Microorganisms need to take in nutrients from their environment to grow and divide. The microbes metabolize these nutrients, which means that the substances the microbe takes in are broken up and the microbe excretes different substances. In bioremediation, the substances they excrete are less harmful than the original pollutant. Basically, the microbes eat the pollution and clean up the area.
Microorganisms perform bioremediation in one of three ways. Sometimes the microbes in a polluted area adapt to the pollution naturally and break it down as part of their food source or adapt to the toxins enough to survive and convert the pollution into substances that are harmless to the microbes and to other forms of life. This natural system is called natural attenuation. If the microbes won't break down the pollutant naturally, addition of nutrients may stimulate bioremediation. This process is bio-stimulation. Lastly, humans can artificially add a new microbial population to an area to deal with the pollutant. This is known as bio-augmentation.
Some microbes can break down petroleum products and the byproducts of petroleum that are carcinogenic. This can work for groundwater contamination or marine oil spills. Bacteria can also remove heavy metals from the environment such as mercury. One bacterium, Geobacter sulfurreducens takes in radioactive uranium from water and stores it so the uranium is easily collectable, says the Saint Louis Science Center (SLSC). Other bacteria can break down solvents and chlorinated substances. Certain pesticides are also edible to bioremediation microbes, according to the SLSC, especially when added nutrients are present to boost the rate of metabolism.
Although some species of microbes naturally have the capability to break down pollutants, some other microbes for bioremediation use are genetically modified to artificially give the microbe those abilities.
Microorganisms are relatively cheap to produce and use compared with other pollution control measures. Landfill is reduced as the contaminated soil does not need to be removed and no materials are used to soak or collect the pollutant. The microbes self-replicate, and their use tends to be more environmentally friendly with fewer side effects than other control methods.
Microorganisms in bioremediation may take several years to completely clean the polluted area. Even after the cleanup is complete, the microorganisms themselves may need to be harvested to remove pollutants such as stored uranium. Climate can also play a role in the efficiency of the process, as the applied microbes may be washed away or killed through drought.