CH4 Yield Research Articles

Well-Designed morphology regulated ZIF-67 derived 0D/1D Co3O4@TiO2 NWs integrated with in-situ grown Ni/Co-Active metals for Low-Temperature driven CO2 methanation

Well-designed morphology regulated MOF-templated Co3O4 over titanium dioxide nanowires (TiO2 NWs) boasting intimate interfacial contact for highly efficient CO2 methanation was synthesized via a facile in-situ grown approach. The synergistic effect of 0D Co3O4 with reducible 1D TiO2 NWs and the role of Ni/Co-active metals were systematically investigated for CO2 methanation. The performance comparison of the Ni dispersed in-situ grown Co3O4 on TiO2 NWs (Insitu-10N7CT) and its mechanically assembled counterpart (M−10N7CT) was further explored. The in-situ grown ZIF-67 acts as a sacrificial template to produce Co3O4 with high dispersion of Ni active sites to enhance CH4 production. By regulating the morphology, 0D Co3O4 promoted a superior methanation performance for Insitu-10N7CT (XCO2 = 97.42 %, SCH4 = 99.29 %) compared to M−10N7CT (XCO2 = 91.45 %, SCH4 = 98.42) due to intimate interfacial contact between the Ni, Co, and Ti species. Comparatively, the MOF-derived composites displayed much higher CH4 yield than uncalcined MOF nanocomposites. This is because the high reaction temperature caused a rapid collapse of the ZIF-67 dodecahedral structure, leading to a lower methanation performance. Insitu-10N7CT exhibited higher reducibility, generating low valence oxidation/metallic states of Ni-Co-Ti, leading to the high density of oxygen vacancies (Ov). An optimal reaction temperature of 350 °C and gas hourly space velocity of 9,400 mL gcat-1h−1 was revealed, suggesting an efficient reactant contact and CO2 conversion into CH4. The Insitu-10N7CT composite exhibited durability up to 100-hour time-on-stream due to the gradual reduction of Co3O4. Thus, the novel MOF-templated ternary nanocomposite revealed a facile method for regulating the structure of MOF derivatives while boosting strong interfacial interactions for efficient renewable fuel production.

Enhanced anaerobic co-digestion under a magnetic field by a synergistic host–guest strategy: Focusing on accelerant, biogas yield, fertilization and coupled effect

Carbon materials are widely used for direct interspecies electron transfer (DIET) to promote CH4 yield in anaerobic digestion (AD). However, the addition of host–guest assembly carbon accelerant has not been reported. This work explores the facilitation of carbon quantum dots (CQDs) immobilized in porous carbon (PC) as a host–guest accelerant in anaerobic co-digestion (AcoD) under a magnetic field. The addition of CQDs and PC increased the biogas yield and TCOD removal efficiency by 30.1–38.6 % and 14.2–24.2 %, respectively, compared with control group (467.8 mL/g VS; 37.7 %). Fertilization efficiency of the optimal CQDs/PC group was 4.9 % and the excellent electronic exchange capability of CQDs (1.04 μmol e-/g) and PC (0.64 μmol e-/g) facilitated DIET. This approach helped in enriching anaerobic microorganisms and strengthened the thermal stability of the digestates. These findings provide new insights for improving AD performance using CQDs coupled PC.

Production of renewable fuels by the photocatalytic reduction of CO2 using magnesium doped natural ilmenite

The photo-reductive performance of natural ilmenite was boosted and the production of renewable fuels from the reduction of CO2 was enhanced by doping the natural mineral with magnesium. The doping was achieved by high energy ball milling in the presence of MgO and Mg(NO3)2. The photo-reduction of CO2 in aqueous solution led to the evolution of H2, CH4, C2H4, and C2H6, and the insertion of Mg in the structure of ilmenite enabled increases of up to 1245% in the fuel production yield, reaching total production of 210.9 µmol h−1 gcat−1. Displacements of the conduction band to more negative potentials were evidenced for the samples doped with magnesium. Indirect effects such as increases in the valence band maximum, and the introduction of intermediate energy levels were also evidenced through the measurement of the crystallite size and the determination of the band structure of the materials. Mott-Schottky analyses of the samples showed the n-type nature of the semiconductor materials and enabled the estimation of the density of charge carriers, which strongly influenced the photocatalytic performance. The strong potential of the application of natural ilmenite in gas phase artificial photosynthesis was proved by the evaluation of CO2 reduction in gas conditions, which allowed the enhancement in the selectivity and significantly increased the production of CH4 as compared to aqueous solution, reaching an important yield of CH4 of 16.1 µmol h−1 gcat−1.

