Mechanism of electro-acclimation shaped microbiota facilitating phosphorus release from iron-containing sludge:...

Iron-based Chemically Enhanced Primary Treatment (Fe-CEPT) can efficiently concentrate phosphorus (P) from municipal wastewater into sludge; however, unfavorable P release efficiency impedes P recovery from Iron-based Chemically Enhanced Primary Sludge (Fe-CEPS). This study developed an electro-digester by applying controlled potentials to bio-electrodes. The electro-acclimated microorganisms on bio-electrodes achieved efficient P release due to microbial Fe(III) reduction and microbial metabolism-induced P-Fe complexes dissolution. In P release potential tests, 53.2 % of total P was released within 60 h after +1.0 V acclimation, 2.2-fold of the control. P fractionation analysis revealed that the proportion of Fe(II)-P, Fe(III)-P, and Reductant-P in Fe-CEPS (substrate) decreased by 9.7 %, 44.8 %, and 37.5 % after P release, respectively, combined with X-ray diffraction analysis, indicating P-release process followed Fe(III)-P and reductant-P first being reduced to Fe(II)-P and then dissolved into P(liquid), while inherent Fe(II)-P directly dissolved into P(liquid). The enhanced electron transfer capacity of electro-acclimated microorganisms, demonstrated by cyclic voltammetry analysis, promoted Fe(III)-P reduction. The lower pH (a minimum of 5.7) in mixed liquor, achieved by the enhanced metabolism of electro-acclimated microorganisms and elevated enzyme activities relating to hydrolysis-acidification, facilitated the dissolution of Fe(II)-P into the liquid phase. These two steps were dominated by enriched iron-reducing bacteria as Deferribacteraceae and fermentative bacteria as Clostridiaceae in electro-acclimation shaped microbiota. Metagenomic analysis showed consistent results as genes encoding cellular respiratory, metabolism and electron transportation upregulated significantly. These findings provided an eco-friendly, cost-effective solution for treating iron-containing chemical sludge and recovering valuable P resources.