Environmental Technology

Byrappa, K.; Lokanatha Rai, K. M.; Yoshimura, M.

doi: 10.1080/09593330.2000.9618994pmid: N/A

Photocatalytic TiO2 was prepared as monodispersed fine particles under mild hydrothermal conditions (T = 150°C, P = ∼ 40 bars). Active elements like W, were introduced into the structure of TiO2 up to 10 wt% in order to obtain enhanced photocatalytic activity in the title compound. The influence of various growth parameters such as pH of the media, crystallization temperature, type of solvent, % fills (pressure) and the type of starting material were studied with reference to the quality of the resultant product and its photocatalytic activity. The disintegration of hexachlrocyclohexane (HCCH) and dichlorodiphenyltrichloroehtane (DDT) was studied using TiO2, and we have proposed the photocatalytic reaction mechanism for the first time. Natural sunlight was used as the main light source in the photocatalytic reaction.

Kadirvelu, K.; Namasivayam, C.

doi: 10.1080/09593330.2000.9618995pmid: N/A

Activated carbon prepared from coirpith waste was used for the adsorptive removal of Pb(II) from aqueous solution. Parameters such as agitation time, metal ion concentration, adsorbent dose and pH were studied. Adsorption equilibrium was reached in 30 min for solution containing 25 and 50 mg l−1 and 40 min for solution containing 75 and 100 mg l−1 Pb(II), respectively. Adsorption parameters were determined using both Langmuir and Freundlich models. The adsorption capacity was 263 mg g−1. Pb(II) removal increased with increased pH from 2 to 4 and remained constant up to pH 10. Desorption studies were also carried out with dilute hydrochloric acid to recover both carbon and Pb(II). As the raw material for the preparation of activated carbon is discarded as waste during coir processing, the production of this carbon is expected to be economically feasible.

Maliszewska-Kordybach, B.; Smreczak, B.

doi: 10.1080/09593330.2000.9618996pmid: N/A

Contamination of agroecosystems with PAHs may affect an ability of a soil to sustain a natural biocenosis or agriculture and create a toxicological risk to plants cultivated in the area. The aim of this study was to evaluate the ecotoxicological activity of soils polluted with PAHs with the respect to their effect on plants. Three different soils (chernozem, rendzina and brown soil) artificially contaminated with the mixture of four PAH compounds (fluorene, anthracene, pyrene and chrysene) at the levels of Σ4PAHs of 1, 10, 50 and 100 mg kg−1 were used in the study (laboratory bioassays). Three of the tested plant species (wheat - Triticum vulgare Vill, oat - Avena sativa L and maize - Zea mays L) were from the monocotyledonous category and three (tomato - Lycopersicon esculentum Miller, bean - Phaseolus vulgaris L and sunflower - Helianthus annus L.) from the dicotyledonous category. Contamination of the soil with PAHs at the level below 10 mg kg−1 stimulated rather than inhibited the growth of the plants at the early stages of their development. The lowest observed level of soil contamination with PAH significantly inhibiting (EC20) plant growth (tomato in sandy soil) was about 20 mg of Σ4PAH per kg of soil while EC20 values for most of the other plants tested exceeded 100 mg kg−1. Phytotoxic activity of soils was negatively related to soil organic matter content regulating concentration of PAHs in the soil water phase.

Cañizares, P.; De Lucas, A.; Rodríguez, L.; Villaseñor, J.

doi: 10.1080/09593330.2000.9618997pmid: N/A

Biodegradation kinetics of bacterial storage substrates can be of prime importance to designing some bioprocesses, as for example biological phosphorus removal. In this work, kinetic parameters of polyhydroxyalcanoates degradation, stored into phosphorus accumulating organisms, were determined through electrolytic respirometry. An experimental procedure, based on anaerobic substrate storage followed by respirometrically-measured aerobic degradation, was used. A lot of experimental data points were easily obtained but a reference test was neccesary in order to remove interferences of other oxygen consuming events. Oxygen uptake simulation curves were obtained through a non linear fitting estimation method, using a mathematical model that described substrate consumption and biomass growth and decay. Simulation curves correlated well with oxygen uptake data, and the parameters obtained (μmax, KS, b and Y) were similar to the ones obtained by several authors.

Philips, S.; Verstraete, W.

doi: 10.1080/09593330.2000.9618998pmid: N/A

Under certain circumstances nitrite can accumulate in activated sludge treatment systems. The influence of a sudden increase of nitrite concentration on the overall removal processes in semi-continuous activated sludge reactors was investigated. It was found that the moment of occurrence of the nitrite peak is important in relation to the time of feeding. Addition of nitrite together with protein rich feed resulted in a higher inhibition of both COD and nitrogen removal, although nitrite itself had totally disappeared within a period of two days. Testing of different doses of nitrite situated the critical dose of single shock addition of nitrite in the range of 50 to 100 mg NO2 −-N l−1. The effluent of the reactors turned yellow after dosing nitrite and feed. It was additionally found that nitrite at relatively high concentrations can react with amino acids to form a yellow compound or compounds. The latter appeared to be more toxic than nitrite alone. Hence, such yellow nitrite reaction products should be watched for in reactors operated in uncoupled nitrification conditions, i.e. stopped at nitrite, with protein rich influents.