A directional built-in electric field assisted 2D/1D g-C3N4/CeO2 S-scheme heterojunction for efficient RhB degradation and highly-selective CO2 photoreduction

This study synthesized a well-designed 2D/1D g-C3N4/CeO2 visible-light-driven photocatalyst through a straightforward approach. The binary photocatalyst emerged remarkable photo-degradation performance with a removal rate of 99.07% towards RhB in 120min and the k value of 0.0361 min−1, which maintained over 95% in four cycles. Fascinatingly more, highly-active converting CO2 to CH4 instead of CO during CO2 photo-reduction. The yield rate of CH4 reached 14.63 µmol·g−1·h−1, which was 26.13 folds than the CO generation rate (0.56 µmol·g−1·h−1). Moreover, the CH4 yield rate of g-C3N4/CeO2 heterojunction was 22.4 and 20.9 times improvement in comparison with pristine CeO2 nanorods and CN nanosheets, respectively. On account of HPLC-MS, ESR, active species scavenger investigation, and accurate energy-band structure analysis, a possible RhB degradation mechanism over 2D/1D g-C3N4/CeO2 heterojunction was elucidated. Meanwhile, an S-scheme mechanism with a built-in electric field was illuminated, which helped understand the preeminent photocatalytic performance. This research offers systematic insights into the preparation, activity, and mechanism of g-C3N4-based photocatalysts for environmental purification projects.

Preloaded oxygen vacancy conditioning Ni/TiO2 to enhance photocatalytic CO2 reduction

The regulation of oxygen vacancy (OV) defects plays a critical role in facilitating photocatalytic reactions. In this study, Nix/TiO2-OV photocatalytic materials with ultra-high oxygen vacancy concentrations (>33%) were prepared by preloading oxygen vacancies on Ni/TiO2 system. The experimental results show that the catalytic performance initially rises and subsequently declines with an increase in oxygen vacancy concentration. Among the samples, the best one (8Ni/TiO2-OV2) exhibits a noteworthy photocatalytic yield of CO (22.654 μmol·g−1·h−1) and CH4 (3.93 μmol·g−1·h−1). Density functional theory (DFT) shows that the excellent catalytic performance of 8Ni/TiO2-OV2 is due to that oxygen vacancy is in favour of the narrowing of the band gap, thereby promoting the excitation and efficient transfer of electrons. This study presents a promising novel method for obtaining ultra-high concentration of oxygen vacancies and explores the relationship between oxygen vacancy concentration and catalytic performance.

N-doped carbon quantum dots enhance anaerobic digestion under light condition: The performances and potential mechanisms

The treatment of organic waste (OW) by anaerobic digestion (AD) conforms to the concept of sustainable development. But AD is facing the issue of low conversion rate. In this work, the photo-AD system using visible light (LED lamp) as the source was constructed and the performances and mechanism of N-doped carbon quantum dots (NCQD) were explored in the system for the first time. The results showed that 0.5 g/L NCQD promoted a 23.1 % increase in cumulative CH4 yield in the photo-AD system. Microbial analysis results showed that in photo-AD with NCQD, the dominant strain was Methanosarciniales, with an abundance of 69.0 %. Microbial activity and structural integrity tests showed that the microorganisms were not damaged by free radicals. In addition, NCQD increased the redox peak intensity of the CV curve and increased photocurrent intensity of photo-AD. Furthermore, it promoted an increase of 18.2 % (0.26 ± 0.03 μmol/mL) in ATP concentration. The photoelectrochemical analysis and quantitative analysis of functional genes results indicated that NCQD mainly promoted methanogenesis by providing photoelectrons. This promotion mechanism increased the copynumber (61,652.8 g−1) of EchA in photo-AD, rather than Vht and Hdr related to cytochrome. This work provided new strategies for the enhancement of AD and clarified potential mechanisms.

