The strategy of crushing and re-granulation promoted anammox granular sludge (AnGS) formation and performance improvement

In this study, a unified mortar crushing method was employed to thoroughly investigate the re-granulation characteristics of anammox granular sludge (AnGS). Specially, the first crush (Crush-I) was inflicted to the total AnGS, while the second crush (Crush-II) was only applied to 25 % of the total AnGS. Meanwhile, by regulating the influent and refluxing flow rates, the anammox performance, particle size variations and functional microbial community structures were monitored respectively in the following two re-granulation stages (termed as RG and P-RG). Results showed that, with the influent ammonia and nitrite concentrations respectively maintained at 40 and 48 mg/L, the total nitrogen removal efficiency (TNRE) and average particle diameter (Dav) both dropped significantly after the crush operation. Hereafter, in the RG stage (115 days), TNRE remained at about 60 %, accompanied by Dav increased remarkably from 168.26 μm to 344.60 μm and the relative abundance of Candidatus Brocadia increased from 0.1 % to 7.9 %; in the P-RG stage (45 days), TNRE gradually reached a maximum of 79.21 %, Dav continued growing from 292.79 μm to 579.67 μm, and Candidatus Brocadia enriched from 1.8 % to 4.9 %. Besides, the relative abundance of nitrite oxidizing bacteria (NOB) increased immediately after Crush-I and Crush-II, but decreased during the two re-granulation stages. Thus, the crush and re-granulation operation facilitated the growth of larger AnGS particles, the enrichment of anammox bacteria, as well as the panning of NOB. This provided an alternative for the rapid formation of AnGS and the maintenance of stable anammox performance in actual practical applications.