Development of a dynamic SBR simulation model for biological nitrogen removal, based on the Activated Sludge Model No.1, is presented. An experimental study for the calibration and validation of the model was carried out using a pilot scale SBR which treated the wastewater of KAIST.
Thirteen water quality components and twenty model parameters are incorporated into this model. The fractions of organic matter are used for mathematical modelling as the model components. The fractions include readily biodegradable($S_S$), inert soluble($S_I$), slowly biodegradable($X_S$), inert particulate($X_I$) substrates and active biomass($X_H$) in the wastewater. In this study, the model components and parameters are evaluated using the simple respirometer. Respirometry is the measurement and interpretation of the biological oxygen consumption rate under well-defined experimental conditions. The fractions of $S_S, S_I, X_S, X_I$ and $X_H$ were 0.14, 0.04, 0.417, 0.11 and 0.28 of TCOD. Also the sensitive model parameters, $Y_H(0.53gCOD$/gCOD), $Y_A(0.208gCOD/gN)$, $μ_H(2.36/d)$, $μ_A(0.936/d)$, $K_NH(2.185mgN/ℓ)$, $η_g(0.88)$ and $η_h(0.7857)$ were evaluated using the simple respirometer.
Using the SBR model simulation, two operating strategies are suggested. First, the optimization of the total cycle time and the phase distribution is developed in order to minimize the effluent nitrogen concentration. The existing operating cycle for SBR is 8hr/cycle(1.5hr agitation-3,5hr aeration-1.5hr agitation-1hr settle-0.5hr idle). However, the aeration period was too long that only the carbon oxidation happens for 2 hours after complete nitrification. It is thought that extended aeration caused shortage of the carbon source in the anoxic period and high DO concentration at the end of the aeration period. As the result, these are inhibition factors on denitrification in the anoxic period. The simulation result shows that the new cycle phase distribution with shortened cycle time (6hr/cycle, 1hr agitation-2hr aeration-1.5hr agitation-1hr settle-0.5hr idle) is more effective than the old one.
Secondly, in order to maintain constant DO concentration in the aeration period, step-aeration was suggested. As a result of model simulation, it is thought that the step-aeration accelerates the nitrification and denitrification and reduces the effluent nitrogen compounds level.
