Captured methane can be turned into plenty of fish food

30 November 2021

Photo: Pixabay/Kanenori

Methane is a far more potent greenhouse gas than carbon dioxide and we emit plenty of methane worldwide through agricultural and industrial processess. A team of scientists, though, has a solution to what to do with at least some of all that excess methane: turn it into food for fish.

After we capture methane from landfills, wastewater treatment plants or gas facilities, methanotrophic bacteria can turn the gas into protein-rich biomass that can then be used as fishmeal. “In the rapidly growing aquaculture industry, methanotrophic additives have a favourable amino acid profile and can offset ocean-caught fishmeal, reducing demands on over-harvested fisheries,” the scientists explain in a study.

The process of converting methane into fishmeal can be scaled up to industrial levels whereby we can at once mitigate climate change and improve food security, say the scientists at Stanford University who have mapped out various scenarios for doing just that.

“Despite decades of trying, the energy industry has had trouble finding a good use for stranded natural gas,” notes Evan David Sherwin, a postdoctoral researcher in energy resources engineering at Stanford. “Once we started looking at the energy and food systems together, it became clear that we could solve at least two longstanding problems at once.”

One problem is that of overfishing, which has caused wild fish stocks to become badly depleted over the past decades so that today fish farms provide about half of all the animal-sourced seafood consumed worldwide.

Meanwhile, the effects of methane on the climate after the gas’s release is around 85 times greater than those of CO2 over a 20-year period. Methane can also worsen air quality by increasing tropospheric ozone in the atmosphere, which causes 1 million premature deaths each year owing to respiratory illnesses.

However, a type of bacteria called methanotrophs can be cultivated in special bioreactors and fed pressurized methane, oxygen and nutrients such as nitrogen, phosphorous and trace metals. “The protein-rich biomass that results can be used as fishmeal in aquaculture feed, offsetting demand for fishmeal made from small fish or plant-based feeds that require land, water and fertilizer,” the scientists explain.

“While some companies are doing this already with pipeline natural gas as feedstock, a preferable feedstock would be methane emitted at large landfills, wastewater treatment plants and oil and gas facilities,” says Craig Criddle, a professor of civil and environmental engineering in Stanford’s School of Engineering.

“This would result in multiple benefits, including lower levels of a potent greenhouse gas in the atmosphere, more stable ecosystems and positive financial outcomes,” the scientist adds

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