Improving nitrogen removal in an IFAS nitritation–anammox reactor treating lagoon supernatant by manipulating biocarrier filling ratio and hydraulic retention time

Abstract

A lab-scale integrated fixed-film activated sludge sequencing batch reactor (IFAS-SBR) was established for a one-stage nitritation–anammox process treating lagoon supernatant and optimized by altering both the biocarrier filling ratio and HRT for 500 days. The reactor’s nitrogen removal rate increased slightly from 0.25 kg N m−3 d−1 to 0.29 kg N m−3 d−1 when biocarrier filling ratio was increased from 35% to 55% at a HRT of 2.5 d, and further increased to 0.46 kg N m−3 d−1 and 0.54 kg N m−3 d−1 when the HRT was reduced to 1.5 d and 1.2 d, respectively. Meanwhile, both NH4+N and TN removal efficiencies increased from 81.8% and 74.8% to 95.2% and 87.4%, respectively, with the increased biocarrier filling ratio; however, they decreased slightly to 91.8% and 82.1% at HRT of 1.5 d and to 89.6% and 78.8% at HRT of 1.2 d, respectively. A distinct segregation of anammox bacteria and ammonium oxidizing bacteria (AOB) was achieved in the IFAS system and was highlighted by the decreased HRTs, which also contributed to the excellent nitrogen removal. The specific anammox activity was higher in biofilm than in suspended flocs, and vice versafor the specific AOB activity. The abundance of major microbial communities involved in this process were analyzed, which supported the observation of reactor performance changes. The present study provides critical knowledge for optimizing the one-stage IFAS nitritation–anammox reactor treating supernatant of anaerobically digested sludge thicken lagoon.