Mechanistic understanding of the NOB suppression by free ammonia inhibition in continuous flow aerobic granulation bioreactors

Free ammonia resistance of nitrite‐oxidizing bacteria developed in aerobic granular sludge cultivated in continuous upflow airlift reactors performing partial nitritation

“…Two identical ALRs with the same design as described elsewhere (Kent et al, 2019) were employed in this study to implement partial nitritation, that is, oxidation of 50% influent NH 4 + ‐N to NO 2 ‐ ‐N and full nitrification, that is, oxidation of 100% influent NH 4 + ‐N to NO 3 − ‐N (Figure ). Briefly, each ALR comes with 1.5 L working volume and a 3‐cm‐diameter internal riser for hydraulic mixing.…”

“…For the full nitrification ALR, aeration rate was maintained at 0.3 L/min without nitrogen gas supplementation. Substrate containing 50–60 mg NH 4 + ‐N/L along with other nutrients as described in previous study (Kent et al, 2019) was continuously pumped into the two ALRs at a flow rate of 0.3 L/hr, giving a same hydraulic retention time of 5.2 hr. The seed aerobic granules for the partial nitritation ALR were collected from a DEMON ® reactor operated by Hampton Roads Sanitation District, Virginia Beach, VA.…”

“…The DO/ammonia ratio control does not suppress K‐strategy NOB for their high affinity to DO (Liu & Yang, 2017); consequently, FA inhibition had to be resorted to (Kowalski, Devlin, di Biase, & Oleszkiewicz, 2019a,2019b). FA was found to selectively inhibit NOB but not AOB (Anthonisen, Loehr, Prakasam, & Srinath, 1976) and has been taken advantage for NOB suppression in a number of mainstream wastewater treatment researches (Cao et al, 2017; Kent, Sun, An, Bott, & Wang, 2019; Poot, Hoekstra, Geleijnse, van Loosdrecht, & Pérez, 2016), which is also believed to be the mechanism underpinning the intermittent aeration strategy (Ma, Domingo‐Félez, Plósz, & Smets, 2017). Although the ability of NOB to acclimate FA inhibition over 100–125 days of operation has been reported previously (Duan, Ye, Lu, & Yuan, 2019; Turk & Mavinic, 1989), all FA acclimation studies were conducted for conventional activated sludge in sequential batch reactors (SBRs) so the long‐term stability of the FA inhibition strategy on granular sludge cultivated in continuous‐flow reactors (CFRs) largely remains unknown.…”

“…Although the ability of NOB to acclimate FA inhibition over 100–125 days of operation has been reported previously (Duan, Ye, Lu, & Yuan, 2019; Turk & Mavinic, 1989), all FA acclimation studies were conducted for conventional activated sludge in sequential batch reactors (SBRs) so the long‐term stability of the FA inhibition strategy on granular sludge cultivated in continuous‐flow reactors (CFRs) largely remains unknown. So far, the longest FA inhibition study for NOB suppression in granular sludge in a CFR reported in the literature was only about eight months (Kent et al, 2019).…”

“…A respirometer (Challenge Technology, AER‐800) was employed to measure AOB:NOB activity ratios to reveal the composition of microbial communities in aerobic granules with different sizes based on the oxygen uptake rate (OUR) measurement described elsewhere (Kent et al, 2019). Briefly, aerobic granules were sieved into six size ranges: 100–150 μm, 150–250 μm, 250–300 μm, 300–350 μm, 350–420 μm, and 420–500 μm.…”