Phosphorus concentration and availability in raw organic waste and post fermentation products

The aim of the study was to determine the mobility of phosphorus forms in raw organic waste and from the solid and liquid fractions of digestate. To achieve the purpose of this study, the components (including livestock manure, agricultural waste, food waste, sewage sludge) and their post fermentation products were considered. Subsequently, the effect of the fermentation process on the mobility of phosphorus forms in post-fermentation fractions (solid and liquid) was investigated. Then, the evaluation of the fertilising potential of digestate fractions was assessed. The available organic and inorganic phosphorus forms were determined according to the Standards in Measurements and Testing (SMT) Programme extraction protocol and according to the acid molybdate spectrophotometric method. It has been shown that phosphorus in digestates occurred mainly in inorganic forms with Fe, Al, Mn, Mg and Ca ions. Its proportion in relation to total phosphorus ranged from 80 to 90%. The lowest phosphorus content was found in digestate from the fermentation of agricultural and food waste (fruit and vegetables), while digestate from livestock manure and sewage sludge fermentation was rich in phosphorus. It was shown that the solid fractions of digestate represented from 30 to 70% of highly labile phosphorus (i.e. phosphorus with organic matter and in bonds with Al, Fe, Mg and Mn oxides and hydroxides) in relation to total phosphorus. However, the share of labile phosphorus forms in the liquid fraction of digestates was much higher and accounted for 80-90% of the total phosphorus.