Overview
Composting facilities are operations that use biological processes (microorganisms) to decompose organic feedstocks such as yard debris, animal manures and food scraps. Aerobic composting uses microorganisms that prefer oxygen, while anaerobic digesters use microorganisms that thrive in low oxygen environments. Aerobic composters produce compost, while anaerobic digesters create and capture methane gas to create electricity or other fuel products. Digesters also create liquid and solid products that can be used for soil fertilizing and conditioning.
The products of composting facilities provide numerous environmental benefits. The use of compost, when incorporated into soil, can improve soil tilth and fertility; it can provide a more stable form of nitrogen less susceptible to leaching into water supplies. Compost also helps reduce compaction and increases infiltration. Incorporation of compost into soil stores carbon, helping to reduce atmospheric carbon. By capturing methane gas, anaerobic digesters avoid the release of methane to the atmosphere, a significant component of greenhouse gas.
DEQ supports and encourages composting. At the same time, DEQ is aware that, if not conducted in the proper manner, or if conducted at an improper location, composting presents potential environmental problems, most notably to surface water and groundwater.
Regulating composting facilities and anaerobic digesters
Rules and permits
Oregon’s composting rules require permits for composting facilities and also provide exemptions from permitting requirements for certain small, low-risk composting facilities. The composting rules include permitting requirements for anaerobic digestion facilities in addition to aerobic composting facilities. Under the rules, anaerobic digesters are considered composting facilities but are issued separate anaerobic digester permits addressing issues specific to anaerobic digesters.
The type and amount of feedstock composted is used to establish criteria for determining when a composting facility permit is required and when a facility is exempt from permitting requirements. Exempt facilities still need to maintain compliance with environmental performance standards. For facilities that do require a composting facility permit, the type of permit is determined based on site-specific physical characteristics, design characteristics and operations.
A permit is required if:
Type 1 and 2 Feedstocks: The facility receives > 100 tons of feedstocks per year
Type 3 Feedstocks: The facility receives > 20 tons of feedstocks per year -OR- the facility receives > 40 tons of feedstocks per year when using an in-vessel system
DEQ’s composting rules are structured such that the type of permit issued is based on the level of risk posed by a composting facility and anaerobic digesters to public health or the environment.
Composting rule highlights:
- The rules establish a base of performance standards for any facility, addressing protection of public health and the environment.
- The rules allow site operators the flexibility in site design, construction and operation to meet those standards.
The rules exempt, from permit requirements, lower-risk facilities that comply with performance standards. - Site screening criteria, established in rule, are used to determine the level of environmental and public health risk posed by a proposed facility, based on site-specific features of the facility.
- The rules establish a tiered permitting system. Facilities not exempt from permitting but considered low-risk, after screening, would operate under a different type of permit than a facility that poses a higher environmental risk.
- Permitting fees are structured so that facilities posing a greater threat and taking more DEQ oversight pay greater amounts.
DEQ’s composting rules contain performance-based standards that all composting facilities must meet, including anaerobic digesters and facilities that are exempt from permitting requirements. These performance standards set a base level of facility performance and provide DEQ flexibility to exempt low-risk facilities from permitting requirements.
The performance standards address:
- Proper management of stormwater, process water, leachate and liquid digestate to prevent pollution
- Odor minimization - to not create foul odors that affect neighbors
- Prevention of vector propagation - eliminate conditions that attract flies, rodents and other pests
- Protection of groundwater through facility design and operations, particularly if some facility liquids will be managed through soil infiltration
- Standards for pathogen reduction to protect public health and the environment, including for digestate.
For Anaerobic Digesters:
- Appropriate collection and storage of biogas in order to minimize risk of explosion and fire
- Adequate storage capacity for liquid digestate for several reasons:
- To store through Oregon’s wet winter months, when land application can cause water quality problems
- To meet pathogen-reduction standards for time and temperature.
Feedstocks are the organic ingredients of composting processes, such as yard debris, animal manures and food scraps. Feedstock definitions also include the solid and liquid by-products of anaerobic digestion, called digestate. DEQ staff use a lot of information, including the type and amount of feedstocks, to determine if a permit is needed and what type of permit.
Feedstock types:
- Type 1: yard and garden wastes, wood wastes, agricultural crop residues, wax-coated cardboard, vegetative food wastes; digestate from Type 1 feedstocks
- Type 2: manure and bedding; also digestate from Type 2 feedstocks
- Type 3: source-separated mixed food waste, meat, eggs, dairy products, mortality; also, digestate from Type 3 feedstocks
- Type X: specified risk material from bovine animals that can be source of prions that can cause Bovine Spongiform Encephalitis. Type X is neither intended nor expected to be a normal composting facility feedstock. The idea is to specifically identify this material for special management.
When does a site need a composting facility permit?
The type and amount of feedstock composted is used to establish criteria for determining when a composting facility permit is required and when a facility is exempt from permitting requirements. Exempt facilities still need to maintain compliance with environmental performance standards. For facilities that do require a composting facility permit, the type of permit is determined based on site-specific physical characteristics, design characteristics and operations.
A permit is required if:
- Type 1 and 2 Feedstocks: The facility receives > 100 tons of feedstocks per year
- Type 3 Feedstocks: The facility receives > 20 tons of feedstocks per year -OR- the facility receives > 40 tons of feedstocks per year when using an in-vessel system