The design of the circulation piping in a pure water unit is crucial for ensuring stable water quality. Controlling the risk of microbial growth is directly related to the biosafety of the produced water and the lifespan of the equipment. Although microbial growth is limited in pure water, temperature fluctuations, residual nutrients, and dead zones in the circulation piping can still create breeding grounds for their growth. Therefore, the piping design of a pure water unit requires comprehensive optimization across multiple dimensions, including fluid dynamics, material selection, and disinfection strategies, to establish a comprehensive microbial control system.
Flow rate design in the circulation piping is crucial for preventing microbial attachment. By increasing the water flow rate, a pure water unit can reduce the residence time of fluid on the pipe wall, thereby reducing the likelihood of microbial adsorption and biofilm formation. Typically, the flow rate in the circulation piping should be maintained above 1.5 m/s to ensure turbulent flow and utilize shear forces to remove attached microorganisms. Furthermore, the pipe diameter should be appropriately selected for the flow rate to avoid reduced flow rate due to an oversized pipe diameter or excessive pressure drop due to a undersized pipe diameter. When selecting a pure water unit's circulation pump, consider both flow rate and head to ensure uniform flow throughout the piping system and avoid the formation of localized stagnant areas.
The antimicrobial properties of the piping material directly impact the risk of microbial growth. Pure water units prioritize materials with smooth, chemically stable inner surfaces, such as 316L stainless steel, PVDF, or PVC-U. These materials are not only corrosion-resistant but also reduce the surface area for microbial attachment. Some high-end pure water units use electropolishing on the inner walls of the piping to further reduce the surface roughness to Ra ≤ 0.4μm, making it difficult for microorganisms to attach. Furthermore, avoid using materials such as copper and galvanized steel that easily release metal ions, as they provide a nutrient source for microorganisms.
Dead corners in pure water unit designs are potential risk points for microbial growth. The circulation piping of a pure water unit must strictly adhere to the "zero dead corner" principle, ensuring smooth transitions between all joints, valves, sensors, and other components and the main pipe. For example, use butt-weld connections instead of threaded connections to reduce residual gaps. When selecting valves, prioritize zero-dead corner diaphragm valves or ball valves, and avoid valve types such as globe valves that are prone to creating stagnant areas. Furthermore, connections between branch pipes and main pipes should adopt a 45° bevel or T-shaped design to ensure effective fluid flushing at branch points and prevent microbial accumulation in low-flow areas.
Integrated disinfection strategies are the last line of defense for microbial control in circulation piping. Pure water units typically combine ultraviolet (UV) sterilization with chemical disinfection to provide dual protection. The UV sterilizer, installed in the circulation piping, uses 254nm ultraviolet light to destroy microbial DNA, achieving continuous online disinfection. Chemical disinfection involves the regular addition of oxidants such as hydrogen peroxide, ozone, or sodium hypochlorite to eliminate established biofilms. Disinfection cycles should be adjusted dynamically based on water quality monitoring results to avoid over-disinfection leading to pipeline corrosion or under-disinfection leading to microbial rebound.
Temperature control is a key measure to inhibit microbial metabolic activity. The circulation piping of pure water units should avoid localized temperatures exceeding 20-25°C, typically maintaining the water temperature between 20-25°C. While high temperatures can accelerate microbial death, they can also accelerate the aging of piping materials. Low temperatures can reduce fluid viscosity and affect flow rate stability. Some pure water units integrate heat exchangers into their circulation systems, using temperature control modules to adjust water temperature in real time to minimize microbial metabolic activity.
The design of pure water unit circulation piping must also consider ease of maintenance. Modular design reduces piping installation and disassembly time, facilitating regular cleaning and disinfection. Visual design (such as transparent PVC pipe sections) allows for direct inspection of the piping's internal conditions, promptly detecting signs of microbial contamination. Furthermore, pipe slopes should be appropriately designed to ensure thorough drainage and prevent residual water from becoming a breeding ground for microorganisms.
The design of pure water unit circulation piping is a comprehensive process, requiring comprehensive considerations from optimizing flow rates, selecting materials, eliminating dead spots, integrating disinfection, temperature control, and ensuring ease of maintenance. Through scientific design and rigorous operation and maintenance management, the risk of microbial growth can be effectively reduced, ensuring the long-term stable operation of the pure water unit and meeting the stringent standards of high-purity water-demanding industries such as electronics, pharmaceuticals, and food.
