PILOT-SCALE DEMONSTRATION OF A 2-STAGE METHANOTROPHIC BIOREACTOR FOR BIODEGRADATION OF TRICHLOROETHYLENE IN GROUNDWATER

A two-stage methanotrophic bioreactor system was developed for remedia tion of water contaminated with TCE and other chlorinated, volatile, a liphatic 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 gro undwater and cell suspension from the culture vessel. The test objecti ves were to determine the applicability of microbial culture condition s reported in the literature for continuous, pilot-scale TCE treatment ; the technical feasibility of plug-now bioreactor design for treatmen t of TCE; and the projected economic competitiveness of the technology considering the cost of methane for growth of methanotrophs. The meth anotrophic organism used in the study was Methylosinus trichosporium O B3b. Information on system operation was obtained in bench tests prior to conducting the pilot tests. In bench- and pilot-scale tests, varia bility in the degree of TCE degradation and difficulty in maintaining the microbial culture activity led to short periods of satisfactory bi otreatment. Further development of the microbial culture system will b e required for long-term operation. During transient periods of high T CE degradation activity, the bioreactor concept proved feasible by exh ibiting 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 t heoretically would be reduced by system modifications. The theoretical minimum methane cost was approximately $0.05 per 1000 gallons.