Project Abstract

Trichloroethene (TCE) Cometabolism in Fluidized-Bed Bioreactors

Principal Investigator

R.L. Segar Jr.
University of Missouri
E-mail: SegarR@missouri.edu

Goal

The goal of this project is to develop a bench-scale, fluidized-bed bioreactor (FBBR) to degrade TCE in extracted groundwater. This study of FBBRs is expected to yield the high performance necessary for pilot or field testing.

Rationale

Our knowledge of organic contaminant biodegradation has advanced from fundamental biochemical/microbiological studies to a stage of active treatment process development. Trichloroethene (TCE), once considered to be nonbiodegradable, can be cometabolized by microorganisms with oxygenase enzymes. The phenol-degrading organisms selected for this work readily form cohesive biofilms, which is a prerequisite for their use in biofilm reactors such as the fluidized-bed bioreactor (FBBR). Development of FBBRs for cometabolizing trace contaminants in extracted groundwater is attractive because they are compact, relatively simple to operate, and their use is widespread in several industries. Biological oxidation of TCE should be less costly than advanced chemical oxidation techniques that use combinations of ultraviolet light, ozone, and hydrogen peroxide. Ongoing research with bioreactors continues to yield improvements in performance as better operating strategies and configurations are tested. Studies with FBBRs, which will be conducted under this project, are expected to yield the high performance necessary for pilot or field testing.

Approach

A mixed-culture of phenol-utilizing microorganisms enriched from domestic wastewater will be grown on sand to form bioparticles in a bench-scale FBBR. Reactor inlet conditions will be varied and TCE removal will be measured. Concentrations of phenol, oxygen, and TCE will be determined at various points in the reactor to select inlet conditions or design variations that improve TCE removal. Several sizes and types of sand will be evaluated to increase biomass holdup and control biomass thickness. Facilitating spatial sequencing of bioparticles between growth and degradation zones will be an important factor in designing high performance FBBRs. High and low dispersion conditions in the reactor will be obtained by modifying the reactor inlet distributor. Periodic pulsing of phenol will be used in some experiments to increase TCE removal by temporal sequencing of substrates. A draft tube reactor will allow greater control over internal sequencing (via circulation) of bioparticles between phenol and TCE degradation. Performance of this innovative reactor type will be characterized in the same manner as the conventional type of FBBR.

Status

All controllable operational problems related to the bioreactor have been solved. Investigators have completed and evaluated abiotic TCE loss rates, oxygen delivery, and dechlorination effectiveness of the new reactor configuration and feed system. Work has also included the characterization of the phenol growth period for fresh and reused 30/35 garnet sand to determine the duration of the start-up and regrowth period, start-up procedures and substrate requirements, and the resulting biomass. Conductivity tracer test data has also been obtained, completed, and evaluated for the 1995 FBBR experiments, including the effect of effluent recirculation on TCE removal and quantification of detention times and dispersion numbers for representative experiments. Investigators have completed and tested a numerical biofilm reactor simulation model for cometabolism. Time-course TCE feeding experiments have been completed for evaluating TCE removal with 30/35 garnet and for verification of variable phenol loading effects observed in prior experiments. Work has also included development of a technique for in-bed sampling of bioparticles and water, which resulted in obtaining phenol and biomass profiles within the bed. Dominant microorganisms in the reactor effluent have been identified. In batch studies, the abiotic reaction rate of various reactor sands with TCE and PCE under oxic and anoxic conditions was assessed. Future plans include design, fabrication, and troubleshooting of a dual-chamber reactor, as well as reactor operation and measurement removal. This project is in its third year.

Clients/Users

This project will be of interest to other researchers, U.S. Department of Defense, and others.

Keywords

Trichloroethene, cometabolism, fluidized-bed bioreactors, chlorinated solvents, water.