| Eutrophication of water causes aquatic plants such as algae to excessively grow, the algal amount has been increasing year by year. The water sources of water plants 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. Therefore, it's very urgent and necessary to research the efficient algae removal technology in water plants. As a new water treatment agent, ClO2 has gradually been recognized by people. The removal effect of algae with chlorine dioxide and their reaction kinetics were studied in this paper, the factors which influenced the removal effect of Cylindrospermopsis, Chlorella and Microcystis aeruginosa with ClO2 were discussed. The technological conditions of algae removal on the raw water containing algae which came from some of the Guangdong reservoirs were tested. The generation and removal of inorganic by-products in removing algae with ClO2 were also studied.In the experiments of removing Microcystis aeruginosa, Tetrahedron, Cylindrospermopsis, Chlamydomonas and Chlorella with ClO2, it was found that during 10 to 15minutes the algae could be removed by chlorine dioxide effectively, removal efficiency of Microcystis aeruginosa, Tetraedron and Cylindrospermopsis was between 89.44% to 92.48%, removal efficiency of Chlamydomonas was 98.26%, and Chlorella's was relatively low, only 60.90%.The results of kinetics research showed that reaction order of Chlamydomonas, Microcystis aeruginosa, Tetraedron, Cylindrospermopsis, Chlorella to chlorine dioxide was 1.3,2,2,2.5 and 6, respectively, their apparent rate constants were 2.1×10-3μg-0.3·L0.3·s-1,5.6×10-3μg-1·L·s-1,3.8×10-3μg·L·s-1,8.3×10-4μg-1.5·L1.5·s-1 and 1.0×10-5μg-5·L5·s-1, respectively. The reaction orders of various algae to chlorine dioxide were different, and the apparent rate constants were also different.The research on the factors which influenced the removal effect of Cylindrospermopsis, Chlorella and Microcystis aeruginosa with ClO2 showed that the best reaction time was 10 minutes, and the removal efficiency increased with the reaction time prolonging, but the removal efficiency decreased with the increase of the pH value. Ammonia nitrogen concentration had little effect on the removal of algea, but the removal efficiency decreased with the increase of the organic matter concentration. The ClO2 dosage and the initial algal concentration both had different effects on removing the three kinds of algae, their removal rate all increased with the increase of the ClO2 dosage, but the rising range of removal rate were differ from one another. The rising rate of Chlorella removal was small, but the Microcystis aeruginosa's was big, and the rising removal rate of Cylindrospermopsis would become slowly after ClO2 dose achieving 0.5 mg/L. The removal rate of Chlorella and Cylindrospermopsis both increased with the increase of the initial algal concentration, but the Microcystis aeruginosa's was on the contrary.The process tests of removal of algae from water sources by ClO2 oxidation combining with coagulation were carried out. One kind of water samples was tested which was taken from Guangdong reservoir and Cylindrospermopsis was the advantage algae, the algal content was 3.562×107cells/L, turbidity was 9.86NTU. The best technological conditions which were ClO20.5 mg/L, PAC 15mg/L, addition of ClO2 and PAC at the same time were attained. After coagulation and precipitation, the removal efficiency of algae was 98.90%, and surplus turbidity was 1.59NTU. Another kind of water sample was also taken from Guangdong reservoir which Chlorella was the advantage algae, the algal content was 6.2×107cells/L, turbidity was 8.60NTU. The best technological conditions were ClO20.5 mg/L, PAC 5mg/L, addition of ClO2 and PAC simultaneously. After the coagulation and precipitation, the removal efficiency of algae was 98.69%, and surplus turbidity was 0.82NTU. The water sample of Microcystis aeruginosa was simulated natural water with turbidity 23.1NTU and 22.64μg/L Chlorophyll-a. The experiment on removal of Microcystis aeruginosa by ClO2 oxidation combining coagulation was done. The result showed that after preoxidation for 10minutes with 0.5 mg/L chlorine dioxide, and 10mg/L PAC on coagulation and precipitation, the removal efficiency of algae was 97.10%, surplus turbidity was 3.56NTU.The studies on the generation and removal of inorganic by-product ClO2- during removing algae with ClO2 showed that the generation of ClO2- increased with the increase of ClO2 dosage, the prolonging of the reaction time and rising of the pH value. Stirring speed, the initial algal concentration, the organic matter content and the ammonia nitrogen concentration all had little effect on the generation of ClO2-. FeSO4 could effectively remove the inorganic by-product ClO2- during removing algae with ClO2. In removing inorganic by-product ClO2-, FeSO4 could effectively reduce the raw water turbidity and reduce the conventional amount of coagulant at the same time. When the dosage of ClO2 was high to 1.17mg/L, the inorganic by-product ClO2- was 0.12mg/L which was lower than the limitation of 0.8 mg/L ClO2- in the national standard of drinking water. If the inorganic by-product ClO2- exceeds the standard, FeSO4 can be used to control ClO2- according to the stoichiometric relation between FeSO4 and ClO2.and/or ClO2-.
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