How Should Sterilization Be Performed During Pretreatment?

Conventional water sterilization involves chemical dosing and ultraviolet (UV) inactivation. For example, purified water, widely used as beverage water, undergoes reverse osmosis desalination followed by UV sterilization. For small-volume water supply (less than 10 t/h), chlorine dioxide or ozone can be used for sterilization. In industrial production, chlorine or sodium hypochlorite is commonly used, although chlorine dioxide or ozone can also be employed. Purchased chlorine is stored in steel cylinders and added using a chlorinator. Electrolysis of salt (or seawater) yields sodium hypochlorite, which can be added to the treated water without specialized dosing equipment.

Ozone is produced from purified air using a high-voltage discharge device. Small to medium-sized ozone generators are currently used for sterilization of community water supply systems or central air conditioning cooling water systems. It is also suitable for inactivation treatment in reverse osmosis systems. Excess ozone can be absorbed by activated carbon. Chlorine dioxide can be produced from sodium chlorate and is widely used in drinking water treatment and industrial cooling water treatment. Sodium chlorate is explosive and should be used with caution.

In reverse osmosis water treatment processes, besides sterilization during operation, there is also the issue of sterilization during equipment shutdown. Generally, equipment can be flushed with raw water within 48 hours of shutdown. After 48 hours, it can be stored in a 1.5% sodium bisulfite solution. After two weeks, it should be sterilized with formaldehyde disinfectant or the manufacturer's recommended disinfectant. Never use commercially available 84 disinfectant to sterilize membrane elements!