SYSU-HKUST Research Center for Innovative Environmental Technology, School of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou, China.
PLoS One. 2012;7(8):e42270. doi: 10.1371/journal.pone.0042270. Epub 2012 Aug 9.
The complex characteristics and unclear biological fate of biomacromolecules (BMM), including colloidal and soluble microbial products (SMP), extracellular polymeric substances (EPS) and membrane surface foulants (MSF), are crucial factors that limit our understanding of membrane fouling in membrane bioreactors (MBRs).
In this study, the microbial transformation of BMM was investigated in a lab-scale MBR by well-controlled bioassay tests. The results of experimental measurements and mathematical modeling show that SMP, EPS, and MSF had different biodegradation behaviors and kinetic models. Based on the multi-exponential G models, SMP were mainly composed of slowly biodegradable polysaccharides (PS), proteins (PN), and non-biodegradable humic substances (HS). In contrast, EPS contained a large number of readily biodegradable PN, slowly biodegradable PS and HS. MSF were dominated by slowly biodegradable PS, which had a degradation rate constant similar to that of SMP-PS, while degradation behaviors of MSF-PN and MSF-HS were much more similar to those of EPS-PN and EPS-HS, respectively. In addition, the large-molecular weight (MW) compounds (>100 kDa) in BMM were found to have a faster microbial transformation rate compared to the small-MW compounds (<5 kDa). The parallel factor (PARAFAC) modeling of three-dimensional fluorescence excitation-emission matrix (EEM) spectra showed that the tryptophan-like PN were one of the major fractions in the BMM and they were more readily biodegradable than the HS. Besides microbial mineralization, humification and hydrolysis could be viewed as two important biotransformation mechanisms of large-MW compounds during the biodegradation process.
The results of this work can aid in tracking the origin of membrane foulants from the perspective of the biotransformation behaviors of SMP, EPS, and MSF.
生物大分子（BMM），包括胶体和可溶性微生物产物（SMP）、胞外聚合物物质（EPS）和膜表面污染物（MSF），具有复杂的特性和不明确的生物命运，这是限制我们对膜生物反应器（MBR）中膜污染理解的关键因素。
在这项研究中，通过精心控制的生物测定试验，在实验室规模的 MBR 中研究了 BMM 的微生物转化。实验测量和数学建模的结果表明，SMP、EPS 和 MSF 具有不同的生物降解行为和动力学模型。基于多指数 G 模型，SMP 主要由缓慢生物降解的多糖（PS）、蛋白质（PN）和不可生物降解的腐殖质（HS）组成。相比之下，EPS 含有大量易于生物降解的 PN、缓慢生物降解的 PS 和 HS。MSF 主要由缓慢生物降解的 PS 组成，其降解速率常数与 SMP-PS 相似，而 MSF-PN 和 MSF-HS 的降解行为与 EPS-PN 和 EPS-HS 分别更为相似。此外，BMM 中的大分子量（MW）化合物（>100 kDa）比小分子量（<5 kDa）化合物具有更快的微生物转化速率。三维荧光激发-发射矩阵（EEM）光谱的平行因子（PARAFAC）建模表明，色氨酸样 PN 是 BMM 的主要成分之一，比 HS 更容易生物降解。除了微生物矿化之外，腐殖化和水解可以被视为大分子量化合物在生物降解过程中的两个重要生物转化机制。
这项工作的结果可以帮助从 SMP、EPS 和 MSF 的生物转化行为的角度追踪膜污染物的来源。
