CH4 Concentrations Research Articles

From thaw till fall: Interacting hydrology, carbon cycle, and greenhouse gas dynamics in a subarctic stream-lake continuum.

Carbon-water interaction studies between aquatic and terrestrial ecosystems are especially needed today in Arctic and Boreal regions, as they are facing drastic warming and precipitation shifts. Despite the importance of streams in the carbon cycle, northern stream-based studies are scarce, owing to a lack of measurements throughout the north, and possibly skewing global greenhouse gas estimates. We used a combination of multiscale measurements to quantify water sources (H2O isotope proxies), carbon availability (dissolved in/organic carbon concentrations) and quality (water absorbance, SUVA254 -index), microbial community structure (16S rRNA sequencing), and carbon dioxide (CO2) and methane (CH4) fluxes and concentrations. Our study site comprises a groundwater-influenced and peatland-dominated second-order stream, along with its adjacent lake inlet located in Northern Finland. Sampling was conducted three times during the summer of 2019 at 21 locations along the stream-lake continuum. Temporal and spatial shifts in water sources altered carbon characteristics, with CH4 concentrations being the key environmental factor shaping the microbial communities, overriding the influence of dissolved organic carbon amount and quality. The prevalence of methanotrophic bacteria highlighted the importance of CH4 as a carbon source and the methanotrophic groups as drivers of the CH4/CO2 source-sink attributes of subarctic stream systems. Our results highlight the value of integrated hydrological, biogeochemical, and microbiological measures to resolve the biocomplexity of carbon-water interactions in northern headwater catchments.

Controls on spatial variation in porewater methane concentrations across United States tidal wetlands

Tidal wetlands can be a substantial sink of greenhouse gases, which can be offset by variable methane (CH4) emissions under certain environmental conditions and anthropogenic interventions. Land managers and policymakers need maps of tidal wetland CH4 properties to make restoration decisions and inventory greenhouse gases. However, there is a mismatch in spatial scale between point-based sampling of porewater CH4 concentration and its predictors, and the coarser resolution mapping products used to upscale these data. We sampled porewater CH4 concentrations, salinity, sulfate (SO42−), ammonium (NH4+), and total Fe using a spatially stratified sampling at 27 tidal wetlands in the United States. We measured porewater CH4 concentrations across four orders of magnitude (0.05 to 852.9 μM). The relative contribution of spatial scale to variance in CH4 was highest between- and within-sites. Porewater CH4 concentration was best explained by SO42− concentration with segmented linear regression (p < 0.01, R2 = 0.54) indicating lesser sensitivity of CH4 to SO42− below 0.62 mM SO42−. Salinity was a significant proxy for CH4 concentration, because it was highly correlated with SO42− (p < 0.01, R2 = 0.909). However, salinity was less predictive of CH4 with segmented linear regression (p < 0.01, R2 = 0.319) relative to SO42−. Neither NH4+, total Fe, nor relative tidal elevation correlated significantly with porewater CH4; however, NH4+ was positively and significantly correlated with SO42− after detrending CH4 for its relationship with SO42− (p < 0.01, R2 = 0.194). Future sampling should focus on within- and between-site environmental gradients to accurately map CH4 variation. Mapping salinity at sub-watershed scales has some potential for mapping SO42−, and by proxy, constraining spatial variation in porewater CH4 concentrations. Additional work is needed to explain site-level deviations from the salinity-sulfate relationship and elucidate other predictors of methanogenesis. This work demonstrates a unique approach to remote team science and the potential to strengthen collaborative research networks.

Gas content, geochemical characteristics and implications of coalbed methane from the Deep Area of Qi'Nan Coalmine in Huaibei Coalfield.

