Cadmium removal at high concentration in aqueous medium: mediated by Desulfovibrio alaskensis

Abstract

Experimental studies were performed to evaluate the high capacity of cadmium removal by Desulfovibrio alaskensis strain 6SR, which is a sulfate-reducing bacterium. The study was conducted in batch cultures of D. alaskensis 6SR in a medium with a high cadmium concentration. The results indicated that bacterial growth was not dramatically affected by the presence of 170 mg/L of cadmium, following a similar behavior to that of the control culture. Besides, we observed a fast production of extracellular polymeric substances, which play an important role in cadmium removal. The bacterium was able to remove 99.9 % of cadmium at the tested concentration. The main mechanism of cadmium removal was its precipitation as cadmium sulfide (yellow precipitate), followed by its adsorption in the polymeric substances. Most cadmium up take occurred within the first 48 h, and the largest cadmium adsorption capacity was achieved at 144 h. Cadmium adsorption dynamics was evaluated by pseudo-first order and pseudo-second-order kinetic models; where the best adjustment was obtained with the pseudo-second-order model. The micrographs, obtained with transmission electron microscopy, showed a very low intracellular and periplasmic accumulation of cadmium in the cells. Thereby, this bacterium facilitates a process of removal and recovery of cadmium at high concentrations without the need of cellular lysis or special washes.