Selection and optimization of a mixed culture for bioaugmentation based on BOD5 and COD reduction in tannery effluents

Abstract

Most current methodologies for the treatment of tannery effluents do not succeed in bringing contaminant levels down to values that fit environmental standards in force, which means there is a need for appropriate optimization. The present work assessed effluent quality to gain further insight into their variability across time, considering both conventional parameters and those specifically related to tannery effluents, such as chromium levels. Most of the effluents analyzed exceeded the contaminant limits established by current national legislation and therefore would require treatment. To improve treatment efficiency, a mixed bacterial culture was selected on the basis of its ability to remove organic matter (OM), measured in terms of chemical oxygen demand (COD) and biochemical oxygen demand (BOD5). The four strains analyzed, belonging to the genera Bacillus, Rhodococcus and Acinetobacter, were isolated from sediments contaminated with effluents with a high organic load. The native consortium SFC 500-1, formed by Acinetobacter guillouiae SFC 500-1 A and Bacillus toyonensis SFC 500-1E, proved to be the most effective at reducing BOD5 and COD. It was selected for bioaugmentation treatment. Dissolved oxygen was found to be key for reduction, and the inoculum size required to treat effluents with different COD values was also determined. All in all, the results confirmed previous characterization of these effluents, which should always be the basis for treatment and management strategies, and also contributed to optimizing some operational parameters so that effective and safe treatment technologies may be developed.