CH4 Concentrations Research Articles

The Used of Variuos Biomass Waste as Raw Material Biogass Production using Cow Dung as Source of Microbe by Continuously-Anaerobic Fermentation on the 15 Liter Reactor

In Indonesia, there were some biomass wastes if there not treatment, will cause quality- environmental decreasing. It is need effort to minimalize negative effect of those biomass wastes by treating to higher value product. The organic materials in the biomass waste could be anaerobically fermentatation degradated to produce biogass. The anaerobic fermentation were depended on the use of raw materials and microorganism. The organic wastes that use as raw material on this research were (1) tapioca industrial wastewater,(2) tofu industrial wastewater, (3) fruits-peel wastes and (4) vegatable wastes. The source of microbe were found from cow dung The reaserch purpose were to know the influence of the kind of raw materials on the biogas production using cow dung as source of microbe. The research were done at Engineering Faculty Laboratry, Malahayati University Bandarlampung on the 15 liter continuously-anaerobic bioreactor with 15 days retention time. The influen were added 2 liter/2days continuously. The tested variable were COD and biogas composition. The research result showed that the COD in the tapioca industrial wastewater were reduced 71.00 – 89.5 %, in the tofu industrial wastewater reduced 70.00 – 75.00 %, in the fruit-peel waste reduced 7.00-86.00 % andin the vegetable waste reduced 65.00 – 67 %. The CH4 concentration in the produced biogas were 57.63 % ; 40,75 %; 41,41 % and 40.64 %. The C/N ratio effluent between 7.94 – 14.08 could be used directly as liquid organic fertilizer The research conclusion were the production biogas using tapioca industrial wastewater showed the best result . That cause tapioca industrial wasterawte contain high carbohydrate concentration. In the anaerobic digestion, the carbohydrate material were degradated to CH4 (methane)

Part-per-Billion (Ppb)-Level Acetylene Sensor Employing Optical Quartz Enhanced Photoacoustic Spectroscopy (QEPAS) with an Erbium-Doped Fiber Amplifier (EDFA) and a Fiber-Optic Fabry–Perot Interferometer

An all-optical double-pass quartz enhanced photoacoustic spectroscopy (QEPAS) sensor for the detection of acetylene (C2H2) at part-per-billion (ppb) levels was developed and experimentally validated. By employing an erbium-doped fiber amplifier (EDFA) capable of emitting up to 1 W of optical power, a commercial quartz tuning fork (QTF) resonating at 30.7 kHz, and double-pass acoustic microresonators, the amplitude of the QEPAS signal was significantly enhanced, thereby improving the sensitivity of the C2H2-QEPAS sensor. Instead of using piezoelectric detection in conventional QEPAS, a highly sensitive fiber-optic Fabry–Perot interferometer (FPI) was employed to measure the vibration of the QTF prong. A working point self-stabilizing technique was exploited to improve the demodulation sensitivity and stability. The linear response of the sensor to laser power and C2H2 concentration confirmed that no saturation occurred. With an excitation laser power of 1 W and a C2H2 absorption line of 1532.83 nm, a C2H2 minimum detection limit (MDL) of 19.1 ppb was achieved, corresponding to a normalized noise equivalent absorption coefficient (NNEA) of 1.58 × 10−8 cm−1∙W∙Hz−1/2. Owing to its high sensitivity, long-term stability, and immunity to electromagnetic interferences, the QEPAS sensor provides considerable potential for remote gas sensing in environmental monitoring and other applications.

Advanced soil-gas geochemical exploration methods for orogenic gold deposits: A case study of Chalapu deposit, Xizang

Orogenic gold deposits play a significant role in the world’s gold reserves, and their distinctive characteristics pose challenges for exploration. The low sulfide content and narrow, fault-controlled sulfide-quartz veins hinder the use of traditional mineral exploration methods to locate deeply buried ore bodies, particularly in regolith-covered areas. Enhanced methods are required to detect deposits at greater depths. Soil gas composition shows promising potential for mineral exploration by conveying information about sulfur-rich and carbon-rich gases related to deep-seated mineralization into surface soils. However, the prospects of this method for gold deposits remain uncertain. In this study, a novel method was introduced to perform an integrated H2S, SO2, CH4, and CO2 soil-gas geochemical survey on gold ore bodies of different scales at the Chalapu deposit in Tibet. The results unveiled notable gas geochemical anomalies of H2S, SO2, CH4, and CO2 above the multi-layered or thick gold ore bodies. For instance, on exploration line 16 at point A1607, H2S reached the regional maximum value of 1.064 ppm, coinciding with the surface exposure of the thickest gold ore body, measuring 19.81 m. While the presence of CH4 and CO2 anomalies alone may not signify potential mineralized zones, the combined presence of anomalous H2S and SO2 values along with CH4 and CO2 concentrations appears to be effective in identifying mineralization. These combinations of geochemical anomalies not only uncover concealed ore bodies, but also delineate the trend and extension direction in strike and dip of ore bodies. Gas intensity may provide insights into the scale of the ore bodies, with stronger gas anomalies observed in areas with thicker ore bodies at similar depths. Thus, the study reveals that soil-gas exploration shows great promise as an exploration technique for orogenic gold deposits, especially in areas with regolith cover hindering traditional methods from detecting mineralized zones for gold exploration.

