Frequently Asked Questions

Anaerobic digestion is a natural process occurring in the absence of air. During this process, micro-organisms stabilize waste organic matter and releases biogas.

Micro-organisms convert a fraction of the organic waste matter into methane-, (CH4) and carbon dioxide (CO2) gases during a process called anaerobic digestion. This mixture of gases is known as biogas. The composition of biogas is 50 to 75 per cent methane and 25 to 45 per cent carbon dioxide. Power generators, engines, boilers and burners can use biogas as a fuel, instead of natural gas.

Anaerobic digesters are specially designed and insulated tanks that are used to facilitate the anaerobic digestion process under a controlled atmosphere in order to achieve the maximum biogas production in the shortest of time.

The capital costs of anaerobic digester plants may range from a few hundred thousand to million of Euros, depending on the size of the plant. The payback period can range from 3 to 16 years depending on country and market conditions.

Most commonly, a fully automated anaerobic digester plant’s daily requirements are only a couple of hours of monitoring by a suitably qualified person. However, plant failure or maintenance during shutdown may require more manpower.

Manure, feed spills, crop residues, offal and most domestic and industrial organic wastes can be used as feed materials for digesters.

Liquid digestion plants uses an intensive stirring reactor, processes substrate containing up to 17% of dry matter and require longer retention time.

Dry digestion plants uses a plug flow reactor, can handle a substrate containing up to 35% of dry matter and require a significant shorter time of retention due to higher temperature of the process. The graphic below provides more details.