Research On Formation Process Of1,1-Dichloroacetone, Disinfection By-Product In Drinking Water And Its Control Techniques

The safety of drinking water has become one of the most concerned issues. Disinfection of drinking water can effectively kill pathogens, microorganisms, etc., and guarantee the quality of drinking water; meanwhile, disinfection process produces a series of disinfection by-products (DBPs), which have great harm to human health. Therefore, research on its analysis method, formation process and control techniques is of great importance and necessity.In this study, a novel method with high accuracy using methyl tertiary butyl ether (MTBE) as extractant and1,2-dibromopropane as internal standard for the determination of1,1-dichloroacetone (DCAce) by gas chromatography/mass spectrumetry (GC/MS) was established. The analysis method for DCAce was highly accurate and the recovery rate was between100.8%and103.4%with relative standard deviation of1.99%-4.72%and limit of detection less than2μg/LThe formation process of DCAce and its influencing factors were discussed with L-leucine as the precursor during the chloramination process. The results indicated that the DCAce production increased with the increase of chloramine dosage when the chloramine addition was in the range of5～30mg/L. The DCAce amount reduced with the increase of pH value. In the range of15～35℃, the higher temperature was, the larger DCAce production was. The formation process of DCAce from L-leucine by chloramine contained a series of complicated reactions, including substitution, oxidation, bond breaking, amino diazotization, reduction and so on, and eventually formed DCAce.In this study, Mg/Al/Fe hydrotalcite-like compounds (HTLcs) were synthesized via coprecipitation method and the product (CHTLcs) was obtained when the Mg/Al/Fe hydrotalcite-like compounds were calcined at500℃. The surface physical and chemical properties of adsorbent were investigated by scanning electron microscope (SEM), surface porosity detector, Fourier transform infrared (FT-IR) spectrometry and X-diffraction (XRD). The results showed that the specific surface area of CHTLcs increased by30%compared to that of HTLcs, and CHTLcs had a "memory effect", which could recover its layered structure in the adsorption process, further improve the adsorption effect.The results of adsorption tests also showed that when the initial concentration of DCAce solution was20μg/L and the reaction time was60min,90.93%removal was achieved using CHTLcs with the addition of0.1g/L, which was1.3times higher than that by HTLcs. The adsorption process of DCAce by the adsorbent could be divided into three phases, which are rapid phase, slow phase and dynamic equilibrium phase. The time of equilibrium adsorption of DCAce by CHTLcs was40min, while the time by HTLcs was increased to60min.It was found that the DCAce adsorption by HTLcs and CHTLcs increased with the increase of their dosage and temperature. When the initial concentration of DCAce was in the range of5～20ug/L, the adsorption effect increased with increasing of the initial concentration. The DCAce adsorption by HTLcs and CHTLcs accorded with the Freundlich adsorption isotherm model and followed the pseudo second-order kinetics model.In the H2O2and UV processes, when the initial concentration of DCAce was10μg/L, after300min, we found that the removal was34.12%when H2O2concentration were30mg/L; the removal was29.68%when the UV light intensity were35μw/cm2.Furthermore, the research on DCAce removal by the UV-H2O2process was conducted, which performed better with higher DCAce removal than the individual process shown above. When the UV light intensity was set at35uw/cm2, after reaction time of300min, removal of DCAce with the initial concentration of lOug/L was improved from56.90%to78.40%with the increase of H2O2addition from5mg/L to30mg/L. The enhancement of UV light intensity also contributed to the DCAce removal. When the H2O2addition was set at30mg/L, after reaction time of300min, removal of DCAce with the initial concentration of10μg/L was improved from78.34%to89.72%with the increase of UV light intensity from35μw/cm2to81μw/cm2. When the initial concentration of DCAce was in the range of5～30ug/L, the removal of DCAce increased with increasing of the initial concentration, was improved from70.29%to85.96%. The DCAce degradation by UV/H2O2process followed the first-order kinetic model.