The backwashing process parameters for ultrafiltration water purification equipment must be set with membrane regeneration efficiency in mind. By precisely controlling backwashing pressure, flow rate, time, and auxiliary methods, contaminants on the membrane surface can be effectively removed and membrane flux restored. The core mechanism of backwashing lies in using reverse water flow to strip impurities trapped on the membrane fiber surface, while simultaneously enhancing contaminant removal through physical or chemical means. Parameter settings must comprehensively consider membrane material characteristics, feed water quality, and operating conditions to achieve a balance between efficient regeneration and extended membrane life.
The backwashing pressure setting for ultrafiltration water purification equipment must balance cleaning effectiveness and membrane structure protection. Too low a pressure will result in insufficient water flow impact force, failing to effectively strip contaminants from the membrane surface; too high a pressure may cause membrane fiber deformation or module leakage, or even irreversible damage. Generally, the backwashing pressure should be controlled below the membrane element's tolerance limit, and adjusted according to the feed water quality. For example, for raw water containing high concentrations of suspended solids, the pressure can be appropriately increased to enhance the stripping effect, but real-time monitoring of the transmembrane pressure differential (TMP) is necessary to avoid exceeding the limit.
The backwashing flow rate setting directly affects the contaminant removal efficiency. Insufficient flow rate leads to uneven water distribution and incomplete cleaning of localized membrane fibers; excessive flow rate can cause severe vibration of the membrane fibers, accelerating membrane material fatigue. A reasonable flow rate setting needs to be considered in conjunction with the membrane module structure and operating flux, and is typically several times the permeate flow rate. For example, the backwash flow rate for internal pressure ultrafiltration membranes needs to ensure sufficient water penetration from the inside to the outside of the membrane to cover all membrane fiber surfaces; external pressure membranes require combined air-water backwashing to enhance floc removal.
The backwash time setting for ultrafiltration water purification equipment needs to balance cleaning effectiveness and water consumption control. Too short a time will result in contaminant residue, affecting the quality of permeate in the next cycle; too long a time increases water consumption and operating costs, and may cause membrane fiber wear due to excessive rinsing. Typically, a single backwash time is set between tens of seconds and several minutes, and the specific time needs to be adjusted according to the concentration of suspended solids in the feed water, the type of membrane fouling, and the backwash intensity. For example, for raw water containing a high amount of organic matter, the backwash time can be appropriately extended to promote contaminant dissolution; for inorganic salt scaling, chemical cleaning should be combined to shorten the physical backwash time.
Enhanced chemical backwashing is a key method for improving membrane regeneration efficiency. For different types of contaminants, acidic or alkaline cleaning agents can be selected for enhanced backwashing. For example, for inorganic salt scale (such as calcium and magnesium ion deposits), citric acid or hydrochloric acid solutions can be circulated for rinsing, dissolving the deposits through chelation; for organic contaminants (such as microbial slime), sodium hypochlorite solution can be used for oxidative decomposition. The concentration of the chemical cleaning agent and the soaking time must be strictly controlled to avoid corrosion of the membrane material. For example, the concentration of sodium hypochlorite is usually controlled at several hundred ppm, and the soaking time should not exceed half an hour to ensure that contaminants are removed while protecting the membrane structure.
Air-water combined backwashing enhances floc removal by introducing compressed air. The air bubbles generated by the compressed air system create intense turbulence on the membrane fiber surface, effectively breaking the binding force between contaminants and the membrane surface, especially suitable for external pressure ultrafiltration membranes. During air scrubbing, the inlet air pressure and flow rate must be controlled to avoid membrane fiber breakage due to excessive air pressure. For example, the air scrubbing intensity of a single membrane module is typically set within a certain range, with the inlet air pressure not exceeding a specific value to ensure uniform bubble distribution and prevent damage to the membrane material.
The backwashing frequency setting needs to be considered in conjunction with the influent water quality and operating load. For scenarios with poor water quality or high operating flux, the backwashing interval should be shortened to prevent contaminant accumulation; for scenarios with stable water quality and low load, the interval can be appropriately extended to reduce water consumption. For example, municipal water pretreatment systems are typically set to backwash every half hour to one hour, while industrial wastewater treatment systems may require backwashing every twenty minutes. Furthermore, the frequency of chemical backwashing needs to be increased during the summer when microbial growth is vigorous, and the backwashing time can be extended or the flushing flow rate increased when low water temperatures cause a decrease in membrane flux in winter.
Parameter optimization requires long-term operational data accumulation and dynamic adjustment. Establishing a backwashing log to record the cleaning frequency, reagent consumption, and membrane performance changes under different water quality conditions can provide a basis for process optimization. For example, by analyzing historical data, the optimal chemical cleaning cycle can be determined to avoid over-cleaning that could lead to membrane damage; by monitoring changes in permeate flow rate and TMP, backwash pressure and flow rate can be adjusted in a timely manner to ensure a continuous and stable membrane regeneration effect.
