Performance of presedimentation and dissolved air flotation to overcome highly turbid raw water

Simultaneous removal of inorganic and algae particles is frequently required during the rainy season in Korea. Although the dissolved air flotation (DAF) process has been successfully applied to the treatment of algae-laden water with low turbidity, it is known that inorganic particles caused by rainfall can highly affect flotation efficiency. A small presedimentation basin was constructed to overcome the decrease in treatment efficiency for the DAF process when highly turbid raw water flows in because of heavy rain in the Songjeon water treatment plant. In this study, a series of operational data from the past 3 years and 9 months was investigated and analyzed to explore the effectiveness of presedimentation and derive empirical information on a complementary operation technique for the combining the presedimentation and DAF processes. For the treatment of highly turbid raw water during the rainy season, solids loadings, including larger particles, decreased substantially with the application of presedimentation in the Songjeon water treatment plant during the rainy season. However, the evaluation results of the particle size distribution indicated that the smaller particles need to be removed by a filtration process even though the DAF process is effective for decreasing solids loadings.