The objective of this work is to investigate the implications of geological influence factors on gas content and geochemical characteristics of deep-buried (> 800m) coalbed methane (CBM) reservoirs. Results show that bituminous coal accounts for the majority, which exhibits similar maturity but differ in maceral and chemical constituents. CBM reservoirs show low porosity, low permeability and moderate temperature, with thickness of 0.85-4.15m. In addition, the total gas content is 4.58-12.33 m3/t (average of 8.83 m3/t). CH4 is the main component with concentration of 92.83-99.22% (average of 96.68%), and the δ13CCH4 and δ13DCH4 is - 53.78‰--44.62‰ (average of - 48.82‰) and - 223.93‰---4.49‰ (average of - 215.37‰), respectively. All CBM samples are the mixtures of thermogenic gases and secondary biogenic gases with CO2 reduction. In addition, gas content characteristic at the critical point of burial depth is the result by positive and negative geological effects. CH4 concentration shows a wide range with the increases of buried depth, while the numerical values of which for the selected samples display complex variation characteristics. Furthermore, the values of δ13CCH4 and δ13DCH4 become heavier with the increases of buried depth. Besides, the above two geochemical parameters are related to Ro, max and reservoir temperature.

Hydrogen-rich water 400ppb as a potential strategy for improving ruminant nutrition and mitigating methane emissions.

The objective of this study was to evaluate the effects of different concentrations of hydrogen-rich water (HRW) on in vitro rumen fermentation characteristics and the dynamics of bacterial communities. The experiment included four treatment groups: a control (CON) and hydrogen-rich water (HRW) at 200, 400, and 800 ppb. Each group was analyzed at 12-hour (h) and 48-hour (h) time points with five replicates, totaling 40 samples. The experimental results highlighted the HRW800ppb group as the top production in terms of gas production and CH4 content. In contrast, the HRW200ppb group exhibited significantly lower methane levels at both 12h and 48h (P < 0.05). Regarding rumen fermentation, the HRW400ppb group significantly increased the levels of ammonia nitrogen (NH3-N) and microbial crude protein (MCP) at 12h fermentation, but reduced the dry matter degradation rate (P < 0.05). After 48h, the HRW400ppb group had highest MCP content (P < 0.05), but no significant differences in NH3-N and dry matter degradation rate compared with the CON group (P > 0.05). Although HRW did not significantly benefit the synthesis of total volatile fatty acids (TVFA) and individual VFA, the HRW800ppb group significantly increased the ratio of acetate to propionate (P < 0.05). Based on CH4 emissions and MCP synthesis, we selected the HRW400ppb group for subsequent bacterial community analysis. Bacterial community analysis showed that at 12h, compared with the CON group, the Bacterial community analysis revealed that the HRW400ppb group had significant increases in the Simpson index, Firmicutes, Streptococcus, Schwartzia, Prevotellaceae_YAB2003_group, and Oribacterium, and decreases in Prevotella, Ruminobacter, Succinivibrio, unclassified_Succinivibrionaceae, and Prevotellaceae_UCG-003 (P < 0.05). At 48h, the Prevotellaceae_YAB2003_group and Oribacterium abundances continued to rise significantly, while Rikenellaceae_RC9_gut_group and Succiniclasticum abundances fell in the HRW400ppb group (P < 0.05). Correlation analysis indicated a negative link between CH4 and Streptococcus, and a positive correlation between the abundance of Rikenellaceae_RC9_gut_group and CH4. Collectively, these results indicate that HRW can modulate rumen fermentation and microbial community structure to reduce methane emissions without significantly affecting VFA synthesis, highlighting its potential as drinking water for enhancing ruminant nutrition and mitigating the environmental impact of livestock farming.

Greenhouse gas emissions from urban river waters of China's major cities

Urban rivers are emerging as potent emitters of greenhouse gases (GHGs). However, the magnitude and drivers of GHG emissions from urban rivers are not well understood at a national level. Using a quantitative synthesis of 4633 data records collected from urban river waters of 23 major Chinese cities, this study delved into a systematic analysis of GHG emissions from urban rivers across China. The study showed that GHG emissions in these urban rivers varied spatially and temporally, with the highest carbon emission (CO2 + CH4) from the rivers draining large metropolitan areas and during the summertime. CO2, CH4, and N2O concentrations in the urban river waters ranged from 22.53 to 1052.20 (188.41 ± 223.10) μmolL−1, 0.02 to 21.32 (1.35 ± 1.59) μmolL−1, and 0.01 to 16.81 (0.21 ± 0.72) μmolL−1, respectively, with an average flux of 148.98 ± 245.30 mmolm−2d−1 for CO2, 9.41 ± 25.08 mmolm−2d−1 for CH4, and 0.19 ± 0.65 mmolm−2d−1 for N2O. Urban rivers also received large domestic sewage with high nutrient and carbon loadings due to huge populations, indicating the effect of wastewater treatment plant effluent and urban runoff on GHG production. These findings imply that direct GHG contributions from rivers in urban areas should be accurately quantified and consequently be included in GHG inventories of riverine GHG emissions.

