Abstract: Effects of concentration of solids in liquid manure and amount ofmixed sulfur bacteria liquid inoculated on bioleaching of heavy metals from pigmanure were studied. Results indicate that the lower the concentration of solids in liquid manure, the shorter the heavymetal bioleaching cycle and the better the heavymetal removing efficiency. Based on the overall consideration of both bioleaching effect and economic benefit, it is app rop riate to have the concentration of solids in liquid manure be kept at 70 - 100 g·L -1. Inoculation rate is also an important factor. Results show that the higher the inoculation rate, the higher the bioleaching rate. However, in pig manure with lower inoculation rate, longer leaching time could lead to higher removal efficiency. In p ig manure with 2% in inoculation rate and 14 days′of leaching, Cu, Zn and Cd removed by 76.9%, 75.2% and 47.8%, respectively. From economic aspect, the inoculation rate of 2% is adequate to meet the need of bioleaching.

Key words: bioleaching, heavymetal, solid concentration, inoculation rate, pigmanure, sulfur-oxidizing bacteria