Removal of heavy metals and dewaterability of pig slurry facilitated by bioleaching

Removal of heavy metals and dewaterability of pig slurry during bioleaching were investigated through batch experiments with co-inoculation of two acidophilic thiobacilli (Acidithiobacillus thiooxidans TS6 and Acidithiobacillus ferrooxidans LX5) and the addition of Fe²⁺ as energy source. During bioleaching, dynamic changes of pH, ORP, Fe²⁺, Fe³⁺, total Fe, Zn, Cu, and dewaterability (expressed as specific resistance γ or Capillary Suction Time CST) of pig slurry were monitored periodically. Results showed that bioleaching process could solubilize pig slurry-borne heavy metals. Moreover, higher addition of Fe²⁺ led to higher removal efficiency of heavy metals. The treatment with 4 g·L^-1 Fe²⁺+2 g·L^-1 S⁰ + bacterial inoculation could achieve the highest metal removal efficiency of 87.3% Cu and 91.9% Zn after 96 h bioleaching. Pig slurry-borne Zn was more easily solubilized than Cu. In addition, the two measured indexes for slurry dewaterability, specific resistance γ and CST of bioleached pig slurry were reduced drastically compared to original pig slurry. Higher Fe²⁺ levels produced slurry with better dewaterability. Bioleached pig slurry dewaterability was increased 117 and 205-fold under the treatments of 2 g·L^-1 S⁰+ 4 g·L^-1 Fe²⁺ and 2 g·L^-1 S⁰+ 5 g·L^-1 Fe²⁺, respectively. It was concluded that bioleaching could not only greatly enhance dewaterability of pig slurry, but simultaneously improve the removal of heavy metals. This study might provide a new approach for treatment and disposal of pig slurry.