Protect the Fish: Predicting Ammonia Toxicity Risk in the Fraser River

Ammonia is known to be acutely toxic to fish and other aquatic organisms at low concentrations. In effort to predict regulatory non-compliance due to ammonia discharged from two of Metro Vancouver’s wastewater treatment plants, regression models were developed to project final effluent ammonia concentrations at each facility over a 25-year period. These ammonia projections were compared with regulatory requirements, and the risk of non-compliance was quantified over the period under various operational scenarios, such as increased centrifuge operation and per capita flow reduction. The risk assessment concluded that some degree of noncompliance was observed in most scenarios evaluated; to target full compliance with the regulations it is estimated that a 13% reduction in effluent ammonia at LIWWTP and a 22% reduction at AIWWTP under baseline conditions is required. At both facilities, implementing side stream ammonia removal on the dewatering centrate stream would increase compliance to 100% at baseline conditions.