Study On The Control Effect Of Combined Process On The Precursors Of Disinfection Byproduct In Surface Water

Disinfection is one of the important processes before drinking water enters the pipe network,which can effectively avoid the growth of microorganisms to ensure the biosecurity of the drinking water.However,the disinfection process is inevitably to cause the formation of poisonous and harmful disinfection byproducts?DBPs?,which will pose the potential threat for the using and drinking of water.Hence,it is of great significance to explore the characteristics of DBP precursors as well as DBPs formation mechanism,and further establish an effective advance treatment process to control the DBPs contained in drinking water.In this study,the typical DBP precursors in the surface water was identified and characterized,their DBPs formation mechanisms were also explored after chlorination.The O₃-ceramic membrane filtration?O₃-CMF?and O₃-biological activated carbon?O₃-BAC?processes were further established for DBPs precursors'removal.The removal effect and mechanism of typical DBPs precursors in surface water advance treatment was further investigated.The main research contents and conclusions were shown as follows.?1?The characteristics of DBP precursors and DBPs formation mechanism in surface water were evaluated,and their control effect by the conventional process was also evaluated.Results indicated that the DBP precursors in raw water mainly included aromatic proteins-like,fulvic acids-like,soluble microbial products and analogues?SMPs-like?as well as humic acids-like,etc.After chlorination,high concentration of carbonaceous disinfection byproducts?C-DBPs?was detected,which primarily consist of trihalomethanes?THMs?and halogenated acetic acids?HAAs?.In addition,THMs had obviously higher formation content in the water during spring and winter,which accounted for 66.76%and 63.94%of the measured total C-DBPs,respectively.And HAAs showed much higher formation content in the water during summer and autumn,which accounted for 42.95%and 51.99%of the measured total C-DBPs,respectively.Compared with C-DBPs,the formation of nitrogenous DBPs?N-DBPs?was much lower than that of raw water.Haloacetonitriles?HANs?was the mainly component of measured N-DBPs,indicating the high production of 34.31?g·L^-1?in summer?and 44.38?g·L^-1?in autumn?.Trihalonitromethanes?THNMs?showed a much lower contribution to the total N-DBPs formation,with the highest production of 7.33?g·L^-1 in spring.Pearson correlation analysis indicated that the formations of THMs,chloral hydrate?CH?,haloketones?HKs?and THNMs during raw water chlorination were significantly relevant with the humic acid-like substances in the raw water,with the correlation coefficient?R²?of 0.88,0.71,0.66 and 0.85,respectively.The formations of HAAs and HANs showed obvious correlation with the SMPs?R²=0.86?and aromatic protein-like components?R²=0.78?in the raw water,recpectively.Conventional processes of drinking water treatment had low removal efficiency for DBPs precursors,resulting in a decrease of 20.43%and 22.45%for C-DBPs and N-DBPs in the effluent respectively.?2?Because of the poor removal efficiency of DBP precursors by conventional processes,the O₃-CMF process was constructed to advanced treat the effluent of conventional processes,the mechanism of different O₃-CMF coupling methods and the removal effect of O₃-CMF on DBPs were investigated synthetically,in this study.Compared with the influent?conventional process effluent?,the ex-situ O₃-CMF led to a decrease of 21.86%in C-DBPs formation and16.19%in N-DBPs formation respectively,while the in-situ O₃-CMF resulted in a decrease of32.35%in C-DBPs formation and 19.13%in N-DBPs formation respectively.Results indicated that the in-situ O₃-CMF was more effective for DBP precursors control than ex-situ O₃-CMF.This might be due to the catalytic ozonation induced by ceramic membrane pores,which led to the decomposition of O₃ and produce more hydroxyl radicals?·OH?.Under the synergistic effect of O₃,·OH oxidation,and ceramic membrane retention,O₃-CMF could effectively reduce the total fluorescence response intensity and high molecular weight?the relative molecular mass>0.3×10³?organic matters,resulting in the decrease of total DBPs formation.However,the oxidation of O₃ and·OH would lead to the formation of low molecular organic compounds which were ineffectively retained by the ceramic membrane,increasing HKs,CH and THNMs formation.In addition,increasing the concentration of O₃ was difficult to enhance the removal of DBP precursors by O₃-CMF.When the O₃ concentration increased from 0.5 mg·L^-1 to 4.0mg·L^-1,the removal rate of ex-situ O₃-CMF to the total DBP precursor increased from 14.03%to 25.72%,and in-situ O₃-CMF removal rate of total DBP precursors increased from 25.19%to27.81%.?3?O₃-BAC process was further applied to advanced treat the conventional process effluent.The effect of operating parameters such as empty bed contact time?EBCT?and O₃concentration on the removal of DBPs and their precursors was also investigated.The results showed that the removal of DBP precursors by O₃-BAC process was better than O₃-CMF,which displayed a decrease of 30.49%in C-DBPs formation and 42.09%in N-DBPs formation respectively.Extending EBCT was in favor of the degradation of aromatic-like proteins and SMPs-like organics by microorganisms,thereby reducing the formation of total DBPs.However,further increase of EBCT had no obvious effect on DBP precursors removal.When EBCT was increased from 20 min to 30 min,the remove efficiency of O₃-BAC for C-DBPs and N-DBPs only increased 1.63%and 1.04%,respectively.Furthermore,the removal rate of C-DBPs increased from 20.64%to 56.05%and N-DBPs increased from 18.58%to 61.89%respectively,when the concentration of O₃ addition increased from 0 mg·L^-1 to 2.0 mg·L^-1.This was mainly attributed to the fact that O₃ oxidized the refractory organic matter in raw water into biodegradable substances,which enhanced the biodegradation of BAC with the microbial activity of 62.52%.However,when the O₃ concentration was further increased to 4.0 mg·L^-1,the microbial survival rate decreased to 49.9%,further led to the release of Intracellular organic matter such as protein and SMPs.Those newly produced DBP precursors would result in an increased formation of C-DBPs and N-DBPs by 12.63%and 18.72%,respectively.In summary,an appropriate dosage of O₃ was beneficial for removing DOM by O₃-BAC,but excessive O₃concentration caused the formation of new DBP precursors.