Enhanced Biorestoration

FIGURE 13.7 Schematic cross sections of enhanced biorestoration of unconfined aquifers. 

Enhanced biorestoration is a means by which naturally occurring processes are deliberately manipulated to increase or enhance the rate of cleanup. Biological activity in the subsurface is controlled by the availability of one or more of the necessary metabolic requirements such as an electron acceptor or nutrient. Although electron acceptors are most often the limiting factor, inadequate availability of nitrogen, phosphorus, or micronutrients (such as potassium, copper, or even vitamins) can restrict optimum restoration. When the proper balance of these factors is established, the rate of chemical degradation is maximized. 

Enhanced biorestoration is thus the process of providing all the materials necessary for optimum degradation of the contaminant of concern. This process can include direct injection of air or nutrients, circulation of groundwater to distribute materials, addition of cometabolites (such as sugar) where additional sources of carbon and attached oxygen are needed, or injection of special inhibitors to limit precipitation of pore-plugging iron oxides. 

Trial and error is often the typical procedure that is used to implement enhanced biorestoration. In simple cases of gasoline cleanups, these may be appropriate however, when the chemicals involved are recalcitrant (difficult to degrade), toxic, or present in a complex geologic environment (i.e., low-permeability soil, lateral or vertical heterogeneities, etc.), enhanced biorestoration can be difficult, and risk assessment-type analyses may be more suited for a particular site. 

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