Unraveling Membrane Fouling Induced by Chlorinated Water Versus Surface Water:Biofouling Properties and Microbiological Investigation

Chlorine is usually applied in the urban water treatment process to deactivate pathogens and prevent waterborne diseases.As a pre-treatment,it remains unclear whether chlorinated water can effectively alleviate membrane fouling during ultrafiltration(UF).In this study,tap water was investigated for its effect on biofilm formation and biofouling in a gravity-driven membrane(GDM)filtration system.For comparison,biofilm/biofouling with untreated surface(lake)water was studied in parallel.It was found that more severe membrane fouling occurred with the filtration of tap water than lake water,and larger quantities of polysaccharide and extracellular DNA(eDNA)were present in the tap-water biofilm than in the lake-water biofilm.The tap-water biofilm had a densely compact morphology.In contrast,a porous,spider-like structure was observed for the lake-water biofilm,which was assumed to be associated with the bacteria in the biofilm.This hypothesis was verified by 16S ribosomal RNA(rRNA)sequencing,which demonstrated that Xanthobacter was the dominant taxon in the tap-water biofilm.Additionally,membrane hydrophobicity/hydrophilicity played a minor role in affecting the membrane fouling properties and microbial community.This study revealed the significant role of chlorine-resistant bacteria in biofouling formation and provides a deeper understanding of membrane fouling,which can potentially aid in searching for effective ways of controlling membrane fouling.

Application of a hybrid gravity-driven membrane filtration and dissolved ozone flotation(MDOF)process for wastewater reclamation and membrane fouling mitigation

This study proposed a novel membrane filtration and dissolved ozone flotation integrated(MDOF) process and tested it at pilot scale. Membrane filtration in the MDOF process was operated in gravity-driven mode, and required no backwashing, flushing, or chemical cleaning. Because ozone was added in the MDOF process, ozonation, coagulation, and membrane filtration could occur in a single reactor. Moreover, in situ ozonation occurred in the MDOF process, which differs from the conventional pre-ozonation membrane filtration process. Significant enhancement of turbidity removal was further achieved through the addition of membrane filtration. Membrane fouling was mitigated in the MDOF process compared to the MDAF process. In situ ozonation in the MDOF process decreased the fluorescence intensity and transformed the high MW dissolved organics into small MW compounds. For the fouling layer, the extracellular polymeric substance(EPS) contents and cake layer morphology were analyzed. The results indicated that the contents of EPS decreased. Furthermore, a thinner and more loosely structured cake layer formed in the MDOF process. Because coagulation and ozonation occurred simultaneously in a single reactor, the generation of hydroxyl radicals was enhanced through the catalytic effect of Al-based coagulants on ozone decomposition, which further alleviated membrane fouling in the MDOF process.

Metabolic uncoupler,3,3’,4’,5-tetrachlorosalicylanilide addition for sludge reduction and fouling control in a gravity-driven membrane bioreactor

The gravity-driven membrane bioreactor(MBR)system is promising for decentralized sewage treatment because of its low energy consumption and maintenance requirements.However,the growing sludge not only increases membrane fouling,but also augments operational complexities(sludge discharge).We added the metabolic uncoupler 3,3’,4f,5-tetrachlorosalicylanilide(TC$)to the system to deal with the mentioned issues.Based on the results,TCS addition effectively decreased sludge ATP and sludge yield(reduced by 50%).Extracellular polymeric substances(EPS;proteins and polysaccharides)decreased with the addition of TCS and were transformed into dissolved soluble microbial products(SMPs)in the bulk solution,leading to the break of sludge floes into small fragments.Permeability was increased by more than two times,reaching 60-70 L/m2/h bar when 10-30 mg/L TCS were added,because of the reduced suspended sludge and the formation of a thin cake layer with low EPS levels.Resistance analyses confirmed that appropriate dosages of TCS primarily decreased the cake layer and hydraulically reversible resistances.Permeability decreased at high dosage(50 mg/L)due to the release of excess sludge fragments and SMP into the supernatant,with a thin but more compact fouling layer with low bioactivity developing on the membrane surface,causing higher cake layer and pore blocking resistances.Our study provides a fundamental understanding of how a metabolic uncoupler affects the sludge and bio-fouling layers at different dosages,with practical relevance for in situ sludge reduction and membrane fouling alleviation in MBR systems.

无清洗重力驱动超滤工艺净水效能及机理

基于分散式供水及常规超滤工艺的不足,研发了重力驱动膜过滤工艺(简称GDM),其结合生物滤饼层和超滤膜双重截留功效,兼具无清洗、无药剂、操作简单、低能耗、低维护等优点.采用GDM工艺净化河水、水库水、江水和模拟配水,长期运行其通量均可达到稳定状态,表明GDM工艺对不同类型的水源水具有普适性.原水水质、驱动压力、膜组件类型、膜材质、膜孔径大小、温度、间歇过滤、预处理等运行条件会影响生物滤饼层的结构和组成特性,从而影响GDM的稳定通量和膜污染特性.GDM工艺通量稳定性主要受生物作用调控的膜面生物滤饼层结构和组成特性影响,生物滤饼层结构越粗糙、孔隙越发达、胞外分泌物(EPS)质量浓度越少,稳定通量越高.相比常规超滤工艺,GDM膜面生物滤饼层可有效地强化对浊度、可生物同化有机碳(AOC)及氨氮等污染物的去除效能.此外,采用缓速滤池预处理工艺可有效地改善膜面生物滤饼层的结构特性,提高GDM稳定通量和污染物去除效能,研究成果有助于推动超滤技术在分散式供水领域中的应用.