Riparian vegetation influences aquatic greenhouse gas production in an agricultural landscape

Although riparian vegetation is widely acknowledged for its positive impact on soil and water quality and its role in regulating terrestrial greenhouse gas emissions in agricultural landscapes, there remains a gap in understanding how different types of riparian vegetation affect aquatic greenhouse gas production. Thus, the objective of this study was to investigate whether the type of vegetation within riparian zones influenced aquatic environmental factors, subsequently impacting aquatic greenhouse gas emissions. To address this, we measured greenhouse gases in the aquatic environment bordered by riparian zones with herbaceous vegetation (GRS) compared to undisturbed natural riparian forests dominated by deciduous (UNF-D) or coniferous (UNF-C) vegetation or a rehabilitated riparian forest (RH). Our findings indicate that aquatic CO2 concentrations were not influenced (p < 0.05) by vegetation type ranging from 9 g L−1 to 11 g L−1. In contrast, aquatic CH4 concentrations were significantly lower (p < 0.05) in treed riparian zones, ranging from 14 μg L−1 to 24 μg L−1, compared to a riparian zone with herbaceous vegetation (34 μg L−1). However, we observed significantly higher (p < 0.05) aquatic N2O concentrations in treed riparian zones (9.5 μg L−1 to 10.3 μg L−1), particularly those dominated by coniferous vegetation (23.0 μg L−1), compared to the riparian zone with herbaceous vegetation (7.7 μg L−1). The total CO2-C equivalent (i.e., CO2 + CH4 + N2O) was highest in the riparian zone with coniferous trees (UNF-C: 10,717 mg CO2-Ceq L−1), followed by the GRS (9494 mg CO2-Ceq L−1), RH (9423 mg CO2-Ceq L−1) and UNF-D (9,183 mg CO2-Ceq L−1) riparian zone. Moreover, riparian vegetation was influenced by various environmental factors that likely controlled physicochemical and biological processes related to the production of greenhouse gases within the aquatic environment.

Could exhaled methane be used as a possible indicator for hemodynamic changes in trauma induced hemorrhagic shock? Scientific basis supported by a case study

IntroductionIdentification of severe blood loss and hemorrhagic shock in polytrauma patients poses a key challenge for trauma teams across the world, as there are just a few objective parameters, on which clinicians can rely. We investigated the relationship between exhaled air methane (CH4) concentration and blood loss in a polytrauma patient. Decreased blood flow in the superior mesenteric artery (SMA) is one of the first compensatory responses to blood loss. Gases produced by the anaerobic flora of the intestinal segment supplied by the SMA are the primary source of exhaled CH4, which diffuses through the intestinal microvessels into the circulation and is finally eliminated through the lungs. We hypothesized that diminution of exhaled CH4 indicates blood loss and tested our theory in a severely injured patient. MethodsExhaled CH4 concentrations of a severely injured patient were measured using a photoacoustic spectroscope (PAS) attached to the exhalation side of the breathing circuit. The primary objective was to investigate the relationship between exhaled CH4 and conventional indicators of hemorrhage including hemoglobin (Hb) levels, base deficit (BD) values and vital parameters (heart rate and systolic blood pressure) in the early phase of in-hospital care (first 4 h). ResultsA severely injured patient was admitted with unstable hemodynamic parameters and incomplete left lower limb amputation, (Injury Severity Score: 38, 74/36 mmHg, 76 bpm). At the time of arrival, considerably lower CH4 levels were detected (22,800 PAU) in the exhaled air. During the first 4 h fluid and massive blood resuscitation, the exhaled CH4 levels were continuously rising in parallel with Htc and Hb values. Corresponding to these changes, BD values displayed a decreasing tendency. DiscussionOur study was conducted to characterize the changes in exhaled air CH4 concentration in response to hemorrhagic shock and to provide data on a viable clinical use of an experimental technique. According to our results, the real-time detection of exhaled air CH4 concentration is an applicable and promising technique for the early detection of bleeding and hemorrhagic shock in severely injured patients. Further research on large sample size and refinement of the PAS technique is required.

