How Anaerobic Digestion Biogas is Produced and the Advantages this Brings


Biogas production using anaerobic (oxygen free) digestion is a biological treatment process to reduce manure spreading odour and produce biogas. Anaerobic digestion biogas produces energy and improves the storage and handling characteristics of manure. A biogas production system must be specifically designed for the feedstock (for example manure), and requires regular attention by someone trained to keep digester running within required operating conditions to ensure optimum biogas production. Associated feed and output material (digestate) handling equipment, plus anaerobic digestion biogas utilization components are also required. The anaerobic digestion biogas digester does not require the addition of significant nutrients but does require an environmentally responsible manure storage and handling system.

A well designed and operated digester will require modest daily attention and maintenance. The care and feeding of a digester is not unlike feeding a cow or a sow.  It responds best to consistent feeding and a close to optimum environment for the biomass to grow. The fact is that the earlier a problem in operation is identified the easier it is to fix and still maintain productivity, so the operators of anaerobic digestion biogas plant should never extend the interval between visits excessively.

Biogas as a rule of thumb contains 60% methane (CH4) and 40% carbon dioxide (CO2), with some other trace chemicals present.

Organic matter decomposing in aerobic conditions (i.e. in the presence of oxygen) does not produce methane, just CO2 which is a greenhouse gas known to contribute to climate change. While Methane is about twenty times more powerful than CO2 as a greenhouse gas, by producing it through anaerobic digestion means it can be captured and put to use.

Anaerobic digestion biogas plants have been being built in increasing quantities since the middle of the noughties, and many governments have become increasingly willing to subsidise the development of anaerobic digestion biogas plants. In the UK there is frustration for the renewable sectors as the EU Commission’s has made an objection to the latest subsidy mechanism (known as the Renewable Heat Incentive (RHI). Their objection relates to the UK government's proposed tariff levels. Their concern is limit to the large biomass plant tariff proposed and the other tariffs/technologies have been given the green light. However, the delay affects the rolling out of the RHI, and is frustrating the anaerobic digestion and biogas sector and delaying growth in the implementation of anaerobic digestion biogas plant.

The UK Coalition Government is committed to raising energy from waste through such technologies as Anaerobic Digestion. Furthermore, the biological basic process of "anaerobic digestion biogas" is now fully proven and is recognised as a technology that is able to remove organic wastes from landfill sites, reduce greenhouse gas production, and to a large extent de-couple the UK from unreliable fossil fuel sources. It also creates green renewable electricity, it enables biogas to be purified before being fed into homes and businesses via the local gas distribution grid. It also recovers green fertilisers, supports jobs, and is providing good rewards for investors.

The potential scale of the technology is estimated at 100 Million Tonnes of farm and food waste in the UK each year being converted in Anaerobic Digestion biogas processing plants that could generate almost half of the current total domestic gas requirement.

Anaerobic Digestion (AD) is the bacterial fermentation of organic matter, in the absence of air, that replicates the conditions in the digestive system of a ruminants ( e.g. cows). The AD process can receive pre-treated organic matter (replicating the manner in which cows chew grass), or any individual or combination of animal manures, food waste or energy crops which are turned into either a shredded woody mass for dry digestion, or a pumpable ‘soup’ in a wet digestion system.

In the anaerobic digestion biogas plant reactor there are bacteria that thrive without oxygen, and in doing so convert the sugars in the feedstock into carbon dioxide and methane. The methane can then be used to generate renewable electricity and heat in a CHP engine, burned directly to produce heat, be cleaned and injected into the grid or used to produce fuel.

Other benefits may include reduced regional community dependency on energy, nutrient and water resources.

Many organic materials can be converted from solid or liquid form to a mix of gases by introducing the correct bacteria and creating the optimum growth conditions. This process is very similar to that of an animals digestive system and so the the most common method of producing Biogas is that of anaerobic digestion. In addition, the AD process creates potentially valuable by-products, such as the solids fraction - fiber, and liquid with available nutrients.

Extensive research efforts are in progress in the UK which seek to make discoveries in improving AD technology for manure, co-digestion of manure with food processing waste, development of nutrient co-products, and demonstration of the use of biogas as a transportation fuel.

Farmers, food and drink producers, agri-business and landowners often look at ways of making the most of their existing, often untapped, resources. Harnessing renewable energies such as wind and anaerobic digestion/biogas can provide an additional income stream.

Our multi-disciplinary team, who also have solid working relationships with other renewable technology advisers, can help guide you through all aspects of your renewable project. They can help with issues from initial funding and corporate set-up, commercial agreements and intellectual property licensing, grid connections and power purchasing agreements, through to land-use, construction and day-to-day operational issues.

Anaerobic digestion (AD) is an effective means of degrading organic wastes which leads to Biogas Generation by the synergistic effort of a consortium of microorganisms. It is a natural treatment process and, as in composting, bacteria break down bulk organic matter into bio-methanated spent wash. Unlike composting, Anaerobic Digestion is carried out in an oxygen-free (anaerobic) environment. Biogas Generation is an eco-friendly process of energy production from wastes.

So, the anaerobic digestion process leads to biogas generation which is a non-conventional source of energy which is effectively used for domestic cooking, heating and power generation resulting into substantial revenue savings at optimum costs.

An increasingly powerful and effective body promoting UK biogas is the Anaerobic Digestion and Biogas Association (ADBA) which was formed in 2009, to help remove the barriers to growth faced by the industry  at that time, and to support its members to grow their businesses to ensure the potential of AD is achieved. ADBA is boosting the country’s production of biogas from anaerobic digestion. It was set-up by combining the reputation of Lord Redesdale, with the entrepreneurial skills of leading businesses from the AD and biogas industries.  Many volunteers are working with this respected Lord in recognition of the importance of anaerobic digestion biogas in providing a renewable energy source that will be able to meet the needs of the country in its task of cutting back on carbon emissions, and minimizing climate change.

Further reading can be found at:

1. Biogas Plant Expert Info
2. New Waste Processing Technologies including Mechanical Biological Treatment (MBT)
3.  The Anaerobic Digestion News Web Site
4.  Information News and Resources in Anaerobic Digestion Technology and Developments.

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