Pilot-Scale Demonstration of a Two-Stage Methanotrophic Bioreactor for Biodegradation of Trichloroethylene in Groundwater

Abstract

A two-stage methanotrophic bioreactor system was developed for remediation of water contaminated with TCE and other chlorinated, volatile, aliphatic hydrocarbons. The first stage of the reactor was a suspended-growth culture vessel using a bubbleless methane-transfer device. The second stage was a plug-flow bioreactor supplied with contaminated groundwater and cell suspension from the culture vessel. The test objectives were to determine the applicability of microbial culture conditions reported in the literature for continuous, pilot-scale TCE treatment; the technical feasibility of plug-flow bioreactor design for treatment of TCE; and the projected economic competitiveness of the technology considering the cost of methane for growth of methanotrophs. The methanotrophic organism used in the study was Methylosinus trichosporium OB3b. Information on system operation was obtained in bench tests prior to conducting the pilot tests. In bench- and pilot-scale tests, variability in the degree of TCE degradation and difficulty in maintaining the microbial culture activity led to short periods of satisfactory biotreatment. Further development of the microbial culture system will be required for long-term operation. During transient periods of high TCE degradation activity, the bioreactor concept proved feasible by exhibiting both a high degree of TCE biodegradation (typically about 90% at influent TCE concentrations of 0.5-4 ppm) and a close approximation to first-order reactor kinetics throughout the length of the reactor. Actual methane usage in the pilot-scale reactor resulted in projected methane costs of $0.33 per 1000 gallons of water treated. This cost theoretically would be reduced by system modifications. The theoretical minimum methane cost was approximately $0.05 per 1000 gallons.

NADH-Regulated Metabolic Model for Growth of Methylosinus trichosporium OB3b. Cometabolic Degradation of Trichloroethene and Optimization of Bioreactor System Performance

“…A better strategy is to use a two-step system, in which growth of the cells is separated from TCE conversion. Similar conclusions have been drawn previously by others (6,17,(29)(30)(31)(32), but primarily based on competitive inhibition considerations.…”

Trichloroethene degradation in a two-step system bymethylosinus trichosporium OB3b. Optimization of system performance: Use of formate and methane

“…Two-step systems demonstrated so far were either small (0.4-1.2 L) (Chang and Alvarez-Cohen, 1997;McFarland et al, 1992) or relatively complicated (Aziz et al, 1995;Tschantz et al, 1995) which may lead to scale-up problems. The only larger system (60 L) described by Dobbins et al (1995) could not be extensively evaluated as a result of culture instability. Moreover, to avoid stripping of the contaminants, in all of these systems the conversion reactor operated without a gas phase present.…”

Methanogenic and perchloroethylene-dechlorinating activity of anaerobic granular sludge

“…So far, it has not been possible to obtain evidence of any C2Cl4 biodegradation under aerobic conditions, although many reports have demonstrated the biodegradability of less-chlorinated ethylenes in the presence of oxygen by aerobic microorganisms (Alvarez-Cohen and McCarty 1991;Dobbins et al 1995;Fogel et al 1986;Nelson et al 1987;Oldenhuis et al 1991;Wilson and Wilson 1985). C2Cl4 is biodegradable by mixed cultures under anaerobic conditions (Bhatnagar et al 1992;DiStefano et al 1992;Smatlak et al 1996;Tandol et al 1994;Vogel and McCarty 1985;Wu et al 1993).…”