Phosphorus recovery from a pilot-scale grate furnace: influencing factors beyond wet chemical leaching conditions

Abstract

Phosphorus is a non-renewable resource going to exhaustion in the future. Sewage sludge ash is a promising secondary raw material due to its high phosphorus content. In this work, the distribution of 19 elements in bottom and cyclone ashes from pilot-scale grate furnace have been monitored to determine the suitability for the phosphorus acid extraction. Moreover, the influence of some parameters beyond wet chemical leaching conditions were investigated. Experimental results showed that bottom ash presented lower contamination in comparison to cyclone ash and low co-dissolution of heavy metals (especially Cr, Pb and Ni), while high phosphorus extraction efficiencies (76–86%) were achieved. High Al content in the bottom ash (9.4%) negatively affected the phosphorus extraction efficiency as well as loss on ignition, while the particle size reduction was necessary for ensuring a suitable contact surface. The typology of precipitating agents did not strongly affect the phosphorus precipitation, while pH was the key parameter. At pH 3.5–5, phosphorus precipitation efficiencies higher than 90% were achieved, with a mean phosphorus content in the recovered material equal to 16–17%, comparable to commercial fertilizers. Instead, the co-precipitation of Fe and Al had a detrimental effect on the recovered material, indicating the need for additional treatments.

Critical assessment and recommendations for sewage sludge management in Poland

“…Sewage sludge can also be a source of secondary raw materials (Smol & Szołdrowska, 2021). Research on the recycling and recovery of raw materials from sewage waste focuses on technologies such as biogas recovery (Siddiqui et al, 2023;Paranjpe et al, 2020), biological recovery of phosphorus and nitrogen (Boniardi et al, 2022;Saoudi et al, 2022), thermal recovery, metal recovery and the production of fertilisers from sewage sludge (Kominko et al, 2019). The aim of these studies is to reduce the amount of waste that goes to landfills and to obtain added value from raw materials derived from sewage sludge (You et al, 2021).…”