Study On The Effect Of Ultraviolet/Chlorine Advanced Oxidation Process On The Generation Of Disinfection Byproducts From Benzene Series Precursors

The ultraviolet/chlorine advanced oxidation process（UV/Cl₂ AOP）has been confirmed by many studies to effectively degrade the refractory micro-polluted organic matter in the water body or kill the chlorine-resistant and UV-resistant pathogens.However,the high chlorine dosage and chlorine free radicals in the system will affect the generation of disinfection by-products（DBPs）.At the same time,bromide ions in the water body will also be converted into brominated free radicals in the system,resulting in chlorinated disinfection by-products.（Cl-DBPs）are transformed into more toxic brominated disinfection by-products（Br-DBPs）.Considering that chlorine and ultraviolet are common disinfection processes in water plants,this technology has a good application prospect in the field of water treatment,and it is of important research significance to evaluate the impact of this process on the formation of DBP in water bodies.This article takes seven kinds of benzene series with common functional groups of natural organics as the research object,adopts high-power medium-pressure mercury lamp irradiation device,and simulates the actual application of the process"short reaction time（6-40 s）,high chlorination（3-10 mg/L）”typical working conditions,explore the formation of DBPs of benzene-based precursors in the AOP system and the change law of DBP formation potential（DBPFP）in the chlorination of the treated effluent in the pipeline network,and The influence of key factors such as pH and bromide ion on the formation of DBPs of benzene precursors in AOP was analyzed.AOP has an activating effect on two inert benzene derivatives and can promote the production of DBP and DBPFP.Compared with dark chlorination disinfection,under the two pH conditions,benzoic acid newly generated haloacetic acid（HAA）and chloroacetaldehyde（CAL）after AOP treatment,and DBPFP increased by about 34-54ug/mg C;Base benzene newly generated THM,CAL,dichloroacetonitrile（DCAN）and trichloronitromethane（TCNM）,DBPFP increased by 17-33 ug/mg C.In addition,acidic conditions have a more significant impact on the precursors,which indirectly reflects the key role of hydroxyl radicals in the formation of DBP.AOP has a passivation effect on the DBP generation of active model compounds,for example:UV/Cl₂ AOP reduces the HAA of phenol by about 41-84 ug/mg C;reduces the THM of resorcinol by about 91-128 ug/mg C;Reduce the HAA of o-chlorophenol by 217-235 ug/mg C,and increase THM by about 20-25 ug/mg C and so on.At the same time,for the five highly active benzene series,the effect of pH on the formation of DBP is also similar.For example,after AOP treatment,the HAA reduction of phenol under acidic conditions is greater than that of alkaline conditions by about 43 ug/mg C;The reduction in THM of hydroquinone is greater than about 37 ug/mg C in alkaline conditions.The type,position and quantity of substituents jointly determine the generation law of DBPs.Under acidic conditions,the active benzene series pre-treated with AOP has high potential for generating THM and HAL,reaching 300 ug/mg C and 50 ug/mg C,respectively;containing ortho and para structures Both of the two monochlorophenols can generate HAA above 600 ug/mg C;2,4,6-trichlorophenol with three chlorine substituents can generate HAA of 753 ug/mg C,much higher than other phenols Compound.pH showed the same trend of influence on DBPFP under the two process conditions,but the influence of different precursor structures on it was not the same.The meta position is more susceptible to pH（resorcinol）,the difference in TCM generation under the two pH conditions is 53 ug/mg C（about 16%of the total generation）;the para position and the ortho position（monochlorophenol）are relatively Stable,the difference in HAA production is about 20-40 ug/mg C（about 6%of the total production）;the more the number of substituents,the greater the pH is affected by it,for example:under different pH conditions,2,4,6-The difference in HAA formation of trichlorophenol accounts for about 8%of the total.The participation of bromide ions can significantly promote the formation of DBPs,and bromide ions have a greater impact on the formation of DBPs under acidic conditions.Because bromide ion has relatively limited promoting effect on the DBPs of inert benzene series,DBPFP is at a very low level.Here are five highly active benzene series as examples.Under the action of bromide ions,HAA is increased to 1.2-1.5 times of the original,THM is increased to 1.3-3 times of the original,and the dominant species in THM is bromotrihalomethane（Br-THM）,the dominant species in HAA is still chlorohaloacetic acid（Cl-HAA）,and the degree of bromination of THM and HAA is higher under acidic conditions.THM is more affected by bromide ion than HAA,which is expressed as bromine binding factor N（THM）>N（HAA）.Ranked from high to low by N（THM）are phenol,2,4,6-trichlorophenol,p-chlorophenol,o-chlorophenol,and resorcinol;ranked from high to low by N（HAA）is resorcinol Diphenol,phenol,o-chlorophenol,2,4,6-trichlorophenol and p-chlorophenol.