Preliminary Studies of Membrane-Aerated BiofilmsEPA Grant Number: FP916413
Title: Preliminary Studies of Membrane-Aerated Biofilms
Investigators: Shanahan, John W.
Institution: University of Minnesota
EPA Project Officer: Carleton, James N
Project Period: January 1, 2004 through December 31, 2006
Project Amount: $110,344
RFA: STAR Graduate Fellowships (2004) RFA Text | Recipients Lists
Research Category: Fellowship - Environmental Engineering , Academic Fellowships , Engineering and Environmental Chemistry
Membrane aerated biofilm reactors (MABRs) offer an innovative new technology for the treatment of municipal wastewaters. Within the MABR, a biofilm grows on gas permeable membranes submerged in wastewater. Oxygen supplied to one side of the membranes diffuses through pores in the membrane fabric and into the base of the biofilm. In contrast, ammonium and organics diffuse from the wastewater into the biofilm at the liquid-biofilm interface. Bacterial cells within the biofilm matrix consume both oxygen and substrates for fulfillment of their energy and mass requirements, thus purifying the wastewater. By eliminating aeration of the bulk wastewater, the MABR provides a significant energy savings over conventional activated sludge systems. Furthermore, cultivation of slow growing nitrifiers is possible within the MABR without the long hydraulic residence times or extensive recirculation systems necessary in conventional systems. The objectives of this research are to: describe the behavior of MABRs using mathematical models and test the accuracy of these models using a laboratory-scale reactor.
To describe the dynamic behavior of MABRs, a mathematical model was developed. This model was constructed using Aquasim software to quantify the behavior of a multiple population membrane-aerated biofilm under various operating conditions. Within the model, the intramembrane partial pressure, biofilm thickness, substrate loading, and average velocity may be varied. Model outputs include reactor performance, profiles of substrates, bacterial populations, and bacterial activity within the biofilm.
A laboratory-scale reactor was operated under a single set of operating conditions to test the accuracy of the model. Reactor performance was characterized via mass balances on chemical oxygen demand, ammonium, nitrate, and nitrite. Oxygen fluxes to the reactor were calculated from the stoichiometry of oxidation for ammonium and nitrite. Results demonstrated that oxygen transfer across the membrane was maintained or increased in the presence of a membrane-aerated biofilm. Model estimates of reactor performance were somewhat conservative by comparison with experimental results. Deviations between model and experimental results may be attributed to the development of irregular biofilms.