Estimated operating costs for a plant with 60,000 tons per year. All figures based on 2014. * German Renewable Energy Sources Act 2014.
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Composting and digestion

Dry, solid organic waste materials are more suitable for composting, whereby a sufficient supply of oxygen (aerobic atmosphere) enables the carbon-containing compounds to be converted into CO2 and heat. This process heat sanitises the compost, enabling it to be used without further heat treatment as fertiliser in agriculture and horticulture.
Liquid or very moist biological waste materials are more suitable for digestion for the purpose of producing biogas. Here, bacteria convert the carbon-containing compounds in the absence of oxygen (anaerobic atmosphere) into biomethane (CH4). Following gas purification, this can be used in CHP plants or fed into the natural gas network. The remaining digestate from the organic waste can be used as fertiliser in agriculture, provided that it has been sanitised by subsequent heating to between 55 and 70 °C.

Capacities and economic prospects

A plant with an annual throughput of 60,000 tonnes produces about 15 million cubic metres of biogas per year. With a methane content of 60 to 65 %, this corresponds to approximately 9 million m³ of natural gas. The figure shows an initial estimate of the costs.

Utilising organic waste for generating energy

Irrespective of whether the biogas originates from organic waste treatment plants or agricultural waste materials, it is initially only raw gas. Depending on the starting material, only 50 to 75 % of it consists of the methane gas required for energy production. The rest consists of carbon dioxide and trace gases such as hydrogen sulphide, hydrogen, oxygen and – when using organic waste – long-chain hydrocarbons. Furthermore, it is 100 % saturated with water. During the gas treatment, some of these associated gases are removed when condensing the water vapour, while others have to be removed in a separate purification step. This pre-treatment prevents corrosion and damage to engines and valves, and also enables low-emission combustion. In addition to combined heat and power (CHP) plants that have proven themselves over many years, gas turbines will also in future provide a means for producing energy from biogas. In the long term, the use of biogas in fuel cells is also a technical option. Biogas is often generated at locations where there is too little local heating demand to be able to operate a CHP plant economically. It then makes sense to feed processed biogas into the natural gas network. The 2010 Gas Network Access Ordinance has paved the way for this. The natural gas network can absorb large amounts of biomethane at any time. According to a report by the German Federal Network Agency to the German federal government, 150 biogas plants fed around 602 million cubic metres of biogas into the gas network in Germany at the end of 2013. A year earlier this figure was 413 million m³. As a climate-friendly energy source, biogas therefore helps to secure energy supplies and, in combination with CHP plants, can balance out the fluctuating energy fed into the grid from wind and photovoltaic systems.


In addition to the generation of biogas, the research is also focussing on pyrolysis as a further option for the energy-based utilisation of biomass. Here, biomass is carbonised under high temperature and pressure. The resulting biochar can be used not only as fuel; there is also interest for this product from agriculture. There it acts as a soil enhancer and provides a relatively long-term form of carbon sequestration. With funding from the German federal government, a demonstration plant for pyrolysing organic waste commenced operation in Halle-Lochau in 2013.

Projektinfo 17/2014:
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Sutco RecyclingTechnik GmbH

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Universität Duisburg-Essen, SiWaWi

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