TREATMENT OF TRICHLOROETHENE (TCE) WITH A FLUIDIZED-BED REACTOR
|J.R. Foeller, S.A. Vivek, S.Y. Leung, and R.L. Segar Jr., Department of Civil Engineering, University of Missouri-Columbia, Columbia, MO 652ll||
Fluidized-bed bioreactors (FBBRs) offer a promising alternative to existing treatment technologies for the treatment of water contaminated with chlorinated solvents. The objective of this research was to test a bench-scale FBBR for removal of trichloroethene (TCE) from ground water and to study the FBBR kinetic behavior so that field-scale reactors could be designed. Phenol was selected as the growth substrate for biofilm-forming microorganisms enriched from activated sludge because phenol induces enzymes capable of cometabolizing TCE and lesser chlorinated ethenes.
Experiments with the conventional, single-pass FBBR focused on TCE removal as effected by TCE loading, phenol loading, detention time, media type and pulsed phenol feeding techniques. Preliminary studies included fluidization studies with various filter sand types and grades, separate stage aeration studies with a downflow-bubble-contactor, conductivity tracer studies, TCE abiotic loss rate studies, and batch TCE degradation studies. Results of those studies are being used to develop basic designs for cometabolizing FBBRs.
Quartz filter sand (25/30 mesh) was selected as the attachment media for the first generation FBBR, which had dimensions of approximately 5 cm diameter and 100 cm of bed depth. Biomass concentrations of 2 l g/L were attained with a sand bed-volume fraction of l 5%. At a flow rate of 0.8 L/min, the TCE removal was governed by phenol loading rate and the proper level of phenol feeding was essential for obtaining high TCE removal. A phenol to TCE mass ratio of 50: l provided 70-80% removal of 0. l mg/L TCE at an empty bed contact time (EBCT) of 3 minutes. Phenol was not detected in the reactor effluent at those conditions. Excessive phenol feeding inhibited TCE removal, presumably due to enzyme competition.
Subsequent studies with TCE-amended ground water from a deep aquifer in Missouri further addressed means to improve TCE removal. The second generation FBBR had an increased length and used denser media (garnet). At a flow rate of l.0 L/min., the highest TCE removal obtained was 50% to 60%. Denser, thinner biofilms resulted from using the garnet media. By decreasing the amount of media in the reactor, thicker biofilms were formed and produced an increase in TCE removal.
Presently, the reactor is being operated with quartz sand and will be operated with ilmenite and hematite. Based on the results to date, the FBBR for TCE removal, when properly scaled to field conditions, will be a useful technology for bioremediation of ground water.
Key words: fluidized-bed, trichloroethene, phenol, biofilm, ground water remediation
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