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Anaerobic ammonium oxidation (anammox) is a promising biological nitrogen removal process, due to its advantages of high efficiency and low cost. However, problems remain in the application, such as long startup period and susceptibility to environmental variations. Quorum sensing (QS), as a means of bacterial communication, attracts more attentions in regulating aggregation behavior and microbial density. Many physiological characteristics of anammox bacteria have been confirmed to be associated with QS, including specific anammox activity, growth rate and the production of extracellular polymeric substances (EPS), which directly affect the performance of anammox process. Therefore, a comprehensive understanding of the QS in anammox process is prerequisite. This work systematically reviewed the role and application of QS in the anammox process with the focus on mechanism. Additionally, current challenges and research needs were proposed. [ABSTRACT FROM AUTHOR]

While the application of mesophilic anammox process is currently the state of the art, the feasibility of a thermophilic anammox bioprocess is still unclear. In this study, we investigate whether glycine betaine (GB) addition can enhance the thermotolerance of mesophilic anammox biomass in the upflow anaerobic sludge blanket (UASB) reactors fed with synthetic wastewater at a nitrogen loading of approximately 4 kg N m–3 d−1. The results showed that during a long-term operation at 45°C with GB (0, 0.1, 1, 2 mM) addition, anammox performance became worse with the final effluent concentrations of NO2–N of 145 ± 11.6 mg L−1 and nitrogen removal efficiency decreased from 92.3–6.9%. Specific anammox activity decreased from 392.1 ± 12.1–6.0 ± 0.8 mg N g−1 VSS d−1, which were not significantly higher than those in the control reactor. The content of heme c showed a stronger downward trend in T1 (with GB addition) than in the control reactor T0. The qPCR results showed that the relative abundance of Candidatus Kuenenia decreased in both the experimental (from 53.5–28.8%) and control reactors (from 54.1–35.1%). Overall, continuous addition of exogenous GB did not improve the thermotolerance of mesophilic anammox consortia at 45°C. [ABSTRACT FROM AUTHOR]

The increasing release of engineered nanoparticles (NPs) from consumer products has raised great concerns about their impacts on biological wastewater treatment. In this study, the widely-used ZnO NP was selected as a model NP to investigate its impact on high-rate denitrifying granular sludge in terms of sludge properties and community structure. A hormesis effect was observed during short-term exposure, in which the specific denitrification activity (SDA) was stimulated by 10% at 1 mg L−1 ZnO NPs, but inhibited by 23% at 5.0 mg L−1 ZnO NPs. When continuously exposed to 2.5 mg L−1 ZnO NPs, the nitrogen removal capacity of the denitrification reactor was nearly deprived within 15 days, and the relative abundance of the dominant denitrifying bacterium (Castellaniella) was decreased from 51.0 to 8.0%. Meanwhile, the dehydrogenase activity (DHA) and the content of extracellular polymeric substance (EPS) significantly decreased to 22.3 and 61.1%, respectively. Nevertheless, the presence of phosphate substantially weakened the adverse effects of ZnO NPs on the SDA, EPS, DHA and the relative abundance of functional genes even exposed to 6.25 mg L−1 ZnO NPs, which was associated with the fact that the level of Zn(II) released from ZnO NPs was significantly reduced in the presence of phosphate. Therefore, the toxicity of ZnO NPs may be mainly attributed to the release of toxic Zn(II) and could be attenuated in the presence of phosphate. Overall, this study provided further reference and meaningful insights into the impact of engineered NPs on biological wastewater treatment. Image 1 • A hormesis effect was observed during short-term exposure. • 2.5 mg L−1 ZnONPs reduced the nitrogen removal capacity by 72.5% within two weeks. • 310 mg P L−1 phosphate increased the metabolic activity and abundance of denitrifying bacteria. • Based on the PICRUSt, the abundance of genes related to zinc ion assimilation was decreased. [ABSTRACT FROM AUTHOR]

Candidatus Microthrix parvicella has been frequently detected as the dominant filamentous bacteria in bulking sludge and thus seriously affects the stable operation of activated sludge processes. The extremely low growth rate of Ca. M. parvicella and its sensitivity to environmental variations greatly limit the development of effective techniques to control filamentous bulking. Based on previous investigations, a variety of restrictive substrates, operating and culture conditions, environmental factors and other potential inhibitors have varying degrees of impact on the growth of this microorganism. This review systematically summarizes the key factors affecting Ca. M. parvicella growth with a focus on the influencing mechanism. Recent filamentous bulking control strategies are also critically reviewed and discussed. Additionally, research needs for the next few years are proposed with the aim of establishing effective and specific control strategies for filamentous sludge bulking. • The influencing factors of Ca. M. parvicella were summarized based on recent studies. • Specific control strategies for the sludge bulking caused by Ca. M. parvicella were reviewed. • Unsolved questions, potential solutions and research needs were clearly proposed. [ABSTRACT FROM AUTHOR]

