Anaerobic Digestion

Overview

Anaerobic digestion systems convey raw or pre-treated manure into a gas tight vessel, either daily or more frequently, typically operating at 38°C. In this vessel, naturally occurring microbes work to break down organic material, such as manure solids, into energy-rich biogas. It is recommended to consider implementing anaerobic digestion on the farm to reap the benefits of biogas production either as electricity or renewable natural gas (RNG).
Reference: NRCS Practice Standard: Anaerobic Digester (366)

Environmental Impact

• Reduced GHG emissions
• Improved air and water quality
• Reduced solids accumulation in waste storage ponds
• Improved nutrient utilization
• Net energy production
• Renewable electrical energy production
• Reduced pathogens

Greenhouse Gas Reduction

Estimated Cost

Scenario Unit: Number

Scenario Typical Size: 1 system

Total Cost/Unit: $1.97M

Reference: NRCS Practice Standard and Scenario: CPS 366 Anaerobic Digester Scenario #1 – Anaerobic Digester: https://www.nrcs.usda.gov/sites/default/files/2024-11/fy25-wa-scenarios.pdf, p. 403.

Financial Considerations

Cost Savings: Anaerobic digestion has the potential to power various operations on the farm, if not the entire farm, reducing costs associated with energy and electric supply. Additionally, some of the produced gas, or heat produced by an engine-generator set as part of the digester is used to heat the digester, making it a net energy production system.

Additional Revenue: Excess energy produced from anaerobic digestion that is not utilized on the farm, whether it be electricity or RNG can be sold to the grid.

Carbon Credit Potential: Anaerobic digestion systems can qualify for carbon credits, as it directly mitigates emissions by capturing the biogas from animal manure to be used for energy production.

Timeline

Midterm

Dependency / Prerequisite

Prerequisites:

• To construct an anaerobic digester, a feasibility study should be conducted, create a design and plan, secure funding, obtain the necessary permits, and evaluate existing facilities for any needed modifications. Consulting an agricultural engineer is essential as the design of the digester and gas components must be in accordance with standard engineering practice for handling a flammable, toxic, and potentially explosive gas.
• Installation of an anaerobic digester must be included as a component of an agricultural waste management system plan.
• It is important to recognize that through anaerobic digestion, a portion of nutrients are converted from organic to inorganic. Meaning, more nutrients are available for immediate uptake by crops and nutrient management plans should be updated to reduce the potential for water quality concerns.
• Pre-treatment to remove bedding sand is necessary if the farm uses sand-bedded stalls.
• Pre-treatment may be used to remove excess moisture in manure, especially with influent from barns where flush systems are used.