Long-term performance and activity study of a two-stage anaerobic EGSB reactors system treating complex and toxic industrial wastewater.

Anaerobic treatment of industrial wastewater using upflow anaerobic reactors is an extended trend due to its high efficiency and biogas production potential, but its implementation in some sectors is limited due to the complexity and toxicity of the wastewaters. In this study, a two-stage expanded granular sludge bed (EGSB) reactors system has been investigated at both bench and pilot scale for the treatment of complex and toxic real wastewater from a petrochemical industry. The effect of different operational parameters including organic loading rate (OLR), hydraulic retention time (HRT) and influent characteristics over COD removal and biogas production and composition have been studied. Additionally, biomass specific methanogenic activity (SMA) and wastewater toxicity have been evaluated after long-term operation. Optimum total HRT of 24 h has been determined resulting in total COD and SO4 2- removal of 56.30 ± 5.25% and 31.68 ± 14.71%, respectively, at pilot scale, and average biogas production of 93.47 ± 34.92 NL/day with 67.01 ± 10.23 %CH4 content and 5210.11 ± 6802.27 ppmv of H2S. SMA and toxicity tests have confirmed inhibitory and toxic effects of wastewater over anaerobic biomass with average maximum inhibition of 65.34% in the unacclimated anaerobic inoculum while chronic toxicity produced a decrease of an order of magnitude in SMA after 600 days of operation. This study demonstrates the feasibility of applying an anaerobic treatment to this wastewater using EGSB reactors between a 0.97-1.74 gCOD/L/day OLR range. Nonetheless, periodic reinoculation would be necessary for long-term operation due to chronic toxicity of the wastewater exerted on the anaerobic biomass. PRACTITIONER POINTS: A two-stage EGSB reactors system has been operated at bench and pilot scale to treat complex and toxic petrochemical wastewater. Optimal total HRT of 24 h resulted in average COD removal ranging from 40% to 60%. SMA and toxicity tests have been performed to study long-term acclimation, detecting an activity depletion of an order of magnitude.

Novel Bacterial Consortium for Mitigation of Odor and Enhance Compost Maturation Rate of Municipal Solid Waste: A Step Toward a Greener Economy

Composting is an integral component of sustainable Municipal Solid Waste (MSW) management within the circular bio-economy platform. However, it faces challenges due to malodorous emissions that impact environmental and societal equilibrium. The present study aims to minimize odorous emissions and expedite compost maturation using a novel, efficient microbial consortium. Bacteria sourced from open dump sites in Sri Lanka were carefully screened based on concurrent enzyme production. Five developed consortia were tested for their performance in reducing malodors during the composting process of MSW. Consortium No. 5 (C5), comprised of Bacillus haynesii, Bacillus amyloliquefaciens, and Bacillus safensis, demonstrated outstanding performance with a significant (p &lt; 0.05) reduction in odorous emissions. Additionally, consortium C5 exhibited impressive control over gas emissions, maintaining VOC, CH4, NH3, and H2S concentrations within ranges of 0.5-6 ppm, 0.5-0.8 ppm, 0.3-0.5 ppm, and 0.5-0.6 ppm, respectively, compared to control concentrations of 4.5-10.2 ppm, 0.5-5.5 ppm, 0.3-5.5 ppm, and 0.5-6.4 ppm, respectively. Additionally, comprehensive Electronic nose (E-nose) analysis substantiated C5’s efficiency in attenuating Methane-Aliphatic compounds, Sulfur and Aromatic compounds, along with low-polarity aromatic and alkane compounds, all with statistical significance (p &lt; 0.05). Further, the developed consortium could reduce the composting time from 110 ± 10 days to 17 ± 3 days, offering a sustainable solution for global MSW management.

