Achieving stable startup and operation of a continuous-flow aerobic granular sludge (AGS) process integrated with one-stage partial nitritation-anammox (PN/A) for low-strength municipal wastewater treatment hinges primarily on chemical dosing and operational parameter control. This study employed an aeration self-circulation upflow sludge expanded bed (Zier) reactor to cultivate AGS, integrating it with the PN/A process (termed Zier-PN/A). Stable NOB suppression and rapid establishment of partial nitritation were achieved via hydroxylamine (NH2OH) addition at 2.3 mg N/L. After inoculation with anaerobic ammonium oxidation (anammox) sludge, anammox was successfully introduced into the system and became one of the primary nitrogen removal pathways. With the hydraulic retention time (HRT) adjusted to 4 h, under operating conditions with an influent Chemical Oxygen Demand exceeding 250 mg/L, and NH2OH dosage of 2.3 mg N/L, the system achieved effluent ammonia nitrogen below 0.1 mg/L, total nitrogen of 5.6 ± 1.2 mg/L, and a nitrogen removal rate of 0.28 ± 0.02 kg/(m3·d). The relative abundance of Anaerobic ammonium-oxidizing bacteria (AnAOB) gradually exceeded that observed seven days post-inoculation, with SBR1031 (6.8%) and Candidatus Brocadia (5%) becoming the dominant functional bacteria, indicating favorable conditions for AnAOB proliferation. Following cessation of NH2OH dosing, the Zier-PN/A maintained stable operation for 144 HRTs; however, due to the waning inhibitory effect of hydroxylamine, the decline in influent concentrations, and aeration instability, the reactor gradually transitioned toward complete nitrification. The successful integration of Zier-based AGS with PN/A offers an alternative strategy for the efficient and stable treatment of municipal wastewater.

Nitrogen removal from ammonium-rich, carbon-limited wastewater remains constrained in continuous-flow microgranular sludge systems. In this study, a three-stage up-flow self-recirculating microgranular sludge reactor was developed to investigate nitrogen removal mechanisms under low chemical oxygen demand to nitrogen ratios (COD/N < 2.5) and high influent total nitrogen (TN > 400 mg/L). During long-term operation, the system achieved stable removal efficiencies of ammonium (98%), TN (94%), and COD (95%). Under ammonium stress, particle size decreased to a mean diameter of 249.2 μm, forming stable, non-flocculent microaggregates. Microgranules < 0.2 mm exhibited pronounced simultaneous partial nitrification-denitrification (SPND) and simultaneous nitrification-denitrification (SND) activities under aerobic conditions. Simultaneous nitrogen removal (SNR) activity peaked at 0.52 g TN/(g VSS·d) at a DO of 2 mg/L. In contrast, microgranules > 0.2 mm primarily followed SND-dominated pathways. Their SNR activity increased with DO and reached a maximum of 0.46 g TN/(g VSS·d). Microbial community and metagenomic analyses revealed a redox-stratified functional structural organization. Rubrivivax (11.5%) dominated the surface layer, likely linking organic matter degradation with nitrogen oxide reduction. Hyphomicrobium (11.9%) was enriched in intermediate layers and was associated with SND. In the core, the co-enrichment of Hyphomicrobium (7.2%) and Methylotenera (6.1%) supported the coupling of SND and SPND processes. These findings provide a basis for improving nitrogen removal from ammonium-rich, carbon-limited wastewater.

This study evaluated the performance and inhibition kinetics of a novel continuous-flow aerobic granular sludge (AGS) reactor (Zier) treating saline wastewater (1%-3% salinity). At 3% salinity and a carbon-to-nitrogen ratio of 2.3, selective inhibition of nitrite-oxidizing bacteria (NOB) maintained a stable partial nitrification-denitrification (PND) pathway, achieving 82% total nitrogen removal. At 1%-2% salinity, NOB activity recovered. This shifted the system to full nitrification and reduced nitrogen removal efficiency. Additionally, the sludge achieved successful granulation and exhibited excellent settleability at all salinity levels. Kinetic analysis showed that the salt tolerance of ammonia-oxidizing bacteria (AOB) increased with acclimation salinity. The half-maximal inhibitory concentration (IC50) values for AOB acclimated at 1%, 2%, and 3% salinity were 27.3, 57.1, and 71.0 g/L, respectively. The Aiba model showed that acclimated NOB were more salt-tolerant than AOB at lower salinities, but it was unsuitable for higher salinities. Instead, the Luong model accurately described salt inhibition across all sludges. AOB adapted to higher salinities exhibited cooperative-type inhibition (n > 1). This provides a tolerance buffer but risks sudden functional collapse beyond critical thresholds. Conversely, NOB exhibited progressive inhibition (n < 1) and higher tolerance limits, demonstrating superior stability during salinity fluctuations. The Zier system achieves efficient nitrogen removal from saline wastewater via the PND pathway, and these kinetic findings offer essential strategies for process control.

