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A rapid start of the completely autotrophic nitrogen removal over nitrite (CANON) process based on granular sludge and efficient nitrogen removal under mixotrophic conditions are important steps in a continuous flow reactor for CANON engineering applications. In this study, an aged CANON granular sludge was mechanically crushed to 0.3 mm as inoculum in an airlift internal-loop reactor (AIR) to achieve simultaneous COD removal and mixotrophic denitrification of the single-stage granular sludge. The system achieved stable partial nitrification by controlling DO after 26 days of startup. Granulation and anaerobic ammonia oxidation were then promoted by shortening the HRT to increase the ammonia nitrogen load to 5.65 kg ·(m

The effects of different hydraulic retention time (HRT) on short-cut nitrification granular sludge were studied in a continuous stirred-tank reactor (CSTR) by maintaining stable influent ammonia nitrogen load. Particle size distribution, extracellular polymeric substances (EPS), and functional bacterial kinetics were analyzed. The morphology of granular sludge, the performance of the CSTR, and the activity of functional microorganisms were investigated. The high throughout sequencing technology of MiSeq was employed to analyze the structure of the microbial community in sludge. The results showed that the ammonia nitrogen removal rate in the reactor was gradually increased from 80% to 95%, and the nitrite accumulation rate was always over 85% when the HRT was decreased from 4 h to 1 h. Particle size distribution of granular sludge was greatly influenced by HRT. The mass fraction of granules with a diameter smaller than 0.3 mm and larger than 1.6 mm was gradually declined, whereas the mass fraction of granules with a diameter between 0.3 mm and 0.8 mm was increased when HRT was shortened from 4 h to 1 h. The dominating proportion of granules with a diameter between 0.3 mm and 0.8 mm reached about 50% when HRT was 1 h. The impact of HRT on the activity of functional microorganisms was studied, and HRT activity was found to be closely related to the size of granular sludge. Proteobacteria were dominant in the system. AOB enrichment was represented by

Partial oxidation of ammonium to nitrite is a pre- and crucial step to achieve shortcut biological nitrogen removal from ammonium-rich wastewater. In the present study, a nitritation granular reactor using activated sludge as inoculum was started up in a sequencing batch reactor (SBR) at a fixed influent C/N ratio of 2:1. Variations in the reactor performance, functional bacteria activities, sludge morphology and bacterial community structure were investigated. Results showed the formation of compact granules was achieved in 55 days, and a stable nitrite accumulation rate of 0.68 kg N·m−3·d−1 was maintained in the following period. With a rapid growth of granular size, the total nitrogen removal by simultaneous nitritation/denitritation was progressively increased to 50%. In sludge granulation, the significant enrichment of r-strategist ammonium oxidizing bacteria (Nitrosomonas) was identified. Additionally, both high free ammonia concentration and extra nitrite competition by heterotrophic denitrifiers were critical to suppress nitrite oxidizing bacteria effectively.

In order to apply partial nitritation-ANAMMOX (PN/A) technology to treat wastewater with high concentrations of ammonia, autotrophic nitrogen-removing granular sludge was crushed and inoculated into a three-stage continuous flow reactor. The nitrogen loading rate (NLR), dissolved oxygen (DO) concentration, and free ammonia (FA) levels in each compartment of the reactor were controlled over a 106-day period. Results showed that the nitritation process occurred with the inoculated granules during the initial phase. A limited aeration strategy was employed in the reactor at relatively high NLRs. Given the effective suppression of nitrite-oxidizing bacteria and the prevention of ANAMMOX bacteria from high DO conditions, the compact structure and nitrogen-removal activity of the granules could be improved. When the ammonia-nitrogen concentration was increased in the influent to 350 mg·L

The start-up and stable operation of single-stage autotrophic nitrogen removal process under low ammonia nitrogen substrate at room temperature appears as the premise and basis for the application in municipal wastewater treatment. In this study, the PN/A (partial nitritation and ANAMMOX) granular sludge for long-term storage was inoculated into an air-lift bioreactor to investigate the nitrogen removal performance during the start-up of single-stage partial nitritation and ANAMMOX process under the following conditions:temperature at (23±2)℃, pH at 7.7-8.0. Synthetic wastewater with ammonia nitrogen concentration of 70 mg·L