Simultaneous modeling of competitive adsorption and dual substrate biodegradation in completely mixed GAC reactors
Traegner, Ulrich Karl
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https://hdl.handle.net/2142/21794
Description
Title
Simultaneous modeling of competitive adsorption and dual substrate biodegradation in completely mixed GAC reactors
Author(s)
Traegner, Ulrich Karl
Issue Date
1990
Doctoral Committee Chair(s)
Suidan, Makram T.
Department of Study
Civil and Environmental Engineering
Discipline
Civil Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Civil
Language
eng
Abstract
The fluidized-bed anaerobic GAC reactor, operating with GAC replacement, has been demonstrated to promote effective treatment of high strength industrial wastewaters which contain refractory and toxic chemicals that resist biodegradation and inhibit the fermentation of the biodegradable constituents of a wastewater.
The objective of this study was, to develop a mathematical model, capable of predicting the steady-state and transient performance of three fluidized-bed anaerobic GAC reactors treating synthetic wastewaters consisting of the readily biodegradable acetate, the biodegradable, adsorbable, but self-inhibitory phenol, and the non-biodegradable, inhibitory but adsorbable o-cresol. These reactors were operated with different GAC mean solids residence times, varying from 8 days to 60 days.
Special features of the activated carbon mixed-culture biofilm model include: diffusional mass transport across a concentration boundary layer and within the biofilm, and the distinction between two microbial species, namely the phenol and the acetate utilizing microorganisms, which compete for attachment surface and spatial occupation within the limited space of the biofilm. Transport of phenol and o-cresol within the GAC particle was modeled using competitive adsorption and the homogeneous surface diffusion model. The model furthermore incorporated the effects of inhibition of phenol degradation by o-cresol, and biomass loss by shearing.
Equilibrium and kinetic parameters in this model were obtained from independent isotherm and closed batch adsorption experiments. Biokinetic constants were determined from closed batch experiments using fermenter effluent as a source for microorganisms.
The model predictions were in good agreement with the experimental data for the full range of operational conditions of the anaerobic reactors. In this study it was found that the overall first-order shear loss coefficient can not be assumed constant, but varies with the degree of biomass coverage of the carbon particles. This finding was supported by experimental results of biological activity measurements on the active biomass. Since no a priori distribution was assigned for the two microbial species present in the biofilm, the composition within the biofilm changed for each steady-state of operation. The non-uniform species distribution of the microorganisms resulted in preferential shearing of one microbial group over another. This differential shear was verified experimentally.
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