厌氧正渗透膜生物反应器中高盐度对正渗透膜污染的影响机制及膜污染控制策略的研究

Recently, a novel technology of anaerobic forward osmosis membrane bioreactor (AnFOMBR) combining the anaerobic biotechnology and forward osmosis (FO) has been proposed for municipal wastewater treatment. The AnFOMBR has attracted growing interests due to its simultaneous achievements of wastewater reclamation and energy recovery in terms of biogas. Currently, instability of FO membrane remains a main drawback for further development of AnFOMBR. We intend to apply a new developing FO membrane, TFC-FO membrane, instead of prior CTA-FO membrane in the AnFOMBR on the basis of its more stable properties. Fortunately, our previous experiments have confirmed that the idea of applying the TFC-FO membrane for ensuing the stable operation of AnFOMBR is feasible. However, the TFC-FO membrane also has a problem of its relatively serious membrane fouling that needs to address, because the serious membrane fouling has influenced the economical feasibility of the AnFOMBR. Therefore, effects of the core impacting fact of high salinity on the FO membrane fouling were focused on in order to understand the membrane fouling mechanisms of FO membrane in the AnFOMBR. In this project, impacts of high salinity on the biofouling layer structure, microbial communities and EPS distributions, and effects of Ca2+ and Mg2+ on the biofouling layer will be investigated by the modern analytic instruments such as SEM, AFM and EDX and molecular biology techniques such as 454 high-throughput pyrosequencing and multiple fluorescent marker combined with CLSM. In addition, correlations between the inorganic ions accumulation induced by the high salinity and the scaling on the FO membrane surface will be analyzed. Moreover, the fouling controlling strategy for TFC-FO membrane will be constructed based on the understanding of membrane fouling mechanisms. This investigation will enrich the understanding of FO membrane fouling mechanisms and provide technical supports for applying the AnFOMBR in treating and reusing municipal wastewater in the future.

厌氧正渗透膜生物反应器（AnFOMBR）是一种将厌氧生物技术和正渗透（FO）组合而成的新型工艺, 可以同步实现污水回用和沼气回收。目前制约AnFOMBR进一步应用的关键问题是FO膜的不稳定。我们设想采用最近开发的TFC-FO膜来代替原有的CTA-FO膜。前期实验证实，TFC-FO膜的稳定性保证了AnFOMBR的稳定运行。然而，TFC-FO膜的污染较重，影响了工艺的经济性，成为急需破解的难题。针对高盐度这一关键影响因素，应用SEM、AFM、EDX等现代分析仪器以及454高通量测序和多重染色结合CLSM等分子生物学技术，探明高盐度对生物污染层结构、微生物种群和EPS分布的影响，解析无机离子积累与无机盐结垢的相关性，并获取钙镁离子对生物污染层的强化作用，以此为基础构建膜污染控制策略。本项目可以丰富和加深FO膜污染机理的认识，为将来AnFOMBR在城镇污水回用领域的应用提供技术支撑。

厌氧正渗透膜生物反应器（AnFOMBR）是一种将厌氧生物技术、正渗透（FO）和反渗透（RO）组合而成的一种新型污水处理工艺。由于具有沼气回收、污水回用和膜污染趋势低等特点，AnFOMBR在污水处理与回用领域具有广阔的应用前景。然而，AnFOMBR存着高盐度和膜污染严重等问题，制约了其在污水处理领域的推广应用。本研究借助构建的盐度变化模型，探明了进水溶质积累、汲取液溶质反向渗透和反应器溶质排放是导致盐度变化的三因素，进而借助微滤（MF）膜可以强化反应器溶质排放的特点，提出了基于MF膜的盐度控制策略，成功解决了AnFOMBR的高盐度问题。受到MF膜缓解盐度积累的启示，进而提出了基于MF和AnFOMBR的组合工艺AnMF-OMBR。AnMF-OMBR比AnOMBR具有更大的甲烷产率和更长的运行时间。无论是CTA材质还是TFC材质的FO膜，在AnOMBR中都发生了生物污染和无机污染，且以生物污染为主，钙离子对生物污染有强化作用。由于膜表面更加粗糙，TFC膜的污染比CTA膜更重。AnFOMBR中FO膜污染分为两个阶段。第一阶段的膜污染归因于污泥混合液中污染物与膜面的相互作用，而第二阶段的膜污染归因于污泥混合液中污染物与膜面污染物之间的相互作用，且第一阶段的膜污染对FO膜通量衰减的贡献更大。基于对FO膜污染机制的解析，构建了基于驱动力控制+钙离子移除耦合物理清洗+化学清洗的三重膜污染控制策略。通过第一阶段采用低汲取液浓度+第二阶段采用高汲取液浓度的变驱动力的运行方式降低第一阶段的膜污染，改善整个膜污染层的结构，从而在整体上缓解膜污染；借助EDTA吸附材料在原位移除污染膜面的有机和生物结合态的钙离子，破坏钙离子形成的凝胶层网络，使污染层结构变得疏松多孔，辅以物理清洗去除大部分膜面污染物；对于仍然无法去除的污染物，采用H2O2进行化学清洗，清洗后的FO膜初始通量可以恢复到新膜的水平。本项目的研究成果破解了AnFOMBR存在的盐度积累和膜污染两个关键问题，并在此基础上提出了基于MF和AnFOMBR的组合工艺AnMF-OMBR，实现了污水处理过程中的水和沼气的同步回收，具有较好的应用前景。