Treatment of inhibitory wastewaters using expanded-bed anaerobic GAC reactors
Nakhla, Girgis Fouad
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https://hdl.handle.net/2142/21102
Description
Title
Treatment of inhibitory wastewaters using expanded-bed anaerobic GAC reactors
Author(s)
Nakhla, Girgis Fouad
Issue Date
1989
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, Chemical
Engineering, Civil
Language
eng
Abstract
The expanded-bed anaerobic GAC reactor, operating with GAC replacement, was demonstrated to effectively treat wastewaters which contain toxic chemicals that resist biodegradation and inhibit the utilization of the biodegradable constituents of the wastewater.
The objectives of the study were to investigate the effect of the GAC replacement rate on the process performance, evaluate the impact of the organic loading and hydraulic retention time (HRT) on the treatment efficiency, and to develop a predictive model for the process. A synthetic wastewater consisting of acetate, phenol and o-cresol, as model compounds of pollutants that exhibit different types of behavior in the anaerobic reactor with respect to biodegradability, adsorbability on GAC and inhibition, was used for the purposes of this study. GAC replacement rates of 25, 37.5, 50, 75, 100, and 150 g/d were employed in this study.
The anaerobic GAC reactors were operated in a wide range of GAC mean residence times and very high organic removal efficiencies due to adsorption on GAC and biodegradation were observed at the different GAC mean residence times investigated in this study. Adsorption and biodegradation complemented each other as removal mechanism in this reactor with a dominance of biodegradation at high residence times and appreciable contributions from adsorption at low GAC residence times. A technique to measure the shear loss coefficients of the microbial populations present in the system was developed. The shear loss coefficients for the acetate and phenol utilizing organisms were found to differ appreciably. The findings of the study demonstrated the importance of biomass shear loss as a phenomenon that can impact the performance of the anaerobic GAC reactor significantly, particularly at low GAC mean residence times.
A steady-state model that includes representations of the various interactions that occur within the anaerobic reactor such as adsorption and biodegradation was developed and tested against experimental data. The model incorporated the effects of inhibition of phenol degradation by o-cresol, biomass loss by shearing, the competition for adsorption between phenol and o-cresol, and the effect of GAC mean residence time on the adsorptive capacity of GAC. Using independently-determined adsorption parameters, the measured shear loss coefficients, and literature values for the kinetic parameters that describe acetate and phenol biodegradation, the developed model was used to predict the reactor's performance. The experimental data were in good agreement with the model predictions.
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