Through anaerobic digestion organic materials are processed in anaerobic conditions by microorganisms which break down the material into biogas and a digestate. More than half of biogas is methane which can be used as a renewable energy source. The digestate can be land applied, composted and used as a soil amendment or processed into fertilizer pellets.
What can go into a digester?
Common materials fed into an anaerobic digester include:
- Food scraps;
- FOG (fats, oils & greases) and;
- Food processing waste
Manure is a common base feedstock as it is produced continuously and contains a healthy population of anaerobic bacteria that is part of the anaerobic digestion process. Not all organic matter is suitable for a digester. Wood, leaves, and other fibrous materials contain lignin, which is difficult to digest in large quantities.
Types of Digesters
There are two basic types of digesters (link leaves DEC's website) categorized by the percentage of water in the feedstock.
- A wet digester accepts material that contains less than 15 percent solids. The feed stock is pumpable.
- A dry digester, otherwise known as high solids anaerobic digestion, generally takes material that is more than 15% but less than 45% solids. The feed stock is stackable; it is too dry to be pumped. The residence time needed to complete the process in the dry digester is faster than in a wet digester.
New York State Regulations
Anaerobic digestion operations in New York State are regulated by 6 NYCRR Subpart 361-3.3 in one of three ways; exempt, registered, or permitted. Regulation of anaerobic digestion facilities and their resulting digestate depend on the location, quantity and type of material fed into the anaerobic digester.
Summary of Anaerobic Digestion Regulations (by quantity and type of material)
Anaerobic digesters located on Concentrated Animal Feeding Operations (CAFOs) must adhere to additional NRCS standards as required by the CAFO general permit.
Use of Solid and Liquid Digestate
Biogas and digestate are two by-products of anaerobic digestion. Biogas is a renewable energy source that can be used for heat, electricity and an alternative fuel source. Digestate is the liquid and solids portion produced by an anaerobic digester and can be used in multiple ways, such as the following,
- Land application
- Animal bedding
Digestate is regulated (link leaves DEC's website) based on the feedstock of the anaerobic digester and the use of the digestate.
Anaerobic Digesters Around the State
- NYS P2I Organics Resource Locator (link leaves DEC's website): An interactive web based mapping tool of organic waste generators, organics processing facilities and much more.