Methane gas is a major contributor to global warming, accounting for approximately ten percent of all greenhouse gas emissions. There are many man-made sources of methane gas, including agriculture and mining, but a major source is food waste decomposition in landfills. Recently, the city of Madison commissioned a study to consider a facility that would take food waste and convert it into natural gas, or methane. It’s called an anaerobic digester. Alder Tag Evers, who is one of the sponsors of the study, says the project is inspired by sustainability concerns.
“Those of us elected officials across the region who are concerned about climate change want to make sure that we are doing all that we can to recover methane gas, because methane gas is a greater contributor to climate change.”
The city of Madison has been working to address food waste for a while now, attempting to use a local manure digester, and having food scrap drop-off sites. Stacie Reece is Madison’s Sustainability Program Coordinator. She says food waste still takes up significant space in the local landfill.
“A recent waste analysis of Dane County landfills is that about 20% of what we send to Dane County landfill is food waste,” says Reece.
Reece says that an anaerobic digester is a unique opportunity to work toward carbon neutrality and more sustainable solutions. It would convert food waste into methane. And the parts that don’t get converted are turned into fertilizer. Any small amounts left over from the process would go to a landfill.
“Being that you can convert it into a transportation fuel, and then even on the back end of that you can take that food waste digestate from a digestor and can turn that into compost material for soil amendment…So instead of burying resources we can re-input those resources back into what we do,” she says.
Dane County installed a natural gas injection pad at the landfill last year. That’s a mechanism that converts gasses generated by the landfill into a commercially viable fuel source. And that existing infrastructure makes an anaerobic food digester – and the possibility of selling methane generated by local food waste – a more viable project.
And so, working in collaboration with Dane County, and funded by a grant from the EPA, the city of Madison commissioned consultants to research the feasibility of an anaerobic digester near the current Madison landfill.
Those consultants, of Iowa-based renewable energy company Eco Engineers, selected Yahara Hills Golf Course, located across from the Dane County landfill, as a potential site for the digester. A separate Madison committee studying the future of Madison’s golf courses – which, have operated at a loss for two decades – is considering closing half of the 36 holes at Yahara Hills, which needs significant investment to continue operating.
The EcoEngineers study found that the digester would cost the city about 20 million dollars to implement, and that it would break even when processing about 18 thousand tons of food waste per year. Currently municipal waste in Madison collects only about 10 thousand tons of food waste, so the project would be dependent on other entities like restaurants, grocery stores, and schools, or even other municipalities. Reece says that next steps for the project include reaching out to these institutions and securing their buy-in.
“To get to a certain level, we need a lot more food scraps than just 10,000 tons, so this should be a regional approach, this shouldn’t just be a city of Madison approach.”
Reece adds that University of Wisconsin-Madison and the city of Middleton supported the feasibility study.
If built, the anaerobic digester would send the natural gas it produces through the ANR Pipeline Company, which operates pipelines from the Great Lakes region to Texas and Oklahoma.
But most of the money would not come from natural gas sales. Instead, it would come from renewable fuel credit markets in individual states, most notably in California, which has a strong renewable credit market.
In these markets, carbon producers buy green energy credits to offset their carbon production. That means carbon producers based mostly in California would buy green energy credits from Madison. And Madison’s sale of those green energy credits would likely account for more than half of the digester’s revenue.
The common council has not decided if it is going to move forward with the project, last week referring the project back to the Sustainable Madison Committee for more research.
Meanwhile, the committee is still determining if there is enough local food waste to make an anaerobic digester viable. If the project does move forward, construction could start as soon as next year.
Image courtesy Eco Engineers report.