Process of nitrogen transformation and microbial community structure in the Fe(0)-carbon-based bio-carrier filled in biological aerated filter.

Nitrogen pollutants in low-organic carbon wastewater are difficult to biodegrade. Therefore, the Fe(0)-carbon-based bio-carrier (FCBC) was firstly used as hydrogen producer in a biological-aerated filter (BAF) to make up for the lack of organic carbon in biological nitrogen removal. Physical and chemical properties of FCBC were detected and compared in this study. The nitrogen removal rate for low COD/TN ratio wastewater, nitrogen transformation process, and microbial communities in the FCBC filled in BAF were investigated. Results showed that the nitrogen removal rates was 0.38-0.41 kg N m(-3) day(-1) in the FCBC filled BAF and reached 0.62 kg N m(-3) day(-1) within the filter depth of 60-80 cm, under the conditions of the dissolved oxygen 3.5 ± 0.2 mg L(-1) and the inlet pH 7.2 ± 0.1. Hydrogenophaga (using hydrogen as electron donor), Sphaerotilus (absorbing [Fe(3+)]), Nitrospira (nitrificaion), and Nitrosomonas (ammonia oxidation) were found to be the predominant genera in the reactor. The reaction schemes in the FCBC filled in BAF was calculated: hydrogen and [Fe(3+)] were produced by Fe(0)-C galvanic cells in the FCBC, ammonia was oxidized into nitrate by Nitrosomonas and Nitrospira genera, hydrogen was used as electron donors by Hydrogenophaga genus to reduce nitrate into N2, and [Fe(3+)] was partly absorbed by Sphaerotilus and diverted via sludge discharging.