During RO membrane cleaning, the specific cleaning method should be selected based on the type and extent of fouling. Chemical cleaning can be performed in two ways: in-place cleaning (CIP) and offline cleaning. Overall, RO membrane cleaning methods can be classified into physical cleaning and chemical cleaning.
Physical cleaning targets reversible fouling and is typically performed by increasing water flow velocity, raising cleaning frequency, applying ultrasonic vibration, or using air scouring. These techniques can be further divided into mechanical cleaning and hydraulic cleaning. Physical cleaning is generally used when the foulants on the membrane surface are loosely attached and have weak adhesion.
Chemical cleaning involves preparing cleaning solutions by mixing chemicals in specific proportions. These solutions act through mechanisms such as hydrolysis, dissolution, chelation, saponification, and dispersion to react with and loosen the fouling layer, thereby reducing the adhesion between deposits and the membrane surface. This method is particularly effective for removing stubborn or strongly adhered contaminants. Common types of chemical cleaning agents include acidic membrane cleaners, alkaline membrane cleaners, and enzyme-based membrane cleaners.
- Acidic Membrane Cleaning Agents
Acidic membrane cleaning agents react with inorganic scale and mineral deposits, effectively dissolving and removing metal ions such as iron, magnesium, and calcium from surface contaminants and gel layers. This process restores the membrane's water production flux. Common acids used in acidic membrane cleaners include hydrochloric acid, nitric acid, citric acid, and phosphoric acid.
- Alkaline Membrane Cleaning Agents
The cleaning principle of alkaline agents is based on initiating a saponification reaction, converting biofilm into water-soluble fatty acids and glycerol, which can be easily removed. These agents also soften and swell dried organic matter, making it easier to dislodge.
- Enzyme-Based Membrane Cleaning Agents
Enzymes, derived from microorganisms and other renewable sources, have unique biological activities. Different types of enzymes can break down various organic foulants into small molecular compounds, which are then removed with the help of surfactants. Compared to conventional cleaning agents, enzyme-based cleaners not only improve cleaning efficiency but also allow for lower cleaning temperatures and shorter cleaning cycles.
In addition to acidic, alkaline, and enzyme-based cleaners, certain chemical formulations containing salts, nitrogen compounds, or oxidizing agents are also effective in removing RO membrane foulants.
After continuous operation, RO membranes inevitably experience fouling from inorganic matter, organic matter, and microorganisms. Acidic, alkaline, and enzyme-based cleaning agents are proven solutions to this problem, significantly improving membrane flux, salt rejection, conductivity, and permeate flow after cleaning. Furthermore, the application of diverse chemical compositions in cleaning agents offers valuable theoretical and technical support for developing high-efficiency and rapid cleaning products. This, in turn, drives innovation, promotes industry development, and enhances economic benefits, with irreplaceable roles in sectors such as water treatment and dairy processing.
