Process Control at Nutrient Removal Wastewater Treatment Plants During Toxic Shock Events

The key to mitigating a toxic shock event is to make informed process control decisions and to have the ability to execute those process controls using built-in operational flexibility. The wastewater treatment industry currently lacks a systematic framework of response guidelines and corrective action protocols to be implemented during and after toxic shock events. Guidelines on the likely process effect(s) and the appropriate corrective actions will help maintain the integrity of the treatment process and mitigate long-term effects on the effluent quality. This paper presents the development and testing of corrective action plan matrices (CAPMs) developed for two representative wastewater treatment plant (WWTP) configurations experiencing a toxic shock event. The two configurations were shocked with calcium hypochlorite and corrective actions stipulated by the CAPMs were performed. Preliminary results suggest that the proposed corrective action strategies may not be suitable for the simulated short-term shock event involving calcium hypochlorite. In fact, trains in which corrective action strategies were implemented took longer to recover to pre-shock nitrification and phosphorus removal capacities than shocked trains without remedial intervention. This study highlights the need for the development of corrective action strategies that are specific to contaminants and WWTP configurations.