The Agricultural Research Council’s (ARC) Institute for Agricultural Engineering has manuals available for the design, building and operations of biogas equipment, updated in January 2008.
Francois Cilliers, the manager for irrigation and natural resources engineering at the ARC, says South Africa’s power shortage and the desirability of renewable energy sources are encouraging farmers to produce their own biogas from manure.
“The global community is searching for clean and renewable energy sources,” says Francois. “In Africa the search is also on for sustainable and environmentally-friendly renewable energy, based on natural processes to replace paraffin, coal, diesel, petrol and other fossil fuel. Economical and environmentally-friendly energy is becoming a priority.”
On the horizon of renewable energy
A solution is to use animal manure – normally a waste product – in an anaerobic digester to produce biogas. “Manure from cattle or piggeries is available over most of South Africa and can be used as raw material for the biogas digester,” says Francois. “Biogas digesters are environmentally friendly and the digestion process produces a natural fertiliser.”
Biogas is a collective term for a variety of gases produced during anaerobic digestion of manure, about 60% being flammable methane gas. A biogas system suitable for a family of five would need the manure of two dairy cows, three beef cattle or 27 pigs. Manure produced daily by two dairy cows can yield energy equivalent to about 2,6â„“ of paraffin or 2,1kg of liquid petroleum gas.
It will cook two meals a day for a family of five and burn a gaslight for three hours. Existing household gas equipment, such as hotplates, stoves and refrigerators, can be easily adapted to run on biogas. The principles of all biogas systems are the same, whether for a small household or large feedlot. “The structures are simply larger,” says Francois. “On a larger scale the gas can be used to generate electricity at feedlots, dairies or piggeries and to heat water at ablution blocks for labourers.”
Biogas systems shouldn’t be built in urban areas or near streams, rivers or dams that could be polluted by manure dumped by accident. In high-rainfall areas or where flooding is a problem, a biogas digester must not be built below the soil surface level as rain water cools the digester and lowers biogas production.
Biogas digesters have to be loaded daily to operate successfully. If this isn’t done then biogas production will drop or even cease. the biogas is needed as a renewable energy source good, daily management of the digester and biogas system is essential.
Broiler manure cannot be used in a biogas system since it’s mixed with bedding and contains too much fibre such as sawdust, peanut shells or straw. Manure from layers can be used if it cannot be collected daily.
Some limits
Farmers with farms under land claims hesitate to invest in biogas equipment.
“A biogas plant large enough to handle a big feedlot is expensive,” says Francois. “Including the infrastructure and electronic control, a unit can cost about R2,5 million.”
The ARC has manuals on biogas design and operations (R100); biogas equipment (R30); biogas purification (and biogas from cattle manure (R30). All are available in English and Afrikaans. The ARC’s Institute for Agricultural Engineering can design units to farmers’ specifications, but they don’t sell ready-built units. – Robyn Joubert
For more information contact Auriel Mitchley on (011) 889 0796 or e-mail [email protected]. |f