Impact of lowering nitrogen content in pig manure through low crude protein diets on anaerobic digestion process stability, biogas yields, and digestate composition

Lowering crude protein in pig diets can reduce nitrogen (N) excretion and alter manure characteristics. Anaerobic digestion (AD) offers potential for converting pig manure into biogas and bio-based fertilizers (i.e., digestate). However, limited research exists on the effects of N content in pig manure on AD when pigs are fed diets with varying crude protein levels. This study investigated how lowering N content in pig manure through low crude protein diets may affect AD process stability, biogas generation, and digestate properties. Manures from different dietary treatments, named as control (CON), low N (LN), and very low N (VLN), with Total Kjeldahl Nitrogen concentrations of 5.87, 5.42, and 5.15 g/L, respectively, were investigated. Daily biogas production, composition (CH4, CO2, and H2S), and digestate properties were monitored over 13 fed-batch cycles (25 ± 4 days per cycle). The experiment was conducted at 20 ± 1 °C, a condition suited for milder climate regions, using six single-stage digesters operated in sequencing fed-batch mode. Data were analyzed by ANOVA using PROC MIXED with repeated measures. Results showed that the differences in N content in pig manure due to the three dietary treatments had a limited impact on biogas generation, with specific methane yields remaining similar over time. CH4 concentrations remained stable between 60 and 65 %, ensuring high-quality biogas despite dietary variations. Differences between treatments became more pronounced with increased organic loading rates (OLRs) due to variations in the amount of volatile solids fed. AD also remained stable (Total Volatile Fatty Acids/Total Alkalinity <0.25) even at an OLR of 2.15 g of chemical oxygen demand L−1 day−1, highlighting AD's robustness at lower temperatures. Digestate samples contained essential minerals beneficial for plant growth. More research is needed to explore varied manure compositions and feeding strategies to better understand the interactions of animal nutrition with AD.

Impacts of O2:CH4 ratios and CH4 concentrations on the denitrification and CH4 oxidations of a novel AME-AD system

Aerobic methane (CH4) oxidation coupled to denitrification (AME-D) is a promising process for the denitrification of low C/N wastewater. Compared with anaerobic denitrifying bacteria, aerobic denitrifying bacteria may enable AME-D have high denitrification ability under aerobic conditions. This study constructed a novel aerobic methane oxidation coupled to aerobic denitrification (AME-AD) system using the typical aerobic denitrifying bacteria Paracoccus pantotrophus ATCC35512 and the typical aerobic methane oxidizing bacteria Methylosinus trichosporium OB3b. The denitrification and CH4 oxidations of AME-AD with different O2:CH4 ratios (0:1, 0.25:1, 0.5:1, 0.75:1, 1:1 and 1.25:1) and CH4 concentrations (0, 14000, 28000, 42000, 56000 and 70000 mg m−3) were investigated in batch experiments. Higher O2:CH4 ratios can significantly improve the denitrification and CH4 oxidations of the AME-AD (P < 0.05). The treatment with an O2:CH4 ratio of 1.25:1 had the highest denitrification rate (0.036 mg h−1) and highest CH4 oxidation rate (0.20 mg h−1). The CH4 concentration in the headspace was positively correlated with the AME-AD denitrification rate. The calculated CH4/NO3−(mol/mol) in most treatments ranged from 5.76 to 6.84. In addition, excessively high O2 and CH4 concentrations can lead to increased nitrous oxide (N2O) production in AME-AD. The N2O production rate was up to 1.00 μg h−1 when the O2:CH4 was 1.25:1. These results can provide data support for the application of AME-AD for low-C/N wastewater treatment and greenhouse gas emission reduction.

A numerical comparison of heavy‐purge and dual‐reflux strategies in pressure swing adsorption for methane enrichment

AbstractDual reflux pressure swing adsorption (DR‐PSA) has been regarded as a state‐of‐the‐art adsorption‐based process which can simultaneously obtain two streams of pure product gases with a narrow pressure window. However, the DR‐PSA has not yet been reported in industrial applications. Herein, a DR‐PSA and a heavy‐purge pressure vacuum swing adsorption (HP‐PVSA) were numerically investigated for the enrichment of 1%, 8% and 15% CH4 from N2 gas mixtures in pilot‐scale. Key separation indicators such as purity, recovery and energy cost of the two cycles were compared to analyze the limitations of the DR‐PSA process while scaling‐up. This study reveals the impact of heavy to feed (H/F) ratios on purity and recovery for both cycles and analyses the energy consumption of each process. For feed gas with 15% CH4, while DR‐PSA can achieve a slightly better purity and recovery (88.3% and 88.3%, respectively) compared to HP‐PVSA (87.5% and 80.3%, respectively), it also involves an order of magnitude higher energy consumption (181.6 versus 24.6 kJ/mol CH4 captured). DR‐PSA shows significantly superior performance than HP‐PVSA when the CH4 content in the raw feed gas is low. Under the investigated operating conditions, HP‐PVSA can only enrich 1% CH4 to 10% with 78.7% recovery while DR‐PSA can obtain 75.3% purity and 77.3% recovery. Results indicate that DR‐PSA exhibits superiority in enrichment of dilute gas, however, its high energy consumption, high capital expenditures and limitations in processing high throughput are the chief reasons hindering its industrial application.

