Promoting potential direct interspecies electron transfer (DIET) and methanogenesis with nitrogen and zinc doped carbon quantum dots

Insights into links between redox cycling of dissolved organic matter ranked by molecular weight and methanogen-bacteria symbiosis-driven methane production

Molecular weight (MW) of dissolved organic matter (DOM) governs its redox capacity, playing pivotal roles in methanogen-bacteria symbiosis-driven CH4 production. However, the effect of redox capacity of DOM ranked by MW on these symbiotic associations during anaerobic digestion have never been investigated. The electron-donating (EDC) and -accepting capacity (EAC) of DOM with different MW were quantified, elucidating their impacts on bacteria-methanogen symbiosis-driven CH4 production. By contrast, DOM with 7000 > MW > 14,000 Da constituted the primary contribution to EAC, with an average contribution of 44.63 %. DOM with MW > 14,000 Da emerged as the predominant contributor to EDC, with an average contribution of 49.10 %. Random forest showed that EAC/EDC of DOM ranked by MW was the important factors for methanogenesis by driving shifts in microbial symbiotic relationships. 46 genera (relative abundance of 69.55 %) of microorganisms exhibited robust associations with EAC/EDC. EDC of DOM with 3500 < MW < 7000 Da exerted positive effect on CH4 by modulating the corporation of Caldicoprobacter, norank_o__TSCOR001-H18, norank_o__MBA03 and Methanobrevibacter. EDC of DOM (7000 < MW < 14,000 Da) promotes CH4 production by regulating cooperation of Corynebacterium, Pseudomonas and Methanosarcina, Methanothermus. EDC of DOM (MW > 14,000 Da) enhances CH4 production by modulating cooperation of Ureibacillus, Treponema and methanomassiliicoccus, methanogenium. EAC of DOMs were negatively correlated with CH4. This study broadens our knowledge on the intricate process of methanogenesis and holds significant importance in developing a microbial symbiosis regulation strategy based on electron transfer system.

Enhancing methane production from corn straw via illumination-assisted Fe3O4/g-C3N4 nanocomposite in anaerobic digestion

This study proposes a novel anaerobic digestion (AD) strategy combining recyclable photoactivated nanomaterials with illumination to enhance electronic transfer for anaerobic microorganisms. Results showed that 7000 Lux illumination increased methane production yield and rate. Incorporating Fe3O4 into graphite carbon nitride (g-C3N4) created a recyclable Fe3O4/g-C3N4 (FG) nanocomposite with improved light absorption, conductivity, redox properties, and methane promotion. The highest methane yield from corn straw was achieved with 7000 Lux and 1.5 g/L FG nanocomposite, 22.6% higher than the dark control. The AD system exhibited increased adenosine triphosphate content, improved redox performance, reduced electron transfer resistance, and higher photocurrent intensity. These improvements bolstered the microorganisms and key genes involved in hydrolysis and acidification, which in turn optimized the acetoclastic pathway. Furthermore, this strategy promoted microorganisms associated with direct interspecies electron transfer, fostering a favorable environment for methanogenic activities, paving the way for future anaerobic reactor developments.

Novel insights into carbon nanomaterials enhancing anammox for nitrogen removal: Effects and mechanisms

Carbon nanomaterials (CNMs) possess the properties including large specific surface area, high porosity, and stable chemical structures, presenting significant application advantages in wastewater treatment. Indeed, CNMs are considered to be added to anammox systems to strengthen anammox function, especially to resolve the challenge of anammox technology, i.e., the slow growth rate of anammox bacteria, as well as its high environmental sensitivity. This paper systematically reviews the promotion effects and mechanisms of CNMs on the nitrogen removal performance of anammox system. Among the zero-, one-, and two-dimensional CNMs, two-dimensional CNMs have best promoting effect on the nitrogen removal performance of anammox system due to its excellent conductivity and abundant functional groups. Then, the promotion effects of CNMs on anammox process are summarized from the perspective of anammox activity and bacteria abundance. Furthermore, CNMs not only enhance the anammox process, but also stimulate the coupling of denitrification pathways with anammox, as well as the improvement of system operational stability (alleviating the inhibitions of low temperature and pH fluctuation), thus contributing to the promoted nitrogen removal performance. Essentially, CNMs are capable of facilitating microbial immobilization and electron transfer, which favor to improve the efficiency and stability of anammox process. Finally, this review highlights the gap in knowledge and future work, aiming to provide a deeper understanding of how CNMs can strengthen the anammox system and provide a novel perspective for the engineering of the anammox process.

