Adsorption of organic compounds by microbial biomass

The adsorption of hazardous organic compounds such as phenol, 2-chlorophenol, 2-nitrophenol, chlorobenzene, and ethylbenzene onto two types of inactive microbial biomass (activated sludge and nitrifying bacteria) was studied. The adsorption isotherms could be expressed by the Freundlich adsorption isotherm and were found to be nearly linear over the range of concentrations (50 - 200 mg/1) studied. Desorption studies showed that the adsorption process was partially reversible. Heat of sorption was estimated and indicate that the biosorption process involves a physical rather than a chemical mechanism. The adsorptive capacity of biomass is about two to three orders of magnitude less than activated carbon.In bisolute systems, the uptake of each solute is reduced in the presence of a second solute, but the combined adsorptive capacity was greater than that for either of the individual substances from its pure solution. The compound with higher octanol/water partition coefficient was observed to be more favorably adsorbed. In the case of activated carbon, the more hydrophobic compound was observed to be more favorably adsorbed. The uptake of each solute is reduced, when the initial concentration of other solute is increased.In multi - solute systems, the equilibrium capacity for each solute is reduced significantly in the presence of other solutes and the effect of competition become more pronounced with the increase in number of solutes in solution. The overall adsorption capacity of biomass was barely affected by the presence of more solutes in solution.Live and inactive biomass do not exhibit the same level of biosorptive uptake, and the differences appear to depend on the specific organic compound.The extent of biosorption is directly related to the organic carbon content of the biomass. Octanol/water partition coefficient is a much better predictor of extent of adsorption on microbial biomass than aqueous solubility. Reasonable estimation of the sorption behavior of organic compounds can be made from a knowledge of organic carbon content of the biomass and octanol/ water partition coefficient of the organic compound.