Modeling of sequencing batch reactors treating inhibitory and noninhibitory wastewaters

Abstract

The mathematical model is developed based on the following assumptions: the reactor is completely mixed with aeration and mixing during react and fill periods; all nutrients are in abundance and only one substrate, whose use follows Monod-type kinetics, is growth limiting; the kinetic constants do not vary from one period to another, i.e., the pertinent parameters during the react period are also applicable for the fill period; and the required solids residence time (SRT) is maintained by wastage of the appropriate volume of mixed liquor at the end of the react period.Based on the aforementioned assumptions, following are the mass balance equations for microbial cell and substrate concentration during fill and react periods, during the nth cycle of operation. It is worth mentioning that the subscript n -I appearing in the fill equations denotes the (n -I )th cycle.Fill period. During fill period, the reactor receives raw wastewater and therefore the volume varies with time and it can be expressed as (Dennis and Irvine, 1979) the mathematical description of the SBR system is not fully developed, and because of the unsteady nature of the SBR treatment, it is quite difficult to formulate a complete mathematical model for the system (Irvine and Ketchum, 1989). However, mathematical expressions that partially describe the SBR operation have been reported in the literature since late 1970s. Dennis and Irvine (1979) developed substrate mass balance equations for the fill and react periods, and later Irvine and Ketchum (1989) presented a more general formulation of SBR modeling. Hsu (1986) presented mathematical expressions for bacterial growth and substrate utilization during the react period using Monod kinetics. Furthennore, although inhibition kinetics have been incorporated in models of continuous flow systems Chudoba et at., 1989), modeling of SBRs treating biologically inhibitory wastewaters is still lacking. Therefore, for improved understanding of the performance and design of the SBR, the development of a rigorous mathematical model of the process is crucial. The purpose of this paper is to develop a mathematical model for the SBR system and use it to analyze impact of process variables on the treatment of biodegradable noninhibitory and inhibitory wastewaters and thus assess inhibition effects, as well as for prediction purposes.ABSTRACT:A mathematical model for sequencing batch reactors (SBR) that takes into account fill and react periods was developed and tested against experimental data from the literature. The Monod equation was used to describe microbial growth kinetics. The proposed model predicts the time dependent microbial cell and substrate concentrations during SBR treatment of wastes. A numerical method was used to solve the governing model equations which comprised nonlinear unsteadystate ordinary differential equations. Model simulations highlighted the importance of feed rate as a major operating parameter. For biodegradable wastes and low strength inhibitory wastes, an instantaneous fill is opt...

Model‐Based Design of Sequencing Batch Reactor for Removal of Biodegradable Organics and Nitrogen

“…The conventional approach does not take advantage of any mathematical modeling to produce costeffective systems. As SBRs are proven to perform well under varying influent flows and shock loadings, a conservative design approach is not required to provide the required safety margin against uncertainties in influent flow conditions (Nakhla et al, 1997). Artan et al (2001) developed a systematic rational approach for dimensioning of SBR based on the principles of process stoichiometry.…”

Modeling of activated sludge wastewater treatment processes

“…As a kinetic model, the Monod type equation including the effects of oxygen limitation [9] and the death of microorganisms [4,5,10] is used. It should be emphasized that, even if more complicated kinetic models are used, the simulation algorithm described below does not require any change and still is very useful.…”