KINETICS OF DENITRIFICATION REACTIONS IN SINGLE SLUDGE SYSTEMS

This paper reports denitrification studies performed using the anoxic reactor of a laboratory scale anoxic-aerobic plant as a batch reactor of variable volume. This was achieved by adding to the anoxic reactor a supplementary flow of nitrate after the shut down of the recirculati on line and the interruption of the hydraulic connection to the aerobi c reactor. By operating in this way, in a relatively short time, it is possible to get a number of experimental data sufficient to describe the biological process kinetics. The system is extremely flexible and gives kinetic data in short times for different experimental condition s. In fact, it is possible to operate at different COD/NO3-N ratios si mply by changing the influent wastewater flowrate to the anoxic reacto r. Two series of tests were performed: in the first series (use of end ogenous carbon) a supplementary flow of nitrate was fed to the anoxic reactor while the wastewater influent flow was interrupted; in the sec ond series (use of internal carbon) the influent wastewater flow was f ed during the addition of nitrate. The importance of the carbonaceous substrate nature on the denitrification rate was also verified. Data a nalysis was performed by utilizing the integral method procedure and a zero order kinetics referring to both the substrates COD and nitrate nitrogen was considered. A satisfactory agreement between predicted an d experimental data was found. Values obtained for k(D) range from 0.0 7 mg NO3-N/mg VSS . d, at which the carbon source is mostly endogenous , to 0.25 mg NO3-N/mg VSS . d, at which the carbon source consists mai nly of readily biodegradable GOD. Intermediate values occur when the r eadily biodegradable COD is limiting and denitrification takes place b y utilizing the slowly biodegradable one.