A thesis submitted in partial fulfillment of the requirement for the degree of Master of Engineering

Thesis (M.Eng.) - Asian Institute of Technology, 1993

This study was carried out to study the nitrogen removal efficiency of anoxic-oxic activated sludge processes. The theoretical analysis and numerical simulation were conducted and compared with the data from wastewater treatment plants from published papers. The key components of influent wastewater considered in the theoretical nitrogen removal efficiencies are ammonia nitrogen, substrate for denitrification process, and alkalinity for nitrification process. The theoretical results show that in the sufficient conditions of these components the nitrogen removal efficiencies of : 1) anoxic and oxic system, depend on the return sludge ratio from the final sedimentation tank and return mixed liquor, and 2) step-feed system, depend on the return sludge ratio from the final sedimentation tank and the portion of influent to the second anoxic tank. The ammonia nitrogen and substrate in the influent and effluent from published papers of anoxic-oxic activated sludge wastewater treatment plants have been reported . From the theoretical analysis of these components for nitrogen removal efficiencies, generally the substrates are enough to perform denitrification process. The results from the theoretical analysis of the nitrogen removal efficiencies compare well with the data from published papers. A mathematical model, which is able to simulate carbon oxidation with nitrification-denitrification process, was used to simulate the data of wastewater treatment plants from published papers. The simulation results indicated that the removal efficiency of total nitrogen can consist with the published papers.