Achieving Partial Nitrification-Anammox Process Dependent on Microalgal-Bacterial Consortia in a Photosequencing...

Partial nitrification coupled with anammox (PN/A) process is an energy-efficient approach for nitrogen removal from low C/N wastewater. In this study, PN/A was achieved with optimal oxygen supply from a green microalga, Chlorella sorokiniana. The PN process was first initiated within 35 days, and the following algae-intensified PN then reached the steady state within the next 32 days. The dissolved oxygen (DO) concentration was gradually maintained at 0.6 mg L^-1 via adjusting the photoperiod to 6-h light/18-h dark cycles, when the accumulation ratio of NO₂ ^--N and the removal ratio of NH₄ ⁺-N were both more than 90%. The nitrogen removal capability of anammox was acclimated via elevating the individual effluent NH₄ ⁺-N and NO₂ ^--N levels from 100 to 200, to 300 mg L^-1. After acclimation, the removal rates of NH₄ ⁺-N and total nitrogen (TN) reached more than 70 and 80%, respectively, and almost all the NO₂ ^--N was removed. Then, the algae-intensified PN/A, algammox biofilm system, was successfully started up. When the NH₄ ⁺-N level increased from 100 to 300 mg L^-1, the TN removal varied between 78 and 82%. In the photosequencing bioreactor, C. sorokiniana, ammonia-oxidizing bacteria (AOB), and anammox coexisted with an illumination of 200 μmol m^-2 s^-1 and a 6-h light/18-h dark cycles. The DO levels ranged between 0.4 and 0.5 mg L^-1. In addition, the microbial community analysis by Illumina MiSeq sequencing showed that the dominant functional bacteria in the algae-intensified PN/A reactors included Nitrosomonas (AOB) and Candidatus Brocadia (anammox), while Nitrospira and Nitrobacter (nitrite oxidizing bacteria), together with Denitratisoma (denitrifier) were largely inhibited. Further studies are required to optimize the microalgal-bacterial consortia system to achieve superior nitrogen removal rates under controllable conditions.