Enhanced photocatalytic reduction of CO2 using a novel 2D/0D SnS2/CeO2 binary photocatalyst with Z-scheme heterojunction and oxygen vacancy

In this work, suitable band gap width, strong photo-response to visible light, and a high photogenerated carrier density offered by an important member of layered sulfides, SnS2, were kept in view for designing and producing a highly effective photocatalyst for CO2 reduction. Hence, SnS2/CeO2 heterojunction composite photocatalysts were triumphally fabricated by a facile in situ hydrothermal synthesis method, combining advantages of the built-in electric field and oxygen vacancies of two materials. Various characterization techniques were exploited to scrutinize the photocatalyst’s structure and confirm that the carrier transport efficiency and photocatalytic performance are enhanced by the synergistic impact of the heterojunction structure and presence of oxygen vacancies. Owing to the successful loading of zero-dimensional CeO2 nanoparticles onto two-dimensional SnS2 nanosheets, the 2D/0D structure improves the photo-response range of the composites and provides faster electron transfer rates. The composite material maintained the hydrophobic characteristic of single SnS2, while inhibiting the hydrophilic property of single CeO2. As a result, CO and CH4 yields of prepared binary Z-type heterojunction photocatalysts are 24.6 and 4.4 folds higher than those of single SnS2, respectively. This innovative study will contribute to exploration of SnS2-based photocatalytic materials and provide a new feasible direction for light energy-driven CO2 reduction.

Methanation of CO2 on Cu in a tubular co-ionic SOEC

This work aims contributing to develop a cathode for CO2 methanation in tubular co-ionic (H+/O2− conducting) SOECs and to cell operation optimization to decrease energy input and costs for advancing process application. It studies the effect of temperature (325-550 °C) and potential (from −2 to +2 V at 450 °C) on CO2 conversion and selectivity to CH4 and CO, at bench scale, at atmospheric pressure and using high flowrates (42 NL/h) and realistic compositions (4H2/CO2 binary mix), over a Cu film (<2 μm) coated by electroless on an anode (Ni-BZCY)-supported solid electrolyte (BZCY) candle. CH4 preferentially forms over CO. CH4 selectivity increases with temperature up to 97.3% at 400 °C, from which, CH4 and CO selectivity decreases and increases, respectively. The optimum potential is −0.5V, as maximizes CH4 selectivity (94.2%) and minimizes energy cost (0.002 kWh/kg CH4) with high CO2 conversion (32.5%) and low CO selectivity (5.8%), resulting in higher CH4 yield and lower CH4 purification cost.

Optimising organic composition of feedstock to improve microbial dynamics and symbiosis to advance solid-state anaerobic co-digestion of sewage sludge and organic waste

This study provided new insight to the underlying mechanisms, by which organic compositions, including protein, fat, degradable carbohydrates and lignocellulose, regulate the performance of solid-state anaerobic digestion (SSAD) for synergistic treatment of organic wastes. Results show that the feedstock with a balanced composition of protein, fat, degradable carbohydrates and lignocellulose could maintain SSAD homeostasis to enhance methane (CH4) production by 14–487%. On the other hand, organic waste with a high content of degradable carbohydrates and fat at 39 and 14%, respectively, showed an initially high CH4 production at the beginning but a lower overall CH4 production. This was because of the accumulation of volatile fatty acids (VFAs) and ammonium nitrogen (NH4+-N) at up to 17.3 and 7227.7 mg·L−1, respectively, leading to anaerobic activity inhibition. Microbial dynamic and modular network analyses indicated that the balanced feedstock secured stepwise biodegradation of different organic substances to reduce the relative abundance of hydrolytic bacteria (e.g. Rikenellaceae_RC9_gut_group and Tepidimicrobium), thus alleviating VFAs and NH4+-N stresses. In particular, fat in the balanced feedstock could not only enrich the phylum Firmicutes for macromolecular biodegradation and genes for VFAs production, but also inhibit relative oxidizers (e.g. Synergistes and Acinetobacter) to facilitate propionate and acetate production to strengthen acetotrophic methanogenesis for effective CH4 yield. Results in this study show that a balanced organic composition could regulate microbial dynamics and symbiosis to advance SSAD homeostasis and methanation in synergistic organic waste treatment.

