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•EPDA possessed higher CODintra efficiency with abundant Candidatus_Competibacter.•Preferred rNO2 and NTR were obtained in EPDA but less stable nitrite accumulation.•A shift from ...Candidatus_Competibacter to Defluviicoccus appeared in EPDA and EPDG.•The combination of EPD and Anammox might be practicable for wastewater treatment.
Although the combination of endogenous partial denitrification (EPD) and Anammox (EPD-AMX) were developed for deep-level nitrogen removal, the effects of different carbon source were not clear. In this study, the EPD performance was investigated comparatively with acetate (EPDA) and glucose (EPDG). Results revealed that through regulating chemical oxygen demand to phosphate ratio, Candidatus_Competibacter was highly enriched in EPDA (54.2%) and EPDG (51.3%), resulting high intracellular carbon storage efficiencies (90.2% and 85.3%, respectively). More stable nitrite accumulation was observed in EPDG than EPDA. But, higher specific nitrite generated rate (rNO2, 8.25 > 7.04 mgN·gVSS−1·h−1) and nitrate-to-nitrite transformation rate (NTR, 87.9% > 85.2%) were achieved in EPDA than those in EPDG. The functional bacterium was also shifted to Defluviicoccus in both EPDA (30.6%) and EPDG (25.8%). Moreover, with whether acetate or glucose, the EPD-AMX processes could achieve the same level of total nitrogen removal efficiencies (88.7% and 91.3%, respectively) via anammox mainly (87.8% and 89.4%, respectively).
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•Nitrogen removal performance of mainstream anammox was improved with increased C/N.•Increasing C/N ratio promoted AnAOB enrichment rather than inhibited them.•Partial nitrification ...and partial denitrification were enhanced when C/N increased.•Increase of particle sizes and aerobic_chemoheterotrophy supported habitat of AnAOB.
The effects of fluctuating organic carbon to nitrogen (C/N) ratios on mainstream simultaneous partial nitrification, anammox, and denitrification (SNAD) process were studied over 376-day period. The nitrogen removal efficiency decreased from 85.0 ± 6.6 % to 75.8 ± 2.8 % as C/N ratio decreased (3.4 → 1.7), but increased to 82.0 ± 1.9 % when C/N ratio raised to 2.9 and to 78.4 ± 3.0 % when C/N ratio decreased again (2.9 → 2.1), indicating that high C/N ratios promoted nitrogen removal. As C/N ratio raised (1.7 → 2.9), anaerobic ammonia-oxidizing bacteria (AnAOB) abundance increased from 1.3 × 109 to 2.0 × 109 copies/L, which explained the improved nitrogen removal. With an elevated C/N ratio, partial nitrification and endogenous partial denitrification reactions were enhanced, providing more nitrite for AnAOB. Additionally, the aerobic_chemoheterotrophy function and particle sizes increased, forming more stable anoxic microenvironment for AnAOB. Overall, increasing C/N ratio promoted the stability of mainstream SNAD.
Oxygen reduction reaction (ORR) activity can be effectively tuned by modulating the electron configuration and optimizing the chemical bonds. Herein, a general strategy to optimize the activity of ...metal single‐atoms is achieved by the decoration of metal clusters via a coating–pyrolysis–etching route. In this unique structure, the metal clusters are able to induce electron redistribution and modulate M−N species bond lengths. As a result, M‐ACSA@NC exhibits superior ORR activity compared with the nanoparticle‐decorated counterparts. The performance enhancement is attributed to the optimized intermediates desorption benefiting from the unique electronic configuration. Theoretical analysis reinforces the significant roles of metal clusters by correlating the ORR activity with cluster‐induced charge transfer. As a proof‐of‐concept, various metal–air batteries assembled with Fe‐ACSA@NC deliver remarkable power densities and capacities. This strategy is an effective and universal technique for electron modulation of M−N−C, which shows great potential in application of energy storage devices.
A general strategy of metal clusters regulating metal single‐atom sites is developed to boost the activities of oxygen reduction reaction (ORR) electrocatalysts (Fe, Co, Ni). Benefiting from the electron redistribution between active sites and substrate, the optimized catalyst exhibits remarkable activity with a half‐wave potential of 0.9 V vs. RHE and achieves high discharge voltages in various metal–air batteries.