The feasibility of using anaerobic ammonium oxidation (anammox) process to treat wastewaters containing antibiotics and heavy metals was evaluated in this study. The nitrogen removal performance and characteristic parameters were monitored during the whole experimental period of 258 d. The single and joint effects of zinc and tetracycline on the microbial community were studied in upflow anaerobic sludge blanket (UASB) reactors. The anammox performance remained at levels comparable with the initial state at the lower inhibitor concentrations (zinc, 0–2.26 mg L−1; tetracycline, 0–0.5 mg L−1). When the concentrations of zinc and tetracycline increased to 3.39 mg L−1 in R 1 and 1.0 mg L−1 in R 2 , an obvious deterioration in performance was observed. Dual inhibitors with a total concentration of ≥3 mg L−1 caused dramatic decreases in the nitrogen removal efficiency of R 3. The quantification results showed that the abundances of eight antibiotic resistance genes (ARGs), czc A and int I1 in the experimental reactors generally increased under stress from metals or/and antibiotics, with final values higher than in the control, while the functional gene abundances were lower. Moreover, most genes exhibited significant correlations. Microbial community analysis indicated that Planctomycetes (represented by Candidatus Kuenenia) was inhibited by both zinc and tetracycline, but still held the dominant position. Furthermore, Caldilinea (belonging to Chloroflexi) maintained a higher abundance during the inhibitory period, implying its potential resistance to both inhibitors. These findings suggested that anammox could be inhibited by metals and antibiotics, but it has the potential to remove nitrogen from wastewaters containing both of them within the concentration threshold. • The inhibition thresholds of zinc and tetracycline on anammox were 3.39 and 1 mg L−1, respectively. • The joint inhibition of zinc and tetracycline on anammox was stronger than the single inhibition. • Caldilinea was the potential resistance bacteria. • Anammox has the potential to treat wastewaters containing small amounts of metals and antibiotics. [ABSTRACT FROM AUTHOR]

Anammox and autotrophic desulfurization-denitrification (AADD) process is feasible for the nitrogen and sulfide removal in the same reactor, and the influence of excess nitrate produced by anammox could also be alleviated simultaneously. This study firstly proposed a novel strategy with inoculating single anammox sludge to start up the AADD process. Results demonstrated that the 90% nitrogen removal efficiency (NRE), 2.55 kg m−3 d−1 nitrogen removal rate (NRR), and 95% sulfide removal efficiency (SRE) were obtained at the influent total nitrogen of 280 mg L−1 and sulfide of 221.5 mg L−1, and the final effluent nitrate concentration was as low as 8 mg L−1 under the appropriate operation conditions. Tryptophan-like and protein-like substances were characterized as the main components in bound EPS. Thiobacillus (35.68%) and Pseudoxanthomonas (11.61%) were identified as the predominant genera. This study will pave a potential avenue to promote the treatment of high concentration nitrogen and sulfide in wastewater in the future. Unlabelled Image • AADD process could be successfully started up by merely seeding the anammox sludge. • Nitrate concentration was under 8 mg L−1 in the final effluent. • Tryptophan-like and protein-like were the main components in bound EPS. • Thiobacillus and Pseudoxanthomonas were the predominant genus in AADD process. [ABSTRACT FROM AUTHOR]

The anaerobic ammonium oxidation (anammox) process has the advantages of a high nitrogen removal rate, low operational cost, and small footprint and has been successfully implemented to treat high-content ammonium wastewater. However, very little is known about the toxicity of the heavy metal element Ni(II) to the anammox process. In this study, the short- and long-term effects of Ni(II) on the anammox process in an upflow anaerobic sludge blanket (UASB) reactor were revealed. The results of the short-term batch test showed that the half maximal inhibitory concentration (IC 50) of Ni(II) on anammox biomass was 14.6 mg L−1. A continuous-flow experiment was performed for 150 days of operation, and the results illustrated that after domestication, the achieved nitrogen removal efficiency was up to 93±0.03% at 10 mg L−1 Ni(II). The settling velocity, specific anammox activity and EPS content decreased as the Ni(II) concentration increased. Nevertheless, the content of heme c increased as the Ni(II) increased. These results indicate that short-term exposure to Ni(II) has an adverse impact on anammox process, but the anammox system could tolerate 10 mg L−1 Ni(II) stress after acclimation during continuous-flow operation for 150 days. High-throughput sequencing results indicated that the presence of Ni(II) had an impact on the microbial community composition in the anammox reactor, especially Candidatus Kuenenia. At Ni(II) concentrations of 0-10 mg L−1, the relative abundance of Candidatus Kuenenia decreased from 36.23% to 28.46%. • The IC50 of Ni(II) on anammox biomass was 14.64 mg L−1 in short-term assay. • The effect of Ni(II) on substrate removal kinetic behavior of anammox was studied. • The long-term effects of Ni(II) in anammox UASB reactor were evaluated. [ABSTRACT FROM AUTHOR]

