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Rapid urbanization and industrialization have put pressure on water resources and centralized wastewater treatment facilities and the need for greywater treatment at decentralized levels is increasing. This paper reviews the studies that used granular filtration for the treatment of greywater. Filter media characteristics that helps in the selection of suitable sustainable and environmental friendly materials without compromising the quality of treated greywater is first reported. The effect of type of filter media, media size and media depth along with the effect of operating conditions are discussed in detail. The choice, role and effect of different pre-treatment alternatives to granular media filtration are also presented. The efficiency of the filters to remove different physicochemical and microbial parameters was compared with different reuse guidelines and standards. Reported studies indicate that not only filter media characteristics and operating conditions but also the quality of raw greywater significantly influence the filter performance. Based on the source of greywater and desired reuse option, different granular media filtration alternatives are suggested. Operation of filters with properly selected media at optimum conditions based on the source of greywater helps filter in achieve the different reuse standards.

Recently waste to energy projects gaining more attraction due to rapid waste generation due to increased urbanization. Improper municipal solid waste (MSW) treatment resulting in environmental risks such as air pollution, ground, and surface water contamination. Anaerobic digestion (AD) is the best method to treat organic solid waste. Mono-AD of organic fraction of municipal solid wastes (OFMSW) leads to lower methane yield due to the accumulation of volatile fatty acids (VFAs). Mixing of two or more substrates (Co-digestion) dilutes the toxic compounds and increases the methane yield by providing proper environment for microbes. In this study anaerobic co-digestion (AcoD) of source segregated OFMSW (particularly food waste, fruit waste, and vegetable waste) with chicken fecal matter (co-substrate), and cow dung (inoculum) was investigated by using batch studies (Duration of 30 days). AcoD carried out in three different batch reactors viz. R1 (food mix), R2 (vegetable mix), and R3 (fruit mix) feed with substrates (S1& S2) and inoculum (I) (S1: S2: I = 0.5:0.5:2). The methane percentage obtained for reactor R1 was 69.60%, which is higher compared to the other reactors (R2- 61.2%, and R3- 57.37%). R1 reactor had higher methane yield due to its higher lipids (higher VFAs), and proteins (sufficient buffer capacity). R3 reactor had lowest methane yield due to its highest carbohydrates (rapid acidification), and lower proteins (lower buffer capacity). Modified Gompertz model gave better results near to experimental studies. The present study proved that mixing OFMSW with proper co-substrate (protein-rich) increases the methane yield by providing proper buffer capacity.

A long-duration laboratory study spanning more than 6 months was conducted to evaluate the effect of operating mode on the performance of sand filters for greywater treatment. Performance of saturated and unsaturated filters operated in continuous or intermittent mode was evaluated using settled real greywater. Effects of pause period and higher loading rate on their performance were also evaluated. Furthermore, the effect of the depth of the filter medium on the performance of the filters was also assessed. The saturated filters operated continuously or intermittently performed significantly better than the respective unsaturated filters. Saturated continuous (SC) and unsaturated intermittent (UI) filters were the best and worst performers amongst the different filters. SC filter removed on an average 98% turbidity, 76% BOD, 88% COD, 84% ammonia-N (NH4-N) and 95% phosphate (PO4-P). Up to 99.68% (2.40 log) removal of faecal coliforms was also achieved by this filter. SC filter showed stable and reliable performance as its effluent quality was insensitive to fluctuations in influent quality. The pause period significantly affected the removal of some of the parameters. Doubling the hydraulic loading rate significantly affected the performance of continuous filters. Though most of the pollutant removal occurred in the top 10 cm in all the filters, a depth of 50 cm was found optimum for the removal of different pollutants. Whilst all the filters produced effluent conforming to different reuse standards except microbial standards, saturated continuous filter (SC) could also meet the faecal coliform standards towards the end of the filter operation.

In a long-duration study, the performance of a physicochemical system for the treatment of raw graywater––namely, coagulation followed by continuous saturated-sand filtration––was investig...

