Anaerobic Digestion
Anaerobic digestion is a series of biological process in which microorganisms break down biodegradable material in the absence of oxygen. One of the end products of this technology is biogas, which is combusted to generate electricity and heat, or can also be processed into renewable natural gas and transportations fuels. “There are four main stages of the anaerobic digestion process” (AD and Bioresources, n.d.). Each stage breaks the matter into smaller parts, until the only remaining substances are methane, carbon dioxide and water. The stages are:
- Hydrolysis
Breaks down the complex organic matter – carbohydrates, fats and proteins – into simple sugars, fatty acids and amino acids.
- Acidogenesis
Breaks down the single sugar molecules, fatty acids and amino acids into alcohols and volatile fatty acids, with by-products of carbon dioxide, ammonia and hydrogen sulphide.
- Acetogenesis
Converts the volatile fatty acids and alcohols into hydrogen, carbon dioxide, and acetic acid.
- Methanogenesis
Methanogenic archea convert the remaining hydrogen and acetic acid into methane, and more carbon dioxide.
The end product of this process are the mixture of methane and carbon dioxide gases (biogas), water and some organic material (disgestate). Biogas can be burned to produce both heat and electricity, while methane can be used as vehicle fuel or injected into the gas grid. Water, after the treatment within the anaerobic digestion process may be returned to the waterhouse.
Image 2: The Anaerobic Digestion Cycle. Source: Anaerobic Digestion and Bioresources Association
Runyon (2016), stated in his article, “if all the food waste processed at the plant were sent to dump instead, it would still release methane as it rotted and decomposed – but all that wasted gas would seep directly into the atmosphere and contribute to climate change as methane is a powerful greenhouse gas”. By using this technology, the amount of food wasted can be reduced and it can help to provide us with a better environment.
The cost of building the plant is expensive but it brings a lot of benefits. Runyon (2016) said, “anaerobic digesters can solve a few problems at once”. The anaerobic digesters not only generate renewable energy, but they also cut down the harmful emission from the food waste and provide a job opportunity along the way.