Performances and enhanced mechanisms of nitrogen removal in a submerged membrane bioreactor coupled sponge iron system.

Abstract

Sponge iron is a potential material for nitrogen removal, but lack of a study about nitrogen removal in a membrane bioreactor (MBR) coupled with sponge iron. The performances and mechanisms of nitrogen removal of SI-MBR were investigated and compared it with that in GAC-MBR. The results showed that the average rate of organic matter removal in the SI-MBR was 92.74%, which was higher than that in the GAC-MBR (87.48%). And the average effluent NO2--N and NO3--N concentration in the SI-MBR (0.02mg/L and 3.73mg/L) was lower than that in the GAC-MBR (0.05mg/L and 7.51mg/L). Meanwhile, the highest nitrification rate and denitrification rate was respectively 3.544±0.25 mg/(g VSS·h) and 6.643±0.2 mg/(g VSS·h) in the SI-MBR, which was higher than that (3.094±0.25 mg/(g VSS·h) and (6.376±0.2 mg/(g VSS·h)) in the GAC-MBR. Additionally, the bacterial activities (e.g., DHA activity and respiratory activity) were obviously enhanced through the iron ion from sponge iron. The bacterial community in the SI-MBR system was more richness and diverse than that in the GAC-MBR. Ultimately, the mechanisms of enhanced biological nitrogen removal with sponge iron in MBR were analyzed. On the surface of sponge iron, the DIRB and FOB could use the iron ion from sponge iron as the electron transfer to improve the nitrogen and organic removal. With sponge iron, there is not only the nitrification bacteria and heterotrophic denitrifying microorganism enriched, but also the autotrophic denitrifying bacteria abounded obviously. The autotrophic denitrifying bacteria could use Fe(II) as an electron donor to achieve denitrification and enhance the nitrogen removal.