How to prevent colloidal contamination of reverse osmosis membrane

Because the reverse osmosis membrane has a very high removal effect on the colloid, the colloidal concentration on the membrane surface in the reverse osmosis device is continuously increased along the flow direction. When the recovery rate is 75%, the concentration of colloidal water in the final membrane element in the device is water. About 4 times the first level. The precipitation of colloids on the membrane surface mainly depends on two factors, namely the colloid concentration and the agglomeration rate constant: The colloid concentration can be measured with the pollution index SDI, and the rate constant is related to the 2ETA potential. In the long-term practice, it has been found that in order to prevent contamination of the membrane by colloids, the SDI value needs to be controlled. For a roll-type device, the SDI value should be controlled below 4 or the MF value should be less than 150 s. In the hollow device, the SDI value should be controlled below 3 or 4 so that the colloid contamination program can be reduced to the point where the reverse osmosis device can operate normally. It is worth mentioning that when the 2ETA potential of the influent is greater than negative 30mV, the SDI value of reverse osmosis water can be increased. For example, hollow fiber components can be increased from SDI <3 to SDI>5. In general, colloidal contamination is mostly present in systems that use surface water as the source of water, since the type and concentration of colloids will change with the seasons, although this change is considered when the pretreatment equipment is selected, but because the fluctuation is too large, Often the original pretreatment system is not adapted, resulting in SDI values ​​often exceeding the standard. Therefore, the monitoring of SDI value is especially important in reverse osmosis operation management. The operator should determine the optimal injection amount of the chemical agent in the actual operation through daily small tests, and at the same time, prevent the injection of overdosage and produce new colloidal contamination.

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