Enhancing pollutants removal in hospital wastewater: Comparative analysis of PAC coagulation vs. bio-contact oxidation, highlighting the impact of outdated treatment plants

While the effectiveness of Poly-Aluminum Chloride (PAC) coagulation for pollutant removal has been documented across various wastewater scenarios, its specific application in hospital wastewater (HWW) treatment to remove conventional pollutants and hazardous genetic pollutants has not been studied. The research compared three hospital wastewater treatment plants (HWTPs) to address a knowledge gap, including the PAC coagulation-sodium hypochlorite disinfection process (PAC-HWTP), the biological contact oxidation-precipitation-sodium hypochlorite process (BCO-HWTP), and a system using outdated equipment with PAC coagulation (ODE-PAC-HWTP). Effluent compliance with national discharge standards is assessed, with BCO-HWTP meeting standards for direct or indirect discharge into natural aquatic environments. ODE-PAC-HWTP exceeds pretreatment standards for COD and BOD5 concentrations. PAC-HWTP effluent largely adheres to national pretreatment standards, enabling release into municipal sewers for further treatment. Metagenomic analysis reveals that PAC-HWTP exhibits higher removal efficiencies for antibiotic resistance genes, metal resistance genes, mobile genetic elements, and pathogens compared to BCO-HWTP and ODE-PAC-HWTP, achieving average removal rates of 45.13%, 57.54%, 80.61%, and 72.17%, respectively. These results suggests that when discharging treated HWW into municipal sewers for further processing, the use of PAC coagulation process is more feasible and cost-effective compared to BCO technologies. The analysis emphasizes the urgent need to upgrade outdated equipment HWTPs.