The Research Of Removal Of NDMA Precursors In Reused Wastewater By Coagulation And Adsorption

Municipal wastewater reclamation and resue is an efficient way to improve the water resource usage,which can not only reduce the water pollution problem but also relieve the water scarity issue.But biotreated water contains variety of pathogenic microorganisms,trace toxic and hazardous chemical contaminants and plant nutrients,which would produce harmful disinfection by-products(DBPs)after disinfection process.N-Nitrosodimethylamine(NDMA)is one of DBPs with stronger toxicity.This study investigated distinguishing characteristic of dissolved organic matter(DOM)in MBR and AAO effluents by UF fractionation,XAD-8 resin adsorption isolation,excitation and emission matrix(EEM)fluorescence spectroscopy and fourier transform infrared(FT-IR)spectroscopy analysis and measured NDMA formation characteristic of NDMA.Meanwhile,removal of various NDMA precursor fractions was also analyzed to evaluate the efficiency of traditional water treatment(coagulation,adsorption and coagulation-adsorption processes)The main results were summarized as follows:(1)Different treatment processes lead to distinct composition of DOM.The MBR effluent contained lower DOM than the AAO effluent,but more halogenated C,N-DBPs in the MBR effluent were formed than in the AAO effluent after chlorination due to its higher percentage of molecular weight(MW)>1kDa materials,fulvic acid-like substances and polysaccharides.For example,the content of TCM in MBR effluent was high as 526 ?g/mg-C,which was about 13 time as that in AAO effluent.In contrast,the NDMA yield of AAO effluent was more than that of MBR effluent because AAO contained higher percentage of MW<1kDa materials,aromatic proteins,polypeptides and amino acids especially secondary amines.(2)In AAO technology treated effluent,NDMA were mainly formed by low molecular weight(MW)fractions(<30 kDa)and hydrophilic fractions(HiS).Integrated coagulation-adsorption treatments showed the highest reduction capacity for NDMA formation potential(57%),followed by isolated adsorption treatment(50%)and isolated coagulation treatment(28%).The powdered activated carbon(PAC)adsorption process could reduce the high MW precursors(>30 kDa)by 48%,which was higher than other treatments.In contrast,the highest uptake(66%)of low MW precursors(<30 kDa)was achieved by the coagulation-adsorption process.All treatments preferentially removed the hydrophobic acids(HoA)fraction compared to other fractions.Coagulation could remove more fulvic acid-like substances and adsorption could remove more microbial byproducts and aromatic proteins.The removal of fulvic acid-like substances leads to lower NDMA formation potential,as well as lower specific NDMA formation potential.This means that fulvic acid-like substances have higher NDMA formation activity with chlorine disinfectant.(3)In MBR effluent,the main precursors of NDMA were low molecular weight(MW)fractions(<1 kDa),hydrophilic fractions(HiS)and fulvic acid-like substances.The coagulation process could reduce more high MW precursors(>100 kDa),while the adsorption process reduced more precursors with MW of 1-10 kDa.All treatments preferentially removed the hydrophobic acids(HoA)fraction compared to other fractions.All MW and hydrophobic/hydrophilic fractions of DOM could be removed by FeCl3 coagulation and PAC adsorption,but the amine-type functional group and fulvic acid-like substances were more difficult to remove than other DOM.The percentage of these substances in DOM,which easily react with disinfectants to form NDMA,would increase after various treatments.Therefore,residual DOM fractions may show higher specific NDMA formation potential than before treating processes...