MICROBIAL-CELLS IMMOBILIZED IN POLY(VINYL ALCOHOL) CRYOGELS .1. MICROBIAL-CELLS IMMOBILIZED IN POLY(VINYL ALCOHOL) CRYOGELS - BIOCATALYTIC REDUCTION OF CO2 BY THE THERMOPHILIC HOMOACETOGENIC BACTERIUM ACETOGENIUM-KIVUI

The formation of acetate from CO2/H-2 gas mixtures by the homoacetate bacterium Acetogenium kivui under various conditions was studied. The advantages and disadvantages of processes based on the use of growing, non-growing and immobilized cells are discussed. Analysis of the kine tics of acetate formation (the concentration of which reached 150-170 mmol/litre in 3 days) in growing culture has shown that the limiting f actor is cell lysis. Batch experiments with non-growing cultures demon strated that, in the absence of lysis, acetate production was constant for at least 1 month, but was considerably inhibited by traces of oxy gen, analogously to growing cultures. The entrapment of A. kivui cells in poly(vinyl alcohol) cryogel beads generated a biocatalyst the acti vity and mechanical strength of which remained constant for at least 1 year. The immobilized cells were practically insensitive to the prese nce of traces of O2. The experiments with the biocatalyst were perform ed under batch, semi-batch and continuous conditions, the latter carri ed out in a flow-through bioreactor with immobilized cells. Constant a cetate concentrations of 100 mmol/litre were achieved under the optima l regime, and process productivity did not change at least for 10 days .