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Anaerobic ammonium oxidation (anammox) is a novel process of deammonification that exhibits superior ecological and economic potential compared to that of traditional heterotrophic processes. Although this process has been successfully implemented in treating high‐strength nitrogen‐contaminated wastewater, it still faces many challenges in treating mainstream municipal wastewater. This review aims to provide an overview of the status and challenges of mainstream anammox‐based processes. The different configurations and crucial factors are discussed in this review. Finally, the future needs for feasible application are stated. Practitioner points: Factors restricting mainstream application of anammox‐based processes are reviewed.Control strategies for selecting and maintaining anammox bacteria are discussed.Recent advances in nitrite production via partial nitrification or denitrification are summarized.Future needs for the feasible application of anammox‐based nitrogen removal technology for mainstream municipal wastewater treatment are outlined. [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]

• Binding of anammox EPS with Cu2+ was endothermic and entropy-increased. • Carboxyl groups of proteins were preferentially responded to Cu2+. • The protein in EPS changed into loose structure after combining with Cu2+. Extracellular polymeric substance (EPS) of anaerobic ammonium oxidation (anammox) sludge plays an important role in resisting the toxicity when treating heavy metal containing wastewater. Understanding the interaction mechanism between EPS and heavy metal is essential for stable and optimal operation of such technology. In this work, the identification and preferential response of the binding sites, as well as the binding thermodynamic and the conformational changes of EPS to Cu2+ were explored. Unlike the activated sludge system, functional groups in EPS would coordinate with Cu2+ to form inner sphere complexes, which is an endothermic and entropy-increasing process. Low concentration of Cu2+ was found to result in the reduced electrostatic repulsion and bridging effect, which promoted the compaction and agglomeration of EPS colloid. Two-dimensional correlation spectroscopy analysis confirmed that carboxyl groups of proteins were preferentially responded to Cu2+ compared to polysaccharides and hydrocarbons. More importantly, the secondary structure of the protein in EPS was disrupted and changed into loose state after combining with Cu2+. This work is of great significance for understanding the binding properties of anammox sludge EPS with Cu2+ and may provide theoretical support for elucidating the resist mechanism of anammox bacteria to heavy metals. [ABSTRACT FROM AUTHOR]

Anaerobic ammonium oxidation (anammox) bacteria are sensitive and susceptible to operating condition fluctuations that can lead to the instability of a bioreactor. Through multivariate spectral analysis, the dynamic changes of intracellular and extracellular metabolites of anammox sludge under the declined temperature stress were characterized. It was found that effluent fluorescence components were positively related to the bacterial activity, and the response of the protein-like substances to the temperature change was more sensitive than that of humic substances. Under the transient disturbance during temperature change from 35 to 15 °C, anammox system tended to considerably excrete extracellular polymeric substances to resist the low temperature inhibition. However, the long-term exposure of the sludge at 10 °C resulted in the considerably inhibition of sludge activity, granular disintegration and heterotrophic denitrification bacteria increase. The two-dimensional correlation analysis further revealed that the humic acid in extracellular polymeric substances was preferentially responded to the temperature change than protein. Anammox bacteria tended to increase the intracellular protein and electron transfer-related reactive substance excretion to counteract the low temperature inhibition. Herein, both the intra- and extra-cellular response characteristics of anammox sludge to temperature variation were successfully resolved via the combined spectra. This work provides a comprehensive understanding on the mechanism of anammox sludge to temperature variation and may be valuable for the development of bioreactor monitoring techniques. Unlabelled Image • The performance of anammox bioreactor was characterized by spectra combination. • 2-dimension correlation spectroscopy was used for extracellular substances analysis. • Effluent fluorescence components were positively related to the bacterial activity. • 15 °C was an inflection temperature for the extracellular substances excretion. [ABSTRACT FROM AUTHOR]

