Cover storyRise of the Anaerobic Digester
Section snippets
Where is AD taking place?
AD usage is popular in parts of Europe, and around the world:
- ▪
In Denmark, for instance, AD plants operated by farm cooperatives provide district heating for local communities as well as electricity;
- ▪
Thousands of ADs in Austria and Germany digest manure, food waste and energy crops, producing biogas that is then used for electricity generation;
- ▪
In Sweden, biogas plants produce fuel for fleets of town buses;
- ▪
Extremely large AD plants exist in the USA;
- ▪
What is claimed to be the world's largest,
What is the process for AD?
Anaerobic digesters range from small, simple systems used in homes and smallholdings in developing countries through farm-scale digesters to sophisticated industrial-scale units found in developed nations. Designs vary according to the feedstocks and bio-outputs intended, as well as the planned scale of operation. Because the AD process is biological, careful seeding and control of micro-organisms is a prerequisite for high efficiency:
- ▪
The process stream typically starts with shredding,
Advances in AD – minimising waste
In some countries (Britain is one example), AD exploitation lags behind that in other European countries – though the sector is not negligible.
One problems is that AD often has to be installed on a substantial scale before it can be ‘economic' in the conventional sense of the word. To address this and other issues, increasing professionalism is characterising the evolution of AD.
Organic Power Ltd, a British company that was formed in 1997. The company was convinced that a major inhibitor to the
What are the best feedstocks for AD?
Another AD and biogas specialist Greenfinch Ltd points out that where the primary aim is to maximise biogas production, cattle and pig slurry may not be the best feedstock, because this is what is left when animals have digested readily-digestible elements of food, and produced their own biogas. Better, says the company, to use food waste or add some wet energy crops such as grass silage, whole crop cereals, or maize. Operators of farm digesters can consider importing food waste from other
Down on the farm
Farmers around the world are showing interest in ADs as a result of higher energy and fertiliser prices, the growing costs of complying with waste disposal legislation in many countries and the continuing need to diversify in order to maintain farm incomes.
Sentiment has previously been depressed by poor experience with earlier digesters that proved insufficiently robust, the uncertain value of renewable electricity, the regulatory environment and difficulties with connection to the electricity