Conventional and (eco) toxicological assessment of batch partial ozone oxidation and subsequent biological treatment of a tank truck cleaning generated concentrate

This paper compares the treatment efficiencies of direct (pH 7.5) and advanced (pH 11.5) partial ozonation followed by biodegradation for the treatment of tank cleaning wastewater concentrate. Both SCOD and toxicity removal efficiencies are examined and direct ozonation is found to perform better in combined toxicity and SCOD removal. Optimal process performance, i.e. the minimal ozone dosage resulting in a maximal removal of SCOD and toxicity in the final effluent, is reached upon reaction of 500 mg O3/l for both ozonation processes. This ozone dosage results in 60% SCOD reduction for direct ozonation and 64% SCOD reduction for advanced ozonation. A 79% toxicity reduction was achieved using direct ozonation compared to 53% toxicity reduction for advanced ozonation as measured with the standard Pseudokirchneriella subcapitata algal 72 h growth inhibition test. Short-term methods for biodegradability (respirometry) and toxicity (30 min Vibrio fisheri luminescence inhibition) estimation are evaluated in view of process control. The maximal specific oxygen uptake rate of an activated sludge culture (respirometry) is found to relate to the 5-day biochemical oxygen demand (SBOD,5) but less to the actual SCOD removal during biodegradation. The 30 min Vibrio fisheri luminescence inhibition test is found to be a good short-term estimator for relative changes in toxicity when compared to the standard P. subcapitata algal 72 h growth inhibition test. The 500 mg O3/l optimal ozone dosage, as determined from P. subcapitata algal 72 h growth inhibition and SCOD removal, could be retrieved using short-term methods.