Salinity stress is a promising strategy for establishing partial nitritation (PN). Nevertheless, the adaptation of nitrifiers and its implications for PN stability under dynamic saline conditions remain poorly understood. In this study, a continuous-flow self-circulating up-flow fluidized bed reactor (AOAN-Zier) was employed to systematically investigate the effects of salt loading rate (SLR) fluctuations on nitrifier functional responses and PN resilience under different salinity backgrounds. PN was rapidly established within 7 d under salt-free conditions, achieving a nitrite accumulation ratio (NAR) of 96% on day 9. Subsequent responses to SLR reduction differed depending on salinity history. At 10 g/L salinity, reduced SLR alleviated nitrite-oxidizing bacteria (NOB) inhibition and resulted in PN deterioration. In contrast, after long-term exposure to 30 g/L salinity, the system maintained an average NAR of 99% despite SLR reduction, owing to the sustained loss of NOB functional activity. Activity assays, microbial succession, and metagenomic analyses revealed that PN resilience was primarily determined by NOB absolute activity rather than the relative activity balance between AOB and NOB. Long-term saline selection promoted functional divergence among nitrifiers, with salt-adapted Nitrosomonas maintaining ammonia oxidation capacity through coordinated osmotic regulation, nitrogen metabolism, oxidative stress defense, and energy conservation. Moreover, the salt-adapted sludge retained high AOB activity after desalination under mainstream-like low-ammonium conditions. This study provides new insights into salinity-dependent nitrifier adaptation and advances the understanding of microbial mechanisms underlying PN resilience under dynamic saline conditions.

Electrochemical CO 2 reduction to multicarbon (C 2+ ) products represents a promising route for sustainable chemical synthesis. However, the complex multielectron/proton transfer process required for C 2+ generation renders single‐catalytic systems inherently limited in optimizing all reaction steps concurrently. Tandem catalysis addresses this constraint by decoupling the overall conversion into two discrete stages: initial CO 2 ‐to‐CO conversion and subsequent CO‐to‐C 2+ coupling. This review systematically summarizes recent advances in tandem CO 2 ‐to‐C 2+ , covering fundamental mechanisms, catalyst design strategies, and two main tandem configurations: integrated tandem catalysis in a single electrolyzer and sequential tandem catalysis in series electrolyzers. The benefits of tandem catalysis in enhancing reaction kinetics, mass transport, and energy efficiency for C 2+ generation are systematically elucidated. Finally, the remaining challenges and future opportunities are outlined for scaling tandem catalysis, highlighting its potential to improve the economic viability of CO 2 ‐to‐C 2+ conversion.

Pervasive residues of antibiotics and pesticides present a dual threat: acute poisoning and chronic antimicrobial resistance (AMR) risks. To address the technical bottleneck of complex sample pretreatment in traditional methods for acute poisoning incidents, this study developed a highly sensitive and stable surface-enhanced Raman scattering (SERS) substrate for rapid detection of poisoning substances. Using electrophoretic deposition, we achieved ordered, dense assembly of tungsten-gold nanoparticles on a gold film. This engineered structure, combined with the excellent adsorption properties of tungsten oxide single atoms, enables a synergistic enhancement in both signal intensity and uniformity. The substrate exhibits high SERS performance, with an enhancement factor of approximate to 107 and a relative standard deviation (RSD) below 20%. The detection limit for various analytes reached 1 ppb. In spiked serum tests, recovery rates were 80%-120% with RSD < 15%, demonstrating strong matrix resistance and practical reliability. This work provides a universal SERS platform for ultrasensitive, rapid (<5 min) detection of multiple antibiotics and pesticides, supporting on-site emergency diagnosis and large-scale monitoring of long-term exposure and AMR risks.

