Study On Membrane Fouling By Typical Pollutants And Membrane Cleaning

The growing shortage of water resources as well as the development of RO membrane technology impeled that the application of RO membrane having extended from the water supply field to the wastewater treatment field.Thus, the deterioration of influent quality caused the membrane fouling more and more serious,but offrequently replacing membrane elements must cause the application of membrane technology to be uneconomic. Therefore, it is signiticant to study deeply the influence of typical pollutants on membrane fouling mechanism and characteristics.In this work,humic acid(HA),BSA and octanoic acid were chosed to be the typical organic pollutants,CaSO4 and CaCl2 to be the typical inorganic pollutants,which were contained in different simulated wastewater as the feed water of RO membrane though different experiment purpose. The rules and quantity of pollutants accumulation on membrane,the influence of pollutants accumulation on membrane's performance parameters and the membrane's cleaning effect were studied systemically.Results indicate that:The rules of HA,BSA and octanoic acid's accumulation on membrane were all obvious and various. There became a HA cake layer on membrane's surface is the main factor of membrane fouling, Because of the large amount of HA's total accumulation quantity on membrane and no HA in the permeant water.It was found that the membrane fouling was accelerated and the cake layer became more dense with increasing Ca2+ concentration.Meanwhile, the results also showed that the pressure rised afer the total accumulation quantity of HA to a level. Compared with HA's total accumulation quantity,both of BSA and octanoic acid's accumulation quantity were small,and the membrane fouling slowed down with increasing Ca2+ concentration. Experiment showed that membrane fouling's reason of unitary BSA was the adsorption of BSA on membrane's surface, and the reason of unitary octanoic acid was the adsorption of octanoic acid on membrane's surface and in membrane. The pressure rised with the extending of running time when the membrane fouled by unitary BSA,unitary octanoic acid and BSA with Ca2+ ,but the phenomenon of pressure riseing when membrane fouled by octanoic acid with Ca2+ was similar with HA.All unitary organic fouling resulted in permeable salt rate decreasing, all synergistic fouling of organic and calcium salt resulted in permeable salt rate increasing. The cleaning effection after both of unitary and synergistic fouling was BSA> HA> octanoic acid, and membrane's permeable salt rate was non-recover after octanoic acid fouling RO membrane but not the same with octanoic acid'synergistic fouling.The cleaning effect was better by using the way of alkali - acid alternately,first alkali then acid in those experiments.The membrane fouling by 1200 mg/L CaSO4 was serious,but the membrane's performance was almost recovery just by hydraulic flush; The fouling time increased by 10 times when the concentration of CaSO4 was 800 mg/L, and the permeable salt rate was non-recover after chemical washing.Both of thesee experiments showed that the rules of CaSO4's accumulation on membrane have two obvious stage. The membrane fouling was decreased when HA existing in 1200 mg/L CaSO4 solution, but not the same with BSA or octanoic acid existing in that, the membrane fouling were all decelerated when HA,BSA or octanoic acid existing in 800mg/L CaSO4 solution.In all synergistic fouling of high concentration of CaSO4 and organic substance experiments, the rules and quantity of CaSO4's accumulation on membrane were decide by the interactions of CaSO4 with organic substance.It's difficult to recover the membrane's performance after the membrane fouling by high concentration of CaSO4 and HA; it's easy to recover the membrane's performance by NaOH cleaning when the membrane was fouled by 1200 mg/L CaSO4 and BSA,but it's not good when 800 mg/L CaSO4 and BSA, but when NaOH was replaced by EDTA,the membrane's performance recovered.The cleaning effect of high concentration of CaSO4 and octanoic acid was similar to that of low concentration of CaSO4 and octanoic acid,because the membrane's performance parameters can all recover.