Macrokinetic Modeling of Chemical Oxygen Demand Removal in Pilot-Scale High-Rate Anaerobic Ponds

Abstract

Research published on bioreactors discusses the importance of integrating reactor kinetics and mixing as the basis for understanding process hydrodynamics and developing sound design procedures. Nonetheless, many studies are focused on either kinetics or mixing, but studies on the integration of both are seldom found in the literature. Despite the availability of several mixing models (e.g., completely stirred tank reactor, plug flow, dispersion model, completely mixed tanks in series model, and the compartments model), there is an intrinsic complexity in studying process kinetics and reactor hydrodynamics experimentally. In this sense, this work reports the results of a 6-month study for three pilot-scale anaerobic ponds (APs); of which, two had modified physical configurations (one with a mixing chamber, the other with horizontal baffles) and the third was a conventional AP run as a control unit. They were evaluated under three different hydraulic loading rates. The AP provided with the mixing chamber closely followed the completely stirred tank reactor model (r2 = 0.89), and the AP with horizontal baffles showed a high correlation with the Wehner–Wilhelm dispersed flow model (r2 = 0.86). The performance of these modified APs was comparable to those reported in the literature for high-rate anaerobic reactors such as Upflow Anaerobic Sludge Blankets (UASBs). The mixing and macrokinetic features of the modified APs (especially the one provided with the mixing chamber) clearly demonstrated their high-rate and better performance characteristics.