Assessment of microbial pollutant degradation during seepage processes< Back

Elimination of environmental pollutants during transport through unsaturated soil layers is essential to protect groundwater resources. For many environmental pollutants, the subsurface represents a buffer system retaining the contaminants, with pollutant retardation being a function of organic carbon content and lithology. However, if pollutants continuously accumulate, thresholds for storage and buffering finally will be exceeded and sudden contaminant release can occur. Microbial degradation results in pollutant elimination and restoration of the buffer capacity. Understanding and quantifying biodegradation in the subsurface is a prerequisite for the application of transport models and assessing the environmental risk of contaminated materials deposition.

To assess the fluxes of pollutants, a sufficient understanding of sorption and biodegradation processes is required. It is the objective of our study to examine the effect of biodegradation on pollutant transport in unsaturated soil. In first experiments, phenanthrene was chosen as a hydrophobic model compound. Biodegradation and sorption was studied for varying flow regimes (i) in two soil types, and (ii) with the original soil microflora and after additional inoculation of adapted microorganisms.

The results demonstrate the important role of microbial adaptation, biomass, and physiological status on biodegradation kinetics. Pollutant biodegradation under unsaturated conditions is not only a function of influent concentration and hydraulic retention time, but also of the mass and physiological state of the microflora. Constant average flow rates seem not to be suitable to represent field conditions. Different scenarios with varying flow rates, but also with varying frequencies of low and heavy rain, have to be considered to model pollutant elimination during transport in unsaturated soil.