Green/sustainable treatment of washing machine greywater for reuse in the built environment

Abstract

Given the growing demand for water in the world, approaches and/or actions are needed to reduce consumption and increase demand. In the latter case, water reuse is a viable alternative to increase the demand for non-potable water in homes. This study aims to optimize washing machine greywater treatment using aqueous solutions of aluminum sulfate and Moringa oleifera seed extract. To this end, an experiment was carried out using washing machine greywater from a residence. The data from this test were evaluated adopting the Response Surface Methodology (RSM). The parameters evaluated in the experiment were the pH, turbidity, sludge volume produced, and the total dissolved solids. Afterward, these were compared with limits established by technical standards and authors regarding non-potable water reuse. The results of this study indicate that using the treatment with the lowest coagulant dosages, i.e., 20 mL L −1 of Moringa oleifera extracted in calcium nitrate and 1 mL L −1 of aluminum sulfate, it is feasible to reuse greywater after treatment in toilet bowl flushing. For these dosages of coagulants, the turbidity removal was 96.22% and the pH varied from 7.2 to 6.8. The association of aluminum sulfate with Moringa oleifera extracted in calcium nitrate is viable for the treatment by coagulation of greywater from the washing machine to reduce the dosage of each coagulant and meet the criteria of the standards. • Combining natural and chemical coagulants to treat the greywater, up to 96.22% of the turbidity was removed. • Modeling the treatment, using response surface methodology, led to optimizing and reducing the use of the chemical coagulant. • Using Moringa oleifera combined with calcium nitrate enhances the effects of the natural coagulant. • Treated water meets the criteria for reuse in toilet flushing.