1. Introduction
Biofouling is a common and often serious problem in system operation, especially when the water source is surface water or water rich in bacteria. Controlling the proliferation of microorganisms in the water is particularly important. Proper system design is the primary condition for preventing microbial fouling. Appropriate pretreatment operations can effectively reduce the risk of biofouling. Complete sampling and analysis procedures are means of preventing and detecting contamination. Finally, for systems that have already become contaminated, appropriate disinfection and cleaning are necessary. The following are the requirements for the use of disinfectants on RO/NF membranes:
- Membrane compatible;
- It can exert a relatively fast disinfection effect;
- Low cost;
- It features easy transportation, storage, and operation, as well as stability;
- It should not permeate the membrane into the product water;
- It has broad-spectrum bactericidal activity;
- Biodegradable;
- It complies with all current regulations.
2. Cleaning of biological contaminants
The following cleaning solutions are specifically designed for biological contamination:
(1) Aldehydes, such as formaldehyde and glutaraldehyde, are suitable for system disinfection with aldehyde solutions of 0.1 to 1.0% concentration, but the membrane element should not be exposed to aldehyde solutions for at least 48 hours after use.
(2) DBNPA ( 2,2-dibromo-3-nitropropionamide ) is a non-oxidizing agent. After the system has been severely contaminated with biofilm and cleaned, continuous disinfection measures must be taken. It is recommended to continuously add 0.5~1.0 ppm of DBNPA. The dosage can be adjusted according to the level of biological activity.
(3) Hydrogen peroxide solution: Systems equipped with membrane elements can be sterilized using hydrogen peroxide or a mixture of hydrogen peroxide and peracetic acid. It is important to note that the presence of iron or other transition metals can cause membrane degradation through catalytic oxidation of hydrogen peroxide.
(4) Copper sulfate can be used to control the growth of algae. The usual continuous dosage is 0.1~0.5 ppm. At the same time, the ph must be low to prevent copper hydroxide from precipitating.