Abstract Both nickel and salinity are often detected in the environment. Especially electroplating wastewater contains some salt and nickel, which affects microbial activity in biological wastewater treatment process. In this study, the effects of sustaining addition of a high-concentration salinity and Ni(II) on the anaerobic ammonium oxidation (anammox) process were examined. The results indicated that the anammox system had an acclimation ability to <0.2 mg L−1 Ni(II) and 20 g L−1 NaCl. After a recovery phase of approximately 70 days, the nitrogen removal efficiency and rate reached at 77.1% and 1.18 kg N m−3 d−1, respectively. The three-dimensional excitation-emission matrix fluorescence and Fourier transform infrared spectra results showed that the introduction of NaCl and Ni(II) caused a substantial variation in the quantity and composition of the bound EPS in the surface of anammox granules. The present study is the first to document the long-term effect of co-existence of salinity and Ni(II) on the performance of the freshwater-derived anammox bacteria in the upflow anaerobic sludge blanket reactor and to provide a reference for the stable operation of anammox bioreactors for the treatment of sulfonamide-containing wastewater. Graphical abstract Unlabelled Image Highlights • Long-term exposure to NaCl and Ni(II) resulted in co-inhibition on the anammox UASB system. • The sludge characteristics changed after chronic exposure to NaCl and Ni(II). • 3D-EEM analyses showed a change in organic compositions in B-EPS. • FTIR analyses suggested a shift in functional groups in B-EPS. • The deleterious impact of NaCl and Ni(II) was reversible. [ABSTRACT FROM AUTHOR]

Abstract The short- and long-term influence of quinoline on the properties of anaerobic ammonium oxidation (anammox) biogranules was evaluated. During batch tests, the bioactivity of anammox granules in the presence of different quinoline concentrations was monitored, and the IC 50 of quinoline was calculated to be 13.1 mg L−1 using a non-competitive inhibition model. The response of anammox granules to pre-exposure to quinoline was dependent on metabolic status, and the presence of both quinoline and NO 2 −-N had a rapid detrimental effect, resulting in a 64.5% decrease within 12 h. During continuous-flow experiments, the nitrogen removal rate (NRR) of the reactor decreased sharply within 3 days in the presence of 10 mg L−1 quinoline and then was restored to 2.6 kg N m−3 d−1. In the presence of quinoline-induced stress, the specific anammox activity and levels of extracellular polymeric substance and heme c were decreased, while settling velocity persistently increased. After cultivation and acclimation obtained by adding a medium level of quinoline to the influent, the anammox granule sludge was able to tolerate 10 mg L−1 quinoline in 178 days. Graphical abstract Unlabelled Image Highlights • The inhibitory effects of quinoline on anammox were investigated for the first time. • Gradient domestication was applied and toleration of 10 mg L−1 quinoline was achieved. • The content of EPS, heme c and diameter decreased after quinoline inhibition. [ABSTRACT FROM AUTHOR]

Abstract Given the increasing applications of NiO nanoparticles (NPs) in battery products, the potential effects of NiO NPs on anaerobic ammonium oxidation (anammox) systems were studied for the first time. The results showed that the anammox system performance obviously differed under the stresses of different NiO NPs concentrations. After the withdrawal of NiO NPs, the nitrogen removal performance of the anammox reactor returned to nearly that of the initial phase within 35 days. Compared with 0 mg L−1 NiO NPs, the specific anammox activity first increased and then decreased to the minimum value of 116.8 ± 13.8 mg TN g−1 VSS d−1 at 60 mg L−1 NiO NPs. The variations in the heme c contents and extracellular polymeric substance amounts were similar to the variations in the specific anammox activity throughout the whole experiment. Additionally, the relative abundance of the dominant bacteria (Candidatus kuenenia) increased from 20.44% at 60 mg L−1 NiO NPs to 23.14% at the end of the last phase. Thus, the potential effects of NiO NPs on anammox systems should be a cause for great concern. Graphical abstract Unlabelled Image Highlights • Long-term effects of NiO NPs on the anammox system were firstly investigated. • The anammox performance was enhanced below 10 mg L−1 NiO NPs and suppressed by 10–60 mg L−1 NiO NPs. • The stability of the reactor operation could be controlled by the (F/M)/SAA ratio. • "Ca. kuenenia " dominated the community in the presence of 1–60 mg L−1 NiO NPs. • The performance of the anammox reactor could recover after withdrawing the NiO NPs. [ABSTRACT FROM AUTHOR]