A year-long study was conducted to assess the quantity and quality characteristics of greywater generated from different sources of an Indian household. The effect of source separation on greywater quantity and pollutant load contribution was also assessed. Composite samples were collected separately over a period of 24 h from each of the greywater source, namely hand basin, bathroom, kitchen, and laundry, and were analysed for different physico-chemical and microbiological parameters. The mean greywater generation averaged 62 L per person per day. Quantitatively, kitchen and bathroom greywater contributed 37 and 31% of the total greywater volume, respectively, while hand basin and laundry greywater accounted for 11 and 21% of the total greywater generation. Kitchen greywater contributed about 60% of the organic load in terms of biochemical oxygen demand (BOD) and chemical oxygen demand (COD), while laundry greywater was the major contributor of heavy metals and PO

The study assessed the speciation of heavy metals in sewage sludge. Sewage sludge samples were collected from three full-scale sewage treatment plants which employ different treatment processes. Sewage sludge samples from activated sludge process (ASP), UASB reactor (UASBR) and moving bed bioreactor (MBBR), and one anaerobically digested activated sludge (ASP-AD) was collected during different seasons of the year. Modified sequential extraction process was used classifying metals into acid-soluble/exchangeable fraction (F1), reducible fraction (F2), oxidizable fraction (F3) and residual fraction (F4). Five heavy metals, namely chromium, copper, mercury, lead and zinc, were analysed for different fractions. Among the heavy metals, Zn (1317–1448 mg/kg) and Cu (925–1196 mg/kg) contents were the highest, followed by Cr (129–151 mg/kg), Pb (60–86 mg/kg), and Hg (18–34 mg/kg). Concentrations of all heavy metals tested except mercury in MBBR were within the limits set by different agencies.

A long-duration laboratory study spanning more than 6 months was conducted to evaluate the effect of operating mode on the performance of sand filters for greywater treatment. Performance of saturated and unsaturated filters operated in continuous or intermittent mode was evaluated using settled real greywater. Effects of pause period and higher loading rate on their performance were also evaluated. Furthermore, the effect of the depth of the filter medium on the performance of the filters was also assessed. The saturated filters operated continuously or intermittently performed significantly better than the respective unsaturated filters. Saturated continuous (SC) and unsaturated intermittent (UI) filters were the best and worst performers amongst the different filters. SC filter removed on an average 98% turbidity, 76% BOD, 88% COD, 84% ammonia-N (NH

The study compared the performance of a biosand filter (BSF) with two BSFs modified by introducing a layer of zero-valent iron (ZVI) during a long-duration test (4 months) mimicking the household use pattern in developing countries. Results of the study showed that for bacterial removal, ZVI-amended BSFs outperformed the BSF by at least 1 log10 unit throughout the filter operation. Effluent turbidity in the BSF and modified BSFs was not significantly influenced by influent values for the turbidity range tested in the study (17.0–45.4 NTU). Removal efficiency of nitrates was higher in the modified BSFs, with up to ∼89% removal in the modified BSFs compared with ∼29% in the BSF. Sharp decline in dissolved oxygen (DO) was observed during the passage of water through the filters. The DO decline was more in the modified filters compared with the conventional BSF. Effluent iron remained within the drinking-water quality standards. The study thus indicates the potential of ZVI to improve the performance of BSFs.

In this study, response surface methodology (RSM)–artificial neural network (ANN) approach was used to optimise/model disperse dye removal by adsorption using water treatment residuals (WTR). RSM was first applied to evaluate the process using three controllable operating parameters, namely WTR dose, initial pH (pHinitial) and dye concentration, and optimal conditions for colour removal were determined. In the second step, the experimental results of the design data of RSM were used to train the neural network along with a non-controllable parameter, the final pH (pHfinal). The trained neural networks were used for predicting the colour removal. A colour removal of 52.6 ± 2.0% obtained experimentally at optimised conditions (pHinitial 3.0, adsorbent dose 30 g/L and dye concentration 75 mg/L) was comparable to 52.0% and 52.2% predicted by RSM and RSM-ANN, respectively. This study thus shows that optimising/predicting the colour removal process using the RSM–ANN approach is possible, and it also indicates that adsorption onto WTR could be used as a primary treatment for removal of colour from dye wastewater.

