Point-of-use (POU) treatment in a pure water unit is crucial for ensuring sterile effluent. Its design must revolve around four dimensions: microbial control, physical interception, chemical inactivation, and system integrity. A typical PPU system consists of an ultraviolet (UV) sterilizer, a microfiltration filter, a storage tank, and circulation piping. These components work together to eliminate residual microorganisms, particulate matter, and organic matter in the water, preventing secondary contamination.
The UV sterilizer is the first line of defense in PPU treatment. It uses specific wavelengths of ultraviolet light (typically 254nm) to destroy the DNA structure of microorganisms, rendering them unable to reproduce. This technology is highly effective against bacteria, viruses, and some fungi without introducing chemical residues. To ensure sterilization effectiveness, the UV lamps must be cleaned regularly to prevent scale or impurities from blocking the light. The irradiation time must also be adjusted according to the water flow rate to ensure all water molecules receive a sufficient dose of UV radiation. Furthermore, UV sterilizers are often linked to sensors to monitor UV intensity in real time. When the intensity falls below a threshold, an alarm is automatically triggered, and water supply is suspended to prevent insufficiently treated water from entering downstream areas.
Microfiltration filters act as a physical barrier in end-of-pipe treatment, intercepting microorganisms and their metabolic products through the microporous structure of the filter membrane. The pore size of the membrane is typically 0.22 micrometers or smaller, effectively trapping bacteria, fungal spores, and some viruses to ensure the effluent meets sterility standards. The membrane material must possess chemical stability to avoid reactions with residual disinfectants or organic matter in the water, which could lead to membrane damage or the release of harmful substances. Some high-end pure water units employ a two-stage filtration design: the first stage removes large particles, and the second stage further refines the filtration, extending membrane life and improving effluent quality. The membrane replacement cycle needs to be dynamically adjusted based on water quality monitoring results to prevent microbial penetration due to membrane clogging or damage.
The design of the end-of-pipe storage tank must avoid environmental conditions conducive to microbial growth. The inner wall of the tank should be made of a smooth, dead-angle-free material (such as 316L stainless steel) to reduce microbial attachment points; the top vent should be equipped with a hydrophobic bactericidal filter to prevent airborne microorganisms from entering the tank; the bottom of the tank should be conical or sloping to facilitate drainage and prevent water accumulation and biofilm formation. Storage tanks require regular cleaning and disinfection. The cleaning process must cover all internal surfaces. Disinfectants must be non-corrosive to the tank material and rapidly decompose (e.g., hydrogen peroxide silver ion composite agent). After disinfection, the tanks must be rinsed with pure water until no residue remains. Furthermore, storage tanks must be equipped with level and temperature sensors to monitor water level and temperature in real time, preventing pump idling due to low water levels or accelerated microbial growth due to excessively high water temperatures.
The circulation pipeline is an often overlooked aspect of terminal treatment, but its design directly affects the maintenance of sterility. Pipelines must be made of sanitary-grade stainless steel or food-grade plastic, avoiding materials prone to microbial growth (such as rubber). Pipeline connections should use clamps or welded connections to reduce dead angles caused by threaded connections. The pipeline slope must be appropriate to ensure thorough drainage and prevent water accumulation. Online ultraviolet sterilizers and periodic disinfection devices must be installed in the pipeline for regular comprehensive disinfection. For long-distance pure water pipelines, sampling ports must be installed at key points to regularly test microbial indicators and promptly identify potential contamination risks.
A comprehensive monitoring system is needed for the operation and management of terminal treatment systems. Operators must regularly test the effluent quality, including microbiological indicators (such as total bacterial count and endotoxins), physical indicators (such as conductivity and pH), and chemical indicators (such as residual chlorine and total organic carbon), to ensure that all indicators meet sterile water standards. Simultaneously, operating parameters of the pure water unit (such as UV intensity, filter membrane differential pressure, and storage tank level) must be recorded. Data analysis can be used to predict pure water unit malfunctions or water quality fluctuations in advance. Furthermore, an emergency plan must be developed. When effluent quality exceeds standards, water supply should be immediately stopped and a troubleshooting process initiated, checking from the source to the terminal step by step to locate the source of contamination and taking targeted measures (such as replacing the filter membrane, strengthening disinfection, and cleaning pipelines) until the water quality returns to acceptable levels.
