Reactors and active biomass potential as inoculum for nitrogen removal

[Display omitted] •Batch tests and 16 s rRNA indicated the best inoculum for nitrogen removal.•MBBR sample demonstrated to be the best inoculum for nitrogen removal.•Suspended/floccular biomass in denitrification tank was the most favorable for SPND.•If aeration is as low as necessary, SPND will be favored in MBBP WWTP. The potential of three different kind of reactors and active biomass to be used as inoculum for nitrogen removal was verified. Sludge samples were collected from a Membrane Bioreactor (MBR), a previous tank of a Moving Bed Biofilm Reactor (MBBR) and a Trickling Filter (TF). Samples were compared according to bacterial activity in batch tests and their microbiology (16 s rRNA sequences). The microorganisms examined were: AOB, NOB, anammox bacteria and OHO. Results showed that the richest sample was from MBR (Chao value equals 581). However, the bacterial activity was greater in MBBR sample (qAOO,NH4 equals 0.002 mgN·mgVSS−1·h−1; qNOO,NO2_NO3 equals 0.001 mgN·mgVSS−1·h−1 and qNOX_N2,SB equals 10.0 mgN·mgVSS−1·h−1). Therefore, MBBR WWTP was shown to have the best inoculum and operating conditions for nitrogen conversion and removal. Besides, if aeration is provided as low as necessary for AOB to start the activity in denitrification tank, simultaneous partial nitrification, and denitrification (SPND) can occur.