Performance of the full-scale biological nutrient removal plant at Noosa in Queensland, Australia: nutrient removal and disinfection

Stringent effluent quality guidelines are progressively implemented in coas tal and sensitive areas in Australia. Biological Nutrient Removal (BNR) pla nts are becoming a standard often including a tertiary treatment for disinf ection. The BNR plant in Noosa-Queensland is designed to produce a treated effluent with less than 5 mg/l of BOD5, 5 mg/l of total nitrogen, 1 mg/l of total phosphorus, 5 mg/l of suspended solids and total coliforms of less t han 10/100 ml. A flexible multi-stage biological process with a prefermenta tion stage, followed by sand filtration and UV disinfection was implemented to achieve this level of treatment. Acetic acid is added for phosphorus re moval because: i) the volatile fatty acids (VFA) concentration in raw waste water varies a lot, and ii) the prefermenter had to be turned off due to od or problems on the primary sedimentation tanks. An endogenous anoxic zone w as added to the process to further reduce the nitrate concentration. This r esulted in some secondary P-release events, a situation that happens when l ow nitrate and low phosphorus objectives are targeted. Long-term performanc e data and specific results on nitrogen removal and disinfection are presen ted in this paper.