Hydroxylamine addition enhances fast recovery of anammox activity suffering Cr(VI) inhibition.

Hydroxylamine (NHOH), one of the most important intermediates of anammox was employed to test the recovery performance because of its stimulation to anammox bacteria. Batch test indicated simultaneous addition of 1.83 ~ 9.17 mg N /L NHOH relieved Cr(VI) inhibition because of extracellular reduction to Cr(III). The recovery efficiency (RE) was over 166%, with the effluent Cr(VI) and Cr(III) below 0.25 and 0.12 mg/L, respectively. Anammox activity after Cr(VI) inhibition was effectively recovered by 8 mg N/L NHOH with RE at 218%. The long-term operation showed 1 ~ 2 mg N/L NHOH accelerated the recover speed of nitrogen removal rate with 2.84 folds, as well as improving NH conversion ratio and reducing NO production. After 55 days recovery, extracellular polymeric substance concentration, anammox activity and heme content recovered better with NHOH addition. This study will provide the theoretical basis for rapid recovery of anammox activity by NHOH when suffering Cr(VI) inhibition.