Zero Waste Discharge in Wastewater Reclamation System for Small Cities

Abstract

Presently, wastewater reclamation plants (WRPs) are widely adopting reverse osmosis (RO) as a polishing treatment in the final operation stage. Sydney Olympic Park Authority’s (SOPAs) WRP adopts a treatment operation of combined biological treatment, microfiltration and lastly RO. RO advantage is in maintaining a consistently good quality standard of water. Nevertheless, major limitations of using RO in SOPAs WRP are (a) high cost of RO and fouling susceptibility and (b) production of substantially large volume of wastewater RO concentrate (WWROC). The aim(s) of this study were to evaluate methods to overcome both these limitations by (i) investigating the integration of nanofiltration (NF) prior to RO to reduce cost and fouling issues; and (ii) evaluating the performance of membrane distillation (MD) for treating WWROC to achieve zero waste discharge. The results of this study highlighted (i) blending NF and RO permeate, acquired from a hybrid two-stage NF–RO process resulted in a water quality suited for irrigation. Utilizing NF prior to RO, reduced RO membrane fouling was more cost-effective compared to direct RO application. The hybrid NF–RO removed most of the micropollutants and therefore achieved reuse water quality that was safe to be applied for irrigation; and (ii) MD displayed minimal flux decline (13–15%) at 85% water recovery of WWROC and achieved freshwater with high quality (10–15 μS/cm, 99% ion rejection). The organic contents of micropollutants in WWROC were effectively reduced with granular activated carbon (GAC). This enabled to achieve good quality water (micropollutants-free) by MD with the potential of reuse.