Individual species of
microorganism have different optimal conditions in which they grow and replicate most rapidly.There is a specific
range around that optimum in which a specie is able to survive. Factors such as the
pH, temperature,
osmotic pressure (often caused by
salinity) all contribute to the optimal condition of all microorganisms. For example, in terms of pressure, some species are able to survive in
extremophile conditions such as extreme radiation, temperature, salinity or pressure.
Piezophile microorganisms have their optimal growth condition at a pressure equal to or above 10 megapascals (99
atm; 1,500
psi). Some bacteria and archaea have adapted to life in the deep oceans, where the pressure (
Hydrostatic pressure) is much higher than at sea level. For example, the methane-producing archaea species
Methanocaldococcus,
Methanothermococcus,
Methanopyrus and
Methanotorris have been found in
hydrothermal vents in the ocean floor. Research at the
University of Groningen (RUG) has shown that the bacterial community is affected by pressure from composition changes. This makes it possible to influence the
anaerobic digestion process.A further development of this technique is the addition of
hydrogen gas to the reactor. According to
Henry's law, this gas also dissolves more at increased pressure. The result is that it can be better absorbed by bacteria and archea. In turn, it converts the hydrogen gas with the already dissolved carbon dioxide into additional methane. This combination of techniques was described in detail by Kim et all in 2021, known to be a process called
biological methanation. On
Michael Liebreich's hydrogen ladder 5.0, this form of biogas upgrading is at step C. This is considerably higher than applications as fuel in vehicles. These are spread over steps D to G. Although the technique is usually used as a fermentation process for thick liquid flows and solid biomass, it can also be applied as anaerobic
Wastewater treatment. In South Korea, they have succeeded in operating a
UASB reactor (a form of anaerobic wastewater treatment) at 8 Bar. A biogas was then created with a methane content of 96.7%. A remarkable finding was that the grains in the sludge that are so similar in characteristic of the UASB technique were well preserved. This was because more
Extracellular polymeric substance (EPS) was formed in the
biofilm. Microorganisms make these to protect themselves against difficult conditions, in this case the extreme pressure. ==See also==