Identifying the major fluorescent components responsible for ultrafiltration membrane fouling in different water sources

Three-dimensional fluorescence excitation–emission matrix(EEM) coupled with parallel factor analysis(PARAFAC) was performed for a total of 18 water samples taken from three water sources(two lakes and one wastewater treatment plant(WWTP) secondary effluent),with the purpose of identifying the major ultrafiltration(UF) membrane foulants in different water sources. Three fluorescent components(C1, C2 and C3) were identified,which represented terrestrially derived humic-like substances(C1), microbially derived humic-like substances(C2), and protein-like substances(C3). The correlations between the different fluorescent components and UF membrane fouling were analyzed. It was shown that for the WWTP secondary effluent, all three components(C1, C2 and C3) made a considerable contribution to the irreversible and total fouling of the UF membrane.However, for the two lakes, only the C3 exhibited a strong correlation with membrane fouling, indicating that the protein-like substances were the major membrane foulants in the lake waters. Significant attachment of C1, C2 and C3 to the UF membrane was also confirmed by mass balance analyses for the WWTP secondary effluent; while the attachment of C1 and C2 was shown to be negligible for the two lakes. The results may provide basic formation for developing suitable fouling control strategies for sustainable UF processes.     

Self-registration methods for increasing membrane utilization within compression-sealed microchannel hemodialysers

More than 1.2 million people worldwide require regular hemodialysis therapy to treat end stage renal failure. Current hemodialysis systems are too expensive to support at-home hemodialysis where more frequent and longer duration treatment can lead to better patient outcomes. The key cost driver for hemodialysers is the cost of the hemodialysis membrane. Microchannel hemodialysers are smaller providing the potential to use significantly less membrane. Prior work has demonstrated the use of sealing bosses to form compression seals in microchannel hemodialysers. In this paper, estimates show that the percentage of the membrane utilized for mass transfer is highly dependent on the design and registration accuracy of adjacent blood and dialysate laminae. Efforts here focus on the development of a self-registration method to align polycarbonate laminae compatible with compression sealing schemes for membrane separation applications. Self-nesting registration methods were demonstrated with average registration accuracies of 11.4 ± 7.2 μm measured over a 50 mm scale. Analysis shows that the registration accuracy is constrained by tolerances in the embossing process. A dialysis test article was produced using the self-nesting registration method showing a measured average one-dimensional misregistration of 18.5 μm allowing a potential 41.4% of the membrane to be utilized for mass transfer when considering both microchannel and header regions. Mass transfer results provide evidence of a twofold to threefold increase in membrane utilization over other designs in the existing literature.     

SBR及其改良型技术分析

通过分析研究SBR及其衍生的各种改良型技术用于污水处理的运行方式及特点,指出SBR及其衍生的改良型技术可在中小型污水处理领域降低建设成本和运行费用,是一种适合中国国情的绿色小区污水回用处理技术.     

Mechanisms of ultraviolet disinfection and chlorination of Escherichia coli: Culturability, membrane permeability, metabolism, and genetic damage

Traditional culture methods may underestimate the tolerance of microorganisms to disinfectants because of the existence of viable but nonculturable or sublethally injured cells after disinfection.The selection of a strict method is crucial for the evaluation of disinfection performance.The actions of 2 typical disinfectants–ultraviolet(UV)and chlorine–on the fecal indicator Escherichia coli were investigated by the detection of culturability,membrane permeability,metabolic activity,deoxyribonucleic acid(DNA),and messenger ribonucleic acid(m RNA).During UV disinfection,the irreversible damages in the cell membrane and cellular adenosine triphosphate(ATP)were negligible at low UV doses(80 m J/cm~2).However,membrane permeability was damaged at low doses of chlorine(5 mg/L),leading to leakage of cellular ATP.Our study showed that a slight lesion in DNA was detected even at high doses of UV(400 m J/cm~2)and chlorine(5 mg/L)treatments.The decay of m RNA was more rapid than that of DNA.The degradation level of m RNA depended on the choice of target genes.After exposure to 50 m J/cm~2UV dose or 5 mg/L chlorine for30 min,the DNA damage repair function(Rec A m RNA)was inhibited.The m RNA involved in the DNA damage repair function can be a potential indicator of bacterial viability.     

