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High-strength nitrogen and antibiotics-containing wastewater can be efficiently eliminated by simultaneous denitrification and methanogenesis (SDM). Heavy metals and antibiotics are two critical factors that can lead to horizontal transfer of antibiotic resistance genes (ARGs), which can be simultaneously detected in wastewater. Unfortunately, the impacts of heavy metals on SDM and antibiotic biodegradation have not been fully elucidated. Herein, the effects of SDM and multiple antibiotics biodegradation, extracellular polymeric substances (EPSs) and protein response mechanisms, and ARG fate under Zn(II) stress were comprehensively evaluated. The results indicated that a high level of Zn(II) (≥5 mg/L) stress significantly decreased the degradation rate of multiple antibiotics and suppressed denitrification and methanogenesis. In addition, Zn(II) exposure prompted the liberation of proteins from microbes into the EPSs, and the combination of EPSs with small molecules quenched the original fluorescent components and destroyed the protein structure. The dominant proteins can bind to both Zn(II) and multiple antibiotics through several types of chemical interactions, including metallic and hydrogen bonds, hydrophobic interactions, and salt bridges, relieving the toxicity of harmful substances. Moreover, metagenomic sequencing revealed that the abundance of zinc resistance genes (Zn-RGs), ARGs (mainly tetracyclines), and mobile genetic elements (MGEs) increased under Zn(II) stress. Mantel test illustrated that the ARGs mecD, tetT, and tetB(60) were most affected by MGEs. Moreover, molecular network analysis revealed that several MGEs can bridge metal resistance genes (MRGs) and ARGs, facilitating the horizontal transfer of ARGs. This study provides theoretical guidance for the environmental risk control of antibiotics-containing wastewater treated by an SDM system., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Ltd.)

Using wastepaper as external carbon sources is an optional way to achieve total nitrogen removal faced with low carbon to nitrogen ratio municipal sewage. Most of studies have primarily focused on using cellulose-rich wastes establishing the separate denitrification units to achieve in-situ fermentation, which can cause blockages and prolong the process chain. In response, a novel in-situ fermentation wastepaper-flora slow-release carbon source (IF-WF) was proposed using in the original denitrification unit. IF-WF could be efficiently utilized in situ and the denitrification rate increased with the increase of nitrate nitrogen. The fermentation products were highly available, but internal acidification of IF-WF inhibited fermentation. Moreover, IF-WF limited the growth of polysaccharides in the extracellular polymeric substances of denitrified sludge. IF-WF finally formed the structure dominated by nitrate-reduction bacteria outside and cellulose-degrading bacteria inside. These results provide guidance for understanding the mechanism of IF-WF for in-situ fermentation to promote nitrogen removal., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

The development of slow-release carbon sources is an effective biological treatment to remove nutrients from wastewater with low carbon-to-nitrogen ratio (C/N). Most filling-type slow-release carbon could not fulfil the needs of current wastewater treatment plants (WWTPs) process. And most adding-type slow-release carbon sources were prepared using some expensive chemical materials. In this study, combining the advantages of the aforementioned types, a novel adding-type wastepaper-flora (AT-WF) slow-release carbon source was proposed, aiming to realise wastepaper recycling in WWTPs. The screening and identification of the mixed flora, AT-WF carbon source release behaviour, and denitrification performance were investigated. The results showed that through the proposed screening method, a considerable proportion of cellulose-degradation-related genera was enriched, and the cellulose degradation ability and ratio of readily available carbon sources of flora T4, S4 and S5 were effectively strengthened. AT-WF had significant carbon release ability and stability, with an average total organic carbon (TOC) release of 8.82 ± 2.36 mg/g. Kinetic analysis showed that the entire carbon release process was more consistent with the first-order equation. Piecewise fitting with the Ritger-Peppas equation exhibited that the rapid-release (RR) stage was skeleton dissolution and the slow-release (SR) stage was Fick diffusion. Denitrification efficiency can achieve a high average removal efficiency of 94.17%, which could theoretically contribute 11.2% more to the total inorganic nitrogen (TIN) removal. Thus, this study indicated that AT-WF could be utilised as an alternative carbon source in WWTPs., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Phenolic compounds are the dominant pollutants in soils contaminated by the coking industry. Ring opening by the hydroxylase gene (bamA) is the key step in the benzoyl-CoA degradation pathway under anaerobic conditions, and a broad spectrum of microorganisms possesses this functional gene, including denitrifiers. The present study analyzed the community structure of denitrifying bacteria and the diversity of the bamA gene for mixed cultures enriched from soil collected at a coking industrial site and then grown under nitrate-reducing conditions on phenol or p-hydroxybenzoate (4HBA), a key intermediate product of anaerobic phenol degradation. Illumina sequencing of the 16S rRNA gene showed different bacterial compositions between the two cultures. The dominant phyla were Proteobacteria, Armatimonadetes, and Planctomycetes in the phenol culture and Proteobacteria and Bacteroidetes in the 4HBA culture. Phylogenetic analysis further demonstrated that bamA genes were associated with four clusters of bacteria, three of known bacteria and one of uncultured bacteria. The diversity of the bamA gene differed from that reported in anaerobic aromatic degradation cultures, suggesting that these enriched cultures may contain new strains unique to coking-contaminated soils. The present study further validates the potential application of this functional gene as a marker for anaerobic biodegradation processes in enrichment cultures from contaminated soil.

