A NOVEL METHOD FOR INVESTIGATING BIODEGRADATION PROCESSES AT THE FRINGE OF A CONTAMINANT PLUME IN POROUS MEDIA

摘要

A novel non-invasive imaging technique was developed to investigate the biodegradation processes occurring at the fringe of a simulated contaminant plume. In conditions where the supply of electron acceptors is limited, biodegradation may be expected to be focused at the plume fringe and transverse dispersion will play a very important role. The technique permitted investigation of the mixing process of dissolved oxygen with the plume in a two dimensional porous media at laboratory scale. A small transparent aquifer (160 mm length, 130 mm width and 3 mm thickness) was made up of quartz plates and quartz sand (60 -100 micrometers). Potassium acetate was used as a substrate and was continuously injected into the aquifer to form a plume. Ruthenium (II)-dichlorotris(1,10-phenanthroline) (Ru(phen)_3Cl_2), a water soluble fluorescent dye which can be quenched by dissolved oxygen, was used as an indicator of dissolved oxygen concentration in the porous media. Under UV light (450 nm), Ru(phen)_3~(2+) can be excited and emits fluorescence (590-600 nm). The intensity of the fluorescence is dependent on the ambient concentration of oxygen. The oxygen distribution within the model aquifer was interpreted from images recorded by a CCD (Charged Coupled Device) camera. The laboratory experiments show that at the core of the plume, oxygen was exhausted by the biodegradation processes and at the fringe, oxygen was supplied only by transverse mixing.