Evaluation of ozone‐adsorption system for tertiary treatment of hospital wastewater and recycling to cooling tower

Abstract BACKGROUND Hospitals are a source of wastewater with various pathogens and complex chemical components. Treating hospital wastewater would reduce discharges of potential pathogens and organic micropollutants to the environment and provide a possibility for water recycling. In this study, a hybrid ozonation‐adsorption (HOA) treatment system was installed and operated to treat the secondary wastewater of a hospital with a working capacity of 300 m 3 /h. The hybrid process consisted of ozonation and activated carbon filtration, followed by another ozonation. RESULTS The results showed that with an ozone dose of 240–300 g/h, the HOA process could effectively remove chemical oxygen demand (>80%) and total coliform, Legionella , Salmonella , Clostridium perfringens , Staphylococcus aureus , and Escherichia coli . The chemical oxygen demand (COD) decreased from 59.15 ± 14.41 mg/L for the secondary effluent to 9.54 ± 8.74 mg/L. However, the HOA process had little effect on dissolved organic carbon (DOC), conductivity, chloride, total and calcium hardness, total alkalinity, phosphate, and total dissolved solids, possibly due to the diminishing effectiveness of activated carbon in the filtration unit. The tertiary treated effluent was used as make‐up water at a rate of 15 m 3 /h, approximately 1.5% of the water circulation rate in the cooling tower. During the investigation period of 5 months, the corrected coefficient of performance (COP* act , the ratio of rates of heat removal to compressor energy consumption corrected to standard temperature) was found not to be significantly different from that when tap water was used as make‐up water (COP* act 4.907 when using tap water and COP* act 4.920 when using tertiary treated water). CONCLUSION With an ozone dose of 240–300 g/h, the process was highly effective for removing COD (> 80% COD removal) and eliminating total coliform, Legionella, Salmonella, C. perfringens , S. aureus , and E. coli. Despite the presence of water hardness and phosphate in the treated wastewater, the COP* act of a water‐cooled chiller during the investigation period of 5 months was not significantly different from that when tap water was used as make‐up water. This might be because the ozonized water had a limited scaling potential, and the ozone remaining dissolved in the tertiary treated effluent could help prevent biofilm formation on heat exchanger surfaces. © 2025 Society of Chemical Industry (SCI).