Bacterial removal during electrocoagulation (EC) was investigated employing samples from four different water/wastewater sources, namely, greywater, river water, secondary treated sewage and tap water spiked with Escherichia coli. Effects of current density and electrolysis time on the bacterial removal with aluminium electrodes were evaluated. For greywater, river water and secondary treated sewage, total coliform and E. coli removal efficiencies were not significantly different for the tested samples and varied in the range of 2.22–2.53 log10 units at a current density of 1 mA/cm2 and electrolysis time of 30 min. Higher removals up to 3.80 log10 units could be obtained at higher current density of 5 mA/cm2. Heterotrophic bacterial removals were higher compared with coliforms for the tested samples. Further, higher removal was obtained with spiked E. coli in tap water compared with naturally occurring coliforms in other samples. A comparison of bacterial removal by chemical coagulation (CC) employing alum at optimum dose with that by EC with 1 mA/cm2 current density and 30 min electrolysis time showed significantly higher removal by EC (2.22–2.53 log10 removal) compared with CC (1.40–1.80 log10 removal) for the three tested samples. Upon storage up to 48 h, no significant regrowth/decay of organisms was observed in the EC-treated samples.

Aluminium-based water treatment sludge (WTS) was investigated for its potential to remove chromium(VI) from simulated wastewater. Batch sorption tests and column tests were carried out using poly aluminium chloride sludge. Results of the batch study showed that chromium sorption decreased with increase in pH for the pH range studied (2.0–12.0). Long-duration column test with an empty bed contact time of 3 h indicated good Cr(VI) removal capacity of WTS as no chromium was present in the effluent for 115 bed volumes, and a sorption capacity of 1.62 mg/g of dry sludge was obtained which was lower than the sorption capacity reported in the literature. In the presence of other metals such as Co, Cu, Hg and Pb, both percentage Cr(VI) removal and sorption capacity was negatively affected in column tests, and Cr(VI) sorption capacity was only 0.96 mg/g of dry sludge.

Suitability of the electrocoagulation (EC) process for the post-treatment of anaerobically treated urban wastewater was assessed, in batch system employing real effluent from an upflow anaerobic sludge blanket (UASB) reactor. Response surface methodology (RSM) was used to optimize three important process parameters, namely current density, electrolysis time and initial pH. At the optimum conditions of pH 7.07, electrolysis time 18.0 min and current density 15.0 mA/cm2, chemical oxygen demand (COD), turbidity and phosphate removal efficiencies observed were 71.0%, 98.5% and >99.9%, respectively, which were very close to the model-predicted values. High removals of suspended solids (SS; 87.5%), biochemical oxygen demand (BOD) (83.3%) and total coliforms (99.994%) were also obtained at the optimum conditions.

This study investigated the effect of raw water quality and coagulant type and dosage on the efficiency of aluminium recovery from water treatment sludge by acidification process. One of the features of this study is to prioritise several factors affecting aluminium recovery using demonstrating experiments and analysing the result using model. The previous studies comparing the aluminium recovery from PACl and alum sludge had collected the sludge from treatment plants treating different source water. However, this study compares aluminium recovery from PACl and alum sludge obtained from treating same source water. Water treatment sludge was prepared in laboratory by coagulating raw water with different inorganic and organic contents using aluminium sulphate (alum) and polyaluminium chloride (PACl) as coagulants. The effect of the different factors on the aluminium recovery efficiency was evaluated using a 23 full factorial experimental design. The aluminium recovery efficiency was higher for PACl sludge compared to alum sludge with recovery ranging from 62.5 to 74.5 % for alum sludge and from 70.7 to 84.0 % for PACl sludge. At higher concentrations of organic matter and turbidity in the raw water, lower aluminium recovery efficiency was observed for both the sludges. The study thus shows the important effects of raw water quality and coagulant type and dose on the recovery process.

Performance of coagulation followed by intermittent saturated sand filtration system was evaluated for greywater treatment using real greywater. Filters with two different grain sizes were used to study the effect of media size on the removal. Filters were charged daily with 20 L of greywater coagulated with polyaluminium chloride (PACl). Performance of the filters were evaluated based on physicochemical and microbial parameters. Results showed that coagulation followed by sand filtration resulted in 94, 76 and 80% reduction in turbidity, BOD and COD respectively. Also, more than 99% of total and faecal coliform removal was observed. Sand filter with smaller grain size performed significantly better than the sand filter with coarser grain size. Coagulation followed by filtration showed stable and reliable performance as the effluent quality was insensitive to fluctuations in influent quality. Combined coagulation and sand filtration produced effluent conforming to different reuse standards.

