AS part of the European Union-funded project BioEcoSIM, 15 European research institutes from five countries aim to convert livestock manure into an organic soil amendment (biochar) and mineral fertilizers.
Large quantities of livestock manure accumulate during the course of pig rearing, poultry production and cattle farming.
This manure is an important agricultural fertilizer due to its high nutrient content. However, since the composition of the livestock manure varies depending on the type of animal, feed and storage, the fertilizer does not precisely meet the plant's nutrient requirements.
BioEcoSIM is using pig manure in its studies. Coordinated by the Fraunhofer Institute for Interfacial Engineering & Biotechnology IGB in Stuttgart, Germany, the partners aim to convert the constituents of livestock manure into biochar — a phosphorous-rich organic soil amendment — and mineral fertilizers such as ammonium sulfate, 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 fertilizers for agricultural purposes," explained Sukhanes Laopeamthong, who is coordinating the project at Fraunhofer IGB. "This prevents over-fertilization. Also, there is a reduction in the use of synthetic nitrogen fertilizers, the production of which requires a very large amount of energy."
The objective of the project is a pilot plant that integrates all of the processing stages for the utilization of liquid pig manure. The watery livestock manure is first 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," Laopeamthong said. "Then, the dried organic components are converted by pyrolysis at a temperature of more than 300 degrees C into phosphorous-rich biochar to be used as soil amendment — as when drying in an atmosphere of superheated steam."
The process destroys antibiotics and pathogens. 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," Laopeamthong said.
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 fertilizing 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 sulfate.
Thus, almost all components of the livestock manure are utilized, according to the announcement. The energy requirements for the process are comparatively low due to the technologies employed and the use of syngas as an energy source.