Unraveling the mechanism of increased synthesis of hydrogen from an anaerobic fermentation by zinc ferrate nanoparticles: Mesophilic and thermophilic situations comparison

In this work, ZnFe2O4 NPs were created using the pyrolysis process, and its effects on thermophilic (TF) and mesophilic (MF) fermentation were examined. In MF, the maximum hydrogen yield (MHY) occurred in the 50 mg/L ZnFe2O4 NPs group (228.01 mL/g glucose), which was 45.24% higher than that of the control group (157.01 mL/g glucose). While in TF, MHY appeared in 100 mg/L ZnFe2O4 NPs was 149.12 mL/g glucose, which was 38.83% higher than the control group (107.41 mL/g glucose). ZnFe2O4 NPs boosted the synthesis of ferredoxin, hydrogenase, and ethanol dehydrogenase by increasing the generation of butyrate in MF and acetate in TF. Moreover, Clostridium sensu stricto 5 and 10 in MF and TF rose by 9.20% and 9.40%, respectively, due to the increased abundance of predominant hydrogen-producing bacteria by ZnFe2O4 NPs.

Antibacterial Carbon Dots: Mechanisms, Design, and Applications

The increase in antibiotic resistance promotes the situation of developing new antibiotics at the forefront, while the development of non-antibiotic pharmaceuticals is equally significant. In the post-antibiotic era, nanomaterials with high antibacterial efficiency and no drug resistance make them attractive candidates for antibacterial materials. Carbon dots (CDs), as a kind of carbon-based zero-dimensional nanomaterial, are attracting much attention for their multifunctional properties. The abundant surface states, tunable photoexcited states, and excellent photo-electron transfer properties make sterilization of CDs feasible and are gradually emerging in the antibacterial field. This review provides comprehensive insights into the recent development of CDs in the antibacterial field. The topics include mechanisms, design, and optimization processes, and their potential practical applications are also highlighted, such as treatment of bacterial infections, against bacterial biofilms, antibacterial surfaces, food preservation, and bacteria imaging and detection. Meanwhile, the challenges and outlook of CDs in the antibacterial field are discussed and proposed.

Strategy to synthesize dual-emission carbon dots and their application for pH variation and hydrogen sulfide sensing and bioimaging

In this work, dual emission nitrogen and sulfur co-doped fluorescent carbon dots (DE-CDs) were designed for pH variation and hydrogen sulfide (H₂S) sensing and bioimaging through fluorescence enhancement. The DE-CDs with green-orange emission were facilely prepared by one-pot hydrothermal strategy using neutral red and sodium 1,4-dinitrobenzene sulfonate as precursors, manifesting intriguing dual-emission behavior at 502 and 562 nm. As the pH increases from 2.0 to 10.2, the fluorescence of DE-CDs gradually increases. The linear ranges are 2.0-3.0 and 5.4-9.6, respectively, which are attributed to the abundant amino groups on the surface of the DE-CDs. Meanwhile, H₂S can be employed as an enhancer to increase the fluorescence of DE-CDs. The linear range is 25-500 μM, and the LOD is calculated to be 9.7 μM. Besides, the DE-CDs can be used as imaging agents for pH variation and H₂S sensing in living cells and zebrafish due to their low toxicity and good biocompatibility. All of the results demonstrated that the DE-CDs can monitor pH fluctuations and H₂S in aqueous and biological environments, and have promising applications in the fields of fluorescence sensing, disease detection, and bioimaging.

Dual utilization of aloe peel: Aloe peel-derived carbon quantum dots enhanced anaerobic co-digestion of aloe peel

Carbon materials have been widely used in anaerobic digestion (AD), but the role of zero-dimensional carbon quantum dots (CQDs) in anaerobic co-digestion (AcoD) has not yet been reported. In this work, the effect of aloe peel-derived CQDs (AP-CQDs) on the AcoD system of aloe peel and dairy manure was investigated. The addition of AP-CQDs accelerants increased the cumulative CH₄ yield from 201.14 to 266.92-339.64 mL/g VS and increased total chemical oxygen demand removal efficiency from 34.72 % to 48.77-57.87 %. The use of a digestate with 0.36 wt.% of AP-CQDs resulted in a thermogravimetric mass loss of 47.15 % and a promising total nutrient content of 46.65 g/kg. The excellent electron exchange capacity of AP-CQDs may facilitate direct interspecies electron transfer during the AD process. Moreover, the use of AP-CQDs can enrich methanogenic microorganisms (Methanosarcina and Methanobacterium). These findings provide a viable strategy for improving methane production and create awareness regarding the dual use of biomass waste.

