The project started with the implementation, monitoring and evaluation of full-scale technologies for nutrient recovery and reuse at five demonstration plants:
• Groot Zevert Vergisting (Netherlands) where digestate of pig manure and residues from agro-industry are processed into a mineral N fertiliser, organic soil improver and a P fertiliser.
• Am-Power (Belgium) where digestate of biowaste is processed into a dried organic P fertiliser, an liquid organic NPK fertiliser and clean water. They thereby reduce the volume the of the end products which in turn reduces costs and impact related to transport.
• Benas (Germany) where energy crops and poultry litter are used to produce biogas and electricity. In addition, mineral N is recovered and organic fibres are extracted and prepared for use in production of carton products.
• Waterleau New Energy (Belgium) where biowaste and pig manure are co-digested and processed into ammonium water and solid organic fertilisers.
• Aqua&Sole (Italy) were sewage sludge serves as a save raw material for the production of organic and mineral fertilisers.
The five demonstration plants were thoroughly monitored by the project team. Phosphorus is mostly recovered in solid fractions and, in GZV, in the form of a phosphate precipitate. Nitrogen is recovered in mineral form through stripping or membrane filtration. Nitrogen strippers, evaporators and dryers consume large amounts of thermal energy. For this, the biogas plants use waste heat that is released during the conversion of biogas to electricity showing the synergy between biogas production and nutrient recovery. Demonstration plants that sell biogas to the grid selected other technologies running on electricity rather than on thermal heat. Overall, it is concluded that the optimal technological solution strongly depends on the type of feedstock, the required composition of end products and the on-site availability of waste heat or electricity.
Biobased mineral N fertilisers (including RENURE fertilisers, e.g. Recovered Nitrogen from manURE) can effectively replace synthetic counterparts without increasing risks for nitrate leaching and are therefore a safe option for NVZs. Levels of heavy metals were generally low and do not possess environmental risks. Screening on residues of herbicides, pesticides and antibiotics revealed that such residues are present in digestate in organic fertilising products but absent in purified water (after reverse osmosis) and mineral N fertilisers. Overall, biobased fertilising products can safely replace raw manure and/or synthetic fertilisers.
Life-cycle analyses showed that nutrient recovery has a small positive effect on the overall carbon footprint of the demonstration plants as compared to the reference scenario in which digestate was used as fertilising product. Production of green energy is far more relevant in terms of CO2 savings as compared to the production of biobased fertilising products. The five demonstration plants were all located in regions with a surplus of nutrients from intensive livestock farming and digestate disposal was a cost item. Nutrient recovery lowers the costs for digestate disposal.
SYSTEMIC explored opportunities for ten other biogas plants interested in nutrient recovery. Several workshops and plant visits were organised. A business development package called the NUTRICAS tool has been developed which is available via www.systemicproject.eu.
