On-site biological remediation of contaminated groundwater: a review.

On-site biological treatment has been used for groundwater cleanup from industrial and agricultural chemicals. The pump-and-treat efficiency is controlled by retardation of contaminants by sorption onto the saturated subsurface solids and by the presence of non-aqueous-phase liquids in the aquifer. On-site bioreactors have been widely used for treatment of contaminants such as petroleum hydrocarbons, monoaromatic hydrocarbons, chlorinated aliphatics and aromatics. The most commonly used reactor types for groundwater include the following: trickling filter, upflow fixed-film reactor and fluidized bed reactor. Bioreactor processes have limitations mainly because of their design to operate at elevated temperatures and thereby by high operational costs.