Bioavailability: a main factor controlling biodegradation

Hauke Harms ,Swiss Federal Institute for Environmental Science and Technology (EAWAG), Ueberlandstrasse 133, CH-8600 Duebendorf

Bioremediation techniques are limited by the efficiency of biodegradation. Undesired phenomena which have been attributed to the insufficient bioavailability of the contaminants include (i) biodegradation rates which are much lower in the intact subsurface materials than in corresponding laboratory trials, (ii) the relative fast degradation of one fraction of the contaminant followed by the extremely slow degradation or stability of the remaining fraction, (iii) ageing of contaminations, i.e., the decreased degradability of old contaminations, and (iv) the reappearance of environmental chemicals in the soil water or groundwater after apparently successful remediation.

Many of these phenomena can be understood, when the living conditions of microorganisms in contaminated subsurface environments are considered (1). Since it can be assumed that microorganisms capable of degrading many high priority contaminants are principally ubiquitous in soils, aquifers, or sediments and able to increase their number upon degrading the contaminant, the availability of chemicals for microorganisms in subsurface environments reduces to a microscopic phenomenon. Experiments and model calculations will be presented that show that biodegradation rates are markedly affected by the unequal spatial distribution of microorganisms and hydrophobic chemicals in concert with unfavorable transport paths on the microscale. Furthermore, it will be shown, how the sensing systems of bacteria can be used to quantify bioavailable fractions of contaminants.

1. Harms, H., and T. N. P. Bosma. 1997. Mass transfer limitation of microbial growth and pollutant degradation. J. Ind. Microbiol. 18:97-105.