analysis of variance (ANOVA) between observations of organic, plastics, and textiles waste components fraction at the three zones studied in the Cairo metropolitan area (Northern and Eastern, Southern and Western, and Giza) showed that there was a statistically significant difference (at 95% confidence level) that was greater than would be expected by a chance. Yet the statistical comparison using the student t-test (at 95% confidence level) between every two groups separately had shown that the difference was statistically insignificant between the observations of organics and plastics in Southern and Western Cairo, and Giza. Thus, the source of difference was the waste composition in Eastern and Northern Cairo, and this could be attributed to the difference in socioeconomic conditions among the three studied zones. The Northern and Eastern zone is predominantly urban residential, administrative, and commercial area, whereas Giza involves urban and rural districts. Finally, the Southern and Western zone involves industrial activities. Notwithstanding this statistically significant difference between mean values of observations between the Northern and Eastern zone of Cairo, besides the obvious difference in socioeconomic activities among the three zones under study, the mean waste components fraction at the three zones was estimated to obtain the percentage of each component at 84% confidence level (Table 1) and to compare the obtained waste composition in Cairo (current study) with that reported by the Egyptian environmental affairs agency (EEAA) for the waste composition in Egypt (Figure 2). The organics were 56% [37] and 64% (current study), while the plastics were 13% (EEAA) and 21% (current study). Moreover, the fraction of paper and cardboard reported by [37] for all Egypt was 10% and in Cairo (current study) was 4%. Hence, the percentage of organics and plastics in Cairo is higher and this could indicate a significant difference in waste composition in Cairo compared to other governorates in Egypt, or a change in the socioeconomic conditions since the EEAA report publication time. Similarly, the percentage of organics in Assiut (a governorate located 400 km to the south of Cairo) was 41% [40] which is less than the values in Cairo (60–71%; current study) and [37]. In conclusion, the statistically significant difference in waste composition across various zones of Cairo, and Assiut compared to the averaged values over Egypt [37] suggests that waste composition analysis shall be presented for each region independently and cannot be generalized all over Egypt. Additionally, the waste composition shall be analyzed periodically to monitor the variation in waste composition; this would highlight the socioeconomic changes and could aid in better waste management, the design of recycling systems, and engineering design for landfills. These socioeconomic changes might involve an increase in the usage of lightweight plastic packaging instead of heavier-weight glass and steel cans packaging [41]. This phenomenon is known as an evolving ton, where the recyclable waste has declining tonnage compared to volume [42], and hence material recovery facilities shall do more recyclables processing for a proximate revenue [41]. Resources 2022, 11, x FOR PEER REVIEW 6 of 23 Resources 2022, 11, 102 6 of 21 Table 1. Municipal solid waste composition (mean ± standard deviation) at the source. Table 1. Municipal solid waste composition (mean  standard deviation) at the source. a Waste Northern a & Southern & b c Waste Composition (%) Northern & Eastern Cairo Southern & Western Cairo Giza c Average Values Giza Average Values a a b Composition (%) Eastern Cairo Western Cairo Organics Organics 71 ± 3.4 71  3.4 60± 2.9 60  2.9 61 ± 61  2.8 2.8 64 ± 64  3.0 3.0 Plastics 15 ± 1.7 25 ±2.8 25 ± 2.3 21 ± 2.3 Plastics 15  1.7 25 2.8 25  2.3 21  2.3 Textiles 2.5 ± 0.4 2.4 ± 0.4 7.4 ± 2.4 4.1 ± 1.1 Textiles 2.5  0.4 2.4  0.4 7.4  2.4 4.1  1.1 Paper & Cardboard 4.0 ± 1.4 4.9 ± 1.7 3.1 ± 0.6 4.0 ± 1.2 Paper & Cardboard 4.0  1.4 4.9  1.7 3.1  0.6 4.0  1.2 Diapers 6.1 ± 2.6 7.5 ± 3.2 2.6 ± 0.8 5.4 ± 2.2 Diapers 6.1  2.6 7.5  3.2 2.6  0.8 5.4  2.2 Wood 0.6 ± 1.1 0.0 ± 0.0 1.0 ± 1.4 0.6 ± 0.8 Wood 0.6  1.1 0.0  0.0 1.0  1.4 0.6  0.8 Metals 0.3 ± 0.4 0.4 ± 0.4 0.3 ± 0.3 0.3 ± 0.3 Metals 0.3  0.4 0.4  0.4 0.3  0.3 0.3  0.3 Glass 1.0 ± 1.0 0.0 ± 0.0 0.5 ± 0.5 0.5 ± 0.5 a b Sampling Glass dates: 10 March 2020 1.0,  20 1.0 February 2021 0.0 , and  0.0 27 February 0.5202  0.5 1; Dates of 0.5 sa mpli 0.5ng: 7 Febr a uary 2021, 15 February 2021, and 23 February 2021; Dates of b sampling: 8 February 2021, 16 Sampling dates: 10 March 2020, 20 February 2021, and 27 February 2021; Dates of sampling: 7 February 2021, Febr 15 Fe uary 2021 bruary 2021 , ,and and 2 24 3 F Febr ebrua uar ry 2 y 2021 021; D . ates of sampling: 8 February 2021, 16 February 2021, and 24 February 2021. Organics Plastics Paper & Glass Metals Others Cardboard Waste component EEAA Current study Figure 2. Comparison between the waste composition in Cairo (current study) and the generalized Figure 2. Comparison between the waste composition in Cairo (current study) and the generalized co composition mposition in in Egypt Egypt issued issuedby by the the Egyptian Egyptiaenvir n environm onmental ental affairs affai agency rs agen “Reprinted/adapted cy “Reprinted/adapte with d with permission from Ref. [17]. 2010, the Authors”. permission from Ref. [17]. 