Biofilm coupled micro-electrolysis of waste iron shavings enhanced iron and hydrogen autotrophic denitrification and phosphate accumulation for wastewater treatment

Abstract

Autotrophic denitrification has attracted more and more attention because it does not require organic carbon sources. A circulation ditch filled with plastic filler and waste iron shavings was established to develop hydrogen and iron autotrophic denitrifying bacteria for nitrogen and phosphorus removal from wastewater. The results demonstrated that Hydrogenophaga (hydrogen autotrophic denitrifying bacteria), Unclassified_f__Comamonadaceae (iron autotrophic denitrifying bacteria), and Sphaerotilus (iron autotrophic denitrifying bacteria) were enriched in biofilms, and the relative abundances were 4.0%, 9.0% and 1.2% in aerobic biofilms; 2.9%, 17.8% and 7.7% in aerobic biofilms (Fe–C); 0.6%, 1.8% and 0.04% in anoxic biofilms, and 13.8%, 13.6% and 0.7% in anoxic biofilms (Fe–C). In the system, the removal rates of chemical oxygen demand, ammonia nitrogen, total nitrogen and total phosphorus reached 91.4%, 93.4%, 80.2%, and 79.2%, respectively. The hypothetic mechanism implies that iron-carbon micro-electrolysis produced Fe2+ and H2 to be electron donors for autotrophic denitrification and enriched autotrophic denitrifying bacteria and formed ferrous phosphate in this wastewater treatment system.