The threat of heavy metal pollution in water sources becomes increasingly serious. Toxic hexavalent chromium is harmful for health. Chitosan is a non-toxic and pollution-free substance, it is a cationic coagulant after protonated in diluted acid solution, it also can complex for many heavy metal ion. The study on removal of Cr (Ⅵ) and turbidity in drinking water by chitosan in this paper was performed. The results showed that the removal efficiency of Cr (Ⅵ) decreased with increasing pH, the removal rate of Cr (Ⅵ) was as high as 100% at pH4 using the chitosan concentration of 1.0g/L, but in these conditions, the turbidity was not removed. The removal efficiency of Cr (Ⅵ) bore relationship to stirring time of slow mixing step and initial concentration of Cr (Ⅵ). The best stirring time was 4 hours. To attain a good removal efficiency of Cr (Ⅵ), the dosage of chitosan must increase with the initial concentration of Cr (Ⅵ) increasing. At pH7, low chitosan dosage had good turbidity removal.
Chitosan is a kind of natural, non-toxic and harmless substance. After its amino-group protonizing, it can form a cationic polymer which has excellent coagulation/flocculation properties. The application of chitosan in potable water treatment for the removal of particulates and dissolved organics has been studied extensively in the last decade. In order to further understand the specific property of chitosan applied in drinking water treatment, this paper introduces the effect of molecule weight and deacetylation of chitosan on coagulation/flocculation and coagulation/flocculation mechanism in drinking water treatment, gives an overview of chitosan characteristics of removal of suspend solids, organics and bacteria in water, particularly, describes the relationship between the removal efficiency of above impurities by chitosan and pH, dosage of chitosan.
The effects of killing Chlamydomonas, Microcystis Aeruginosa, Cylindrospermopsis, Chlorella and Tetraedron by chlorine dioxide were studied. The reaction orders and rate constants of algae oxidated by chlorine dioxide were determined. The results show that these algae can be killed effectively by chlorine dioxide in raw water. the efficiencies of killing Microcystis Aeruginosa, Tetraedron and Cylindrospermopsis are 89.44%~92.48% during 10 to 15 Minutes. The efficiency of killing Chlamydomonas is high to 98.26%, but the efficiency of killing Chlorella is low, only 60.90%. The reaction orders for various algae are different. The reaction orders of Chlamydomonas, Microcystis Aeruginosa, Cylindrospermopsis, Chlorella and Tetraedron are 1.3, 2, 2.5, 6 and 2, respectively. The apparent rate constants are 2.1×10-3 μg-0.3L 0.3s-1, 5.6×10-3μg -1Ls -1, 8.3×10-4μg -1.5L 1.5s -1, 1.0×10-5μg -5 L 5s -1 and 3.8×10-3 μg -1Ls -1 , respectively.
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