Due to depletion of water resources and increased water demand, greywater reuse is gaining popularity as a means of water conservation all over the world. Availability of reliable data on greywater generation and quality characteristics is important in deciding the treatment system and the reuse option. This paper summarises quantity and quality characteristics of greywater reported from different parts of the world. Greywater generation from different countries is compared and its variability is discussed. Important pollutants of concern in greywater such as organic content, nutrients, microorganisms, metals and organic micropollutants from different greywater sources such as bathrooms, hand basins, kitchen and laundry are described. The review shows large variations in greywater quality and quantity with respect to time and source, and the selection of a treatment system would largely depend on this variability. The review also shows that at the levels found in greywater, heavy metals and organic micropollutants in recycled greywater generally do not pose a threat to human health if treated properly.

Gray water (GW) has attracted global attention as an alternative water source over the last few decades. This chapter discusses the quantity and quality characteristics of GW in developed and developing countries. A number of systems varying from low-cost devices to complex treatment systems have been used/studied for GW treatment. Different combinations of chemical, physical, and biological processes such as coagulation, sedimentation, filtration, biodegradation, and disinfection have been used for GW treatment. In order to reduce cost, treatment of GW by natural systems is gaining importance in both developed and developing countries. Several factors such as type of GW, scale of treatment, land availability, reuse applications, posttreatment requirements, capital and maintenance costs, and reliability and replicability should be considered while selecting an appropriate GW treatment technology. The chapter also analyzes the health risk associated with the use of treated GW.

In the present study, chemical coagulation with alum and polyaluminium chloride (PACl) was utilized for greywater treatment. More than 140 jar tests on greywater with varying characteristics were conducted in order to determine the optimum coagulant dosage and treated greywater characteristics. The average removal efficiencies of turbidity, chemical oxygen demand (COD) and total suspended solids were obtained as 91, 73 and 83% using alum and 93, 74 and 89% using PACl, respectively. For similar initial turbidity levels, optimum PACl dosages required were significantly less compared to optimum alum dosages. Further, PACl produced treated greywater with lower levels of turbidity compared to alum. Results of the coagulation tests were used to design artificial neural network (ANN) models for the prediction of the optimum coagulant dosage and treated greywater quality parameters. ANN models with initial turbidity, pH, conductivity and alkalinity as the input parameters could predict the optimum coagulant dose and treated greywater quality. The performance of the models was found to be good, with correlation coefficient values greater than 0.80. Empirical formulas for the prediction of alum and PACl dosages were also derived using the algorithm weights and bias values from the networks eliminating the need for running the ANN software.

The potential of aluminum-based water treatment residuals (WTR) discharged from water treatment plants was evaluated as a coagulant for color removal from a disperse dye solution. The effects of WTR dose, initial dye concentration, and initial pH on color removal were studied. The results showed higher color removal at lower pH values. Maximum color removals of 88, 87, and 76% were obtained for initial dye concentrations of 25, 50, and 75 mg/L, respectively, at pH 3.0 with a WTR dose of 3,000 mg/L. Different artificial neural networks (ANN) were developed for predicting the color removal. The performance of the models was found to be very good, with correlation coefficient (R2) values greater than 0.90. The results showed that simulation employing ANN incorporates non-linear behavior of the system, and the model-predicted and observed values of color removals were in close agreement with each other. The study thus indicates that reusing water treatment sludge as a coagulant for color removal would...

The influence of three important parameters, namely, pause time, charge volume and influent turbidity on the performance of a biosand filter (BSF) was assessed by employing response surface methodology with a Box-Behnken design. Fifteen runs were conducted in triplicate using a full-scale BSF with a pore volume of 19.6 L, and the performance of the filter was assessed by monitoring total coliforms, Escherichia coli and turbidity of the effluent. Results showed that there was a significant improvement in the microbiological quality of filtered water when the pause time was increased from 12 to 36 h, while it deteriorated as charge volume was increased from 10 to 30 L. The effluent microbiological quality was unaffected by changes in the influent turbidity in the range of 10–50 NTU. Further, effluent turbidity was not significantly affected by the changes in any of the operating parameters, and it remained below 1.5 NTU in all the runs. At optimum conditions of pause time 23 h, charge volume 19.4 L and influent turbidity 32 NTU, bacterial removal exceeded 99.4%. The results show that charging of the filter with about one pore volume of water once a day would be the ideal operating strategy for a BSF.

