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The cleaning of the membrane is generally divided into physical cleaning and chemical cleaning, and the higher the frequency of chemical cleaning, the greater the damage to the membrane, which seriously affects the service life of the membrane system. Therefore, it is difficult for the relevant technical personnel to master the chemical cleaning of the membrane system. The frequency of membrane cleaning is closely related to the perfection of pretreatment measures. The more perfect the pretreatment, the longer the cleaning interval; on the contrary, the simpler the pretreatment, the higher the cleaning frequency. Generally, membrane cleaning follows the (10% rule)-cleaning is required when the ratio of the corrected fresh water flow rate to the flow rate in the first 200h of operation (after compaction) is reduced by 10% and (or) the pressure difference is observed to rise by 10% ~ 20%. As far as possible, measures should be taken before the decline in desalination rate is shown. Formally scheduled protective maintenance cleaning is not sufficient to protect the reverse osmosis system. For example, due to the abnormal operation of the pretreatment equipment, the influent conditions will change in a short period of time. Backwashing is effective to prevent clogging of certain forms of reverse osmosis membrane modules by large particles. But not all pollution can be removed by simple backwashing, but also need to have a cycle of chemical cleaning. Chemical cleaning in addition to the need to increase the cost of chemicals and labor, there is a pollution problem, so it can not be too frequent, should not exceed 1 to 2 times a month, each cleaning time of about 1 to 2h. The chemical cleaning system usually includes a chemical mixing tank and its matching pump, mixer, heater, etc. Chemical cleaning is often based on operating experience to determine (can be based on each column of equipment pressure drop readings and operating time curve, or based on water production, fresh water quality and membrane pressure drop, etc.). Chemical cleaning agents and methods used, according to the source of pollution to decide. The following table can be used for reference, but the experience of this unit should be paid more attention to and applied. In order to ensure the effect, before the chemical cleaning to rinse. Before flushing, the pressure is reduced, and then the membrane is flushed with 2 to 3 times the normal flow rate of water, and the dirt is peeled off and washed away from the membrane surface by the agitation of the fluid. Then, according to the pollution characteristics, the cleaning solution is selected to clean the membrane chemically. In order to protect the reverse osmosis module, the liquid temperature should not exceed 35 · C. If the system is stopped for more than 5 days, it can be flushed with formaldehyde before use. If the system is disabled for two weeks or longer, 0 is required. 25% formaldehyde soak, to prevent the growth of microorganisms in the film. Chemical agents should be replaced once a week.