CEN and the German Federal Environment Ministry published a study comparing different analytical methods for recycled nutrients products, including struvites, sewage sludges and sludge incineration ashes. The aim of the research was to understand if existing methods could be used also for new fertilisers. The comparison of 6 chemical digestion methods brought strongly different results, depending on the recycled product and the element being investigated. The extraction temperature was identified as a sensitive parameter in this context, among others: NAC P-availability results vary with temperature and drying of struvites at an analysis temperature of 105°C results in 30-50% mass loss, consequent to the thermal molecular decay. The conclusions call for specific EU standards to test recycled nutrient fertilisers, in order to support the EU Fertilisers Regulation, which is currently ongoing the trilogue negotiations.
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