Most water treatment devices become contaminated with contaminants contained in the water to be treated as the device operates. In the case of ultraviolet sterilization systems, various ionic substances (iron, calcium, magnesium, aluminum, etc.) present in the water to be treated are deposited on the surface of the quartz tube installed to protect the ultraviolet lamp, which reduces the amount of ultraviolet ray irradiated to microorganisms, lowering the efficiency of the ultraviolet sterilization system. Therefore, surface cleaning of the quartz tube is necessary to increase the efficiency of the system. The United States Environmental Protection Agency (US EPA) mentions three types of cleaning methods for cleaning the surface of quartz tubes: off-line chemical cleaning (OCC, manual chemical cleaning), on-line mechanical cleaning (OMC, automatic mechanical cleaning), and on-line mechanical-chemical cleaning (OMCC, automatic mechanical chemical cleaning) (US EPA, 2006). According to the National Water Research Institute (NWRI) regulations (NWRI, 2003), the cleaning method for quartz tubes refers to the CAF (Combines Aging and Fouling factor) value that determines the performance of the UV system.
The CAF value is calculated as in “Formula (1)” by multiplying the EOLL (End of lamp life) related to the life of the lamp and the fouling factor according to the cleaning method of the quartz tube. In the case of the fouling factor, until 2003, according to the NWRI regulations, 0.5 was applied when no cleaning device was used (OMC), 0.75 was applied when a mechanical cleaning device (OMC) was used, and 0.95 was applied when a mechanical chemical cleaning device (OMCC) was used. Currently, only the test results are applied after testing through a third-party organization. Since the CAF value determines the installation cost and operating cost of the UV disinfection system, the cleaning device can be said to be an important system within the UV disinfection system.
Currently, our company has experience developing a mechanochemical cleaning device that can be applied to a low-pressure ultraviolet sterilization system, but it cannot be applied to a medium-pressure ultraviolet sterilization system. In the case of a low-pressure ultraviolet lamp, the heat generated from the surface is about 100°C and the amount of heat transferred to the surface of the quartz tube is small, but in the case of a medium-pressure ultraviolet lamp, the heat generated from the surface is very high at 600 to 900°C, unlike a low-pressure ultraviolet lamp. Therefore, there is a problem that a quartz tube cleaning device developed for a low-pressure ultraviolet sterilization system cannot be applied. In addition to this problem, previously developed cleaning devices were limited to disinfection systems applied to general open channels, but in the case of the medium-pressure ultraviolet sterilization system to be developed in this study, it is a pipe-type product, so there is a concern that leakage may occur due to the pressure inside the pipe. In this study, a seal material with high heat and pressure resistance was selected so that it can be applied to a pipe-type ultraviolet sterilization system equipped with a high-temperature, medium-pressure ultraviolet lamp, and an online mechanochemical cleaning device was developed that can clean quartz tubes together with the cleaning solution by generating microbubbles using a cleaning solution and applying a cleaning solution leakage detection and prevention system.