Due to their potential to reduce greenhouse gas emissions and generate valuable and renewable biogas energy, anaerobic digesters are a topic of growing interest within the agricultural sector.

To ensure that agricultural facilities with anaerobic digesters operate in an environmentally responsible manner, the Nebraska Department of Environment and Energy (NDEE) regulates and permits agricultural facilities with digesters in the state.

Anaerobic digestion is the natural process in which microorganisms break down organic matter, like manure, in the absence of oxygen. Anaerobic digesters can also be referred to as “biodigesters” or simply “digesters.”

According to the EPA, manure-based anaerobic digestion systems were responsible for reducing CO2 equivalent emissions by 6.23 million metric tons in 2021.

EPA statistics also indicate that manure-based digesters generated approximately 1.76 million megawatt-hours (MWh) of energy from biogas in 2021. According to data from the U.S. Energy Information Administration, that’s enough energy to power approximately 166,000 average American homes for a year.

Digesters can also minimize odors, reduce pathogens, and reduce solid wastes, according to EPA.

All agricultural digesters in Nebraska are required by NDEE to meet the same design specifications as digesters employed in wastewater facilities that are regulated under Title 123 – Rules and Regulations For The Design, Operation And Maintenance of Wastewater Works.

NDEE evaluates every permit application from agricultural facilities with digesters to determine if the proposed digester requires a permit under Title 119- Rules and Regulations Pertaining to the Issuance of Permits under the National Pollutant Discharge Elimination System, Title 130 – Livestock Waste Control Regulations, or both.

Among other regulatory requirements, Title 119 and Title 130 require a facility that intends to land apply digested material to do so in accordance with a nutrient management plan.

NDEE also requires applicants to evaluate the potential air emissions associated with the digester and biogas conditioning system. If those potential emissions exceed the thresholds outlined in Chapter 3 of Title 129 – Nebraska Air Quality Regulations, the applicant needs to obtain an air quality construction permit prior to initiation of construction.

While biogases are often thought of as an animal manure byproduct, they are also a byproduct in wastewater treatment as well as some food and beverage production.

Any facility seeking to operate a digester in Nebraska is required to submit one or more permit applications to NDEE prior to beginning construction. Once operational, NDEE performs regular site inspections of these facilities to ensure regulatory compliance.