Anaerobic reduction of hexavalent chromium in filter sludge of an electrochemical process

The potential of an anaerobic system to remediate hexavalent chromium containing waste was investigated. Experiments were performed at laboratory scale in the batch mode. The variables studied were the concentrations of waste, of inoculum, of yeast as an additional carbon source, of sulfate and the initial pH. The gas development, the final pH and the final concentrations of hexavalent and total chromium were measured. The evaluation was based on Multivariate data analysis. It could be shown that a remediation is possible. The influence of pH and sulfate were negligible in the given range. High yeast concentrations and low waste concentrations were favorable for a strong gas development and a complete elimination of chromate. Possible mechanisms are the active reduction of chromate by the microorganisms, its use as electron acceptor in bacterial respiration, and its sorption on organic material. Especially the last explanation is strongly supported by the experiments.