Biodegradation of isopropanol in a three phase fixed bed bioreactor: Startup and acclimation using a previously-enriched microbial culture

The aerobic biodegradation of high liquid phase concentrations of 2-propano l (IPA) by a previously enriched solvent-tolerant bacterial consortium with in a 1.9 l fed-batch three phase fixed bed bioreactor was investigated. Sol vent concentrations of up to 7.9 g l(-1) were investigated. Previously enri ched solvent-tolerant bacterial cells were immobilised onto porous glass cy linders as a means of bioprocess intensification. Bioreactor start-up and a cclimation was studied and acetone concentration tracked as an indicator of IPA utilization, as the sole carbon source within a minimal salts medium ( MSM). The initial batch treatment of IPA exhibited a biodegradation rate of 0.11 g l(-1) h(-1) prior to biofilm. formation. Biofilm growth during the second batch treatment was consistent with an increase in metabolic activit y and an IPA biodegradation rate of 0.34 g l(-1) h(-1), followed by a reduc tion of biodegradation rate to a constant value of 0.078 g l(-1) h(-1) afte r 650 h. A maximum acetone generation rate of 1.3 l(-1) h(-1) was obtained during the fourth IPA addition although the maximum acetone biodegradation rate of 0.38 g l(-1) h(-1) was observed during the initial IPA addition. It is proposed that the metabolic lag resulting from switching from alcohol d ehydrogenase to acetone carboxylase is a major rate-limiting step in the de ep oxidation of IPA to acetone. The results demonstrate the potential of a previously enriched solvent-tolerant bacterial consortium in fixed bed bior eactor systems, for the aerobic treatment of concentrated solvent-containin g wastestreams.