Facilitated Degradation

Dissolved organic macromolecules have been found to facilitate the transport of hydrophobic organic compounds in the soil. The facilitated transport increases the speed with which toxic and carcinogenic compounds reach the ground water drinking supply. The bacterial degradation of hydrophobic pollutants attached to the dissolved organic macromolecules is unknown. A better understanding is crucial for assessing the importance of the facilitated transport concept for drinking water quality.

The degradation of C-14 labelled hexachlorobenzene (HCB) in a saturated soil, with and without 500 mg Blue Dextran/l (BD, model macromolecule) was measured by the amount of radioactive carbon dioxide produced. The soil was contained in stainless steel columns which were purged continuously with sterile air. The lag phase was much shorter in the columns with BD and at the end of the experiment all BD was consumed.

In a current batch study with HCB-adapted bacteria the possibility of differentiating between degradation of HCB free in solution and HCB associated with the macromolecule is examined by evaluating three different mathematical models.

Model 1 assumes only HCB free in solution is degraded, only by bacteria in solution.

Model 2 assumes only HCB associated to BD is degraded, only by associated bacteria.

Model 3 assumes associated HCB is degraded by associated bacteria and HCB free in solution is degraded in solution.