Effect of a blend of cinnamaldehyde, eugenol, and Capsicum oleoresin on methane emission and lactation performance of Holstein-Friesian dairy cows

This study aimed to investigate the effect of administering a standardized blend of cinnamaldehyde, eugenol, and Capsicum oleoresin (CEC) to lactating dairy cattle for 84 d (i.e., 12 wk) on enteric CH4 emission, feed intake, milk yield and composition, and body weight. The experiment involved 56 Holstein-Friesian dairy cows (145 ± 31.1 d in milk at the start of the trial; mean ± standard deviation) in a randomized complete block design. Cows were blocked in pairs according to parity, lactation stage, and current milk yield, and randomly allocated to 1 of the 2 dietary treatments: a diet including 54.5 mg of CEC/kg of DM or a control diet without CEC. Diets were provided as partial mixed rations in feed bins, which automatically recorded individual feed intake. Additional concentrate was fed in the GreenFeed system that was used to measure emissions of CO2, CH4, and H2. Feeding CEC decreased CH4 yield (g/kg DMI) by on average 3.4% over the complete 12-wk period and by on average 3.9% from 6 wk after the start of supplementation onward. Feeding CEC simultaneously increased feed intake and body weight, and tended to increase milk protein content, whereas no negative responses were observed. These results must be further investigated and confirmed in longer-term in vivo experiments.

Enhanced thermal-assisted photocatalytic CO2 reduction by RGO/H-CN two-dimensional heterojunction

Carbon dioxide (CO2) can be reduced to high-value fuels using the photocatalysis (PC) technique, which holds immense potential for tackling environmental issues and energy crises. The construction of metal-free photocatalyst capable of utilizing infrared light to execute thermal-assisted photocatalysis (TPC) remains a challenge. In this study, reduced graphene oxide (RGO) with full-spectrum absorption was used as a thermal-assisted photocatalyst in CO2 reduction. It exhibited higher CO2 reduction efficiency under the visible and infrared irradiation than the sole visible irradiation. RGO-5 (GO treated at 120 °C for 5 h) presented the highest defect density and C-OH/C-O-C content, leading to the best PC and TPC efficiencies. RGO was further engineered with HCl protonated g-C3N4 (H-CN) to obtain two-dimensional heterojunction RGO/H-CN, which demonstrated the S-scheme charge transfer process. Owing to the synergistic effect of heterojunction and thermal assistance, RGO/H-CN exhibited better CO2 reduction efficiencies in both PC and TPC than RGO. The largest yields of CO and CH4 were achieved in 15% RGO/H-CN. This research provides new insights for applying RGO as thermal-assisted heterojunction photocatalyst for efficient CO2 reduction.

Photocatalytic Oxidative Coupling of Methane over Au1 Ag Single-Atom Alloy Modified ZnO with Oxygen and Water Vapor: Synergy of Gold and Silver.

C-H dissociation and C-C coupling are two key steps in converting CH4 into multi-carbon compounds. Here we report a synergy of Au and Ag to greatly promote C2 H6 formation over Au1 Ag single-atom alloy nanoparticles (Au1 Ag NPs)-modified ZnO catalyst via photocatalytic oxidative coupling of methane (POCM) with O2 and H2 O. Atomically dispersed Au in Au1 Ag NPs effectively promotes the dissociation of O2 and H2 O into *OOH, promoting C-H activation of CH4 on the photogenerated O- to form *CH3 . Electron-deficient Au single atoms, as hopping ladders, also facilitate the migration of electron donor *CH3 from ZnO to Au1 Ag NPs. Finally, *CH3 coupling can readily occur on Ag atoms of Au1 Ag NPs. An excellent C2 H6 yield of 14.0 mmol g-1 h-1 with a selectivity of 79 % and an apparent quantum yield of 14.6 % at 350 nm is obtained via POCM with O2 and H2 O, which is at least two times that of the photocatalytic system. The bimetallic synergistic strategy offers guidance for future catalyst design for POCM with O2 and H2 O.

