BioEcoSIM^® – Combined process for the treatment of liquid manure and fermentation residues

Liquid manure and fermentation residues - raw material suppliers for mineral fertilisers and soil conditioners

Liquid manure and fermentation residues contain valuable plant nutrients, above all nitrogen, phosphorus and potassium; indigestible plant fibres are further components. In the EU-funded BioEcoSIM project, coordinated by the Fraunhofer IGB, various treatment processes were developed and the individual process stages were combined in a plant on a demonstration scale. This turns waste and residual materials into valuable raw materials and closes the natural nutrient cycle.

For processing, various process steps were integrated as separate modules in one plant. After treatment, all that remains is water that contains only traces of phosphorus and nitrogen, but is rich in potassium - and can be used to irrigate agricultural land.

Pretreatment and solid-liquid separation

In a first step, the aqueous manure is pre-treated so that phosphorus is completely dissolved and separated into a solid and a liquid phase via a multi-stage filtration.

Thermal processes for the treatment of solids

The dewatered solid phase is dried using an energy-efficient process developed at Fraunhofer IGB. The dried organic components can optionally be torrefied with this process at approx. 250 °C or converted to biochar via a pyrolysis step at 450 °C.

Phosphate precipitation and ammonium recovery

The liquid fraction contains the dissolved inorganic nutrients. Phosphorus is first recovered in a reactor and precipitated as calcium phosphate, magnesium phosphate and magnesium ammonium phosphate as crystals and filtered off.

Nitrogen is recovered in a second step. For this purpose, the aqueous fraction is separated as ammonium sulphate by membrane adsorption and crystallised.

Integration of the processes in pilot plant

At a potential user on site, an agricultural enterprise with animal husbandry, the modules were integrated into a semi-technical plant. The plant processed about 50 kilograms of pig manure per hour to produce about 500 grams of mineral phosphate fertilizer (a mixture of calcium phosphate, magnesium ammonium phosphate and magnesium phosphate), 500 grams of mineral nitrogen fertilizer (pure ammonium sulfate) and 900 grams of organic biochar (or 4.5 kilograms of organic soil conditioners).

Extensive greenhouse and field trials have shown that the mineral fertilizers processed from liquid manure or fermentation residues can be used directly as fertilizers that are readily available to plants, and the organic soil conditioners as humus-forming substrates in agriculture. The biomass yield of the fertilizers is comparable to that of commercially available mineral fertilizers of similar phosphorus content.

• Cost-efficient and sustainable, cycle-based process
  
• Automated, simple operation of the systems
  
• Robust operation with low maintenance costs
  
• Modular design allows adaptation to changes in substrate quality
  
• Dewatered and processed products can be marketed with added value.