Nitrogen Removal and N2O Accumulation during Hydrogenotrophic Denitrification: Influence of Environmental Factors and Microbial Community Characteristics

Hydrogenotrophic denitrification is regarded as an efficient alternative technology of removing nitrogen from nitrate-polluted water that has insufficient organics material. However, the biochemical process underlying this method has not been completely characterized, particularly with regard to the generation and reduction of nitrous oxide (N2O). In this study, the effects of key environmental factors on hydrogenotrophic denitrification and N2O accumulation were investigated in a series of batch tests. The results show that nitrogen removal was efficient with a specific denitrification rate of 0.66 kg N/(kg MLSS center dot d), and almost no N2O accumulation was observed when the dissolved hydrogen (DH) concentration was approximately 0.40 mg/L, the temperature was 30 degrees C, and the pH was 7.0. The reduction of nitrate was significantly affected by the pH, temperature, inorganic carbon (IC) content, and DH concentration. A considerable accumulation of N2O was only observed when the pH decreased to 6.0 and the temperature decreased to 15 degrees C, where little N2O accumulated under various IC and DH concentrations. To determine the microbial community structure, the hydrogenotrophic denitrifying enrichment culture was analyzed by Illumina high-throughput sequencing, and the dominant species were found to belong to the genera Paracoccus (26.1%), Azoarcus (24.8%), Acetoanaerobium (11.4%), Labrenzia (7.4%), and Dysgonomonas (6.0%).