| Conventional drinking water treatment process, the most common techniquefor the water supply, encounter series of problems such as complicated procedures,low cost-effectiveness, complex pre-treatment needed, rather large footprint, andmost seriously, microorganis m leakage and high formation potential of disinfectionby-products, as treating micro-polluted water resource supply to meet the newdrinking water standards enacted recently. With the development of membranematerials and related technologies, membrane filtration, especially nano-filtration（NF） is recognized as one of most promising technologies for the micro-pollutedwater resource treatment, owing to its various outstanding own merits. In thepresent work, the efficiency of the short-cut nanofiltration system formicro-polluted source water treatment and the problem of membrane fouling.Firstly, the impurities interception efficiency and membrane fouling behaviorcharacteristics in NF were investigated through the flat membrane underbrushexperiment. Afterwards, both pretreatment unit and influence parameters wereoptimized to analyze the membrane throughput attenuation mechanism andestablish an innovative short-cut NF system which had efficiency micro-pollutantsremoval performance and membrane fouling mitigation capability. Fina lly, along-term experimental operation of the system was carried out to evaluate itsstability.NF unit is capable of removing dissolved organic matters （DOC）, typicalmicro-pollutants （includ ing trichloroethylene, nitrobenzene, trichlorophenol and soon）, assimilated organic matters （AOC）, turbidity, and iron ion from waterresource supply, and the removal effic iency is stably kept around95%,90%,70%,93%and96%, respective ly, which was slightly affected by operational parametersand inlet properties. However, the removal effic iencies of N-compounds, such asnitrate, nitrite and ammonia, ranged from20%to30%, all of which are much lowerthan conventional water treatment technologies. It is revealed that coagulation andultrafiltration （UF） seem as the suitable pre-treatment methods for NF, by whichup to85%of ammonia can be removed stably.Through series of cross-flow filtration tests for NF separation and membranefouling investigation, it is recognized that the humic-like substances with highhydropholic in water resources were the dominant foulants to deteriorate NF flux.Almost all of pre-treatment methods can alleviate membrane fouling rate in acertain level, and coagulation combined with UF was the most effective one,accompanying with a higher removal effic iency of impurities. Notwithstanding, the mitigation extent on membrane fouling have to be affected by the coagulants and itsdosage, as well as settling time.It is evident that NF system has rather good and stable performance in treatingmicro-polluted water resource through a long-term examination. As the mutualfunction of Donnan and size screen effect, the DOC and AOC removal rate waskept about90%. At the same time, the removal rate of ammonia could also bemaintained around80%, although which is affected significantly by membranefouling behavior. The fouling layer on the NF surface have eventually influenceonto nitrate removal rate, indicated by a dramatically decline of removal effic iencyfrom70%~75%to30%~45%after the fouling layer formed. The NF system alsodisplayed a quite stable removal capability on the typical unconventionalmicro-pollutants （trichloroethylene, nitrobenzene, trichlorophenol）, whoseremoval rate was50%,20%, and60%, respectively. However, with the continuouspermeate production and flux decline, these removal efficiencies displayed apparentdecline trend, mainly due to the concentration polarization on the NF surface. Themembrane fouling can be well recovered by simple physical cleaning, and thus ofmore than85%membrane flux can be obtained. |
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