Determination of Particle Size for Optimum Biogas Production from Ouagadougou Municipal Organic Solid Waste

Anaerobic digestion’s contribution to sustainable development is well established. It is a sustainable production process that enables energy to be saved and produced and efficient pollution control processes to be implemented, thereby contributing to the sustainable development of our societies. Optimizing biogas yields from the anaerobic digestion of municipal organic waste is crucial for maximum energy recovery and has become an important topic of interest. Substrate particle size is a key process parameter in biogas production and precedes other pretreatment methods for most organic materials. This study aims to evaluate the impact of particle size and incubation period on biomethane production from municipal solid waste. Sampling of municipal solid waste was carried out in waste pre-collection in the city of Ouagadougou, Burkina Faso. Waste characterization showed lignocellulolytic green waste (grass, dead leaves), waste composed of fruit and leafy vegetables and leftover food waste. TableCurve 3D v4.0 software was used to develop an optimal mathematical model to correlate particle size and biomethane productivity to describe optimal production parameters. Particle sizes ranging from 2000 to 63 µm high biogas production values, specifically 385.33 and 201.25 L·kg−1 of MSV. PCA analysis clearly showed a high correlation between particle size and biogas production, with optimum production recorded for size 250 µm with a biomethane production value of 187.53 L·kg−1 of MSV. The average relative errors and RMSE for CH4 content were improved by 24.31% and 44.97%, respectively. The data calculated with the developed mathematical model and the existing experimental data were compared and permutated to validate the model. This work enabled the identification of a mathematical model that describes the correlations between the input parameters of an experiment and the monitored parameters, as well as the definition of the particle size that allows for the optimal production of biomethane.

Analysis of syngas and power production from tannery waste via gasification process using integrated thermal equilibrium simulation model

Managing high-ash sludge from tanneries is a significant challenge and requires investigating their conversion to valuable goods. This study explores the use of gasification processes to convert tannery waste into syngas and the use of syngas for power generation. In this respect, the integrated process thermal equilibrium simulation model has been developed using the Aspen Plus® V12. This model consists of (1) a steam gasification model for syngas production and (2) a power generation model for converting syngas into electricity. In addition, sensitivity analysis has been carried out to determine the effects of temperature (650–900 °C), steam flow (500–2000 kg/h), and CaO flow (0.1500 kg/h) on the composition and power generation of syngas. Changes in steam flow rate at constant temperature (cao flow rate 1500 kg/h) show an increase in H2 content to 80 % and a decline in CO and CH4 content. This increases total power output from 3680 kW to 4001 kW, temperature increases from 650 to 900 °C, and steam flow increases from 500 to 2000 kg/h from 3500 to 4600 kW. Finally, the impact of CaO as a sorbent is significant in electricity generation and CO2 mitigation, increasing to over 600 kW of energy output. This work could contribute to converting waste into energy, which could have a significant financial impact on the tannery industry.

Upgrading co-pyrolysis products from ternary biomass: An investigative study of commercial and locally-made catalysts

Catalysts play a pivotal role in influencing product yields and compositions in pyrolysis processes, offering significant advantages for biomass conversion. This study investigates the impact of natural and commercial catalysts on the co-pyrolysis of ternary biomass at two different temperatures (550 °C and 750 °C). At higher temperatures, secondary decompositions become prominent, leading to increased gas yields and decreased char and liquid oil yields. The introduction of catalysts generally enhances char yields across both temperature regimes. Notably, CaCO3 exhibits the highest bio-oil yield, while Ca(OH)2 shows the lowest, with reversed trends observed for gas yields. The influence of catalysts extends to gas composition, with Ca(OH)2 and zeolite notably increasing CH4 and CO2 concentrations at 750 °C. Each catalyst type exerts specific effects on gas production and composition, underscoring the intricate interplay between catalysts and reaction pathways. Additionally, catalysts significantly alter the composition of bio-oil, with calcium-based catalysts reducing acid content and increasing aromatics, while zeolites exhibit contrasting trends at different temperatures. Noteworthy compounds identified in the resulting bio-oil include bisphenol A, levoglucosan, phenols, and p-cresol, offering potential applications in plastics, biofuels, resins, and more. Overall, catalysts offer the potential to enhance specific compound yields, reduce corrosiveness, and optimize bio-oil and char composition for diverse industrial applications, highlighting the need for further research into synergistic effects when combining different catalysts.