2010, the Authors”. MSW was tracked through the successive waste management stages in Northern & MSW was tracked through the successive waste management stages in Northern & Eastern Cairo, from source to El-obour landfill passing through a transfer station and a recy- Eastern Cairo, from source to El-obour landfill passing through a transfer station and a cling plant. Three samples were analyzed at each stage and the waste components fraction recycling plant. Three samples were analyzed at each stage and the waste components was obtained (Table 2). The analysis showed that the organic fraction was reduced, and fraction was obtained (Table 2). The analysis showed that the organic fraction was re- the plastic fraction increased at the transfer station compared to the source. Furthermore, duced, and the plastic fraction increased at the transfer station compared to the source. the coefficient of variation increased from 5.3% and 11.6% to 8.6% and 28.4% for organics Furthermore, the coefficient of variation increased from 5.3% and 11.6% to 8.6% and 28.4% and plastic waste, respectively, indicating greater dispersion around the mean value. Since for organics and plastic waste, respectively, indicating greater dispersion around the the waste at source samples was collected from areas covered with collection services, mean value. Since the waste at source samples was collected from areas covered with col- the results imply direct disposal of waste at the transfer station. Hence, the results imply lection services, the results imply direct disposal of waste at the transfer station. Hence, a deficiency of waste collection coverage in Northern and Eastern Cairo. Comparing the the results imply a deficiency of waste collection coverage in Northern and Eastern Cairo. transfer station samples to that at the recycling plant manifests the scavenging activities oc- Comparing the transfer station samples to that at the recycling plant manifests the scav- curring at the transfer station. For instance, the plastics fraction decreased from 23%  7% enging activities occurring at the transfer station. For instance, the plastics fraction de- to 17%  5%, and the percentage of papers and carboards decreased from 3.3%  1.2% to creased from 23% ± 7% to 17% ± 5%, and the percentage of papers and carboards decreased 1.4%  1.4%. Finally, the MSW landfilled at El-obour landfill was composed of organic from 3.3% ± 1.2% to 1.4% ± 1.4%. Finally, the MSW landfilled at El-obour landfill was waste (75%  4.4%) and plastics unsuitable for reprocessing (20%  3.6%), and textiles composed of organic waste (75% ± 4.4%) and plastics unsuitable for reprocessing (20% ± (5.2%  5.2%). The textile fraction of the landfilled waste was minor. However, the coeffi- 3.6%), and textiles (5.2% ± 5.2%). The textile fraction of the landfilled waste was minor. cient of variation for the textiles waste reaching the landfills was 100% (mean = standard However, the coefficient of variation for the textiles waste reaching the landfills was 100% deviation) because the data points were highly distant from the mean implying a significant (mean = standard deviation) because the data points were highly distant from the mean variability in the landfilled textiles waste fraction. implying a significant variability in the landfilled textiles waste fraction. Percentage (%) Resources 2022, 11, 102 7 of 21 Table 2. Municipal solid waste composition (mean  standard deviation) in the various waste management stages in Northern & Eastern Cairo; rounded to two significant digits. Waste Transfer Recycling Landfill Source Composition (%) Station Plant (El-Obour Landfill) Organics 71  3.4 63  5.4 65  3.4 75  4.4 Plastics 15  1.7 23  6.5 17  5.0 20  3.6 Textiles 2.5  0.4 3.9  2.0 6.0  7.0 5.2  5.2 Paper & Cardboard 4.0  1.4 3.3  1.2 1.4  1.4 0.0  0.0 Diapers 6.1  2.6 5.3  1.4 8.1  4.0 0.2  0.3 Wood 0.6  1.1 0.0  0.0 1.3  2.3 0.0  0.0 Metals 0.3  0.4 0.0  0.0 0.8  0.8 0.0  0.0 Glass 1.0  1.0 1.6  1.4 0.9  1.1 0.0  0.0 Sampling dates: 10 March 2020, 20 February 2021, and 27 February 2021. In Southern & Western Cairo, waste collected from the source was processed at a recycling plant before disposal at the landfill. Waste composition analyses were performed to obtain the waste component fraction at the source, recycling plant, and landfill (Table 3). Plastics, textiles, paper, and cardboard fractions decreased at the recycling plant compared to the source, and consequently, the organic waste fraction increased. The statistical comparison between the organic and plastics fraction at the recycling plant and the landfill using the student t-test (confidence level = 95%) showed that the difference in the mean values between the two groups was not great enough and it could be relevant to random variability in sampling. For instance, the p-value (probability that difference between observations occurred by chance) was 0.518 (>0.05) for organics and 1.00 (>0.05) for plastics. The higher coefficient of variation for organics in the landfill (COV = 10%) compared to the recycling plant (COV = 1%) could be attributed to the presence of a composting plant at 15th May city in the vicinity of the landfill analyzed herein. Table 3. Municipal solid waste composition (mean  standard deviation) in the various waste management stages in Southern & Western Cairo; rounded to two significant digits. a b Waste Composition (%) Source Recycling Plant Landfill (15th May Landfill) Organics 61  2.9 74  0.8 71  7.3 Plastics 25  2.8 19  1.5 19  5.9 Textiles 2.4  0.4 0.7  1.1 6.2  5.7 Paper & Cardboard 4.9  1.7 1.3  0.4 0.0  0.0 Diapers 7.5  3.2 3.4  1.4 4.1  3.9 Wood 0.0  0.0 0.5  0.7 0.0  0.0 Metals 0.4  0.4 0.0  0.0 0.0  0.0 Glass 0.0  0.0 1.1  0.1 0.0  0.0 a b Sampling dates: 7 February 2021, 15 February 2021, and 23 February 2021; Composting plant exists in the vicinity of the 15th May landfill. In Giza, the waste was transferred directly from the source to the dumpsite without intermediate waste reduction processes. Thus, the waste components were analyzed at the source and Shabramant dumpsite (Table 4). The difference in mean values of all waste components with the exception of glass was not great enough (p > 0.05) suggesting that the Resources 2022, 11, 102 8 of 21 source of this difference was random variability in sampling. Furthermore, this statistically insignificant difference could be attributed to the absence of any waste reduction processes in Giza such as recycling and composting. Additionally, most of the scavenging activities probably occur at the dumpsite in this zone. Table 4. Municipal solid waste composition (mean  standard deviation) in the various waste management stages in Giza; rounded to two significant digits. a b Waste Composition (%) Source Dumpsite Organics 61  2.8 58  7.1 Plastics 25  2.3 28  6.6 Textiles 7.4  2.4 4.2  1.4 Paper & Cardboard 3.1  0.6 3.2  1.2 Diapers 2.6  0.8 1.9  1.9 Wood 1.0  1.4 1.1  1.9 Metals 0.3  0.3 0.6  0.5 Glass 0.5  0.5 2.7  1.2 a b Sampling dates: 8 February 2021, 16 February 2021, and 24 February 2021; Composting plant exists in the vicinity of 15th May landfill. In short, the waste management processes had an