Photocatalytic Oxidative Coupling of Methane over Au1Ag Single‐Atom Alloy Modified ZnO with Oxygen and Water Vapor: Synergy of Gold and Silver

AbstractC−H dissociation and C−C coupling are two key steps in converting CH4 into multi‐carbon compounds. Here we report a synergy of Au and Ag to greatly promote C2H6 formation over Au1Ag single‐atom alloy nanoparticles (Au1Ag NPs)‐modified ZnO catalyst via photocatalytic oxidative coupling of methane (POCM) with O2 and H2O. Atomically dispersed Au in Au1Ag NPs effectively promotes the dissociation of O2 and H2O into *OOH, promoting C−H activation of CH4 on the photogenerated O− to form *CH3. Electron‐deficient Au single atoms, as hopping ladders, also facilitate the migration of electron donor *CH3 from ZnO to Au1Ag NPs. Finally, *CH3 coupling can readily occur on Ag atoms of Au1Ag NPs. An excellent C2H6 yield of 14.0 mmol g−1 h−1 with a selectivity of 79 % and an apparent quantum yield of 14.6 % at 350 nm is obtained via POCM with O2 and H2O, which is at least two times that of the photocatalytic system. The bimetallic synergistic strategy offers guidance for future catalyst design for POCM with O2 and H2O.

Effects of dietary fat, nitrate, and 3-nitrooxypropanol and their combinations on methane emission, feed intake, and milk production in dairy cows

The objective of the present study was to investigate the effect of individual and combined use of dietary fat, nitrate, and 3-nitrooxypropanol (3-NOP) on dairy cows' enteric methane (CH4) emission and production performance. Twenty-four primiparous and 24 multiparous Danish Holstein cows (111 ± 44.6 d in milk; mean ± standard deviation) were included in an incomplete 8 × 8 Latin square design with six 21-d periods. Dietary treatments were organized in a 2 × 2 × 2 factorial arrangement aiming for 2 levels of FAT (30 or 63 g of crude fat/kg of dry matter [DM]; LF or HF, respectively), 2 levels of NITRATE (0 or 10 g of nitrate/kg of DM; UREA or NIT, respectively), and 2 levels of 3-NOP (0 or 80 mg/kg DM; BLANK or NOP, respectively). Treatments were included in ad libitum-fed partial mixed rations in bins that automatically measured feed intake and eating behavior. Additional concentrate was offered as bait in GreenFeed units used for measurement of gas emission. For total DM intake (DMI), a FAT × NITRATE interaction showed that DMI, across parities and levels of 3-NOP, was unaffected by separate fat supplementation, but reduced by nitrate with 4.6% and synergistically decreased (significant 2-way interaction) with 13.0% when fat and nitrate were combined. Additionally, 3-NOP decreased DMI by 13.4% and the combination of 3-NOP with fat and nitrate decreased DMI in an additive way (no significant 3-way interaction). The decreasing effects on DMI were more pronounced in multiparous cows than in primiparous cows. For treatments with largest reductions in DMI, eating behavior was altered toward more frequent, but smaller meals, a slower eating rate and increased attempts to visit unassigned feed bins. Energy-corrected milk (ECM) yield increased by 6.3% with fat supplementation, whereas ECM yield did not differ among diets including nitrate (FAT × NITRATE interaction). Cows supplemented with 3-NOP had 9.0% lower ECM yield than cows fed no 3-NOP. Based on three 2-way interactions including FAT, NITRATE, and 3-NOP, the combined use of the additives resulted in antagonistic effects on CH4 reduction. A 6% to 7% reduction in CH4 yield (CH4/kg of DMI) could be ascribed to the effect of fat, a 12% to 13% reduction could be ascribed to the effect of nitrate and an 18% to 23% reduction could be ascribed to the effect of 3-NOP. Hence, no combinations of additives resulted in CH4 yield-reductions that were greater than what was obtained by separate supplementation of the most potent additive within the combination. The CH4 yield reduction potential of additives was similar between parities. Increased apparent total-tract digestibility of organic matter (OM) in cows fed combinations including nitrate or 3-NOP was a result of a NITRATE × 3-NOP interaction. Apparent total-tract digestibility of OM was also increased by fat supplementation. These increases reflected observed decreases in DMI. In conclusion, combined use of fat, nitrate, and 3-NOP in all combinations did not result in CH4 reductions that were greater than separate supplementation of the most potent additive within the combination (3-NOP > nitrate > fat). Additionally, separate supplementation of some additives and combined use of all additives reduced DMI.

