School of Engineering and Information Technology, Murdoch University, 90 South Street, Murdoch, Western Australia 6150, Australia.
J Environ Manage. 2018 Oct 1;223:586-599. doi: 10.1016/j.jenvman.2018.05.088. Epub 2018 Jun 30.
Biofouling in seawater reverse osmosis (SWRO) membranes is a critical issue faced by the desalination industry worldwide. The major cause of biofouling is the irreversible attachment of recalcitrant biofilms formed by bacteria and their extracellular polymeric substances (EPS) on membrane surfaces. Transparent exopolymer particles (TEP) and protobiofilms are recently identified as important precursors of membrane fouling. Despite considerable amount of research on SWRO biofouling, the control of biofouling still remains a challenge. While adoption of better pretreatment methods may help in preventing membrane biofouling in new desalination setups, it is also crucial to effectively disperse old, recalcitrant biofilms and prolong membrane life in operational plants. Most current practices employ the use of broad spectrum biocides and chemicals that target bacterial cells to disperse mature biofilms, which are evidently inefficient. EPS, being known as the strongest structural framework of biofilms, it is essential to breakdown and disintegrate the EPS components for effective biofilm removal. To achieve this, it is necessary to understand the chemical composition and key elements that constitute the EPS of major biofouling bacterial groups in multi-species, mature biofilms. However, significant gaps in understanding the complexity of EPS are evident by the failure to achieve effective prevention and mitigation of fouling in most cases. Some of the reasons may be difficulty in sampling membranes from fully operational full-scale plants, poor understanding of microbial communities and their ecological shifts under dynamic operational conditions within the desalination process, selection of inappropriate model species for laboratory-scale biofouling studies, and the laborious process of extraction and purification of EPS. This article reviews the novel findings on key aspects of SWRO membrane fouling and control measures with particular emphasis on the key sugars in EPS. As a novel strategy to alleviate biofouling, future control methods may be aimed towards specifically disintegrating and breaking down these key sugars rather than using broad spectrum chemicals such as biocides that are currently used in the industry.
海水中反渗透 (SWRO) 膜的生物污染是全球海水淡化行业面临的一个关键问题。生物污染的主要原因是细菌及其胞外聚合物 (EPS) 在膜表面不可逆地附着形成顽固的生物膜。透明的外聚物颗粒 (TEP) 和原生物膜最近被确定为膜污染的重要前体。尽管对 SWRO 生物污染进行了大量研究，但生物污染的控制仍然是一个挑战。虽然采用更好的预处理方法可能有助于防止新的海水淡化装置中的膜生物污染，但在运行工厂中有效地分散旧的、顽固的生物膜并延长膜的寿命也至关重要。目前大多数做法都采用使用广谱杀菌剂和化学物质来靶向细菌细胞以分散成熟的生物膜，但这种方法显然效率低下。EPS 作为生物膜的最强结构框架，分解和瓦解 EPS 成分对于有效去除生物膜至关重要。为了实现这一目标，有必要了解构成多物种成熟生物膜中主要生物污染细菌群 EPS 的化学成分和关键元素。然而，由于在大多数情况下未能有效预防和减轻污染，对 EPS 复杂性的理解存在明显差距。造成这种情况的部分原因可能是难以从全规模运行的工厂中采样膜，对微生物群落及其在海水淡化过程中动态运行条件下的生态变化了解不足，选择不适合实验室规模生物污染研究的模型物种，以及 EPS 的提取和纯化过程繁琐。本文综述了 SWRO 膜污染和控制措施的新发现，特别强调 EPS 中的关键糖。作为一种缓解生物污染的新策略，未来的控制方法可能旨在专门分解和破坏这些关键糖，而不是像目前行业中使用的广谱化学物质那样使用杀菌剂。
