Pyrolysis treatment of sewage sludge: A promising way to produce phosphorus fertilizer

Direct use of sewage sludge for application in agriculture is frequently discouraged with reference to toxic compounds. Therefore, methods for sewage sludge conversion and modification to decrease heavy metals mobility are required. Our study was conducted to assess and compare municipal and industrial sewage sludge for the production of carbonaceous pyrolysis products as a potential soil amendment with high phosphorus content. For carbonization at 430 degrees C a lab-pyrolysis reactor was used. The feedstocks and pyrolysis products were characterized (pH, electrical conductivity, FTIR, SEM, CHNS elemental composition, polycyclic aromatic hydrocarbons (PAH) and toxic metal concentration). The obtained results explored the possibility of sewage sludge conversion by pyrolysis process to stable and valuable products with a 2- to 3-fold increase of phosphorus content. Using DTPA extraction protocol we confirmed the good stability of toxic metals in both sewage sludge pyrolysis products compared to feedstocks. The incorporation of pyrolysis products into P-deficient and toxic metal polluted soil was effective to reduce pollutant mobility and to add available phosphorus. Our characterization study highlighted the potential of pyrolysis for closure of the phosphorus cycle and for the production of fertilizers from complex materials such as sewage sludge. (C) 2017 Elsevier Ltd. All rights reserved.