Module Three 13.6 What other useful substances can we make using microorganisms?
Microorganisms can be grown in large vessels called fermenters to produce useful products such as antibiotics.
Microbes can be used by industry to mass produce certain important chemicals. Some of these, like antibiotics are used in medicine to treat patients. Microbes are very efficient and produce less waste than chemical means. Often a product cannot be made any other way.
A typical fermenter:
The vessel itself is made from stainless steel which does not corrode or affect the microbes and fermentation products. It can also be easily cleaned.
· air is bubbled through so that the microbes can respire aerobically.
· the gas outlet releases carbon dioxide to avoid build up of pressure.
· a water jacket surrounding the fermenter maintains an optimum temperature so the proteins do not become denatured.
· temperature, pH and oxygen probes are linked to a computer which monitors the conditions inside the vessel - so they allow the optimal rate of growth.
· paddle stirrers ensure that the microbes, nutrients and oxygen are well mixed and distributes the heat evenly.
The product is run off from the bottom. It is separated from the microbes and purified so that it can be sold or distributed.
There are a number of different chemicals which can be made using microbes in fermenters:
- The antibiotic, penicillin, is made by growing the mould Penicillium, in a fermenter. The medium contains sugar and other nutrients eg a source of nitrogen. The Penicillium only starts to make penicillin after using up most of the nutrients for growth.
Growing Micro-organisms in Fermenters - The fungus Fusarium is used to make mycoprotein, a protein-rich food suitable for vegetarians. The fungus is grown on starch in aerobic conditions and the biomass is harvested and purified.
- Vinegar is made by converting ethanol into ethanoic (ascetic) acid using microbes. Ethanol, microbes and oxygen are mixed in a fermenter. Wood shavings are added to increase the surface for the fermentation by the microbes.
- Alcohol can be made from cane sugar waste and yeast. The resulting ethanol is often mixed with petrol to create Gasohol, a cheap fuel for cars.
A simplified version of the fermenter can be used to create natural gas for use as a fuel. Household or farm waste is put in the fermenter. Anaerobic bacteria produce methane as the waste is broken down.
What is Biogas?
Biogas is a renewable alternative fuel, which is produced by breaking down organic matter by a process of microbiological activity. Basically this means that rotting municipal waste, food waste or sewage (both human and animal) is turned into gas by means of "anaerobic conversion" in a digester. Organic matter such as sugarbeet and maize can be grown specifically for biogas production.
The process of anaerobic conversion is what occurs naturally at the bottom of ponds and gives rise to marsh gas (or methane).
Methane is the main component of natural gas. Biogas is then processed to the same specifications as natural gas and fed into the piped network (like green electricity is co-distributed).
Biofuels