Anaerobic digesters offer a way to cut methane emissions from organic waste, but without strong regulation to protect water quality and prevent increased livestock production, their climate benefits could be lost.
HRWC supports the limited use of anaerobic digesters to process organic waste, but these facilities need to be tightly regulated by the Department of Environment, Great Lakes, and Energy (EGLE). Anaerobic digestors, when properly run, can reduce planet-warming methane emissions, an urgent need. But conflicts of interest, poor system design, or sloppy operations can degrade local water quality or even lead to increased greenhouse gas emissions overall.
More broadly, anaerobic digestors treat a symptom of an agricultural framework that prioritizes environmentally detrimental livestock production over growing less energy-intensive food supplies. Whenever possible, planet warming emissions should be reduced through sustainable agricultural policy and tighter regulation to avoid the need for anaerobic digestors.
Reducing Planet-Warming Emissions
Cows release methane when they burp and when their poop breaks down. Methane is an extremely potent planet-warming greenhouse gas. Over the first twenty years after its release, methane is more than 80 times more potent than carbon dioxide in terms of warming the climate system. Reducing methane emissions, by capturing it and burning it, is a way to reduce the overall pace of planet-warming emissions.
How They Work
Anaerobic digesters use bacteria to break down organic waste manure, sewage sludge, food waste, and other organic materials. Bacteria in a contained system eats the material producing methane-rich biogas. Similar to natural gas, biogas can be burned to produce energy. The byproducts, called digestate, have been widely reused in various applications, often as fertilizer.
To be clear, this does not mean that biodigesters eliminate planet-warming greenhouse gases. Marketing materials from companies looking to build biodigesters often oversell the benefits. Biodigesters take potent methane gas from cow waste and burn it, releasing less potent carbon dioxide. By most measures, this is a definite improvement, but they do still emit planet-warming gases that cause climate change.
Water Quality Harm
The digestor process concentrates nutrients like nitrogen and phosphorus that are overused in agricultural practice and impair waters in every part of the state. EGLE and federal experts have identified phosphorus in farm runoff as a primary cause of toxic algae blooms in Lake Erie, Saginaw Bay, and Lake Macatawa. Concentrating nutrients in digestate makes them more mobile when introduced in the environment and even more likely to reach waterways.
In more recent years, PFAS have been found in wastewater sludges applied to farm fields, contaminating crops and livestock. The digestion process can concentrate these toxic, “forever chemicals,” rendering them risky to discharge back into waterways and dangerous to apply to agricultural lands.
Strong Oversight Needed
Protections for the environment in agricultural areas near digesters can work, but it is also very common for large-scale industrial agriculture operations to disregard the health of the local environment when they know no one is looking. Big livestock operations often spread manure and digestate on cropland already saturated with phosphorus, or they apply manure and digestate on the frozen ground of winter when it serves no benefit, just to discharge it somewhere. Drainage and storage retention systems often fail without recourse. Negligence is widespread throughout the industry. Even many farming-dependent Midwestern states have cracked down on such unscrupulous practices. IN recent years, regulators in Michigan have been trying to catching up.
EGLE developed updated rules that were are arguably among the most protective in the country. They were immediately challenged by industry representatives. In 2024, the Michigan Supreme Court ruled that EGLE has authority to ensure that manure produced by Michigan’s industrial livestock and poultry operations do not pollute state waters. It was seen as a win for the environment, but industrial agriculture lobbyists and have continued to mount legal challenges and a steady onslaught from legislators in both major parties has ensued. Proposed bills have attempted to undermine EGLE’s authority, attempted to redefine the scientific meaning of “anaerobic,” and have tried to erode or defund environmental protections.
The Beef with Anaerobic Digesters
The real problem, and the reason there is a need for anaerobic digesters at all, is that we consume too much beef and dairy. Raising cattle is one of the most environmentally burdensome activities humans undertake. The planet-warming emissions associated with growing cows, keeping them in a milk-producing state or slaughtering them, then processing their beef and transporting it to our kitchen tables far exceeds the emissions associated with other food types.
They also dominate the landscape. A commonly cited analysis found that land used for raising cattle amounts to more than 1/3 of the land area in the continental United States.
Many scientists and environmental organizations have pointed out that anaerobic digesters can actually incentivize livestock production and cattle production specifically. In extreme cases, farmers can make a significant portion of their profits from the sale of manure to digester operators, pushing them to prioritize manure production over raising cattle efficiently. That can lead to a net increase in greenhouse gas emissions than if the digester had never been built in the first place, a result that is exactly the opposite of what digester advocates promise. Digesters should never have the effect of increasing manure production or increasing the heads of cattle raised. Incentives for livestock reduction should go hand-in-hand with strict oversight of digester operations.
In the immediate future, digesters have a role to play in addressing greenhouse gas emissions and repurposing organic waste. In the long-term, however, they may be prolonging inherently unsustainable activities. The real solution is to address the root cause of livestock-related emissions by reducing livestock consumption.
Rebecca Esselman, executive director, and David Lossing, government relations director, contributed to this post.