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Biogas technology and its application

The electricity crisis in South Africa is forcing pig farmers to look at alternative energy sources. In this article, Neil Parker of Biogas Technology Africa explains that biogas may be such an alternative.Overview of biogas technology and applications
Biogas is a low cost form of energy derived from renewable “waste” resources: animal manures, agricultural residues, industrial wastewater, human waste and other organic materials.  In China, India and Nepal, biogas has been used widely as a source of energy and waste treatment, and as liquid fertiliser for soil enhancement, since the 1950’s.  By 2005, there were over 100 000 large biogas plants capturing biogas for conversion to useful energy.
Biogas technology is one of the fastest growing renewable energy sectors worldwide, with the annual market growth exceeding 30% each year.  Anaerobic digestion — the underlying biological process of biogas technology — leads to a renewable energy service that ensures a distributed energy production, in which the energy is produced at the point of consumption or demand.
A biogas digester, which produces the biogas, also provides an excellent agricultural waste management solution, most notably animal manures.
Also, capturing methane generated in a biogas digester has an immensely important role to play with respect to rural energisation, poverty alleviation and development, increased industrial and agricultural efficiency and competitiveness, and improved management of our greenhouse gas emissions.  In 1994, agricultural emissions alone accounted for nine percent of South Africa’s total greenhouse gas emissions.
This article summarises how biogas is produced, considers the advantages of the technology, describes common inputs and outputs, and describes the current status of the technology in South Africa.
Description of biogas technology
A biogas digester is a container in which a wet mixture of organic wastes is acted upon by anaerobic bacteria i.e. those bacteria that thrive in the absence of oxygen.  Biogas is formed by bacterial action on the organic matter, with the result of this process being the production of methane (CH4) and carbon dioxide (CO2), which make up two thirds and one third of the total gas produced, respectively.  Small amounts of nitrogen, hydrogen and hydrogen sulphide also occur.  Scrubbing, or cleaning, of the biogas can result in a methane percentage of up to 97%, but involves the use of additional energy and plant.
Typically, 1 m3 of unscrubbed biogas will provide a cooking time of two hours, or 1.5 kWh electrical output. Alternatively, each 2.5 m3 of unscrubbed biogas is equivalent to 1kg of LP Gas.  Different substrates have differing biogas production potentials: one m is produced from one dairy cow, or four pigs, or 100 chickens per day.
Biogas can be used for cooking, lighting, heating and electrical and mechanical generation. The amount of gas produced depends on how much organic solid organic waste verses water going into the system. In an agricultural environment maximum amounts of solids entering a system will produce
* optimal amounts of energy, and
* an output sludge (or bioslurry) which contains all the nutrients which have originally been contained in the input material (like phosphates and nitrogen), which can be utilised as a fertiliser, to the extent that no other organic fertilisation system can compete with such a favourable form of nutrients conservation and recovery.
The most attractive use of biogas technology in the agricultural sector is on pig farms, particularly where the ambient temperature is high enough.  Because the rate of gas production is related to the temperature of the digester, if the air temperature is too cold then the digester has to be heated, requiring energy and additional capital cost.  For pig farmers, particularly in the warmer parts of the country, the normal waste management procedure is flushing of barns into lagoons.
These lagoons, being deep, are by definition anaerobic as can be witnessed by the continuous bubbling of methane gas.  The most cost effective digester then is the so-called covered lagoon digester, which at its simplest level involves covering the first lagoon so that the gasses can be captured, and used.
Advantages of biogas technology on farms
1. Odour reduction – up to 95% of bad odours removed
2. Improved energy security from on-site generation of energy, particularly electricity.
3. A payback period of five years for pig farms, potentially longer for other livestocks.
4. Overflow water or slurry, a residue from the process, is a high-grade fertiliser that can replace expensive mineral fertilisers, in particular nitrogen.
5. The technology is ideal for effective and productive management of livestock wastes.
6. It provides an integrated system for energy production, fertiliser production and waste treatment.
7. Biodigesters relieve the environmental impact by capturing and utilising harmful gasses.
8. A biogas digester can be locally produced or built, and locally operated.
At this stage the use of biogas technology is quite new and relatively unknown in South Africa.  AGAMA Energy – through its Biogas Technology Africa business unit – has built over twenty biogas digesters for different applications around the country.  In parallel with this, a large number of feasibility studies and opportunity assessments for biogas utilisation on different farms and for different applications have been undertaken.
Until recently Biogas Technology Africa was building biogas digester systems according to overseas specifications. Due to local demand escalations, Biogas Technology Africa works with specialist professional partners in the engineering and construction industries to deliver projects.
How to get started? Best place to start is by undertaking a pre-feasibility analysis, which can be based on general data which you can adjust to your situation.  The output of this is a GO/NO GO decision point, and should provide an energy balance as well as projected economics.
For further information contact: Neil Parker at tel:  021 7013364, fax: 021 7013365 or Email: neil.parker@agama.co.za Web: www.agama.co.za


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