To address the problem of poor retention capacity of anaerobic ammonia oxidation(Anammox)flocculated sludge,rice straw biochar RB650 was used as the sludge carrier of anaerobic sequencing batch reactor(ASBR),and Anammox granular sludge was cultured through coordinated regulation of stirring rate and hydraulic retention time,and the variation pattern of nitrogen conversion and sludge characteristics during the culture process were inspected,and the formation mechanism and nitrogen removal mechanism of Anammox granular sludge were elaborated.The results indicated that the granularity of Anammox flocculent sludge could be successfully achieved after 58 days by gradually increasing the mixing rate to 120 r/min and shortening the hydraulic retention time to 12 hours,and the mean values of TN removal rate and volumetric nitrogen removal rate reached 90.6％and 0.21 kgN/(m3·d),respectively,indicating superior nitrogen removal performance.During the incubation process,the wet density,particle size,settling rate and mechanical strength of the sludge increased continuously,and finally formed brick-red mature granular sludge with obvious granular feeling,compact structure,and average particle size of 2.0-2.5 mm in the majority.The excellent structural properties of RB650 provide the basis for the granulation of the Anammox flocculated sludge.Candidatus Brocadia and Candidatus Kuenenia increased from 13.07％to 25.38％in relative abundance,which were the main Anammox bacteria in the system;norank_c_OLB14 and norank_o_SBR1031 increased from 3.40％to 33.93％in relative abundance,which provided skeletal support for granular sludge formation.Also,the final nitrogen removal performance was influenced by the combination of several nitrogen removal pathways such as heterotrophic denitrification,short-range denitrification.
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