The potential of free-living ground water bacteria to degrade aromatic hydrocarbons and heterocyclic compounds

This study has documented that a considerable degradation potential related to aromatic hydrocarbons and aromatic nitrogen-, sulphur- and oxygen- containing compounds is associated with the free-living ground water bacteria. All studies were performed under aerobic conditions and with surplus of nitrogen and phosphorus.

After a lag period, which differs considerably between locations upstream and downstream of hydrocarbon spills, the free-living bacteria are able to degrade the hydrocarbons to concentrations less than 1 µg/l. The bacteria from one site were able to degrade naphthalene according to a zero order reaction even at 1 µg/l.

Preliminary experiments indicate that the free-living bacteria may have a relatively high activity compared to the attached bacteria when compared on the basis of the same total bacteria numbers.

The hypothesis is put forward that, although the attached biomass concentration in the aquifer may be much higher than the free-living biomass, the latter is still very important for the degradation capability if the attached bacteria are fixed in the fine soil fractions (silt, etc), the reason being that the flow of water, and with this the flux of substrate, is relatively small to the attached bacteria due to low hydraulic conductivity in the fine soil fractions.