(Ⅱ)
01 Periodic disinfection
This treatment is used on systems with a moderate biocontamination hazard, but in systems with a high biocontamination hazard, disinfection is only an adjunct to continuous biocide treatment.
Preventive disinfection is more effective than corrective sterilization, because isolated bacteria are easier to kill and remove than thick, aging biofilms.
Generally, the disinfection interval is once a month, but systems with strict hygienic requirements (such as pharmaceutical process water) and highly polluted raw water (such as wastewater) may be once a day. Of course, the life of the membrane is affected by the type and concentration of chemicals used. After intensive disinfection, the life of the membrane may be shortened.
02 Ozone sterilization
It is more oxidizing than chlorine, but it decomposes quickly, so it is necessary to maintain a certain level to kill microorganisms, and also consider the ozone resistance of the equipment used, usually stainless steel should be used.
In order to protect the element, the ozone must be removed carefully, and UV irradiation can successfully achieve this goal.
03 UV irradiation
Ultraviolet light at 254 nanometers has been shown to have a bactericidal effect, and it has been used in small water plants. It does not require chemicals to be added to the water, and the equipment maintenance requirements are low, requiring only regular cleaning or replacement of mercury vapor tubes.
However, the application of ultraviolet radiation treatment is very limited, only suitable for cleaner water sources, because colloids and organic matter will affect the penetration of light radiation.
04 Sodium bisulfite
When its concentration in the influent of the seawater desalination system reaches 50 mg/L, the control of biological pollution is effective. In this way, colloidal contamination can also be reduced.
An additional advantage of sulfurous acid is that it does not require the addition of acid to control calcium carbonate due to the acidic reaction of sulfurous acid to produce hydrogen ions.
