The Technical Research Centre of Finland (VTT) has developed a solution for converting even small sources of methane-rich biogas into raw materials for animal feed or bioplastic on farms, landfills and wastewater treatment plants. This emission-reducing solution is based on the ability of methanotrophic bacteria to grow on methane in gas fermenters.

Methane-rich biogas is generated on farms, landfills and wastewater treatment plants in anaerobic digestion of biological material. Until now, the processing of such gas into biomethane has been viable only on large biogas-producing sites; small biogas sources such as farms have remained largely unexploited, VTT said.

The method developed by VTT would reduce emissions, increase the use of biogas and improve protein self-sufficiency.

It is based on the ability of methanotrophic bacteria to grow in aerobic conditions in gas fermenters, using methane as the source for carbon and energy. The process is as follows: The methane gas generated by anaerobic digestion is fed into a gas fermenter. A growth medium containing the methanotrophic bacteria circulates through the pipes of the gas fermenter, creating a single-cell protein biomass with a protein content of around 60%. The cell mass is filtered, pasteurized and dried.

The methanotrophic bacteria and, depending on the growth conditions, cell mass may also contain polyhydroxybutyrate (PHB) plastic — a natural substance in the cells that enables them to store conserve energy. For example, PHB can be used as a raw material for biodegradable packaging material, instead of oil-based and non-biodegradable plastics such as polypropylene.

The cell mass may contain 50% of the PHB, in which case, the protein content is around 30%. Extraction is used to separate the PHB and protein fractions from the dried cell mass.

The production rate of the method needs to be improved, VTT said, adding that a couple of years of development work still lie ahead. In addition, the protein fraction's suitability as a feed component needs to be tested.

Based on previous studies, single-cell proteins produced using microorganisms can be substituted for ingredients such as meat meals, soybean meal, egg whites or fish in food and feed.

In Europe and Finland, attempts are being made to meet the challenge of protein feed for domesticated animals by improving protein self-sufficiency. This mainly involves promoting the production of vegetable protein. The production of single-cell proteins represents a good opportunity to improve protein self-sufficiency.