50Hz低频环境磁场对细胞增殖的影响及其机理探讨

本文以细胞株LO2(人肝细胞)和CHL(中国仓鼠肺成纤维细胞)为研究对象，用50Hz正弦磁场以不同强度、不同时间作用于细胞。长时间作用后，2种细胞的增殖均受到抑制，但抑制程度与磁场作用量并非呈简单的线性关系；磁场短时间作用对细胞增殖无明显影响，但细胞膜的流动性变差，在磁场撤去后膜的流动性又有所恢复。这一现象说明，低频弱磁场引起宏观生物效应需要时间的积累。同时观察到磁场短时间作用导致的CHL细胞上表皮生长因子受体(EGFR)的聚集，这可能是低频弱磁场引起宏观生物效应的一种机制。     

超滤膜结构参数特性的分析研究

用电镜法和渗透率法对PVDF-300超滤膜表面的孔径分布、孔隙率以及膜孔密度等结构参数进行了测定.结果表明,用扫描电镜法和场发射扫描电镜法测定膜平均孔径及膜孔密度等结构参数是比较吻合的.从而可以根据膜结构参数在透水过程中的变化规律研究膜污染的机理,为以后建立以膜结构参数为参数的膜污染模型奠定了理论基础.     

无机膜分离技术在水处理领域的应用研究

对无机膜分离技术在含油废水、生活污水及工业废水等水处理领域的研究现状、工程实例和应用前景进行综述,指出无机膜具有耐高温、耐腐蚀、耐污染、机械强度高等优异性能,在苛刻反应条件下的工业废水处理方面优势明显,尤其是陶瓷微滤和超滤膜在水处理领域的商品化应用已日渐成熟和稳定,并提出未来在无机膜应用领域的发展方向.     

Advanced treatment of municipal wastewater by nanofiltration: Operational optimization and membrane fouling analysis

Municipal sewage from an oxidation ditch was treated for reuse by nanofiltration (NF) in this study. The NF performance was optimized, and its fouling characteristics after different operational durations (i.e., 48 and 169 hr) were analyzed to investigate the applicability of nanofiltration for water reuse. The optimum performance was achieved when transmembrane pressure = 12 bar, pH = 4 and flow rate = 8 L/min using a GE membrane. The permeate water quality could satisfy the requirements of water reclamation for different uses and local standards for water reuse in Beijing. Flux decline in the fouling experiments could be divided into a rapid flux decline and a quasi-steady state. The boundary flux theory was used to predict the evolution of permeate flux. The expected operational duration based on the 169-hr experiment was 392.6 hr which is 175% longer than that of the 48-hr one. High molecular weight (MW) protein-like substances were suggested to be the dominant foulants after an extended period based on the MW distribution and the fluorescence characteristics. The analyses of infrared spectra and extracellular polymeric substances revealed that the roles of both humic- and polysaccharide-like substances were diminished, while that of protein-like substances were strengthened in the contribution of membrane fouling with time prolonged. Inorganic salts were found to have marginally influence on membrane fouling. Additionally, alkali washing was more efficient at removing organic foulants in the long term, and a combination of water flushing and alkali washing was appropriate for NF fouling control in municipal sewage treatment.     

Towards a better hydraulic cleaning strategy for ultrafiltration membrane fouling by humic acid: Effect of backwash water composition

As a routine measurement to alleviate membrane fouling, hydraulic cleaning is of great significance for the steady operation of ultrafiltration (UF) systems in water treatment processes. In this work, a comparative study was performed to investigate the effects of the composition of backwash water on the hydraulic cleaning performance of UF membranes fouled by humic acid (HA). Various types of backwash water, including UF permeate, Milli-Q water, NaCl solution, CaCl₂ solution and HA solution, were compared in terms of hydraulically irreversible fouling index, total surface tension and residual HA. The results indicated that Milli-Q water backwash was superior to UF permeate backwash in cleaning HA-fouled membranes, and the backwash water containing Na⁺ or HA outperformed Milli-Q water in alleviating HA fouling. On the contrary, the presence of Ca^2 + in backwash water significantly decreased the backwash efficiency. Moreover, Ca^2 + played an important role in foulant removal, and the residual HA content closely related to the residual Ca^2 + content. Mechanism analysis suggested that the backwash process may involve fouling layer swelling, ion exchange, electric double layer release and competitive complexation. Ion exchange and competitive complexation played significant roles in the efficient hydraulic cleaning associated with Na⁺ and HA, respectively.     

平片膜生物反应器中膜污染特性的实验研究

采用聚偏氟乙烯平片膜生物反应器 ,通过测定不同运行条件下的水通量研究其污染特性 ,重点考察了运行时间、操作压力、曝气状况对膜污染的影响。实际结果表明 ,在曝气量为 3m3 h、操作压力为 0 .0 2MPa条件下运行 6h后 ,膜水通量从2 4 0mL min·m2 降至 5 5mL min·m2 ,下降率超过 77%。