obvious effect on the waste compo- nents fraction disposed of at the landfill or the dumpsite. The recycling process resulted in a reduction in plastics (25% to 19%) and an increase in organics (61% to 74%) as evident from the waste analysis in Southern and Western Cairo, and Giza (Tables 3 and 4). The waste management in the earlier zone involved the recycling process, while the latter did not involve the recycling process. Both zones had statistically insignificant differences between the mean values of organics and plastics fraction in the source. The increase in organic fraction associated with the recycling process can be reduced by composting considering environmental protection measurements. The foregoing results present the waste composition along the waste track from source to disposal at a dumpsite or a landfill. These results could not be used to assess the efficiency of waste recovery by recycling due to the scavenging activities which are common in Cairo at source, transfer stations, and recycling plants. 3.2. Leachate Composition Leachate samples were collected from two landfills and a dumpsite in Cairo metropoli- tan area and were analyzed according to the parameters indicated by [43] for leachate characterization (Table 5). ANOVA one-way analyses were performed to compare the mean values of the concentration of various elements composing the leachate. The difference between the mean values of all concentrations was statistically significant (at confidence level = 95%) and greater than would be expected by chance, except for the BOD and NH . This finding was in good agreement with the statistical comparison between the waste components fraction at these zones of Cairo metropolitan area. Similarly, the difference in the mean values of the leachate concentrations was statistically significant (confidence level = 95%) with the exception of BOD, TFA, N , and NH , while the difference in the org mean values of the waste component fraction between Giza and Southern and Western Cairo was statistically insignificant (at confidence level = 95%). This statistically significant difference in leachate quality between the two waste streams of statistically insignificant difference could be relevant to various factors. The most important is that the leachate samples were collected from the waste stream in the dumpsite (Giza), since there was no leachate collection system at that site, while in the landfill (Southern and Western Cairo) the leachate samples were collected from a leachate collection system. Although samples collected from a well within the waste mass should have higher strength than those col- Resources 2022, 11, 102 9 of 21 lected from a leachate collection system [44,45], the strength of the leachate collected from the dumpsite was mostly less than the one collected from the leachate collection system in the landfill based on the concentration of various leachate parameters (Table 5). This could be attributed to the difference in leachate age at both sites (fifteen years for the Shabramant dumpsite, and three years for the 15th May landfill). Similarly, the leachate samples collected from El-waffa & El-amal landfill (Northern & Eastern Cairo; 16-year- old; TDS = 45,800 ppm) could have lower TDS compared to the leachate collected from the 15th May landfill (Southern & Western Cairo; 3-year-old; TDS = 88,700 ppm) due to various factors such as the difference in waste composition and age, the efficiency of the leachate collection system (clogging, leachate flow rate), and the variation concentration of key contaminants in leachate with time. The range of leachate quality concentrations was estimated (Table 5) for comparison purposes with leachate quality presented in the literature in different regions/countries over the world (Tables 6 and 7). Table 5. Leachate composition (mean  standard deviation) in Cairo metropolitan area; digits are rounded to three significant digits. Southern & Western Northern & Eastern Giza (Shabramant Parameter Unit Cairo Landfill Cairo (El-Wafaa & Range Dumpsite) b c (15th May Landfill) El-amal Landfill) COD mg/L 29,500  1470 24,600  1230 23,300  1160 23,300–29,500 BOD mg/L 4530  1380 3880  660 4860  830 3880–4860 pH - 6.14  0.06 6.30  0.06 8.14  0.08 6.14–8.14 TFA mg/L 1.98  0.10 1.74  0.09 1.45  0.07 1.45–1.98 TDS mg/L 72,600  4360 88,700  5320 45,800  2750 45,800–88,700 NH mg/L 2460  120 2550  130 2250  110 2250–2550 N mg/L 390  20.0 380  20.0 340  20.0 340–390 org CaCO mg/L 26,000  1300 30,000  1500 24,000  1200 24,000–30,000 Na mg/L 18,900  380 22,000  440 12,500  250 12,500–22,000 2+ Ca mg/L 9800  490 133,00  660 2320  120 2320–13,300 2+ Mg mg/L 6620  130 5640  110 530  10.0 530–6620 2+ Mn mg/L 20.6  0.41 9.90  0.20 0.25  0.01 0.25–20.6 2+ Fe mg/L 317  6.34 129  2.58 9.50  0.19 9.50–317 Cl mg/L 14,000  700 28,000  1400 11,000  550 11,000–28,000 SO mg/L 400  10.0 980  20.0 770  20.0 400–980 PO mg/L 0.30  0.01 71.0  1.42 0.08  0.00 0.08–71.0 3+ Cr mg/L 1.00  0.02 0.21  0.00 0.89  0.02 0.21–1.00 2+ Cd mg/L 0.60  0.01 0.09  0.00 0.01  0.00 0.01–0.60 2+ Pb mg/L 0.70  0.01 0.80  0.02 0.86  0.02 0.70–0.86 2+ b Zn mg/L 37.4  0.75 0.50  0.01 <0.01 <0.01–37.4 a b c Sampling dates: 8, 16, and 24 February 2021; Sampling dates: 7, 15, and 23 February 2021; 1, 6, and 10 March 2020; based on the minimum and maximum mean values obtained in the three zones investigated in Cairo; below detection limit; COD: Chemical oxygen demand; BOD: Biological oxygen demand; TFA: + 3 trifluoroacetic acid; TDS: total dissolved solids; NH : ammonium; N organic nitrogen; PO : phosphate; org: 4 4 2 + CaCo3: Calcium carbonate and it expresses total alkalinity of leachate; Cl : chloride; SO : sulfate; Na : sodium; 2+ 2+ 2+ 2+ 2+ 2+ 3+ Mg : magnesium; Ca : calcium; Zn : zinc; Mn : manganese; Fe : iron; Cd : cadmium; Cr : chromium; 2+ Pb : lead. Resources 2022, 11, 102 10 of 21 Chemical oxygen demand (COD) ranged between 23,300 and 29,500 mg/L, while biological oxygen demand (BOD ) range was 3880–4860 mg/L. Thus, the BOD /COD 5 5 ranged between 0.15 and 0.21 indicating young leachate in the landfills and dumpsite examined [46]. The COD range in Cairo was only preceded by the leachate collected from the United Kingdom and Nova Scotia, Canada ([47,48]; Tables 6 and 7). Similarly, the BOD was higher than all