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Pretreatment Process Selection Of Membrane Fouling Caused By Inorganic Fouling Materials
- Sep 04, 2018 -

Pretreatment process selection of membrane fouling caused by inorganic fouling materials


During the operation of the double membrane system, the scale mainly occurs on the reverse osmosis membrane element. If the hardness and alkalinity of the ultrafiltration influent water are too high, it is easy to cause scaling in the reverse osmosis membrane section, causing reverse osmosis water production. The amount drops rapidly. Therefore, in order to reduce the fouling contamination of the reverse osmosis membrane section, pretreatment of the sewage is required. There are mainly the following pretreatment methods for preventing fouling of reverse osmosis membranes: adding scale inhibitors, adjusting acid, removing hard, and the like.


The addition of a scale inhibitor can control carbonate scale, sulfate scale and calcium fluoride scale, and can also inhibit silicon scale.


The added scale inhibitors can be divided into three categories: sodium hexametaphosphate, organic phosphates and polyacrylates.


The advantage of adding scale inhibitor is that the operation is simple, there is no processing step before the membrane, and the amount of additive can be precisely controlled; the disadvantage is that the concentrated water COD will be increased, the high recovery rate may be invalid, the scale inhibitor content is high or the scale inhibitor type is selected. It is still possible to block the film.


Calcium carbonate can be maintained in a dissolved state by acid adjustment. The advantage of acid treatment is that the operation is simple, when the pH of the sewage is not high, the cost is lower than the hard treatment; the disadvantage is that the acid treatment has no removal effect on Ca and Mg ions, and the content of Ca and Mg ions on the concentrated water side is still high, and Pipeline anti-corrosion requirements are higher. In addition, when only acid is used to control calcium carbonate scaling, the LSI or S&DSI index in concentrated water must be negative.


In addition to hard treatment, lime-soda ash can be used to remove hard or sodium hydroxide-soda ash. The addition of calcium hydroxide to water removes the hardness of the carbonate, and the non-carbonate hardness can be further reduced by the addition of sodium carbonate (soda). The advantage of removing the lime is that the hardness and alkalinity can be reduced at the same time, the cost is lower than that of the sodium hydroxide, and the concentrated water LSI is obviously reduced; the disadvantage is that the amount of sludge is large, and the sludge sedimentation or filtration operation is cumbersome. The advantage of removing sodium hydroxide is that the amount of sludge is small; the disadvantage is that the alkalinity removal effect is not good, the concentrated water LSI is still high, and the treatment cost is higher than the lime method