Sulfate availability affect sulfate reduction pathways and methane consumption in freshwater wetland sediments

Methane (CH4) emissions from wetlands significantly contribute to global greenhouse gas fluxes, yet the mechanisms regulating CH4 production and oxidation in freshwater wetlands remain underexplored, particularly in the role of sulfate in the anaerobic oxidation of CH4. This study investigated the production, consumption, and release of CH4 in the sediments of the Qilihai wetland, focusing on the roles of hydrogenotrophic methanogenesis and sulfate dynamics across different seasons. CH4 concentrations ranged from 2.42 to 2290.52 μmol L⁻1, and δ13C–CH4 values became progressively more negative with depth, ranging from −87.37‰ to −57.18‰. Results indicate that hydrogenotrophic methanogenesis is the dominant pathway for CH4 production, particularly in sulfate-depleted environments, with CH4 concentrations in the sulfate-methane transition zone (SMTZ) strongly correlated with sulfate availability. Sulfate consumption through Sulfate Anaerobic Oxidation of Methane (SAOM) and Organoclastic Sulfate Reduction (OSR) demonstrated significant seasonal variation, with OSR accounting for up to 73% of sulfate consumption in the SMTZ. The SMTZ exhibited variations ranging from 2 to 40 cm in October, narrowing to 2–4 cm in July. These findings emphasize the complex interactions between sulfate availability, methanogenic pathways, and CH4 emissions in freshwater wetlands, highlighting the need for further research on sulfate dynamics and their implications for greenhouse gas emissions in the context of global climate change.

In vitro ruminant fermentation, degradation, and methane production of four agro-industrial protein-rich co-products, compared with soyabean meal

Soyabean is considered an unsustainable protein source for livestock feeds because of the large quantity of input and energy required to cultivate and process it. Other protein-based agro-industrial co-products that are less input-intensive, can mitigate methane (CH4) production and may therefore be more sustainable options instead soyabean. The objective of this study was to compare the effect of replacing the same amount of protein (40g/kg DM crude protein) as soyabean meal (SBM) with low-carbon local agro-industrial co-products, (brewers’ spent grains, BSG; dried wheat distillers’ grains, WDG; dried corn distillers’ grains, CDG and corn steep liquor CSL), on in vitro rumen degradation, fermentation and gas and methane production. The study used a 72-hour in vitro gas production method with a basal substrate of dried, ground grass silage and wheat. Gas volumes were measured at eleven different specific intervals, and CH4 concentrations were analysed via gas chromatography. After 72hours, in vitro DM degradability (IVDMD) and volatile fatty acid (VFA) concentrations were assessed. Gas and CH4 production curve profiles were fitted to models to determine asymptote production, the extent of degradation in rumen proper (RoP), and the fractional degradation rate (μ) (h-1) in the halfway 50% of the asymptote production. The IVDMD and estimated RoP at 0.04h and 0.025h were lower (P<0.05) for BSG compared to the other treatments, by 4.9 – 6.6%; 5.8 - 9.9%; 5.2 - 9.0%. Gas and CH4 yield (mL/g substrate and mL/g substrate degraded), and pH (SB = 6.77, BSG = 6.80, WDG = 6.74, CDG = 6.84, and CSL = 6.73; P>0.05), were not significantly affected by treatment. Butyrate and valerate were lower (P<0.05) for BSG compared to CSL, and caproate was lower (P<0.001) for BSG compared to the other treatments and in CSL compared to SBM. The results regarding degradability and VFAs concentrations of this study demonstrated that dried wheat distillers’ grains, dried corn distillers’ grains, and corn steep liquor have the potential to replace soyabean meal as protein sources for ruminants, but further reduction of CH4 emissions as a result of such practice may not be expected. Although slightly less degradable, based on their nutrient composition and the fact they did not affect rumen fermentation characteristics, brewers' spent grains can still play a complementary role in ruminant diets, especially in regions where they are locally readily available.