Developing high-performance bifunctional electrocatalysts for the oxygen reduction/evolution reaction (ORR/OER) is crucial for solving environmental and energy challenges. Herein, we systematically investigate the geometric structures, stability, electronic properties, and ORR/OER performance of a series of two-dimensional (2D) metal-organic frameworks (MOFs), called TM3(HITT)2 (TM = Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt), by means of density functional theory (DFT) calculations. The computational results indicate that all proposed frameworks possess excellent structural stability and potential experimental feasibility, as evidenced by cohesive energy, formation energy, and ab initio molecular dynamics (AIMD) simulations. Among all candidates, Fe3(HITT)2 and Rh3(HITT)2 exhibit excellent bifunctional catalytic activity with relatively low overpotentials for both the ORR and OER, and their catalytic performances are comparable to those of well-studied ORR and OER electrocatalysts. Scaling-relation and volcano-plot analyses reveal that the catalytic activity is closely associated with the adsorption strength of oxygen-containing intermediates, and that an appropriate balance between intermediate adsorption and desorption is essential for achieving efficient bifunctional catalysis. This work not only identifies Fe3(HITT)2 and Rh3(HITT)2 as promising bifunctional ORR/OER electrocatalysts but also provides valuable theoretical insights for the rational design of advanced 2D MOF-based catalytic materials.

Achieving simultaneous nitrogen and phosphorus removal in continuous-flow municipal wastewater remains challenging. This study evaluated an aerated-volume-optimized continuous self-circulating fluidized bed (ACOAAP-Zier) treating real municipal wastewater inoculated with either flocculent sludge (R_floc) or anaerobic granular sludge (R_AnGS). Distinct seed-sludge evolutionary trajectories fundamentally shaped the structural and functional development of microbial aggregates. R_floc followed a bottom-up aggregation pathway and formed predominantly small-to-medium aggregates, whereas R_AnGS underwent a physical "top-down" structural reconstruction and retained a greater proportion of large aggregates. Under comparable conditions, the 500-1000 µm and > 1000 µm fractions in R_AnGS (P3) were 3.0- and 5.4-fold higher than in R_floc (P2), respectively. The resulting structural heterogeneity provided differentiated ecological niches for functional microorganisms. P2 exhibited superior ammonia oxidation, whereas P3 favored the enrichment of denitrifying and phosphorus-removing microorganisms, with denitrifying polyphosphate-accumulating organisms (DPAOs) being approximately 3.1 times higher than that in P2. Consequently, enhanced phosphorus removal and coupled nitrogen-removal pathways were achieved. Aggregate size was significantly positively correlated with polyphosphate-accumulating organisms abundance. These findings provide a basis for optimizing continuous-flow biological nutrient removal in municipal wastewater treatment.

This study successfully cultivated algal-bacterial granular sludge (ABGS) in-situ from floccular activated sludge, using a continuous-flow self-circulating reactor (namely Zier process). Over 180 days of operation, the system demonstrated stable and efficient removal of chemical oxygen demand (COD) (95 %) and ammonia nitrogen (NH4+-N) (90 %) at hydraulic retention times of 4-11 h and organic loading rates of 0.6-2.6 kg-COD/(m3·d). Ammonium removal was contributed by nitrifying bacteria (≈52.1 %) and algal assimilation (≈47.9 %). Despite nitrogen source competition between algae and bacteria, the system maintained stable performance. Under the unique hydrodynamic conditions that promoted biomass densification and excellent settleability (SVI30 ≈40 mL/g). Algal-bacterial synergy (O2 supply, N assimilation, nitrification) and protein-dominated extracellular polymeric substance (EPS) drove granulation, evidenced by a 31 % increase in >0.2 mm particles. This system operated with a high non-aerated to aerated volume ratio (2:1), highlighting its energy-efficient potential and providing a theoretical basis for scalable continuous-flow ABGS processes.

