POTENTIAL BIOMASS LIMITATIONS ON RATES OF DEGRADATION OF MONOAROMATIC HYDROCARBONS BY INDIGENOUS MICROBES IN SUBSURFACE SOILS

The rates of biodegradation of benzene, toluene and xylene by indigenous microorganisms in a natural aquifer sand were investigated. Despite highly favorable nutrient and electron acceptor conditions, the onset of measurable microbial oxidation of these readily degraded compounds was observed to be delayed in systems containing small populations of microbes. The delays varied inversely with the initial of microbes capable of degrading a particular compound, suggesting the need for development of some critical population of microorganisms. In terms of the onset of oxygen consumption, xylene involved the longest critical population development period, consistent with the low comparative numbers of indigenous microbes found capable of degrading this compound.