Dissolved Nitrous Oxide and Methane in the Taiwan Strait: Distribution, Seasonal Variation, and Emission

AbstractThe global ocean plays an important role in the overall budgets of nitrous oxide (N2O) and methane (CH4), especially in continental estuaries and shelf areas. Four cruises were conducted between 2021 and 2022, covering the spring, summer, and fall seasons, to study the spatial and seasonal characteristics of N2O and CH4 distributions and emissions in the Taiwan Strait (TWS). The surface N2O and CH4 concentrations gradually decreased from the coast to the open sea, with maximum values (14.3 and 15.6 nmol L−1) occurring near the Jiulong and Minjiang estuaries, respectively. The mean surface N2O concentration (8.2 nmol L−1) was highest in the spring and approximately the same in the summer as in the fall. The mean surface concentrations of CH4 (8.8 nmol L−1) were greater in summer than in spring and fall, probably because of the high freshwater input in summer. Except for several stations in fall, surface waters were oversaturated with N2O and CH4 relative to the atmosphere in other seasons, and the TWS was a net source of atmospheric N2O and CH4 in the spring, summer, and fall. In situ production is the main source of N2O and CH4 in the TWS, with nitrification being the dominant mechanism of N2O production in the TWS. In contrast, physical influences (riverine inputs and water mass mixing) reshape the distributions of N2O and CH4. The annual emissions of N2O and CH4 from the TWS were estimated to be 0.9 × 10−3 ± 2.9 × 10−3 Tg yr−1 and 1.6 × 10−3 ± 3.0 × 10−3 Tg yr−1, respectively. Taken together, the TWS accounts for 0.025% of the surface area of the world's oceans and 0.022% ± 0.07% and 0.017% ± 0.033% of global oceanic N2O and CH4 emissions, respectively.

Unexpected inhibition roles of methane nanobubbles on hydrate decomposition

Uncontrolled hydrate decomposition poses extraordinary risks, such as submarine landslides during hydrate exploitation, and gas leakage during hydrate storage/transportation. Previous studies suggested inhibitors can effectively prevent hydrate decomposition by adsorbing onto the hydrate surface. However, herein, we find inhibitors have very limited adsorption coverages on hydrate, which cannot fully explain their good performance. In this study, by combining experiments and molecular simulations, a new inhibition mechanism is proposed, in which nanobubbles act as the primary factor in inhibiting hydrate decomposition. Specifically, when PVP (a typical inhibitor) is added into the solution, its hydrophobic groups interact strongly with CH4, thereby increasing CH4 solubility and inducing the formation of CH4 nanobubbles. These nanobubbles are then encapsulated within the hydrate and inhibit hydrate decomposition by the following process: nanobubbles gradually become exposed to the aqueous phase during hydrate decomposition and release CH4 to the region near the nanobubble-hydrate interface. The high local CH4 concentrations near the nanobubble-hydrate interface would promote the formation of microstructures necessary for hydrate nucleation, thereby amplifying the driving force toward nucleation and consequently inhibiting hydrate decomposition. Our proposed “nanobubble inhibition mechanism” can provide a theoretical foundation for developing and applying inhibitors to prevent hydrate decomposition in various industrial applications.

Comparative Study of Mesophilic Biomethane Production in Ex Situ Trickling Bed and Bubble Reactors

Biomethane production via biogas upgrading is regarded as a future renewable gas, further boosting the biogas economy. Moreover, when upgrading is realized by the biogas CO2 conversion to CH4 using surplus renewable energy, the process of upgrading becomes a renewable energy storage method. This conversion can be carried out via microorganisms, and has attracted scientific attention, especially under thermophilic conditions. In this study, mesophilic conditions were imposed using a previously developed enriched culture. The enriched culture consisted of the hydrogenotrophic Methanobrevibacter (97% of the Archaea species and 60% of the overall population). Biogas upgrading took place in three lab-scale bioreactors: (a) a 1.2 L bubble reactor (BR), (b) a 2 L trickling bed reactor (TBR) filled with plastic supporting material (TBR-P), and (c) a 1.2 L TBR filled with sintered glass balls (TBR-S). The gas fed into the reactors was a mixture of synthetic biogas and hydrogen, with the H2 to biogas CO2 ratio being 3.7:1, lower than the stoichiometric ratio (4:1). Therefore, the feeding gas mixture did not make it possible for the CH4 content in the biomethane to be more than 97%. The results showed that the BR produced biomethane with a CH4 content of 91.15 ± 1.01% under a gas retention time (GRT) of 12.7 h, while the TBR-P operation resulted in a CH4 content of 90.92 ± 2.15% under a GRT of 6 h. The TBR-S operated at a lower GRT (4 h), yielding an effluent gas richer in CH4 (93.08 ± 0.39%). Lowering the GRT further deteriorated the efficiency but did not influence the metabolic pathway, since no trace of volatile fatty acids was detected. These findings are essential indicators of the process stability under mesophilic conditions.

