A study opens up the possibility of converting greenhouse methane into fish food. The report, published in Nature Sustainability and driven by researchers at Stanford University, explains that the production costs associated with methane captured from certain sources in the US are lower than the market price of conventional fishmeal.
The study reveals that methane, a powerful greenhouse gas, can be captured and transformed into sustainable, protein-rich feed for farmed fish. The new analysis highlights potential cost reductions that could make the approach cost-effective using other methane sources and capable of meeting the entire global demand for fishmeal.
“Industrial sources in the U.S. are emitting a truly staggering amount of methane, which is uneconomical to capture and use with current applications,” said study lead author Sahar El Abbadi, who conducted the research as a graduate student in civil and environmental engineering.
As the researcher explains, the feed used by fish farming is based in many cases on fishmeal produced thanks to extractive fishing. “Our goal is to flip that paradigm, using biotechnology to create a high-value product,” added El Abbadi, who is now a lecturer in the Civic, Liberal and Global Education program at Stanford.
“Although carbon dioxide is becoming increasingly abundant in the atmosphere, the global warming potential of methane is approximately 85 times greater over a 20-year period.”
Methane also threatens air quality by increasing the concentration of tropospheric ozone, exposure to which causes approximately one million premature deaths annually worldwide due to respiratory disease.
The relative concentration of methane has grown more than twice as fast as that of carbon dioxide since the beginning of the Industrial Revolution due in large part to man-made emissions.
Cultivation in a refrigerated bioreactor
One possible solution lies in methane-consuming bacteria called methanotrophs. These bacteria can be grown in a refrigerated bioreactor filled with water fed with pressurized methane, oxygen and nutrients such as nitrogen, phosphorus and trace elements. The resulting protein-rich biomass can be used as fishmeal in aquaculture feeds, offsetting the demand for fishmeal made from small fish or plant-based feeds that require land, water and fertilizer.
“While some companies are already doing this with piped natural gas as a feedstock, a preferable feedstock would be methane emitted from large landfills, wastewater treatment plants, and oil and gas facilities,” study co-author Craig Criddle, professor of Civil and Environmental Sciences at Stanford’s School of Engineering, explained in a statement.
“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 challenge for aquaculture activity is growing as global demand for aquatic animals, plants and algae grows. A comprehensive review of the sector led by researchers at Stanford and other institutions sees it likely to double by 2050.
The important cost of electricity
To clarify the approach’s potential to meet demand profitably, the Stanford researchers modeled scenarios in which methane is sourced from relatively large wastewater treatment plants, landfills, and oil and gas facilities, as well as natural gas purchased from the commercial natural gas grid. Their analysis looked at a range of variables, including the cost of electricity and labor availability.
In the scenarios involving methane captured from landfills and oil and gas facilities, the analysis found methanotrophic fishmeal production costs – $1,546 and $1,531 per ton, respectively – were lower than the 10-year average market price of $1,600.
For the scenario in which methane was captured from wastewater treatment plants, production costs were slightly higher – $1,645 per ton – than the average market price of fishmeal. The scenario in which methane was purchased from the commercial grid led to the most expensive fishmeal production costs – $1,783 per ton – due to the cost of purchasing natural gas.
“For every scenario, electricity was the largest expense, accounting for over 45 percent of total cost on average.”
In states such as Mississippi and Texas with low electricity prices, production costs came down over 20 percent, making it possible to produce fishmeal from methane for $1,214 per ton, or $386 less per ton than conventional fishmeal production.
Electricity costs could be reduced further, the researchers say, by designing reactors that better transfer heat to require less cooling, and switching electric-powered applications to those powered by so-called stranded gas that would otherwise be wasted or unused, which can also reduce reliance on grid electricity for remote locations.
In scenarios involving methane from wastewater treatment plants, the wastewater itself could be used to provide nitrogen and phosphorus, as well as cooling.
If efficiencies like these could bring down the production cost for a methanotroph-based fishmeal by 20 percent, the process could profitably supply total global demand for fishmeal with methane captured in the U.S. alone, according to the study.
“Similarly, the process could replace soybean and animal feeds if further cost reductions were achieved.”
“Despite decades of trying, the energy industry has had trouble finding a good use for stranded natural gas,” said study co-author Evan David Sherwin, a postdoctoral researcher in energy resources engineering at Stanford, in a press communicate from Stanford University. “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.”
It’s important to say that the study was funded by the Stanford Center for Innovation in Global Health and the Stanford Natural Gas Initiative.