| Microalgae are not only a kind of the best raw material that can produce biodiesel, and also have a remarkable advantage in wastewater treatment. However, at present, the difficulty of influencing the extensive use of microalgae wastewater treatment is how to effectively separate and enrich of microalgae. Therefore, this study is concerned with membrane separation technology and micro algae combination such that the wastewater treatment and reject of micro algae can be achieved.Different aperture of polyvinyl chloride (PVC) and poly (vinylidene fluoride) (PVDF)blend membranes were first synthesized in the study. The three membranes samples of good performance, microfiltration membrane (M-10) and ultra-filtration membrane samples (M-0,M-12) were selected and short-term filter micro algae test was carried out at different transmembrane pressure (TMP). Research shows that Ultra-filtration (UF) and microfiltration(MF) membranes of microalgae filtration have high reject rate, reach 99.9%. The cake layer on membrane surface is a major reason that causes membrane fouling during filtration. Under the condition of low TMP, the cake layer density of membrane surface was higher, which result in a declined flux recovery rate. While under low TMP, cake layer formed on the membrane surface was easy to back wash down, so the flux recovery rate is higher. Compared with MF membranes surface, UF membranes surface can easily produce more extracellular polymer gel layer during micro algae filtration, which results in the decrease of membrane flux recovery rate.This study further prepared microfiltration and ultra-filtration membrane modules, and builds membrane-photobioreactor (MPBR) and examines its sewage treatment performance and membrane fouling characteristics. The results show that all the MF/UF membrane modules can reach 99.9% reject rate. UF membrane bioreactor has higher COD removal rate than MF membrane bioreactor. The performances of both bioreactors were similar, ammonia nitrogen, total nitrogen and total phosphorus removal rate.The fouling of UF membrane surface had a rapid growth under long-term running condition. There was a large amount of extracellular polymer (EOM) formed gel layer on the membrane surface, which can cause the increase of membrane resistance and membrane fouling accumulation, and eventually result in the serious flux decline of filtration microalgae.The fouling of MF membrane surface can be divided into slow increase period,rapid increase period, rapid pollution period three parts. Membrane fouling mechanism analysis shows that:in the first 0-15 d, the MF membrane surface is mainly covered by the cake layer which was produced by many micro algae cell body, and most of EOM would cross through membrane,flux recovery rate was higher; But at filtration 15 d-25 d, parts of the micro algae cell body can adhere to the membrane surface, and some EOM would adhere to internal membrane.Thus, membrane resistance would increase and membrane fouling would aggravate, moreover filtration flux decreased; Further filtration at 25 d-40 d, the MF membrane surface was blocked seriously by micro algae cell body and internal membrane aperture have been plugged by EOM. The MF membrane surface as well as UF membrane surface formed dense gel layer, all the MF/UF membranes reached rapid fouling period. |
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