Since 2008, Massachusetts has made enormous strides in the field of renewable energy. While you are probably familiar with solar panels and wind turbines, there are many more options that are friendlier to the environment than fossil fuels. With the ability to turn organic waste into a gas that can be used to produce electricity and thermal energy, anaerobic digestion (AD) is a growing player in the Commonwealth’s renewable energy arsenal. By diverting some organic waste from landfills, AD can reduce landfill emissions of methane and landfill expansion.
What is Anaerobic Digestion (AD) and how does it work?
Anaerobic digestion (AD) is a biological process in which micro-organisms break down organic materials in the absence of oxygen and form an energy-rich biogas. In the “wet” version of AD, pumpable organic feedstocks (such as food processing waste or animal manure) are placed in an enclosed chamber that is maintained between 95 to 140 degrees Fahrenheit, typically for about three to four weeks. Naturally occurring micro-organisms that thrive in this heated environment break down the organic solids and produce biogas, comprised primarily of methane and carbon dioxide. “Dry” AD systems operate similarly, but can handle feedstocks with lower moisture content like table scraps or yard waste.
While the digestion process greatly reduces the volume of solids, reduction varies depending on the feed source, temperature, and amount of time the solids are retained in the digester. The leftover digested material is rich in nutrients and may be used directly as a fertilizer or soil amendment, or mixed with other materials and composted.
There are several ways in which biogas can be used to produce energy: as fuel to heat the digester itself to maintain proper temperature, create heat for other industrial processes, fed into a generator to create electricity, and used in a combined heat and power (CHP) system to simultaneously produce both electricity and heat. Biogas can also be converted to compressed natural gas (CNG) and used to fuel vehicles, such as buses or trucks.
What types of facilities use AD?
Since the 1940s, Massachusetts wastewater treatment plants have used AD to reduce solids that would otherwise be put into landfills or incinerated. The process also sufficiently reduces pathogens to make the solids safe for use as a fertilizer. In addition to wastewater treatment plants, AD with CHP has applications at farms, industrial and food processing facilities, stand-alone organics recycling centers and is used widely in Europe for waste reduction and renewable energy production.
For more on anaerobic digestion general information, policies and regulations, please visit MassDEP’s web page:
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