D-氨基酸预处理对MBR膜化学清洗过程消毒副产物生成的影响机制

Membrane biofouling is an inevitable problem in membrane bioreactors (MBR). Chemical cleaning with sodium hypochlorite (NaClO) is the most essential process for the permeability recovery of fouled membranes. However it leads to formation of toxic disinfection byproducts (DBPs). Since methods to control DBP formation during membrane chemical cleaning are limited so far, biofilm inhibitor D-amino acids will be used to pretreat membrane biofouling to control the DBP formation during following NaClO cleaning in this project. In MBR operated at different sludge retention time (SRT) and aeration intensity conditions, the biofilm removal efficiency by D-amino acids, and the effects of D-amino acid type, concentration and time will be analyzed. In order to illuminate mechanisms of biofilm disassembly and detachment triggered by D-amino acids, the biofilm disassembly and detachment kinetics and the quorum sensing inhibition will be investigated and the microorganisms targeted by D-amino acids will be identified. Effects of D-amino acids on membrane biofilm characteristics including structure, microbial communities and physico-chemical properties of extracellular polymeric substance will be also revealed. Impacts of D-amino acid pretreatment on the following membrane chemical cleaning efficiency and DBP yields, and the effects of D-amino acid type, concentration and time will be investigated. Quantitative relationships between characteristics of biofilm on membrane surface and chlorine concentration, cleaning time and DBP formation potential during NaClO cleaning will be established to explore mechanisms of control effects of D-amino acids on DBP formation during membrane chemical cleaning in MBR. The results of this study will provide theoretical and technical supports to establish a safe method for membrane fouling control in MBR.

膜生物污染是膜生物反应器（MBR）运行中不可避免的问题。目前，次氯酸钠膜清洗是保证MBR稳定运行的关键环节，但次氯酸钠与膜污染物反应会产生大量消毒副产物（DBPs），造成二次污染。针对膜化学清洗过程DBPs生成现状以及控制手段匮乏的问题，本课题拟采用信号分子D-氨基酸对MBR膜污染进行预处理，研究不同运行条件下MBR膜生物污染的去除效能与影响因素，分析D-氨基酸的目标微生物及群体感应抑制作用，解析生物膜破碎与脱落动力学，阐明D-氨基酸对MBR膜表面生物膜的破碎与去除机制，明确其对生物膜结构、组成等特性的影响；研究D-氨基酸预处理对后续膜化学清洗效率和DBPs生成的影响，明确影响因素，建立生物膜特性与膜化学清洗过程加氯量、清洗时间、DBPs生成能力之间的定量关系，揭示D-氨基酸预处理对MBR膜化学清洗过程DBPs生成的影响机制。研究成果将为建立生态安全的膜污染控制工艺提供理论依据和技术支持。

针对城市污水再生工艺膜生物反应器（MBR）次氯酸钠膜清洗产生大量消毒副产物（DBPs），造成二次污染的问题，本项目采用信号分子D-氨基酸对MBR膜污染进行预处理，诱导膜表面生物膜解体与脱落，研究D-氨基酸预处理控制MBR膜化学清洗DBPs生成的效能与机制。浓度为200 nM的D-酪氨酸、25 μM的D-色氨酸及其组合均可高效诱导污染的MBR膜表面生物膜解体与脱落（生物膜去除率37-66%），显著降低了后续膜化学清洗过程中DBPs生成势（65-85%），提高了后续次氯酸钠清洗效率，极大地降低了膜化学清洗产生DBPs的潜在毒性（92-97%）。D-氨基酸预处理导致生物膜中AI-2浓度下降，不动杆菌属（Acinetobacter）占比降低，丛毛单胞菌属（Comamonas）占比显著上升，单位质量生物膜EPS含量显著升高。MBR膜次氯酸钠清洗过程中，EPS是限制膜清洗效率的关键因素，但是胞内物质是主要的DBPs前体物，且更容易生成高毒性N-DBPs。通过上述研究，本项目提出D-氨基酸通过群体淬灭以及促进微生物鞭毛基因表达提高微生物运动性两方面作用破坏生物膜的三维结构，导致生物膜解体脱落，高效去除了生物膜中的生物细胞，不仅使得DBPs前体物数量总体下降，还特异性去除了具有较高DBPs生成势和毒性的微生物细胞体，有效降低了残余污染物的DBPs生成势；除此以外，也降低了次氯酸钠的使用量和清洗时间，进一步避免了具有高DBPs生成活性的胞内物质的释放，最终有效控制了DBPs的生成量和毒性；开发了D-氨基酸预处理-分布式加氯膜清洗方技术。本项目研究成果填补了D-氨基酸用于膜污染控制过程中在DBPs生成与毒性风险控制方面的理论空白，并为城市污水回用的生态安全保障提供了新的膜清洗技术，具有重要的实际意义。