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.
Highlights
The United Nations has reported that nearly 850,000 people die every year from lack of access to clean water, sanitation and hygiene (WASH, WHO and UNICEF, 2017)
Water that passed through the membrane was collected in a permeate reservoir (10 cm polyvinyl chloride pipe connected to the membrane module permeate outlet, holding volume of 4 L), from where it was pumped through a granular activated carbon (GAC) filter (Norit 830, ~1.5 mm grain diameter, Cabot, Boston, USA) to the clean water tank (CWT) at regular intervals
In the case of Prototype 2 (P2) and Prototype 3 (P3), maximum usage was significantly below the design capacity, which may have an influence on the performance presented in the subsequent sections
Summary
The United Nations has reported that nearly 850,000 people die every year from lack of access to clean water, sanitation and hygiene (WASH, WHO and UNICEF, 2017). WASH challenges are interdependent: access to safe water, improved sanitation facilities or washing facilities do not, independently of one another, necessarily lead to improved health (Eisenberg et al, 2007). Adequate sanitation facilities should protect water sources from contamination, and provide access to improved hygiene. Reliable water supplies are required for flush-based sanitation systems, which are, to this day, still what most people aspire to (Flores, 2011). One of the great challenges for the provision of WASH services is to provide, process, and distribute the required water
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