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Biogas is a mature technology.  The production of Bio-methane from the Anaerobic Digestion of Organic Material has been observed since ancient times, and has been utilised as a source of fuel since the late 1800’s.  Since the mid-1900’s the process has received increasing interest and more recently extensive research, and has now developed into a recognised source of Renewable Energy that is of growing importance.  Typical  biogas plant sizes start as small as 20kWe through to multiple MWe range.

The utilisation of bio-methane from the anaerobic digestion process ranges from small home digesters producing gas used for cooking and heating purposes, to utility-scale power plants feeding electricity or natural gas into national grids.

As opposed to sun and wind based renewable energy sources, Biogas is available 24/7.

The manure generated from livestock farming represents a significant waste disposal problem – particularly in a modern, intensive farming environment.  Cattle manure is utilised extensively in biogas facilities on a global scale.  As an example, 200 cows will produce at least 5t of manure per day, which will produce 125m3 of biogas in a well-designed and operated digester, of which approximately 60% will be Methane.  Combusted in a gas engine, this could produce 20kW of electrical power and 40kW of heat, on a continuous basis.  Of all the potential agricultural waste streams, cow manure is one of the lowest-yield sources of bio-methane and yet it is still successful in providing cost-effective renewable energy. 

A dairy farmer with 200 cows could save over R8 000/month on his utility bill, and further benefit from the use of the liquid fertiliser for irrigation of his pastures and use the compost substrate as cattle bedding, or sell it to a commercial compost producer.   Pig manure has similar bio-methane potential, is also available in massive quantities, and represents a serious waste disposal problem to the farmer.

Abattoirs and meat-processing industries also have serious waste disposal constraints.  The most widely used method of disposal for abattoir waste is by discharge into municipal sewers.  Costs due to the high Chemical and Biological Oxygen Demand of untreated abattoir waste are high.  Abattoirs often have difficulty in meeting municipal requirements for fats, oils, greases and suspended solids – all of which have excellent bio-methane potential though anaerobic digestion.

Fruit and vegetable farming is another sector that represents a significant portion of the South African potential biogas market.  Approximately 30% of the fruit and vegetables produced in South Africa are discarded due to bruising, damage and blemishes.  Large volumes of waste, including leaves and stalks, are trimmed from fruit and vegetables harvested prior to retail.  These are all excellent sources of bio-methane, with very much higher yields than manure.  One limiting factor in this market segment is the seasonal variation in production.  However, many fruit and vegetable farmers are farming with multiple crops to manage seasonal fluctuations, and using greenhouses to extend the growing season, so this is not seen as a major constraint in terms of market limitation

A medium-sized vegetable farmer producing 3t/day of waste from spoiled produce and trimmings could save R7 500 per month on his utility bill. More significantly, he could save over R25 000/month on waste disposal costs.  As a further benefit, he could utilise the waste heat from process to heat his greenhouses and use the liquid fertiliser and compost produced to improve crop yield.  

In terms of the fruit and vegetable food processing industry, routine use of multiple produce streams largely eliminates seasonal variations in throughput, which for any production-type business is the ideal mode of operation.  Sugary liquid waste, which is high in oxygen demand and can contain in excess of 15% dissolved solids, is costly to dispose of in municipal sewage works and represents a serious environmental threat if released, yet it is an excellent source of bio-methane through anaerobic digestion, as is the pulp from juicing and canning processes.

The solid and liquid waste from brewerieswineries and other alcoholic beverage production also represents a large potential source of biogas, and furthermore requires significant amounts of heat and electric power input to the process that could be supplemented through an on-site biogas facility, whilst also alleviating problems and costs associated with waste disposal.

 

 Biogas Information 

 World Bioenergy Association Biogas Factsheet

South African Biogas Industry Association

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