Effect of hydraulic selection pressure on the characteristics of partial nitritation/anammox granular sludge in a continuous-flow reactor

In this study, efficient nitrogen removal was achieved in a continuous partial nitritation/anammox (PN/A) granular reactor at a short hydraulic retention time (HRT),high-throughput pyrosequencing revealed that strong hydraulic selection pressure promoted the niche segregation of aerobic and anaerobic ammonium-oxidizing bacteria (AOB and AnAOB) and washout of nitrite-oxidizing species in the granules, the effective retention of k-strategists AnAOB (dominated by genus Candidatus Kuenenia) occupying the interior layer of the granules exhibited a sludge retention time 10-fold longer than that of AOB (identified as Nitrosomonas) enriched in the aerobic zone.