Managing the reverse osmosis concentrate from the Western Corridor Recycled Water Scheme

The Western Corridor Recycled Water Scheme consists of three advanced water treatment plants (AWTPs), with the combined capacity to recycle 232 ML/d. Each AWTP process consists of pre-treatment, microfiltration (MF), reverse osmosis (RO), UV/peroxide advanced oxidation and chlorination. A key objective of the project is to improve the environmental health of regional waterways, particularly in relation to nutrient discharges. Reverse osmosis processes produce a concentrate stream (ROC), which is the main reject stream of the AWTPs. Options for management of ROC were assessed, and ultimate disposal to nearby waterways was the only feasible option identified. ROC flows for the scheme total 41 ML/d at full capacity, divided between the three AWTPs. The contaminants in this stream are generally 6 to 7 times more concentrated than in the feed water. Environmental risks were identified due to potential increased toxicity associated with these higher concentrations, which were exacerbated due to chlorine and ammonia dosed in the AWTP process. Target ROC contaminants have been identified as nitrogen, phosphorus, ammonia, metals and chlorine. The paper presents the selected toxicity management and nutrient reduction strategies for each AWTP, and the results of full-scale operation to date are also summarised.