The coupling of anammox with microalgae-bacteria symbiosis: Nitrogen removal performance and microbial community.

The partial nitrification-anammox process for ammonia nitrogen wastewater treatment requires mechanical aeration to provide oxygen, which is not conducive to energy saving. The microalgae-bacteria symbiotic system (MaBS) has the advantages of low carbon and energy saving in wastewater biological nitrogen removal. Therefore, this study combined the MaBS with an anammox process to provide oxygen, through the photosynthesis of microalgae instead of mechanical aeration. We investigated the nitrogen removal efficiency and long-term operation of a co-culture system comprising microalgae, nitrifying bacteria (NB), denitrifying bacteria (DnB), and anaerobic ammonium-oxidation bacteria (AnAOB) in a sequencing batch reactor without mechanical aeration. The experiment was divided into three steps: firstly, cultivating NB; then, adding three kinds of microalgae which were Chlorella sp., Anabaena sp., and Navicula sp. to the bioreactor to construct a microalgae-bacteria symbiotic system; finally, adding anammox sludge to construct the anammox and microalgae-bacteria symbiosis (Anammox-MaBS) system. The results demonstrated that nitrification, denitrification, and anammox processes were coupled successfully, and the maximum TN removal efficiency of the stable Anammox-MaBS system was 99.51 % when the concentration of the influent NH-N was 100 mg/L. The addition of microalgae in ammonia wastewater promoted the enrichment of DnB and AnAOB, which were Denitratisoma, Haliangium, unclassified_Rhodocyclaceae, and Candidatus_Brocadia. Furthermore, the unique biofilm structure could effectively alleviate the photoinhibition of light-sensitive bacteria, which may be the reason for the long-term adaptation of Candidatus_Brocadia to light conditions. This research can provide a low-cost solution to bacterial photoinhibition in the coexistence system of microalgae and bacteria without mechanical aeration, offering theoretical support for low-carbon and energy-efficient treatment of wastewater.