Bioretention has been widely used in urban non-point source (NPS) pollution management for effectively reducing downstream pollution loads and peak flows. However, nitrogen (N) removal in conventional bioretention systems has been uniformly unstable and highly variable due to a lack of anaerobic denitrification. To improve the stability and effectiveness of N removal, two bioretention columns with bilayer media (C1 and C2) were designed. High permeability quartz sand (~2 mm diameter) was used as the upper media, and low permeability modified media (~0.6 mm diameter, adding 5% organic substance) as the lower media. The bilayer media structure formed an anaerobic zone for promoting denitrification processes. The results showed that the retrofitted columns performed well and that the removal efficiencies of various forms of N were considerably enhanced to 76.8%-95.3%, 85.1%-98.3%, and 87.5%-97.4% for TN, NH 4 + -N, respectively. Additionally, copying numbers of the denitrification functional genes detected via FQ-PCR in the lower media of C1 and C2 were accounted for 46.06% and 44.16% of the 16S rDNA gene, respectively. These results confirmed the presence of anaerobic denitrification processes. Consequently, bilayer media bioretention systems are worth promoting in cities where nitrogen in urban runoff poses a threat to the receiving surface water, due to the systems' remarkable performance in nitrogen removal, simple structure, and easy implementation.3 - -N, respectively. Additionally, copying numbers of the denitrification functional genes detected via FQ-PCR in the lower media of C1 and C2 were accounted for 46.06% and 44.16% of the 16S rDNA gene, respectively. These results confirmed the presence of anaerobic denitrification processes. Consequently, bilayer media bioretention systems are worth promoting in cities where nitrogen in urban runoff poses a threat to the receiving surface water, due to the systems' remarkable performance in nitrogen removal, simple structure, and easy implementation., (Copyright © 2019 Elsevier B.V. All rights reserved.)

The positive effects nitrogen removal capability in a plug-flow microaerobic sludge blanket at low temperature are confirmed by inducing periodic high temperature shocks. This method enables enhancement of metabolic activity and an optimized bacterial community structure of microbes under the conditions of low C/N ratio and temperature. The control reactor was operated at a constant temperature of 20 °C, and the plug-flow microaerobic sludge blanket was subjected to a high temperature shock treatment with three cycles for 94 d. Starting with the initial temperature of 20 °C, after three cycles at temperature (30 °C) shock, the removal efficiencies of ammonium and total nitrogen at the terminal period increased to 68.0% and 54.7% from 51.1% to 35.6%, respectively. The activity and relative abundance of ammonia oxidizing bacteria, nitrite oxidizing bacteria, and anammox bacteria, dominated by Candidatus Brocadia at low temperature, were accordingly enhanced after periodic temperature shocks., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