Wastewater treatment plant effluents increase the global warming potential in a subtropical urbanized river

Rivers play a pivotal role in global carbon (C) and nitrogen (N) biogeochemical cycles. Urbanized rivers are significant hotspots of greenhouse gases (GHGs, N2O, CO2 and CH4) emissions. This study examined the GHGs distributions in the Guanxun River, an effluents-receiving subtropical urbanized river, as well as the key environmental factors and processes affecting the pattern and emission characteristics of GHGs. Dissolved N2O, CO2, and CH4 concentrations reached 228.0 nmol L–1, 0.44 mmol L–1, and 5.2 μmol L–1 during the wet period, and 929.8 nmol L–1, 0.7 mmol L–1, and 4.6 μmol L–1 during the dry period, respectively. Effluents inputs increased C and N loadings, reduced C/N ratios, and promoted further methanogenesis and N2O production dominated by incomplete denitrification after the outfall. Increased urbanization in the far downstream, high hydraulic residence time, low DO and high organic C environment promoted methanogenesis. The strong CH4 oxidation and methanogenic reactions inhibited by the effluents combined to suppress CH4 emissions in downstream near the outfall, and the process also contributed to CO2 production. The carbon fixation downstream from the outfall were inhibited by effluents. Ultimately, it promoted CO2 emissions downstream from the outfall. The continuous C, N, and chlorine inputs maintained the high saturation and production potential of GHGs, and altered microbial community structure and functional genes abundance. Ultimately, the global warming potential downstream increased by 186 % and 84 % during wet and dry periods on the 20-year scale, and increased by 91 % and 49 % during wet and dry periods on the 100-year scale, respectively, compared with upstream from the outfall. In urbanized rivers with sufficient C and N source supply from WWTP effluents, the large effluent equivalently transformed the natural water within the channel into a subsequent "reactor". Furthermore, the IPCC recommended EF5r values appear to underestimate the N2O emission potential of urbanized rivers with high pollution loading that receiving WWTP effluents. The findings of this study might aid the development of effective strategies for mitigating global climate change.

Methane Storage and Purification of Natural Gas in Metal-Organic Frameworks.

Natural gas, primarily composed of methane (CH4), represent an excellent choice for a potentially sustainable renewable energy transition. However, the process of compressing and liquefying CH4 for transport and storage typically results in significant energy losses. In addition, in order to optimize its efficacy as a fuel, the CH4 content of natural gas needs to be increased to a level of at least 97% to ensure its quality and efficiency in various applications. Metal-organic frameworks (MOFs) represent a novel category of porous materials that possess exceptional capability in modifying pore size and chemical environment, making them ideally suited for the storage of CH4 and the adsorption of propane (C3H8), ethane (C2H6), carbon dioxide (CO2), nitrogen (N2), and hydrogen sulfide (H2S) to facilitate the purification process of CH4 from natural gas. In this paper, we systematically summarize the mechanism by which MOF materials facilitate the storage of CH4 and the purification of CH4 from natural gas, leveraging the structural characteristics inherent to MOF materials. The focus of further research should also be directed towards the investigation of CH4 storage by flexible MOFs, the resolution of the trade-off dilemma, and the commercial application of MOFs.

Temporal characteristics and vertical profiles of atmospheric CH4 at the northern foot of the Qinling Mountains in China

A two-year (March 2021 to February 2023) continuous in-situ atmospheric CH4 measurements and periodic vertical CH4 measurements (<2000 m) in July and November 2021 were conducted at the northern foot of the Qinling Mountains in Xi'an, China, aiming to study the temporal and vertical variations in atmospheric CH4 and the influence of air mass transport. The two-year average CH4 concentration at this site was 2119.6 ± 108.8 ppb. Seasonal CH4 concentrations were the highest in winter (2177.6 ± 121.5 ppb) and lower in summer (2079.1 ± 77.6 ppb) and spring (2073.9 ± 68.4 ppb). Diurnal CH4 peaked at 10:00–11:00. Atmospheric CH4 there was mainly from local source emissions from Xi'an and short distance transport from the southern Qinling Mountains through the valleys. On the July sampling days, vertical CH4 concentrations increased in the morning (08:00) and at mid-night (23:30), while they decreased in the early afternoon (13:00) and late afternoon (18:00) from near the surface (20 m) to 200 m, increased at 200–500 m, and then decreased at 500–1000 m. During the heating period in November, vertical CH4 concentrations increased by 20.0–86.8 ppb at 20–200 m due to horizontal transport and poor atmospheric dispersion conditions, and then decreased up to 2000 m, with the fastest decrease rate (−44.4 ± 51.4 ∼ −17.6 ± 19.3 ppb/100 m) at 500–1000 m. Vertical CH4 concentrations increased at all heights especially below 500 m in serve haze, mainly attributed to horizontal transport from the northwestern and southeastern polluted regions. Vertical observations further confirmed the important influence of transport on CH4 levels at this site.

