Technologies for greywater recycling in buildings

Abstract

The potential of four pilot-scale wastewater treatment processes for in-building greywater recycling has been assessed. The evaluation of three membrane bioreactors (MBRs) and a biological aerated filter (BAF) was principally with reference to the non-potable water reuse quality standards. In the steady-state trials the feedwater quality was changed from synthetic greywater to blackwater (primary sewage influent) simulating the variability of domestic wastewater. The submerged MBR met both the chemical and microbiological water reuse quality standards independent of the feedwater strength. The BAF mostly achieved a significant reduction in organic pollutants but failed to meet the microbiological water quality criteria. Greywater treatment by the side-stream MBR resulted in a very good effluent quality whilst the membrane aeration bioreactor (MABR) had the most limited capacity to remove the pollutants measured. The unsteady-state trials were carried out on the submerged MBR and the BAF. The performance of the former remained relatively unchanged in the feedwater transitions and the intermittent operation of feed and/or air with synthetic greywater. These tests on the BAF resulted in a loss of performance such that in some cases the recovery took several days. In the supplementary experiments nutrient deficiency, variability in strength and degradation during storage were found typical of both real and synthetic greywater, hence potentially affecting the treatability of greywater. A survey on behavioural patterns in households indicated that perceived harmfulness of a substance did not necessarily affect the frequency with which it was discharged. Laboratory experiments suggested that some substances discharged with the greywater may increase the risk of failure of the biological treatment process.