Removal Pathway Research Articles

Enhanced removal of tetracycline using three-dimensional electrochemical system with Fe/N/S co-doped coffee grounds biochar particle electrodes: Performance and mechanism

In this study, Fe/N/S co-doped biochar was prepared from coffee grounds for using as particle electrodes (PE) to construct a three-dimensional electrochemical system (3DES). Tetracycline (TC) was selected as the simulated contaminant to evaluate the performance of 3DES in removing trace organic contaminates form water. First, characteristics analysis revealed that the PE was the micron-level carbon-based solid material with good electric conductivity, excellent catalytic performance and stability. Then, the performance of the 3DES was evaluated. About 92% of TC and 76% of total organic carbon (TOC) was removed under optimal operation conditions of potassium peroxydisulfate (PDS) addition of 3mM, current density of 100mA·cm−2, PE dosage of 0.5g·L−1 and solution initial pH of 7. The 3DES exhibited satisfactory stability and application prospect for trace organic contaminates treatment in real water. Furthermore, analysis of the reactive oxidized species (ROS) revealed that the 1O2 and O2•− contributed much more to the TC removal than •OH and SO4•−. In addition, three possible pathways of TC removal in 3EDS was proposed. TC was degraded to organics with simple structures through functional group removal, ring-opening, and C=O bond rupturing, and finally mineralized into CO2, H2O, and NO3-, etc. Finally, toxicity evaluation of the intermediate products indicated that the ecological risks of TC was effectively reduced through 3DES. This study provided a new strategy for resource utilization of carbon-based solid waste and efficient treatment of refractory wastewater.

Redundant pathways for removal of defective RNA polymerase II complexes at a promoter-proximal pause checkpoint.

The biological purpose of Integrator and RNA polymerase II (RNAPII) promoter-proximal pausing remains uncertain. Here, we show that loss of INTS6 in human cells results in increased interaction of RNAPII with proteins that can mediate its dissociation from the DNA template, including the CRL3ARMC5 E3 ligase, which ubiquitylates CTD serine5-phosphorylated RPB1 for degradation. ARMC5-dependent RNAPII ubiquitylation is activated by defects in factors acting at the promoter-proximal pause, including Integrator, DSIF, and capping enzyme. This ARMC5 checkpoint normally curtails a sizeable fraction of RNAPII transcription, and ARMC5 knockout cells produce more uncapped transcripts. When both the Integrator and CRL3ARMC5 turnover mechanisms are compromised, cell growth ceases and RNAPII with high pausing propensity disperses from the promoter-proximal pause site into the gene body. These data support a model in which CRL3ARMC5 functions alongside Integrator in a checkpoint mechanism that removes faulty RNAPII complexes at promoter-proximal pause sites to safeguard transcription integrity.

Novel insights into revealing the intrinsic degradation mechanism of ciprofloxacin by Chlorella sorokiniana: Removal efficiency, pathways and metabolism

Microalgae-mediated biodegradation of antibiotics has attracted increasing interest. However, the exact degradation mechanism behind it remains elusive, which is crucial for improving its efficiency and large-scale implementation. Therefore, this study aims to thoroughly investigate how Chlorella sorokiniana (C.sorokiniana) degrades ciprofloxacin (CIP) from the molecular level to elucidate its complicated degradation mechanism. Results show that C.sorokiniana exhibited an impressive removal rate of 38.05–74.29 % for CIP, the synergistic effect of biosorption and biodegradation was the main removal mechanism of CIP. The content of EPS increased by 11.84–103.31 %, acting as a carrier to increase the bioavailability of CIP. Enzyme activity analysis identified POD, CYP450, and GST as the major catalytic enzymes responsible for the biotransformation process of CIP with increases of 6–41.2 %, 18.78–102.1 % and 3.53–58.15 %, respectively. Molecular docking further revealed that the binding affinity of 146.24 μM, 27.71 μM and 16.33 μM was observed for POD,CYP450, and GST, respectively, indicating the high metabolic efficiency of CIP by CYP450. Finally, DFT calculations elucidated the enzyme-mediated biodegradation pathway of CIP, including hydroxylation, decarboxylation, and ring opening. These findings are expected to further fill the knowledge gap on the catalysis mechanism of CIP degradation by enzymes and improve the practical application of microalgae to antibiotic wastewater.

