| The residue and reduction technology of micro-pollutants in water has become a hot-spot issue in recent years. As a kind of AOP technology, UV/chlorine has been carried out numbers of studies on micro-pollutants in drinking water. Vacuum ultraviolet (VUV) is a new source of ultraviolet light which can excite water molecules to generate hydroxyl radicals to promote the degradation of micro-pollutants in water. Currently, the research on VUV combined with chlorine has not been reported, the mechanism of this process is also unclear. Therefore, this article took Sulfadimidine (SMN) as target pollutant, focused on the performance of VUV/chlorine removing trace contaminants. We studied different environment factors on SMN degradation, then discussed the mechanism of VUV/chlorine technology. Finally the formation of disinfection by-products and treatment efficiency on real water are investigated. The Electrical Energy per Order (EE/O) was discussed by developing a tubular reactor and the main results are as follows:(1) Studied the SMN degradation during VUV/chlorine in water, analysed the function of different light sources (UV, VUV, MP UV), chlorine dosage (0.05-5mg/L), SMN concentrations (0.05～0.5mg/L), pH values (5,6,7,10) and the presence of HCO3’, humic acid and tert-butanol (TBA). The results showed that SMN degradation rate under VUV got39-186times to UV, while5-17times to MP UV; the degradation rate accelerated when chlorine dosage increase, and SMN concentration decrease; SMN disappeared fastest at pH6with half dacay time (T1/2)0.716min; by adding10mg/L HCO3-and5mg/L humic acid, SMN degradation efficiency increased30.15%and1.63%, respectively. TBA would inhibit the degradation of SMN.(2) Methylene blue (MB) can be considered as the hydroxyl radical probing matter to discuss concerted reaction mechanism of the VUV/chlorine process. Under conditions of pH5and10(free chlorine present in the form of HOCl and OCl-, respectively), SMN degradation by VUV/chlorine process was much higher than that of the combination of VUV and UV/chlorine with HOC1, while the effect of the two were substantially same when OCl-dominanted. By adding the hydroxyl radical inhibitor (TBA) we found that, the VUV/chlorine strengthening effect disappeared at pH5, indicating that the enhancement of the effect appeared by hydroxyl radical and HOCl molecule interation. In addition, SMN degradation rate under VUV/H2O2process is approximately equal to the combination of two separate process (VUV and UV/H2O2), confirming the presence of free chlorine can enhance the effect.(3) VUV/chlorine technology was used for drinking water treatment. First, SMN removal efficiency in actual water was studied by ultraviolet disinfection dose (80mJ/cm2), chlorine dosage0.05～0.5mg/L, and the result showed raw water got29.8%and32.3%decline, respectively, less than pure water (both over99.9%), while filtered water got99.1%and99.5%decline, respectively, indicating VUV/chlorine has great potential in advanced treatment. The experiment of disinfection by-product formation showed that, with160mJ/cm3VUV radiation does, the generation of CHCl3and haloacetic acids decreased6.72%and36.50%, respectively compared with chlorine disinfection. By using EE/O method for evaluating the running costs of tube VUV reactor, under the condition of0.5mg/L chlorine dosage,10L/min flow rate, the removal efficiency of seven sulfa could reach more than90%, EE/O value can be0.58kWh/m3, which is much lower to UV/H2O2(50kWh/m3,10mg/L DOC) in reported paper. |
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