Endogenous decay and bioenergetics theory for aerobic wastewater treatment

A thermodynamic analysis of aerobic biological treatment of wastewater is presented. Previous thermodynamic models have only considered the net endogenous decay of biomass. Thermodynamically, endogenous decay is the metabolism of the biomass itself to sustain life. Its metabolism results in oxidation and resynthesis as well as release of suspended organic debris that is refractory in the biological process. These concepts are incorporated into the more recent mechanistic IAWQ models. A thermodynamic analysis of endogenous resysnthesis is made to determine the endogenous yield factor and verify concepts in the IAWQ models. The endogenous yield factor is not, in general, the same as the yield factor from exogenous substrate as assumed in the IAWQ model. The development is applied to modeling aerobic sludge digestion. The production of refractory suspended solids is a dynamic process that is improperly accounted for in existing models. A new model for aerobic digestion is proposed based on the revised bioenergetics model. The continuous decay of degradable mass and production of refractory suspended solids is described in the model.