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 Russia, USA, EU, 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 25 million small-scale operational biogas systems worldwide – with over a million now being installed each year – as well as over 100,000 large centralised biogas plants capturing biogas for conversion to useful energy.
A biogas digester – in which the biogas is produced – also provides an ideal on-site water-borne sanitation system, as well as an integrated organic kitchen and garden waste recycling opportunity.
Capturing of methane through the use of biogas technology has an immensely important role to play with respect to rural energisation, poverty alleviation and development, increased industrial efficiency and competitiveness, and improved management of our greenhouse gas
emissions. For example, there are over 300,000 rural South Africa households that are technically viable beneficiaries of onsite energy production through biogas technology to meet all their cooking needs; in 1994, agricultural emissions alone accounted for 9% of South Africa’s total greenhouse gas emissions.
2. Description of biogas technology
Biogas digesters are airtight containers in which a wet mixture of organic wastes are 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 three primary sets of bacteria being involved in
the biological breakdown. The result of this process is the production of methane (CH4) and carbon dioxide (CO2), which make up 2/3 and 1/3 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 2 hours, or 1.5 kWh electrical output. Alternatively, each 2.5 m3 of unscrubbed biogas is equivalent to 1 kg of LP Gas.
Different substrates have differing biogas production potentials ranging from 40 litres per kilogram (cow manures, faeces) to 80 litres per kilogram (chicken litter).
Electricity produced from such a system (producing 750 m3 of biogas per day to power a 60 kW generator) produces electricity at a price in the order of R0.50/kWh (at the breakeven point in time).
The generalised process flow for a small-scale ecological system looks as follows:
3. Advantages of biogas technology
1. Utilizing biogas technology can make an important contribution to the protection and improvement of natural resources and environment.
2. Overflow water or slurry, a residue from the process, is a high-grade fertilizer that can replace expensive mineral fertilizers, in particular nitrogen.
3. The technology is ideal for effective and productive management of livestock wastes.
4. The technology provides an efficient wet sanitary system – that enhances effective waste product disposal.
5. It provides an integrated system for energy production, fertiliser production and waste treatment.
6. Bio digesters relieve the environmental impact by capturing and utilizing harm full gasses.
7. In rural environments conventional fuels such as indigenous fire wood and kerosene are saved and improve the health and safety of the environment by their replacement.
8. The use of biogas enables rural women to save time for productive agriculture, leisure and family care and welfare.
9. Use of biogas technology improves the standard of living and can directly contribute to economic and social development of a country.
10. Biogas systems result in halving of waste solid collection volumes and frequency and landfill disposal costs.
11. A biogas digester can be locally produced or built, and locally operated.
12. The technology has the potential to permanently employ many thousands of people should its potential be reached in the country.
4. Frequently Asked Questions
Who can use/have a biogas digester?
Households + Small holdings
Community centres + institutions
What is needed for a biogas system to work?
Systems can be fed with human waste, separated organic (kitchen) waste, landscape and agricultural off cuts and agricultural waste and manures.
Water is also required, to avoid this being a limiting or primary cost
factor, it is best to use a waste water stream if available. In the farming
context this can be urine from animals, in the urban context this can be
flush and grey water.
What are the different types of biogas systems?
Small low tech systems are made from bricks and mortar or plastic.
Larger high tech systems are made from concrete and steel.
What are the outputs from the biogas system?
A biogas system can be used for
A. Energy generation and
B. Waste water treatment or both.
A. Biogas is a source of energy 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. If
the solid input is high and liquid in put low more energy will be produced.
For example in an agricultural environment maximum amounts of solids
entering a system will firstly produce optimal amounts of energy and
secondly an output sludge which contains all nutrients which have originally been contained in the feeding material like phosphates or
nitrogen can be utilized as a fertilizer, no other organic fertilization system can compete with such a favourable form of nutrients onservation and recovery.
B. In an urban or peri-urban environment utilization of a biogas system to
act as a partial or full waste water treatment system may take priority over the energy requirement, here a system could be designed to recycle water for irrigation or other forms of reticulation.
What are the impacts of a biogas system
Use of a bio digester system relieves the environment enormously. Energy generated reduces energy required from carbon fuel emitting power plants. In an agricultural environment methane gas emitted from animal manure is contained and used to produce energy.
Overflows from bio digester systems can be used for fertilizers, irrigation
or recycling thereby reducing the need to import fertilizers and water.
In rural environments digester systems help to save conventional fuels
such as indigenous fire wood and kerosene and improve the health and
safety of the community and environment by their replacement.
Systematic extension of biogas technology is a way to strengthen
decentralization, create jobs, save money and time and generally improve
the quality of life even if the starting point is urban or peri-urban, rural
area’s will be the long term beneficiaries
African Green Developments has planned to build a number of biogas digesters around the country. In parallel with this, African Green Developments has undertaken a range of feasibility studies and opportunity assessments for biogas utilization in different sectors and for different applications. These have been