A single-stage partial nitrification, anammox and denitratation (SPNADA) process for treating low C/N ratio wastewater in an air-lift internal circulation reactor: performance and microbial interaction

This study developed a single-stage partial nitrification, anammox and denitratation (SPNADA) intergrated bioprocess for the treatment of low C/N ratio wastewater in an air-lift internal circulation reactor (AIR). During the 245 operated days, the reactor showed a high total nitrogen (TN) removal efficiency of 93.2% under limiting dissolved oxygen concentration of 0.5~1.0 mg/L. Reads-based metatranscriptomic analysis found that the expression of the amoA and hao genes for partial nitrification were as high as 3053.4 and 1394.6 RPM, respectively. In addition, the expression of hzsA and hdh genes for anammox were as high as 2706.5 RPM and 4290.6 RPM, respectively. Another notable trend in reads occurrence was that the expression of napA and narG gene for denitratation, were 78.7 and 321.8 PRM, and the sum of which was 3-fold higher than that of nirK and nirS genes. The genome-based analysis revealed that Nitrosomonas and Candidatus Brocadia with 5.5% and 10.0% relative expression were the dominant genera of ammonia-oxidizing bacteria and anammox bacteria, respectively. Besides, the narG expression of Thiolinea (relative expression of 8.5%) that contained the only narG and no nirK or nirS gene accounted for 84.12% of the total narG expression. These results indicate Thiolinea was a potential denitratation bacteria, which played a major role in denitratation. Stoichiometric and kinetic evaluations confirmed that anammox as the dominant nitrogen removal pathway, accounting for 67.0% of the TN removed. Moreover, in terms of nitrite production, the contribution ratio of denitratation was 17.3%. Overall, these findings indicated the SPNADA process was successfully invented in an AIR, which provides a new perspective for nitrogen removal in low C/N ratio wastewater treatment.