Growth of homoepitaxial single crystal diamond by microwave plasma CVD in H2-CH4-O2 gas mixtures at high microwave power densities

Single crystal diamond growth by microwave plasma assisted CVD in oxygen-containing gas mixtures is attractive in view of possibility to realize a prolonged non-stoped synthesis process and to minimize defects and impurities in the produced material. We studied the homoepitaxial diamond growth on (100) oriented substrates in H2-CH4-O2 environment at high pressures (300 Torr) and high microwave power density (≈400 W/cm3) at variable O2 content (up to 3.5 %) in the plasma. A low-coherence optical interferometry and optical emission (OE) spectroscopy was used to measure in situ the growth rate and probe the plasma chemistry, respectively. Depending on CH4 content the growth rate dependence on the concentration [O2] either shows a maximum at certain [O2], or a monotonic decline, up to complete stop of the growth at some critical O2 percentage (specific for each methane content) in the mixture. We found CH, Hβ, C2 and C3 lines in OE spectra from the plasma to monotonically quenched with O2 adding, particularly, disappearance of the C2 line coincidences with growth rate going to zero. High-quality homoepitaxial diamond layers were produced at moderate growth rate at optimal gas composition and characterized with Raman spectroscopy. Moreover, a significant reduction in the stress on (111) oriented substrates owing to O2 addition was observed.

Simultaneous detection of soot, temperature, and C2H2 in laminar premixed flames using a multi-pass diode laser absorption spectrometer

We report the development of a multi-pass diode laser absorption spectroscopy system for simultaneous measurements of soot volume fraction (SVF), temperature, and C2H2 concentration using a single diode laser near 1.543 µm. A line-shaped beam spot pattern is chosen for the open-path Herriott multi-pass cavity, enabling sensitive detection at various heights above the burner with an effective optical absorption path length of approximately 1.2 m in a 6 cm diameter flame region. The gas parameters (temperature and C2H2 concentration) and the SVF are determined from the absorption spectra of the target C2H2 line pair and the laser extinction of the soot, which can be extracted from the detected signal, respectively. The performance of the system was confirmed in laminar premixed ethylene and air (C2H4/air) sooting flames produced by a standard bronze plug McKenna burner at four representative equivalence ratios. All the measurement results were compared with the two-dimensional (2D) computational fluid dynamics (CFD) simulations using a skeletal mechanism with the Moss−Brookes model. The good quantitative and qualitative agreement between the TDLAS measurements and 2D CFD simulations confirms the powerful capability of the developed system.

Expanding seawater carbon dioxide and methane measuring capabilities with a Seaglider

Abstract. Warming, ocean acidification, and deoxygenation are increasingly putting pressure on marine ecosystems. At the same time, thawing permafrost and decomposing hydrates in Arctic shelf seas may release large amounts of methane (CH4) into the water column, which could accelerate local ocean acidification and contribute to climate change. The key parameters to observing and understanding these complex processes and feedback mechanisms are vastly undersampled throughout the oceans. We developed carbon dioxide (CO2) and CH4 gliders, including standard operational procedures, with the goal that CO2 and CH4 measurements will become more common for glider operations. The Seagliders with integrated Contros HydroC CO2 or CH4 sensors also include conductivity, temperature, depth, oxygen, chlorophyll a, backscatter, and fluorescent dissolved organic matter sensors. Communication via satellite allows for near-real-time data transmission, sensor adjustments, and adaptive sampling. Several sea trials with the CO2 Seaglider in the Gulf of Alaska and data evaluation with discrete water and underway samples suggest nearly “weather-quality” CO2 data as defined by the Global Ocean Acidification Network. A winter mission in Resurrection Bay, Alaska, provided the first insights into the water column inorganic carbon dynamics during this otherwise undersampled season. The CH4 Seaglider passed its flight trials in Resurrection Bay but needs to be tested during a field mission in an area with CH4 concentrations beyond background noise. Both sensing systems are available to the science community through the industry partners (Advanced Offshore Operations and -4H-JENA engineering GmbH) of this project.

