“A Natural Process Returns to Prominence”
So, what is Anaerobic Digestion? Anaerobic Digestion involves using the natural process wherein organic matter is broken down by germs, in the absence of oxygen, inside a sealed tank.
For both processes, a digester tank is made use of: a gas-tight, sealed vessel with draw-off points, in which plant and animal material (biomass) is naturally digested by micro-organisms, which then release functional methane.
Here is the definition by the US Government Massachusetts website:
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.
— Watch Our Video Below for an Explanation of “What is Anaerobic Digestion”. —
- Biogas – usable as a renewable energy source, for heat and power
- Biomethane – usable as a transport fuel or it can be injected into the UK natural gas grid, and
- Carbon dioxide – usable in fire extinguisher systems, aerosol cans, soft drinks, food production in greenhouses, coffee decaffeination, and for numerous other purposes
Plus, afterwards, the treated material (digested effluent, or “digestate”) can be used as a nutrient-rich fertiliser and soil conditioner.
- Fossil fuel use
- Greenhouse gas emissions from landfill, and
- Methane emissions to the atmosphere from manures and slurries.
It allows farmers and other rural business owners to:
- Cut their energy bills
- Reduce their environmental footprint, and
- Enjoy an increased income – the sale of surplus energy and digestate offers a potential additional revenue stream
With all this, it is not surprising that many businesses and communities are increasingly looking to benefit from Anaerobic Digestion; there is also a growing trend of AD plants being set up by entrepreneurs looking to gain market presence as an energy supplier, and to win government contracts for energy supply at subsidised rates known as the “Feed-in-Tariff” and “Renewable Heat Inititaive” (RHI) in the UK.
Types of AD
There are two basic AD processes:
- Mesophilic digestion, which occurs between a temperature range of 20-40ºC, and can take a month or two to complete
- Thermophilic digestion, which occurs between 50-65ºC and is faster, resulting in smaller reactor tank sizes, but the bacteria are more sensitive to imperfect conditions.
We hope that this clarifies your question: “What is anaerobic digestion“.