Synchronous detoxification and reduction treatment of tannery sludge using Cr (VI) resistant bacterial strains. 
This investigation focused on the simultaneous decrease of tannery sludge and the reduction of its high chromium (Cr(VI)) content.  This was accomplished through the addition of mixed bacterial strains that were cultured in the laboratory, subsequent to their isolation from tannery sludge.  The results indicated that under anaerobic conditions, the amount of the tannery sludge was decreased by 27% with these mixed bacteria.  The impacts of various parameters were explored, such as pH, processing duration, strain inoculation, and temperature.  Along with the decreased volume of sludge, the Cr(VI) concentration was lowered as well.  Among the isolated bacterial strains, WY601 (belonging to Stenotrophomonas sp.)  demonstrated the highest Cr(VI) resistance; from an initial concentration of 300 mg L-1, the Cr(VI) level was decreased by 90% within 65 h. Hexavalent chromate reductase was found to be localized primarily within the extracellular membrane or adsorbed to its surface, and a mechanism was proposed for the removal of Cr(VI) via WY601.  Further, the WY601 isolate was found to be tolerant to other toxic heavy metals.  In summary, the isolated mixed bacterial strains in our study demonstrated a strong potential for the treatment of tannery sludge, as they could simultaneously decrease its volume while lowering high Cr(VI) levels.