Uncovering pathway and mechanism of simultaneous thiocyanate detoxicity and nitrate removal through anammox and denitrification

Thiocyanate (SCN−) exists in various industries and is detrimental to the ecosystem, necessitating cost-effective and environmentally benign treatment. In response to alleviate the bacterial toxicity of SCN−, this study developed a two-stage coupled system by tandem of anammox in reactor 1 (R1) and SCN−-driven autotrophic denitrification in reactor 2 (R2), achieving simultaneous removal of SCN− and nitrogen. The total nitrogen removal efficiency of the coupled system was 92.42 ± 1.98%, with nearly 100% of SCN− elimination. Thiobacillus was responsible for SCN− degradation. The deduced degradation pathway of SCN− was via the cyanate pathway before coupling, followed by the co-action of cyanate pathway and carbonyl sulfide pathway after coupling. Although scaling-up study is needed to validate its applicability in real-world applications, this study contributes to the advancement of sustainable and cost-effective wastewater treatment technologies, being an attractive path for low-carbon nitrogen removal and greenhouse gas emission-free technology.

Pathways and enhancement strategies for magnesium hardness removal in modified induced crystallization softening

Elevated levels of total hardness in drinking water can readily result in scaling, which poses a threat to both the safety of water quality and the convenience of its use. While there is a wealth of research on the removal of calcium hardness, there is a dearth of studies focusing on the removal of magnesium hardness. In light of this, the present study employs modified induced crystallization softening (MICS) to delineate the removal pathways and mechanisms of magnesium hardness, and to investigate viable methods for its enhancement and application. Our research has determined that magnesium hardness can be effectively removed from water through the MICS, with the dosage of softening agents (NaOH) being a significant factor that influences this removal, whereas the fixed bed height within the fluidized bed exerts minimal impact on the process. In the low-dose stage (less than 250 mg/L), when the pH is below 10.0, up to 20% of magnesium hardness can be removed, predominantly through the crystallization of (Ca0.936Mg0.064)CO3. As the dosage increases to the moderate stage (250–400 mg/L), the conversion of excess bicarbonate (HCO3−) to carbonate (CO32−) in the water hinders further removal of magnesium hardness. In the high-dose stage (exceeding 400 mg/L), when the pH rises above 10.5, the removal rate of magnesium hardness can be enhanced to over 75%, with the crystallization of Mg(OH)2 being the primary removal mechanism. Density functional theory calculations, along with molecular dynamics simulations of cohesive energy and bond energy, substantiate the feasibility of the identified magnesium removal pathways. The addition of coagulants (FeCl3) and an decrease in the up-flow velocity can further augment the removal efficiency of magnesium hardness by promoting the crystallinity of Mg(OH)2 during the high-dose stage (exceeding 400 mg/L). In practical engineering applications, the strategic control of softening agent dosages enables the achievement of varying levels of magnesium hardness removal, tailored to specific water quality requirements.

Comammox rather than AOB dominated the efficient autotrophic nitrification-denitrification process in an extremely oxygen-limited environment

The discovery of complete ammonia oxidizer (comammox) has challenged the traditional understanding of the two-step nitrification process. However, their functions in the oxygen-limited autotrophic nitrification-denitrification (OLAND) process remain unclear. In this study, OLAND was achieved using comammox-dominated nitrifying bacteria in an extremely oxygen-limited environment with a dissolved oxygen concentrations of 0.05 mg/L. The ammonia removal efficiency exceeded 97 %, and the total nitrogen removal efficiency reached 71 % when sodium bicarbonate was used as the carbon source. The pseudo-first- and second-order models were found to best fit the ammonia removal processes under low and high loads, respectively, suggesting distinct ammonia removal pathways. Full-length 16S rRNA gene sequencing and metagenomic results revealed that comammox-dominated under different oxygen levels, in conjunction with anammox and heterotrophic denitrifiers. The abundance of enzymes involved in energy metabolism indicates the coexistence of anammox and autotrophic nitrification-heterotrophic denitrification pathways. The binning results showed that comammox bacteria engaged in horizontal gene transfer with nitrifiers, anammox bacteria, and denitrifiers to adapt to an obligate environments. Therefore, this study demonstrated that comammox, anammox, and heterotrophic denitrifiers play important roles in the OLAND process and provide a reference for further reducing aeration energy in the autotrophic nitrogen removal process.