Electrochemical CO2 reduction to multicarbon (C2+) products represents a promising route for sustainable chemical synthesis. However, the complex multielectron/proton transfer process required for C2+ generation renders single‐catalytic systems inherently limited in optimizing all reaction steps concurrently. Tandem catalysis addresses this constraint by decoupling the overall conversion into two discrete stages: initial CO2‐to‐CO conversion and subsequent CO‐to‐C2+ coupling. This review systematically summarizes recent advances in tandem CO2‐to‐C2+, covering fundamental mechanisms, catalyst design strategies, and two main tandem configurations: integrated tandem catalysis in a single electrolyzer and sequential tandem catalysis in series electrolyzers. The benefits of tandem catalysis in enhancing reaction kinetics, mass transport, and energy efficiency for C2+ generation are systematically elucidated. Finally, the remaining challenges and future opportunities are outlined for scaling tandem catalysis, highlighting its potential to improve the economic viability of CO2‐to‐C2+ conversion.

Two-dimensional (2D) materials, which are characterized by their large lateral dimensions and ultrathin thickness, offer extensive solid-liquid interfaces, making them ideal for the hydrogen evolution reaction (HER). Furthermore, strategies in which 2D materials are doped to modify these materials allow dopant elements to be fully exposed on the surface, maximizing the enhancement of their electrocatalytic HER performance. In this work, we successfully synthesized large, ultrathin Ce-doped RuO2 nanosheets, denoted as Ce-RuO2, via a simple one-step thermal decomposition method. When employed as an alkaline HER electrocatalyst, Ce-RuO2 has an overpotential of only 6 mV at a current density of 10 mA cm-2 and a Tafel slope as low as 21.72 mV dec-1, outperforming recently reported ruthenium-based catalysts and commercial Pt/C catalysts. In situ Raman spectroscopy analysis revealed that Ce bonds with Ru through oxygen, forming a Ce-O-Ru interface. The Ce species promote H2O adsorption and facilitate the generation of *H intermediates, whereas Ru acts as the active site for *H association. The synergistic interaction between Ce and Ru modulates the HER catalytic mechanism and accelerates the reaction kinetics.

The development of efficient, stable bifunctional electrocatalysts for sustainable hydrogen production via water electrolysis remains challenging due to the high cost and instability of precious metal catalysts. This study addresses this by constructing a heterointerfacial CoFe2O4/CeO2 composite anchored on carbon (CoFe2O4/CeO2@C) through a facile hydrothermal-pyrolysis approach. The optimized catalyst demonstrates exceptional activity, achieving overpotentials of 243 mV for oxygen evolution reaction (OER) and 82 mV for hydrogen evolution reaction (HER) at 10 mA cm-2 in 1 M KOH, significantly outperforming benchmark RuO2 and Pt/C, alongside requiring only 1.57 V to drive overall water splitting at 10 mA cm-2. Structural and electronic analyses confirm that the heterointerface between CoFe2O4 and CeO2 facilitates charge redistribution, thus optimizing the electronic environment. Remarkably, the catalyst demonstrated only a 6.1% decay in current density after a 24-h stability test and exhibits high Faradaic efficiency. This work provides a scalable strategy for designing non-precious metal bifunctional catalysts for overall water splitting.

Charge and proton transfer in photocatalytic CO2 reduction reaction (CO2RR) are considered primary steps for effectively utilizing sustainable solar energy to meet environmental and renewable energy demands. The rational design of active sites is crucial for accelerating charge and proton transfer. In this study, we develop a ligandcoordinated single site strategy to improve photocatalytic CO2 efficiency by anchoring homogeneously single strontium (Sr) atom and its coordinated hydroxyl-terminal glycol on TiO2. The ligands can not only induce Sr to precisely anchor on the surface of TiO2, but also interact with Sr to boost photocatalytic efficiency, achieving a CO production of 25.37 mu mol g-1 h-1-about 14.7 times higher than that of pristine TiO2(1.73 mu mol g-1 h-1). Furthermore, Raman experiments reveal the durability of ligand sites on inorganic substrate surfaces. The enhanced mechanism relies on single sites to increase photocarrier transfer and suppress the recombination. The introduction of the Sr1 site and the ligand site facilitates CO2 adsorption and lowers the energy barrier, thereby accelerating the CO2 reduction reaction. Therefore, constructing and understanding multi-sites provides insights for rational design of catalytic sites for numerous important chemical and biological reactions.

