Anaerobic digestion is a great process for creating renewable energy, and it is also unique in that it solves many other problems, especially if the feedstock material which is used as the substrate to “fuel” the anaerobic digestion is a waste material, and not a food crop.
So, to avoid this article becoming excessively long I am limiting this article to a discussion of anaerobic digestion pros and cons, for anaerobic digestion (AD) plants where the feedstock is 100% waste material and to commercial anaerobic digestion plants built in the industrialized nations. AD plants, which are more often called “biogas plants” in the industrializing nations, have a slightly different list of advantages and disadvantages. That’s because by their nature they are much smaller, and usually built for different reasons from biogas in Europe, or the US, for example.
Anaerobic Digestion Pros
1. Produce renewable energy with the smallest possible impact in terms of carbon dioxide emissions.
2. Can be used to process diseased and infected organic matter, and as long as a suitably high temperature is attained during the process, a safe pasteurized output is produced which will not spread disease.
3. When waste feedstock materials like food waste are digested,which would otherwise have been sent to a landfill, the volume of waste which goes to landfill is reduced.
4. Diversion of organic waste away from landfill, will also have the effect of reducing the amount of organic “rottable” (putrescible) matter in landfills, making them less likely to cause pollution in the future.
5. The output, known as digestate, can be used as a crop fertilizer which also has the ability to make many plants more disease resistant. When used in arid climates it can improve the water retaining ability of the soil, and reduce irrigation requirements.
6. The liquid digestate is a better fertilizer in many ways than normal chemical fertilizers.
7. The fibrous digestate the fibrous digestate has many uses. If it is not spread immediately on fields it may be used in some circumstances as a leading for livestock.
8. The digestate produces less odour when it is spread on farmland, and is less likely cause pollution of local rivers and streams and spreading untreated manure.
9. When the biogas is used on-site to generate electricity there is spare heat in the form of the engine cooling water, which can be used on the site it is created (e.g. on the farm for heating, or to heat the factory where the biogas plant is installed, or a near neighbour. That is known as CHP (Combined Heat and Power).
10. Certain businesses that pay a carbon levy for their carbon dioxide emissions can offset their levy costs against the carbon savings from running their own biogas plant.
Anaerobic Digestion Cons
1. Commercial anaerobic digestion plants are costly to build and usually need bank loans to finance them.
2. The plants need expert people to design, construct build, and operate them. They must be attended pretty much every day, to ensure they run correctly, and are more complex than say installing a solar cell.
3. To be successful each anaerobic digestion plant must have a reliable source, and usually a number of different reliable sources, of feedstock materials. That can be diffilcult to obtain.
4. Suitable sites can be difficult to find as the public may object to planning applications for AD plants.
These are the main advantages and disadvantages of anaerobic digestion. We hope that this article has helped you understand that there are many more advantages to using the anaerobic digestion process than disadvantages.