Synergistic effects of zero-valent iron-carbon galvanic cells on the microalgal-bacterial symbiosis system for efficient anaerobic digestion effluent treatment

A novel microalgal-bacterial symbiosis (MABS) system was established with the in-situ introduction of zerovalent iron-carbon galvanic cells (Fe-0/C-MABS) for anaerobic digestion effluent (ADE) treatment. The results indicated that the removal efficiencies of COD, HN4+-N, TN and TP in Fe-0/C-MABS reached 96.4 %, 97.4 %, 96.7 % and 99.7 %, respectively. And the removal rates of COD, TN and TP were significantly increased compared to the single MABS system. Fe-0/C facilitated microalgae growth, increased biomass of microalgal-bacterial consortium and enhanced microalgal-bacterial consortium flocculation, thereby enhancing its structural stability. Fe-0/C-supported autotrophic denitrification and Fe3+-accelerated PO4--precipitation further strengthened TN and TP removal. Enrichment of Comamonas and Brevundimonas confirmed the promotion of microalgae-bacteria synergistic effects by Fe-0/C, and the increased abundance of Actinobacteria proved the contribution of autotrophic denitrification on TN removal. Accordingly, the synergetic effect between Fe-0/C galvanic cells and MABS played a significant role in ADE treatment. Therefore, these results will provide a reference for future application of the Fe-0/C-MABS system for efficient ADE treatment.