Biogas is a renewable energy gas chemically similar to natural gas. Biogas can be produced from a variety of substrates, including sewage sludge from treatment plants and organic wastes from the food processing industry, manure and source-separated household waste. Biogas is produced when organic material is broken down by microorganisms in oxygen-free environments. Biogas can also be produced by thermal gasification of wood fuels. To use biogas as vehicle gas, the gas must be upgraded to natural gas quality, which means a methane content of at least 97%.
Today, annual production of biogas in Sweden is approximately 1.5 TWh. The total production potential of indigenous raw materials, excluding raw materials from forests, amounts to about 10 TWh/year with current technology. From the residual products from forestry and forest industry the total biogas potential is estimated at about 59 TWh with gasification technology.
Alternative vehicle fuel
From both an economic and environmental perspective biogas is the best alternative vehicle fuel available on the market today. The total emission of carbon dioxide, hydrocarbons and dust particles decreases sharply in comparison with fossil fuels, as well as if pure organic residual products are used in the process then the digested residue (biofertilizer) can be returned to agriculture as fertilizer.
There are biogas-powered vehicles in many cities today, and measurements have been made which indicate a marked improvement in urban environments after the introduction of biogas-powered vehicles. It also costs less to run on biogas in comparison with gasoline. In the current situation biogas-powered vehicles also have a lower taxation level for benefits than gasoline cars.
Reducing greenhouse gas emissions
Combustion of biogas means just about no net addition of carbon dioxide to the atmosphere as the carbon originates from the carbon dioxide in the air that plants take up. The size of the environmental benefit depends on the energy system being replaced.
When biogas is used as an alternative to oil the need for finite energy is reduced and carbon dioxide emissions are reduced dramatically. But it is not just oil that poses a threat to the climate. Manure wells also affect the climate adversely. Here methane is formed naturally which escapes into the atmosphere, and because methane is a greenhouse gas with about 25 times more greenhouse effect than carbon dioxide, there is a major environmental benefit in anaerobically digesting the manure to biogas, thereby reducing methane emissions. If biogas is then used as vehicle fuel it gives a double climate benefit by means of both methane and carbon dioxide emissions being reduced. The reduction will then be 180 percent.
Other environmental benefits
Further positive environmental effects that are evident include a decrease in plant nutrient losses into lakes and watercourses. The reason for this is that the nitrogen is converted in the anaerobic digestion process to become more accessible to plants to take up. A reduction in the smell during the spreading of digested residue from manure-based biogas production can also be included here. The smell is otherwise something else that many now see as a growing environmental problem.
Now it is important that biogas production starts on a larger scale, partly to reduce fossil fuel dependency, and partly to reduce some of the environmental impact of agriculture. Today much of the plant nutrients that are produced are transferred via our food into urban areas. For this reason the residual products should be collected, processed and then returned in a cycle in the form of biofertilizer.
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