Anaerobic Digesters
Anaerobic digesters take farm waste and turn it into something valuable: renewable energy, reduced emissions, and improved nutrient management.
Poop Can Be Power đź’©
Hey, we got your attention! Now let us explain. Anaerobic digesters take manure, grasses, and sometimes other ingredients (called feedstock) and turn them into renewable gas. It happens through a process called anaerobic digestion. This can have several environmental benefits including renewable resources, reduced greenhouse gas emissions, and even nutrient loss reduction when prairie and cover crops are used as feedstock.
How it Works
Feedstock is transformed into biogas, digestate, and natural gas
Feedstock
The process starts with the collection of “feedstock” (ingredients) for the digester. This might include livestock manure and grasses. Like composting, the right combinations are important.
Digestion to Biogas
The digester uses time, temperature, pH levels, and microbes to break down feedstocks to produce biogas. Biogas is not the final product. It can’t be used until it’s treated to become natural gas.
Digestate
A byproduct of digestion is the liquid and solid that remain – called “digestate”. The liquid is a quality natural fertilizer and can be stored in lagoons until the appropriate time to apply. The solids can be used as animal bedding.
Renewable Natural Gas
Meanwhile, biogas is cleaned and purified to become renewable natural gas. At this point, it’s either used on-site by the farmer for energy, or connected to a pipeline for others to use as energy.
Learn more about anaerobic digestion from ISU Extension.
Myth vs Fact
Biogas, renewable gas, and fossil fuels
Myth or fact? biogas is the final product of digestion.
Myth
Biogas is not the final product. It’s the raw gas produced by anaerobic digestion and is about 60% methane and 40% carbon dioxide. Biogas has to be cleaned and purified to become renewable natural gas, which is 98% methane. Meanwhile, fossil fuels are not renewable and are formed beneath the Earth’s surface.
Did You Know?
After manure is digested, the solids that remain can be used to make biodegradable planters for your garden and home. “CowPots” were created by a dairy farmer looking to improve sustainability!
Digesters that use prairie and cover crops as feedstock are a multi-systems approach. Not only do you get renewable energy, but you get the soil health and nutrient loss reduction benefits of prairie and cover crops!
More Resources
Iowa State University Extension’s Air Management Practices Assessment Tool (AMPAT) provides an in-depth look at anaerobic digestion as a strategy within storage and handling.
Iowa State University Extension’s “What is Anaerobic Digestion?” publication is a free downloadable 2-page PDF published in November, 2023 and provides an accurate but brief summary of the anaerobic digestion process.
Iowa State University Extension’s “Anaerobic Digesters for Renewable Natural Gas” publication is a free, two-page infographic-style PDF published in March 2923 explains how on-farm anaerobic digesters function, outlines common feedstocks, and identifies key components of a digester system.
American Biogas Council’s “Why Biogas?” page highlights the multifaceted benefits of biogas systems, outlining how they serve as critical tools for sustainable waste management and clean energy production.