Calcium regulates nitrogen removal in constructed wetlands: The interactions between dissolved organic matter and microbial response

Limited carbon bioavailability in low C/N tailwater aggravated the difficulty of nitrogen (N) removal. Calcium (Ca) can regulate carbon transformation, but the effects of Ca on N removal in constructed wetlands (CWs) remain elusive. To fill the gap, this study constructed two types of Ca-based CWs, and the results revealed that the removal efficiencies of nitrate (NO3−-N) and total nitrogen (TN) in Ca-based CWs increased by 9.83–22.25 % and 8.59–18.72 %, respectively, compared to control group. The proportion of protein-like DOM and P/H index (represent bioavailability of DOC) increased in Ca-based CWs, supporting the growth of heterotrophic denitrifiers and facilitated NO3−-N and TN removal. In addition to directly enhancing complete denitrification, Ca-based CWs also optimize the N removal pathway. Moreover, Ca enhanced complexity and robust of the microbial network, increased microbial communication, thereby jointly facilitating N removal. This study highlighted Ca improved N removal by collaborating the interactions of DOM transformation and microbial activity, which provided an abundant and cheap substrate for the treatment of low C/N wastewater by CWs

Interactions between antibiotic removal, water matrix characteristics and layered double hydroxide sorbent material

Sorption by layered double hydroxides (LDH) is gaining substantial interest for remediating emerging contaminants, including pharmaceuticals from wastewaters. Findings from a sorbent material performing successfully in lab-based studies using non-environmental (laboratory-sourced) water cannot be assumed to translate to equal performance under environmental downstream applications. However, studies evaluating sorbent material performance for removal of pollutants and understanding material interactions with environmental waters are limited. This study evaluates the removal of the antibiotic amoxicillin (AMX) using a Mg2Al–NO3-LDH sorbent material from laboratory-grade water and wastewater effluent (WWE). AMX is successfully removed (94.53 ± 4.30 % within 24 h) in laboratory-grade water (under batch sorption conditions: 100 μg/L AMX, 0.2 g/L LDH, 20 °C). The comparison of LDH removal performance in laboratory grade and WWE shows a decreased maximum removal of AMX in WWE (13.39 ± 5.53 %). A lower final AMX concentration is observed in the WWE without the presence of LDH, compared to the ‘removal’ experiments in WWE with the presence of LDH, indicating a contribution of non-sorption removal pathways of AMX. This is proposed to be due to the difference in metal concentrations in the WWE with and without LDH present. The presence of LDH is found to decrease concentrations of metal pollutants in WWE, such as Zn concentration decreasing by 85 % over 24 h, changing water characteristics. Overall, this paper reports that an LDH performs differently in laboratory-sourced water and a wastewater effluent. This provides evidence that sorbent material performance needs to be evaluated in complex water matrices to ensure that it is representative of how a sorbent material will perform in an environmental application, which is the end goal of developing such technologies. Finally, good practice recommendations are provided for future lab-scale sorption experiments evaluating the performance of any new sorbent materials for water treatment applications.

Nutrient removal efficacy and microbial dynamics in constructed wetlands using Fe(III)-mineral substrates for low carbon-nitrogen ratio sewage treatment.

This study evaluated the roles of two common sources of Fe(III)-minerals-volcanic rock (VR) and synthetic banded iron formations from waste iron tailings (BIF-W)-in vertical flow-constructed wetlands (VFCWs). The evaluation was conducted in the absence of critical environmental factors, including Fe(II), Fe(III), and soil organic matter (SOM), using metagenomic analysis and integrated correlation networks to predict nitrogen removal pathways. Our findings revealed that Fe(III)-minerals enhanced metabolic activities and cellular processes related to carbohydrate decomposition, thereby increasing the average COD removal rates by 10.7% for VR and 5.90% for BIF-W. Notably, VR improved nitrogen removal by 1.70% and 5.40% compared to BIF-W and the control, respectively. Fe(III)-mineral amendment in bioreactors also improved the retention of denitrification and nitrification bacteria (phylum Proteobacteria) and anammox bacteria (phylum Planctomycetes), with increases of 3.60% and 3.20% using VR compared to BIF-W. Metagenomic functional predictionindicated that the nitrogen removal mechanisms in VFCWs with low C/N ratios involve simultaneous partial nitrification, ANAMMOX, and denitrification (SNAD). Network-based analyses and correlation pathways further suggest that the advantages of Fe(III)-minerals are manifested in the enhancement of denitrification microorganisms. Microbial communities may be activated by the functional dissolution of Fe(III)-minerals, which improves the stability of SOM or the conversion of Fe(III)/Fe(II). This study provides new insights into the functional roles of Fe(III)-minerals in VFCWs at the microbial community level, and provides a foundation for developing Fe-based SNAD enhancement technologies.

