Abstract

Currently, the applications of oxidation ditch process for small scale domestic waste water treatment facilities have been recommended because of several benifits such as easy maintenance, decrease of waste activated sludge and etc. Although the process design manuals have been past published, they have not descrived in detail regarding various types of special aerators respectively each having different characteristics are adapted.
As one of special aerators, one-point oxygen supply type oxidation ditch process using down draft aerator was developed in 1980, and the kinetic analysis of the process on biological nitrification, denitrification and carbonaceous BOD reduction were reported.
This special process and the down draft aerator are explained schematically, and the constructed process model and the kinetic equations are also described. Further, the rational design factors of this process, such as capacity and length of ditch, flow velocity, adding-point of influent and pulling-out-point of effluent in ditch, influence to reaction of DO, temperature and MLSS concentration and etc. are discussed from the results of the kinetic calculations.