TRANSPORT AND BIODEGRADATION OF QUINOLINE IN HORIZONTALLY STRATIFIED POROUS-MEDIA

An experimental study of the movement and biodegradation of quinoline was conducted in a saturated, 2-layer system (1 m long) to identify pr ocesses that may result in increased microbial growth at hydraulic lay er interfaces. The system contained two layers of contrasting hydrauli c conductivity (1:12) and flow was parallel to layers. Tracer breakthr ough, used to quantify interlayer mass transfer, showed that the trans verse dispersivity was 0.3 cm near the interface and 0.036cm within th e low-conductivity (low-K) layer. Interlayer mass transfer resulted in arrival of substrate (quinoline) and oxygen 10's to 100's of hours so oner in the low-K layer near the interface compared to other locations within the low-K layer where substrates arrived via only advection. E arly arrival of substrates near the interface resulted in biodegradati on of quinoline for a longer period than within layers, yielding incre ased growth in a 1- to 3-cm-thick zone, as measured by plate counts. B ecause biodegradation was oxygen limited in this system, microbial gro wth at all locations was small [log(maximum increase) less-than-or-equ al-to 1.0] and measured porous-medium hydraulic properties (dispersion , hydraulic gradient) were not affected by the biomass production. Alt hough the thickness of the effected interface zone was small in this s ystem, the effect on the overall transport of quinoline was significan t; 19% of the growth (and corresponding degradation of substrates) in the low-K layer was in the relatively small interface zone. The effect of microbial biomass production at interfaces on overall solute movem ent is likely to be maximized in environments that have a high density of hydraulic or geochemical interfaces, particularly in settings wher e the interfaces serve as mixing zones between nutrient-limited waters .