The feasibility of reusing polyaluminium chloride-based water treatment sludge as a coagulant for the post-treatment of upflow anaerobic sludge blanket (UASB) reactor treating urban wastewater was assessed. Response surface methodology with Box-Behnken design was employed to optimise three variables affecting coagulation/flocculation process namely sludge dose, initial pH and fresh coagulant dose. Results of the modelling study gave the following optimum conditions: sludge dose 15 g/L, initial pH 9 and fresh coagulant dose 4.2 mg Al/L; and predicted 72% COD removal and 88% turbidity removal. Confirmative experiments at the optimum conditions gave COD and turbidity removals of 74% and 89%, respectively, which were in close agreement with the predicted values. Further, at optimum conditions high removals of phosphate (79%), suspended solids (84%), BOD (78%) and total coliforms (99.7%) were obtained. The experiments also showed that a combination of water treatment sludge with fresh coagulant would give a substantially higher contaminant removal compared to the removals obtained by fresh coagulant alone. The study presents a novel reuse alternative for water treatment sludge and the results suggest that reuse of water treatment sludge as a coagulant for the post-treatment of UASB reactor effluent would be an attractive option.

Rooftop rainwater harvesting (RWH) is receiving increased attention as an alternative source of drinking water. In urban areas, RWH can bring many benefits and may serve to cope with current water shortages, urban stream degradation, and flooding. The present study examined the effect of some of the factors that affect the quality of roof-harvested rainwater, namely, type of the roofing material, age of the roof and characteristics of rainfall event, on the quality of roof-harvested rainwater. More than 100 roof-harvested rainwater samples collected from newly constructed pilot-scale roofs and existing full-scale roofs of different materials were analysed for different physico-chemical and microbiological water quality parameters. Enrichment factor, correlation analysis and other statistical techniques were used to arrive at conclusions. Results showed that, in general, the physico-chemical characteristics except pH, turbidity and some heavy metals conformed to the drinking-water quality standards. Bacteriological contamination was found for most of the runoff samples from roofs. The results showed high variability in the concentration of different water quality parameters between different roofing materials. Enrichment factor (that is the ratio of concentration in roof runoff to that in free fall) was found to be different for different roofing materials and its value was >1 for most of the parameters tested indicating the significant effect of roofing material on the concentration of various parameters by weathering and/or by deposition. The enrichment factor was high for old roofs compared to new roofs. Correlation analysis revealed a positive correlation between the concentration of different water quality parameters and the dry period, and a negative correlation between some water quality parameters and the amount of rainfall. Thus, roofing material and characteristics of rainfall event were found to have a significant influence on the quality of roof-harvested rainwater.

Aluminium-based water treatment sludge was used as a coagulant for removing/recovering phosphate from the effluent of upflow anaerobic sludge blanket (UASB) reactor treating municipal wastewater. The effect of three variables, namely sludge dose, initial pH and fresh coagulant (poly-aluminium chloride, PACl) dose was studied using response surface methodology. About 87% phosphate removal could be obtained at the optimum conditions of sludge dose 13.8 g/L, initial pH 6, and fresh PACl dose 5.8 mg Al/L. In order to achieve a similar phosphate removal, a dose in the range of 30–40 mg Al/L of fresh PACl was required. The results suggest that water treatment sludge can be reused as a coagulant for post-treatment of UASB reactor effluent treating municipal wastewater and can be considered as a promising alternative for removing phosphate which can substantially reduce the consumption of fresh PACl. The sludge generated during this process could potentially be used in land application which results in recycling of phosphate.

