Operation of a high-flow UV-LED water treatment reactor with secondary effluent for stress testing

For various applications, including water disinfection, the ultraviolet light emitting diode (UV-LED) has recently emerged as a sustainable alternative to the conventional mercury lamp. We performed an accelerated life and stress testing field study of a custom-designed high-flow UV-LED drinking water disinfection reactor operating 24/7 with 20 L per minute (LPM) of extreme quality secondary effluent. The low UV transmittance (55-64 %) and high turbidity (4-10 NTU) considerably affected the performance of the system. Organic and inorganic fouling were observed on the reactor walls and protective quartz windows. However, the surface areas that were exposed to higher irradiance were found to be less prone to an organic fouling formation. Despite the low operating temperature of the UV-LEDs, the chemical deposition, the extent of which correlated with the UV irradiance profile, was observed over the quartz windows. This indicates the effect of UVC in promoting quartz scaling formation when the water contains high levels of calcium and iron. Unexpected levels of zinc in the fouling, despite its low concentration in the water, showed the importance of this element in the formation of fouling in the UV-LED water disinfection systems. After 22 days of field testing, the UV transmittance of the protective windows dropped by 50-60 %, which, along with the radiant power reduction of the UV-LEDs, resulted in a 67 % overall reduction in an equivalent dose of the reactor. The study showed that optimally designed drinking water UV-LED reactors can maintain notable performance, even after exposure to accelerated life testing in extreme water conditions. Furthermore, the fouling was reversible, and the reactor was easily cleaned using household cleaning solutions in a two-step process with bleach and CLR (R), where the cleaned quartz had a UV transmittance equal to an unused quartz window.