leachates presented in Tables 6 and 7, except for that reported by [47] in the United Kingdom. This high BOD value might indicate relatively higher organic constituents in the leachate in Cairo, or deficiency in the leachate collection system in the landfills examined [49]. The leachate samples collected from the Shabramant dumpsite (Giza), and the 15th May landfill (Southern and Western Cairo) were slightly acidic (pH= 6.14–6.30), while the leachate samples collected from El-wafaa & El-amal landfill (Northern and Eastern Cairo) were slightly basic (pH = 8.14). These values reflected the landfill age (Shabramant dumpsite: fresh leachate collected from the waste mass; 15th May landfill: 3 years; El Wafaa & El-Amal: 16 years) with lower pH values for relative new landfills (pH = 4.5–7.5) and relative higher pH values (pH closer to 9) for relatively old landfills [50,51]. The concentration range of macro inorganic constituents (Table 5) was higher than the typical ranges for MSW landfills indicated by [43]. For instance, the concentration of am- + + monium (NH ) was 2250–2550 mg/L (typical values: 50–2200 mg/L), sodium (Na ) was 2+ 12,500–22,000 mg/L (typical values: 70–7700 mg/L), Calcium (Ca ) was 2320–13,300 mg/L (typical values: 10–7200 mg/L), and chloride was 11,000–28,000 mg/L (typical values: 2+ 150–4500 mg/L). Similar high concentrations of Ca were reported for a landfill in Riyadh, Saudi Arabia [52] and Nova Scotia, Canada [48] as presented in Tables 6 and 7. The concen- tration of chloride in the leachate samples collected in Cairo (11,000–28,000 mg/L; current study) and other samples from another Egyptian mega-city, Alexandria (11,400 mg/L; [53]) were far higher than counterparts presented in Tables 6 and 7 with the exception for the leachate collected from landfills in Germany [6,54]. The heavy metals concentrations detected in the leachate were 9.5–317 mg/L (iron; 2+ 2+ 3+ Fe ), 0.01–0.60 mg/L (cadmium; Cd ), 0.21–1.0 (chromium; Cr ), and <0.01–37.4 (zinc; 2+ Zn ). These values were higher than the typical values that could be encountered in an 3+ 2+ MSW landfill young leachate [55]. These typical values are 1 mg/L (Cr ), 0.1 mg/L (Cd ), 2+ 2+ 1 mg/L (Pb ), and 0.01 mg/L (Zn ). These findings are common in developing countries due to the uncontrolled disposal of industrial and electronic waste in MSW streams [56]. More important these findings showed the positive impact of intermediate processing of waste, either in a transfer station or a recycling plant, on the reduction of heavy metals concentration in leachate. This was obvious from the higher heavy metals concentration in leachate collected from Shabramant, Giza (waste directly disposed from source to the dumpsite) compared to leachate collected in the landfills located at Northern and Eastern Cairo; Southern and Western Cairo and was subjected to intermediate processing. For 2+ example, the concentration of Fe was 317  6.34 (Table 5) compared to 9.50  0.19 (El- Wafaa & El-Amal landfill) and 129  2.58 (15th May landfill). Similarly, the concentration 2+ of Zn was 37.4  0.75 at Shabaramant dumpsite, 0.50  0.01 (15th May landfill), and <0.01 (below detection limit; El- wafaa & El-amal landfill). Furthermore, the highest 2+ Cd concentration among the leachates presented in Tables 6 and 7, was detected in the leachate collected from Shabramant dumpsite (0.60  0.01 mg/L; current study), followed by leachates collected from two sites in Zhejiang, China (0.24–0.60 mg/L; [57]), then the leachate collected from Alexandria, Egypt (0.09  0.03 mg/L; [53]). These high values might indicate a disposal of electronic waste in the MSW stream at these locations [58]. Resources 2022, 11, 102 11 of 21 Table 6. Chemical composition of municipal solid waste leachate collected from landfills in various regions/countries; digits are rounded to three significant digits. Site 1, Site 2, Site 3, Site 1 Site 2 Site 3 Tsuen-Wan Sai-Kung Jaleeb Nova Ouled City or Region Central Central Central Sulaibiyah Zhejiang Zhejiang Zhejiang Hong Hong AlShiookh Scotia Fayet Country area of area of area of Kuwait China China China Kong Kong Kuwait Canada Algeria Taiwan Taiwan Taiwan Parameter Unit [57] [59] [60] [61] [48] [62] Study date - NA NA NA Feb. 2001–July 2003 March 1990–Jan. 1991 May–Oct.2000 NA 2006 pH - 8.01 7.75 7.66 7.03–8.50 7.30–8.40 6.82–8.37 7.20–8.00 7.20–8.40 6.90–8.20 7.82–8.06 5.10 8.27 BOD mg/L 1000 876 834 12–97 26.0–492 16.0–312 - - 30–600 210–345 - 980 COD mg/L 1490 1100 1900 320–1340 400–4300 840–4200 489–1670 147–1590 158–9440 6400–8800 11,6000 3790 CaCO mg/L NA NA NA NA NA NA NA NA NA NA NA 85.8 NH mg/L NA NA NA NA NA NA NA NA NA NA NA - N mg/L NA NA NA NA NA NA NA NA NA NA NA 58.2 org 3- PO mg/L NA NA NA NA NA NA NA NA NA NA NA NA Cl mg/L 1430 819 3150 NA NA NA 464–1340 140–1100 NA NA 3720 4570 2- SO mg/L NA NA NA NA NA NA - - NA NA - 3060 Na mg/L NA NA NA 320–1340 297–3530 431–3140 484–1190 132–743 NA NA 3800 NA 2+ Mg mg/L NA NA NA 27.8–103 23.0–163 15.7–157 35.0–63.0 9.00–26.0 5.20–20.8 86.0–268 1020 NA 2+ Ca mg/L NA NA NA 47.2–137 67.2–133.7 15.9–61.0 NA NA 5.60–67.6 52.0–122 6300 NA 2+ Zn mg/L 17.2 533 1330 0.04–1.61 0.003–0.56 0.03–0.66 0.24–2.55 0.13–0.39 0.00–0.20 0.20–4.80 13.5 NA 2+ Mn mg/L 0.54 2.39 5.98 0.18–5.27 0.02–0.74 0.02–0.75 0.05–0.24 0.05–1.30 NA NA 51.0 0.41 2+ Fe mg/L 1.94 15.5 38.6 0.26–5.44 0.26–15.3 0.39–28.0 1.14–3.25 1.26–5.00 0.30–18.1 1.40–54.6 297 8.23 2+ Cd mg/L 0.01 0.24 0.60 <0.15 <0.01 <0.01 <0.01 <0.02 NA NA 0.02 NA 3+ Cr mg/L 0.17 0.31 0.78 0.01–0.18 0.12–0.52 0.04–1.26 0.03–0.15 0.02–0.23 NA NA 0.40 0.20 2+ Pb mg/L 0.23 4.56 11.4 <0.02 <0.01–0.09 0.02–0.18 0.03–0.12 <0.10 0–0.10 NA 0.81 3.49 Resources 2022, 11, 102 12 of 21 Table 7. Chemical composition of municipal solid waste leachate collected from landfills in various regions/countries; digits are rounded to 3 significant digits. Riyadh Site 1 Site 2 City or Region Southern Thessaloniki New Alexandria Saudi USA Italy Germany UK South South Hong Kong Cairo Egypt Country Italy Greece Zealand Egypt Arabia Africa Africa Parameter Unit [52] [6] [47] [63] [64] [65] [53] Current study March Study Feb.–May Jan.