Water samples from four different sources of varying physico-chemical and microbial quality with their naturally occurring microorganisms were exposed to sunlight in polyethylene terephthalate bottles under similar conditions. Up to 3-log10 reduction of total coliforms (TC) was observed during a 6-h exposure period under weak/moderate radiation conditions (

With a view to evaluating the effects and interactions of three influential factors, turbidity, pH and dissolved oxygen (DO), on the efficiency of solar water disinfection process, response surface methodology (RSM) based on Box–Behnken design was employed. Total coliform (TC) removal and heterotrophic plate count (HPC) removal were used as response factors. The RSM models were developed based on the experimental results of four-hour solar exposure in polyethylene terephthalate bottles. The measured and predicted removals were close to each other. Though the HPC removal and TC removal showed similar trends, the HPC removal was much lower (40–66%) compared to TC removal (68–97%) for the conditions studied. The results showed that turbidity up to certain levels (10–20 NTU) did not adversely impact the bacterial removal. In the range studied (6.0–9.5), pH showed little influence on the removals. While bacterial inactivation showed significant reduction at low DO levels, increasing DO beyond a certain...

The biosand filter (BSF), an intermittently operated household slow sand filter, is one of the commonly used household water purification methods in the rural areas of developing countries. In this study, long-duration tests were conducted in the laboratory to investigate the influence of two important operating parameters, namely the pause period (idle time) and the charge volume on the performance of BSF by using full-scale BSFs. The filters were charged daily with 20 or 40 L of tap water spiked with Escherichia coli or sewage with different pause periods. Results indicated that during the ripening (maturation) of the filter, which took about one month, E. coli removal was low, with an average value

In recent years, response surface methodology (RSM) has been used for modelling and optimising a variety of water and wastewater treatment processes. RSM is a collection of mathematical and statistical techniques for building models, evaluating the effects of several variables, and obtaining the values of process variables that produce desirable values of the response. This paper reviews the recent information on the use of RSM in different water and wastewater treatment processes. The theoretical principles and steps for its application are first described. The recent investigations on its application in coagulation–flocculation, adsorption, advanced oxidation processes, electro-chemical processes and disinfection are reviewed. The limitations of the methodology are highlighted. Attempts made to improve the RSM by combining it with other modelling techniques are also described.

One of the sources of pathogens in the environment is wastewater that is discharged with or without treatment or recycled for many purposes. Treatment technologies for wastewater have been continuously improving due to the stringent limits set, including microbial control, and also due to reuse practices because of the increasing water scarcity in a number of regions of the world. As secondary treatment, many biological processes have been applied. However, these are able to remove pathogens only to some extent. Thus, tertiary treatment has been used for microbial removal. Still, many resistant pathogens need to be removed, and for this purpose the use of advanced oxidation as tertiary or disinfection processes is required so as to ensure the safe discharge and reuse potential of the effluent.

In the present study, feasibility of an integrated composting–vermicomposting process is assessed for stabilization of human faecal slurry using matured vermicompost as bulking material and Eisenia fetida as earthworm species. A preliminary study showed the dominant role of relative humidity over temperature on the water loss from the slurry–vermicompost mixture. The composting stage, spanning 5 months, produced sufficient enrichment of bulking material with organic matter after 20 cycles of recycling and mixing with faecal slurry, and produced materials acceptable for vermicomposting under ambient conditions. Vermicomposting of composted material was conducted for a duration of six months with a stocking density of 3.0 kg/m2. Vermicomposting resulted in significant reduction in volatile solids (from 527 to 340 mg/g dry weight), oxygen uptake rate (from 29.40 to 0.82 mg-O2/g/h), total carbon (43%), total organic carbon (41%), and significant increase in total phosphorus (from 14.0 to 20.5 mg/g dry weight) and potassium (24.8–54.3 mg/g dry weight). No total coliforms, faecal coliforms, Salmonella and viable helminth ova were detected in the processed vermicompost. The results of the study indicated the potential of the integrated composting–vermicomposting system for converting human faecal slurry into organic manure.

