A B S T R A C TGraywater treatment systems must inactivate pathogens, prevent regrowth, be low cost, and be simple to operate to support their widespread adoption for alleviating water stress. A treatment system comprised only of filtration and disinfection could meet these constraints. To investigate pathogen disinfection and regrowth in such a system with minimal organic matter removal, herein three disinfectants (chlorine, ultraviolet irradiation, and ozone) were tested in combination with three filter types (coarse, sand, and cartridge) for inactivation of pathogens in graywater from the showers and hand washbasins of 14 student residences. Graywater was spiked with bacterial and viral pathogens or surrogates post-filtration. Chlorination post-filtration achieved log reductions greater than 7.1, 8.0, and 7.4 for Escherichia coli, Salmonella enterica, and Pseudomonas aeruginosa, respectively, and 3.8 for MS2 bacteriophage. UV was similarly effective, but would not prevent regrowth without a disinfectant residual. Ozonation generally was ineffective at the doses tested, with the exception that MS2 log removal was 3.7. Pathogen regrowth could be prevented for 4 d with a chlorine residual of 2.75 mg/L even for a simulated high-contamination event (6 log each pathogen). When chlorine residual was maintained, regrowth of indicators and pathogens was prevented for the light graywater investigated.

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Many states are adopting more stringent nutrient load restrictions, requiring utilities to invest in costly improvements. To date, substantial research has been done to independently assess the nutrient removal efficacy of wastewater treatment technologies and stormwater control measures. The analysis presented here provides a unique assessment by evaluating combinations of nutrient load reduction strategies across water supply, wastewater, and stormwater sectors. A demonstration study was conducted evaluating 7812 cross-sector removal strategies in the urban water system using empirical models to quantify efficacy of common wastewater treatment, water management, and stormwater control measures (SCMs). Pareto optimal solutions were evaluated to identify the most cost-effective strategies. To meet stringent nutrient requirements, wastewater treatment facilities (WWTFs) will likely require advanced biological nutrient removal with carbon and ferric addition. Even with these technologies, WWTFs may still be unable to obtain target nutrient requirements. In addition, municipalities can consider water management practices and SCMs to further reduce nutrient loading or provide a more cost-effective nutrient removal strategy. For water management practices, source separation and effluent reuse were frequently identified as part of the most effective nutrient strategies but face engineering, political, and social adoption barriers. Similarly, SCMs were frequently part of effective nutrient removal strategies compared to only adopting nutrient removal practices at WWTFs. This research provides the framework and demonstrates the value in using an urban water system approach to identify optimal nutrient removal strategies that can be easily applied to other urban areas.