–March - 1972–1979 1987 1991 NA NA 1999–2003 1990–1991 1986–1987 NA 2020–March date 2008 2000 pH - 5.94–6.32 5.10–6.90 6.00–8.50 5.70–8.10 6.70 8.20 7.90 7.50 8.20 7.80 7.00 7.00–7.80 6.14–8.14 BOD mg/L NA 13400 2130–10,400 400–45,900 18,600 2300 1050 170 550 117 737 10,824 95 3880–4860 COD mg/L 13,900–22,400 1340–18,100 7750–38,500 1630–63,700 36,800 10,500 5350 760 4560 873 1700 15,600 206 23,300–29,500 CaCO mg/L NA NA NA NA 7250 21,500 4950 2420 9650 4940 NA NA 24,000–30,000 NH mg/L NA NA NA NA 922 5210 940 435 1550 1160 NA 321  68.0 2250–2550 N mg/L NA NA NA NA NA NA NA NA NA NA NA NA 340–390 org 3- PO mg/L NA NA NA NA 5.00 32.0 8.80 1.40 13.0 22.2 NA NA 0.08–71.0 Cl mg/L NA 180–2260 1870–3650 1490–21,700 1810 4900 4120 1690 4630 821 973 11,400 119 11,000–28,000 2- SO mg/L NA NA NA NA 676 NA 210 NA NA NA 1.00 596  87 400–980 Na mg/L 4140–7770 160–1380 1300–1400 NA 1370 3970 NA 590 2830 217 429 NA 12,500–22,000 2+ Mg mg/L 693–2610 233–410 830–1470 100–270 384 24.1 140 80.0 195 18.0 160 NA 530–6620 2+ Ca mg/L 5300–8600 354–2300 70.0–290 130–4000 2240 15.7 NA 105 198 22.0 NA NA 2320–13,300 2+ Zn mg/L 0.11–0.23 18.8–67.0 5.00–10.0 NA 17.4 0.16 NA 0.17 NA 0.90 1.65 0.75  0.24 <0.01–37.4 2+ Mn mg/L 9.25–13.2 NA NA NA 32.9 0.04 NA 0.86 NA NA 6.56 0.84  0.17 0.25–20.6 2+ Fe mg/L 134–190 4.20–1190 47.0–330 8.00–870 654 2.70 16.2 18.8 9.35 7.80 0.89 6.31  1.83 9.50–317 2+ Cd mg/L <0.002 NA NA NA 0.02 NA NA NA NA NA 0.02 0.09  0.03 0.01–0.60 3+ Cr mg/L 0.21–0.34 NA NA NA 0.13 2.21 1.91 0.08 NA NA 0.07 0.06  0.04 0.21–1.00 2+ Pb mg/L <0.04 0.00–0.46 NA NA 0.28 NA NA NA 0.02 NA 0.15 0.02  0.01 0.70–0.86 + 3- NA: not available; COD: Chemical oxygen demand; BOD: Biological oxygen demand; NH : ammonium; Norg: organic nitrogen; PO : phosphate; CaCo : Calcium carbonate and it 4 4 3 2 + 2+ 2+ 2+ 2+ 2+ 2+ 3+ expresses total alkalinity of leachate; Cl : chloride; SO : sulfate; Na : sodium; Mg : magnesium; Ca : calcium; Zn : zinc; Mn : manganese; Fe : iron; Cd : cadmium; Cr : 2+ chromium; Pb : lead. Resources 2022, 11, 102 13 of 21 In short, the strength of leachate collected from three sites in Cairo was high but not exceptional compared to leachate quality in other countries (Tables 6 and 7). The high concentrations of sodium, iron, magnesium, manganese, chloride, and the organic con- stituent expressed by BOD were significant in comparison with other leachates presented in Tables 6 and 7. The practical implications of these high concentrations, their effect on the environment, and methods of mitigations will be discussed later in Section 5. 4. Variation of Leachate Quality with Time Leachate characteristics vary with time, and after passing through a leachate collection system due to the interaction between leachate and the granular soil particles of the leachate collection system. This section presents a comparison between the leachate quality from the same landfill (El-wafaa & El-amal; Northern & Eastern Cairo) in 2006 and 2020 (Table 8). The landfill understudy is located in Eastern Cairo, and it serves about four million residents with a capacity of 8.8 million tons of waste that was disposed of directly to the landfill without intermediate processing such as recycling or composting. The landfill was built in 2004 and it was one of the earlier engineered landfills in Egypt with baseliners and a leachate collection system. The landfill was closed in 2018 with clear signs of failure in the leachate collection system (Figure 3) implied by the leachate pond formed beside the landfill and side slopes failure probably caused by leachate seepage force acting on the slopes (Figure 4). Two-year-old leachate samples were collected from the end of the leachate collection system in 2006 [66], and other samples were collected in 2020 (sixteen-year-old) from the end of the leachate collection system (current study). The variations in the concentration of leachate quality among the two-year-old and sixteen-year-old specimens are presented in Figure 5. The ammonia concentration decreased from 12,100 ppm (2006) to 2250 (2020), while the chloride concentration increased extensively from 325 ppm to 11,000 pm during the same period (Table 8). Similarly, higher concentration was observed for sodium (301 ppm in 2006; 12,520 ppm in 2020), calcium (137 ppm in 2006; 2320 ppm in 2020), magnesium (104 ppm in 2006; 530 ppm in 2020), phosphate (33.5 ppm in 2006; 80.0 ppm in 2020), and chromium (2.26 ppm in 2006; 890 ppm in 2020). In contrast, the concentration of lead remained constant at 855–860 ppm. The leachate became more alkaline with pH increased from 8.10 to 8.90 mostly due to the 3200% increase in the concentration of the soluble inorganic load represented by chloride. Additionally, the remarkable increase in COD from 7350 mg/L in 2007 to 23,250 mg/L in 2020 could be attributed to the 1600% increase in the insoluble fraction of inorganic loading represented by calcium, besides a possible increase in the organic loading in the leachate. The BOD value decreased from 18,630 mg/L (two-year-old leachate; 2006) to 4860 mg/L (sixteen-year-old leachate; 2020) probably due to the biodegradation of the organic component of the waste [65]. The ratio of BOD /COD was 2.5 in 2006 indicating that the leachate was young leachate in the acetogenic phase (BOD /COD > 0.4; [10]) and decreased to 0.21 in 2020 indicating old leachate in the methanogenic phase. The changes in concentration of various leachate and key parameters mentioned earlier could be attributed to various causes; some are engineering, and others are relevant to socioeconomic changes in the surrounding districts served by this landfill. Firstly, the engineering reason was the failure of the leachate collection system at the time of collecting the sixteen-year-old sample, which subsequently resulted in the leachate mounding and formation of leachate ponds surrounding the landfill cell. Thus, the high concentration of calcium in the analyzed sixteen-year-old sample was not consumed by deposition in the leachate collection system [45]. The socioeconomic reason could be attributed to the noticeable expansion of the nearby districts accompanied by an increase in the population served by the landfill. More importantly, the increased number of commercial and administrative facilities in nearby districts could influence the waste stream disposed of at that landfill and subsequently change the leachate quality. Resources 2022, 11, 102 14 of 21 Table 8. Variation in municipal solid waste