Modeling and experiment for removal of algae and nutrient using a DAF system installed on a ferryboat

Abstract

Many lakes or irrigative reservoirs in Korea are rapidly polluted with algae because of the increasing amounts of pollutants discharged from nonpoint sources. Though dissolved air flotation (DAF) is one of the most efficient processes for removing algae, there are limitations associated with conveying polluted water to a plant located on the lakeside. In this study, a reaction tube was optimized to enhance collision between microbubbles and pollutants. The length, diameter, and space of the reaction tube were modified and tested in the laboratory. A numerical model using three-dimensional Navier–Stokes equations was set up for the analysis of flow around the reaction tube. The laboratory tests showed that the efficiency of phosphorus removal is improved as the reaction tube length is reduced. Phosphorus removal efficiency was improved, as the tube diameter was larger and the reaction space was reduced. A pilot test was performed to verify these results and modeling results. A ferryboat installed with an air saturator of DAF on the main deck and an underwater screen curtain was introduced to remove suspended solids (SS), chlorophyll-a (Chl-a), and phosphorus in the middle of the lake. The results showed that removal of SS, Chl-a, and phosphorus were efficient as the reaction space was reduced in length.