Degradation of tetrachloroethene using aerobic Sphingopyxis ummariensis bacteria in a gas-recycling fixed-bed bioreactor

Abstract Tetrachloroethene (Perchloroethylene, PCE) is an industrial chlorinated solvent and a slowly degradable compound. The degradability of PCE by Sphingopyxis ummariensis bacteria in both suspended and immobilized culture systems was investigated under aerobic conditions. For this purpose, yeast extract and glucose were used as co-substrates. Various experiments were performed on immobilized cells in a gas-recycling fixed-bed batch (GRFB) bioreactor packed with polyethylene. The results showed that PCE could be highly removed in the concentration range of 0.04–0.76 mM, but the removal occurred more efficiently in lower concentrations. It was also observed that the rate of PCE degradation decreased from 100% to 80%, and the dechlorination percentage decreased from 84 to almost 70% as the initial PCE concentration increased from 0.04 to 0.76 mM. The first-order kinetic model was best fitted to the degradation behavior in the bioreactor with kinetic rate constants in the range of 0.088–0.044 h–1. In addition, the degradation trend of an equimolar mixture of PCE and trichloroethylene (TCE) in the GRFB bioreactor showed, TCE is a competitor of PCE and its degradation rate is higher than that of PCE. The performance of the GRFB bioreactor proved that it is reliable for the aerobic removal of chlorinated hydrocarbons.