Cometabolic Transformation of High Concentrations of 4-Chlorophenol in an Immobilized Cell Hollow Fiber Membrane Bioreactor

The cometabolic transformation of high concentrations of 4-chlorophenol (4-cp) in the presence of phenol (growth substrate) was investigated in an immobilized cell hollow fiber membrane bioreactor. The biotransformation rates of 4-cp and phenol by free cells and immobilized cells were compared and it was found that biotransformation by immobilized cells was more efficient than that by freely suspended cells, especially at high substrate concentrations. Even when the initial substrate concentrations were both 1,000  mg  L-1, the substrates could still be transformed completely within 45  h in the hollow fiber membrane bioreactor. It was found that removal rates of the substrates were dependent not only on absolute substrate concentration, but also on the concentration ratios of 4-cp to phenol. With increased concentration ratios, phenol depletion rate decreased while 4-cp depletion rate increased. This was attributed to increased competitiveness of 4-cp in the competitive inhibition with phenol since the membranes had relatively better sorption for 4-cp over phenol. The bioreactor was operated batchwise for 18 times to investigate the feasibility of the bioreactor for long term operation. It was found that there was no significant decrease in the bioactivity, which demonstrates a potential for continuous operation.