Types of Reverse Osmosis Membrane Cleaning Methods

Reverse osmosis membrane cleaning methods are divided into physical and chemical methods, both of which can effectively clean the membrane:

Physical Methods: This method uses mechanical force to remove contaminants from the membrane surface. No chemical reaction occurs during the entire cleaning process.

1. Manual Wiping Method

This is a relatively primitive but effective method. The basic procedure involves gently wiping the surface of the disassembled sheet membrane with a soft material (such as a sponge), rinsing it with water as you wipe. This method effectively removes a large amount of contaminants from the membrane surface. However, it is ineffective against smaller impurities deep within the membrane pores.

2. Isobaric Hydraulic Flushing Method

This method can be used to clean membranes of any configuration. Specifically, the permeate valve is closed, the concentrate outlet valve is opened, and the membrane surface is flushed with increased flow rate. This is effective in removing large amounts of soft impurities from the membrane surface. The effectiveness of isobaric flushing is also related to the frequency of continuous flushing.

3. Backwashing Method

Backwashing is a method of flushing the membrane from the back side (porous support layer) to the front side (closed layer). This is an effective cleaning method. After backflushing the membrane, a pressure-equalizing hydraulic flushing method is performed, resulting in a very significant cleaning effect.

4. Hot Water Flushing Method

Using heated water (30-40°C) to flush the membrane surface is highly effective in removing viscous and heat-soluble impurities (such as sugars).

5. Water-Air Mixed Cleaning Method

Purified compressed air and water are fed into the ultrafiltration unit. The water-air mixture creates vigorous agitation on the membrane surface, removing stubborn impurities. The effect is also quite good.

Chemical Method: This method uses a chemical reagent to react with the filter cake on the membrane surface to clean the membrane. The principles for selecting chemicals for reverse osmosis membrane cleaning are: firstly, they must not react chemically with the membrane or other component materials; secondly, they must not cause secondary pollution. When using chemical cleaning methods, pressure-equalizing flushing and backflushing are often combined for more effective removal of contaminants from the membrane surface.

1. Oxidizing cleaning agents, such as 1%–3% H₂O₂ or 500–1000 mg/L NaCl, are used to clean the 4040 reverse osmosis membrane. This removes fouling and kills bacteria. H₂O₂ is a commonly used bactericide.

2. Enzyme-based cleaning agents, such as 0.5%–1.5% pepsin or trypsin, are effective in removing protein, polysaccharides, and oily contaminants when cleaning the 4040 reverse osmosis membrane.

Reverse osmosis membrane elements are a crucial component of water treatment systems; therefore, regular cleaning of the reverse osmosis membrane is essential.