The Study On The Formation And Influencing Factors Of Drinking Water Disinfection Byproducts Haloacetonitriles

The use of disinfectants in drinking water can lead to the generation of disinfection by-products（DBPs）.Haloacetonitrile（HANs）is a new type of nitrogen-containing disinfection by-products（N-DBPs）,because it has more carbon-containing disinfection by-products（C-DBPs）have higher toxicity and have attracted wide attention from researchers.The control of disinfection by-products is one of the important tasks of drinking water safety technology.It is of great significance to study the formation and influencing factors of HANs in the chlorination process of drinking water.This paper established an online liquid-liquid extraction-gas chromatography-mass spectrometry method for the determination of haloacetonitrile in drinking water.The online extraction parameters were optimized.The extraction efficiency of haloacetonitrile was the highest when 4g Na₂SO₄ was added,the p H value was 6,the speed of the stirrer was 600 rpm,and the stirring time was 3 minutes.This method has good detection sensitivity for 7haloacetonitriles,including chloroacetonitrile,dichloroacetonitrile,trichloroacetonitrile,bromoacetonitrile,dibromoacetonitrile,bromochloroacetonitrile and iodoacetonitrile.The method is sensitive,simple,non-interference,and highly automated.It is suitable for the detection of haloacetonitrile disinfection by-products in drinking water.Using humic acid as the precursor of the chlorination reaction and sodium hypochlorite as the disinfectant,the effects of chlorination time,chlorine dosage,p H value,bromide ion concentration and other factors on the formation of haloacetonitrile were investigated.With the increase of the reaction time and the amount of added chlorine,the amount of haloacetonitrile generated first increased and then decreased.When the reaction time was 48h and the chlorine dosage was 10mg/L,the haloacetonitrile produced the largest amount,and then decreased with the increase of time and chlorine dosage.The increase of p H value will promote the decomposition of haloacetonitrile.Under weakly acidic conditions（p H=5）,haloacetonitrile produces the largest amount.With the increase of bromide ion concentration,the production of dichloroacetonitrile（DCAN）continues to decrease,the production of bromochloroacetonitrile（BCAN）first increases and then decreases,and the production of dibromoacetonitrile（DBAN）continues to increase.It shows that the presence of bromide ions in the raw water will promote the conversion of chloroacetonitrile to bromoacetonitrile.Metal ions are widely present in natural water bodies,and will act on the reaction of disinfectants and natural organic matter（NOM）in the water body,affecting the formation and distribution of DBPs.This paper selects common metal ions that are common in natural water bodies and easy to leak in pipes and channels,including Cu²⁺,Fe²⁺,Fe³⁺,Al³⁺and Mn²⁺.Humic acid is used as the precursor of the chlorination reaction to study the formation of haloacetonitrile by metal ions.Impact.Different metal ions have different effects on the formation of HANs.Cu²⁺promotes the formation of haloacetonitrile first and then inhibits it;Fe²⁺,Fe³⁺,Mn²⁺and Al³⁺all exhibit different degrees of inhibition to the formation of haloacetonitrile,and the inhibition effect is Mn²⁺<Fe²⁺<Fe³⁺≈Al³⁺.This paper uses LC-OCD-OND to characterize the humic acid solution before and after the reaction,simply speculates the formation mechanism of haloacetonitrile,and further explores the mechanism of the influence of metal ions on the formation of haloacetonitrile.In humic acid,biopolymers,humic acids,degradation products of humic acid,low-molecular-weight acidic organic matter and low-molecular-weight neutral organic matter account for 10%,69%,11%,0%,and 11%,respectively,and participate in the reaction The main components are biopolymers and humic acids,while low-molecular neutral substances are the main products of the chlorination reaction.During the chlorination process of humic acid,HANs are mainly generated through the"decarboxylation pathway",and the nitrogen source mainly comes from the dissolved organic nitrogen（DON）in the biopolymer component and the humic acid-like component.Cu²⁺promotes the formation of DBPs mainly through the complex adsorption reaction with humic acid to increase the reactivity of related functional groups;Fe²⁺mainly inhibits the reaction of sodium hypochlorite and DON,thereby inhibiting the generation of disinfection by-products;Fe³⁺can interact with aromatic hydrocarbons in humic substances The complex reaction with phenolic compounds reduces the chance of the reaction between the active carbon sites of humic acid and chlorine,thereby reducing the formation of DBPs;Al³⁺mainly reduces the formation of DBPs through the hydrolysis reaction.