Reactions between humic acid solutions and excessive ClO2 or Cl2 have been investigated. Under various experimental conditions, the removal efficiency of TOC, UV254and A410 from humic acid solutions were examined. The relationship between the removal efficiency and the consumption of ClO2 or Cl2 was discussed. The results showed that the maximum demand of ClO2 was 2.19 mg/mg TOC for the humic acid solution under the experimental conditions, and that of ClO2 was 1.88 mg/mg TOC. The variation tendency of ClO2 consumption was similar to that of Cl2. TOC of humic acid solutions decreased 15.2% and 15.6% after the reaction with ClO2 or Cl2 respectively. Under the experimental conditions, 21.4% of unsaturated bonds and 52.8% of humic acid color were removed by ClO2 in 168 h. As for Cl2, removal efficiency of unsaturated bonds and humic acid color were 16.8% and 41.7% respectively. Larger molecules from humic acid were oxidized to smaller molecules by ClO2 and Cl2. Higher oxidation potential of ClO2 than that of Cl2 was also indicated by variation of UV254/A410 ratios. The similar tendency, that exhibited faster variation in the initial 24 h, existed for all the research factors.
On the basis of gas chromatography（GC） coupled with a short capillary column and an electron capture detector （ ECD）, a simple and rapid method for the determination of five haloaceric acids （ HAAs ） in drinking water was developed by the optimization of derivation conditions and the modification of gas chromatographic program. HAAs formarion potential（HAAFP） of the reaction of humic acid with chlorine was determined via this method. The major advantages of the method are the simplicity of chromatographic temperature program and the short run time of GC. Dichloroaceric acid（DCAA） and Trichloroacetic acid（TCAA）, which were detected in the determination of HAAFP, were rapidly formed in the first 72 h of the reaction of humic acid with chlorine. HAAFP of the reaction of humic acid with chlorine increased with the increase in the concentrations of humic acid and chlorine. The average HAAFP of the reaction of humic acid with chlorine was 39.9μg/mg TOC under the experimental conditions. When the concentration of humic acid was 4 mg/L, the concentration of HAAs, which were produced in the reaction of humic acid with choline, may exceed MCL of 60μg/L HAAs as the water quality standards for urban water supply of China and the first stage of US EPA disinfecrion/disinfection by-products（D/DBP） rule; when the concentration of humic acid was 2 mg/L, the concentration of HAAs may exceed MCL of 30 μg/L HAAs for the second stage of US EPA D/DBP rule. When humic acid was reacted with chlorine dioxide, only DCAA was detected with a maximum concentration of 3.3 μg/L at a humic acid content of 5 mg/L. It was demonstrated that the substitution of chlorine dioxide for chorine may entirely or partly control the formation of HAAs and effectively reduce the health risk associated with disinfected drinking water.
ZHU Zhi-liang GE Yuan-xin ZHANG Rong-hua MA Hong-mei ZHAO Jian-fu
