Mechanisms governing the dissolution of phosphorus and iron in sewage sludge by the bioacidification process and its correlation with iron phosphate speciation

• Published in: Chemosphere (Oxford) 2022-11, Vol.307, p.135704-135704, Article 135704
• Main Authors: SAOUDI, Mohamed Amine, DABERT, Patrick, VEDRENNE, Fabien, DAUMER, Marie-Line
• Format: Article
• Language: English
• Subjects: Biological acidification; Environmental Sciences; Iron phosphate speciation; Phosphorus recovery; Phosphorus removal; Waste activated sludge
• ISSN: 0045-6535; 1879-1298
• DOI: 10.1016/j.chemosphere.2022.135704

In the last two decades, phosphorus (P) recovery from sewage sludge liquors gained much interest for its high-quality product potential. However, the consistently reported constraints are the low phosphorus availability and the technical-economical difficulties to increase it through chemical acidification. This article discusses the mechanisms of phosphorus dissolution by the biological acidification process (Biological acidification or acidic fermentation) as an alternative to chemical acidification. In addition, we investigate the potential correlation between the phosphorus dissolution and iron phosphate speciation of several types of sludge from different sewage treatment plants and P removal technologies. The results show that the percentage of P dissolution by bioacidification is always higher than the P dissolution by chemical acidification at equal pH for all types of sludge except for the settled primary sludge. The highest P dissolution was recorded for the sludge from the Enhanced Biological P Removal process assisted with Chemical P Removal process (EBPR-CPR) with around 65% of P dissolution. Three mechanisms were identified as contributing to the increased P dissolution by bioacidification: P release by the Polyphosphate Accumulating Organisms (PAO), P dissolution by pH decrease, and P dissolution by a biological activity at acidic pH (3.7–4) that includes iron reduction and aluminum dissolution. The principal component analysis and Pearson's correlation indicate that P dissolution by bioacidification is negatively correlated with the P-bound to ferric iron, hence positively correlated with the P-bound to ferrous iron, which characterizes the sludge from the EBPR-CPR process. This study suggests that the choice of the P removal technology significantly influences the P recovery from sewage sludge liquors. [Display omitted] •Bioacidification resulted in a better P dissolution than chemical acidification.•Three mechanisms govern the bioacidification: P release by PAO, pH decrease and iron reduction.•Phosphorus bound to reducible ferric iron is the most resistant fraction to dissolve.•P dissolution by bioacidification is correlated with phosphorus bound to ferrous iron compounds.•P dissolution by bioacidification is most efficient with sludge from EBPR-CPR process.