The biosand filter (BSF), intermittently operated household slow-sand filter, was modified by introducing a 10-cm thick layer of iron oxide-coated sand. Long-duration (about four months) tests were conducted to compare the performance of the modified BSF (MBSF) with the conventional BSF in terms of their efficiency in removing bacteria and turbidity under different operating conditions. Filters were charged daily with 20 L or 40 L natural canal water (turbidity 10.0 ± 1.2 NTU; faecal coliforms 365 ± 251 MPN/100 mL; pH 8.4 ± 0.4) or seeded tap water (turbidity 14.7 ± 4.3 NTU; Escherichia coli 3850 ± 736 CFU/mL; pH 7.9 ± 0.3). Results showed that the performance of MBSF in terms of faecal coliform and E. coli removals was better by at least one-log10 unit throughout the filter operation. The mean bacterial removal was low for BSF for the first month (90.0%), while it was 99.3% for MBSF during the same period. Bacteria and turbidity removals increased with time as filter ripening (maturation) occurred in both the filters. No significant difference was observed in turbidity removal between BSF and MBSF, and mean effluent turbidity was around 1 NTU for BSF and MBSF representing > 90% removal. When daily charge was increased from 20 L to 40 L, a reduction in bacterial removal was noted in both the filters indicating the influence of operating conditions. Effluent physico-chemical quality remained within the guideline values for drinking water.

The present study was conducted to compare the performance of a dual-media filter consisting of manganese oxide-coated (MOCS) and iron hydroxide-coated sand (IOCS) with that of IOCS filter and uncoated sand filter in treating water contaminated by microorganisms, heavy metals and turbidity with a view to its use in simple household water purification devices in developing countries. Long-duration column tests were conducted using two natural waters namely, roof-harvested rainwater and canal water. Performance of the filters showed that dual-media filter was more efficient in removing bacteria and heavy metals compared to IOCS filter, while uncoated sand filter showed very poor performance. The average effluent levels for dual-media filter when tested with rainwater were: turbidity 1.0+/-0.1 NTU; total coliforms 3+/-2 MPN/100 mL; heterotrophic plate count 170+/-20 CFU/mL; zinc 0.06+/-0.01 mg/L, while that for IOCS filter were: turbidity 1.0+/-0.1 NTU; total coliforms 4+/-2 MPN/100 mL; heterotrophic plate count 181+/-37 CFU/mL; zinc 0.20+/-0.07 mg/L. Similar results were obtained for canal water also. Up to 900 bed volumes (BV) could be treated without affecting the efficiency in the case of rainwater, while the filter operation had to be terminated after 500 BV due to excessive headloss in the case of canal water. The study thus showed the potential of the dual-media for use in low-cost household water filters for purification of natural waters.

The present study examined the suitability of vermicomposting technology for processing source-separated human faeces. Since the earthworm species Eisenia fetida could not survive in fresh faeces, modification in the physical characteristics of faeces was necessary before earthworms could be introduced to faeces. A preliminary study with six different combinations of faeces, soil and bulking material (vermicompost) in different layers was conducted to find out the best condition for biomass growth and reproduction of earthworms. The results indicated that SVFV combination (soil, vermicompost, faeces and vermicompost - bottom to top layers) was the best for earthworm biomass growth indicating the positive role of soil layer in earthworm biomass growth. Further studies with SVFV and VFV combinations, however, showed that soil layer did not enhance vermicompost production rate. Year-long study conducted with VFV combination to assess the quality and quantity of vermicompost produced showed an average vermicompost production rate of 0.30kg-cast/kg-worm/day. The vermicompost produced was mature as indicated by low dissolved organic carbon (2.4+/-0.43mg/g) and low oxygen uptake rate (0.15+/-0.09mg O(2)/g VS/h). Complete inactivation of total coliforms was noted during the study, which is one of the important objectives of human faeces processing. Results of the study thus indicated the potential of vermicomposting for processing of source-separated human faeces.

The effectiveness of solar disinfection in treating roof-harvested rainwater contaminated with microorganisms was evaluated with a view to its use as a household technology. Coliform and heterotrophic bacteria inactivation kinetics were studied using bottles with different backing surfaces. The effects of various parameters such as turbidity, solar intensity, type of organisms (naturally occurring versus laboratory grown) and bottle volume on bacterial inactivation were studied. Complete inactivation of total coliforms was observed in 6 h when solar radiation exceeded ∼500 W/m2.Under high contamination and overcast conditions, prolonged exposure was needed. Moderate turbidity (38 NTU) did not reduce the inactivation efficiency, but slightly enhanced it. No regrowth of microorganisms was observed after 24 h following solar disinfection. No significant difference in the inactivation kinetics was observed for bottle sizes in the range of 0.5 to 2.0 L. Tests with naturally occurring and laboratory-grown organisms indicated that laboratory-grown organisms were inactivated faster than naturally occurring organisms.