Anaerobic ammonium oxidation (anammox) is a low-carbon biological nitrogen removal process, that has been widely applied to treat high-strength wastewater. However, the practical application of mainstream anammox treatment is limited due to the slow growth rate of anammox bacteria (AnAOB). Therefore, it is important to provide a comprehensive summary of the potential impacts and regulatory strategies for system stability. This article systematically reviewed the effects of environmental fluctuations on anammox systems, summarizing the bacterial metabolisms and the relationship between metabolite and microbial functional effects. To address the shortcoming of mainstream anammox process, molecular strategies based on quorum sensing (QS) were proposed. Sludge granulation, gel encapsulation and carrier-based biofilm technologies were adopted to enhance the QS function in microbial aggregation and reduction of biomass loss. Furthermore, this article discussed the application and progress of anammox-coupled processes. Valuable insights were provided for the stable operation and development of mainstream anammox process from the perspectives of QS and microbial metabolism. [Display omitted] • The environmental factors affecting anammox process were introduced. • Metabolic feedback and quorum sensing (QS) effects of anammox bacteria were discussed. • Biomass retention strategies and microbial aggregation under QS effects were reviewed. • Anammox coupled processes in mainstream was practical and promising. [ABSTRACT FROM AUTHOR]

As a key component of extracellular polymeric substances (EPS), extracellular deoxyribonucleic acid (eDNA) acts as a bridge in maintaining the structural stability of granular sludge. However, its ability of carrying antibiotic resistance genes (ARGs) promotes the gene horizontal transfer, raising a high risk for human health. In this study, a series of batch tests were performed to elucidate the response of anammox granular sludge (AnGS) with different sizes (S-AnGS with diameters lower than 0.9 mm and L-AnGS with diameters of 0.9–2 mm) to the removal of eDNA and corresponding mechanism. The results showed that the highest bioactivity of S-AnGS and L-AnGS was achieved by adding DNase I, and the absolute abundance of hzs A in the systems also increased. The dominant microorganism in each sludge was Candidatus Kuenenia, which maintained a higher relative abundance of 24% in S-AnGS. Settling experiments demonstrated that the permeability of AnGS was positively correlated with the addition of DNase I. The permeability index of granular sludge, Г , rose by 58.54% in S-AnGS and 11.79% in L-AnGS. The absence of eDNA is conducive to the increase in the permeability and porosity of AnGS. Similarity in the functional genes and microbial communities of intracellular and extracellular DNA implied the occurrence of gene transmembrane transfer. The findings enrich our knowledge of eDNA in anammox granules and provide a guidance for the specific control of gene transfer through reducing eDNA. [Display omitted] • Responses of different-sized anammox granular sludge (AnGS) to DNase I varied. • Removal of extracellular DNA (eDNA) by DNase I is beneficial for AnGS. • DNase I increased the permeability, porosity and mass transfer of AnGS. • L-AnGS exhibited a relatively stable performance by removing eDNA. • Gene transfer occurred between eDNA and intracellular DNA (iDNA). [ABSTRACT FROM AUTHOR]

The preservation of anammox granules is of great significance for the rapid start-up of the anammox process and improvement of performance stability. Therefore, it is necessary to explore an economical and stable preservation strategy. Exogenous extracellular polymeric substances (EPS) were used as protective agents for the preservation of anammox granules in this study. In brief, EPS from anammox sludge (A-EPS) and denitrifying sludge (D-EPS) were added to preserve anammox sludge at 4 °C and room temperature (15–20 °C). The results showed that A-EPS addition at 4 °C was the optimal condition for the preservation of anammox granules. After 90 days of preservation, the specific anammox activity (SAA) of the anammox granules remained at 92.7 ± 2.2 mg N g−1 VSS day−1 (remaining ratio of 33.4%), while that of the sludge with D-EPS addition at the same temperature was only 77.1 ± 3.2 mg N g−1 VSS day−1 (remaining ratio of 27.8%). The nitrogen removal efficiency of the experimental group with D-EPS at room temperature was 85.9%, and that of the A-EPS group reached 90.6% under the same temperature conditions. The abundance of the functional genes hzs A, hdh and nir S of the sludge (4 °C; A-EPS addition) after recovery were 138.5%, 317.1%, and 375.9%, respectively, of those of sludge from the D-EPS-added group at the same temperature. RDA revealed the contribution of proteins to the preservation process. Overall, this study provides an economical and robust strategy for the preservation of anammox granules. Unlabelled Image • Exogenous EPS was used as protective agents for the anammox sludge preservation. • Addition of exogenous EPS significantly increased anammox activity in short term. • Adding A-EPS at 4 °C led to the optimal recovery performance. • The protein in EPS is a potential factor in optimizing preservation performance. [ABSTRACT FROM AUTHOR]