Improved energy supply, waste management and climate effects by use of biogas technology in South African prison farms
Energy needs for room heating, warm water and steam production in South African prisons are normally acquired from electricity produced via fossil fuels.
Due to increased national electricity consumption severe shortages in supply result that must be substituted by emergency generators driven by diesel fuel. On the other hand, prisons are also operating agricultural farms that include pig and cattle farming. The manure mostly remains either untreated or is partly used as a fertiliser and directly applied in crop production. Both effects are accompanied by negative environmental impacts in the region, such as water pollution of nearby rivers and air pollution by odour substances.
To improve the situation a change towards the use of solar energy and biomass instead of fossil fuels, as well as the proper management of animal manure and its use as a renewable energy source in a biogas plant, is proposed and its feasibility is studied in the case of a typical prison farm.
As a basic scenario the application of a 'full†biogas plant, including cogeneration through combined heat and power production, the use of waste heat for warm water production, the application of digested manure in agriculture and the direct use of biogas for steam and warm water production were studied. Variants of crops and manure, both qualitatively and quantitatively, were considered. The technical layout and implementation into the prison farm management were proposed based on experiences in planning and operation of European biogas plants. Economic results, ecological consequences in terms of environmental impacts and social impacts were studied and generalised based on waste type and amount, energy needs and local climatic factors.
Best results would be achieved if biogas is used as an alternative fuel to petrol, with the equivalent of 1 400 litres of petrol per day being produced, which exceeds the needs of the prison transportation sector and is available for selling. The variant is economically feasible in case of a petrol price higher than € 0,35/l, which is about one-third of the current fuel market price. The second option involves the preparation of warm water for room heating, which is able to substitute about one third of the currently used electricity. The option is economically viable if the energy price exceeds € 0,045/kWh. In the case of higher prices for electricity other variants such as cogeneration (combined heat and power) will be possible. Environmental impacts are between 1 000 and 3 000 tons CO2-equivalents annually, depending on the realised biogas plant.
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