Experimental study on the desorption behavior of high-volatile bituminous coals following CO2 and CH4 injection at various compositional ratios

CO2-ECBM (Enhanced Coalbed Methane recovery) offers the dual benefits of increasing methane production and reducing carbon emissions through sequestration. Previous studies have primarily focused on the competitive adsorption effects of different gas compositions during the CO2-ECBM. However, the dynamic changes in desorption volume, desorption strain, and gas composition for different compositional ratios of CO2/CH4 after injecting CO2 remain unclear. Therefore, high-volatile bituminous coals from the southern margin of the Junggar Basin are chosen for desorption experiments with five different compositional ratios of CO2/CH4. Desorption volume, desorption strain, and gas composition of the coal samples are monitored during the desorption process. Finally, the mechanism influencing the dynamic changes in gas composition during desorption is analyzed. The results indicate that as CO2 concentration increases, both desorption volume and desorption strain correspondingly increase. At the same desorption volume, a higher CO2 concentration results in greater desorption strain. For different compositional ratios of CO2/CH4, CH4 concentration gradually decreases while CO2 concentration gradually increases over desorption time. The concentration of the desorption gas is influenced by the initial CO2 concentration and the pore structure. Specifically, higher initial CO2 concentrations, better pore opening, and more developed mesopores and macropores lead to greater changes in composition concentrations during desorption. Different concentrations of CO2 all promote CH4 production, with higher CO2 concentrations enhancing CH4 production efficiency more significantly, especially for samples that are more difficult to produce. The research findings can provide guidance for the efficient production of CBM after CO2 injection.

The Sulfur Conversion Functional Microbial Communities in Biogas Liquid Can Participate in Coal Degradation.

The addition of biogas liquid is a practical way to improve the yield of biological coalbed methane. The microbial composition in biogas liquid is complex, and whether it could participate in the sulfur conversion of coal remains unknown. In this study, sulfur conversion-related microbial communities were enriched from biogas liquid, which was dominated by genera Anaerosolibacter, Bacillus, Hydrogenispora, and Oxobacter. The co-culture of these groups with coal significantly changed the coal microbial community composition but did not increase the content of CH4 and H2S. The changed microbial communities mainly belonged to phyla Firmicutes, Proteobacteria, and Actinobacteriota, and increased the relative abundance of genera Bacillus, Thermicanus, Hydrogenispora, Oxobacter, Lutispora, Anaerovorax, Desulfurispora, Ruminiclostridium, and Fonticella. From the microscopic structure of coal, an increase in the number of holes and roughness on the surface of the coal was found but the change of surface functional groups was weak. In addition, the addition of S-related microbial communities increased the contents of phoxim, methylthiobenzoylglycine and glibornuride M5 in aromatic compounds, as well as the content of lauryl hydrogen sulfate in alkyl compounds. Furthermore, the dibenzothiophene degradation-related microbial communities included Bacillus, Brevibacillus, Brevundimonas, Burkholderia-Caballeronia-Paraburkholderia, and Thermicanus, which can break C-S bonds or disrupt benzene rings to degrade dibenzothiophene. In conclusion, the S-related microbial communities in biogas liquid could rebuild the coal microbial community and be involved in the conversion process of organic sulfur in coal.

