Enhancement of metal bioleaching from sewage sludge by cotton stalk

Abstract

A B S T R A C TIt was found that the distribution of heavy metals in liquid and solid phases at the end of bioleaching of sewage sludge could be described by adsorption isotherm model. Cotton stalk could be used to improve heavy metal leaching efficiency in bioleaching of sewage sludge. Amended with 5 g/L cotton stalk in late bioleaching, leaching efficiency increased from 56. 75, 56.42, and 62.28 to 73.18, 81.34, and 82.39% for copper, lead, and chromium, respectively, with 6% pulp density. Relationship between heavy metals in liquid phase and that adsorbed onto cotton stalk could be described by Freundlich equation. Adsorption onto cotton stalk lowered heavy metal concentration in liquid phase. Consequently, more heavy metals were released from sewage sludge. The increased section of heavy metals released from sludge was mainly attributed to mobile fractions. Content of heavy metals in stable fractions was left unchanged. Mobility of residual heavy metals in sludge after bioleaching with treatment was also lowered greatly.