Successful operation performance and syntrophic micro-granule in partial nitritation and anammox reactor treating low-strength ammonia wastewater.

The stable operation of the partial nitritation and anammox (PN/A) process is a challenge in the treatment of low-strength ammonia wastewater like sewage mainstream. This study demonstrated the feasibility of achieving stable operation in the treatment of 50 mg/L ammonia wastewater with a micro granule-based PN/A reactor. The long-term operation results showed nitrogen removal efficiencies of 71.8 ± 9.9% were stably obtained under a relatively short hydraulic retention time (HRT) of 2 h. The analysis on the physicochemical properties of the granules indicated most of the granules were in a size in a range of 265–536 μm, and the elementary composition of the granules was determined to be CH 1.61 O 0.61 N 0.17 S 0.01 P 0.03. The microbial analysis revealed Candidatus Kuenenia stuttgartiensis anammox bacteria and Nitrosomonas- like AOB were the two most dominant bacteria with 27.6% and 10.5% abundance, respectively, both of which formed spatially syntrophic co-immobilization within the micro-granules. The ex-situ activity tests showed the activity of NOB was well limited through DO regulation in the reactor. These results provide an alternative PN/A process configuration for low-strength wastewater treatment by sustaining microstate granules. Optimization of the nitrogen sludge loading rate and DO regulation are important for the successful performance. Graphical abstract Image 1 Highlights • High anammox activity was reached in a micro-granule reactor with 50 mgN/L influent. • The reactor succeeded stable operation and 72 ± 10% nitrogen removal at a short HRT 2 h • Anammox-AOB co-immobilizing in micro-granules kept efficient PN/A. [ABSTRACT FROM AUTHOR]