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What is Anaerobic Digestion and Biogas?

16 July 2015

Bethan Stones headshot

Bethan Stones

Group Marketing Manager


What is Anaerobic Digestion?

Anaerobic Digestion is the process of micro-organisms breaking down organic waste material – also known as feedstock – in the absence of oxygen. The process happens naturally, for example in soils, but is becoming increasingly popular as an athropogenic solution for dealing with organic wastes.

The outputs from anaerobic digestion are biogas, principally constituted of methane and carbon dioxide with some impurities and solid and/or liquid digestate. If undertaken on a large enough scale, AD can create biogas to be used as a fuel in a combustion appliance such as an engine or boiler. Digestate is typically used as a compost/fertilizer.

In the UK anaerobic digestion is still a relatively new process, however the technology is very widespread and proven in the majority of Europe.

Why Operate Anaerobic Digestion?

Many industrial and agricultural processes inherently create organic waste(s). In this respect, the process operator has a free supply of potential input material to an anaerobic digestion plant. By investing in the technology to operate anaerobic digestion an operator has the opportunity to convert his ‘waste’ in an environmentally friendly way into financially valuable products (biogas & digestate). Biogas is typically combusted on-site to generate heat and/or power to a facility; excess power generated can even be exported to the grid. Digestate is typically used on-site or sold to third parties as a fertilization medium.

Anaerobic Digestion & Permitting

Anaerobic Digestion plants may be subject to regulation under the Environmental Permitting Regulations (2010). Plants that burn AD derived biogas in appliances which have a net thermal input of <0.4MW are exempt from the regulations. Appliances that exceed this threshold are subject to regulation, primarily on account of the potential for atmospheric pollution generation from appliance exhaust gases.

The Environment Agency have provided the following rules for such installations: Standard Rule Permit SR2012 No12 “Anaerobic digestion facility including use of the resultant biogas”

Monitoring of Biogas Emissions  

Monitoring the emissions of exhaust gas from biogas combustion plants is a mandatory requirement for process operators. Typically operators who burn biogas in engines to produce electricity are required to have the emissions of NOx, CO, SO2 & VOC assessed annually to demonstrate compliance with limits.

Envirocare offers a fully UKAS & MCERTS accredited monitoring service for anaerobic digestion facilities and biogas combustion plants. Envirocare are also able to offer consultancy advice to AD Plant operators.

Call us on 01274 738668 or fill out our Envirocare Enquiry Form for any queries regarding our wide range of stack emissions monitoring services.