ReNu2Farm focusses on nutrient recycling and upscaling of biomass from pilot to farm scale, and one of the tasks of the project was to characterise RDFs obtained from processing streams like animal manure, sewage sludge and food waste. 24 RDFs were collected from 20 biomass processing units and characterised for their total and plant-available nutrient composition by performing specific chemical extractions. The analysed RDFs include ashes, struvite, composts, digestate and its various derivatives, ammonium sulphate, ammonium nitrate, ammonia water, liquid fraction of manure, pig urine, flowering pots made of manure, and foliar spray rich in keratin made from chicken feathers.
Ghent University (Belgium) has led this task, assisted by other project partners (Arvalis - Institut du végétal, France; and University of Limerick, Ireland) who characterised a few RDFs like ashes, struvites and composts (relevant to their location and individual experiments). The physico-chemical characterisation of RDFs included parameters like dry matter and organic matter analyses, pH, electrical conductivity and total elemental analysis (including trace elements and other heavy metals). Mineral N, and water- and neutral ammonium citrate-soluble P analyses were also performed on relevant RDFs. In the final chapter of the report, potential theoretical tailor-made RDF blends were proposed, based on the characterisation results and based on findings from the deliverable 1.2 of Work Package 2 (Exploring the demand for recycling-derived nutrients and organic matter in regions of Northwest Europe) that reports on nutrient demands of crops in the North-West European region.
It can be concluded from this task that RDFs like ammonium nitrate, ammonium sulphate, and ammonia water are entirely mineral N products and do not contain considerable quantities of other macro- and micronutrients (except S in ammonium sulphate). RDFs like composts have a substantial content of NPK, among other nutrients. There are also products like ashes produced from different thermochemical processes that are rich in P and K, but they also contain higher amounts of heavy metals. The report also points to a lack of harmonised protocols for assessment of RDFs on the European level, thus causing incongruities in analyses conducted and subsequently, the results obtained. This emphasises greatly on the need to establish coherent and consistent protocols for not only inorganic synthetic fertilisers (as currently done in Fertiliser Regulation 2003/2003), but also for novel RDFs fertilisers.
