Kinetics of Phenol Biodegradation by an Immobilized Methanogenic Consortium †

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A phenol-degrading methanogenic enrichment was successfully immobilized in agar as shown by the stoichiometric conversion of phenol to CH4 and CO2. The enrichment contained members of three physiological groups necessary for the syntrophic mineralization of phenol: a phenol-oxidizing bacterium, a Methanothrix-like bacterium, and an H2-utilizing methanogen. The immobilization technique resulted in the cells being embedded in a long, thin agar strand (1 mm in diameter by 2 to 50 cm in length) that resembled spaghetti. Immobilization had three effects as shown by a comparative kinetic analysis of phenol degradation by free versus immobilized cells. (i) The maximum rate of degradation was reduced from 14.8 to 10.0 μg of phenol per h; (ii) the apparent Km for the overall reaction was reduced from 90 to 46 μg of phenol per ml, probably because of the retention of acetate, H2 and CO2 in the proximity of immobilized methanogens; and (iii) the cells were protected from substrate inhibition caused by high concentrations of phenol, which increased the apparent Ki value from 900 to 1,725 μg of phenol per ml. Estimates for the kinetic parameters Km, Ki, and Vmax were used in a modified substrate inhibition model that simulated rates of phenol degradation for given phenol concentrations. The simulated rates were in close agreement with experimentally derived rates for both stimulatory and inhibitory concentrations of phenol.

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