What is Anaerobic Digestion?

First Official Post

My research question is how does Anaerobic Digestion benefit the Earth and us, but first, what exactly is Anaerobic Digestion? I will be talking about it in my first post. Before that, let me give an overview of everything.

How does Anaerobic Digestion benefit the Earth and us?

Post 1. What is Anaerobic Digestion?
Post 2. The current situation of Earth
Post 3. Treating of wastewater
Post 4. Reducing the emission of greenhouse gasses
Post 5. Biogas- Renewable source of energy
Post 6. Digestate- Fertilizer
Post 7. Conclusion

Anaerobic Digestion is similar to the digestion which takes place in our body. However, rather than digesting food, it digests biodegradable materials. These materials will be broken down by microorganisms in a chain of processes.

Anaerobic Digestion can be used to treat wastewater and organic waste. It also reduces the emission of landfill gas into the air and is a renewable energy source. It may be used as fertilizer as well. These are the few advantages of Anaerobic Digestion. I will be talking more about all these in the next few posts.

Anaerobic Digestion is actually recognized by the United Nations Development Programme. The few microorganisms involved in the whole process are acetic acid-forming bacteria (acetogens) and methane-forming archaea (methanogens). A number of processes will convert the initial input material into intermediate molecules like sugars, hydrogen and acetic acid by allowing the organism to feed on them. Biogas will be produced in the end.

Similarly to the aerobic system, the microorganisms in the Anaerobic system also requires oxygen to survive and reproduce. The organic material itself or the inorganic oxides within it will provide the oxygen.

So what exactly are the processes? The 4 important biological and chemical key stages of Anaerobic Digestion are:
1. Hydrolysis
2. Acidogenesis
3. Acetogenesis
4. Methanogenesis

(A diagram is provided on the next page to facilitate understanding)

In order for the bacteria to access the energy in the input material, the material must be broken down first. Hydrolysis is like the stage whereby enzymes in our bodies break down food into smaller pieces in our mouth. Similarly, after hydrolysis, the complex and large molecules will be broken down into simple sugars, amino acids and fatty acids.

Using acidogenic (fermentative) bacteria, acidogenesis goes on to break down the remaining components.

A simplified chemical equation for the whole process: C6H12O6 → 3CO2 + 3CH4

At the third stage, the simple products produced at the second stage will be digested by acetogens, producing largely acetic acid together with hydrogen and carbon dioxide.

Lastly, methanogens will convert everything into methane, carbon dioxide and water. These end-products form the bulk of the produced biogas. The indigestible remnants will form the digestate.