In situ cultivation and long-term stabilization of continuous-flow aerobic granular sludge (AGS) pose significant challenges for the sustainable advancement of wastewater technology. Herein, we demonstrated the successful 330-day operation of a novel continuous-flow self-circulating AcOA-Zier reactor. Aeration-driven liquid recirculation achieved recirculation-to-influent (R/I) ratios of 26-70, optimizing dissolved oxygen gradients and enabling exceptional contaminant removal of 96 % for chemical oxygen demand (COD) and 95 % for total inorganic nitrogen (TIN). High hydrodynamic shear promoted granulation, yielding an average particle size of 369.7 μm, with >83 % of the granules in the optimal 200-600 μm range being used to ensure operational stability. Microbial community profiling revealed Proteobacteria (80 %), Chloroflexi (7.1 %) and Bacteroidota (10.2 %) as keystone taxa underpinning granule formation, structural integrity, and pollutant degradation. Metagenomics identified narG, nirK, norBC, nosZ and nxrB as core nitrogen cycling genes, with Methylotenera and unclassified_c_Betaproteobacteria serving as the dominant functional microorganisms. In this work, we established granulation dynamics and particle stability as pivotal factors for scalable AGS systems, providing a framework for optimizing energy-efficient, high-performance wastewater treatment processes.

The search for stable, efficient, and cost-effective electrocatalysts for the hydrogen evolution reaction (HER) is essential towards a sustainable hydrogen production. Herein, density functional theory (DFT) calculations using Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional with Grimme's D3 dispersion (PBE-D3) are performed to evaluate the potential of single atom electrocatalysts (SACs) for HER based on 3d, 4d, or 5d transition metal (TM) atoms supported on novel N-doped grazyne (NG) two-dimensional materials, accurately described by slab models. The present study firstly analyses the stability of such SACs compared to their clustering tendency, which is a general feature except for Pt-group Ru, Re, Os, and Ir atoms. The HER performance is assessed by H adatom adsorption Gibbs free energy values compared to the top-tier performing Pt(111) model. The results reveal that Sc, Y, and Nb early TMs mimic quite well the reaction Gibbs free energy profile of Pt(111), underlining the chemical activity taming feature of N-doped grazyne, which makes early TMs behave as late TMs. Further analysis, though, discards Nb SAC since the protonation of the unsaturated N atoms would destabilize the SAC. Still, Sc and Y are posed as excellent, economic materials in theory performing quite similar to Pt(111) surface, with estimated overpotentials of 0.01 and 0.06 V, respectively.

Optimizing reactor design and understanding aerobic granular sludge metabolism are crucial for wastewater treatment. Unlike previous methods where each column operated independently, this study explored floc sludge granulation feasibility and stability in a continuous self-circulating fluidized bed (AcOA-Zier) reactor with aeration-induced high-speed liquid sludge circulation. For the first time, granular sludge was stratified to analyze microbial vertical distribution and interactions. Over 290 days of operation, the AcOA-Zier reactor successfully granulated sludge, increasing the average particle diameter from 93 to 378 mu m while maintaining a low SVI5 below 55 mL/g. Throughout the granulation process, the reactor demonstrated high removal efficiencies for COD (95 %) and TN (90 %). Stratified analysis showed the third layer had higher microbial diversity. Methylotenera, Ideonella, g_unclassified_f_37-13, and g_unclassified_f_Saprospiraceae were predominantly found on the surfaces, whereas Hyphomicrobium, 996-1, and Nitrospira were more abundant near the granule core. The abundance of g_unclassified_f_Anaerolineaceae, SBR1031, and g_unclassified_f_A4b reached its maximum in the third stratum. Surface microbes removed pollutants and secreted extracellular polymers. Inner microbes underwent denitrification reaction and stored nutrients for stability. Metagenomics identified key genes (nxrB, narG, norB, NRT) driving nitrogen removal via nitrification, denitrification, and assimilatory nitrate reduction. Methylotenera, g_unclassified_c_Betaproteobacteria, and Hyphomicrobium were identified as the dominant nitrogen-metabolizing microorganisms. This study offers novel insights into granular sludge microbial spatial organization and strategies to enhance pollutant removal, advancing sustainable wastewater treatment technologies.

