Constructed wetlands for greywater recycle and reuse: A review

Concern overdwindlingwater supplies for urban areas aswell as environmental degradation fromexisting urban water systems has motivated research into more resilient and sustainable water supply strategies. Greywater reuse has been suggested as a way to diversify local water supply portfolios while at the same time lessening the burden on existing environments and infrastructure. Constructed wetlands have been proposed as an economically and energetically efficient unit process to treat greywater for reuse purposes, though their ability to consistently meet applicable water quality standards, microbiological in particular, is questionable. Wetherefore review the existing case study literature to summarize the treatment performance of greywater wetlands in the context of chemical, physical and microbiological water quality standards. Based on a cross-section of different types of wetlands, including surface flow, subsurface flow, vertical and recirculating vertical flow, across a range of operating conditions, we showthat although microbiological standards cannot reliably be met, given either sufficient retention time or active recirculation, chemical and physical standards can. We then review existing case study literature for typical water supply disinfection unit processes including chlorination, ozonation and ultraviolet radiation treating either raw or treated greywater specifically. An evaluation of effluent water quality from published wetland case studies and the expected performance from disinfection processes shows that under appropriate conditions these two unit processes together can likely produce effluent of sufficient quality to meet all nonpotable reuse standards. Specifically, wesuggest that recycling vertical flowwetlands combined with ultraviolet radiation disinfection and chlorine residual is the best combination to reliably meet the standards. (C) 2018 Elsevier B.V. All rights reserved.