Comparative evaluation of different pre-treatment alternatives for granular media filters treating greywater and their ranking using analytical hierarchy process.

In this study, the performance of four different pre-treatment alternatives for granular media filtration, namely, settling, aeration, coarse media filtration and chemical coagulation were compared experimentally. Further, analytical hierarchy process (AHP) was used to compare their performance based on economic, environmental, technical and performance criteria. Performance of settling and aeration were evaluated up to 24 h duration. The coarse media filter was intermittently operated with 10 L of greywater in downflow mode while alum was used for chemical coagulation. Experimental results showed that settling up to 6 h did not show significant removal of different pollutants whereas 24 h settling resulted in moderate removal of turbidity and organic content but was not efficient in the removal of nutrients and faecal coliforms. Chemical coagulation reduced 93, 66, 48 and 97% of turbidity, COD, NH4-N and faecal coliforms, respectively from greywater but resulted in excessive sludge generation and is difficult to adopt on-site and requires skilled supervision. Coarse filtration of greywater resulted in 61, 41, 36 and 35% removal of turbidity, COD, PO4-P and faecal coliforms, respectively. Considering different criteria AHP gave coarse filtration as the best pre-treatment option to the granular media filters treating greywater.

Granular media filtration for on-site treatment of greywater: A review.

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.

Quantity and quality characteristics of greywater from an Indian household.

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 PO4-P loads. Hand basin and bathroom greywaters were the major sources of total coliforms. The analysis shows that separation of kitchen and laundry greywater is beneficial as it reduces pollutant load considerably.

Quantity and quality characteristics of greywater: A review.

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.

Use of zero-valent iron-modified sand filters for greywater treatment: performance evaluation and modelling using response surface methodology.

The conventional sand filter when used alone for on-site treatment of greywater fails to meet different reuse standards, and hence there is a need to improve the potential of sand filters to remove different contaminants from greywater. Performance of zero-valent iron-modified (ZVI) sand filters is investigated in the present study for the treatment of real greywater. The experiments were conducted using three filters: an unmodified filter (SF) and two iron-modified filters, MSF-2 (with 2 kg of ZVI) and MSF-4 (with 4 kg of ZVI). The study evaluated the performance of these filters under different conditions: daily feed volumes of 10 L (72 L/m2/day), 20 L (144 L/m2/day), and 30 L (217 L/m2/day), as well as pause periods of 12, 24, and 36 h. The results showed that the ZVI-modified filters outperformed the unmodified filter significantly. Specifically, MSF-4 showed higher pollutant removal compared to MSF-2. The filter MSF-4 achieved 58% COD removal, 59% BOD removal, 56% NH4-N removal, 82% PO4-P removal, and a significant 1.96 log reduction in fecal coliforms. To optimize the filter operation, three key parameters, amount of ZVI, feed volume, and pause period were considered. The Box-Behnken design (BBD) with response surface methodology was employed to achieve optimization. The results of the optimization study indicated that the optimal conditions for the filters were 2.67 kg of ZVI quantity, a feed volume of 30 L (217 L/m2/day), and a pause period of 32.1 h.

Effect of operating mode on the performance of sand filters treating greywater.

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.