Identification of wastewater biodegradation kinetics

For good control of activated sludge plants information on the degradation kinetics of readily biodegradable matter (RBM) is necessary, because RBM greatly affects the oxygen consumption of the activated sludge. The concentration of RBM can be expressed by the short-term biochemical oxygen demand (BOD_st). In this paper batch experiments are used in which samples of wastewater and activated sludge are mixed in a lab scale aeration tank while the respiration rate is monitored until all the RBM is oxidized. Since BOD_st is simply the integral of the respiration rates at successive time instants, BOD_st is calculated from time series of respiration rates. In this way kinetic models can be obtained from dynamic measurement of respiration rate only. The aim of this paper is to provide and analyse the conditions under which the equivalence of the relationship between BOD_st and respiration rate obtained from chemostat or batch experiments holds. Furthermore, the problem of obtaining an appropriate model structure with associated model parameters from given respiration rate data is investigated and evaluated for this type of biological systems. Four different classes of kinetic models are identified from several batch experiments. The data sets consist of only respiration rate as a function of time. It is concluded that batch respirometric experiments can be employed for kinetic model identification if sludge concentration and initial substrate concentration are carefully chosen. The occurrence of slowly degradable components hinders the identification of degradation kinetics of the dominant component