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In this study, the behavior, distribution and form dynamics of overloaded Cu(II) in anaerobic ammonium oxidation (anammox) granular sludge reactors were investigated. The performance and physiological characteristics were tracked by continuous-flow monitoring to evaluate the long-term effects. High Cu loading (0.24 g L −1 d −1 ) exceeded sludge bearing capacity, and precipitation dominated the removal pathway. The Cu distribution migrated from the extracellular polymeric substances-bound to the cell-associated Cu and the Cu forms shifted from the weakly bound to strongly bound fractions over time. Pearson correlation and fluorescence spectra analyses showed that the increase in protein concentrations in the EPS was a clear self-defense response to Cu(II) stress. Two remediation strategies, i.e., ethylenediamine tetraacetic acid (EDTA) washing and ultrasound-enhanced EDTA washing, weakened the equilibrium metal partition coefficient from 5.8 to 0.45 and 0.34 L mg −1 SS, respectively, thereby accelerating the external diffusion of the Cu that had accumulated in the anammox granules. [ABSTRACT FROM AUTHOR]

Starvation of anaerobic ammonium oxidation (anammox) bacteria can occur in underloaded bioreactors or during the storage of sludge. In this study, the impacts of intermittent and persistent resting modes and phosphates on the endogenous metabolism of anammox bacteria during long-term starvation were investigated. Batch experiments were performed to evaluate the response of anammox granules to different modes of starvation (persistent-resting and intermittent-resting cells) in the presence and absence of phosphates. The endogenous decay coefficient of anammox granules (based on the decreased biomass) over a 30-d persistent starvation period was 0.0062 d −1 , while the intermittent starvation by means of providing substrates every 10 days accelerated the biomass decay approximately twice (0.0110 d −1 ). Moreover, the intermittent-resting cells displayed exacerbated decreases in specific anammox activity relative to the persistent-resting cells, whereas no significant difference was observed in the heme c contents. Regardless of the physiological status of the cells, the presence of low levels of phosphates may be beneficial; however, a high level of phosphates is not recommended. Although different metabolic strategies were adopted depending on the starvation mode, anammox bacteria possessed a better survival strategy via a relatively low maintenance energy requirement to ensure their survival in nutrient-limited systems. In addition, the variations in extracellular protein-like components were indicative of different intracellular metabolic regulation mechanisms. These results provide a better understanding of the endogenous metabolism of anammox bacteria. [ABSTRACT FROM AUTHOR]

In this study, the individual and interactive effects of influent substrate concentration ( TN inf ), hydraulic retention time (HRT) and upflow velocity ( V up ) on the performance of anaerobic ammonium oxidation (anammox) in a granule-based upflow anaerobic sludge blanket (UASB) reactor were investigated by employing response surface methodology (RSM) with a central composite design. The purpose of this work was to identify the optimal combination of TN inf , HRT and V up with respect to the nitrogen removal efficiency (NRE) and nitrogen removal rate (NRR). The reduced cubic models developed for the responses indicated that the optimal conditions corresponded to a TN inf content of 644–728 mg N L −1 , an HRT of 0.90–1.25 h, and a V up of 0.60–1.79 m h −1 . The results of confirmation trials were similar to the predictions of the developed models. These results provide useful information for improving the nitrogen removal performance of the anammox process in a UASB reactor. [ABSTRACT FROM AUTHOR]

The floatation of flocculent and granular sludge was investigated in this study. An anaerobic ammonium oxidation (anammox) upflow anaerobic sludge blanket (UASB) reactor was operated for 665 days. During this time, the maximum nitrogen removal rate was 52.6 kgN m −3 d −1 . Floccule floatation occurred between days 100 and 140, which potentially resulted from the sudden increase in gas yield and the poor settling ability of the floccules. Increasing the shear rate from 0.084 to 0.135 s −1 was effective at eliminating floccule floatation. In addition, granule floatation occurred between days 572 and 665, which likely resulted from the formation of hollows within the granules. Floatation may be effectively prevented by maintaining a shear rate of more than 0.778 s −1 . Furthermore, the mechanisms of granule floatation and the floatation processes were proposed. Overall, controlling the shear force may effectively overcome sludge floatation. [ABSTRACT FROM AUTHOR]

Highlights: [•] The role of bio-augmentation in assisting recovery of ANAMMOX from OS was studied. [•] The bio-augmentation time (BAT) was optimized. [•] The bio-augmentation dosage (BAD) was optimized. [•] The changes in sludge characteristics were monitored. [•] The mechanisms of bio-augmentation were discussed. [ABSTRACT FROM AUTHOR]