An investigation into constructed wetlands for domestic greywater treatment and reuse in Ontario

Chan, Carolyn
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University of Guelph

The reuse of domestic greywater for toilet flushing has the potential to reduce both water consumption and wastewater production, but there is a need for low-cost, low-maintenance greywater treatment systems that can meet reclaimed water quality standards. The purpose of this thesis is to develop a horizontal subsurface flow wetland design that can be sited in a greenhouse, to document the initial performance of the design treating real greywater, to determine the effect of plants, and to provide recommendations for design. Pilot wetlands (planted and unplanted replicates) were constructed in a passively heated greenhouse and fed real domestic greywater. Effluent quality was compared to national reclaimed water quality guidelines. After the first five months of the study, operational changes (reduced loading, aeration of influent, fill and drain) were tested to determine their effect on effluent quality. The results show that the original design basis, 7.5 gBOD m-2d-1, is not appropriate for greywater wetland design under the conditions of this study due to insufficient removal of BOD and turbidity (although suspended solids removal was acceptable). Anoxic conditions within the wetlands led to reduction of sulfate to hydrogen sulfide, which demands oxygen and leads to odour and turbidity problems. Plants did not affect treatment during the first five months. Aerating influent and operation in fill and drain mode may improve BOD removal at relatively high hydraulic loading rates, but effluent disinfection is required to completely remove E.coli. Design recommendations were developed, including tentative loading rates and plant species.

greywater, constructed wetlands, water reuse, horizontal subsurface flow, greenhouse, ornamental plants