The study was based on the removal of nitrate and sulfide, and aimed to nitrite accumulation. The process of autotrophic denitrification driven by sulfide as an electron donor was investigated in a ...sequencing batch reactor. The research showed that autotrophic denitrification successfully started on day 22, and the removal rates of NO3−-N and S2--S were 95.8% and 100%, respectively, when the S/N molar ratio was 1.45. When the S/N ratio was reduced to 0.94, the phenomenon of NO2−-N accumulation was observed. NO2−-N continuously accumulated, and the maximum accumulation rate was 55.3% when the S/N ratio was 0.8. In the batch test, the study showed that NO2−-N accumulation was optimal when the S/N ratio was 0.8, and the NO2−-N concentration increased with increasing NO3−-N concentration at the same S/N ratio. Microbial communities also changed based on the high-throughput analysis, and Proteobacteria (59.5%–84%) was the main phylum. Arenimonas (11.4%–28.2%) and uncultured_f_ Chromatiaceae (5.7%–27.5%) were the dominant bacteria, which complete denitrification and desulfurization throughout the operating system. Therefore, this study provided a theoretical basis for the simultaneous removal of NO3−-N and S2--S, as well as the accumulation of nitrite, and provided material support for anaerobic ammonia oxidation technology.
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•Autotrophic denitrification driven by sulfide as an electron donor was researched.•Nitrite can stably accumulate when the S/N ratio of 0.8•Phototrophic and autotrophic denitrifying bacteria synergistically remove pollutants.
Dual‐sites single atom catalysts hold promise for efficiently regulating multiple reaction processes and explicitly explaining the underlying mechanisms. However, delicate atomic engineering for ...dual‐site single atom catalysts remains a huge challenge. Herein, atomically dispersed Fe‐Ni single atoms embedded in a nitrogen‐doped carbon matrix (FeNi SAs/NC) are successfully developed with extraordinary activity for electrocatalytic oxygen reduction and evolution reactions (ORR/OER). The atomic FeNi SAs/NC catalyst displays high onset potential (0.98 V) and half‐wave potential (0.84 V) for the ORR, as well as, low overpotential of (270 mV) at 10 mA cm−2 for the OER. The density functional theory calculations indicate that the Fe site as the active center can facilitate the four‐electron reaction process, while Ni sites regulate the electronic structure of Fe sites and further reduce the energy barrier of the rate‐determining step. In addition, the nitrogen‐doped carbon matrix prevents the metal atoms from aggregation and corrosion, leading to the improvement of catalyst durability. As a proof of concept, flexible quasi‐solid‐state zinc– and aluminum–air batteries assembled with the FeNi SAs/NC catalyst exhibit superior peak power densities and discharging specific capacities outperforming the commercial Pt/C. This work provides rational guidance for the synthesis of bifunctional electrocatalysts in next‐generation energy devices for flexible consumer electronics.
Unique noble metal‐free electrocatalysts with atomically dispersed Fe‐Ni dual‐sites are precisely designed and present superior oxygen reduction and evolution reaction reactivity under alkaline conditions, which provides a perspective and guidance for the design of efficient catalysts for metal–air batteries.
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•SPNA-IFAS reactor was started up by seeding nitrification sludge and anammox biofilm.•NOB migrated from flocs to biofilm while AnAOB enriched in flocs when SRT decreased.•Short SRT ...of flocs may play a limited role in inhibiting NOB.•Short SRT of flocs may decrease AnAOB abundance and deteriorate nitrogen removal.•Simultaneous fermentation, partial denitrification-anammox was speculated in biofilm.
The feasibility of starting up mainstream single-stage partial nitrification-anammox (SPNA) system by inoculating nitrification sludge and anammox biofilm was investigated. The SPNA system treating low-strength synthetic wastewater was rapidly started up with TN removal efficiency of 88.5 ± 1.8% and effluent nitrate concentration of 7.2 ± 1.2 mg/L. Both the abundance and maximum activity of nitrite oxidizing bacteria (NOB) in flocs decreased obviously. Interestingly, the abundance of anaerobic ammonium oxidizing bacteria (AnAOB) in flocs increased from 0.213% to 0.346% despite the sludge retention time (SRT) of flocs decreased to 60 days, the AnAOB in biofilm was 0.434%. That meant AnAOB gradually enriched in flocs and accounted for a fairly high proportion. The inhibition of NOB, partial denitrification and increased aerobic_chemoheterotrophy function in flocs might be the main reasons for AnAOB enrichment. The possibility of simultaneous fermentation, partial denitrification and anammox reaction was predicted in biofilm, further improving the stability of the system.
Due to the unique electronic structure of aluminum ions (Al3+) with strong Coulombic interaction and complex bonding situation (simultaneously covalent/ionic bonds), traditional electrodes, ...mismatching with the bonding orbital of Al3+, usually exhibit slow kinetic process with inferior rechargeable aluminum batteries (RABs) performance. Herein, to break the confinement of the interaction mismatch between Al3+ and the electrode, a previously unexplored Se2.9S5.1‐based cathode with sufficient valence electronic energy overlap with Al3+ and easily accessible structure is potentially developed. Through this new strategy, Se2.9S5.1 encapsulated in multichannel carbon nanofibers with free‐standing structure exhibits a high capacity of 606 mAh g−1 at 50 mA g−1, high rate‐capacity (211 mAh g−1 at 2.0 A g−1), robust stability (187 mAh g−1 at 0.5 A g−1 after 3,000 cycles), and enhanced flexibility. Simultaneously, in/ex‐situ characterizations also reveal the unexplored mechanism of SexSy in RABs.
