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UV-LED disinfection no longer a myth in the public water supply and municipal wastewater treatment industries
Citation:
Kim, H., S. Kim, S. Byun, H. Ryu, Y. Oh, H. Woo, AND Y. Shim. UV-LED disinfection no longer a myth in the public water supply and municipal wastewater treatment industries. To be Presented at WQTC 2022 Conference, Cincinnati, OH, November 13 - 17, 2022.
Impact/Purpose:
This work was carried out as a part of Cooperative Research and Development Agreement (CRADA) between Korea Water Partnership (KWP) and the Center for Environmental Solutions and Emergency Response of the U.S. Environmental Protection Agency (EPA). In this collaboration, we applied multiple wavelength ultraviolet (UV) light emitting diodes (LEDs) for the disinfection of municipal wastewater effluent. Our challenge was to achieve comparable (even greater) reliability for compliance with bio-stability goals, especially by replacing conventional UV lamps to reduce the use of mercury. South Korea is one of the 97 countries to ratify the Minamata Convention on Mercury that is an international treaty designed to protect human health and the environment from anthropogenic emissions and releases of mercury and mercury compounds. The United States also signed the Minamata Convention on November 6, 2013. The Minamata Convention requires that party nations phase-out or take measure to reduce mercury use in certain products. Although the use of UV lamps for purposes other than lighting are not currently banned, there should create initiatives to reduce the use of mercury in the public water supply and municipal wastewater treatment industries. There are more than 4,200 water resource recovery facilities (commonly known as wastewater treatment plants) in South Korea, of which 85% have a facility capacity of less than 500 m3/d. Almost all of these small facilities use mercury lamps for UV disinfection and replace them annually.
Description:
The collaboration between KWP and EPA demonstrated the possible applicability of using UV-LED water treatment systems for the disinfection of municipal wastewater effluent. The on-site evaluation was conducted over 6 months using secondary treated wastewater from a local water resource recovery facility in Seoul. The UV transmittance of the wastewater was constant between 82% and 84% during the evaluation period. The active power draw required for UV-LEDs was 107 W, and the operating flow rate varied up to 70 L/min (100 m3/d). A dramatically improved performance was achieved with patented devices and designs for UV-LED water treatment systems. Our result shows a robust inactivation of total coliform by 97- 99%, which successfully complied with discharge permit standards that limit total coliform to 1,000 CFU/mL in the effluent. The energy required for the UV-LEDs was 0.025 kWh/m3. Energy consumed by UV disinfection can account for approximately 10 to 25 % of total energy use at a municipal wastewater treatment facility. The energy consumption calculated in the on-site evaluation was comparable to the lowest value for low¿pressure lamps (0.026 to 0.066 kWh/m3) and was much lower than that for medium pressure lamps (0.122 to 0.148 kWh/m3). Despite of the outstanding performance (UV intensity per unit area) of UV-LEDs and their robustness in disinfection, the marketplace has been reluctant to use UV-LEDs for municipal water and wastewater services. Although recently a UV-LED disinfection system started operation at a municipal water supply in Japan, the showcase for the industries still lacks relevant products. In this collaboration, our observation reveals the high adaptability of UV-LED as a game changer and shows that mercury-free alternatives may become a reality in the nearest future.