Bacteria, methane and biodegradable plastics
The importance of methane in global warming
Methane is a potent greenhouse gas, even more effective than carbon dioxide in its capacity to trap heat in the Earth’s atmosphere. The gas can originate from lakes and swamps, natural-gas pipelines, deep-sea vents, livestock, and is produced as a component of biogas by anaerobic digestion facilities.
The global levels of methane, along with the levels of other greenhouses gases, such as carbon dioxide and nitrous oxide, have been rapidly increasing over the last century.
NASA-led study solves a methane puzzle, 2018
Problems with non-biodegradable plastics
Most plastics, such as polyethylene, and polypropylene, are not biodegradable. This means that they accumulate in the environment causing many problems with the pollution of land and the oceans.
Plastic waste prevention system analysis & applications, 2018
These combined problems of global warming, and the need to replace non-biodegradable plastics, make the technologies capable of converting methane into biodegradable plastics very attractive options. One such method is to use bacteria to convert methane into a biodegradable polymer - PHA.
Making biodegradable plastics from methane using bacteria
Polyhydroxyalkanoates (PHA) are a group of biodegradable biopolymers produced naturally as minute globules within some types of bacteria under nutritional stress such as excess carbon and reduced nitrogen.
The globules can represent up to 90% of the bacteria's dry weight. The mechanical properties of PHAs are useful, in that they can be modified, they are biodegradable, and their production does not depend on petroleum-based feedstocks. The main type of PHA produced by bacteria is polyhydroxybutyrate (PHB). Over 300 strains of bacteria have been identified as being able to produce PHB.
Mango Materials, 2018
Typically, the bacteria producing PHAs are grown with sugars as the carbon source. This can represent up to 40% of the production costs. To reduce these costs, several waste streams have been trialled as a carbon source, including whey waste, sugar industry waste, agricultural crop waste and glycerol. Such systems normally require an expensive sterilisation stage.
Methane, from landfills, natural gas, and as a component of biogas produced by anaerobic digestion facilities, has been demonstrated to be an energy-rich feedstock and a much cheaper alternative to the above materials.