Influence of pH on the performance of anaerobic piggery wastewater treatment coupled with membrane-based NH3 extraction

The influence of the pH of piggery wastewater (PWW) on both ammonia recovery and anaerobic digestion performance during PWW treatment was evaluated in a continuous stirred tank reactor coupled with a membrane-based extraction module. The anaerobic digester was operated at a hydraulic retention time of 20 days at 37 °C, while the flat sheet PTFE membrane module operated continuously at liquid recirculation rates of 250 mL min−1. The membrane module was able to gradually decrease the total ammoniacal concentration from 1.27 ± 0.01 to 0.62 ± 0.01 g L−1 after 360 days of operation. Membrane-based NH3 extraction induced a CH4 yield increase of 1.3-fold. Moreover, COD and VS removal efficiencies increased up to 1.2-fold and 1.5-fold, respectively, along with the increase in PWW pH from 7.5 to 12. Total VFAs removal efficiencies were higher at a PWW pH of 9.

Self‐sacrificial Templated Synthesis of Fe/N Co‐doping TiO2 for Enhanced CO2 Photocatalytic Reduction

AbstractAs a green photocatalyst, TiO2 has been widely used in adsorption, desorption and redox reactions, but the wide energy band and moderate visible light absorption have greatly inhibited its applications in photocatalysis. The effective method of enhancing the performance of catalysts is the development of heterojunction and metal‐nonmetal co‐doping. Herein, Fe−N co‐doped TiO2 heterojunction photocatalysts (FexTi@C) were successfully synthesized by calcining a self‐sacrificial template (NH2−MIL‐125(Ti)) injected with Fe3+ solution. X‐ray diffraction (XRD), transmission electron microscopy (TEM), X‐ray photoelectron spectroscopy (XPS), N2 adsorption/desorption analysis, and photoelectrochemical tests were used to characterize FexTi@C, showing multiple rutile/anatase TiO2 heterojunction structure, low bandgap, and significant absorption in visible light. In addition, the Ti−O−Fe tetrahedra and more oxygen vacancies were provided since the doped N is from the pristine MOF and the radii of Fe3+ and Ti4+ are similar, which improved the photocatalytic efficiency of CO2 reduction to CH4, especially the Fe0.8Ti@C reached 7.8‐fold and 10.2‐fold CH4 yield increase compared with the original TiMOF template and the undoped Ti@C, respectively. This work presents a simple method for the fabrication of low bandgap semiconductors, and also makes a new attempt at the synergistic effect between the in‐situ elements and valence bonds of MOF‐derived catalysts.

Carbon nanotubes @Cu/Ni loaded BFO for photothermal catalytic conversion of CO2 by H2O

Bismuth ferrite (FeBiO3, BFO) has excellent photocatalytic activity and a reasonable bandgap width (approximately 2.1 eV), making it a promising material for CO2 catalytic reduction research. In order to enhance the CO2 catalytic reduction performance of BFO, Cu/Ni (molar ratio = 6:5) metal particles were supported on carbon nanotubes (CNTs) at a fixed mass ratio of 38.6% in this study, and it was discovered that adding polyvinylpyrrolidone (PVP) might improve metal particle dispersion. Following that, CNTs @Cu/Ni were supported on hydrothermally produced BFO at mass ratios of 1%, 3%, 5%, and 7% to produce BFO-CNTs @Cu/Ni ternary composites. We investigated its CO2 catalytic reduction capability under photothermal and mild settings and discovered that BFO-3% CNTs @Cu/Ni had the greatest CO2 catalytic conversion efficiency (CH4 yield = 24.2 mol g−1 h−1). This is due to the fact that BFO-CNTs @Cu/Ni have superior light absorption and carrier separation efficiency than pure BFO.