The practical adoption of surface-enhanced Raman scattering (SERS) technology is often hampered by the high cost, complex fabrication, and poor reproducibility of conventional substrates, which typically rely on noble metals or inefficient semiconductors. Herein, we address key challenges in the practical commercialization of surface-enhanced Raman scattering (SERS) technology by reporting a facile, scalable, and environmentally benign strategy for fabricating a hybrid SERS substrate. This approach integrates Au nanoparticles (NPs) with hydrothermally synthesized WO3 nanowires through a green photoreduction process, which is rapid, organic-solvent-free, and amenable to large-scale production. The design of the Au/WO3 nanocomposite capitalizes on the synergistic effect between electromagnetic (EM) enhancement from Au NPs and chemical mechanism (CM) enhancement via charge transfer involving the WO3 semiconductor. This synergy empowers the substrate with exceptional SERS activity, enabling the sensitive detection of Rhodamine 6G (R6G) down to 10−11 M and yielding an enhancement factor (EF) of 4.09 × 106. More importantly, this EM-CM synergy proves critical for detecting molecules with weak affinity, such as the nerve agent simulant dimethyl methylphosphonate (DMMP), achieving a significant signal enhancement of 102–103 times, which is notably challenging for conventional plasmonic substrates. Beyond sensitivity, the substrate exhibits excellent reproducibility and operational stability, which are paramount for real-world applications. This work presents a nanohybrid strategy that successfully balances scalability, stability, and sensitivity, offering a reliable and cost-effective pathway for advancing SERS technologies toward practical implementation.

Mainstream partial nitritation/anammox (PN/A) is recognized as a promising method for sustainable nitrogen removal from wastewater. However, its practical implementation remains challenging to date. In this study, a full-scale mainstream partial-nitritation activated sludge system, coupled with an anammox fixed-film (PN-AF) process, has been developed to treat municipal wastewater. The process was initiated by inoculating fixed biofilm with a mature anammox consortium sourced from a side-stream PN/A. The integrated application of chemical inhibition and ecological niche selection was practically implemented in engineering for the first time, enabling the PN-AF process to achieve two years of continuous operation within a wide temperature range (11.6–28.9 °C). The average total nitrogen (TN) removal efficiency was 91.8 ± 4.6 %, with an average effluent TN concentration of 4.5 ± 2.3 mg/L and a nitrogen removal rate of 0.072 ± 0.01 kg N·m−3·d−1. Molecular analysis revealed a remarkably high relative abundance of Candidatus Brocadia (17.87 %), accompanied by an eight times higher activity of anammox than that of denitrification. Overall, this work presents a reliable mainstream partial nitritation/anammox process for sustainable wastewater treatment.

Peroxynitrite (ONOO−) plays a pivotal role in environmental pollution and ecosystem health, necessitating its detection for assessing ecological impacts and risks. Surface-enhanced Raman scattering (SERS) offers high sensitivity but is often limited by narrow Raman cross sections of analytes. Specialized molecules can aid SERS detection, but are complex to design and may cause nonspecific reactions in biological systems. Therefore, developing new SERS strategies is crucial for simpler, more accurate ONOO− detection. Herein, the shape instability of Ag nanomaterials in the hotspots, due to oxidation and dissolution of Ag atoms at the edges and corners, is investigated, and the detection of ONOO− is performed by SERS probes. ONOO− reacts first with the (111) facet, especially at the edges and corners. Consequently, the SERS signal of the adsorbed probe, Rhodamine 6G in hotspots can be used to monitor edge and corner dissolution that positively related to the ONOO− concentration. As a result, ONOO− concentration from 0.1 to 25 μM was detected, achieving a coefficient of determination of R2 = 0.9896. The method exhibits good reproducibility (RSD < 3.25

In recent years, near-infrared (NIR) light-sensitive photothermal agents (PTAs) with excellent photothermal conversion efficiency have shown great potential in enhancing the performance of advanced photothermal therapy (PTT). In this study, polyethylene glycol (PEG)-modified tungsten nitride/tungsten oxide nanoparticles (PEGylated W4.6N4/WO3-NPs) with heterojunction structures were designed and constructed. The PEGylated W4.6N4/WO3-NPs showed strong absorbance ability in the NIR window and photothermal conversion under 808 nm irradiation. The PEGylated W4.6N4/WO3-NPs exhibited good biocompatibility and efficient tumor ablation function. Therefore, the PEGylated W4.6N4/WO3-NPs can be used as a photothermal agent.