In this study, a process that combines iron-carbon micro-electrolysis (IC-ME) with the anammox process was successfully established for promoting nitrogen removal, especially the removal of nitrate by-product. Compared with the conventional anammox process, the average total nitrogen removal efficiency of the combined system increased from 64.6% to 90.2% and 83.8% when the system was effectively operated for 4 days (Phase 2) and 13 days (Phase 3), respectively. In this combined system, IC-ME played a dual role: 1) converting the nitrate to ammonia as the nitrogen substrate for further degradation, and 2) producing Fe 2+ , Fe 3+ and H 2 for the nitrogen removal processes of NH 4 + oxidation with Fe 3+ oxidation (NDFO), and denitrification, in addition to the anammox process. Microbial analysis using 16S rRNA high-throughput sequencing revealed Candidatus Kuenenia and Candidatus Brocadia as the major anammox genera, accounting for 1.01% and 0.15%, respectively.2+ oxidation (NDFO), and denitrification, in addition to the anammox process. Microbial analysis using 16S rRNA high-throughput sequencing revealed Candidatus Kuenenia and Candidatus Brocadia as the major anammox genera, accounting for 1.01% and 0.15%, respectively., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

For quinoline-denitrifying degradation, very few researches focused on shortcut denitrification process and its bacterial community characteristics. In this study, complete and shortcut denitrification systems were constructed simultaneously for quinoline degradation. By calculation, specific quinoline removal rates were 0.905 and 1.123 g/(gVSS d), respectively, in the complete and shortcut systems, and the latter was 1.24 times of the former. Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE), high-throughput sequencing, and quantitative PCR (qPCR) techniques based on 16S rRNA were jointly applied to compare microbial community structures of two systems. Many denitrifying bacteria phyla, classes, and genera were detected in the two systems. Phylum Proteobacteria, Class Gammaproteobacteria, and Genus Alicycliphilus denitrificans were the dominant contributors for quinoline-denitrifying degradation. In the shortcut denitrification system, main and specific strains playing crucial roles were more; the species richness and the total abundance of functional genes ( narG, nirS, nirK, and nosZ) were higher compared with the complete denitrification system. It could be supposed that inorganic-nitrogen reductase activity of bacterial community was stronger in the shortcut denitrification system, which was the intrinsic reason to result in higher denitrification rate. [ABSTRACT FROM AUTHOR]

Constructed wetlands have been widely employed as a cost-effective and environmentally friendly alternative for treating primary and secondary sewage effluents. In this study, biochar and pyrite were utilized as electron donor substrates in intermittent-aerated vertical flow constructed wetlands to strengthen the nutrient and heavy metals removal simultaneously, and the response of nutrient reduction and microbial community to heavy metals stress was also explored. The results indicated that biochar addition exhibited a better nitrogen removal, while pyrite addition greatly promoted the phosphorus removal. Moreover, the high removal efficiencies of Cu2+, Pb2+ and Cd2+ (above 90%) except for Zn2+ were obtained in each system. However, the exposure of heavy metals decreased phosphorus removal while had little effect on nitrogen removal. The influent load and intermittent aeration implementation led to a significant shift in microbial community structures, but microbial biodiversity and abundance decreased under the exposure of heavy metals. Particularly, Thiobacillus and Ferritrophicum , associated with sulfur autotrophic denitrification and iron autotrophic denitrification, were more abundant in pyrite-based wetland systems. • Biochar and pyrite addition was beneficial to nitrogen and phosphorus removal. • Biochar-mediated heterotrophic denitrification played significant role in enhancing total nitrogen removal. • Exposure to heavy metals had little impact on denitrification but hindered phosphorus removal. [ABSTRACT FROM AUTHOR]

Graphical Abstract Highlights • First investigated the high COD/NO 3 −-N ratio of indole wastewater in mixed culture. • Through nitrate to observe the denitrification and methanogenesis co-existence. • Nitrate was found to facilitate indole degradation and inhibit methane formation. • The metabolites were identified based on 13C-indole isotope analysis. • A dynamic community analysis was presented to study the microbial structures. Abstract Batch experiments were conducted to investigate the effect of nitrate on indole degradation characteristics and methanogenesis under mixed denitrification and methanogenesis culture for the first time. The degradation characteristics were studied under various nitrate concentrations. Nitrate was found to facilitate indole degradation and inhibit methane formation, and the optimum concentration was 50 mg L−1 (COD/NO 3 −-N = 12). Balance analyses showed that nitrate mainly affected indole-C, which generated a higher degree of indole mineralization under NO 3 −-N treatment than in the control. Furthermore, GC–MS combined with 13C-isotope analyses conclusively identified the intermediate metabolites, which included the hydroxylated compounds oxindole and isatin, and the methylated compound 3-methylindole. The results indicated that oxindole did not accumulate and was quickly reduced when nitrate was added, but 3-methylinole, as a recalcitrant material, accumulated without reduction. High-throughput sequencing technology was used to analyse the dynamic microbial community. Results showed that the denitrifying bacterial genera Acinetobacter , Candidimonas and Longilinea accumulated in denitrification stage and decreased in methanogenesis stage, whereas the fermentation genera Alcaligenes and Thermogutta increased in methanogenesis stage. The genera Methanosphaerula and Methanothrix constituted the dominant archaeal communities. The findings obtained in this work may provide a theoretical basis for treatment with N-heterocyclic compounds under mixed culture. [ABSTRACT FROM AUTHOR]

