Plant-availability of phosphorus removed from wastewater by different processes

Abstract: The objective of this thesis was to investigate the plant-availability of P removed from wastewater by different processes, with focus on agronomic aspects. Short-term P availability was assessed by greenhouse studies, utilizing four different filter substrates and a sludge-recovered iron phosphate. It was shown that the plant-P availability of these products was not significantly different from that obtained with a water-soluble P fertilizer. It was also found that dewatering method exerted on one FeCl3- precipitated sludge did not influence the plant-P availability. The long-term effects of sludge amendment to agricultural soil was assessed by P ion concentration in solution and P transfer from soil solid phase to solution for soil samples collected from a 19-year old field experiment. The relative plant-P availability (RPA) was found to be 60% for the sludge treatments, a value that was not significantly different from 100%.