Singapore Membrane Technology Centre, Nanyang Environment and Water Research Institute, Nanyang Technological University, 1 Cleantech Loop, CleanTech One #06-08, Singapore 637141, Singapore.
Singapore Membrane Technology Centre, Nanyang Environment and Water Research Institute, Nanyang Technological University, 1 Cleantech Loop, CleanTech One #06-08, Singapore 637141, Singapore.
Water Res. 2015 Mar 1;70:158-73. doi: 10.1016/j.watres.2014.12.001. Epub 2014 Dec 9.
In this study gravity-driven membrane (GDM) ultrafiltration is investigated for the pretreatment of seawater before reverse osmosis (RO). The impacts of temperature (21 ± 1 and 29 ± 1 °C) and hydrostatic pressure (40 and 100 mbar) on dynamic flux development and biofouling layer structure were studied. The data suggested pore constriction fouling was predominant at the early stage of filtration, during which the hydrostatic pressure and temperature had negligible effects on permeate flux. With extended filtration time, cake layer fouling played a major role, during which higher hydrostatic pressure and temperature improved permeate flux. The permeate flux stabilized in a range of 3.6 L/m(2) h (21 ± 1 °C, 40 mbar) to 7.3 L/m(2) h (29 ± 1 °C, 100 mbar) after slight fluctuations and remained constant for the duration of the experiments (almost 3 months). An increase in biofouling layer thickness and a variable biofouling layer structure were observed over time by optical coherence tomography and confocal laser scanning microscopy. The presence of eukaryotic organisms in the biofouling layer was observed by light microscopy and the microbial community structure of the biofouling layer was analyzed by sequences of 16S rRNA genes. The magnitude of permeate flux was associated with the combined effect of the biofouling layer thickness and structure. Changes in the biofouling layer structure were attributed to (1) the movement and predation behaviour of the eukaryotic organisms which increased the heterogeneous nature of the biofouling layer; (2) the bacterial debris generated by eukaryotic predation activity which reduced porosity; (3) significant shifts of the dominant bacterial species over time that may have influenced the biofouling layer structure. As expected, most of the particles and colloids in the feed seawater were removed by the GDM process, which led to a lower RO fouling potential. However, the dissolved organic carbon in the permeate was not be reduced, possibly because some microbial species (e.g. algae) could convert CO2 into organic substances. To further improve the removal efficiency of the organic carbon, combining carrier biofilm processes with a submerged GDM filtration system is proposed.
在这项研究中，重力驱动膜（GDM）超滤被用于反渗透（RO）前海水的预处理。研究了温度（21±1 和 29±1°C）和静水压力（40 和 100 mbar）对动态通量发展和生物污垢层结构的影响。数据表明，在过滤的早期阶段，孔堵塞污染占主导地位，在此期间，静水压力和温度对渗透通量几乎没有影响。随着过滤时间的延长，滤饼层污染起主要作用，在此期间，较高的静水压力和温度提高了渗透通量。在轻微波动后，渗透通量稳定在 3.6 L/m(2) h（21±1°C，40 mbar）到 7.3 L/m(2) h（29±1°C，100 mbar）范围内，并在实验期间保持恒定（近 3 个月）。通过光学相干断层扫描和共聚焦激光扫描显微镜观察到生物污垢层厚度随时间的增加和生物污垢层结构的变化。通过光显微镜观察到生物污垢层中真核生物的存在，并通过 16S rRNA 基因序列分析了生物污垢层的微生物群落结构。渗透通量的大小与生物污垢层厚度和结构的综合效应有关。生物污垢层结构的变化归因于：（1）真核生物的运动和捕食行为增加了生物污垢层的异质性；（2）真核生物捕食活动产生的细菌碎片减少了孔隙率；（3）随着时间的推移，优势细菌种类发生了显著变化，这可能影响了生物污垢层结构。正如预期的那样，GDM 过程去除了大部分进料海水中的颗粒和胶体，从而降低了 RO 结垢的潜力。然而，渗透物中的溶解有机碳并没有减少，这可能是因为一些微生物物种（如藻类）可以将 CO2 转化为有机物质。为了进一步提高有机碳的去除效率，建议将载体生物膜工艺与浸没式 GDM 过滤系统相结合。