Efficient nitrogen and phosphorus removal performance and microbial community in a pilot-scale anaerobic/anoxic/oxic (AOA) system with long sludge retention time: Significant roles of endogenous carbon source

Stringent wastewater discharge standards require wastewater treatment plants (WWTPs) to focus on enhancing nitrogen (N) and phosphorus (P) removal efficiency. Increasing sludge concentration by regulation of sludge retention time (SRT) would enhance wastewater treatment loads. However, phosphorus-accumulating organisms (PAOs) would be outcompeted by glycogen-accumulating organisms (GAOs) under long SRT, leading to a collapse of P removal. In this work, pilot-scale anaerobic-oxic-anoxic (AOA) and anaerobic-anoxic-oxic (AAO) systems with long SRT (30 d) were parallelly established for actual urban wastewater treatment. The results indicated that sludge reflux ratio, temperature, and C/N ratio significantly impact N and P removal performance of AOA and AAO systems with long SRT, and removal efficiency of AOA system significantly exceeded that of AAO system. AOA system with long SRT achieved the optimal performance at sludge reflux ratio of 200%, temperature of 25 °C, and C/N ratio of 8, with COD, NH4+-N, TN, and PO43--P removal ratio of 92.80 ± 2.24%, 97.38 ± 0.89%, 88.97 ± 2.47%, and 94.33 ± 3.27%, respectively. In addition, compared to AAO system, AOA system could save 23.08% of the aeration volume. This work highlighted that AOA system with long SRT included multiple coupled nitrogen and phosphorus removal pathways, such as autotrophic/heterotrophic nitrification, anoxic/oxic denitrification, endogenous denitrification, and denitrifying phosphorus removal. Among these, the synergistic effect of endogenous denitrification and denitrifying phosphorus removal driven by internal carbon sources contributed to satisfactory nitrogen and phosphorus removal efficiency in AOA system with long SRT.

Tripolyphosphate-functionalized cellulose: A green solution for cadmium contamination

This study introduces a highly efficient tripolyphosphate -tethered cellulose sorbent for cadmium (Cd2⁺) removal from aqueous solutions. Characterization through FTIR and SEM revealed the material's structural properties. The sorbent achieved 99% Cd2⁺ removal even at a minimal dosage of 0.05 g. Optimal sorption occurred within the pH range of 4–6, influenced by the sorbent's weak acidic functional groups. Rapid kinetics, reaching equilibrium within a minute, and a high sorption capacity (up to 18.03 mg/g at 50 °C) were observed. Langmuir isotherm modeling confirmed monolayer sorption, and thermodynamic studies indicated a spontaneous, endothermic process with increased randomness at the solid-liquid interface. Selectivity studies demonstrated strong Cd2⁺ removal performance in the presence of competing ions, with minimal interference from monovalent ions but notable effects from divalent ions. The sorbent exhibited consistent reusability over multiple cycles. XPS analysis conclusively established an ion exchange mechanism between Cd2⁺ and negatively charged P3O105− groups as the primary removal pathway. This research highlights the potential of TPP-tethered cellulose as a promising sorbent for effective Cd2⁺ remediation.

Unveiling the synergism and reaction pathway of ethyl acetate removal in DBD/absorption integrated reactor

