ADSORPTION AND DESORPTION OF PENTACHLOROPHENOL ON CELLS OF MYCOBACTERIUM-CHLOROPHENOLICUM PCP-1

The sorption behavior of pentachlorophenol (PCP) by the Gram-positive bacterium Mycobacterium chlorophenolicum PCP-1 was quantitatively char acterized in this work, with emphasis on the effects of biomass and pH and on the reversibility of PCP adsorption. Both the adsorption and d esorption of PCP showed a fast kinetic, reaching an equilibrium in les s than 1.5-min mixing under the experimental conditions. For PCP conce ntrations up to 600 mu mol/L no saturation of the adsorption was obser ved and the adsorption isotherms can be adequately described by the Fr eundlich equation. The adsorption capacity (q(ads)) of M. chlorophenol icum PCP-1 increased significantly with decreasing biomass in the low concentration range (below 0.5 g/L). The biomass concentration merely affected the capacity constant K of the Freundlich model while the int ensity parameter n remained constant. The q(ads) also increased with d ecreasing pH, particularly at acidic pH values. Again, the pH effect w as mainly reflected by the change of K. Based on these results a corre lation for q(ads), in which K is a function of both biomass concentrat ion and pH, was obtained to describe the adsorption isotherms at diffe rent biomass concentrations and pH values. The desorption of PCP was a lso found to be strongly affected by pH. At pH 5.4 the adsorption was almost completely irreversible, while a nearly complete desorption was obtained at pH 7. The effect of pH on the sorption behavior was found to be related to the ionization of PCP. The irreversibly adsorbed PCP is a strict function of concentration of undissociated PCP, while the reversibly adsorbed PCP correlates well with the concentration of ion ic PCP. The irreversible adsorption has a much higher adsorption capac ity than the reversible adsorption. These findings led to the derivati on of a semimechanistic model that satisfactorily describes the sorpti on of PCP by M. chlorophenolicum. The results obtained also give clues to the patterns and mechanism(s) of PCP adsorption by microbial cells . (C) 1997 John Wiley & Sons, Inc.