Case history of a toxicity identification/reduction evaluation (TI/RE) at a petroleum refinery

During an operational turn-around at a high conversion petroleum refinery, the final wastewater effluent became toxic to three fish species used in continuous on-line flow-through acute toxicity tests. Discharge of effluent to the receiving bay was promptly halted. Wastewater treatment continued and the treated effluent was diverted to a series of holding ponds with limited capacity. A refinery team was formed to coordinate toxicity identification studies as well as to facilitate modifications of waste disposal practices and treatment operations. A test program was conducted, consisting of one rainbow trout Phase 1 TIE and 84 strategic acute toxicity tests. As a result, a treatment methodology was identified within three days and within eight days of first observing toxicity a cationic water treatment polymer was identified as the primary toxicant. The toxicity was due to increased bioavailability of the polymer when suspended solids loads dropped during turn-around. Use of the polymer was immediately stopped and discharge to the bay was resumed with 100% survival of all three monitoring species. The authors present an overview of the studies and decisions leading to the successful identification and management of this situation.