Expanded Process Model Describes Biomass Distribution, Free-Ammonia/Nitrous Acid Inhibition and Competition between Ammonia Oxidizing Bacteria (AOB) and Nitrite Oxidizing Bacteria (NOB) in Submerged Biofilm and Integrated Fixed Film Activated Sludge (IFAS) Bioreactors
Significant additions to the submerged biofilm and integrated fixed-film activated sludge reactor model previously presented and evaluated by Boltz et al. (2009a; 2009b) are described. The expanded model considers activated sludge and biofilm biochemical transformation processes (and competition for electron donors, electron acceptors, and macronutrients), mass transfer resistances internal and external to the biofilm; and bacterial competition for space inside the biofilm. Microorganisms considered include ammonia oxidizing bacteria (AOB)XAOB , nitrite oxidizing bacteria (NOB)XNOB , non-methanol degrading facultative heterotrophs, XH, type I methanol degrading heterotrophs, XM1, type II methanol degrading heterotrophs, XM1, slowly biodegradable substrates (which includes high molecular weight, colloidal, and particulate organic matter), XS , and inert biomass, XI . Analytical flux expressions describing soluble substrate flux across the biofilm surface are used to simulate 1-D biofilms. Autotrophic nitrifiers have been separated into AOB and NOB. Four-step denitrification that includes emission of a potent greenhouse gas (GHG) nitrous oxide, free-ammonia and free-nitrous acid inhibition are simulated. These additions are based on previous work with activated sludge (Hiatt and Grady, 2008a; 2008b). Pseudo two-dimensional bioreactor modeling is executed with a series of continuous flow stirred tank reactors. The work described in this manuscript presents a more fundamental description of submerged biofilm and IFAS bioreactors. However, additional research is required to elucidate, amongst others items, clear and transparent calibration protocol and establish a more extensive database consisting of biokinetic constant values for these systems.
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Document Type: Research Article
Publication date: 2009-01-01
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