Research project VeNGA
Technical support and advice of subarea fermentation & treatment in the BMBF-project VeNGA
Partner: - BTU Cottbus
- GICON GmbH
- IASP Berlin
Funding: Federal Ministry of Education and Research (BMBF)
Duration: July 2013 - June 2017
Contact: Prof. Dr. Christina Dornack
Project description:
Across Germany, approximately 50 million tons of digestate are produced annually, primarily from NaWaRo biogas plants, the utilization of which is almost exclusively on agricultural land as fertilizer. With the amendment of the Renewable Energy Sources Act in 2012, the principle of exclusivity is being abolished, whereby renewable raw materials and biowaste can be used equally for fermentation in order to supply humus- and structure-forming substances that promote aggregation in the soil as well as the stability and development of a stable and functional soil structure.
Within the scope of the project, various biological wastes from separately collected biowaste are fermented as models and examined with regard to their suitability as soil improvers. The fermentation residues will be agglomerated in order to achieve higher biomass growth compared to untreated fermentation residues. In the further course of the investigations, the composition of the digestate, the release and availability of nutrients as well as the long-term influence on plant and soil will be investigated. In particular, there is a high demand for basic research in the interrelated consideration of (bio-) waste fermentation, digestate utilization and effects on soil and plants after application of these digestate residues. These investigations are to be combined with methods of plant nutrient recovery from the liquid phase of the fermentation residues.
First of all, the material characterization of residues from the biowaste fermentation. For this purpose, digestate from waste plants in Germany, digestate from the large-scale fermentation of the company GICON and digestate from the laboratory plant of the BTU Cottbus-Senftenberg were investigated. The digestate properties are heterogeneous and strongly dependent on the nature of the input substrate. The total nitrogen content averages 20 g/kg dry matter (DM), of which 25% is in the form of ammonium. The phosphate content averages 8 g/kg dry matter and potassium oxide 14 g/kg dry matter. The C/N ratio is 14. The digestate from biowaste fermentation thus has a similar nutrient potential to green manure or fresh compost. The heavy metal content of the digestate for all samples is below the limit values for the maximum ordinance for the maximum application of 30 t dry matter/ha within three years.
Various digestate samples were processed into pellets. The residue was dried, crushed and then pelletized with the addition of liquid. The resulting fermentation products were tested in pot experiments in the greenhouse of the BTU Cottbus-Senftenberg and in field experiments at IASP Berlin. A final evaluation of the fertilization effect will take place in 2017.
The Institute for Waste and Recycling Management at the TU Dresden is supporting the project scientifically in the waste management part.