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

The aerobic biodegradation of high liquid phase concentrations of 2-propanol (IPA) by a previously enriched solvent-tolerant bacterial consortium within a 1.9 l fed-batch three phase fixed bed bioreactor was investigated. Solvent concentrations of up to 7.9 g l^-1 were investigated. Previously enriched solvent-tolerant bacterial cells were immobilised onto porous glass cylinders as a means of bioprocess intensification. Bioreactor start-up and acclimation 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 I^-1 h^-1 prior to biofilm formation. Biofilm growth during the second batch treatment was consistent with an increase in metabolic activity and an IPA biodegradation rate of 0.34 g l^-1 h^-1, followed by a reduction of biodegradation rate to a constant value of 0.078 g l^-1 h^-1 after 650 h. A maximum acetone generation rate of 1.3 g 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 dehydrogenase to acetone carboxylase is a major rate-limiting step in the deep oxidation of IPA to acetone. The results demonstrate the potential of a previously enriched solvent-tolerant bacterial consortium in fixed bed bioreactor systems, for the aerobic treatment of concentrated solvent-containing wastestreams.