INDUSTRIAL REFINERY TOXICITY REDUCTION EVALUATIONS – CASE STUDIES

Many NPDES permits now require the development of Toxicity Reduction Evaluation (TRE) programs designed to reduce toxicity to acceptable levels when Whole Effluent Toxicity (WET) is detected. The first of two approaches commonly used in the abatement of effluent toxicity is treatment without the specific identification and confirmation of the causative toxicants. The second method involves specific identification and confirmation of the causative toxicants with the goal of locating and eliminating the problem(s) at the source and/or treatment of the causative toxicants. The latter approach to reducing WET by specifically identifying refractory toxicants in refinery wastewater treatment plants is presented, along with three successful refinery case studies. The objective of the TRE projects was to determine the actions necessary to achieve permit compliance in terms of the WET limits and chemical specific limits. In some cases the TRE's identified remedial actions as simple as improved wastewater treatment plant operations, housekeeping procedures, and minor process flow modifications to resolve effluent toxicity.Refinery wastewaters represent very complex wastewater relative to defining and controlling aquatic toxicity. The chemical characteristics can vary significantly from refinery to refinery and even temporally within the same refinery. Conventional physical/chemical parameters are not typically reliable indicators or predictors of toxicity. Testing and analytical methodologies must be varied and flexible. Identification of specific toxicants can be like looking for a needle in a haystack. Wastewater treatment is normally the most viable option for managing/controlling toxicity as compared to source control/elimination. The methodology, test results, and conclusions of three successful case studies by end-of-pipe wastewater treatment is presented. Implemented solutions consisted of projects involving both improved preliminary (pretreatment) processes and secondary biological treatment processes.Typical compounds/constituents found to cause toxicity in refinery effluents include the following:AlkanesBranched AlkanesBranched KetonesPhenolic CompoundsSulfur CompoundsAminesAromaticsAmmonia-Nitrogen