Injection Wells
One promising strategy to reduce nitrate pollution is to add a carbon source to stimulate denitrification. Frequently the electron donor necessary to reduce NO3- to N2 is missing from the environment. Hydrocarbons can easily serve as the electron donor for this process. Furthermore, microbe metabolism of hydrocarbons depletes oxygen to ensure that the anaerobic conditions necessary for denitrification are in place.
Soluble organic substrates like vegetable oil are easily added by injection wells. This is advantageous because it allows bioremediation to take place in situ. The wells also function to regulate the amount of carbon source added since too much could have adverse effects on soil quality.
The research by the USGS has shown that evenformate can be injected to bioremediate nitrate. The formate produces hydrogen gas (H2) and carbon dioxide (CO2) which provide an electron donor and carbon source, respectively, for the denitrifying bacteria. With this technique the only biproducts are innocuous water and nitrogen gas.
Injection wells can also be used to bioremediate metals. Adding a carbon source as a nutrient is also common in remediation of halogenated organic solvents.
Sources:
Hunter (1999); Smith (2001); Tartakovsky (2002, 2003)