| Eutrophication of water causes aquatic plants such as algae to excessive grow, the algal amount has been increasing year by year. The water sources in Guangdong Pearl River delta region such as Zhuhai, Zhongshan, Shenzhen and other places are mainly reservoirs. Once algae outburst, the water plants will be threaten. As a new water treatment agent, ClO2 has gradually been recognized for its effect of killing algae. The subject studied on organic by-product generating during killing algae by C102.The organic species of by-product formed under different conditions were tested. Quantitative analysis on toluene was carried out. Factors affecting the amount of toluene formed were discussed. The potential of chloroform formed when ClO2 killed algae was investigated.With GC-MS detection, it was found that organic matters generated were alkanes, esters, alcohols, ketone, organic acids, heterocyclic material, alkene and alkyne, the alkanes were more than the others. Different organic species generated under different conditions. In addition, toluene formed in any conditions except that ClO2 dose was 0.5mg/L.With GC-FID detection, there wasn’t toluene when the ClO2 dose was 0.5mg/L, Which was consistent with the result detected by GC-MS. In killing Chlamydomonas, the amount of toluene formed increased obviously when ClO2 dose increased from 1mg/L to 2mg/L, but the amount decreased after the ClO2 dose was over 2mg/L. When the ClO2 dose was greater than 2mg/L, the amount of toluene increased with the increase of ClO2 dose. In killing Cylindrospermopsis rackiborskii, the amount of toluene also increased with the increase of ClO2 dose. Toluene formed under different pH value in killing Chlamydomonas or Cylindrospermopsis rackiborskii with ClO2. In killing Chlamydomonas, the amount of toluene had little change from weakly acidic to neutral, but was higher than that in acidic and alkaline conditions. In killing Cylindrospermopsis rackiborskii, the amount of toluene slightly decreased with the increase of pH value between weakly acidic and weakly alkaline, but was higher than that in acid and alkaline. When the time of reaction between algae and ClO2 was less than 10 minutes, the amount of toluene increased with the extension of reaction time, but decreased with the extension of reaction time after 10 minutes. There was more toluene formed at 27.5℃,but in conditions of 20℃ or 35℃, the amount of toluene reduced at different degree. In the process of killing algae in drinking water with ClO2, changing the order of PAC and ClO2 added would lead to different amount of toluene. The amount of toluene was low when ClO2 was added after coagulation and sedimentation. Humic acid didn’t affect the formation of toluene, but the dose of humic acid influenced the amount of toluene formed. When the ClO2 dose was 8mg/L, the amount of toluene formed was the highest, achieving 35.4μg/L,which was lower than the requirement for 0.7mg/L toluene in GB5749-2006 national standard of drinking water. So toluene wouldn’t affect the safety of ClO2 killing algae in drinking water.The study on potential of generating chloroform in killing algae by ClO2 showed that chloroform didn t form without adding chlorine, however, chloroform would generate after adding chlorine into the water in which algae were killed by ClO2. The amount of chloroform would be influenced by changing the ClO2 dosage, initial algae concentration and chlorine dosage. The amount of chloroform would increase with the increase of the initial algae concentration. The chloroform concentration increased with the increase of the ClO2 dosage when the ClO2 dose was from 0.5mg/L to 2mg/L. When the ClO2 dose was greater than 2mg/L, the amount of chloroform reached to a steady value. As the ClO2 dosage and the initial algae concentration were constant, the amount of chloroform increased with the increase of the chlorine dosage. The amount of chloroform was only 27.53μg/L when the chlorine dosage was high, which was lower than the requirement for 0.06 mg/L chloroform in the GB5749-2006 national standard of drinking water. In fact, the dosage of chlorine was low in the process of disinfection after killing algae with ClO2, so chloroform wouldn’t affect the safety of killing algae with ClO2 in drinking water. |
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