Javier Luisa, Farhat Nadia M, Vrouwenvelder Johannes S
King Abdullah University of Science and Technology (KAUST), Water Desalination and Reuse Center (WDRC), Division of Biological and Environmental Science and Engineering (BESE), Thuwal, 23955-6900, Saudi Arabia.
Delft University of Technology, Faculty of Applied Sciences, Department of Biotechnology, Van der Maasweg 9, 2629, HZ Delft, the Netherlands.
Water Res X. 2020 Dec 14;10:100085. doi: 10.1016/j.wroa.2020.100085. eCollection 2021 Jan 1.
A critical problem in seawater reverse osmosis (RO) filtration processes is biofilm accumulation, which reduces system performance and increases energy requirements. As a result, membrane systems need to be periodically cleaned by combining chemical and physical protocols. Nutrient limitation in the feed water is a strategy to control biofilm formation, lengthening stable membrane system performance. However, the cleanability of biofilms developed under various feed water nutrient conditions is not well understood. This study analyzes the removal efficiency of biofilms grown in membrane fouling simulators (MFSs) supplied with water varying in phosphorus concentrations (3 and 6 μg P·L and with constant biodegradable carbon concentration) by applying hydraulic cleaning after a defined 140% increase in the feed channel pressure drop, through increasing the cross-flow velocity from 0.18 m s to 0.35 m s for 1 h. The two phosphorus concentrations (3 and 6 μg P·L) simulate the RO feed water without and with the addition of a phosphorus-based antiscalant, respectively, and were chosen based on measurements at a full-scale seawater RO desalination plant. Biomass quantification parameters performed after membrane autopsies such as total cell count, adenosine triphosphate, total organic carbon, and extracellular polymeric substances were used along with feed channel pressure drop measurements to evaluate biofilm removal efficiency. The outlet water during hydraulic cleaning (1 h) was collected and characterized as well. Optical coherence tomography images were taken before and after hydraulic cleaning for visualization of biofilm morphology. Biofilms grown at 3 μg P·L had an enhanced hydraulic cleanability compared to biofilms grown at 6 μg P·L. The higher detachment for biofilms grown at a lower phosphorus concentration was explained by more soluble polymers in the EPS, resulting in a lower biofilm cohesive and adhesive strength. This study confirms that manipulating the feed water nutrient composition can engineer a biofilm that is easier to remove, shifting research focus towards biofilm engineering and more sustainable cleaning strategies.
海水反渗透（RO）过滤过程中的一个关键问题是生物膜积累，这会降低系统性能并增加能源需求。因此，膜系统需要通过结合化学和物理方法进行定期清洗。给水中的营养限制是控制生物膜形成、延长膜系统稳定性能的一种策略。然而，在各种给水营养条件下形成的生物膜的可清洗性尚未得到充分了解。本研究分析了在膜污染模拟器（MFS）中生长的生物膜的去除效率，该模拟器供应的水中磷浓度不同（3和6μg P·L，可生物降解碳浓度恒定），在进料通道压降增加140%后，通过将错流速度从0.18 m/s提高到0.35 m/s持续1小时进行水力清洗。这两种磷浓度（3和6μg P·L）分别模拟了未添加和添加了磷基阻垢剂的RO给水，是根据全尺寸海水RO淡化厂的测量结果选择的。膜解剖后进行的生物量量化参数，如总细胞计数、三磷酸腺苷、总有机碳和细胞外聚合物，与进料通道压降测量一起用于评估生物膜去除效率。水力清洗（1小时）期间的出水也进行了收集和表征。在水力清洗前后拍摄了光学相干断层扫描图像，以可视化生物膜形态。与在6μg P·L下生长的生物膜相比，在3μg P·L下生长的生物膜具有更高的水力可清洗性。较低磷浓度下生长的生物膜具有更高的脱离率，这是由于EPS中更多的可溶性聚合物，导致生物膜的内聚和粘附强度较低。本研究证实，控制给水营养成分可以设计出更易于去除的生物膜，将研究重点转向生物膜工程和更可持续的清洗策略。