Effect of homemade compound microbial inoculum on the reduction of terramycin and antibiotic resistance genes in terramycin mycelial dreg aerobic composting and its mechanism

In order to tackle the issue of terramycin mycelial dreg (TMD) diagnosis and removal of terramycin and antibiotic resistance genes (ARGs), this study adopted aerobic composting (AC) technology and added homemade compound microbial inoculum (HCMI) to promote the AC of TMD and enhance the removal of terramycin and ARGs. The findings demonstrated that terramycin residue could be basically harmless after AC. Moreover, HCMI not only reduced QacB and tetH but also increased the degradation rates of VanRA, VanT, and dfrA24 by 40.81%, 5.65%, and 54.18%, respectively. The HCMI improved the removal rate of ARG subtypes to a certain extent. According to redundancy analysis, during AC, the succession of the microbial community had a stronger influence on the variance of ARG subtype than the environmental conditions. Differences in the abundance of various bacteria due to changes in temperature may be an intrinsic mechanism for the variation of ARG subtypes.

Highly Fluorescent Collagen-Based Quantum Dots as an Efficient Interlinkage in the 2D Perovskite Bulk for Improved Solar Cells

A design-inexpensive, effective, and easy-to-prepare additive in the large-scale preparation of perovskite solar cells (PSCs) is urgently desired to alleviate the future energy crisis. Carbon-based quantum dots have demonstrated novel nanomaterials with excellent chemical stability and high electrical conductivity, which exhibit great potential as additives for perovskite optoelectronics. Herein, we designed novel highly fluorescent collagen-based quantum dots (Col-QDs) and thoroughly studied the micromorphological characteristics, photoluminescence properties, and the states of surface-functionalized groups on the Col-QDs. It is found that the introduction of Col-QDs in the two-dimensional (2D) perovskite precursor can be further confirmed as an efficient interlinkage via Col-Pb bands in the pure 2D perovskite heterojunction, which significantly improves the crystallinity, orientation, and interlayer coupling of perovskite crystal plates, as observed by grazing incidence X-ray diffraction (GIWAXS) and X-ray photoelectron spectroscopy (XPS). Finally, the champion Col-QD additive can efficiently modulate the photovoltaic performance of pure 2D PSCs with a significant increase of photoelectric conversion efficiency (PCE) from 8.18% up to 10.45%, which ranks among the best efficiencies of highly pure 2D PSCs. These results provide a facile and feasible approach to modulate the interlayer interaction of pure 2D perovskites and further improve their output of PSCs, which would further facilitate the burgeoning applications of the Col-QDs in various perovskite-based optical-related fields.

Use of bag-filter gas dust in anaerobic digestion of cattle manure for boosting the methane yield and digestate utilization

Plenty of refractory and environmentally hazardous bag-filter gas dust (BGD) is produced in the iron-making process. The effects of untreated BGD on anaerobic digestion (AD) with cattle manure were investigated. The BGD had the potential to boost the methane yield and digestate utilization considerably. The digester with 2.0 wt% BGD gained the highest methane yield (256.3 mL/g VS) and chemical oxygen demand removal rate (56.8%), 51.3% and 20.1% higher than that (169.4 mL/g VS, 47.3%) of the control group, respectively. The digestates with BGD possessed a utilization potential with the stability of 49.5-57.9% and fertility of 4.65-4.86%. Electrochemical measurements demonstrated that 2.0 wt% BGD improved the electron transport capacity of the AD system and increased the limiting current and redox peak current by 40.3% and 12.9%, respectively. A strategy for understanding the BGD reinforcing methanogenesis was proposed. This work also provides a technical support for recycling the BGD.