• PA caused oxidative stress in the anammox system. • PA exacerbated the CFX inhibition on anammox consortia. • Most antibiotics were adsorbed by PA in the anammox system. • The most dominant bacterium changed from Candidatus Kuenenia to norank_o_SBR1031. Emerging pollutants pose high risks to human health, and also put huge pressures on wastewater treatment. Their interactions would also affect the activity of functional microorganisms. This study investigated the response and mechanism of anaerobic ammonium oxidation (anammox) consortia to the long-term stress of common microplastics (polyamide, PA) and a broad-spectrum antibiotic (cephalexin, CFX). Although 0.1 g L−1 PA microplastics (MP) did not significantly inhibit the nitrogen removal performance, adsorption assays revealed that large amounts of cephalexin were adsorbed by PA. Thus, 0.5 mg L−1 CFX and 0.1–0.2 g L−1 PA caused a deterioration of anammox process. Simultaneously, the most dominant genus changed from Candidatus Kuenenia to norank o SBR1031 , and expressional levels of functional genes dramatically decreased. In addition, the abundance of gene encoding superoxide dismutase (SOD) increased by 10.7 %, verifying that PA also caused the oxidative stress of anammox bacteria. PA promoted the accumulation of CFX in the anammox system through adsorption and extended its side effects on anammox consortia. This study provides a new direction into the implementation of anammox process in complex wastewater treatment. [ABSTRACT FROM AUTHOR]

• High-intense light would inhibit anammox sludge activity decline. • Light induced · OH and · O 2 − were able to destruct ladderane lipids structure. • Se-CQDs would greatly mitigate the photoinhibition and maintain a stable performance. • The potential mitigation mechanism by Se-CQDs was clarified. External stimulus such as light irradiation is able to deteriorate intracellular redox homeostasis and induce photooxidative damage to non-photogenic bacteria. Exploiting effective strategies to help bacteria resisting infaust stress is meaningful for achieving a stable operation of biological treatment system. In this work, selenium-doped carbon quantum dots (Se-CQDs) were blended into anaerobic ammonia oxidation (anammox) bacteria and an inorganic nanoparticle-microbe hybrid was successfully fabricated to evaluate its nitrogen removal performance under solar-simulated irradiation. It was found that the specific anammox activity decreased by 29.7 ± 5.2% and reactive oxygen species (ROS) content increased by 134.8 ± 4.1% under 50,000 lux light. Sludge activity could be completely recovered under the optimum dosage of 0.42 mL·(g volatile suspended solid) -1 Se-CQDs. Hydroxyl radical (·OH) and superoxide anion radical (·O 2 −) were identified as the leading ROS inducing lipid peroxidation and antioxidase function detriment. Also, the structure of ladderane lipids located on anammoxosome was destroyed by ROS and functional genes abundances declined accordingly. Although cell surface coated Se-CQDs could absorb ultraviolet light and partially mitigated the photoinhibition, the direct scavenging of ROS by intracellular Se-CQDs primarily contributed to the cellular redox homeostasis, antioxidase activity recovery and sludge activity improvement. The findings of this work provide in-depth understanding the metabolic response mechanism of anammox consortia to light irradiation and might be valuable for a more stable and sustainable nitrogen removal technology, i.e., algal-bacterial symbiotic system, development. [Display omitted] [ABSTRACT FROM AUTHOR]

The arsenic in livestock wastewater would induce adverse impact on the biological treatment technology such as anaerobic ammonium oxidation (anammox) process. Extracellular polymeric substances (EPS) play an important role in resisting such toxicity. Unfortunately, the role of EPS in protecting anammox from As(III) and the mechanisms underlying the protection still remains unclear. This work comprehensively evaluated the acute toxicity of arsenic on anammox sludge and investigated the binding property and interaction mechanism. The results revealed that the half maximal inhibitory concentration (IC 50) of As(III) on anammox sludge was estimated to be 408 mg L−1, which decreased to 41.97 mg L−1 when EPS was exfoliated. Complexation and hydrophobic interactions were the leading forces in preventing arsenic invasion. Protein was the main component that complexes with As(III), and O–H, –NH, –C O were binding sites. The response sequence of organic component in EPS to As(III) was ordered as hydrocarbons-proteins-polysaccharides-aliphatic amines. [Display omitted] • The IC 50 of As(III) was estimated as 408 mg L−1 in anammox process. • EPS was able to construct buffer zones to prevent As(III) invasion. • Protein is the main component within EPS to complex with As(III). • Response sequence of functional groups to As(III) was clarified via spectra analysis. [ABSTRACT FROM AUTHOR]