Zero valent iron (ZVI) is a low-cost, earth-abundant reactive metal, and it has a strong reducing ability with a standard redox potential of − 0.44 V. Therefore, it is an effective and widely used reducing agent for pollutant degradation. Since nanoscale zero valent iron (nZVI) shows a larger specific surface area which leads to the faster reaction rate and higher conversion efficiency, it has been widely used in NO 3 − nitrogen reduction reaction, however, it shows disadvantages of poor chemical stability, narrow applicable pH, and low total nitrogen (TN) removal efficiency. To solve these problems, in this paper, the nZVI nanoparticles were deposited on the g-C 3 N 4 /rGO composite, and its NO 3 − removal efficiency under visible light irradiation was investigated. The effects of nZVI loading, initial pH of solution, catalyst dosage and initial NO 3 − concentration on NO 3 − reduction performance were studied. The results showed that the g-C 3 N 4 /rGO/nZVI material achieved 100% of NO 3 − reduction efficiency in 60 min. And the TN removal efficiency of g-C 3 N 4 /rGO/nZVI was 82.8%, superior to nZVI and g-C 3 N 4 /nZVI (13.3% and 38.2%, respectively). Finally, the denitrification mechanism of g-C 3 N 4 /rGO/nZVI was proposed as follows: Under light irradiation, the photogenerated electrons on g-C 3 N 4 transferred via rGO to the nZVI surface, thus improving the reactivity and stability of nZVI. The photogenerated electrons and active electrons on the surface of nZVI reduced NO 3 − to N 2 , NH 4 +, and other products, while the photogenerated holes further oxidized part of NH 4 + to N 2 and other gaseous products. During this process, the rGO material could inhibit the oxidation of nZVI by the photogenerated holes from g-C 3 N 4. [Display omitted] • g-C 3 N 4 /rGO serves as a support for nZVI to enhance its stability and activity. • The rGO in g-C 3 N 4 /rGO hindered the oxidation of nZVI by photogenerated holes. • The NO 3 − reduction mechanism was explored and the reduction products were analyzed. • NO 3 − was completely removed and the selectivity of gaseous products were 82.8%. [ABSTRACT FROM AUTHOR]

Deposition of bimetals on Z-scheme photocatalysts has been reported to improve the nitrate nitrogen (NO 3 −) reduction properties. However, it is not clear whether bimetal deposition possesses advantage over single metal deposition and what is the different reaction mechanisms. In this work, the g-C 3 N 4 (Pd-Cu)/rGO/TiO 2 and g-C 3 N 4 (Ag)/rGO/TiO 2 composites with bimetallic Pd-Cu and single metal Ag deposited on the graphitic carbon nitride/reduced graphene oxide/titanium dioxide (g-C 3 N 4 /rGO/TiO 2) Z-scheme photocatalyst were prepared, and their photocatalytic NO 3 − reduction properties and the mechanisms under visible light irradiation were studied. The results showed that the NO 3 − and total nitrogen (TN) removal efficiencies of g-C 3 N 4 (Pd-Cu)/rGO/TiO 2 were 57.78% and 20.1%, respectively, 1.15 and 1.72 times higher than those of g-C 3 N 4 (Ag)/rGO/TiO 2. This can be ascribed to that Pd-Cu enriched more electrons and absorbed more NO 3 − molecules due to the different charge densities, and the NO 3 − reduction process were enhanced by the staged NO 3 −→NO 2 − and NO 2 −→N 2 /NH 4 + processes on Cu and Pd. The effects of reductive species were demonstrated to be photogenerated electrons > ·OH (·CO 2 −) > ·O 2 − in g-C 3 N 4 (Ag)/rGO/TiO 2 , while it was photogenerated electrons > ·O 2 − > ·OH (·CO 2 −) in g-C 3 N 4 (Pd-Cu)/rGO/TiO 2 , which may be caused by the better O 2 reduction property of the latter. Finally, the cyclic experiment proved the good stability of both materials. This work provided some reference for design of metal deposited Z-scheme photocatalysts for various reduction reactions. [Display omitted] • The g-C 3 N 4 (Cu-Pd)/rGO/TiO 2 and g-C 3 N 4 (Ag)/rGO/TiO 2 composites were prepared. • The NO 3 − reduction performances and mechanisms were studied and compared. • The reductive species in g-C 3 N 4 (Ag)/rGO/TiO 2 were e– > ·OH (·CO 2 −) > ·O 2 −. • The reductive species in g-C 3 N 4 (Cu-Pd)/rGO/TiO 2 were e– > ·O 2 − > ·OH (·CO 2 −). [ABSTRACT FROM AUTHOR]

