Abstract
The purpose of this study is to investigate the deposit and decomposition characteristics of microalgae using the gravel bed contact-purification method. The following results were obtained : The deposit ratio of Tetraselmis tetrathele is higher than that of Nitzchia closterium due to the shape and size of their cells. The deposit characteristic is expressed by the Iwasaki's filtration equation, and the filter coefficient is a function of real velocity and specific surface area of gravel bed. The decomposition rate constant of deposited microalgae is ranged from 0.10 to 0.14 hr-1 winch is 20-30 times as high as that under suspended condition. The decomposition rate has a proportional relation to the specific surface area in case enough amount of microalgae deposit in gravel bed. Under a few assumptions, both the deposit and decomposition rates are defined by gravel diameter. Therefore, it is possible to design the optimum gravel diameter for the effective and sustainable removal of microalgae using this system.
