Environmental Technology

Shivaraju, H. Puttaiah; Egumbo, Henok; Madhusudan, P.; Anil Kumar, K. M.; Midhun, G.

doi: 10.1080/09593330.2018.1430853pmid: 29347885

Affordable clay-based ceramic filters with multifunctional properties were prepared using low-cost and active ingredients. The characterization results clearly revealed well crystallinity, structural elucidation, extensive porosity, higher surface area, higher stability, and durability which apparently enhance the treatment efficiency. The filtration rates of ceramic filter were evaluated under gravity and the results obtained were compared with a typical gravity slow sand filter (GSSF). All ceramic filters showed significant filtration rates of about 50–180 m/h, which is comparatively higher than the typical GSSF. Further, purification efficiency of clay-based ceramic filters was evaluated by considering important drinking water parameters and contaminants. A significant removal potential was achieved by the clay-based ceramic filter with 25% and 30% activated carbon along with active agents. Desired drinking water quality parameters were achieved by potential removal of nitrite (98.5%), nitrate (80.5%), total dissolved solids (62%), total hardness (55%), total organic pollutants (89%), and pathogenic microorganisms (100%) using ceramic filters within a short duration. The remarkable purification and disinfection efficiencies were attributed to the extensive porosity (0.202 cm3 g−1), surface area (124.61 m2 g−1), stability, and presence of active nanoparticles such as Cu, TiO2, and Ag within the porous matrix of the ceramic filter.

Andrade, Laura H.; Pires, Wadson L.; Grossi, Luiza B.; Aguiar, Alice O.; Amaral, Míriam C. S.

doi: 10.1080/09593330.2018.1432692pmid: 29385951

The aim of this study was to evaluate an innovative treatment route for gold-mining effluents rich in calcium, arsenic, and sulfate. This treatment route comprised two nanofiltration (NF) stages and a two-step intermediate precipitation. Arsenic and iron coprecipitation (first step) and calcium carbonate precipitation (second step) were assessed aiming to treat the first-stage NF concentrate and increase the permeate recovery rate in a second-stage NF. The pH, the molar ratio of Fe/As (first step), and the molar ratio of CO3/Ca (second step) were optimized by using rotational central composite design. Under optimal conditions, the arsenic removal was 99.8% (at pH = 7.0 and Fe/As = 4.0), and the calcium removal was 99.5% (at pH 11.5 and CO3/Ca = 3.5). The supernatant of Ca precipitation had very basic pH and had to be acidified before the second-stage NF. The pH 8.5 proved to be the best one regarding retention efficiency and flux. The flux decay of the second-stage NF was attributed to both osmotic pressure increase and reversible fouling resistance. It was concluded that the proposed treatment system is efficient for the treatment of gold-mining wastewater, ensuring higher production of treated effluent and an easy disposable of the final concentrate.

Hwang, Hyewon; Lee, Jae Hoon; Choi, In-Gyu; Choi, Joon Weon

doi: 10.1080/09593330.2018.1427799pmid: 29333927

Hydrothermal liquefaction (HTL) of lignocellulosic biomass has been widely investigated for the production of renewable and alternative bio-crude oil. In this study, catalytic hydrothermal processing of two biomasses (larch and Mongolian oak) was performed using different K2CO3 concentrations (0, 0.1, 0.5, 1.0 wt% of solvent) to improve fuel yield and properties. HTL oil, hydrochar, water-soluble fraction (WSF) and gas were characterized, and carbon balance was investigated. As a result, the maximum yield of HTL oil, 27.7 wt% (Mongolian oak) and 25.7 wt% (larch), and the highest carbon conversion ratio was obtained with 0.5 wt% of catalyst. The high catalyst concentration also resulted in an increase in higher heating values up to 31.9 MJ/kg. In addition, the amount of organic compounds in HTL oil also increased, specifically for lignin-derived compounds including catechol and hydroquinone which can be derived from secondary hydrolysis of lignin. On the other hand, formation of hydrochar was suppressed with the addition of alkali catalyst and the yield dramatically decreased from 30.7–40.8 wt.% to 20.0–21.8 wt.%. Furthermore, it was revealed that WSF had low organic carbon content less than 3.4% and high potassium content mostly derived from alkali catalyst, indicating that it may be reusable with simple purification. This work suggests that the addition of the proper amount of alkali catalyst can improve the production efficiency and quality of bio-crude oil, and another potential of WSF to be recyclable in further work.

