Performance Of Nanofiltration For Improving The Drinking Water Quality In A Water Supply Plant With Micropolluted Water Resource

Some southern cities of China are deficient in fresh water resources for quality.Source water is polluted by trace organic pollutants.Four nanofiltration membranes connected in series were set up at the water plant G,of which the influent was supplied by the effluent of the traditional treatment process,to study the performance of different series on water quality improvement,and the performance of the nanofiltration was compared with that of current treatment process.The possibility to further improve the water quality of this plant was discussed based on the experimental data,which was expected to support the update of the water plant G.The coagulation-settling-filtration process followed by ozone(O3)oxidation and two-biological activated carbon(BAC)was employed as the current treatment process of water plant G.Samples along the treatment process were withdrawn during January to October in 2015,of which the traditional water pollution indicator,disinfection by-products,16 kinds of polycyclic aromatic hydrocarbon(PAHs),7 kinds of organochlorinated pesticides(OCPs)and SOS-umu based genotoxicity were detected.The results showed that totally 50~100 n g·L-1 PAHs,20~40 n g·L-1 OCPs and 100 ng·L-1 4-NQO toxic equivalent quantity(TEQ4-NQO)were detected in source water.Conventional process was efficient on the traditional pollution indicators,however,only less than 20% of PAHs and OCPs were removed,and more serious tendency was observed for genotoxicity.Performance of O3+BAC process on PAHs and OCPs was influenced by their concentration in influent.For samples of January,April and June,average 64.8% PAHs and 50.6% OCPs were removed,respectively.However,the remove efficiency reduced to 15% when the influent concentration become lower such as for samples from August and October.For all samples,85% genotoxicity was removed by O3+BAC.Nanofiltration experiment,equipped with NF270-400 and 3 NF90-400 membranes,was set up in water plant G.This nanofiltration system was run for 60 days with the capacity of 180 L/day and the water production rate was 75%.Results showed high removal efficiency of traditional indicators and organic pollutants.Over 95% of TOC and UV254 were removed;for the trace organic pollutant,60%?85%?50% and 95% of HAAFP,THMFP,PAHs and OCPs were removed,respectively;The genotoxicity cannot be detected in the effluent.Similar removal efficiency of disinfection by products and OCPs with high relative molecular weight.Significant difference,however,was observed for those with lower molecular weight.Those results indicated that physical filtration was the predominant mechanism of the nanofiltration membrane.In summary,the nanofiltration system can improve the drinking water quality efficiently.Nonetheless,complicate design and operation,high investment and high operating cost make it more suitable for new water plants and high quality-required water plants.