Successful enhancement and related characteristics of anammox bacterial activity by hydraulic supply strategy under limited inoculum

Abstract

Two EGSB (expanded granular sludge bed) reactors (R0 and R1) with 2 g-VSS L−1 anammox sludge were established to intensify specific anammox activity (SAA) and biomass growth under limited inoculum, and in response to a hydraulic strategy. During the start-up period, HRT (hydraulic retention time) was set at 12h in R0, while sharply decreased from 12h to 4h in R1. The sludge characteristics, abundance, and community shifts were also investigated to explore their correlations with SAA enhancement. The results showed that after 120 days, SAA of R1 finally reached 1.6 kg-N kg-VSS−1 per day, which was 1.8- times that of R0. The initial shortened HRT in R1 changed the assembly mode of granulation, and unlike the flocculant sludge in R0, the formation and growth of small granules played a more critical role in improving SAA in R1. Also, the tightly bound layer of extracellular polymeric substances promoted a rapid increase in the proportion of particles larger than 0.6 mm in size, which significantly enhanced SAA. QPCR showed the corresponding abundance of anammox bacteria was gradually saturated to 5.72E+10 copies g-SS−1 when the SAA tended to be stable. While the increase in “saturated abundance” particles (>1.0 mm) speeded up the proliferation of anammox bacteria. The corresponding doubling time was shortened from 36.8–10.0 d in R1, which made up for the disadvantage of the initial biomass loss. The high-throughput analysis revealed Candidatus Kuenenia stuttgartiensis was the dominant genus (34.22 %) in R1.