leachate quality with time in Northern and Eastern Cairo (Al Wafaa & Al Amal landfill); digits are rounded to three significant digits. a b 2006 2020 Parameter Units (LCS) (Sump) COD mg/L 7350 23,300  1160 BOD mg/L 18.6 4900  830 pH - 8.10 8.90  0.08 TFA mg/L NA 1.45 TS mg/L NA 45,800 TDS mg/L 32,900 54,000 Resources 2022, 11, x FOR PEER REVIEW 16 of 23 N mg/L NA 340  20 org NH mg/L 12,100 2300  110 TFA mg/L NA 1.45 Na mg/L 301 12,500  250 TS mg/L NA 45,800 2+ Ca mg/L 137 2300  120 TDS mg/L 329,00 54,000 2+ MgNorg mg/L mg/L NA 104 340 ± 530 20 10 NH4 mg/L 12,100 2300 ± 110 2+ Mn mg/L NA 0.25  0.01 Na mg/L 301 12,500 ± 250 2+ Fe mg/L NA 9.50  0.19 2+ Ca mg/L 137 2300 ± 120 2+ Mg mg/L 104 530 ± 10 Cl mg/L 325 11,000  550 2+ Mn mg/L NA 0.25 ± 0.01 SO mg/L NA 770 20 2+ Fe mg/L NA 9.50 ± 0.19 TA − mg/L NA 24,000  1200 Cl mg/L 325 11,000 ± 550 2− SO4 mg/L NA 770 ±20 PO mg/L 33.5 80.0  0.0 TA mg/L NA 24,000 ± 1200 3+ Cr mg/L 2.26 890  20 3− PO4 mg/L 33.5 80.0 ± 0.0 2+ 3+ Cd mg/L NA 10.0  0.00 Cr mg/L 2.26 890 ± 20 2+ Cd 2+ mg/L NA 10.0 ± 0.00 Pb mg/L 855 860  20 2+ Pb mg/L 855 860 ± 20 a b mean value cited from Eid et al., (2009); mean  standard deviation estimated in the current study. a b mean value cited from Eid et al., (2009); mean ± standard deviation estimated in the current study. Figure 3. Signs of failure of the leachate collection system in El- Wafaa & El- Amal landfill located Figure 3. Signs of failure of the leachate collection system in El- Wafaa & El- Amal landfill located in in Eastern Cairo in 2020 after landfill closure (sixteen-year-old). Eastern Cairo in 2020 after landfill closure (sixteen-year-old). Figure 4. El-wafaa & El-amal landfill (Eastern Cairo) cell side slope failure due to seepage of mound- ing leachate after leachate collection system failure. The photo was taken in 2020 after landfill clo- sure (sixteen-year-old). Resources 2022, 11, x FOR PEER REVIEW 16 of 23 TFA mg/L NA 1.45 TS mg/L NA 45,800 TDS mg/L 329,00 54,000 Norg mg/L NA 340 ± 20 NH4 mg/L 12,100 2300 ± 110 Na mg/L 301 12,500 ± 250 2+ Ca mg/L 137 2300 ± 120 2+ Mg mg/L 104 530 ± 10 2+ Mn mg/L NA 0.25 ± 0.01 2+ Fe mg/L NA 9.50 ± 0.19 Cl mg/L 325 11,000 ± 550 2− SO4 mg/L NA 770 ±20 TA mg/L NA 24,000 ± 1200 3− PO4 mg/L 33.5 80.0 ± 0.0 3+ Cr mg/L 2.26 890 ± 20 2+ Cd mg/L NA 10.0 ± 0.00 2+ Pb mg/L 855 860 ± 20 a b mean value cited from Eid et al., (2009); mean ± standard deviation estimated in the current study. Resources 2022, 11, 102 15 of 21 Figure 3. Signs of failure of the leachate collection system in El- Wafaa & El- Amal landfill located in Eastern Cairo in 2020 after landfill closure (sixteen-year-old). Figure 4. El-wafaa & El-amal landfill (Eastern Cairo) cell side slope failure due to seepage of mound- Figure 4. El-wafaa & El-amal landfill (Eastern Cairo) cell side slope failure due to seepage of Resources 2022, 11, x FOR PEER REVIEW 17 of 23 ing leachate after leachate collection system failure. The photo was taken in 2020 after landfill clo- mounding leachate after leachate collection system failure. The photo was taken in 2020 after landfill sure (sixteen-year-old). closure (sixteen-year-old). Figure 5. Variations in the concentration of leachate quality in El-wafaa & El- amal landfill (Eastern Figure 5. Variations in the concentration of leachate quality in El-wafaa & El- amal landfill (Eastern Cairo). The two-year-old leachate quality was reprinted/adapted with permission from Ref. [64]. Cairo). The two-year-old leachate quality was reprinted/adapted with permission from Ref. [64]. 2003, the Authors,while the sixteen-year-old sample was analyzed in the current study. 2003, the Authors, while the sixteen-year-old sample was analyzed in the current study. 5. Practical Implications 5. Practical Implications Th The e out outputs puts of of tthis his s study tudy revea revealed led a a ne need ed for for incre increasing asing tthe he co collection llection cov coverage erage and and building a national waste tracking information system to avoid misuse of some waste building a national waste tracking information system to avoid misuse of some waste components such as medical waste (e.g., paper masks and syringes, especially in times of components such as medical waste (e.g., paper masks and syringes, especially in times of pandemic), and hygiene waste. Further use of such items might have drastic effects on pandemic), and hygiene waste. Further use of such items might have drastic effects on public health. Moreover, developing a waste tracking database and a good identification of public health. Moreover, developing a waste tracking database and a good identification waste management scenarios in various cities in Cairo will help with proper identification of waste management scenarios in various cities in Cairo will help with proper identifica- of waste streams disposed of at a landfill that serves a certain district. Hence, a more tion of waste streams disposed of at a landfill that serves a certain district. Hence, a more sustainable design for various components of a landfill can be achieved. sustainable design for various components of a landfill can be achieved. The waste composition analysis that has been done in this study indicated that recy- The waste composition analysis that has been done in this study indicated that recy- cling had a positive impact on reducing the concentration of some key contaminants in cling had a positive impact on reducing the concentration of some key contaminants in the leachate such as iron, while the concentration of other contaminants was not reduced the leachate such as iron, while the concentration of other contaminants was not reduced such as chloride, since the chloride concentration is mainly attributed to the type of waste such as chloride, since the chloride concentration is mainly attributed to the type of waste disposed of and cannot be reduced by recycling activities [67]. For instance, the chloride disposed of and cannot be reduced by recycling activities [67]. For instance, the chloride concentration in the leachate collected from the landfill in the Southern and Western parts of concentration in the leachate collected from the landfill in the Southern and Western parts Cairo was 28,000 ppm compared to 14,000 ppm in the dumpsite in Giza (Table 5). However, of Cairo was 28,000 