Cellulosic ethanol stillage for methane production by integrating single-chamber anaerobic digestion and microbial electrolysis cell system

Anaerobic digestion provides a solution to the inefficient use of carbon resources caused by improper disposal of corn stover-based ethanol stillage (CES). In this regard, we developed a single-chamber anaerobic digestion integrated microbial electrolysis cells system (AD-MEC) to convert CES into biogas while simultaneously upgrading biogas in-situ by employing voltages ranging from 0 to 2.5 V. Our results demonstrated that applying 1.0 V increased the CH4 yield by 55 % and upgraded the CH4 content in-situ to 82 %. This voltage also promoted the well-formed biofilm on the electrodes, resulting in a 20-fold increase in current. However, inhibition was observed at high voltages (1.5–2.5 V), suppressing syntrophic organic acid-oxidizing bacteria (SOB). The dissociation between SOB and methanogens led to accumulation of propionic and butyric acid, which, in turn, inhibited methanogens. The degradation of CES was accelerated by unclassified_o_norank_c_Desulfuromonadia on the anode, likely leading to an increase in mixotrophic methanogenesis due to the synergistic interaction among Aminobacterium, Sedimentibacter, and Methanosarcina. Furthermore, the enrichment of electroactive bacteria (EB) such as Enterococcus and Desulfomicrobium likely facilitates direct interspecies electron transfer to Methanobacterium, thereby promoting the conversion of CO2 to CH4 through hydrogenotrophic methanogenesis. Rather than initially stimulating the EB in the bulk solution to accelerate the start-up process of AD, our study revealed that applying mild voltage up to 1.0 V tended to mitigate the negative impact on the original microorganisms, as it gradually enriched EB on the electrode, thereby enhancing biogas production.

Distribution of methane in the upper water layer of the northern Black Sea: Seasonal and daily trends and seawater-air emissions

We report on methane (CH4) concentration measurements in the northern Black Sea area conducted during 6 cruises with R/V Professor Vodyanitsky from 2017 to 2019. Our work is a multi-season study at a uniform station grid covering an area of 88 × 103 km2 and including three latitudinal transects that comprises both surface and vertical profile water-column measurements. The main goal of the work was to assess the seasonal patterns of vertical CH4 structure in the aerobic water column (upper 100 m) and its emission to the atmosphere.In surface waters, the mean dissolved CH4 concentration ranged from 2.6 nmol L−1 detected in November 2018 to 11.5 nmol L−1 measured in June–July 2018, respectively. Calculated CH4 seawater-air fluxes and saturations were mostly positive (i.e. net flux to atmosphere), and winter fluxes (2.6 μmol m−2 d−1) were higher than summer fluxes (1.6 μmol m−2 d−1) due to the higher wind speed. The integral CH4 flux from the whole study area (88 × 103 km2) ranged from 84 to 235 kM day−1.It was shown that, on average, the methane concentration in the upper layer for deep-water stations where the seabed is located at depths >160 m (σt >16.2) was lower compared to stations at shallow water depths (28–140 m, σt <16.2). The most distinct difference was obtained for the summer season (June–July 2018) and a less significant difference – for spring (April–May 2019) and winter season (November–December 2018). During these seasons the water column was also considerably less saturated in CH4 compared to the entire monitoring period. We observed subsurface maxima, which were generally located at the base of the thermocline and exceeded 100 nmol L−1 at some stations. Exceptions were observed in October 2019 (cruise 110), when vertical CH4 distributions were characterized by two-peaks at ∼20 and ∼50 m depth. The strong influence of the thermohaline structure on the water column CH4 distribution has also been shown in studies of daily dynamics of CH4 vertical profiles in the shallow water region. Despite the high variability of CH4 concentrations, significant similarities in vertical distributions of CH4 and chlorophyll-a for which sub-surface maxima coincided at some stations, are shown. Extremely high concentrations of CH4 (up to 351 nmol L−1) in the near-bottom water layer were revealed during all seasons at the station near the Dnieper paleo-channel at the northwestern edge of the study area. This enrichment is assumed to be caused by methane emissions from gas seeps densely located in this region.

Multiple-model based simulation of urban atmospheric methane concentration and the attributions to its seasonal variations: A case study in Hangzhou megacity, China

