Abstract
Since the wastewater regulation on nitrogen and phosphate was enforced in October 1991, measures against stockbreeding waste have been an urgent subject. Furthermore, the consolidation of the standards on nitrogen and phosphate as for nutrient substrate is expected, because of the new environmental standards for public water established in June 1993.
But, it is difficult to expect the construction of advanced treatment plants for stockbreeding wastewater, as almost of all stockbreeding, such as hog and cattle raising and poultry farming, facilities are small scale and the burden of the wastewater treatment plant construction cost is heavy. For the solution of the problem, several stockbreeding farms are lumped together, and intensive farms are constructed. The wastewater from all of the farms in the lump is treated at one plant. Simultaneously, wastewaer treatment technologies applicable for small scale plant have been extensively developed.
An existing small scale oxidation ditch process plant, in which dairy cattle stockbreeding farms and domestic wastewater had been treated, was reconstructed and established effective advanced treatment with easy maintenance. The details of the reconstruction were as follows; 1) existing brush type sixsurface aerators were taken away, 2) a barrier was constructed in one section of the ditch, 3) two units of down draft type submerged turbine aerators were mounted at the upper stream of the barrier and mixed liquor with air bubbles were discharged down stream of the barrier. Thereby, effluent quality improved, especilly an increase in nitrogen removal and a clearing away of the problems involved in pH decrease, and maintenance become easy.
In this paper, test performance is explained and investigetion results based on the performance, applicability of this process to stock breeding wastewater treatment, advanced treatment object nitrogen removal and plant design factors are repoted.