Via constructing sufficient valence electronic energy overlapped with aluminum ions and easily accessible structure, an unexplored high‐performance Se2.9S5.1 cathode in rechargeable aluminum batteries is proposed with detailed mechanism characterizations. Through this new strategy, multichannel selenium sulfide@carbon nanofiber (Se2.9S5.1@MCNF) exhibits high capacity (606 mAh g−1 at 50 mA g−1), high rate‐capacity (211 mAh g−1 at 2 A g−1), and robust stability.
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•It should cautiously pursue high PRA when aiming at improving PRE.•PRE plateaued at 75.68% with influent C/P ratio of 40 mgCOD/mgP.•Ca. Competibacter and Defluviicoccus were ...unexpectedly highly enriched.•Ca. Accumulibacter and Tetrasphaera were found absented from EBPR.
Competition between polyphosphate- and glycogen-accumulating organisms (PAOs and GAOs) is problematic in the enhanced biological phosphorus removal (EBPR) process. Aiming at a high phosphorus removal efficiency (PRE), the phosphorus release amount (PRA) is considered an essential evaluating indicator. However, the correlations between PRE and PRA and the abundance of PAOs are not clear. In this study, the EBPR was established and optimized via adjusting influent carbon to phosphorus ratio (C/P). After 110-day operation, 17.67 mg/L of PRA and 75.86% of PRE simultaneously achieved with influent C/P of 40 mgCOD/mgP. As for PAOs, Candidatus_Accumulibacter and Tetrasphaera were absent, while Hypomicrobium (3.69%), Pseudofulvimonas (1.02%), and unclassified_f_Rhodobacteraceae (2.41%) were found at a low level. On the contrary, Candidatus_Competibacter and Defluviicoccus were unexpectedly enriched with high abundance (24.94% and 16.04%, respectively). These results also suggested that it was difficult to distinguish whether PAOs were enriched merely based on the variations of PRA and PRE.
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•ST-PDA process was established for dealing with saline wastewater.•Stable nitrogen removal of PD and Anammox was achieved under 10 g·L-1 salinity.•Inhibition of NO3–-N and FNA was ...verified and FNA inhibition could be eliminated with self-alkalization.•The TN of effluent from ST-PDA process was average 17.8 mg·L-1.•Thauera showed a high tolerance to fluctuating salinity levels.
In the study, the salt-tolerant partial denitrification and Anammox (ST-PDA) process was established, meanwhile, the feasibility of salinity inhibition model as the boundary control method and the subsequent operation performance were studied. Study indicated that the performance of salt-tolerant PD sludge was the optimum under the 10 g·L-1 salinity, and AnAOB also maintained high activity at the salinity. Haldane and Aiba models verified that NO3–-N (substrate) and FNA (product) would have negative consequences for performance of ST-PDA system. However, the effect of FNA would be eliminated by self-alkalization in the denitrification process. A 90% nitrogen removal rate was achieved and the average effluent total nitrogen of 17.8 mg·L-1 was maintained in the system. The high throughput sequencing revealed that the species richness decreased with the salinity increased, while Thauera played a major role in nitrogen removal in saline environment. The study provides a novel insights for salt-containing industrial wastewater.
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•A novel DPR-SPNED process was established to treat municipal and nitrate sewages.•High PO43−-P and TN removal (97.5% and 90.8%) was obtained without extra carbon.•Dechloromonas, ...Candidatus Competibacter and Nitrosomonas dominated the DPR-SPNED.•Bottleneck of inefficient carbon use and high NH4+-N residues in DPRs were solved.•Integrating DPR-SPNED in WWTPs was proposed for further nutrient removal.
The feasibility of coupling denitrifying phosphorus removal (DPR) with simultaneous partial nitrification-endogenous denitrification (SPNED) was investigated in a single-sludge sequencing batch reactor for deep-level nutrient removal from municipal and nitrate wastewaters. After 160-day operation, the DPR process simultaneously reduced most PO43−-P and NO3−-N anoxically, and the SPNED process achieved further total nitrogen (TN) removal at low dissolved oxygen condition with TN removal efficiency of 90.8%. The effluent NH4+-N, PO43−-P and TN concentrations were 1.0, 0.1 and 7.2 mg/L, respectively. Microbial analysis revealed that Dechloromonas (6.7%) dominated DPR process, whereas the gradually enriched Nitrosomonas (4.5%) and Candidatus Competibacter (6.8%) conducted SPNED process accompanied with sharply eliminated Nitrospirae (1.4%). Based on these findings, a novel strategy was proposed to achieve further nutrient removal in conventional treatment through integrating the DPR-SPNED process. As a result, ∼100% of extra carbon and ∼10% of oxygen consumptions would be reduced with satisfactory effluent quality.