Cities are treated as global methane (CH4) emission hotspots and the monitoring of atmospheric CH4 concentration in cities is necessary to evaluate anthropogenic CH4 emissions. However, the continuous and in-situ observation sites within cities are still sparsely distributed in the largest CH4 emitter as of China, and although obvious seasonal variations of atmospheric CH4 concentrations have been observed in cities worldwide, questions regarding the drivers for their temporal variations still have not been well addressed. Therefore, to quantify the contributions to seasonal variations of atmospheric CH4 concentrations, year-round CH4 concentration observations from 1st December 2020 to 30th November 2021 were conducted in Hangzhou megacity, China, and three models were chosen to simulate urban atmospheric CH4 concentration and partition its drivers including machine learning based Random Forest (RF) model, atmospheric transport processes based numerical model (WRF-STILT), and regression analysis based Multiple Linear Regression (MLR) model. The findings are as follows: (1) the atmospheric CH4 concentration showed obvious seasonal variations and were different with previous observations in other cities, the seasonality were 5.8 ppb, 21.1 ppb, and 50.1 ppb between spring-winter, summer-winter and autumn-winter, respectively, where the CH4 background contributed by −8.1 ppb, −44.6 ppb, and −1.0 ppb, respectively, and the CH4 enhancements contributed by 13.9 ppb, 65.7 ppb, and 51.1 ppb. (2) The RF model showed the highest accuracy in simulating CH4 concentrations, followed by MLR model and WRF-STILT model. (3) We further partition contributions from different factors, results showed the largest contribution was from temperature-induced increase in microbial process based CH4 emissions including waste treatment and wetland, which ranged from 38.1 to 76.3 ppb when comparing different seasons with winter. The second largest contribution was from seasonal boundary layer height (BLH) variations, which ranged from −13.4 to −6.3 ppb. And the temperature induced seasonal CH4 emission and enhancement variations were overwhelming BLH changes and other meteorological parameters.

Cyanobacteria decay alters CH4 and CO2 produced hotspots along vertical sediment profiles in eutrophic lakes

Cyanobacteria-derived organic carbon has been reported to intensify greenhouse gas emissions from lacustrine sediments. However, the specific processes of CH4 and CO2 production and release from sediments into the atmosphere remain unclear, especially in eutrophic lakes. To investigate the influence of severe cyanobacteria accumulation on the production and migration of sedimentary CH4 and CO2, this study examined the different trophic level lakes along the middle and lower reaches of the Yangtze River. The results demonstrated that eutrophication amplified CH4 and CO2 emissions, notably in Lake Taihu, where fluxes peaked at 929.9 and 7222.5 μmol/m2·h, mirroring dissolved gas levels in overlying waters. Increased sedimentary organic carbon raised dissolved CH4 and CO2 concentrations in pore-water, with isotopic tracking showing cyanobacteria-derived carbon specifically elevated CH4 and CO2 in surface sediment pore-water more than in deeper layers. Cyanobacteria-derived carbon deposition on surface sediment boosted organic carbon and moisture levels, fostering an anaerobic microenvironment conducive to enhanced biogenic CH4 and CO2 production in surface sediments. In the microcosm systems with the most severe cyanobacteria accumulation, average CH4 and CO2 concentrations in surface sediments reached 6.9 and 2.3 mol/L, respectively, surpassing the 4.7 and 1.4 mol/L observed in bottom sediments, indicating upward migration of CH4 and CO2 hotspots from deeper to surface layers. These findings enhance our understanding of the mechanisms underlying lake sediment carbon emissions induced by eutrophication and provide a more accurate assessment of lake carbon emissions.

EFFECT OF ADDING N2/H2O TO ETHYLENE LAMINAR DIFFUSION FLAME ON SOOT FORMATION

Abstract The method of adding exhaust gas to fuel to reduce soot and NOX is called Exhaust Gas Recirculation (EGR). This paper was carried out to investigate the effect of adding N2 and H2O to the fuel side to dilute ethylene on soot generation in laminar diffusion flame by combining experiment and numerical simulation. In the experiment, the flame was optically detected, and the volume fraction of soot and temperature was reconstructed. The numerical simulation adopts a simplified GRI-Mech 3.0 ethylene 23-step combustion reaction mechanism. It introduces virtual species FX (F1H2O, F2H2O, F3H2O) to isolate the effects of H2O addition on thermal, transport, chemical, and density effects. The results show that the numerical values agree well with the experimental results. At the same dilution ratio, the direct involvement of H2O in the reaction affects the flame temperature and intermediate products, leading to a more significant suppressing effect on soot than N2 dilution. After decoupling the effects of H2O, it was found that there are two main reasons for the decrease of soot caused by the addition of H2O. The first is the dilution effect and thermal effect, which hinder the HACA reaction by reducing the concentration of intermediate component C2H2, greatly inhibiting the surface growth rate of soot, and playing a decisive role in reducing the formation of soot. The second is the chemical effect, which mainly enhances the oxidation process of soot by increasing the concentration of OH free radicals during combustion through the elementary reaction OH+H2↔H+H2O. Additionally, the degree of influence of various effects on soot was qualitatively determined as follows: dilution effect &amp;gt; chemical effect &amp;gt; thermal effect &amp;gt; density effect &amp;gt; transport effect.