Reverse osmosis membrane chemical cleaning process
The frequency of membrane cleaning is closely related to the perfection of the pretreatment measures. The more perfect the pretreatment, the longer the cleaning interval; On the contrary, the simpler the pretreatment, the higher the cleaning frequency. The specific cleaning process is as follows:
Reverse osmosis membranes are used for low pressure flushing at 4Bar(60psi) or lower pressure conditions, where clean water is pumped from a cleaning tank (or suitable water source) into the pressure vessel and discharged for a few minutes. Rinse water must be clean, RO product water or deionized water that has been removed from hardness and is free of transition metals (Fe, Mn, etc.) and residual chlorine.
(2) the reverse osmosis membrane prepares the specified cleaning solution in the cleaning tank. The water used for preparation must be RO product water or deionized water that has been removed from hardness and is free of transition metals and residual chlorine. The temperature and pH of the cleaning solution should be adjusted to the required values.
(3) Start the cleaning pump and pump the cleaning liquid into the membrane module, and cycle the cleaning for about 1 hour or the required time. During the initial phase, the initial backflow should be drained before the cleaning solution is returned to the RO cleaning tank to avoid dilution of the cleaning solution by residual water in the system. After the chemical agent comes into contact with the RO device, the pollutants in the device will be flushed out in large quantities under the action of chemical reaction. In order to avoid contaminating the cleaning liquid, the cleaning liquid should also be discharged until the color of the cleaning liquid turns pale and then enter the cycle for cleaning. For the first 5 minutes of the cycle, slowly adjust the flow rate to 1/3 of the maximum flow rate. In the second 5 minutes, increase the flow rate to 2/3 of the maximum design flow rate, and finally increase the flow rate to the maximum wash flow rate. If necessary, readd the drug to adjust the pH when the pH change is greater than 0.5.
(4) Cyclic cleaning and soaking procedures can be used alternately according to needs. Reverse osmosis membrane immersion time can be selected from 1 to 8 hours according to the manufacturer's recommendations. Be careful to maintain the proper temperature and pH throughout the cleaning process.
(5) After chemical cleaning, clean water (RO product water or deionized water that removes hardness and does not contain metal ions such as iron and chlorine) shall be used for low-pressure flushing, and the residual chemical agents shall be flushed from the cleaning device and relevant pipelines, and the cleaning tank shall be discharged and flushed, and then the cleaning tank shall be completely filled with clean water. Pump all rinse water from the wash tank to flush the pressure vessel and drain. Until the chemical residues in the RO device are basically removed.
(6) After the reverse osmosis membrane is completely rinsed with clean water, the final low pressure rinsing can be carried out with pretreated water. The feedwater pressure shall be less than 4bar and the final flush shall be continued until the rinse water is clean and free of any foam and detergent residue. This usually takes 15-60 minutes. The operator can sample with a clean flask, shake it well, and monitor the residue of detergent and foam in the rinse water at the discharge outlet. The removal of the lotion can be carried out by testing the conductance. If the conductance of the flushing water to the discharge water is within 10-20% of the conductance of the water supply, the flushing can be considered to be near the end point. The pH meter can also be used to determine whether the pH value of the flushing water is close to that of the discharge water.
(7) After the low-pressure flushing, the RO unit can start running again, but the initial product water should be discharged and monitored until the RO water production can meet the process requirements (conductance, pH value, etc.). This recovery time can sometimes range from a few hours to a few days to obtain stable RO produced water quality, especially after a high pH wash.
