ENHANCED IN-SITU BIODEGRADATION OF DIESEL FUEL BY CYCLIC VERTICAL WATER-TABLE MOVEMENT - PRELIMINARY STUDIES

Bioremediation normally employs injection of a nutrient solution and an oxygen source into the contaminated zone. The success of the process depends in part on effective transport of the injected substances through the contaminated zone. Field experiences have shown that the transport is limited by the permeability of the subsurface geologic materials and by the stability of the oxygen source. Vertical movement of the water table can serve to alternately expose the bacteria in the contaminated zone to moisture (when the water table is up) and air (when the water table is down and the pores hold some air) while the organic substrate is available from a continuous layer atop the water table or residuals in the unsaturated zone. The cyclic manipulation of the water table may be accomplished by injection and production of water or air in the contaminated zone. In this paper the results of preliminary laboratory experiments dealing with diesel fuel degradation are presented. A mixed culture of diesel-degrading bacteria was isolated from a soil sample contaminated with bunker oil. Soil columns were used to study the effects of interface movement on the biodegradation of diesel fuel. The bacterial consortium was used to inoculate the soil columns prior to addition of the diesel fuel. After 9 weeks of exposure, with an interface movement cycle period of 48 hours, the effects of the water table manipulation on the amount of diesel fuel degraded were compared to those of an appropriate control with no water table movement. The columns subjected to water table movement had 15% less residual diesel than the static controls after 9 weeks.