Biogas technology has found important applications around the world since its discovery in the 17th Century. Over the years, the applications have evolved from domestic uses to more advanced grid tied electricity generation applications as well as fuel for motor vehicles.
Biogas is a combustible gas generated from the anaerobic digestion of organic matter. Anaerobic digestion is a naturally occurring process that occurs when organic matter decomposes under anaerobic conditions producing methane gas. Natural systems that harbour this process include rumen digestive system of a cow and swamps.
The development of biogas can be traced back to China and India. The two countries developed self-named biogas units which became the backbone of biogas development. The Chinese biogas was known as the fixed dome pipe whilst the Indian biogas was known as the floating drum digester. Germany led the development of industrial biogas digester by developing a combination of the two types and significantly improving the biogas generation, storing and purification methods. To date more than 9000 biogas plants have been constructed. Biogas accounts for up to 8 % of the national energy supply of Germany and constitutes more than 50% of energy from renewables.
The emergence of biogas in Africa has experienced a number of false starts over the past decades .Lack of research, and limited financing of emerging technologies have led to Africa playing catch up in renewable energy technologies especially biogas development. Introduction of biogas in Africa was driven by missionaries with aim of solving both energy and waste management problems they came across a as they developed their missionary infrastructure across Africa.
Tanzania, Ethiopia and Zimbabwe have been at the fore front runners in adopting the biogas technology. Tanzania has invested in research and adoption the technology for African conditions; the Centre for Agricultural Research Mechanisation and Rural Technology (CARMATEC) has adopted the fixed dome digester and some improvements to adapt it to African conditions. A model known as the Modified CARMATEC was developed and has gained popularity in Africa.
Zimbabwe has developed two biogas programmes, the Zimbabwe National Domestic Biogas Programme (ZNDBP) and the Zimbabwe Institutional Biogas programme. Both programmes are aimed at increasing capacity of local institutions and builders to support biogas development, dissemination of biogas information to create awareness and construct biogas digesters. Under the ZNDBP, over 120 builders have been trained to construct digesters and 300 biogas digesters constructed, whilst the institutional biogas programme trained 23 builders and has constructed 80 to date. According the National Renewable Energy Policy, Zimbabwe has a target to construct 8000 domestic biogas digesters and 283 institutional biogas digester
According to the World Biogas Association (WBA) anaerobic digestion has the potential to reduce greenhouse gas emissions. Indeed, it has been reported that emissions can possibly decrease from 4,360 to 3,290 Mt CO2eq, which is equivalent to 10-13% of the world’s current greenhouse gas emissions. This result can be achieved through the anaerobic digestion of wastes and landfill gases, in addition to supply of energy biogas produces organic fertiliser, therefore the technology available enables, fossil fertilisers manufacture, crop burning and deforestation are avoided. The sum of these actions results in greenhouse gases reduction. According to the WBA report, despite the 50 million micro-digesters, 132,000 small, medium and large scale digesters and 700 upgrading plants operating globally, we are tapping into just 1.6-2.2% of the global potential of AD. The potential for the growth of the biogas industry is therefore extraordinary and involves every country”
Biogas cooking can also improve the livelihoods of rural households, as by-products of biogas production such as slurry and fertiliser boost agricultural productivity. Modern biogas use reduces the amount of time spent by women and children collecting wood. Despite these clear advantages, the potential of domestic biogas has not been fully exploited due to constraints including;
• Limited awareness about biogas applications
• The initial cost of installation
• Lack of skilled labour for installation and operation
• Inadequate and intermittent government support; feedstock availability
• The need for consistent maintenance
• Behavioural and social acceptance
• Competition from fossil-based alternatives.
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