Experiences in Toxicity Reduction Evaluations for Petroleum Refineries

Whole effluent toxicity (WET) testing of wastewater effluents to identify and control constituents and properties that are potentially toxic to aquatic organisms has been an important component of water quality protection for over 35 years. Because WET testing integrates the toxicity effects of effluent constituents, both measurable and unmeasurable, it has proven to be a valuable tool to assure that a discharge will be of a quality that is protective of aquatic life in the receiving water.The U.S. Environmental Protection Agency (EPA) has developed guidance and protocols for identifying specific toxicants in an effluent as part of a process referred to as a toxicity reduction evaluation (TRE). NPDES permits for dischargers have, for a number of years, required that permittees conduct TREs when WET testing indicates that an effluent is toxic to the aquatic test organisms.This paper summarizes selected case history data from TREs conducted at petroleum refineries and chemical plants over the past 25 years to identify common toxicants in these wastewaters and the conditions required for a TRE to be successful. It also describes cases where EPA's conventional guidance for the identification of specific toxicants is insufficient and how refineries and chemical plants have identified toxicants and toxic properties when this occurs. The controls (both treatment and/or management) that facilities have employed to eliminate effluent toxicity are also presented.