Biodegradation of Ethylene Glycol in Simulated Subsurface Environments

Ethylene glycol is regularly used as an industrial solvent and in vehicular anti-freeze and de-icing compounds. Significant quantities of it are released into treatment streams and onto land. The aim of this study was to establish rates of biodegradation of ethylene glycol in simulated subsurface environments. The utilization of ethylene glycol as substrate by microorganisms naturally occurring in soil and groundwater was monitored over time while substrate concentration, soil type, temperature and nutrient level were varied. Batch studies at 100 and 1000-ppm ethylene glycol demonstrated that increasing substrate concentration decreased the rate of its biotransformation as the first-order kinetic rate constant decreased from 1.01 to 0.95 days⁻¹. Further increase in initial concentration to 10,000-ppm resulted in minimal substrate disappearance from solution which was likely due to oxygen limitation. Studies with two different soils under identical environmental conditions and substrate concentrations indicated soil type had a clear effect on biodegradation rate. Lowering the temperature from 25° to 10°C for a given soil retarded the degradation rate by a factor of 2.44, but at each temperature greater than 99% removal was achieved in less than 7 days. Removal of nutritional amendments from the microbial population had only a slight impact on biotransformation rate. Unamended microcosms still exhibited nearly complete ethylene glycol transformation in 3 days as compared to 2 days for amended microcosms. Groundwater served as a satisfactory bacterial inoculum and generated a rate constant only slightly lower (0.76 days⁻¹) than that found for the soils. All results were comparable to those found by others for the biotransformation of linear alkylbenzene sulfonates (LAS) or of ethylene glycol by activated sludge.