Physicochemical and microbial properties of settled and floating anammox granules in upflow reactor

A lab-scale UASB reactor was used to assess the high-rate performance of anammox process after long-term operation by shortening HRT. The nitrogen removal rate (NRR) was developed to 15.51 kg N m(-3) d(-1) with a relative high nitrogen removal efficiency (NRE) of 90.5% under the short HRT of 1.0 h. However, continuous granules' flotation consequently initiated and was enhanced under the high nitrogen gas production condition, accompanying by the decrease in NRE to 69.8%. The physical, chemical and microbial characteristics of the settled and floated anammox granules were compared. Results indicated that the alternation of chemical properties (e.g. EPS over-secretion) of granules helped to prevent gas escaping out, thus decreasing sludge density. Therefore, granules' flotation becomes inevitable in high-rate anammox reactors. Microbial analysis showed that Brocadiacea dominated in settled and floated granules with abundance of 42% and 36%, respectively. Whereas, the abundance of Chloroflexi in floated sludge (20.69%) was much higher than that in settled sludge (12.66%). (C) 2017 Elsevier B.V. All rights reserved.