Using microbes to convert CO₂ to natural gas

Biogas is mostly methane, but it contains about 40 percent CO2, which is typically vented to the atmosphere.

Lawrence Livermore National Laboratory (LLNL), in collaboration with Southern California Gas Co. and Stanford University, are using microbes to convert carbon dioxide directly to renewable natural gas.

The U.S. Department of Energy recently awarded the power-to-gas project $800,000. SoCalGas will provide co-funding of $400,000 in addition to $125,000 of seed funding it provided in 2017.

Using microbes to convert carbon dioxide directly to methane using renewable electricity is known as microbial electromethanogenesis (ME). ME more easily stores excess renewable electricity, significantly reducing the cost of producing renewable natural gas, increasing renewable natural gas availability and reducing carbon dioxide emissions.

The research will leverage past research by Stanford’s Spormann Laboratory on microbes that create methane, as well as advances in 3Dprinted carbon aerogel electrode materials made by LLNL, which will be assessed for their viability as reactor materials. Biogas will be supplied by Delta Diablo, an Antioch, California wastewater treatment plant. Raw biogas is mostly methane, but also contains about 30 to 40 percent carbon dioxide, which is typically vented to the atmosphere in a biogas production facility.

“Through this project we intend to devise scalable, efficient prototype reactors that enable both economical upgrading of biogas and storage of renewable electricity as methane,” said LLNL chemist Sarah Baker. “To do this, we will leverage recent advances in materials synthesis and manufacturing to fabricate reactors tailored to the requirements of the microbes and the overall process.”

The research is part of SoCalGas’ development of technologies known as power-to-gas (P2G), which stores excess renewable electricity in gas form rather than in batteries. Power-to-gas has two distinct advantages over storing renewable energy in batteries: nearly unlimited amounts of electricity can be easily stored for very long periods of time, and it can be stored and used with existing infrastructure.

“This technology has the potential to cut the cost of processing biogas to make pipeline-quality renewable natural gas while producing nearly twice the amount of this easily stored renewable energy and reducing carbon dioxide emissions,” said Yuri Freedman, SoCalGas senior director of business development. “It could make a big difference for small-scale biogas producers like dairy farms and feedlots, which collectively make up the majority of California’s renewable natural gas potential.”

Between 3,300 and 7,800 gigawatt-hours of excess solar and wind energy will be curtailed in California by 2025 due to time-of-day supply/demand mismatch, according to a recent Lawrence Berkley National Lab study. If that excess solar and wind energy were converted to methane and stored as renewable natural gas, it would provide enough renewable energy to heat 158,000 to 370,000 homes or provide renewable electricity to 80,000 to 187,000 homes.

Capturing methane and carbon dioxide from farms, wastewater treatment plants and landfills and then delivering it through existing pipelines is a cost-effective option to reduce greenhouse gas emissions. A recent analysis found that California could achieve the same greenhouse gas reductions as electrifying buildings at a much lower cost by replacing just a fraction of the natural gas delivered through pipelines with renewable natural gas.

The University of California, Davis estimates that the natural gas needs of around 2.4 million California homes could be fueled with renewable natural gas derived from the state’s existing organic waste. Already, 60 percent of the fuel used in natural gas vehicles in California is renewable, and SoCalGas expects that to increase to 90 percent by 2019.

Technological advances like power-to-gas and renewable natural gas can reduce greenhouse gas emissions while providing energy resiliency and meeting consumers’ fuel preferences. Across Southern California, people prefer natural gas 4 to 1 over electricity because it is more affordable and reliable, and more than 90 percent of residents use natural gas for space and water heating.

The research will be conducted at both LLNL and Stanford University beginning around Aug. 15 and is expected to be complete by late 2020.

Source: Lawrence Livermore National Laboratory, press release, 2018-08-06.