Study On Membrane Fouling Control Based On Micro - Interface Interaction Of MIEX - UF Integral Process

UF membrane filtration has become the core of the third generation drinking water treatment technology. However, membrane fouling control remains the bottleneck for wider implementation of UF. In recent years, magnetic ion exchange resin (MIEX) has attracted many scholars at home and abroad because of its excellent water purification performance and become a new type of water treatment method. The current researches about MIEX and UF are mainly separated process, namely MIEX pretreatment water are followed by UF membrane filtration. According to the previous research, Our research group found that integrated MIEX-UF process was better than separated process in relieving membrane fouling. But the further investigations are necessary to illustrate the mechanism of membrane fouling control.This study uses humic acid(HA), sodium alginate(SA) and bovine serum albumin(BSA) as typical model substances caused UF membrane fouling and puts the immersed PVDF hollow fiber UF membrane module as the research object to systematically investigate the relief mechanism of membrane fouling and changing rule based on the different foulants in integrated MIEX-UF process from three aspects(organic matter removal in liquid subject, on the membrane surface scratches and the formation of MIEX dynamic membrane nearly membrane wall). The interfacial forces of MIEX-foulant and PVDF-foulant were determined by atomic force microscopy (AFM) in conjunction with self-made foulant-coated colloidal probe, respectively. And they provided molecular level information to elucidate the mechanism of membrane organic fouling control from microscopic interfacial forces. On this basis, the influence of resin surface morphology change (saturation, regeneration), chemical cleaning of the membrane, ionic strength and typical ion in aqueous solution on the microscopic interface forces were further discussed, as well as the effect of the change on membrane fouling control law in integrated process.The results showed that MIEX particle dynamic membrane formed on the membrane surface is the most main factor to control membrane fouling caused by HA, SA and BSA, and they were accounted for the total contribution rate of 80%,60% and 70%, respectively. Microscopic interfacial forces analysis showed that "MIEX-pollutant" were bigger than the interfacial forces between "PVDF-pollutant", so the resin dynamic membrane has the ability to capture the pollutants preferentially and strengthen hydraulic backwashing to alleviate the membrane fouling effectively. It also proved that the difference between "MIEX-pollutant" and "PVDF-pollutant" directly affect the membrane fouling control effect, the greater the difference, the better the membrane fouling control effect will be. The further study found that resin form obviously affect the interfacial forces, "saturated MIEX-pollutant" were significantly less than "PVDF-pollutant", dynamic membrane effect disappeared and membrane fouling control effect were poor. "MIEX-pollutant" gradually decreased with the increase of MIEX regeneration times, membrane fouling control effect also weaken. The changes of the interfacial forces after chemical cleaning were directly related to membrane cleaning effect. For HA, "PVDF-HA" after NaOH cleaning was slightly larger than NaCIO cleaning, however, for the SA and BSA, NaCIO cleaning had contributed to the restore of the "PVDF-pollutant". The differences between "MIEX-pollutant" and "PVDF-pollutant" decreased with the increase of the ionic strength. The presence of Ca2+、SO42- and NO3- reduced the differences in different degrees. For mitigating the membrane fouling caused by HA or SA, inhibiting effect was in the following order:Ca2+> SO42->NO3-. But for the BSA, the order was SO42->Ca2+>NO3-. The change rule of TMP in a single hydraulic backwashing cycle confirmed that the change of "MIEX-pollution" and "PVDF-pollutant" was closely related to membrane fouling control, which further confirmed the interfacial force played a key role in membrane fouling control in the integrated MIEX-UF process.