Large quantities of livestock manure accumulate during the course of pig rearing, poultry production and cattle farming. This manure is an important agricultural fertiliser due to its high nutrient content. However, since the composition of the livestock manure varies depending on the type of animal, feed and storage, it does not permit fertilisation that precisely meets the plant nutrient requirements. As a result, more livestock manure is frequently applied to the fields than the plants actually require. Excess, dissolved nutrients leach into ground and surface water and contribute to the eutrophication of waters. The fact that antibiotics are being used to an increasing extent in livestock farming is also an argument against the application of livestock manure over large areas.

In the EU-funded project BioEcoSIM, a project consortium with 15 partners from 5 countries is using pig manure as a valuable resource. Coordinated by the Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB in Stuttgart, the partners aim to convert the constituents of livestock manure into various fertilisers: biochar as phosphorous-rich organic soil amendment as well as mineral fertilisers such as ammonium sulphate, calcium phosphate and magnesium ammonium phosphate (struvite). “The products are mixed to a nutrient composition depending on the plant species and soil conditions and can be used as easy-to-dose fertilisers for agricultural purposes,” explains Sukhanes Laopeamthong, who is coordinating the project at the Fraunhofer IGB. “This prevents overfertilisation. Also, there is a reduction in the use of synthetic nitrogen fertilisers, the production of which requires a very large amount of energy.”

The objective of the project is a pilot plant that integrates all the processing stages for the utilisation of liquid pig manure. The watery livestock manure is first of all separated into a solid and a liquid phase. “We will dry the dewatered, solid phase with an energy-efficient process by means of superheated steam, for which we have already built several different plants together with our project partner Heckmann,” says Laopeamthong. “Then the dried organic components are converted by pyrolysis at a temperature of over 300 °C into phosphorous-rich biochar to be used as soil amendment – as when drying in an atmosphere of superheated steam.” As a result, antibiotics and pathogens are destroyed. Syngas is also produced in the pyrolysis, a mixture mainly of methane, carbon monoxide and hydrogen. “The gas is burned in a combined heat and power plant to generate energy,” says Laopeamthong. From the liquid manure fraction, which still contains inorganic nutrients, struvite and calcium phosphate are precipitated by means of electrochemical processes to produce directly usable fertilising salts. The remaining water, which now contains only traces of nutrients, can be used for irrigation purposes. Finally, ammonia is also found in the excess steam from the drying and in the gas stream of the electrochemical precipitation. This is separated selectively by means of a gas-permeable membrane and recovered in the form of ammonium sulphate.

Thus, almost all the components of the livestock manure are utilised. The energy requirements for the process are comparatively low due to the technologies employed and the use of syngas as an energy source. The sustainability of the process is therefore to be evaluated against standards of the EU Environmental Technology Verification (ETV). “Our objective is that an organisation accredited according to ISO/IEC Guide 17020 rate the process in accordance with the EU General Verification Protocol (GVP) as the best available technology for valorisation of livestock manure,” Laopeamthong sums up.

For 4 years since October 2012 “BioEcoSIM – An innovative bio-economy solution to valorise livestock manure into a range of stabilised soil-improving materials for environmental sustainability and economic benefit for European agriculture” – is being funded within the scope of the 7th Framework Research Programme of the EU (Grant Agreement No. 308637). The project partners, besides the Fraunhofer IGB, are Stichting Dienst Landbouwkundig Onderzoek (Netherlands), Centre de Recerca i Innovació de Catalunya (Spain), the University of Hohenheim (Germany), Centro Technologico Agrario y Agroalimentario (Spain), Acondicionamiento Tarrasense Associacion (Spain), Gospodarstwo Rolne Jacek Śliwka (Poland), Biocompostajes Españoles S.L. (Spain), Dofco BV (Netherlands), YFlow Sistemas y Desarrollos SL (Spain), Initial Projects Limited (UK), Geltz Umwelttechnologie GmbH (Germany), Agroenergie Hohenlohe GmbH (Germany), ASB Grünland Helmut Aurenz GmbH (Germany) und Heckmann Maschinenbau und Verfahrenstechnik GmbH (Germany).

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