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01 Chlorine sterilization
The efficiency of chlorine depends on the concentration of chlorine, the contact time and the pH of the water.
It is commonly used to sterilize and disinfect drinking water, and the residual chlorine concentration is generally 0.5 ppm.
In industrial water treatment, microbiological contamination on heat exchangers and sand filters can be prevented by maintaining the residual chlorine concentration in the water above 0.5-1.0 ppm. The chlorine dosage depends on the amount of organic matter in the influent, which consumes chlorine.
Surface water treatment usually requires chlorine disinfection in the reverse osmosis pretreatment section to prevent microbial contamination by adding chlorine at the intake and maintaining a reaction time of 20-30 minutes to maintain a residual chlorine concentration of 0.5-1.0 ppm throughout the pretreatment pipeline.
However, before entering the membrane element, it must be thoroughly dechlorinated to prevent the membrane from being damaged by chlorine oxidation.
02 Impact sterilization treatment
Shock treatment is the addition of a biocide to the influent of reverse osmosis or nanofiltration for a limited period of time and during normal operation of the water treatment system.
Sodium bisulfite is often used for this purpose, and in general, 500-1000 ppm NaHSO3 can be added for about 30 minutes.
Shock treatment may be carried out periodically at regular intervals, for example every 24 hours, or when biological growth is suspected.
The effluent produced during this shock treatment will contain 1-4% of the added sodium bisulfite concentration.
Depending on the use of the produced water, it can be decided whether the produced water during the shock sterilization period should be recycled or discharged. Sodium bisulfite is more effective against aerobic bacteria than anaerobic microorganisms.
Therefore, the use of shock sterilization should be carefully evaluated in advance.