The experiment employs dielectric barrier discharge (DBD) combined with absorption integrated reactor (DCAIR) for higher concentration ethyl acetate removal and studies the synergism of DCAIR technology and the reaction pathway of ethyl acetate. Among three technologies of DCAIR, DBD and DBD combined with absorption series reactor (DCASR), DCAIR achieved the highest removal efficiency (RE) of ethyl acetate at similar input power. Fixed gas flow rate of 1000 ml/min and cC4H8O2in of 5000 mg/m3, the average REs of DCASR and DCAIR are higher than that of DBD by 31.2 % and 34.2 %, respectively. For the efficiency compensation mechanism, one of synergies in DCAIR, RE of ethyl acetate could exceed 80 % at the input power of 15 W. Energy consumption evaluation shows when RE > 80 %, the max energy efficiency of three technologies is in the order 70.0 g/kWh (DCAIR) > 5.1 g/kWh (DCASR) > 3.0 g/kWh (DBD). Tail gas and absorbent analysis reveals DCAIR can enhance mineralizing ethyl acetate and eliminating the secondary pollutants (e.g., O3, gaseous organic intermediates, and COD, etc.) effectively, due to its special structure of reactor. According to FT-IR spectra, the degradation mechanism and reaction pathway of ethyl acetate in DCAIR has been unveiled.

Microalgal–Bacteria Biofilm in Wastewater Treatment: Advantages, Principles, and Establishment

The attached microalgal–bacterial consortium (microalgae–bacteria biofilm, MBBF) has been increasingly recognized in wastewater treatment for its superior pollutant removal efficiency, resilience to toxic substances, and improved harvesting performance. This review initially discusses the advantages of MBBFs compared to activated sludge and suspended microalgal–bacterial consortia. These advantages stem from the coexistence of pollutant removal pathways for the bacteria and microalgae in MBBFs, as well as the synergistic interactions between the microalgae and bacteria that enhance pollutant removal and resilience capabilities. Subsequently, the establishment of the MBBF system is emphasized, covering the establishment process, influencing factors of MBBF formation, and the utilization of photobioreactors. Lastly, the challenges associated with implementing MBBFs in wastewater treatment are deliberated. This study aims to present a detailed and comprehensive overview of the application of MBBFs for wastewater treatment and biomass production.

Enhanced 3D electrochemical degradation of acrylonitrile with Fe-Cu@CB nanoparticles via the hydrogenation-oxidation synergistic processes

Acrylonitrile is a highly toxic and hazardous pollutant present in industrial wastewater at high concentrations, posing significant environmental and health risks. There is an urgent need for efficient, cost-effective, and environmentally friendly treatment methods for acrylonitrile. The electron-withdrawing –CN group in acrylonitrile offers potential pathways for degradation via superoxide radicals (O2•-), but this approach remains underexplored with limited research efforts. To investigate the degradation mechanism of acrylonitrile by O2•-, we synthesized particle electrodes Fe-Cu@CB using a novel one-step co-hydrolysis method and applied them for the 3D electrochemical degradation of acrylonitrile. Batch experiments showed that acrylonitrile with an initial concentration of 100 mg·L−1 was removed by 95 % at a voltage of 2.73 V (vs. RHE) for one hour. Compared with 2D electrochemical degradation, 3D electrochemical degradation of acrylonitrile increased the removal rate from 57 % to 95 %, and the TOC removal rate was also enhanced from 23.59 % to 88.33 %. Additionally, the energy consumed by this system was remarkably lower than the reported 3D electronic reaction system. Based on electron paramagnetic resonance (EPR), oxygen species (ROS) quenching experiments, and GC–MS results, we proposed a new hydrogenation-oxidation synergistic pathway for acrylonitrile removal, which could be depicted as that acrylonitrile suffered hydrogenation, followed by O2•- reduction, and finally the intermediate products were degraded speedily. Other pollutants in acrylonitrile wastewater such as acrylic acid, acrylamide, and fumaronitrile could also be eliminated in this reaction system, and the degradation efficiency varied with the electronic structure of the pollutants. These findings offer new insights into the treatment of acrylonitrile wastewater and present a highly efficient, sustainable solution for industrial pollutant degradation.

Genome-resolved metagenomics reveals the nitrifiers enrichment and species succession in activated sludge under extremely low dissolved oxygen

