Treating graywater using quartz sand filters: The effect of particle size, substrate combinations, and reflux ratio

Abstract

To achieve simple, efficient, and low-cost treatment and reuse of graywater, this study evaluated the effect of particle size, substrate combination, and reflux ratio on the treatment of graywater by quartz sand filters. Three 1,500 mm column filters were fed with synthetic graywater at a hydraulic loading rate of 1.87 m3 /(m2 d) for approximately 7 months, and the particle sizes, combinations, and reflux ratio were set according to a layered plot design. Results showed that the purification performance followed the order combination > reflux ratio > size. The best combination of particle size was 4–8 mm and 1–2 mm quartz sand. It removed up to 90%, 93%, and 36% of turbidity, biochemical oxygen demand, and methylene blue active substances (MBAS), respectively. In addi-tion, scanning electron microscopy showed that differences of the microforms and structures for quartz sand particles of different sizes, and the attachment of substrates caused a similar change in the microstructure of the quartz sand surface. This explained, to some extent, why there was no significant difference in the experimental results for each single stage. According to these results, graywater purified using a quartz sand filter is suitable for uses such as irrigation and flushing toilets.