Out with the Old, In with the New…Disinfection Technologies
- Patricia Drummey Stiegel, PE, Melanie Mann, PE - Hazen and Sawyer
Disinfection technologies for wastewater are changing rapidly. As the first generation of sodium hypochlorite and ultraviolet disinfection systems installed in the 1990s and earlier reach the end of their useful lives, some utilities must make decisions about what type of disinfection to use going forward. Other utilities are becoming more conscious about the safety of continued use of chlorine gas and are looking for economical new technologies. Fortunately, technology and design experience have improved greatly over the years, and more options than ever are available to provide safe, reliable, cost-effective wastewater disinfection. High-watt low pressure ultraviolet disinfection technologies are being rolled out by multiple manufacturers, on-site generation of sodium hypochlorite is becoming more mainstream, and ozone is getting a second look as a disinfectant with the added benefit of reducing concentrations of emerging contaminants.
This presentation will explore multiple case studies, including a plant in Tennessee that had its UV system destroyed by flooding. A disinfection alternatives analysis showed that use of liquid sodium hypochlorite was more cost effective for this plant than replacing the UV system or providing on-site generation of sodium hypochlorite. An evaluation in Alabama showed that repairing an existing medium pressure UV system had the lowest life cycle cost as compared to constructing a low pressure UV system or using sodium hypochlorite. A North Carolina plant looking to replace aging UV technology was able to retrofit within their existing channels and reduce energy costs by 70%.
A disinfection alternatives screening analysis for a facility in Virginia included technologies such as low and high strength on-site sodium hypochlorite generation, ozone, low pressure high output (LPHO) and medium pressure (MP) UV as well as continued use of delivered sodium hypochlorite and sodium bisulfite. Each of these case studies highlights the pros and cons of the many disinfection options available to utilities.
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