Study On Fouling Characteristic Of Ultrafiltration For Fe And HA Coexist In Second Effluent And Analysis Of Operation

This study is aiming at investigating the effect of humic acid and Fe on PVDF hollow fiber membrane pollution based on the secondary effluent water, which contains humic acid and Fe as the main pollutants. From the microscopic mechanism, discussing the membrane fouling when different forms of Fe coexist with humic acid. Macroscopically, analyzing the process of chemical cleaning and operating condition of the actual sewage. The conclusions achieved were as followed:(1) Results show that with the increase of pH, the dominant role of membrane fouling from ionic complexation of HA to ferric hydroxide and then to repulsion of HA, and in contrast, those pollutants could mostly wash off by Citric acid. The specific conclusions achieved are as followed:①The form of deposition of pollutants on membrane surface changed by iron ions through increase pollution layer space and mitigate membrane fouling. Atomic force has the same result. ②The form of Iron ions changed with the change of pH, ionic state converted into hydroxide flocs, and gradually aggravated membrane fouling. However, when pH is 10, membrane fouling is lighter than 5 and 8, because of repulsion force of dissociation of humic acid, and water flux also rebounded. Atomic force microscopic measurement also be given to this conclusion that the smaller the average adhesion, the weaker the interaction between pollutants and the slower membrane flux decline. ③From the view of cleaning results, light fouling caused by iron ionic combined with HA is easily washed, making the irreversible contamination of the membrane reduced. Along with the increase of Alkaline, cleaning effect obviously reduced and flux recovery rate also lower than before. Besides, the cleaning effect also rised as previously described. Atomic force images also show that roughness and morphology of membrane surface along with the change of different conditions, and the results are consistent with the above.(2) Secondary effluent pollution of ultrafiltration membranes is a combined result among a variety of pollutants in wastewater. Therefore, with different periods cleaning experiments of actual sewage to explore the fundamental properties of contaminants and irreversible fouling removal. The 5h filtration results show that the flux attenuation curve of other cleaning agents changed little, except for Citric acid that flux recovery significantly increased with concentration become larger and the average flux recovery is 95%. Citric acid also performed well in 1h filtration process. Above results show that membrane fouled with secondary effluent pollution can be washed by Citric acid.(3) During the actual operation, selecting the appropriate hydraulic cleaning conditions also can slow down the membrane fouling, and increasing the backwash flow rate and chemical cleaning with suitable transmembrane pressure growth can effectively control membrane fouling. Under normal conditions, the effluent index of ultrafiltration membrane can achieve the standard of recycling of urban sewage- urban miscellaneous water.