Biotechnology for in situ restoration of ground water contaminated by the petroleum industry.

As a result of increasing incidents of ground water contamination, several methods to restore polluted aquifers have been developed. These include 1) physical containment, 2) hydrodynamic controls, 3) withdrawal and treatment, 4) in situ physical and chemical treatment, and 5) in situ biological treatment. The fifth technology, in situ biological treatment (in situ biorestoration), is an innovative technique which involves the use of the indigenous subsurface microflora to degrade ground water pollutants. The most important factor in successful application of the process is the presence of metabolically appropriate microorganisms in a perfusable aquifer. As a result of the high levels of carbonaceous material contaminating the subsurface as petroleum waste, nutrients such as oxygen, phosphorus, and nitrogen are often limiting. Stimulation of the microflora is therefore achieved by perfusing the aquifer with the limiting nutrients; the nutrients must be transported to the zone of contamination to be effective. Aquifers with high clay contents and low permeabilities are not good candidates for in situ biorestoration systems nor other treatment strategies which involve plume management using well systems. In conclusion, in situ biorestoration is an innovative technique that can be used to remediate contaminated aquifers which are permeable and contain a metabolically active microflora; in contrast to other remedial methods, the contamination can be completely destroyed rather than transferred to another part of the environment.