Jaouen, P.; Lanson, J. M.; Vandanjon, L.; Maleriat, J. P.; Quemeneur, F.

doi: 10.1080/09593330.2000.9618999pmid: N/A

The study deals with the treatment, by nanofiltration, of effluents generated after rinsing the vats used for the manufacture of inks (pen cartridges). The first part of the study (bibliographical) shows that membrane processes are operational in different industrial areas for the decoloration of effluents but the number of nanofiltration plants is still limited. In the second part (experimental) two tubular organic membranes (Koch-Weizmann MPT20 an MPT31), selected according to their molecular weight cut-off (450 dalton) and their resistance to solvents and acid solutions, are performed and compared. The study shows that performances (i.e. permeation flux and retention rate) of MPT20 membrane are linked noticeably to hydrodynamic parameters (pressure, velocity). Furthermore, for the two membranes tested the transport mechanism across the medium is typically diffusional. The studies, at the laboratory scale, conducted for a first time at constant solute concentration thereafter in a ‘concentration mode’, were followed by pre-industrial and long-term runs. The 3 weeks continuous experiments were found to be indispensable for the selection of the most suited membrane. Finally, the MPT31 membrane exhibited the best performances (no drift in flux nor alteration of selectivity with time). Under the operating conditions – 25×105 Pa, 2.5 m.s−1, 30 °C – the following performances were obtained: flux 41 l h−1 m2, decoloration > 99 %, COD divided by 4, volumic reduction > 10, easy cleaning. This study has allowed the design and economical evaluation of an industrial equipment (running in France since February 1997) which is probably the first nanofiltration plant for this type of application in Europe.

Zaiat, M.; Passig, F. Hermes; Foresti, E.

doi: 10.1080/09593330.2000.9619000pmid: N/A

This paper focuses on the evaluation of the start-up period and the performance of a pilot-scale horizontal-flow anaerobic immobilized biomass (HAIB) reactor treating pre-screened domestic sewage. The pilot-scale HAIB reactor comprises a 14.5 cm internal diameter PVC tube 14.4 m long divided into five stages of 2.88 m each. Polyurethane foam cubic matrices with 1 cm sides were used as support for biomass immobilization. The reactor was operated at the mean hydraulic detention time of 4.3 hours and the experimental results presented refer to 15 weeks of operation at mean sewage temperature of 25°C and mean liquid flow rate of 20 l h−1. The mean chemical oxygen demand (COD) of the sewage, based on composed samples, was found to be 350 mg l−1. A short start-up period lasting nearly 8 weeks was observed by monitoring several parameters such as COD, biogas composition, methane concentration and total volatile acid (TVA) concentration. By the end of the start-up period onward, the effluent COD attained approximately constant values of 100 mg l−1 and 75 mg l−1 for non-filtered and filtered samples.

Kabdasli, I.; Gürel, M.; Tünay, O.

doi: 10.1080/09593330.2000.9619001pmid: N/A

Textile printing is becoming an important wastewater source as the water-based materials replace the organic solvents. The wastewaters originating from this operation are often strong and may contain toxics, although their volume is quite low. In this study, a textile printing plant was evaluated to assess pollution characteristics and treatment alternatives. Rotation printing wastewaters were found to be relatively diluted compared with other printing wastewaters, having a COD of around 800 mg l−1 and responded with a high efficiency to both chemical precipitation and biological treatment. On the other hand, tube and item printing wastewaters contained solvents as well as high COD and TKN. Chemical treatment and aeration used as a pretreatment resulted in over 90 % COD removal together with high degree of color and solvent removal. Biological treatment following pretreatment resulted in an effluent COD of 250-500 mg l−1. Nitrogen removal in the pretreatment stage was also assessed using magnesium ammonium phosphate (MAP) precipitation and air stripping. Results of the study were evaluated considering alternative treatment schemes.

Houghton, J. I.; Stephenson, T.; Quarmby, J.

doi: 10.1080/09593330.2000.9619002pmid: N/A

Anaerobic digestion of wastewater sludge has found widespread use as a method of sludge stabilisation, but the waste sludge remaining can be more difficult to dewater. One factor thought to influence sludge dewaterability is the level of microbial extracellular polymer present in the sludge. Utilising laboratory scale anaerobic digesters, this study aimed to assess the effect that digester retention time has on extracellular polymer production and its associated impact on sludge dewaterability. Six digesters were constructed and operated, as matched pairs, over a range of retention times (10, 15, and 30 days) for 4 full retention periods. The end point extracted extracellular polymer yield was related to the sludge dewaterability, as measured using the capillary suction time test. There was a strong, positive correlation (r2=0.999) between the extracellular polymer yield and sludge dewaterability, but no relationship was found between extracellular polymer yield and digester retention time. Further analysis of the extracted polymer organic and inorganic content demonstrated that the digester retention time had no effect on polymer composition, but polymer composition did appear to have an impact on the sludge dewaterability.

Hu, H.-Y.; Goto, N.; Fujie, K.

doi: 10.1080/09593330.2000.9619003pmid: N/A

Energy efficiency is one of the important factors that should be taken into account when selecting a treatment method of wastewater. In this study, the present status of the operating conditions (hydraulic retention time, aeration amount and BOD loading) and energy consumption characteristics of small-scale conventional activated sludge plants for sewage treatment in Japan was clarified through statistical analyses. A small-scale sewage plant was defined as one with a real influent flow-rate of sewage less than 5 000 m3 d−1 in this study. Our analytical results showed that the small-scale activated sludge plants investigated in this study had very good performance of BOD and COD removals but poor energy efficiency. The total power consumption in the small-scale activated sludge plants averaged at 1.0 kWh m−3, which was twice as high as the average value for all of the sewage plants in Japan. It was demonstrated that the ‘working efficiency’ of an activated sludge plant, defined as the ratio of real influent flow rate to its capacity (designed value of influent flow rate), was the most important factor controlling the energy efficiency. Lower working efficiency significantly brought down the energy efficiency of an activated sludge plant. Optimal design of the capacity of activated sludge plants is strongly desired to have higher energy efficiency in sewage treatment.