June 1997
CONTENTS
Earth Summit II
A Large Digester for a cold climate
A Small digester for a hot climate.
Practically Green Internet site a success
Earth Summit II
By all accounts there were some gains, some shortages, some hopes dashed and some positive moves. Tony Blair, UK premier, pointed to the elimination of poverty as the next focus of the UK and managed to find praise for John Major's government for meeting the CO2 reduction target. We have linked to the UN sources website in our connections page. From here it is possible to read all the texts delivered by the world's heads of state and for balance the Non Governmental Organisations' web site is included.
The first thing you notice when approaching the Vaarst Fjellerad digester site is that it is well -invisible! Not diminutive, in a large landscape, but totally invisible.
This is a large unit with a final effluent tank 50 meters in diameter and the whole site is hidden behind a 'crater wall' - the remnants of an old sand and grit quarry.
Standing on the crater edge reveals the structure of the plant. Very large input tanks (right hand side) to take pig and cattle manure, industrial organic waste and source separated municipal solid wastes (MSW) are built with conditioning pumps and screens. A pair of comparitively small digesters sit behind the very large final effluent tank - quite simply the largest I have seen in Europe on this type of plant . The connection pipes are visible between the tanks, coloured for wastes and gas, insulated for hot water connections. Most noticeable is a large blue pipe running out of the site. This is the gas export pipe which will be the major source of revenue for the plant.
A scar in the ground locates the buried pipe travelling over a kilometre to a point beyond a line of trees hiding a small red brick building. This is the Combined Heat and Power (CHP) plant in which a gas engine is fuelled on natural gas and biogas mixture to generate electricity for use on the grid and hot water for the town of Fjellerad.
Local farmers will eventually own the commissioned plant, supplying pig and cattle manure. Industrial waste and MSW provide extra revenues from gate fees. The final effluent is taken back to the farms by the farmers for use as fertiliser and in the process the tank storage provides control over ground pollution (particularly nitrates) by enabling the slurry spreading to take place only in the spring - the correct time of year for nutrient use by fast growing plants. Odour control should be very effective - 85% or more of the odour producing chemicals are digested in the process in similar digesters.
The town approves. The farmers also get the bonus of the nutrients from the industrial proteins and meat plant wastes in the final effluent. It is a good deal for the farmer and they see the benefits like a story from 'Aladdin', new enriched manure for old malodorous manure, light and heat for sale, environmental benefits and they own the cave of riches.
Technically the digester is a thermophilic high rate Continuously Stirred Tank Reactor (CSTR) with low speed mechanical stirring. New pasteurisation rules mean that the digester contents must reside for 8 hours at 53 degrees C. as a minimum. In practise, the digester will be loaded three times a day. The small digester vessels are scheduled to produce about 5 volumes of gas per volume of digester per day - the same rate as the Vegger plant. However, by means of good management and the use of a small but sophisticated onsite laboratory to control the reactors, up to 12 volumes of gas per volume of digester per day may be possible making this plant one of the most efficient in the world.
Time will tell how the plant operates in practise. We will report progress here in Practically Green News. The contractors for this EU sponsored project are Jysk Biogas (pronounced Yooosk Bee Oh Gaz for the non-Viking speakers!), Planenergi and Practically Green .
In the early 1970's the work of Ram Bux Singh in India was a milestone in the development of village scale digesters in hot climates. He visited the Folkecentre in Hurrup, Denmark and this is where we found the old demonstration unit of a Bux Singh digester. - now cut away to reveal the working design and protected by a steel mesh for safety.
These digesters are still being built in large numbers by a number of organisations including the very professional GATE organisation (also listed in connections from the Practically Green homepage) The digesters are characterised by long retention time (70days or more), little or no heating and stirring and low construction costs.
These units have revolutionised the quality of life for millions of people and some of the basic design features have been included in most of the more sophisticated high tech digesters in the West. We have yet to see one in a UK agricultural college - any takers?
We had no idea how much interest there would be in our embryonic site, but since Mid March over 1125 people have visited the site and email is now running at several enquiries per day from every continent of the world, the USA and Europe are still the main areas of activity but Africa and Asian contacts are becoming noticeable. With such encouragement you can be sure that this site will be growing steadily over the next year - thanks for your support.
Practically Green News is the newsletter of Practically Green Environmental Services. Practically Green, Practially Green News and Practically Green Environmental Services are trade marks belonging to Dr.L.K.Gornall. AJAX is the trade mark of Cooper Energy Services. The articles in this newsletter represent the views of Practically Green Environmental Services. Whilst every attempt is made to represent products and services accurately, errors can occur and no liability can be accepted for errors and omissions. This newsletter is not a contract.