ppm compared to 14,000 ppm in the dumpsite in Giza (Table 5). How- the earlier landfill receives waste from a recycling plant, and the later dumpsite receives ever, the earlier landfill receives waste from a recycling plant, and the later dumpsite re- ceives landfill from the source. This variation implies that recycling the waste did not re- sult in a lower chloride concentration acknowledging the difference in the waste stream. In the meantime, the recycling had resulted in a reduction in the iron concentration in the leachate collected from the 15th May landfill (129 ppm; Table 5; Southern and Western Cairo) compared to that detected in the leachate collected from the dumpsite (317 ppm; Northern and Eastern Cairo). This reduction in iron concentration due to recycling might result in better long-term performance for a leachate collection system [68]. Moreover, the waste processing before disposal in the landfills either in a recycling plant or by scaven- 2+ gers in a transfer station resulted in the reduction of Cd concentration from 0.60 mg/L at Shabramant dumpsite (direct waste disposal from source) to 0.01–0.09 mg/L in 15th May and El-wafaa and El-amal landfills. In short, intermediate waste processing before the dis- posal of the waste directly into the landfill resulted in a reduction of the concentration of heavy metals (Table 5) such as iron and cadmium in the leachate, and subsequently better protection for the environment since these elements have an adverse effect on the envi- ronment associated with their bioaccumulation and long lifetime [69]. The leachate samples collected at the end of the leachate collection system from land- fills in Cairo had a high concentration of ammonia (2400 mg/L) which was defined as a primary source of toxicity of MSW landfill leachate [5]. Thus, the leachate treatment Concentration (mg/l) COD BOD5 pH Ammonia Sodium Calcium Magnesium Chloride Phosphate Chromium Lead Resources 2022, 11, 102 16 of 21 landfill from the source. This variation implies that recycling the waste did not result in a lower chloride concentration acknowledging the difference in the waste stream. In the meantime, the recycling had resulted in a reduction in the iron concentration in the leachate collected from the 15th May landfill (129 ppm; Table 5; Southern and Western Cairo) compared to that detected in the leachate collected from the dumpsite (317 ppm; Northern and Eastern Cairo). This reduction in iron concentration due to recycling might result in better long-term performance for a leachate collection system [68]. Moreover, the waste processing before disposal in the landfills either in a recycling plant or by scavengers 2+ in a transfer station resulted in the reduction of Cd concentration from 0.60 mg/L at Shabramant dumpsite (direct waste disposal from source) to 0.01–0.09 mg/L in 15th May and El-wafaa and El-amal landfills. In short, intermediate waste processing before the disposal of the waste directly into the landfill resulted in a reduction of the concentration of heavy metals (Table 5) such as iron and cadmium in the leachate, and subsequently better protection for the environment since these elements have an adverse effect on the environment associated with their bioaccumulation and long lifetime [69]. The leachate samples collected at the end of the leachate collection system from landfills in Cairo had a high concentration of ammonia (2400 mg/L) which was defined as a primary source of toxicity of MSW landfill leachate [5]. Thus, the leachate treatment method must reduce the ammonia to an acceptable level. Two options could be adopted, either an aerobic biological treatment with extended aeration or subsequent nitrification and denitrification of the leachate [70]. Additionally, the BOD /COD of the leachate samples analyzed in this study were mostly 0.2 indicating biologically stable leachate that is difficult to degrade [71,72]. Therefore, it is recommended to treat leachate using phsico-chemical treatment techniques that introduce chemicals to alter the physical state of the colloidal particles in the leachate [73]. The concentration of contaminants in leachate influences the selection of a landfill barrier system configuration and subsequently the design of various components of this barrier system. For instance, the thickness and hydraulic conductivity of a compacted clay liner along with the thickness of the geomembrane shall be estimated to limit the concentration of contaminants in an aquifer within the allowable limits of drinking water. The chemical analysis of MSW leachate in the Cairo metropolitan area revealed a far higher concentration of chlorides of 17,700 mg/L compared to 1000–4500 mg/L for leachates analyzed in landfills in other countries (Tables 6 and 7); this concentration is much higher than drinking water allowable values [74]. Furthermore, chloride mobility in leachate is one of the highest [75], and 100–150 years are needed before chloride in MSW leachate can be directly released without attenuation to the environment [76]). Consequently, a high- density polyethylene (HDPE) geomembrane base liner shall be implemented in MSW landfills in Cairo because the non-polar matrix of polyethylene reduces the diffusibility of inorganic salts into the geomembrane [67,77,78]. Specifically, the diffusion of chloride into the HDPE geomembrane is extremely low [75]. The service life of geomembrane (GMB) base liners is dependent on the concentra- tion of various elements in leachate [78,79] along with other factors including the GMB thickness, polymer resin, ambient temperature, antioxidant/stabilizer package, surface con- dition (white coated, smooth or textured), production residual stresses, and strains induced in the GMB [6,80–87]. The time to nominal failure of various high-density polyethylene geomembranes reported by [86] ranged between 100 and >2000 years at a temperature range of 5–20 C when exposed to municipal solid waste leachate whose fewer salt con- centrations compared to the MSW leachate in Cairo. For instance, the concentration range of calcium and magnesium ions for leachate samples in Cairo was 2300–13,300 mg/L and 530–6630 mg/L, respectively, compared to 732 mg/L (calcium) and 395 mg/L (magnesium) for the MSW leachate adopted by [86] and was simulating