Optimizing the in-line ozone injection and delivery strategy in a multistage pilot-scale greywater treatment system: System validation and cost-benefit analysis

•Evaluation of commercial pilot-scale greywater treatment system.•Multistage treatment with sand filter, GAC filter and ozone disinfection.•Effect of greywater flowrate and ozone dosing rate on treatment performance.•Introduction of recirculation in the in-line ozone injection system.•Cost-benefit analysis of commercial pilot-scale greywater treatment system.

Greywater is a potential source of recycled water for household that has often been overlooked. Although greywater is lightly contaminated, a holistic treatment and disinfection system of greywater is still warranted to ensure public health issues associated with the cross-connection of third pipe reticulation in household are minimized. This study assessed on the treatment performance of a commercial pilot-scale greywater treatment system comprising of a multi-medium sand filter, granulated activated carbon (GAC) filter and an ozonation disinfection system. The operational volume flow rate (10–20 L/min) and ozone dosing rate (5–20 g/h) for maximum removal of contaminants in greywater were investigated. This study found that the increase in operational volume flow rate decreased the overall performance of the greywater treatment and disinfection system. The optimum operating volume flow rate was found to be 10 L/min, removing 72.6% of chemical oxygen demand (COD) and 42.9% (0.85-log removal) of Escherichia coli without recirculation. Recirculation of greywater was introduced to the ozonation disinfection system in order to improve the disinfection efficiency. It was found that all bacteria present in the treated greywater effluent were completely disinfected with a recirculation period of 1 h.