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https://hdl.handle.net/2142/19045
Description
Title
Modeling for anaerobic fixed-bed biofilm reactors
Author(s)
Liu, Yeong-Ming Bill
Issue Date
1989
Department of Study
Civil and Environmental Engineering
Discipline
Environmental Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Civil Engineering
Environmental Sciences
Language
eng
Abstract
Biofilm models, developed by previous researchers, were incorporated with an equilibrium model to study the physical and chemical aspects of the anaerobic fixed-bed biofilm reactors. In order to investigate the mechanism of equilibrium in an anaerobic biofilm reactor, a non-equilibrium model was derived from the equilibrium model to simulate the gas transfer process involved in biogas production. The equilibrium model well described the behavior of anaerobic fixed-bed biofilm reactors, which was verified in the experimental results. The non-equilibrium model showed that the contact area between the gas and the liquid phases is the pivotal factor controlling the state of equilibrium. This condition can only exist where there is sufficient contact area.
Operation of three different anaerobic fixed-bed biofilm reactors has substantiated that a packing material with higher specific surface area can immobilize more microorganisms, thus resulting in better treatment efficiency. However, the shear stress caused by different material might reduce the amount of biofilm retained in the reactor. In addition, the characteristics of the material also affect the effectiveness of the reactor. For example, granular activated carbon is so light and dense that the abrasion between these particles offsets the advantage of its large surface area. Experimental results also show that all biofilms are close to fully-penetrated, which simplifies the biofilm model by disregarding the resistances of the liquid layer and biofilm. Anaerobic fixed-bed biofilm reactors, in reality, behave like suspended-growth reactors.
The out-diffusion of end products in anaerobic biofilms was simulated by a diffusional model. Prediction of this model suggests that the methane concentration at the rear of biofilms is a function of the substrate concentration in the bulk liquid. As a result, a high substrate concentration in the reactor causes the biogas build-up at the back of biofilms and, eventually, sloughing. It is therefore concluded that the effective way to restore an unbalanced biofilm reactor is to decrease the feed until the bulk substrate concentration has been reduced to a level that will not cause sloughing.
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