Nitrogen contamination is regarded as a major threat to terrestrial net productivity and environmental sustainability. Anaerobic ammonium oxidation (anammox) is a cost-effective and promising technology in wastewater treatment. In this study, the effects of pH/temperature and their short-term shocks on a hybrid system of anammox coupled with iron-carbon micro-electrolysis (IC-ME) were investigated. Results indicated that the hybrid system significantly enhanced the total nitrogen (TN) removal and expanded the stable pH operating range (TN removal efficiencies over 50%) from pH 6.5–8 to pH 5.5–8.5. Free nitrous acid (FNA) in acid environment, when its concentration was higher than 396.36 ± 5.51 μg/L, was thought to be one critical degradation inhibitor. After suffering a short-term (one day) pH shock, the hybrid system exhibited the improved performance of both stability and nitrogen removal, mainly because Fe corrosion maintained the pH value by IC-ME. More diverse nitrogen removal processes promoted by IC-ME enhanced the TN removal of hybrid after high temperature shocks. However, the susceptibility and inferior adaptability of anammox bacteria were considered to inhibit the nitrogen removal performance of the hybrid and individual anammox system. Microbial analysis identified Candidatus Kuenenia as the major anammox genus, accounting for 3.61% of the microbial community biomass, and the genus of SM1A0 2 might be one novel potential strain that help the anammox process. • Effects of pH/temperature on anammox with Fe–C micro-electrolysis were explored. • Hybrid system showed better stability and nitrogen removal under acid environment. • Free nitrous acid in acidic condition was thought to be a critical inhibitor. • A short-term shock of high temperature was positive for promoting nitrogen removal. [ABSTRACT FROM AUTHOR]

Extraction of short-chain fatty acids (SCFAs) from fermentation liquid of waste activated sludge (WAS) is the key bottleneck hindering its application as electron donor in denitrification. This study explores the feasibility of polyether-type polyurethane (PU)-modified layered double hydroxides (LDHs, prepared using eggshell waste as calcium source) in SCFAs adsorbing from WAS fermentation liquid (SFL). The adsorption parameters were first optimized by adsorption tests using artificial fermentation liquid (AFL). Then, adsorption kinetics, thermodynamic and isotherms were explored to further understand the adsorption mechanism. It revealed that SCFAs absorption by PU-LDHs from SFL was an endothermic and spontaneous process with positive enthalphy (ΔH◦) values and negative Gibbs free energy (ΔG◦) values. In addition, the maximum adsorption capacity of 208.0 mg SCFAs/g PU-LDHs was obtained from the Langmuir isotherm. Noting that both soluble carbohydrates and soluble proteins were simultaneously extracted, with efficiencies of 30.9%, 6.2%, respectively, compared with 62.9% SCFAs. The reuse tests confirmed that the prepared PU-LDHs can be used at least three times with high adsorptive capacity. With PU-LDHs-loaded SFL as external carbon source in the biodenitrification process, a denitrification rate of 0.014 mg NO 3 −-N/mg mixed liquid suspended solids (MLSS)·d was recorded. This study provided a sound basis for the preparation of cost-effective biodenitrification carbon source from SFL by a novel adsorbent. Image 1 • A waste-to-resource concept was established for eggshell waste and WAS treatment. • PU-LDHs can be repeatedly used as the carrier of SCFAs with high adsorption capacity. • PU-LDHs retained SFL showed good performance as electron donor in denitrification. • Recycle test confirmed PU-LDHs can be reused multiple times for biodenitrification. [ABSTRACT FROM AUTHOR]