Cleaning Of Hollow Fiber Ultrafiltration Membranes

Hollow fiber ultrafiltration membranes require regular cleaning using various methods during continuous operation. Common cleaning methods include:

1. Backpressure backwashing: Clean water is introduced from the ultrafiltrate side and flushes towards the front. Due to the different pressure resistance of the membrane on both sides, backwashing is generally limited to low pressure, resulting in weak backwashing intensity and limited effectiveness. For best results, a membrane with high pressure resistance must be selected, and backwashing should be performed at higher pressure and flow rate. The flushing time should be 30-60 seconds.

2. Isobaric hydraulic flushing: The ultrafiltration water outlet valve is closed, while the concentrate outlet valve is fully opened to increase the flow velocity across the membrane surface. This method is effective in removing loosely attached substances.

3. Chemical cleaning: Depending on the type of fouling substances on the membrane surface, appropriate chemicals are selected to dissolve, oxidize, or otherwise react with the fouling substances to achieve removal. The selection of commonly used chemicals must be based on the properties of the membrane material, including acids, alkalis, oxidants, bactericides, surfactants, and enzyme-added detergents. The procedure is the same as a normal ultrafiltration process. The cleaning solution enters through the raw solution inlet, and the concentrate and ultrafiltrate are all returned to the cleaning solution container. After circulation, the solution is discharged and rinsed with clean water.

Ultrafiltration uses a new hollow fiber filtration technology, combined with three-stage pretreatment filtration to remove impurities from tap water. The ultrafiltration micropores are smaller than 0.01 microns, thoroughly filtering out bacteria, rust, colloids, and other harmful substances from the water, while retaining beneficial trace elements and minerals. Ultrafiltration membrane filtration prevents large molecular solutes from passing through, leaving them on one side of the membrane, thus partially purifying the large molecules. The principle of ultrafiltration is also a membrane separation process. Ultrafiltration utilizes a pressure-activated membrane that, under external driving force (pressure), retains colloids, particles, and substances with relatively high molecular weights in the water, while water and small solute particles permeate through the membrane.