Removal of ecotoxicity and COD from tank truck cleaning wastewater

Tank truck cleaning (TTC) activities generate highly complex wastewater. In a previous study, we found that a significant ecotoxic effect was still present in biologically treated TTC wastewater. The aim of the present study was therefore to investigate the removal of acute toxicity from TTC wastewater by a sequence of technologies routinely applied for industrial wastewater. Acute toxicity was assayed with the widely applied and standardized Vibrio fischeri bioluminescence inhibition test. During a 5-month period, raw wastewater was grab-sampled from a full-scale TTC company and treated by the different unit operations on a laboratory scale. Chemical pretreatment of the wastewater by coagulation with FeCl₃ removed approx. 38% of the influent chemical oxygen demand (COD) and reduced the bioluminescence inhibition by 8%. Biological treatment with activated sludge subsequently removed another 77% of the remaining COD. This treatment step also reduced the bioluminescence inhibition but the removal efficiency varied strongly from 5 to 92% for the different samples. Powdered activated carbon almost completely removed the remaining COD and inhibition in all samples. The results suggest that conventional technologies did not suffice for complete removal of toxicity from TTC wastewater, and that advanced wastewater treatment technologies such as activated carbon are required for a satisfactory detoxification.