Callidus Design Consulting Engineers

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Anaerobic Digester

Renewables - Anerobic Digestion

Anaerobic digestion is an established process for treating organic waste residues. It is used in the UK for digestion of sewage and agricultural sludges. Anaerobic digestion works on the principle of microbiological degradation of organic material and waste in the absence of oxygen. It is essentially the same process which takes place within a landfill site, but can be managed to a much greater extent.

60% of the waste can be converted into biogas — the rate of breakdown depends on the nature of the waste and the operating temperature. The biogas has a calorific value typically between 50% and 70% that of natural gas and can be combusted directly in modified natural gas boilers or used to run internal combustion engines. Apart from biogas, the process also produces a digestate which may be separated into liquid and solid components. The liquid is fertiliser and the solid is organic compost.

The advantages of anaerobic digestion are as follows:
• There is a significant reduction of waste in a clean process with useful end products
• The process deals with a waste stream that cannot be recycled or reused; there is no conflict with waste hierarchy.

The disadvantages are that the technology generates only small amounts of energy and collection and waste handling are complex and costly. There is also a risk of smells during use and when waste is handled. Anaerobic digestion is an excellent technology for treating biodegradable organic waste. A future attraction of anaerobic digestion is the opportunity to integrate it with gasification.

Please get in touch if Callidus Design can be of assistance with the design of your new Anaerobic Digestion plant.

(extracted from CIBSE Guide L - Sustainability)