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

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 NO(2) (−)-N and the removal ratio of NH(4) (+)-N were both more than 90%. The nitrogen removal capability of anammox was acclimated via elevating the individual effluent NH(4) (+)-N and NO(2) (−)-N levels from 100 to 200, to 300 mg L(−1). After acclimation, the removal rates of NH(4) (+)-N and total nitrogen (TN) reached more than 70 and 80%, respectively, and almost all the NO(2) (−)-N was removed. Then, the algae-intensified PN/A, algammox biofilm system, was successfully started up. When the NH(4) (+)-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.