Performance characteristics and community analysis of a single-stage partial nitritation, anammox and denitratation (SPANADA) integrated process for treating low C/N ratio wastewater

This study describes the development of an air-lift internal circulation reactor that integrates partial nitrification, anammox and denitratation (SPANADA) into a single stage bioprocess for the treatment of low C/N coal gasification wastewater. During 245 days of operation, the compartmental fluidized bed reactor achieved a total inorganic nitrogen (TIN) removal efficiency of 91.4%. Reads-based metatranscriptomic analysis found the expression of the amoA and hao genes essential for nitritation and the hzsA and hdh genes essential for anammox increased dramatically as reactor performance improved and stabilized. Another notable trend was that the total expression of the napA and narG genes, essential for denitratation, was 3-fold higher than the combined reads for nirK and nirS whose products, nitrite reductases, would lower nitrite levels reducing available substrate for anammox. Analysis of metagenome-assembled genomes revealed members of Nitrosomonas and Candidatus Brocadia, were the dominant genera of ammonium-oxidizing bacteria and anammox bacteria, respectively, and accounted for 5.5% and 10.0% of the total reads in the transcriptome. For denitratation, Thiolinea, whose only relevant gene involved in N-metabolism is narG, accounted for 8.5% of the total reads in the transcriptome and, remarkably, 84.1% of narG expression. Mass balance confirmed anammox was the dominant nitrogen removal pathway, accounting for 67.0% of the TIN removed. Nitritation and denitratation accounted for 82.7% and 17.3% of the nitrite production, respectively. The analysis reported demonstrates the development of a novel and effective one-stage nitrogen removal alternative for low C/N wastewater treatment and also helps gain insight into the underlying microbial interactions.