Converting Food Waste into Energy Through Anaerobic Digestion, with Brett Reinford

Climate Break

If you’ve ever been near a farm with livestock, you might agree that farm odors can be carried far from the farm itself. Farms often face criticism from nearby residents over the offensive odor of manure. While manure is an unavoidable part of raising livestock, there is one technological innovation that can remove the smell from manure. Anaerobic digesters are a simple concept—instead of leaving manure rotting outside, the digester encloses the manure as bacteria decompose it, keeping the odor in. But could the same technology also deal with food waste and cut carbon emissions?

How do Anaerobic Digesters work?

Anaerobic Digesters leverage the biology of decomposition to turn organic waste including manure and food scraps into useful products. The digestion process starts with pumping the waste into the digester, an enclosed tank containing microorganisms in the absence of air, hence the term anaerobic. In this digestor, a diverse community of different bacterial types ferment and feed off the waste in tandem with each other.

First, bacterial hydrolysis breaks down large complex molecules like cellulose and carbohydrates into simpler forms that other bacteria can use. Acidogenic bacteria produce carbon dioxide, hydrogen, ammonia, and volatile fatty acids that are converted into acetic acid by acetogenic bacteria. Finally methanogenic bacteria take in these products to release methane and carbon dioxide. At the end of the process, the disgestor is left with biogas including methane and carbon dioxide, leftover solids called solid digestate, and leftover liquids called liquid digestate. Owners of digesters can aid these bacterial processes by adding water, heat, and supplemental nutrients, minerals, and pH buffers to keep the right conditions for fermentation.

A farmer wanting to install anaerobic digesters will need to choose between many different forms of digesters that can suit different farm types. A major consideration is the solid content of the input waste, also called feedstock, which affects how difficult it is to mix and to heat, both of which keep fermentation going. If the feedstock is more solid and difficult to mix, then it must be either diluted with water which requires more heat, or used with a digester that can handle more solid material, usually with less mixing. While the decision to install a digestor is a complex one, farmers can enjoy numerous benefits from having one on the farm.

Why Choose a Digester?

An anaerobic digester can be a source of money from the sale of its valuable products. In addition to trapping odor, digesters also hold biogas, and the deodorized end products, called digestate, all of which can be sold. Solid digestate can be repurposed as bedding for livestock or nutrient-rich soil material. Liquid digestate can be used around the farm as a fertilizer for crops. Biogas is a versatile alternative fuel that can be purified and used for cooking and heating, condensed and used for vehicle fuel, or burned and used as electricity. These products can bring in extra profit for farmers, and even before the digestion takes place, grocery stores and other companies that produce food waste will pay farmers to digest their waste.

In addition to the economic incentives to digesters, they are also a climate solution. When food and manure decompose outside or in landfills, they release large quantities of methane into the air. Methane is an extremely potent greenhouse gas, and though it stays in the atmosphere for a shorter amount of time than carbon dioxide, it traps so much heat that it is 80 times as potent as CO2 over a 20 year period. If methane is captured and burned instead, it turns into CO2, a much less potent greenhouse gas. In this way, burning methane trapped from digesters still releases greenhouse gasses, but these glasses lead to much less warming compared to letting the methane escape into the atmosphere. In addition, burning biogas for energy production gives us a naturally occurring and renewable source of energy, which can help make up for energy demands from switching away from fossil fuels. Biogas can be a promising waste management, energy and climate change solution.

Digester Drawbacks

Though digesters can provide many benefits to farmers and serve as a valuable climate solution, there are great controversies over promoting them. Dairy farms are often located near environmental justice (EJ) communities, which are disproportionately impacted by pollution and often home to people of color and low income. These communities face the brunt of impacts from dairy farms, including respiratory issues, poor water quality, and air pollution from burning biogas. Funding dairy farms for producing biogas from manure could extend the lifetimes of dairy farms, prolonging these negative impacts. Industrial agriculture has been criticized for its high environmental impact, and because large industrial farms have the capital to install digesters, opponents argue that funding biogas will benefit industrial farms over small farms. These myriad environmental issues raise questions about if funding biogas made from digesters will lead to more harm to human health in already vulnerable communities. This debate reveals how complex the web of stakeholders in digesters really is, and that presenting biogas as a “silver bullet” oversimplifies the considerations that go into policies around anaerobic digesters.

The Future of Digesters

If digesters are so beneficial for farmers, why aren’t digesters common practice on farms? One of the biggest barriers is that digesters are extremely expensive to install, and can take a while to pay back for their costs. According to the EPA, a typical anaerobic digester on the farm costs about $1.2 million, and this number varies based on the size of the farm and type of digester. However, there are many avenues for farmers to get funding to be able to afford this technology. The USDA and EPA manage lists of funders and other resources that farmers can refer to. Federal policies also provide assistance with funding, including the recent Inflation Reduction Act, which offers tax reductions for investing in biogas. According to Brett Rienford, who manages a dairy farm with a digester, one key policy yet to be ruled on that could favor biogas producers is the EPA’s proposed policy for eRINs (credits produced when qualifying biogas is used to generate renewable electricity).

The eRIN policy has to do with tradable credits that are generated by creating or using renewable fuels. Under the EPA’s current Renewable Fuel Standard, these credits, called RINs or Renewable Identification Numbers, are generated by liquid biofuel producers. The proposed addition to the standard would allow producers of electric vehicles to generate electric RINs, or eRINs, if they purchased electricity made from biogas. The biogas industry lobbied against this, stating instead that the biogas producers themselves should generate eRINs that they can then sell, similar to liquid biofuel producers under the current rule. Because of this debate, the EPA has deferred a decision till a later date. If modified, the policy could greatly benefit biogas producers and bring in extra income for farmers with digesters. Regardless of the outcome, this policy reveals the complex stakeholders invested in policies surrounding biogas, and the acknowledgement of biogas as a major source of renewable energy.

About the guest

Brett Reinford is a manager and second generation dairy farmer at Reinford Farms. He helped shift the farm to using an anaerobic digester for manure, and the farm has since expanded to providing solutions for food waste from grocery stores. Reinford Farms is a leader in terms of on-farm anaerobic digesters, and Reinford advocates for the adoption of digesters on farms. Reinford holds a bachelor's degree in business management from Colorado Christian University.

Further Reading

• Reinford Farms: How We Make Power
• EPA: How Does Anaerobic Digestion Work?
• American Biogas Council: Digester Biology and Types
• EPA: Anaerobic System Design and Technology

Resources

• Environmental and Energy Study Institute: Biogas Fact Sheet
• EPA: Inflation Reduction Act Biogas Provisions
• EPA: Digester Project Planning and Financing
• Climate Solutions Law: Proposed eRIN Rules
• EP: Understanding Global Warming Potential
• MIT: Natural Gas Contribution to Climate Change

For a transcript of this episode, please visit https://climatebreak.org/converting-food-waste-into-energy-through-anaerobic-digestion-with-brett-reinford/