| Title |
Effects of Prechlorination on Diatoms Coagulation |
| Authors |
전항배(Hang Bae Jun),이영주(Young Ju Lee),이병두(Byung Doo Lee),이종대(Jong Dae Lee) |
| Abstract |
The effects of prechlorination on diatoms coagulation were investigated. The dominant diatom that caused filter clogging in both Han river and Daecheong lake water sources was Synedra acus. The optimum alum dose for coagulation of Synedra spp. was 1.62 ㎎-Al/L, which was 50% higher than that for optimum turbidity removal. The coagulation pH was above 6.8 and alum dose was above 1.6 ㎎-Al/L(30 ppm), that actually coincided with optimum sweep coagulation zone. As chlorine dose increased, the removal efficiency of slender type diatoms, such as Synedra spp. and Asterionella spp. remained constant or decreased a little. However, the removal efficiency of short cylinder type diatom, such as Aulacoseira spp. and Stephanodiscus spp. increased. The removal efficiencies of Synedra spp. in Daecheong lake water were 32% at chlorine dose of 1.0 ㎎-Cl₂/L, and 72% at 1.2 ㎎-Cl₂/L, respectively. which showed lower than 88% without chlorine. From the Jar-test result using Han river water, the removal efficiency of Synedra spp. was lower up to chlorine dose of 1.5 ㎎-Cl₂/L than that without chlorine, however, it increased at chlorine dose above 3.0 ㎎-Cl₂/L. With SEM`s images after 10 minutes chlorine contact, diatoms cell wall was partly destroyed. The accumulated sludge on the surface of sand filter was sticky lump of alum floc with numerous broken Synedra cells. The broken Synedra cells in sticky lump of alum floc could be formed by both long chlorine contact at low chlorine concentration and hydraulic shear stress exerted during surface and back washing. |