Enhanced degradation of monoaromatic hydrocarbons in sandy aquifer materials by microbial inoculation using biologically active carbon reactors.

Abstract

A technique using biologically active carbon reactors for seeding the subsurface with adapted microbes was proposed and tested to enhance the degradation of monoaromatic hydrocarbons in aquifer materials. Biodegradation experiments with indigenous and adapted microorganisms from a non-contaminated aquifer solids and sorption studies under abiotic conditions were developed to determine the reasons for the lag phase prior to the onset of biodegradation. It was concluded that enhanced rates of degradation could be obtained when the number of adapted microbes seeded to the soil matrix was increased above 10$\sp5$ cells/g of soil. Under these conditions, immediate degradation of benzene, toluene and xylene (added as single carbon sources) was observed at concentrations ranging from 25 $\mu$g/l to 9 mg/l. The use of BAC adsorbers was demonstrated to be an efficient technique for growth, acclimation, and enrichment of adapted microbes for subsequent inoculation into sandy aquifer materials. Empty bed BAC reactor contact times of less than one minute were sufficient for microorganisms to degrade BTX compounds and to produce a continuous mass of adapted microbes in effluent streams for inoculation. A lag period preceding onset of measurable biodegradation of the monoaromatic hydrocarbons was observed in batch and column experiments. This lag period varied according to the initial number of adapted microbes present, suggesting that this phase was primarily dependent on the presence of an initial biomass of microorganisms significant enough to accomplish measurable degradation of the target compound. The Monod-with-growth model adequately described the aerobic degradation of BTX compounds for concentrations ranging from 25 $\mu$g/l to 3.5 mg/l. The bioremediation model used to simulate column experiments under oxygen limiting conditions described the data well. The model agreed with the laboratory estimations that the number of xylene degraders originally present in Kalkaska, MI solids was approximately one order of magnitude smaller than the number of benzene degraders.