Is it Worth Investing in Manure Digesters?

Published on Wed, 05/11/2022 - 11:30am

Is it Worth Investing in Manure Digesters?

By Jaclyn Krymowski.

 As dairies and other livestock facilities continually advance, so are they investing to improve sustainability via management practices and technology. One of the newer and growing ways to do this is via biogas digestion with on-farm manure digesters. These systems are able to absorb the toxic gases emitted from manure and convert it into “clean energy” like heat, electric and biofuel. As an extra bonus, this is all done with less manure solids left over.

Right now, open lagoons are among the most common manure management system for dairies. However, with increasing environmental regulations and dairies expanding, many operators have outgrown their traditional lagoon sizes. In addition, lagoons also pose a risk to human health and the environment as biogases are released through manure decomposition.

Digesters eliminate this, sealing them in an airtight environment, to allow for full anaerobic (without air) digestion. The primary gases emitted in this process are carbon dioxide and methane.

According to Aaron Smith of the University of California-Davis (UCD) in an article The Dairy Cow Manure Goldrush, there are now 260 anaerobic digesters operating on America’s 40,000 dairy farms, up from 207 a year ago.
Moving on from traditions?

Lagoons have the perfect anaerobic environment to break down the organic waste, although almost 10% of methane emissions in the U.S. come from general manure management practices, according to Alice Rocha of UCD in an article. However, anaerobic digesters can mimic that ideal lagoon environment as it captures gas and greatly reduces total greenhouse gas output.

Perhaps most interesting is that the captured biogas can be converted into heat, electricity or a biofuel that can be used on-farm or even sold as a form of passive income. Additionally, the manure solids after the digestion process are easier to handle, less in volume, have decreased odor and are more nutrient dense.

With manure digesters becoming more popular, there are different sizes and systems that can fit a variety of operations. According to the EPA, the benefits in 2021 was 1.73 million megawhatts/hour equivalent of energy generated from all digesters in the U.S. all while avoiding 5.95 million metric tons of carbon dioxide equivalents in greenhouse gas emissions.

With their AgSTAR program, the EPA is actively working to promote digester systems specifically in livestock industries while helping farmers place them affordably.

The means of placing and utilizing digesters are certainly there – arguably more accessible than ever before. But before jumping in with such a huge investment, there is lots to evaluate in regard to a particular operation.

Digester benefits and considerations
Whenever there is an upgrade or change to any aspect of manure management, some of the primary concerns are about overhead equipment and building costs, as well as cost of maintenance and integration with the rest of the operation.

Before diving into how digesters can offset or increase income, operators should step back and evaluate it as any other manure management system. Essentially, that should start with considering the current system on the farm and what issues a digester might help resolve.

These include:
• Excessive odor which may be straining community relationships
• An increasing herd size with more manure than current storage can hold OR more than can be applied to fields or sold
• Difficulty meeting environmental regulations with current manure management
• Lack of nutrient quality in current manure solids
• High equipment and/or energy costs, especially associated with current manure management

Such issues or desired improvements in manure management are an excellent starting point for a farm wanting to incorporate a digester. Even if there are no major issues with the current manure handling and management system, a digester may still be a good edition.

However, it should never be looked at solely as an income generation technique. Rather, it should be a good fit for the dairy and other non-financial goals. (The AgSTAR program has some excellent reports on different dairies who implemented digesters that outline their experiences.

As with any system, digesters come with their own equipment, implementation and maintenance costs, especially upfront. But in the long-term these system usually end up easily paying for themselves and their maintenance.

The Minnesota Department of Agriculture cites many cost-savings and income-generating benefits including: lower electrical, natural gas and heating costs in addition to potentially selling any excess energy. Digesters also assist in reducing odor and harmful pathogens in manure while also creating an enhanced fertilizer that provides more readily available nitrogen for crops. These benefits from managing manure not only benefit the farmer and their operation, but also any surrounding landowners and the environment.

“A farmer considering the construction of a digester of this size can expect to invest from $18,000 to $30,000,” reads the Penn State Extension article Biogas from Manure, “depending on local prices, the labor the farmer contributes, and the choice of components included in the system.”

The possibility of grants and loans specifically available for farms pursuing digesters and renewable energy further enhance the affordability. And as they become more available – as almost all technology eventually does – manure digesters are expected to be a more commonplace sight on American dairies. But instead of just hot new tech, digesters should be considered with the same thought process as any other manure system as to their value on any one specific operation.