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Practical implementation of true on-site water recycling systems for hand washing and toilet flushing.

ABSTRACT: On-site wastewater reuse can improve global access to clean water, sanitation and hygiene. We developed a treatment system (aerated bioreactor, ultrafiltration membrane, granular activated carbon and electrolysis for chlorine disinfection) that recycles hand washing and toilet flush water. Three prototypes were field-tested in non-sewered areas, one in Switzerland (hand washing) and two in South Africa (hand washing, toilet flushing), over periods of 63, 74 and 94 days, respectively. We demonstrated that the system is able to recycle sufficient quantities of safe and appealing hand washing and toilet flush water for domestic or public use in real-life applications. Chemical contaminants were effectively removed from the used water in all prototypes. Removal efficiencies were 99.7% for the chemical oxygen demand (COD), 98.5% for total nitrogen (TN) and 99.9% for phosphate in a prototype treating hand washing water, and 99.8% for COD, 95.7% for TN and 89.6% for phosphate in a prototype treating toilet flush water. While this system allowed for true recycling for the same application, most on-site wastewater reuse systems downcycle the treated water, i.e., reuse it for an application requiring lower water quality. An analysis of 18 selected wastewater reuse specifications revealed that at best these guidelines are only partially applicable to innovative recycling systems as they are focused on the downcycling of water to the environment (e.g., use for irrigation). We believe that a paradigm shift is necessary and advocate for the implementation of risk-based (and thus end-use dependent) system performance targets to evaluate water treatment systems, which recycle and not only downcycle water.

SUBMITTER: Reynaert E

PROVIDER: S-EPMC7242789 | biostudies-literature | 2020 May

REPOSITORIES: biostudies-literature

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Practical implementation of true on-site water recycling systems for hand washing and toilet flushing.

Reynaert Eva E Greenwood Esther E EE Ndwandwe Bonginkosi B Riechmann Michel E ME Sindall Rebecca C RC Udert Kai M KM Morgenroth Eberhard E

Water research X 20200408

On-site wastewater reuse can improve global access to clean water, sanitation and hygiene. We developed a treatment system (aerated bioreactor, ultrafiltration membrane, granular activated carbon and electrolysis for chlorine disinfection) that recycles hand washing and toilet flush water. Three prototypes were field-tested in non-sewered areas, one in Switzerland (hand washing) and two in South Africa (hand washing, toilet flushing), over periods of 63, 74 and 94 days, respectively. We demonstr ...[more]

PMID: 32462136

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Project description:Innovative solutions are necessary to enable the decentralized recycling of greywater for applications requiring high-quality water, such as hand washing. While physical barriers such as ultrafiltration membranes effectively prevent the passage of bacteria, and chemical and biological treatments can effectively reduce the carbon content of the treated water, there exists a knowledge gap regarding the application of anti-bacterial strategies to prevent the growth of harmful bacteria following treatment. In this study, the effluent water from a household-scale greywater treatment system was fed to seven parallel experimental post-treatment tanks: three receiving direct chlorination with free chlorine residuals of 0.2, 1 or 5 mg Cl2/L, three with chlorine produced through electrolysis at the same residual concentrations, and one control with no chlorine added. For increasing concentrations of direct chlorination, the median total cell count (TCC) values were 9 × 104, 2.9 × 104 and 1.8 × 103 cells/mL, respectively. Electrolysis treatment produced very similar TCC concentrations, 8.8 × 104, 1.1 × 104 and 2.3 × 103 cells/mL. The TCC concentrations were lower than the concentration of the water entering each tank (∼3 × 105 cells/mL). Intact cell count (ICC) measurements indicated that the viable cell concentrations, were less than 10% of the TCC values. Though electrolysis treatment can produce powerful oxidants, such as hydroxyl radical, there was no evidence that electrolysis in this system provided additional benefits beyond chlorine production for control of total or intact cell counts. Oxidation of bacteria by chlorine was the dominant anti-bacterial mechanism in our system. Monitoring of dissolved organic carbon (DOC) and assimilable organic carbon (AOC) did not suggest that carbon-limitation significantly impacted cell counts when chlorination or electrolysis treatment was applied. This work demonstrates that either direct chlorination or electrolysis treatment are able to reduce bacteria concentrations over long-term operation of a hand washing water treatment system. We recommend selecting chlorine residual targets such that a chlorine residual is maintained during periods of challenging operating conditions. We observed that a target residual of 1 mg Cl2/L, in our system, maintained the TCC below the concentration found in Zurich drinking water.

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Practical implementation of true on-site water recycling systems for hand washing and toilet flushing.

Publications

Practical implementation of true on-site water recycling systems for hand washing and toilet flushing.

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