Spatial disorder and degradation kinetics in intrinsic biodegradation schemes

The restoration of contaminated soils by intrinsic biodegradation employs m icroorganisms in the subsurface that degrade the contaminant substrate infi ltrating the subsurface matrix. The outcome of intrinsic biodegradation has been difficult to predict. We examine a source of the difficulty with a co mputational model of diffusive-reactive transport that introduces spatial d isorder in the arrangement of the degrading microorganisms. Spatial disorde r alone, even on the small scales that characterize the distance between ag gregates of microorganisms, is enough to induce a wide range of times to co mplete the degradation to an arbitrary limit. The mean time for the concent ration to achieve the limit becomes twice that for the case of spatial orde r. Bounds on the range of the effective degradation kinetics can be obtaine d by computing the distribution of times to complete degradation.