Confortin, Tássia C.; Todero, Izelmar; Soares, Juliana F.; Luft, Luciana; Brun, Thiarles; Rabuske, Jéssica E.; Nogueira, Cicero U.; Mazutti, Marcio A.; Zabot, Giovani L.; Tres, Marcus V.

doi: 10.1080/09593330.2018.1427800pmid:

Wang, Huoqing; Sun, Yuepeng; Wu, Guangxue; Guan, Yuntao

doi: 10.1080/09593330.2018.1427801pmid: 29333979

Characteristics of nitrogen removal and nitrous oxide (N2O) emission in the multiple anoxic/aerobic (AO) process were examined in three sequencing batch reactors (SBRs) with different anoxic durations (50 min, SBRH; 40 min, SBRM; 30 min, SBRL) and a fixed aerobic duration of 30 min. The highest total inorganic nitrogen removal percentage of 85.8% was obtained in SBRH, while a minimum N2O emission factor of 1.9% was obtained in SBRL. During nitrification batch experiments, the N2O emission factor and emission rate were both lower in SBRH than SBRL. More N2O production was obtained during denitrification in SBRH when denitrifiers utilized intracellular organic carbon. Nitrite reduction by heterotrophs was the main N2O production pathway during simultaneous nitrification and denitrification in SBRH and SBRL, with the N2O emission factor of 31.3% and 36.3%, respectively. Adequate anoxic duration and lowering aerobic nitrite concentrations could be adopted to mitigate N2O emission in the multiple AO process. The dominant microorganisms at the phylum level in all reactors were Proteobacteria and Bacteroidetes, while the abundance of Nitrospira was the highest in SBRH with relatively lowest dissolved oxygen concentrations.

Yu, Zhan; Wang, Dan; Yang, Yue; Meng, Xuan; Liu, Naiwang; Shi, Li

doi: 10.1080/09593330.2018.1427802pmid: 29363408

Low-cost activated carbon (KAC) was functionalized by HNO3, (NH4)2S2O8 and air oxidation, respectively, to remove dibenzothiophene (DBT) from model fuel. The changes in physical and chemical properties of these activated carbons were characterized by thermal analysis, elemental analysis, nitrogen adsorption apparatus, Raman spectra, scanning electron microscope and Boehm’s titration method. HNO3 and (NH4)2S2O8 oxidation result in a significant decrease in pore structure, while air oxidation only causes slight pore reduction due to the re-activation by O2. The oxygen-containing functional groups (OFGs) increase markedly after oxidative modification, in which (NH4)2S2O8 oxidation is considered as the most efficient method with respect to the introduction of OFGs. HNO3 and (NH4)2S2O8 oxidation are more selective to generate carboxyls and lactones, whereas air oxidation creates more phenols, carbonyls and ethers. The DBT adsorption capacity follows the order: NAC (HNO3-oxidized KAC) > OAC (air-oxidized KAC) > KAC > SAC ((NH4)2S2O8-oxidized KAC), implying the introduction of OFGs is beneficial for the DBT adsorption process, especially for selectivity, but excessive OFGs have a negative effect on the removal of DBT. Thus, to achieve high DBT adsorption performance, there should be a trade-off between the micropore volume and the OFGs amount.

