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 Cu and Zn 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 Cu and Zn removal with efficiencies of 99 % and 49 % respectively. The sulfide precipitation mediated by AnGS could be another significant pathway for Zn removal with efficiency of 18-27 % in Protein/M experiments and 16-46 % in SO/M experiments (M represents the total concentration of Cu and Zn). The results of continuous experiment showed, with SO/M larger than 1.5, the influent Cu and Zn could be effectively removed in an anaerobic methanation bioreactor and its effluent Cuand Znconcentrations were below 1 mg/L and 2 mg/L separately. The main removal mechanism of Cuand Zn 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 Cu and Zn with organic pollutants simultaneously to eliminate environmental risk of swine wastewater.