Granular Characteristics of Anaerobic Ammonia Oxidation Sludge During the Recovery Process

Operation instability has become one of the factors restricting the application of the anaerobic ammonia oxidation (ANAMMOX) process. Under the condition that the substrate is not suppressed, the effects of the substrate concentration on the granulation and activity of ANAMMOX granular sludge in the recovery process were studied by restoring the activity of ANAMMOX sludge, which was derived from early-stage operation instability of the continuous stirred tank reactor (CSTR). The results show that the activity of ANAMMOX sludge was recovered and the denitrification capacity increased significantly after 126 days of operation. When the NH4+-N and NO2--N concentrations were 450 mg·L-1 and 560 mg·L-1, respectively, the nitrogen removal was achieved in both the high-and low-substrate concentration reactors and the maximum NRR was 16.97 kg·(m3·d)-1 and 14.43 kg·(m3·d)-1, respectively. With the improvement of the nitrogen removal capacity of the reactor (the granular diameter of the sludge is increased), the extracellular polymeric substance (EPS) content increased in both reactors from 34.45 to 77.52 and to 94.18 mg·g-1, respectively, and the PN/PS increased from 1.89 to 6.25 and 6.84, respectively. To a certain extent, the increase of PN/PS is conducive to the granulation of ANAMMOX sludge, but a too large PN/PS would lead to the instability of granular sludge and sludge loss.