Phosphorus recovery from organic waste for its agronomic valorization: technical and economic evaluation

Abstract

The present work investigates the use of municipal mixed waste compost (MMWC) residue for phosphorus(P) recycling from a technical, economic, and environmental perspective. The study aims to obtain liquid extracts rich in P from MMWCwith a low heavy metals content, suitable for their subsequent precipitation in the struvite form. The effect of inorganic (sulfuric/nitric)and organic (oxalic/citric) acids at different molarities and temperatures was studied using technical analysis. The preliminary eco-nomic analysis allows the costs of the extraction section for the optimal extraction strategies to be estimated and compared.RESULTS: Based on the multilevel factorial design, the P extraction optimization shows that sulfuric acid 0.5 M and 30 °C pro-vided the highest P extraction yield, 94.2%. However, oxalic acid 0.1 M and 30 °C is the best choice to maximize the P extractionyield, while also minimizing the heavy metals concentration, reaching a P recovery of 2.5 g P/kg. The extraction kinetics for alltested acids were satisfactorily modelled using a second-order model (r2> 0.99). The preliminary economic analysis, estimatedfor a P extraction pilot plant of 100 kg h−1of MMWC, noted that sulfuric acid 0.5 M provided the lowest total investment cost(130 000 €) and a minimum sale price of theoretical struvite at 4.96 €/kg.CONCLUSION: MMWC is a promising raw material for P recycling as fertilizer due to an appreciable P concentration (7 g P/kg),which can be used together with other residues rich in P to obtain an economical and sustainable extraction process.