The authors really appreciate the feedback from the reviewers. The authors have assessed the comments and revised carefully the manuscript to clarify all the questions raised. Format and presentation of the paper have been improved according to the suggestions of the reviewer #5. The detailed answers to the comments are summarized below. All changes in the text are highlighted in red in the revised version.
ANSWER:We have checked capitalization, inconsistent spacing and all suggestions marked by the reviewer throughout the manuscript.
ACTION:All changes are highlighted in red in the manuscript. Some examples are given below.Space between a value and the symbol (%) was deleted throughout the manuscript (e.g. L 38: 6.9% w/w, 47.6%).Reviewer #5 suggested add a separator for the numbers above 1,000 in the manuscript, tables and figures (see L46: 1,600 k€).Capitalization was checked and corrected (e.g. L51: Soil organic carbon. L191-192: The relative seed germination (RSG) and the relative root growth (RRG)).Complete description of the equipments (model name, company, country) is now provide, as suggested by the reviewer 5 in the text (e.g. L137:
BACKGROUND: 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 MMWC with 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 economic 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 provided the highest P extraction yield, 94.2%. However, oxalic acid 0.1 M and 30 °C is the best choice to maximize the P extraction yield, while also minimizing the heavy metals concentration, reaching a P recovery of 2.5 g P/kg. The extraction kinetics for all tested acids were satisfactorily modelled using a second-order model (r 2 > 0.99). The preliminary economic analysis, estimated for a P extraction pilot plant of 100 kg h −1 of 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.
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