Biochar addition for accelerating bioleaching of heavy metals from swine manure and reserving the nutrients

Highlights: • Biochar simultaneously improved HMs solubilization and nutrients reserve from SM. • HMs leaching time was remarkably decreased from 10 to 7 days with biochar addition. • TN loss efficiency decreased from 32.3% to 18.5% with biochar addition. • Bioavailable P was elevated by 13.7% with biochar addition after bioleaching. • Biochar enriched some functional bacteria during bioleaching. Biochar was applied during the bioleaching of heavy metals (HMs) from swine manure (SM), in an attempt to accelerate the HMs removal rates and to reduce the losses of nutrient elements (nitrogen and phosphorus). Results showed that the addition of biochar (5 g L⁻¹) could not only significantly shorten the leaching time of HMs (Cu, Zn, Mn and Cd) from 10 (control) to 7 days with a high solubilization efficiency of 90%, but also decrease the total nitrogen loss efficiency by 42.7% from 180.3 (control) to 103.3 mg L⁻¹ in the leachate. In addition, biochar addition facilitated Fe²⁺ oxidation rate, achieving much better pH and ORP conditions. Electronic conductivity and adsorption properties of biochar with changed microbial community probably contributed a lot to the enhanced HMs solubilization and reduced nitrogen loss during bioleaching. Although the addition of biochar only slightly reduced the total amount of phosphorus loss, the bioavailable phosphorus in SM after bioleaching was markedly increased by 13.7%.