This group brings together the best thinkers on energy and climate. Join us for smart, insightful posts and conversations about where the energy industry is and where it is going.

Roger Arnold's picture
Director, Silverthorn Institute

Roger Arnold is a former software engineer and systems architect. He studied physics, math, and chemistry at Michigan State University's Honors College. After graduation, he worked in...

  • Member since 2018
  • 1,084 items added with 147,546 views
  • Jun 27, 2021

The sources of the CO2 are interesting: production of ethanol and scrubbing of CO2 from biogas anaerobic digesters of dairy cow manure for RNG. I was also surprised by the scale of the project revenue cited in the article. The figure was $500 million of revenue per year from sequestration of 2 million tons of CO2. That would correspond to $250 per metric ton of CO2. Both the IRS 45Q tax credit rules and the California LCFS rules are complex, but I don't think they total up to anywhere close to $250 per ton of CO2. Either it's an error in reporting, or there's a lot of leveraging going on. 

Matt Chester's picture
Matt Chester on Jun 27, 2021

biogas anaerobic digesters of dairy cow manure for RNG

I wonder what the entire environmental footprint looks like for this vs. creation of fertilizer? Or is fertilizer one of the byproducts of this process (I'm admittedly no agricultural expert!)

Roger Arnold's picture
Roger Arnold on Jun 27, 2021

Fertilizer is definitely a byproduct of anaerobic waste digesters. "Fertilizers" are nitrates, phosphates, and potassium (NPK). Anaerobic digestion releases carbon dioxide and methane from the waste biomass, while leaving its NPK content behind in a wet solution. Biogas as it comes from the digester is combustible, but its high CO2 content precludes selling it as natural gas. The big thing that Aemetis is doing is building a network of small pipelines to transport raw biogas from dairies to a central scrubbing facility where most of the CO2 content is removed. The scrubbed product meets specs and can be sold as RNG.

The nutrient-rich liquid from the digesters can be (and usually is?) applied locally to fields and pastures on the farms where it's produced. It's sufficient to sustain plant growth there, but I believe it's too bulky and low grade to be sold commercially.

Roger Arnold's picture
Thank Roger for the Post!
Energy Central contributors share their experience and insights for the benefit of other Members (like you). Please show them your appreciation by leaving a comment, 'liking' this post, or following this Member.
More posts from this member

Get Published - Build a Following

The Energy Central Power Industry Network is based on one core idea - power industry professionals helping each other and advancing the industry by sharing and learning from each other.

If you have an experience or insight to share or have learned something from a conference or seminar, your peers and colleagues on Energy Central want to hear about it. It's also easy to share a link to an article you've liked or an industry resource that you think would be helpful.

                 Learn more about posting on Energy Central »