The Formation Rule And Mechanism Of Bromide Or Iodide Disinfection By-products During Chlorination

Bromide and iodide ions are present in the raw water of special geological areas such as seawater intrusion and saline inversion.Disinfectant reacting with this raw water would generate bromoide or iodide disinfection by-products?Br/I-DBPs?which are more cytotoxic and genotoxic than chlorinated disinfection byproducts.In this paper,sodium hypochlorite and chloramine were used to disinfect the lignin distribution water,and the formation of adsorbable organic halogen?AOX?and trihalomethane?THMs?were detected respectively after disinfection to explore the formation rule of Br/I-DBPs.Firstly,the ion chromatography detection method of AOX was optimized.Four kinds of absorption solutions of pure water,H₂O₂,Na₂SO₃,and Na₂S were compared.The results confirmed that the sodium sulfide absorbent has the best absorption effect on the hydrogen halide gas generated by pyrolysis.It was found that when the Na₂ S concentration was 200mg/L and the burning time was 12 min,the recovery rates of absorbable organic bromine?AOBr?and absorbable organic iodine?AOI?could be as high as 90% and 75%,respectively.Using NaClO and NH₂Cl to disinfect the lignin solution containing bromide iodide ion to explore the generation of AOX.It was found that after NaClO disinfection,the conversion rate of bromine ion to AOBr could be as high as about 60%.Meanwhile,we found that bromine in THMs accounts for about 30% of AOBr.When using NH₂Cl to disinfect the lignin solution,the conversion rate of bromine ions to AOBr is less than 3%.But the bromine in THMs can account for more than 60% in AOBr.When adopting NaClO to disinfect lignin solution,AOI could not be detected,but AOI can be detected after NH₂Cl disinfection.The conversion of iodide ions to AOI was about 8%.The proportion of iodine in I-THMs in AOI can be as high as 25%.Nextly,the four factors including lignin concentration,chlorine dosage,halogen ion,and pH were used to explore the effect on the formation of Br/I-THMs when NaClO and NH₂Cl were used for disinfection.Under disinfection by NaClO,the production of bromotrihalomethane?Br-THMs?showed a downward trend,while the production of iodotrihalomethane?I-THMs?showed an upward trend with the increase of lignin concentration;The production of Br-THMs tends to increase first and then decrease,while the production of I-THMs produced decreases with chlorine dosage increasing;Br-THMs and I-THMs both increase with the increasing of concentration of bromide and iodide ion;Br-THMs and I-THMs both increase with the increase of pH;Under disinfection by NH₂Cl,the formation of Br-THMs and I-THMs both show a downward trend as the concentration of lignin increases;the amount of Br-THMs and I-THMs both increase with with chlorine dosage increasing under disinfection by NH₂Cl;The formation of Br-THMs and I-THMs,both increase with the increasing of concentration of bromide and iodide ions under disinfection by NH₂Cl;The amount of Br-THMs increased,while the I-THMs decreased with the increase of pH.