Biostimulation

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Biostimulation involves the modification of the environment to stimulate existing bacteria capable of bioremediation. This can be done by addition of various forms of limiting nutrients, such as phosphorus, nitrogen, or carbon (e.g. in the form of molasses). Additives are usually added to the subsurface through injection wells, although injection well technology for biostimulation purposes is still emerging. Removal of the contaminated material is also an option, albeit an expensive one. Biostimulation is an alternative to bioaugmentation.

The primary advantage of biostimulation is that bioremediation will be undertaken by already present native mocroorganisms that are well suited to the subsurface environment, and are well disributed spatially within the subsurface. The primary disadvantage is that the delivery of additives in a manner that allows the additives to be readily available to subsurface microorganisms is based on the local geology of the subsurface. Tight, impearmeable subsurface lithology (tight clays or other fine-grained material) make it difficult to spread additives throughout the affected area. Fractures in the subsurface create preferential pathways in the subsurface which additivies preferentially follow, preventing even distribution of additives.

Investigations to determine subsurface characteristics (such as natural groundwater velocity during ambient conditions, hydraulic conductivity of the subsurface, and lithology of the subsurface) are important in developing a successful biostimulation system. In addition, a pilot-scale study of the potential biostimulation system should be undertaken prior to full-scale design and implementation.