Synchronous vivianite and hydrogen recovery from waste activated sludge fermentation liquid via electro-fermentation mediated by iron anode.

[Display omitted] • Fe anode achieved 101–743% higher of hydrogen productivity than other iron sources. • Fe anode led complete removal of phosphate within 2 d (vs. 0–39.4% in other groups). • More crystalline vivianite particles were observed in EF system assisted by Fe anode. • Homo-acetogens (78.0%), EAB (8.0%) and DIRB (2.3%) were enriched in Fe anode group. • Correlation and syntrophy between functional microbes and metabolites were explored. Electro-fermentation (EF) is a promising technology for extracting valuable metabolites from waste biomass, while its effectiveness for phosphorus recovery has received little attention. In this study, we investigated the impact of different iron sources, i.e., FeCl 3 , FeOOH, Fe 2 O 3 , zero-valent iron (ZVI), a built-in Fe anode, and stainless-steel mesh (SSM), on concurrent biohydrogen and vivianite (Fe 3 (PO 4) 2 ·8H 2 O) recovery from sludge fermentation liquid (SFL) in an EF system. Results indicated that the Fe anode group achieved the highest hydrogen productivity of 17.7 mmol/g COD at 5 d, which was 101–743% higher than that of other iron sources. The utilization efficiency of short-chain fatty acids (SCFAs) peaked at 79.1% within 5 d, which was 1.2 folds higher than that of Control (without iron addition). Moreover, the phosphate removal efficiency reached 100% within 2 d and 5 d in Fe anode and SSM group, respectively, while the other groups achieved only 0–39.4% removal. SEM and XRD analyses demonstrated the existence of vivianite particles in the recovered products in the groups of FeCl 3 , FeOOH and Fe anode. Electrochemically active bacteria (EAB), e.g., Geobacter , Comamonas , and Desulfovibrio , accounted for 3.6–60.2% of all groups. Geobacter , Azospira , Comamonas , and Desulfovibrio , which are also considered dissimilatory iron reducing bacteria (DIRB), were enriched to 0.1–40.7% in all groups. Acetoanbacterium and Acetoaerobium , typical homo-acetogens, were enriched to 78.0% in the Fe anode group, while was only 9.0–29.3% in other groups. Correlation and molecular ecological network (MEN) analyses of the functional microbial consortia further indicated the intertrophic interaction. This study provides a theoretical basis for synchronous hydrogen and phosphorus recovery from WAS in the further industrial implementation. [ABSTRACT FROM AUTHOR]