Nitrification, a process carried out by aerobic microorganisms that oxidizes ammonia to nitrate via nitrite, is an indispensable step in wastewater nitrogen removal. To facilitate energy and carbon savings, applying low dissolved oxygen (DO) is suggested to shortcut the conventional biological nitrogen removal pathway, however, the impact of low DO on nitrifying communities within activated sludge is not fully understood. This study used genome-resolved metagenomics to compare nitrifying communities under extremely low- and high-DO. Two bioreactors were parallelly operated to perform nitrification and DO was respectively provided by limited gas-liquid mass transfer from the atmosphere (AN reactor, DO < 0.1 mg/L) and by sufficient aeration (AE reactor, DO > 5.0 mg/L). Low DO was thought to limit nitrifiers growth; however, we demonstrated that complete nitrification could still be achieved under the extremely low-DO conditions, but with no nitrite accumulation observed. Kinetic analysis showed that after long-term exposure to low DO, nitrifiers had a higher oxygen affinity constant and could maintain a relatively high nitrification rate, particularly at low levels of DO (<0.2 mg/L). Community-level gene analysis indicated that low DO promoted enrichment of nitrifiers (the genera Nitrosomonas and Nitrospira, increased by 2.3- to 4.3-fold), and also harbored with 2.3 to 5.3 times higher of nitrification functional genes. Moreover, 46 high-quality (>90 % completeness and <5 % contamination) with 3 most abundant medium-quality metagenome-assembled genomes (MAGs) were retrieved using binning methods. Genome-level phylogenetic analysis revealed the species succession within nitrifying populations. Surprisingly, compared to DO-rich conditions, low-DO conditions were found to efficiently suppressed the ordinary heterotrophic microorganisms (e.g., the families Anaerolineales, Phycisphaerales, and Chitinophagales), but selected for the specific candidate denitrifiers (within phylum Bacteroidota). This study provides new microbial insights to demonstrate that low-DO favors the enrichment of autotrophic nitrifiers over heterotrophs with species-level successions, which would facilitate the optimization of energy and carbon management in wastewater treatment.

Intercalation of novel Ocimum Sanctum leaves derived carbon dots between g-C3N4/CoFe2O4 Z-scheme heterojunction system for boosting the radicals’ generation in photo-Fenton degradation and synchronized electrochemical sensing of sulfamethoxazole antibiotic

Deeming about incessant consumption and disposal of pharmaceutical antibiotics in natural water bodies, this study demonstrates the synthesis of a novel Tulsi leaves (Ocimum Sanctum) derived carbon dots modified Z-scheme g-C3N4/CoFe2O4 heterojunction system. Characterization techniques namely XRD, FT-IR, XPS, FE-SEM, HR-TEM and EDX supported composite formation. Fabricated catalysts presented excellent photocatalytic performance towards removal of sulfamethoxazole (SMX). UV–vis DRS, PL and EIS findings suggested the augmented visible light absorption capability, suppression of electron-hole pairs recombination and effective separation of charge carriers which were accountable for degradation process. Probable mechanistic pathway for SMX removal was photo-Fenton assisted with Z-scheme separated electron-hole pairs via activation of H2O2, where hydroxyl radicals (•OH) were main reactive species. Additionally, the prepared material was employed as electrochemical sensor for individual as well as simultaneous detection of SMX and trimethoprim with quite impressive detection limits of 0.042 µM and 0.047 µM, respectively.

Long-lasting organics removal via •OH adsorbed transition metal flocs: Electron transfer-mediated H-bond and van der Waals force

Homogenous advanced oxidation processes (AOPs) based on transition metal catalysts toward the activation of H2O2 to hydroxyl radical (•OH) have been widely applied to organic pollutants removal, such as Fenton and Fenton-like processes. These transition metal catalysts mostly flocculate as the pH increases. It's worth noting that the formed transition metal flocs are complex heterogeneous aggregations with active substances, providing diverse reaction spaces and interfaces. However, it is a challenge to distinguish the roles of transition metal flocs in the organic pollutants removal from homogeneous catalytic reactions. Herein, we unveiled a pathway for the long-lasting removal of organic pollutants via Cr flocs adsorbed with •OH (HO•-Cr flocs) using a stepwise method. First, adsorbed •OH (•OHads) within the HO•-Cr flocs was proved to be the active site forming hydrogen bond (H-bond) and van der Waals force with organic pollutants. Then, the presence of switchable electron transfer between Cr and OH groups within the HO•-Cr flocs was revealed, contributing to the persistent existence of •OHads and consequently ensuring the long-lasting organics removal. Further, this removal pathway of organic pollutants was confirmed during the leather wastewater treatment. These findings will complement a different pathway for organic pollutants removal via transition metal flocs and extend the lifetime of homogeneous AOPs based on transition metal catalysts, providing significant implications for their design and optimization.