the leachate of Keele Valley land- fill in Ontario [88,89]. Calcium and magnesium function as catalysts for the auto-oxidative degradation of a polymer [78], therefore a geomembrane exposed to leachate with higher calcium and magnesium concentrations will most likely suffer faster chemical degradation. Resources 2022, 11, 102 17 of 21 This might imply that for two identical geomembranes, theoretically speaking, the service life for one installed in a landfill in Cairo could have a shorter service life compared to a counterpart in Ontario, assuming all other factors are the same (temperature, stresses, and barrier system configuration). The rate of accumulation of chemical precipitates and small particles (e.g., silt and sand) and buildup of a biofilm inside leachate collection system pipes are influenced by the leachate characteristics, besides the leachate flow rate and configuration of the leachate collection system [45,67]. The faster rate of the clogging of drainage gravel and a geotextile wrapped around a leachate collection system is associated with higher COD expressing volatile fatty acids, and inorganic elements especially calcium [90], besides the leachate flow rate [91]. Thus, special attention is needed for designing the leachate collection system elements in Cairo (geotextiles, drainage gravel, and pipes) because of the noticeably high concentration of calcium (2320–13,300 mg/L) in leachate compared to leachate from other regions (Tables 6 and 7), and the COD higher than the most of leachates presented in Tables 6 and 7. In summary, the high concentrations observed for inorganic and organic constituents, and heavy metals in leachate samples collected from Cairo could be mitigated by adopting the following waste management scenarios: (i) construction of recycling plant(s) along with a new landfill that serves certain districts, (ii) HDPE base liners shall be used in all landfills currently in the design phase in Cairo either alone or combined with compacted clay liner or geosynthetic clay liner to contain the MSW leachate with significantly high chloride concentration, and (iii) leachate collection system compatible with the leachate in Cairo shall be investigated and designed. 6. Conclusions The municipal solid waste composition was identified at different locations in the Cairo metropolitan area, namely, Northern and Eastern Cairo, Southern and Western Cairo, and the city of Giza. The effect of various waste disposal scenarios on waste composition was investigated by sorting the waste in the source, transfer stations, recycling plants, a dumpsite, and landfills. Furthermore, chemical analysis was performed for leachate samples collected from 3–16 year-age dumpsites or landfills covering the aforementioned regions of Cairo. The following conclusions were reached for the conditions examined at the time of the study: 1. The main components of municipal solid waste in Cairo were organics (58–75%) and plastics (19–28%). 2. The percentage of organics was higher in the waste disposed of in the landfills exam- ined compared to the dumpsite since landfilling was accompanied by the recycling process that consumes plastics and paper/cardboard components. 3. The leachate analyzed at different locations in Cairo contained ammonia concentra- tions higher than most of the values reported for MSW leachate from other countries. Hence, aerobic biological treatment of leachate with extended aeration is needed. 4. The chloride concentration detected in the MSW leachate in Cairo is high but not exceptional. HDPE geomembrane base barrier shall be mandatory in landfills planned in Cairo since it has excellent resistance to chloride diffusibility. 5. The high, but not exceptional, COD (23,250–24,570 mg/L) and BOD (3880–4860 mg/L) values of the MSW leachate examined in this study might indicate clogging in the leachate collection system of the two landfills examined. Consequently, the grain size distribution of the leachate collection system used in MSW landfills in Cairo shall be investigated. 6. The relatively high concentration of Calcium (8470 mg/L) and magnesium (4260 mg/L) suggests an expected shorter service life for HDPE geomembranes used as baseliners in MSW landfills in Cairo, assuming every other factor is kept the same, compared to values reported in the literature. Resources 2022, 11, 102 18 of 21 7. The concentration of the soluble inorganic load, alkalinity, and COD of an MSW leachate in Cairo increased with time. For instance, the concentration of chloride for the two-year-age leachate analyzed was 325 ppm compared to 11,000 ppm for the sixteen-year-old specimen. This study has shown the effect of waste management scenarios on the waste com- position and subsequently the leachate quality. A further study is needed to monitor the leachate quality effluent from various waste streams with different organic components un- der controlled conditions (e.g., bioreactors in a laboratory) to mimic various recycling levels and, hence, better understanding of the outcomes of various waste management scenarios. Author Contributions: Conceptualization, M.S.M. and S.E.; methodology, M.A.H.; investigation, M.A.H.; resources; data curation, M.A.H. and M.S.M.; writing—M.S.M., M.A.H. and M.A.; writing—review and editing, M.S.M. and S.E.; visualization, M.A.H. and M.S.M.; supervision, M.H.A., S.E. and M.S.M.; project administration, M.S.M. and M.A.H.; funding acquisition, M.S.M. and M.A.H. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded by the Science, Technology, and Innovation Funding Authority (STDF), grant number 43001. Acknowledgments: The research reported in this paper was supported by the Science, Technology, and Innovation Funding Authority (STDF) grant to Morsy for research project number 43001. Egypt’s solid waste management center of excellence generously provided the instruments needed for some experiments. Conflicts of Interest: The authors declare no conflict of interest. References 1. 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Journal

ResourcesMultidisciplinary Digital Publishing Institute

Published: Nov 1, 2022

Keywords: municipal solid waste; waste stream; landfills; municipal solid waste leachate; leachate age; barrier systems; geomembranes

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