The removal of copper and zinc from swine wastewater by anaerobic biological-chemical process: Performance and mechanism.

Copper and zinc are often used as feed additives and frequently detected in swine wastewater. Anaerobic granular sludge (AnGS) plays an important role in high-rate anaerobic methanation biotechnologies which are widely applied to treat swine wastewater. The removal of Cu2+ and Zn2+ by AnGS was investigated in the batch and continuous systems. The results of batch experiments showed the adsorption by AnGS could be a significant method for Cu2+ and Zn2+ removal with efficiencies of 99 % and 49 % respectively. The sulfide precipitation mediated by AnGS could be another significant pathway for Zn2+ removal with efficiency of 18-27 % in Protein/M2+ experiments and 16-46 % in SO42-/M2+ experiments (M2+ represents the total concentration of Cu2+ and Zn2+). The results of continuous experiment showed, with SO42-/M2+ larger than 1.5, the influent Cu2+ and Zn2+ could be effectively removed in an anaerobic methanation bioreactor and its effluent Cu2+and Zn2+concentrations were below 1 mg/L and 2 mg/L separately. The main removal mechanism of Cu2+and Zn2+ in the anaerobic methanation system was that the biological production of sulfide from sulfate was followed by chemical precipitation and reduction. It is helpful for the removal of Cu2+ and Zn2+ with organic pollutants simultaneously to eliminate environmental risk of swine wastewater.