Evaluation of Heavy Metal Contamination from Large-scale Swine-Farming Wastewater in Sichuan Province, China: Removal Efficiency, Spatial Distribution and Risk Assessment.

The widespread application of swine-farming wastewater to soil and water is increasingly contributing to heavy metal contamination, posing significant environmental risks. This study investigated the concentrations of eight heavy metals in swine-farming wastewater following different treatment processes, and assessed their ecological risks in Sichuan Province, China. The findings revealed that zinc, copper and nickel exhibited the highest concentrations, potentially causing heavy or strong contamination levels and leading to heavy or slight ecological risks. Advanced treatment processes employing physical-chemical, biochemical and ecological technologies, significantly reduced heavy metal concentrations compared to anaerobic fermentation, mitigating the widespread and severe ecological risks in Sichuan. However, the utilization of biogas slurry poses a high potential for severe ecological risks associated with heavy metals, particularly in the Panxi and Northwest regions. To control the ecological risks of heavy metals, advanced treatment processes should be strongly recommended alongside diverse resourceful utilization strategies tailored to large-scale swine farms in different regions of Sichuan Province.