Protocol for measuring VOC biotransformation rates

A protocol has been developed to determine kinetic parameters for the biotransformation of volatile organic compounds (VOCs). The protocol employs a batch system with zero headspace and utilizes a bubbleless oxygenation system to minimize losses due to volatilization. The reactor is filled with a suitable wastewater solution, primary clarified effluent or a synthetic mixture, and a volume of active biomass. It is then dosed with a solution of VOCs. The VOC biotransformation rates are determined by withdrawing samples from the reactor over a period of four to eight hours. Abiotic experiments have been completed to confirm that losses due to sorption and volatilization are negligible. Experiments have also been completed to verify that biotransformation rates observed with the protocol reactor accurately predict those observed in full scale operations. The protocol has been used to examine effects of varying the chemical oxygen demand (COD) concentration of the primary substrate and the dissolved oxygen (DO) concentration in the bioreactor under aerobic conditions. Primary substrate COD concentrations of 20, 100 and 500 mg/L and DO concentrations of 0.5 and 5.0 mg/L were selected. The effects of varying the primary substrate COD concentration in anaerobic and anoxic environments were also examined. Significant differences in biotransformation rates were observed under aerobic conditions when the COD and DO concentrations in the bioreactor were changed. It was found that biotransformation kinetic parameters varied by up to an order of magnitude for certain compounds. The highest biotransformation rates were observed under low COD, high DO conditions. No significant effects were found for the anaerobic and anoxic environments. This study will help provide a better understanding of VOC biotransformation in municipal and industrial wastewater treatment works. Results from this study can be utilized by predictive fate models such as WATER8 or TOXCHEM.