Asha, Raju C.; Yadav, M. S. Priyanka; Kumar, Mathava

doi: 10.1080/09593330.2018.1428227pmid: 29336216

In this study, the efficacy of membrane-photocatalytic reactor (MPR) in sulfamethoxazole (SMX) removal was explored at a fixed initial SMX concentration, i.e. 100 mg/L. A supported catalyst, i.e. TiO2 on granular activated carbon (GAC–TiO2), was used for MPR experiments. The SMX removal efficiency of the MPR was investigated under a range of hydraulic retention time (i.e. HRT from 51 to 152.5 min) and TiO2 catalyst dosage (55–50 mg/L). A maximum SMX removal efficiency of 83.6% was observed under 220 mg/L catalyst dosage and 80 min HRT. The increase in catalyst dosage from 55 to 550 mg/L has increased the transmembrane pressure of the reactor from 9.8 to 22.2 kPa. A multiple non-linear regression model was developed based on the experimental data and its significance was analyzed using two-way ANOVA. Based on the model, the optimal HRT and catalyst dosage for complete SMX removal (100%) were found out. The comparison of photocatalytic degradation experiments with sorption experiments conducted earlier revealed that SMX removal in the MPR was mainly by photocatalytic degradation and not by adsorption onto GAC–TiO2 catalyst. However, the performance of MPR in removing other emerging pollutants from real-time wastewaters could be explored before its field-scale application.

Dehghani, Mansooreh; Nozari, Majid; Fakhraei Fard, Atefeh; Ansari Shiri, Marziyeh; Shamsedini, Narges

doi: 10.1080/09593330.2018.1428228pmid: 29336214

Direct Red 81 (DR-81) dye with a very high water solubility is widely used in many industries particularly textile industries. This study aimed to evaluate the practicability of using iron filings for the adsorption of DR-81 dye from the aqueous solutions. The effects of pH, adsorbent dose, initial DR-81 dye concentration, and adsorption time on adsorption process were also evaluated. The maximum of adsorption efficiency of DR-81 dye achieved in the optimum pH: 3, adsorbent dose: 2.5 g/L, contact time: 30 min, and initial dye concentration: 50 mg/L. The dye adsorption efficiency is increased by increasing the adsorbent dose and adsorption time. The kinetic and isotherm studies indicated that the adsorption process obeys a pseudo–first–order and Langmuir isotherm models. The experimental studies indicated that iron filings had the potential to act as an alternative adsorbent to remove the DR-81 dye from an aqueous solution.

Wang, Yongliang; Lv, Cuicui; Xiao, Li; Fu, Guoyan; Liu, Ya; Ye, Shufeng; Chen, Yunfa

doi: 10.1080/09593330.2018.1429495pmid: 29345188

The alkaline leaching solution from arsenic-containing gold concentrate contains a large amount of arsenate ions, which should be removed because it is harmful to the production process and to the environment. In this study, conventional Fe (III) precipitation was used to remove arsenic from the leaching solution. The precipitation reaction was carried out at the normal temperature, and the effects of pH value and Fe/As ratio on the arsenic removal were investigated. The results show that the removal rate of arsenic is distinctive at different pH values, and the effect is best within the pH range of 5.25–5.96. The removal rate can be further increased by increasing the ratio of Fe/As. When the pH = 5.25–5.96 and Fe/As > 1.8, the arsenic in the solution can be reduced to below 5 mg/L. However, the crystallinity of ferric arsenate is poor, and the particle size is small, most of which is about 1 μm. The leaching toxicity test shows the leaching toxicity of precipitates gradually decreased by the increase of Fe/As. The precipitates can be stored safely as the ratio of Fe/As exceeded 2.5.

Hoekstra, Maaike; Geilvoet, Stefan P.; Hendrickx, Tim L. G.; van Erp Taalman Kip, Charlotte S.; Kleerebezem, Robbert; van Loosdrecht, Mark C. M.

doi: 10.1080/09593330.2018.1470204pmid: 29697015

The aim of this research was to study the biological feasibility of the Partial Nitritation/Anammox (PN/A) technology to remove nitrogen from municipal mainstream wastewaters. During stable process operations at summer temperatures (23.2 ± 1.3°C), the total nitrogen removal rate was 0.223 ± 0.029 kg N (m3 d)−1 while at winter temperatures (13.4 ± 1.1°C) the total nitrogen removal rate was 0.097 ± 0.016 kg N (m3 d)−1. Nitrite-oxidizing bacteria (NOB) suppression was successfully achieved at the complete temperature range of municipal mainstream wastewater. Despite the presence of NOB as observed in activity tests, their activity could be successfully suppressed due to a relative low dissolved oxygen concentration. An overcapacity of ammonia-oxidizing bacteria and anammox activity was always present. Long-term stability is a focus point for future research, especially in relation to the stability of the biological oxygen demand removing step, preceding the PN/A reactor.