Estimating the allowable ammonia concentrations in wastewater treatment plant discharge to ensure protection of aquatic biota

Ammonia, a common constituent of wastewaters, is toxic to a wide range of aquatic organisms. Fish are the most sensitive species and cold-water, oxygen-sensitive, fish such as trout are the most vulnerable. The US Environmental Protection Agency (USEPA) has developed models of fish-tolerance to ammonia levels. These criteria have been adopted in Australian Water Quality Guidelines for Fresh and Marine Waters [1]. Given that the toxicity of ammonia is dependent on the prevailing temperature and pH, allowable concentrations of ammonia in aquatic systems such as lakes and estuaries must take these factors into account. We describe a simple procedure for estimating the allowable ammonia concentrations in discharges from wastewater treatment plants to ensure protection of aquatic biota. The procedure incorporates the USEPA fish-tolerance models and considers the dependency of ammonia on ambient temperature and pH levels and the volume of discharge and recieving waters.