Biomethanation of syngas at high CO concentration in a continuous mode

Syngas from pyrolysis/gasification process is a mixture of CO, CO₂ and H₂, which could be converted to CH₄, so called syngas biomethanation. Its development is obstructed due to the low productivity and CO inhibition. The aim of this study was to demonstrate the feasibility of using syngas as the only carbon source containing high CO concentration (40%) for biomethanation. Lab-scale thermophilic bioreactor inoculated with anaerobic sludge was operated continuously for over 900 h and the shift of microbial structure were investigated. Results showed that thermophilic condition was suitable for syngas biomethanation and the microbes could adapt to high CO concentration. Higher processing capacity of 12.6 m³/m³/d was found and volumetric methane yield of 2.97 m³/m³/d was observed. These findings could strengthen the theoretical basis of syngas biomethanation and support its industrialization in the future.

Bio-based carbon materials with multiple functional groups and graphene structure to boost methane production from ethanol anaerobic digestion

This study evaluated the effects of bio-based carbon materials on methane production by anaerobic digestion. The results showed that biochar and hydrochar can promote cumulative methane yield by 15% to 29%. However, there was no statistical significance (p > 0.05) between hydrochar and biochar produced at different temperature on methane production. 16S rRNA gene sequencing and bioinformatics analysis showed that biochar and hydrochar enriched microorganism that might participate in direct interspecies electron transfer (DIET) such as Pseudomonadaceae, Bacillaceae, and Clostridiaceae. The the surface properties of the modified biochar were characterized with BET, Raman, FTIR and XPS. Bio-based carbon materials with uniform dispersion provided a stable environment for the DIET of microorganisms and electrons are transferred through aromatic functional groups on the surface of materials. This study reveals bio-based carbon materials surface properties on methane production in anaerobic digestion and provides a new approach to recycling spent coffee grounds.

Nitrogen-Doped Carbon Dot and CdTe Quantum Dot Dual-Color Multifunctional Fluorescent Sensing Platform: Sensing Behavior and Glucose and pH Detection

A novel fluorescent probe based on a nitrogen-doped carbon dot (N-CD) and CdTe quantum dot (CdTe QD) platform has been constructed for H₂O₂/glucose detection and pH sensing. In this work, H₂O₂-tolerant blue fluorescence N-CDs were added to the H₂O₂-mediated yellow fluorescence quenching of CdTe QDs to construct a dual-color ratiometric fluorescent H₂O₂ probe. H₂O₂-induced passivated group detachment and action on deep nanocrystals promoted CdTe QD fluorescence quenching. Meanwhile, the addition of the blue fluorescent background of N-CDs sharply reflected the color change in CdTe QDs. Under the optimized experimental conditions, the platform was effectively applied to the detection of H₂O₂ produced by the enzymatic reaction of glucose, showing high sensitivity (limit of detection 7.86 μM) and wide linear range (26-900 μM) for glucose detection. The pH-sensing behavior of CdTe QDs and N-CDs was attributed to the displacement of a weak acid (3-mercaptopropionic acid) by a strong acid (HCl) and the acid titration process of two coexisting bases (N-CDs and NH₃·H₂O), respectively. The loss of passivation and doping effects led to a decrease in the fluorescence intensity of CdTe QDs and N-CDs. Moreover, utilizing the ability of bimaterial system fluorescence to pH sensing, a semiquantitative pH detection based on the linear response was developed. The pH range was analyzed by three kinds of N-CD (F_ex = 440 nm) and CdTe QD (F_ex = 548 nm) typical emission spectral shapes. In addition, the recovery results showed that the bimaterial system was proved to be appropriate for the assay of glucose in spiked serum samples.

Timing of biochar dosage for anaerobic digestion treating municipal leachate: Altered conversion pathways of volatile fatty acids

In this study, the anaerobic digestion (AD) applications of early & late biochar dosage were compared for municipal leachate treatment, with the objective of studying the flexible use of biochar as a mitigation measure for biomethane recovery. In two experimental phases, biochar was favourable for the immediate promotion of AD performances, as revealed by Gompertz's model of reduced lag phases, higher biomethane generation rates, and increased biomethane yields. Irrespective of late biochar dosage, it could still retrieve 89% of the ultimate biomethane potential. Comparing the residual VFAs (volatile fatty acids) compositions, it was found that the fraction of long-chain VFAs accounted for 81% of total VFAs in reactor set of early biochar dosage, while it was only 38% in the reactor of late one. Parallel evidence suggested that the schedule of biochar dosage not only could affect methanogenic responses but also the VFAs conversion pathways.