The Characters Of Dissolved Organic Matters From Litter-Mimic With The Different Humification States And Their Effects On Drinking Water Treatment Processes

Natural dissolved organic matter(NOM)with different molecular weights mainly includes humus,protein,polysaccharide-like structures,which naturally exists in surface water bodies and is an important component in the process of drinking water treatment.In surface water bodies,the sources of NOM are generally divided into two parts,namely(1)endogenous NOM from photosynthesis/heterotrophs and sedimentation,and(2)exogenous NOM from terrestrial ecosystems.In freshwater ecosystems,the increase in NOM content mainly occurs during the rainy season,and enters into the water body through surface runoff.In general,The NOM is generally considered as non-toxic pollutant,but it may directly cause many of the problems in the drinking water treatment processes,such as adsorption of other toxic organic substances,causing membrane fouling,generation of toxic disinfection by-products(DBP),etc.Therefore,this paper aims to analyze the migration and transformation of NOM and its impact on drinking water treatment by simulating the humification process of forest litter in two different NOM sources i.e.,soil and surface water.Firstly,simulating the soil humification process of forest litter,a continuous 8-week study was conducted to explore the changes in chemical properties such as NOM composition,polysaccharide/protein content,average molecular weight,aromaticity,affinity/hydrophobicity,etc.,together with their effects on coagulation,and ultrafiltration/nanofiltration(UF/NF)processes.The results showed that during the humification process,the removal rates of coagulation(from 67.5% to 37.0%)and ultrafiltration(from 14.4% to 5.8%)decreased significantly as a function time.However,the removal rates of nanofiltration first increase from 40.0% to 72.9%,and then decreased up to 47.4%.The disinfection byproduct formation potential(DBPFP)of different humified samples decreased with the increase of humification time,including trihalomethane formation potential(THMFP)and haloacetic acid formation potential(HAAFP),with THMFP decreasing from 1027.25 μg/L to 457.65 μg/L and HAAFP from 48.03 μg/L to 29.81 μg/L.The relationship between DBPFP and various indicators suggests that aromatic compounds and amino acids are more likely to produce DBP during the disinfection phase.Among them,humus is more likely to produce THM,while low molecular weight carboxylates and carbonyl organic compounds are associated with the production of HAA.Secondly,the forest litter humification process was also applied using surface water samples,and a continuous 21-week study was conducted to examine the chemical properties of NOM composition,polysaccharide/protein content,average molecular weight,aromaticity,hydrophilicity/hydrophobicity,etc.Furthermore,the impacts of these changes on coagulation,disinfection by-product formation potential(DBPFP)was also explored.The results showed that during the humification process,increased removal rate was observed for Oxic/Anoxic humic pond coagulation.However,the decreased removal rate was witnessed for Oxic/Anoxic humic river coagulation.In addition,the trihalomethane formation potential(THMFP)of Oxic/Anoxic humic pond increased(from 51.28 μg/mg to 186.07 / 163.44 μg/mg);whereas,the trihalomethane formation potential of Oxic/Anoxic river first increased from 51.28 μg/mg to 72.43 / 129.05 μg/mg,and then decreased to 53.03 / 62.795 μg/mg,respectively.The haloacetic acid formation potential(HAAFP)of the Oxic/Anoxic humic pond increased(from7.62 μg/mg to 150.51 μg/mg / 117.07 μg/mg),while in the river system,the formation potential of HAA first increase and then decrease(increased from 7.62 μg/mg to 29.226 /28.772 μg/mg,and then decreased to 18.197 / 18.075 μg/mg).PCA ranking of DOM characteristics affecting DBPFP revealed that the large hydrophobic humic acids and biopolymers were found to be the main precursors of THM,while small organic molecules had a greater contribution to HAA production.This study provides an insight into the effects of different humification ages of NOM on drinking water treatment processes affected by seasonal and vegetation surrounding water sources,with the ultimate aim of improving drinking water treatment.