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Wastewater and sewage contain a wide range of microorganisms and organic pollutants. Ozone is frequently employed to eliminate these contaminants because it is more effective than chlorine at destroying pathogens. However, its application is accompanied by several significant drawbacks that wastewater treatment professionals must consider.
Ozone is only 12 times less soluble in water than chlorine, limiting the maximum disinfectant concentration achievable. If the ozone dose is too low, resilient organisms—especially cyst‑forming bacteria and viruses—can survive. High ozone levels are therefore desirable, but they are difficult to maintain because ozone degrades rapidly, with faster decay at elevated temperatures and higher pH values. In waters rich in organic matter or suspended solids, much of the ozone is consumed reacting with these substances, leaving insufficient residual to disinfect pathogens. This makes ozone a less economical choice for wastewater with high levels of organic load or solids.
Ozone’s strong oxidizing power is both its strength and its limitation. It can corrode metal surfaces, including the stainless‑steel or titanium liners used in treatment reactors, necessitating the use of corrosion‑resistant materials that increase capital costs. Additionally, ozone is a toxic gas; proper containment, ventilation, and monitoring are essential to protect workers, which further drives up operational expenses.
Generating ozone typically involves passing an electric current through air in a corona‑discharge system. Approximately 85 % of the electrical energy is lost as heat, making ozone production highly energy‑intensive. The equipment required—high‑voltage power supplies, air‑pumps, and ozone‑generating units—is also more complex than conventional chlorination systems, resulting in higher capital and maintenance costs.
Unlike chlorine, ozone leaves no residual disinfectant once the process ends; any unreacted ozone decomposes to oxygen. This absence of a measurable residual makes it harder to verify disinfection efficacy in real time. When ozone reacts with organic compounds, it can form a range of byproducts. In the presence of bromide ions, for example, ozone can produce bromate—a compound classified as a potential human carcinogen. Operators must therefore monitor pH and bromide concentrations carefully, or avoid ozone treatment when bromide levels are high.
