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Using AOPs in drinking Water treatment

The use of O3 for drinking water

1. Introduction

Safe and reliable drinking water treatment is essential for protecting public health. While conventional methods such as coagulation, sedimentation, filtration, and chlorination are widely employed, they may not adequately address emerging contaminants, taste and odor problems, or chlorine-resistant pathogens. Ozone (O₃) and associated advanced oxidation processes (AOPs) are increasingly applied as powerful alternatives or complements to conventional treatment, due to their strong oxidative capacity and broad-spectrum disinfection properties (von Gunten, 2003).

2. Ozone in drinking water treatment

Ozone is a triatomic allotrope of oxygen and one of the strongest oxidants used in water treatment, with a standard redox potential of 2.07 V (compared to 1.36 V for chlorine). Its applications include:

  • Disinfection: Ozone effectively inactivates bacteria, viruses, and protozoan cysts, including Giardia lamblia and Cryptosporidium parvum, which are resistant to conventional chlorination (Langlais et al., 1991; Korich et al., 1990).
  • Oxidation of organic and inorganic contaminants: Ozone reacts with taste- and odor-causing compounds (e.g., geosmin, 2-methylisoborneol), natural organic matter (NOM), and inorganic compounds such as iron, manganese, and sulfide (Camel & Bermond, 1998).
  • By-product precursor transformation: Pre-ozonation modifies NOM structure, often lowering the formation potential of chlorination by-products such as trihalomethanes (THMs) and haloacetic acids (HAAs). However, it can also lead to the formation of aldehydes, ketones, and carboxylic acids (von Gunten, 2003).

Despite these benefits, ozone decomposes rapidly in water and does not provide residual disinfection in the distribution system, necessitating a secondary disinfectant such as chlorine or chloramine.

3. Advanced Oxidation Processes (AOPs) based on ozone

AOPs enhance the oxidative potential of ozone by generating hydroxyl radicals (•OH), which have an even higher redox potential (2.8 V) and react non-selectively with a wide range of organic pollutants.

Key ozone-based AOPs include:

  • O₃/H₂O₂ (Peroxone process): The addition of hydrogen peroxide accelerates ozone decomposition, leading to enhanced •OH generation. This process has been widely applied for the removal of micropollutants, pesticides, and pharmaceuticals (Staehelin & Hoigné, 1982).
  • O₃/UV: Ultraviolet irradiation of ozone produces hydroxyl radicals through photolysis. This combination is particularly effective for trace organic contaminant removal but requires high energy input (Glaze et al., 1987).
  • Catalytic ozonation: Transition metals or solid catalysts can promote ozone decomposition to radicals, though large-scale applications remain limited (Beltrán, 2004).

These processes are effective for degrading compounds resistant to direct ozonation, such as endocrine-disrupting chemicals, pharmaceuticals, and perfluorinated substances (Pétrier & Debacq, 2000; Rosal et al., 2010).

4. Advantages of ozone and AOPs

  • Broad-spectrum disinfection effective against viruses, bacteria, and protozoa.
  • Oxidation of emerging contaminants such as pesticides, pharmaceuticals, and industrial chemicals.
  • Improvement of aesthetic quality (taste, odor, and color removal).
  • Synergy with other processes: Ozone pre-treatment can enhance coagulation and biofiltration by breaking down high-molecular-weight organic matter into more biodegradable fractions (Hübner et al., 2015).

5. Conclusion

Ozone and associated AOPs represent powerful technologies for drinking water treatment, offering superior disinfection and effective removal of emerging contaminants. Their implementation, however, requires careful consideration of by-product formation, operational costs, and integration with other treatment barriers. As regulatory requirements evolve and new pollutants of concern are identified, ozone-based treatment is likely to expand, especially in utilities seeking advanced solutions for microbial safety and micropollutant control.

Some references

  • Beltrán, F. J. (2004). Ozone Reaction Kinetics for Water and Wastewater Systems. CRC Press.
  • Camel, V., & Bermond, A. (1998). The use of ozone and associated oxidation processes in drinking water treatment. Water Research, 32(11), 3208–3222.
  • Glaze, W. H., Kang, J. W., & Chapin, D. H. (1987). The chemistry of water treatment processes involving ozone, hydrogen peroxide and ultraviolet radiation. Ozone: Science & Engineering, 9(4), 335–352.
  • Hübner, U., von Gunten, U., & Jekel, M. (2015). Evaluation of the persistence of transformation products from ozonation of trace organic compounds—a critical review. Water Research, 68, 150–170.
  • Korich, D. G., Mead, J. R., Madore, M. S., Sinclair, N. A., & Sterling, C. R. (1990). Effects of ozone, chlorine dioxide, chlorine, and monochloramine on Cryptosporidium parvum oocyst viability. Applied and Environmental Microbiology, 56(5), 1423–1428.
  • Langlais, B., Reckhow, D. A., & Brink, D. R. (1991). Ozone in Water Treatment: Application and Engineering. CRC Press.
  • Pétrier, C., & Debacq, M. (2000). Wastewater treatment: Ozonation and advanced oxidation technologies. Encyclopedia of Environmental Control Technology.
  • Richardson, S. D., Plewa, M. J., Wagner, E. D., Schoeny, R., & DeMarini, D. M. (2007). Occurrence, genotoxicity, and carcinogenicity of regulated and emerging disinfection by-products in drinking water. Mutation Research, 636(1–3), 178–242.
  • Rosal, R., Rodríguez, A., Perdigón-Melón, J. A., Mezcua, M., Hernando, M. D., Letón, P., … & Fernández-Alba, A. R. (2010). Degradation of carbamazepine, diazepam and diclofenac by advanced oxidation processes. Chemosphere, 75(2), 199–206.
  • Staehelin, J., & Hoigné, J. (1982). Decomposition of ozone in water: rate of initiation by hydroxide ions and hydrogen peroxide. Environmental Science & Technology, 16(10), 676–681.
  • von Gunten, U. (2003). Ozonation of drinking water: Part I. Oxidation kinetics and product formation. Water Research, 37(7), 1443–1467.
  • World Health Organization (WHO). (2017). Guidelines for Drinking-water Quality: Fourth edition incorporating the first addendum. Geneva: WHO.