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<p>This study investigated the synergistic effects of chlorine or ozone application to secondary effluent prior to ultraviolet (UV) disinfection on the inactivation of <i>E. coli</i>, total coliforms, <i>Clostridium perfringens</i>, <i>Giardia</i> spp. cysts, and <i>Cryptosporidium</i> spp. oocysts. The physicochemical parameters remained statistically similar in the chlorine assays. In contrast, ozonation reduced the COD, solids, turbidity, and absorbance at 254&#xa0;nm. The order of microorganism resistance was as follows: <i>E. coli</i> = total coliforms &lt; <i>C. perfringens</i> across all treatments (both individual and sequential). The ozone dosage was more strongly correlated with microbial inactivation than was the applied CT (concentration × contact time), indicating greater efficacy with greater ozone consumption. Chick’s kinetic model provided the best fit for UV radiation, whereas the Hom model was more suitable for chlorination. Standalone ozone treatment notably reduced <i>Giardia</i> cyst concentrations, and standard fluorescence reduction after sequential treatments suggested oxidative damage to cyst walls. The high viability of <i>Cryptosporidium</i> oocysts after disinfection raises significant public health concerns. Synergistic inactivation varied by treatment: ozone-UV (0.02 to 1.28 log) and chlorine-UV (0.07 to 0.82 log), depending on the target organism. These findings indicate that lower CT values for primary disinfectants can effectively reduce pathogen levels, offering a more sustainable approach to wastewater treatment.</p>

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Synergistic effects of chlorine and ozone on ultraviolet disinfection of different microorganisms in secondary wastewater effluent

  • 期刊论文

  • 发表日期：

    2025年9月1日

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  • Raphael Corrêa Medeiros,
  • Kamila Jessie Sammarro Silva,
  • Maria Teresa Hoffmann,
  • Bárbara Luiza Souza Freitas,
  • Mariza de Camargo,
  • Patrícia Rodrigues Fortes,
  • Lyda Patricia Sabogal-Paz,
  • Luiz Antonio Daniel

摘要

This study investigated the synergistic effects of chlorine or ozone application to secondary effluent prior to ultraviolet (UV) disinfection on the inactivation of E. coli, total coliforms, Clostridium perfringens, Giardia spp. cysts, and Cryptosporidium spp. oocysts. The physicochemical parameters remained statistically similar in the chlorine assays. In contrast, ozonation reduced the COD, solids, turbidity, and absorbance at 254 nm. The order of microorganism resistance was as follows: E. coli = total coliforms < C. perfringens across all treatments (both individual and sequential). The ozone dosage was more strongly correlated with microbial inactivation than was the applied CT (concentration × contact time), indicating greater efficacy with greater ozone consumption. Chick’s kinetic model provided the best fit for UV radiation, whereas the Hom model was more suitable for chlorination. Standalone ozone treatment notably reduced Giardia cyst concentrations, and standard fluorescence reduction after sequential treatments suggested oxidative damage to cyst walls. The high viability of Cryptosporidium oocysts after disinfection raises significant public health concerns. Synergistic inactivation varied by treatment: ozone-UV (0.02 to 1.28 log) and chlorine-UV (0.07 to 0.82 log), depending on the target organism. These findings indicate that lower CT values for primary disinfectants can effectively reduce pathogen levels, offering a more sustainable approach to wastewater treatment.