Research On Formation Process Of Dichloroacetonitrile,Disinfection By-Product In Drinking Water And Its Control Strategies

The disinfection by-products that are formed after the chlorination in drinking water have carcinogenic, teratogenic and mutagenic effects, which are harmful to human health. Therefore, the study on its formation process and control strategies is of great importance for the safety of drinking water.In this study, a novel method with high accuracy was established using1,2-dibromopropane as internal standard and methyl tertiary butyl ether (MTBE) as extractant for the determination of dichloroacetonitrile (DCAN) by liquid-liquid micro-extraction and gas chromatography/mass spectrometry (LLE-GC/MS). The measurement method for DCAN was highly accurate and the recovery rate was between98.6%and107.6%with relative standard deviation of3.30%-7.93%and limit of detection less than3μg/L.The aspartic acid was used as the precursor of the DCAN formation during chlorination and the influencing factors were evaluated. The results showed that the DCAN amount increased with the increase of pH value under the neutral and acid conditions, however, the amount of DCAN decreased with the increase of pH value under the alkali condition, and the final amount of DCAN under the alkali condition was much less than that under the neutral and acid conditions. It was also found that the DCAN amount increased with the increase of chlorine addition when the dosage of chlorine ranged from1mmol/L to8mmol/L.The produced amount of DCAN didn’t change a lot when the temperature turned higher from10℃to30℃. The formation process of DCAN from aspartic acid by chlorination experienced seven steps which included substitution reaction, decarboxylation reaction, oxidation reaction, and so on.In the UV-H2O2process, the UV intensity had a greater effect on the removal efficiency of DCAN and the removal efficiency increased obviously with the increase of the UV intensity. When the dosage of H2O2was10mg/L and after reaction time of240min, the removal efficiency of DCAN with the initial concentration of100μg/L was improved from68.44%to96.11%with the increase of UV intensity from31μw/cm2to80μw/cm2. In addition, the influence of H2O2dosage on the removal efficiency of DCAN was also obvious. When the UV intensity was set at64μw/cm2, and after reaction time of240mm, the removal efficiency of DCAN with the initial concentration of100μg/L was improved from67.81%to95.90%with the increase of H2O2 addition from15mg/L to45mg/L. The results of the experiment on the effect of the initial concentration of DCAN showed that it’s not an important factor to affect the removal efficiency of DCAN by the UV-H2O2process. The DCAN degradation by UV/H2O2process followed the first-order kinetic model.The O3-GAC process was applied to remove DCAN, which performed better with higher DCAN removal than the individual process of O3and GAC. When the concentration of O3was controlled at10.06mg/L and after reaction time of180min, the removal efficiency of DCAN with the initial concentration of100μg/L was improved from34.78%to97.43%with the increase of GAC dosage from0.2g/L to1.Og/L. In addition, the removal efficiency of DCAN increased with the increase of O3concentration. When the dosage of GAC was0.6g/L and after reaction time of240min, the removal efficiency of DCAN with the initial concentration of100μg/L was improved from57.02%to94.79%with the increase of the O3from7.88mg/L to11.72mg/L. The results on the effect of the temperature showed that the removal efficiency of DCAN increased with the increase of the initial concentration of DCAN during the O3-GAC process. The DCAN degradation by O3-GAC process also accorded with the first-order kinetic model.