Coagulation, flocculation, and dissolved air flotation (DAF) experiments were performed with humic acid to evaluate the influence of operational conditions on removal efficiencies. We investigated coagulation, flocculation, and flotation conditions of humic acid removal using a laboratory-scale DAF system. This paper deals with coagulant type (aluminum sulfate and PSO-M) and the most relevant operational conditions (velocity gradients for coagulation and flocculation, retention time and recycle ratio and flotation time). Results showed that optimal conditions for removing humic acid, yielding CHA removal efficiencies of approximately 85 %, are a recycle ratio of 40 %, coagulant dosages of 0.15 – 0.20 gAl/gHA as aluminum sulfate and 0.03 – 0.12 gAl/gHA as PSO-M, coagulation(400s-1 and 60s), flocculation(60s-1 and 900s or more), and flotation(490 kPa or more and at least 10 min).

Abstract
 1. Introduction
 2. Materials and methods
  2.1. Materials
  2.2. Analysis methods
  2.3. Coagulation and flotation procedures
 3. Results and discussion
  3.1. Coagulation and flocculation conditions
  3.2. Flotation conditions
  3.3. Effect of initial CHA and coagulant dosages
 4. Conclusions
 References

• Chang-Han Lee(Department of Environmental Administration, Catholic University of Pusan) Corresponding author