Zheng-Zhe Zhang

Evaluation of the inhibitory effects of heavy metals on anammox activity: A batch test study.

This study evaluated the interactive effect of Cu(II) and Zn(II) on anaerobic ammonium oxidation (anammox) activity using response surface methodology with a central composite design. A regression model equation was developed and validated to predict the normalized anammox activity (NAA) of anammox granules exposed to various heavy metal concentrations. The joint inhibitory effect tended to exacerbate initially and reversed as the concentrations increased and then moderated again. The most severe inhibition, resulting in a NAA of 20.1%, occurred at Cu(II) and Zn(II) concentrations of 16.3 and 20.0mgL(-1), respectively. Notably, the cumulative toxicity was mitigated with the aid of intermittent exposure acclimatization. Additionally, pre-exposure to Cu(II) in the absence of substrates strongly inhibited anammox activity. However, the presence of NO2(-) significantly enhanced Cu(II) inhibition. Therefore, such conditions should be avoided to minimize the disturbance of the anammox process.

Short-term impacts of Cu, CuO, ZnO and Ag nanoparticles (NPs) on anammox sludge: CuNPs make a difference

The increasing application of engineered nanoparticles (NPs) has posed an emerging challenge to wastewater treatment processes. The short-term impacts of CuNPs, CuONPs, ZnONPs and AgNPs on anaerobic ammonium oxidation (anammox) process were investigated firstly in this study. CuONPs, ZnONPs and AgNPs up to 50mgg-1 suspended solid (SS) did not affect anammox activity, reactive oxygen species (ROS) production or cell membrane integrity. However, 1.25mgg-1SS CuNPs significantly inhibited the anammox activity and the loads that caused 50% inhibition were 4.64±1.24 and 3.27±0.79mgg-1SS for anammox granules and flocs, respectively. 5mgg-1SS CuNPs caused serious accumulation of the toxic intermediate N2H4. Furthermore, CuNPs interacted with extracellular polymeric substances by specifically bonding to tyrosine or tryptophan-containing groups, C-O-C in polysaccharides and -OH in polymeric compounds. Therefore, this study calls for more attention to the risks of NPs to the anammox-based processes.

Combined impacts of nanoparticles on anammox granules and the roles of EDTA and S2− in attenuation

Previous studies investigating the risk of engineered nanoparticles (NPs) to biological wastewater treatment have primarily tested NPs individually; however, limited data are available on the impact of NPs on the anaerobic ammonium oxidation (anammox) process. In this study, the toxicity of CuNPs on anammox granules was investigated individually and in combination with CuONPs or ZnONPs. Exposure to CuNPs at 5mgg-1 suspended solids (SS) decreased the anammox activity to 47.1±8.5%, increased the lactate dehydrogenase level to 110.5±3.4% and increased the extracellular N2H4 concentration by 16-fold but did not cause oxidative stress. The presence of CuONPs or ZnONPs at 5mgg-1 SS did not significantly aggravate or alleviate the toxicity of the CuNPs; however, the introduction of EDTA or S2- could attenuate the adverse effects of the CuNPs, CuONPs and ZnONPs on the anammox granules. EDTA captured Cu ions, whereas S2- shielded and deactivated Cu ions and passivated CuNPs. Therefore, our results indicated that the toxicity of NPs was dependent on the amount of active metal reaching the anammox cells. Overall, the results of this study have filled knowledge gaps and provided insights into the combined toxicity of NPs on anammox biomass.

Behavior and fate of copper ions in an anammox granular sludge reactor and strategies for remediation

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.

Insight into the short- and long-term effects of inorganic phosphate on anammox granule property

The short- and long-term effects of inorganic phosphate on property of anaerobic ammonium oxidation (anammox) granule were investigated in this study. Acute exposure to high-level phosphate (⩾50 mM) induced the cytoplasm leakage. During a 195-day continuous-flow operation, the gradually increasing phosphate (up to 500 mgP L(-1)) slightly affected the specific anammox activity, hardly impacted the heme c content, remarkably decreased the extracellular polymeric substances production and significantly stimulated the dehydrogenase activity of anammox granules. Microbial community analysis showed no shift in the dominant anammox strain and higher population but lower relative abundance of anaerobic ammonium-oxidizing bacteria compared to the control granules. Interestingly, novel anammox granules with a hydroxyapatite core were cultivated, which possessed excellent settleability, huge granule diameter and superior mechanical strength. This study supported the application of granule-based anammox process as a pre-processing treatment in phosphate-containing and ammonia-rich wastewaters.

Roles of EDTA washing and Ca²⁺ regulation on the restoration of anammox granules inhibited by copper(II).