Isotope analysis of nitrogen removal pathways and N2O production potential in the SDAD-anammox system under different N/S ratios

This study explored the impact of varying nitrate to sulfide (N/S) ratios on nitrogen removal efficiency (NRE) in the sulfide-driven autotrophic denitrification and anammox (SDAD-anammox) system. Optimal nitrogen removal was observed at N/S ratios between 1.5 and 2.0. Isotope tracing results showed that the contribution of anammox to nitrogen removal was enhanced with increasing N/S ratios, reaching up to 37 % at the N/S ratio of 2.5. Additionally, complex nitrogen pathways were identified, including dissimilatory nitrate reduction to ammonium (DNRA). Furthermore, isotope tracing was innovatively applied to investigate N2O emissions, demonstrating that higher N/S ratios significantly reduced N2O emissions, with the lowest emissions at N/S ratio of 2.5. Gene expression analysis indicated that nitrogen and sulfide transformation genes decreased with increasing N/S ratios, while anammox-related genes first increased and then decreased, reflecting the system's microbial dynamics. These findings offer insights into nitrogen transformation pathways and N2O production mechanisms in the SDAD-anammox process.

Simultaneous nitrogen and phosphorus removal from polluted water using a novel bacterial consortium (BACON-38): Promising application for wastewater remediation

A novel mixed bacterial consortium, BACON-38, was developed with efficient heterotrophic nitrification, aerobic denitrification, and phosphorus accumulation abilities. The BACON-38 exhibited efficient NH4+-N, NO3−-N, PO43−-P, and COD removal from real wastewater with removal efficiencies of 93.4 ± 1 %, 90 ± 0.75 %, 87.8 ± 0.25 % and 92 ± 1.5 %, respectively, under aerobic condition. Further, efficient removal of these pollutants from synthetic wastewater was also achieved by employing this consortium. Optimal conditions for maximum N and P removal efficiency were identified through response surface methodology (dissolved oxygen: 3.75 ± 0.5 mg L−1, pH: 7.5 ± 0.55, C/N ratio: 8.96 ± 0.75, temperature: 23.5 ± 1.25 °C). Amplification of key genes (amoA, hao, napA, narG, nirK, nirS, ppk) and enzyme expression confirmed simultaneous nitrification, denitrification, and phosphorus removal by BACON-38. The proposed nitrogen and phosphorus removal pathway aligned with the N and P balance, showing their assimilation into intracellular components. These results indicate that BACON-38 has significant potential for effectively removing nitrogen and phosphorus, making it a promising and sustainable solution for wastewater remediation.

Amino polycarboxylic acid complex agent modified Fe0 enhanced activation of H2O2 double decomposition pathways for tetracycline removal under neutral condition

The summary of this study explores the modification of Fe0 with amino polycarboxylic acid complex agents (APCAs) to enhance H2O2 catalysis for tetracycline (TC) removal under neutral conditions. The ethylenediaminetetraacetic acid-modified Fe0/H2O2 system (EDTA-Fe0/H2O2) achieved a removal efficiency of 90.2 % for 50 mg/L TC, significantly higher than the 23.9 % efficiency of the traditional Fe0/H2O2 system. The removal rate of various pollutants by the EDTA- Fe0/H2O2 process is 2.9 to 8.4 times higher than that of the Fe0/H2O2 process. After four cycles of use, the removal rate of TC by the EDTA-Fe0/H2O2 system can still reach 76.3 %. Additionally, the effect of treating TC in natural freshwater can also achieve 80.1 %. Characterization revealed that EDTA-Fe0 had a larger Fe(II) proportion, better hydrophobicity, and lower corrosion potential than Fe0, indicating higher activity. Quenching experiments and electron paramagnetic resonance tests confirmed that •OH was the major reactive species. Shell-isolated nanoparticle-enhanced Raman spectroscopy indicated the presence of *OOH species, suggesting the involvement of a dioxygen coordination reaction. Density functional theory calculations showed that both dioxygen and single oxygen coordination H2O2 decomposition pathways played significant roles, and EDTA-Fe0 exhibited high catalysis ability for H2O2 in both pathways. Analysis of the relationship between APCAs’ group structure and APCAs-Fe0 properties indicated that the number of carboxyl groups was crucial for enhancing catalytic activity, while the number of amino groups also impacted antibiotic removal efficiency. Overall, this study provides a solid theoretical foundation for further Fe0 applications and suggests a new method to improve TC removal.