Effects of Solids Concentration on Removal of Heavy Metals from Sewage Sludge via Bioleaching

A technologically and economically feasible process called bioleaching was used for the removal of heavy metals from sewage sludge by Acidithiobacillus ferrooxidans,and the effects of sludge solids concentration on the bioleaching process were examined.Laboratory results showed that 99.57% Zn,94.97% Cu,59.50% Pb and 43.40% Cr could be removed from sewage sludge by the bioleaching experiment after 12 days at 2%(w/w) solids concentration.Due to the buffering capacity of sludge solids,the rates of pH reduction,ORP rise and metal solubilization were reduced with the increase of the solids concentration.The results also indicated that,among the five solids concentration tested(2%,4%,6%,8% and 10%),the concentration at 2% was found to be best to bacterial activity and metal solubilization under the chosen experimental conditions.