Doctoral Dissertations

Date of Award

5-1993

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Chemical Engineering

Major Professor

Paul R. Bienkowski, Tommy J. Phelps

Committee Members

Gary S. Sayler, Terrence L. Donaldson

Abstract

This study investigated the feasibility of utilizing native microbial consortia for the on-site bioremediation of trichlorethylene and other chlorinated organic groundwater contaminants. Experimental bioreactors, including a single-pass packed-bed reactor, a differential volume reactor system and a recirculating expanded-bed reactor, were constructed and used to study TCE and mixed-organic waste degradation. A mathematical simulation was developed to describe the fate of TCE in packed-bed soil systems. Additional batch studies were used to monitor toxicant degradation, and the changes in the microbial community structure by monitoring signature fatty acid biomarker trends during TCE degradation. Pure and multi-species microbial consortia and bioluminescent reporter technology were used in both reactor and batch studies to increase the fundamental understanding of the microbial fortuitous metabolism of TCE (and metabolites) and the biodegradation of the BTEX compounds (benzene, toluene, xylene, and ethyl benzene).

Significant data were obtained from the construction of a 1.9 L single- pass horizontal packed-bed reactor using sand as a solid support substratum for a TCE-degrading consortia. With inlet TCE concentrations ranging from 1 to 2 mg/L, and 1.9 to 3.2 days residence time, effluent concentrations of 5 to 10 µg/L were obtained, which approach drinking water quality standards. Pulse feeding regimes were typically necessary for the TCE effluent concentrations to be less than 10 µg/L. Introducing mixed organic wastes into the system showed an increased recalcitrance of TCE as the complexity of the mixture increased, with first order TCE degradation rate constants varying from 0.20 with TCE the only toxicant present to 0.16 when there were 12 organic wastes in the system.

Data from the differential volume reactor system verified the increased recalcitrance of TCE when experiments were conducted with mixed organic wastes. The reactor also provided a rapid and effective tool for abiotically determining dispersion and mass-transfer coefficients. Mass-transfer coefficients were found to decrease as the diameter of the particles in the bed increased. Such variables are critical for describing flow characteristics in packed-bed soil or sand systems.

The mathematical simulation developed describes transport properties such as dispersion, advection, and sorption. It describes the fortuitous metabolism process and the microbial cometabolic degradative properties of TCE in packed-bed reactors. The simulation portrayed the ability to correlate reactor TCE effluent concentrations in mixed organic-waste systems very accurately. The largest error observed when comparing experimental to simulation results was~9%. A parameter sensitivity analysis performed on the simulation showed the variables Peclet Number (Pe), the donor V saturation constant (KSD) and the electron donor concentration (Co) to have a large effect on simulation predictions.

Successful on-site or in-situ bioremediation is often limited by the scarcity of internal biodegradation markers and the inability to rapidly assess catabolic gene expression. Preliminary results are presented addressing the feasibility of using bioluminescent reporter technology to provide continuous information on microbial biodegradation activity. To correlate microbial activity and/or inducer concentration with bioluminescence, batch studies, expanded-bed bioreactor and differential volume reactor experiments were conducted using bacteria containing the lux gene cassette. The results indicate that engineered bacteria containing the lux gene cassette show promise as a continuous monitor of the biodegradation process.

This study endeavors to increase the fundamental understanding of the microbial fortuitous metabolism of TCE and the biodegradation of the BTEX compounds, utilizing microbial consortia. Through the complementary methodologies demonstrated in this report, integrated bioremediation techniques could be realized that remediate mixed-organic wastes on-site rather than first transferring the toxicants from one environment to another.

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