Feasibility testing for the on-site bioremediation of organic wastes by native microbial consortia

Abstract

Microbial consortia capable of degrading chlorinated hydrocarbons and organic solvents may exist in many contaminated sediments. These native microbial communities with the capability to bioremediate toxicants on-site may prove to be a resource during remediation efforts. For this study, microbial consortia capable of degrading trichloroethylene (TCE) and mixtures of chlorinated and aromatic toxicants were enriched from contaminated sediments and the feasibility of their participation in on-site bioremediation was examined. Batch studies were used to monitor changes in the microbial community structure by monitoring signature fatty acid biomarker trends during TCE degradation. Experimental bioreactors, which utilized sand as a support matrix for the microbial community, were constructed to study TCE and organic mixed waste degradation. In continuously recycled expanded-bed bioreactors and a single-pass packed-bed reactor, mixtures of organic wastes were degraded including: benzene, xylene, toluene, tetrachloroethylene, trichloroethylene, dichloroethylenes and vinyl chloride. Degradation proceeded to >99% depletion for many contaminants. Bioreactors were stable over an 18-month period of operation while using propane or methane plus propane as energy sources and oxygen as the electron acceptor. Biodegradation was most efficient when the bioreactors were pulsed-fed, maintaing the consortia in suboptimal conditions. For the single-pass packed-bed reactor, metabolic efficiencies of 20–70 μmol substrate per μmol TCE degraded were observed for pulse-feeding regimes while continuous substrate availability experiments required >180 μ mol substrate per μmol TCE. Continuous feeding experiments utilizing mixtures of organic wastes showed metabolic efficiencies of 83–240 μmol substrate utilization per μmol total organic wastes degraded. These results demonstrated efficient and simultaneous degradation of organic solvents and chlorinated hydrocarbons by environmentally derived microorganisms in laboratory reactors.