A fundamental analysis of dynamics of waste biodegradation in aerobic processes

Abstract

This paper studies the static and dynamic behavior of a biological wastewater treatment process consisting of an aerobic bioreactor and a settler. The process is described by a three-variable model that takes explicitly into account the mass balance of oxygen. The analysis is carried out for the general case where the biomass specific growth rate is assumed to depend arbitrarily on substrate, biomass, and oxygen. The biomass yield coefficient is also assumed to depend arbitrarily on the substrate. General conditions describing the behavior of the model are derived. The general analysis is applied to an experimentally validated model where the specific growth rate depends on substrate and oxygen following a multiplicative Monod form. Practical diagrams are constructed that delineate the effect of various operating parameters on the performance of the biodegradation. The model is also studied for the case of a variable yield coefficient. The analysis shows the existence of a periodic behavior for some range of model parameters. The results of the paper allowed a useful understanding of the dynamics of the aerobic biodegradation including the effect of operating parameters, the specific growth rate, and the biomass yield coefficient on the existence of instabilities in the process. Figure 1. Schematic diagram of the bioreactor-settler process.