Thermodynamic and Kinetic Aspects of Mercury Sorption on Activated Carbon in the Process of Mercury Bioreduction

A unique biotechnological method for remediation of industrial wastewater contaminated by toxic mercury, based on the enzymatic reduction of ionic mercury by live bacteria, has been developed by prof. Deckwer and co-workers at GBF (at present HZI), Germany, and implemented in a pilot-plant scale. The experience gained during operation of this installation led to the idea, that the process of bioremediation may be integrated in one bioreactor with the adsorption of mercury by immobilization of the bacteria onto the activated carbon. For this it was necessary to define several significant parameters of the activated carbon selected for the process and the adsorption process itself. The paper presents results of the equilibrium and kinetics investigations of the process of ionic mercury sorption from aqueous solutions onto 8 different types of activated carbon. The effective diffusion coefficients in the carbon particles were obtained from the transient-state experiments using a mathematical model of the process and the sorption isotherms as well as the saturation capacity of the sorbents in relation to ionic and metallic mercury were identified. From the temperature dependence of adsorption constants the values of adsorption enthalpy for both metallic and ionic mercury on activated carbon impregnated with sulfur were estimated. The obtained results enabled selection of the optimal sorbent for the fixed-bed activated-carbon bioreactor which will be applied for the modified, integrated process of biological detoxification of mercury in industrial wastewaters.