17 Oct Biogas

National Academy of Technologies of France (NATF)

The 14 members of the NATF working group on biogas published its report in early 2016.  Historically speaking, biogas, resulting from the decomposition of organic matter, has been known since the late 18th century, when Alessandro Volta analysed the composition of swamp gas, finding methane as the main component.  In France and India, the exploitation of this process through bacterial “fermentation” in digesters started in the late 19th century while China builds a whole infrastructure around biogas, but always on a local scale, taking advantage of carbon credits from European industry for their funding.  In Europe, the production of biogas on an industrial scale takes off somewhere between 1980 and 1990, while France joins in at a somewhat slower pace than some other countries

The report describes the various sources and processes for the generation of biogas, such as:
1) hermetically sealed waste dumps and the capture of biogas from anaerobic digestion – this source of biogas is declining;
2) anaerobic fermentation on an industrial scale of household waste (difficult to handle because of heterogeneity of such waste) with different species of bacteria developing peak activity at different temperatures;
3) fermentation of agricultural crop waste (including maize) and animal droppings (including dung);
4) processing of biodegradable sludge from waste water treatment plants (and other biological waste) using a controlled thermophilic aerobic fermentation; etc.

The valorisation of the resulting digestates as fertilizer is not yet well regulated.
Biogas plants using a second generation methanisation process, dubbed Bio-methane 2G, a thermo-chemical process of methanisation of dry organic material at temperatures of 750 to 1000°C have been built at Ulm, Germany and Gothenburg, Sweden.

With regard to climate change, biogas is regarded as a renewable energy reducing the generation of greenhouse gases and EU policies therefore promote the generation and utilisation of biogas.  The report describes policies and practices of a few selected countries. However, untreated biogas is not fit for burning in industrial installations, for generating electricity or being injected into the gas grid.  It contains various contaminants such as Nitrogen, CO2, H2S, siloxanes, etc.  These need to be filtered (using scrubbers, membrane technology and other purification processes).  The report describes these processes.
The success of biogas as a substitute for natural gas, including for electricity generation and injection into the gas pipelines, depends entirely on the amount of financial incentives granted and the report argues that such incentives should be decided and given at the local level where the installations are to be built.  The authors believe that in France biogas has the potential to attain about 1 million toe (tons of oil equivalent) per year by 2020, somewhat less than what official sources tend to communicate.

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