What is Anaerobic Digestion and how does it work?
Anaerobic digestion is a process that involves the fermentation of biodegradable organic waste in the absence of oxygen, which turns into methane that releases a natural energy called biogas – a renewable fuel.
Biogas derives from substances rich in carbon such as manure, green waste and agricultural crops that can be converted into gas, liquid, electricity and heat. The resources needed are widely available all year round, low cost and do not produce any environmental hazards.
Ultimately, the process anaerobic digestion combines waste management with energy production and is also a popular wastewater treatment method.
The Four Stages of Anaerobic Digestion
Stage 1 - Hydrolysis:
The anaerobic digestion process begins with the fermentation of bacteria that optimizes in the absence of oxygen, performing hydrolysis. Hydrolysis is a chemical reaction that breaks down polymers.
Stage 2 - Acidogenesis:
This is the biological reaction that converts the organic molecules into volatile fatty acids.
Stage 3 - Acetogenesis:
Acetogenic bacteria convert the volatile fatty acids into acetic acid, carbon dioxide and hydrogen.
Stage 4 - Methanogenisis:
This is final stage of anaerobic digestion where a biological reaction causes the acetates, carbon dioxide and hydrogen to convert into methane.
Principles
AsiaBIOGAS has over 50 years of experience in anaerobic digestion and will select the best solution for a project’s circumstances, taking into consideration their climate and geography.
Given that AsiaBIOGAS’ primary territory is in Southeast Asia, the technical team has found that the ‘Covered in Ground Anaerobic Reactor’ (CIGAR™) produces the best results in exceeding performance standards compared to other digesters in terms of:
- Higher conversion of BOD to biogas
- Greater overall biogas volume
- Higher methane gas content
AsiaBIOGAS’ technical team have developed and consulted on a wide variety of technologies, including:
- UASB – Upflow Anaerobic Sludge Blanket
- CIGAR™ - Covered In Ground Anaerobic Reactor
- CSTR – Continually Stirred Tank Reactor
- Covered Lagoons
- Expanded Bed Reactors
- Hybrid Reactors
Temperature
Temperature plays an important role in the anaerobic digestion process. An airtight chamber called a digester is required. To increase bacterial activity the anaerobic climate should be no less than 30 °C.
There are two main types of bacteria:
- Mesophilic: A bacteria that works optimally at human body temperature.
- Thermophilic: A bacteria that operates only in high temperatures above 40 °C to nearly boiling point.