膜-光生物反应器处理污水性能及膜污染机理

膜-光生物反应器处理污水性能及膜污染机理

摘要

微藻不仅是一种生产生物柴油的最佳原料，而且在污水处理方面也具有优势。但是，目前影响其在污水处理领域广泛应用的主要难点是如何高效的分离和富集微藻，因此，本论文将开展膜分离技术与微藻联用进行废水处理并实现藻-水分离的试验研究。

本研究首先合成了不同孔径的聚氯乙烯(PVC)与聚偏氟乙烯(PVDF)共混膜分离材料。选取成膜性能较好的三种平板膜，微滤膜样品(M-10)和超滤膜样品(M-0、M-12)，在不同压力条件下对微藻溶液进行了短期过滤试验。研究表明：微滤膜和超滤膜对溶液中的微藻都具有高于99.9%的截留率。微藻在膜表面形成的滤饼层是导致膜污染的主要原因，在较高过滤压力下，膜表面形成致密的滤饼层，导致膜的出水通量恢复率下降，在较低压力条件下，膜表面形成的滤饼层容易被反冲洗下去，因此通量恢复率更高。相对于微滤膜，超滤膜表面更容易形成由胞外聚合物形成的凝胶层污染。

本研究进一步制备了微滤、超滤膜组件，并构建了微藻-超滤/微滤膜联用的膜-光式生物反应器(MPBR)，考察其长期运行条件下污水处理性能及膜污染特征。研究结果表明，微滤、超滤膜组件对微藻有高于99.9%的截留率。超滤膜-光式生物反应器比微滤膜光式生物反应器具有更高的COD去除率，而在脱氮除磷方面，二者性能接近。

长期运行条件下，超滤膜表面膜污染一直处于快速污染期，其主要原因是大量胞外聚合物在膜表面形成凝胶层，膜污染不断累积，过膜阻力增大，过滤通量下降。微滤膜表面污染可分为缓慢增长期、加速增长期和快速污染期三部分。通过膜污染机理分析认为：在过滤最初的0-15d内，膜表面以微藻细胞体形成的滤饼层污染为主，大部分胞外聚合物可以透过微滤膜，膜通量恢复率较高；但随着过滤时间的延长(15-25d)，胞外聚合物会附着在膜内部，过膜阻力增大，导致严重的膜内污染，膜污染加速，过滤通量降低；过滤末期(25-40d)，膜表面存在的微藻细胞体和胞外聚合物会分别堵塞膜表面和内部膜孔，微滤膜表面同超滤膜表面一样形成了致密的凝胶层污染，进入快速污染期。

关键词：超滤膜；微滤膜；微藻；截留；膜污染

ABSTRACT

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 algaecan 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 increaseof 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: