Fe-C wrapped in polyurethane sponge cubes tied in anoxic zones to enrich multiple denitrifying bacteria enhancing wastewater nitrogen removal

To enhance nitrogen removal in wastewater treatment, a novel method of wrapping waste iron shavings (Fe-C) in polyurethane sponge cubes tied in anoxic zones of a continuous reactor was proposed. Three types of denitrifying bacteria were enriched simultaneously in biofilms and activated sludge, including iron autotrophic denitrifying bacteria (7.83-8.71 %), heterotrophic denitrifying bacteria (10.60-11.95 %), and heterotrophic nitrification-aerobic denitrifying bacteria (23.47-40.06 %). Iron autotrophic denitrifying bacteria (Dechloromonas and Sphaerotilus) can remove NO3--N using Fe2+ as electron donor produced by micro-electrolysis of iron shavings without organic carbon demand, and heterotrophic nitrification-aerobic denitrifying bacteria (Ferribacterium and Zoogloea) can simultaneously accomplish nitrification and denitrification under aerobic conditions. The enrichment of these two functional bacteria strengthened the nitrogen removal performance compared to conventional heterotrophic denitrifying process, which could achieve efficient and stable total nitrogen removal (87.4 %) even with low organic carbon. In addition, the synergy of biological and chemical processes through Fe-C micro-electrolysis also enhanced total phosphorus removal (86.0 %).