Bioremediation – is a process used to treat contaminated media, including water, soil and soil material, by altering environmental conditions to stimulate the growth of microorganisms, to break down and degrade the target contaminants. In many cases, bioremediation is cheaper and more sustainable than other remediation alternatives. Biological remediation is a similar approach, used to treat waste, including sewage, industrial waste and solid waste. Most bioremediation processes involve oxidation-reduction reactions in which either an electron acceptor (usually oxygen) is added to stimulate the oxidation of a reduced pollutant (e.g. hydrocarbons) or an electron donor (usually an organic substrate) is added to reduce oxidized pollutants (nitrate perchlorate, oxidized metals, chlorinated solvents, explosives and fuels). In both approaches, additional nutrients can be added,vitamins, minerals and pH buffers to optimize the conditions for microorganisms. In some cases, specialized microbial cultures (bioaugmentation) are added to further improve biodegradation.