Biodegradation of benzoate and 3-chlorobenzoate by a mixed microbial community under denitrifying, microaerobic, and cyclic aerobic/anoxic conditions

Biological nutrient removal (BNR) processes are widely used for domestic and industrial wastewater. In these processes, bacteria are alternately exposed to aerobic and anoxic conditions. These conditions require bacteria to regulate their terminal electron acceptor system, which involves cytochrome oxidases and nitrogen oxide reductases. Studies have shown that bacteria can easily handle these conditions when dealing with domestic wastewater. Industrial wastewater often contains aromatic compounds, which also requires regulation of a different set of enzymes under cyclic aerobic/anoxic conditions. Anaerobic ring-cleavage enzymes catalyze aromatic ring reduction and are adversely affected by oxygen while aerobic ones require oxygen as a reactant for aromatic ring-cleavage. We have very limited knowledge about the regulation and the fate of these enzyme systems in BNR processes, yet it is essential to understand the regulation of these enzymes for better process design. Therefore, we fast determined the response of bacteria to cyclic aerobic/anoxic conditions when growing on a readily biodegradable aromatic compound (benzoate). Three different cyclic aerobic/anoxic conditions (3hr/9hr, 6hr/6hr, 9hr/3hr) were applied to a chemostat. The performance of the culture was excellent without any transient benzoate or metabolite accumulation. High levels of aerobic and anoxic enzymes were maintained by the culture, even under the opposite electron accepting condition, enabling them to act on the aromatic substrate immediately once the appropriate redox conditions were reestablished. Therefore, the process was robust.; For the next set of experiments, the impact of oxygen leakage into the anoxic tank of a BNR process was investigated when a problematic aromatic compound (3-chlorobenzoate) was present in the feed, in addition to benzoate and pyruvate. Microaerobic conditions were created by applying a variety of oxygen mass input rates (OMIRs) to a denitrifying chemostat. Even the highest tested OMIR (67.3% of the terminal electron acceptor requirement) did not affect the performance of the culture adversely. Bacteria used the provided oxygen as the terminal electron acceptor, while using anoxic pathways to degrade both benzoate and 3-chlorobenzoate.; Lastly, the response of a mixed microbial culture to cyclic aerobic/anoxic conditions was determined when the feed contained both a readily biodegradable aromatic compound (benzoate) and a problematic halogenated aromatic compound (3 chlorobenzoate). (Abstract shortened by UMI.)...