New insight into effects of waste scrap iron on sludge anaerobic digestion: Performances, microbial community, and potential metabolic functions

The low sludge degradation efficiency and hydrogen sulfide (H2S) generation impair the development of sludge anaerobic digestion. This study explored the effects of waste scrap iron (WSI) addition on methane (CH4) production and H2S control in sludge anaerobic digestion. The maximum cumulative CH4 yield of 205.02 mL/g VSS was obtained at the WSI dosage of 0.7 g/g VSS, which increased by 21.34 % compared to that of control without WSI addition. The increase in CH4 yield was attributed to the enhancement of sludge degradation and soluble organic conversion. Meanwhile, the cumulative H2S yield reduced by 62.00 % compared to that of control. The pH value and content of insoluble sulfide precipitate increased with the increase in WSI dosage, which were two main reasons for H2S control. Microbial community results indicated that relative abundance of unclassified_f_Clostridiaceae_1, Bacteroides, vadinBC27_wastewater-sludge_group, Clostridium_sensu-stricto-1, Macellibacteroides, and hydrogenotrophic methanogens increased with WSI addition, meaning that WSI addition promoted syntrophic interaction between key bacteria and hydrogenotrophic methanogens. Gene prediction analysis demonstrated that WSI addition promoted microbial proliferation and respiration, carbohydrate and amino acid metabolism, and activity of butyrate kinase, acetate kinase, pyruvate ferredoxin oxidoreductase, and coenzyme F420 hydrogenase. In view of the enhancement of ABC transporters, lipopolysaccharide biosynthesis, quorum sensing, two-component systems, and ribosome metabolic pathway, it could be considered that WSI addition promoted information recognition and substance exchange among microorganisms, increasing microbial metabolic activity of anaerobic system.

Measurement of Long-Term CH4 Emissions and Emission Factors from Beef Feedlots in Australia

One of the major challenges for the Australian feedlot and meat sectors is to have accurate and robust long-term greenhouse gas (GHG) emissions data. Long-term measurements of methane (CH4) emissions (2015–2017) were made at two Australian beef feedlots having different climates, cattle types, and management practices. Emissions were measured using the inverse-dispersion model (IDM) micrometeorological technique, using CH4 concentrations measured at the feedlots with a closed-path Fourier transform infrared spectroscopic technique (CP-FTIR). The emissions data were used to evaluate methods used by the Department of Climate Change, Energy, the Environment and Water to estimate CH4 emissions from feedlots in Australian national inventory calculations. Expressed as a CH4 yield (emissions per unit dry matter intake, DMI), the two feedlots had emissions of 13.1 and 18.9 g CH4 kg−1 DMI. The lower-emitting feedlot had emissions that were 30% lower than the national inventory calculations based on feed intakes, while the second feedlot had emissions that were similar to the inventory calculations. The accurate quantification of emissions from feedlots, as demonstrated as part of this study, is important for validating the national accounting methods and therefore the sector’s GHG emissions profile.

Bioenergy recovery and carbon emissions benefits of short-term bio-thermophilic pretreatment on low organic sewage sludge anaerobic digestion: A pilot-scale study

Sewage sludge in cities of Yangzi River Belt, China, generally exhibits a lower organic content and higher silt contentdue to leakage of drainage system, which caused low bioenergy recovery and carbon emission benefits in conventional anaerobic digestion (CAD). Therefore, this paper is on a pilot scale, a bio-thermophilic pretreatment anaerobic digestion (BTPAD) for low organic sludge (volatile solids (VS) of 4%) was operated with a long-term continuous flow of 200 days. The VS degradation rate and CH4 yield of BTPAD increased by 19.93% and 53.33%, respectively, compared to those of CAD. The analysis of organic compositions in sludge revealed that BTPAD mainly improved the hydrolysis of proteins in sludge. Further analysis of microbial community proportions by high-throughput sequencing revealed that the short-term bio-thermophilic pretreatment was enriched in Clostridiales, Coprothermobacter and Gelria, was capable of hydrolyzing acidified proteins, and provided more volatile fatty acid (VFA) for the subsequent reaction. Biome combined with fluorescence quantitative polymerase chain reaction (PCR) analysis showed that the number of bacteria with high methanogenic capacity in BTPAD was much higher than that in CAD during the medium temperature digestion stage, indicating that short-term bio-thermophilic pretreatment could provide better methanogenic conditions for BTPAD. Furthermore, the greenhouse gas emission footprint analysis showed that short-term bio-thermophilic pretreatment could reduce the carbon emission of sludge anaerobic digestion system by 19.18%.