We investigated the feasibility of using ethylene diamine tetraacetic acid (EDTA) washing followed by Ca(2+) enhancement for the recovery of anammox reactors inhibited by Cu(II). Kinetic experiments and batch activity assays were employed to determine the optimal concentration of EDTA and washing time; and the performance and physiological dynamics were tracked by continuous-flow monitoring to evaluate the long-term effects. The two-step desorption process revealed that the Cu in anammox granules was primarily introduced via adsorption (approximately, 80.5%), and the portion of Cu in the dispersible layer was predominant (accounting for 71.1%). Afterwards, the Cu internalized in the cells (approximately, 14.7%) could diffuse out of the cells and be gradually washed out of the reactor over the next 20 days. The Ca(2+) addition that followed led to an accelerated nitrogen removal rate recovery slope (0.1491 kgN m(-3) d(-2)) and a normal biomass growth rate (0.054 d(-1)). The nitrogen removal rate returned to normal levels within 90 days and gradual improvements in granular characteristics were also achieved. Therefore, this study provides a new insight that externally removing the adsorbed heavy metals followed by internally repairing the metabolic system may represent an optimal restoration strategy for anammox consortium damaged by heavy metals.

Optimization of process performance in a granule-based anaerobic ammonium oxidation (anammox) upflow anaerobic sludge blanket (UASB) reactor.

In this study, the individual and interactive effects of influent substrate concentration (TNinf), hydraulic retention time (HRT) and upflow velocity (Vup) 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 TNinf, HRT and Vup 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 TNinf content of 644-728mgNL(-1), an HRT of 0.90-1.25h, and a Vup of 0.60-1.79mh(-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.

Unraveling the impact of nanoscale zero-valent iron on the nitrogen removal performance and microbial community of anammox sludge

Given the increasing use of nanoscale zero-valent iron (NZVI) particles for environmental remediation and wastewater treatment, their potential impact on anaerobic ammonium oxidation (anammox) bacteria was investigated in this study using anammox sludge. Batch assays showed that NZVI concentrations up to 200mgL-1 did not affect anammox activity, reactive oxygen species production, and cell membrane integrity. The nitrogen removal efficiency of the continuous-flow reactor fluctuated in the presence of 20 or 50mgL-1 NZVI, but it could return to normal over time, even at 200mgL-1 NZVI. 16S rDNA-based high-throughput sequencing indicated that although the presence of 10, 20, 50, and 200mgL-1 NZVI to some extent affected microbial composition, the anammox bacteria (Candidatus Kuenenia) never lost its dominance. The abundance of gene families that are related to the assimilation and utilization of iron was down-regulated in response to the stress of high-level NZVI.

Bio-augmentation for mitigating the impact of transient oxytetracycline shock on anaerobic ammonium oxidation (ANAMMOX) performance.

The feasibility of applying bio-augmentation tactics to remit the influence of transient oxytetracycline (OTC) shock on the anaerobic ammonium oxidation (ANAMMOX) process was evaluated. The bio-augmentation was applied together with shock test, with OTC shock concentration of 518 mg L(-1) and 1-h duration. 0.655-2.62 g volatile suspended solid (VSS) sludges were varied to optimize bio-augmentation dosage (BAD), and appropriate bio-augmentation time (BAT) was determined. The validity of the bio-augmentation was indicated by recovery performance and sludge characteristics. The restoring time of 38 h for bio-augmented reactor was shorter than that of non-bio-augmented reactor (45 h), and heme c content was increased respectively from 0.195 ± 0.001, 0.267 ± 0.047, 0.301 ± 0.049, to 0.340 ± 0.053 μmol g(-1) VSS with the BAD of 0.655, 1.31, 1.97, 2.62 g-VSS. The results suggest that bio-augmentation enhances the recovery of ANAMMOX performance following OTC shock and BAT and BAD are key operational factors.

Susceptibility, resistance and resilience of anammox biomass to nanoscale copper stress

The increasing use of engineered nanoparticles (NPs) poses an emerging challenge to biological wastewater treatment. The long-term impact of CuNPs on anaerobic ammonium oxidation (anammox) process was firstly investigated in this study. The nitrogen removal capacity of anammox reactor was nearly deprived within 30days under the stress of 5.0mgL-1 CuNPs and the relative abundance of anammox bacteria (Ca. Kuenenia) was decreased from 29.59% to 17.53%. Meanwhile, copper resistance genes associated with the Cus, Cop and Pco systems were enriched to eliminate excess intracellular copper. After the withdrawal of CuNPs from the influent, the nitrogen removal capacity of anammox biomass recovered completely within 70days. Overall, anammox biomass showed susceptibility, resistance and resilience to the stress of CuNPs. Therefore, the potential impacts of ENPs on anammox-based processes should be of great concern.