subject: About Anaerobic Digestion And Why It Is Important [print this page] The 2009 EU Renewable Energy Directive sets a target for the UK to achieve 15 per cent of its energy consumption from renewable sources by 2020, according to The Department for Energy and Climate Change. Companies and organisations across the country are therefore being urged by the Government to do all they can to achieve this objective.
Many farmers, other rural business owners, and water utility companies are certainly doing their bit towards producing renewable energy and reducing greenhouse gases, by diverting biodegradable wastes to Anaerobic Digestion (AD): a process that involves the natural breakdown in digester tanks of organic materials into methane, carbon dioxide gas and fertiliser.
Suitable boilers supplied by a boiler hire company experienced in AD applications are sometimes utilised by plant managers, to heat digester tanks to precise temperatures when on-site heating systems fail or extra heating capacity is required.
A natural process
Anaerobic Digestion involves harnessing the natural process whereby organic matter is broken down by bacteria, in the absence of oxygen, inside a sealed tank.
This produces:
Biogas usable as a renewable energy source, for heat and power
Biomethane usable as a transport fuel or it can be injected into the UK gas grid, and
Carbon dioxide usable in fire extinguisher systems, aerosol cans, soft drinks, food production in greenhouses, coffee decaffeination, and for numerous other purposes
Plus, afterwards, the treated material (digested effluent, or digestate) can be used as a nutrient-rich fertiliser and soil conditioner.
AD reduces:
Fossil fuel use
Greenhouse gas emissions from landfill, and
Methane emissions to the atmosphere from manures and slurries
It allows farmers and other rural business owners to:
Cut their energy bills
Reduce their environmental footprint, and
Enjoy an increased income the sale of surplus energy and digestate offers a potential additional revenue stream
With all this, it is not surprising that farmers are increasingly looking to benefit from Anaerobic Digestion; there is also a growing trend of AD batching plants being set up by entrepreneurs looking to gain market presence as an energy supplier, to win government contracts.
Types of AD
There are two basic AD processes:
Mesophilic digestion, which occurs between a temperature range of 20-40C, and can take a month or two to complete
And:
Thermophilic digestion, which occurs between 50-65C and is faster, but the bacteria are more sensitive
For both processes, a digester tank is used: a gas-tight, sealed vessel with draw-off points, in which plant and animal material (biomass) is naturally digested by micro-organisms, which then
release useable methane.
Note: According to Biogas Info, although a digester tank can accept waste from industry, homes and supermarkets, it is slurry and manure from farms that is most frequently processed. As long as the tanks contents are mechanically stirred and heated properly throughout, the settling of solids and crust formation can be avoided and the process can be successful.
Boilers can be hired from a boiler hire specialist for both Mesophilic and Thermophilic digestion; although, it is for the latter that there is usually the most frequent need.