Suppression of cross-interference in the absorption spectra of gas mixtures

In the quantitative analysis of mixed gases by tunable diode laser absorption spectroscopy, the overlapping of absorption spectra and mutual interference of multi-component gases can lead to problems of large measurement errors and low analysis accuracy. In this paper, an improved firefly algorithm is proposed and applied to the support vector machine regression model to solve this problem. The specific method includes introducing an adaptive step size to balance the local and global searches and using the gradient descent method to accelerate the parameter optimization process so as to improve the model’s generalization ability and prediction accuracy. The experimental results show that the maximum errors of the improved algorithm in the prediction of CH4 and CO gas concentrations are no more than 0.0443 % and 2 ppm, with coefficients of determination, R2, of 0.9994 and 0.99815. The promising results obtained by the system provide theoretical support for the realization of high-precision detection of multicomponent gases with a single source of light, and also demonstrate the high efficiency and feasibility of the method in practical detection.

The effects of influent 5-Deoxystrigol concentrations on integral biogas upgrading and nutrient removal by different algal-fungal-bacterial consortium

The low quality of biogas and the difficulties in treating biogas slurry are important bottlenecks that limit the development of the fermentation industry. The effects of 5-deoxystrigol (5DS) on the growth rate, daily productivity, and photosynthetic performance of different algal-fungal-bacterial consortia were investigated, and the auxiliary activities of endophytic bacteria (S395–2), Ganoderma lucidum (G. lucidum), Bacillus licheniformis (B. licheniformis), and activated sludge in these systems were examined. The consortium Chlorella vulgaris (C. vulgaris) + G. lucidum + S395–2 was found to be the most effective combination for both biogas upgrading and nutrient removal. Removal efficiencies of chemical oxygen demand (COD), total nitrogen (TN), and total phosphorous (TP) were approximately 82.94 ± 7.88 %, 81.36 ± 7.79 %, and 83.27 ± 8.09 %, respectively, and the CO2 removal efficiency was observed to be about 69.89 ± 6.57 % at the optimum 5DS concentration of 10−11 M. On day 7 of the treatment, the CH4 content was elevated from 66.07 ± 4.84 % to 86.24 ± 8.44 %. The effect of 5DS treatments in different algal-fungal-bacterial consortia was positive in terms of growth performance and photosynthetic rate. The present study provides a framework for efficient biogas upgrading and nutrient removal by the three-phase symbionts.

Portable alkaloid discrimination via nanozyme-mediated colorimetric paper-based sensor array integrated with smartphone detection.

Apaper-based colorimetric sensor array mediated by a novel nanozyme (CuCo2O4) was developed using a screen-printing technology. The aim was to facilitate the identification of different kinds of alkaloids. Typically, three chromogenic substrates (3,3',5,5'-tetramethylbenzidine, 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid), and o-phenylenediamine) were selected as sensing elements, which can be catalyzed by a CuCo2O4 nanozyme with peroxidase-like activity to yield corresponding oxidized products, thereby inducing color changes. Owing to the varying inhibitory ability of different alkaloids on acetylcholinesterase (AChE), a decrease in choline (Ch) concentration occurs and subsequently results in the restoration of color within the units of sensor array. Color data can be transformed into hue information with a smartphone. The above color variations generated a unique "fingerprint" pattern on five alkaloids (berberine, palmatine, jatrorrhizine, eserine, and harmane), which can be successfully discriminated through linear discriminant analysis in the range0.2 to 20µM. Furthermore, the sensor arrays allowed successful discrimination of the above five alkaloids in Chinese herbal medicine samples and recognition of 22 blind samples. This work presents a novel nanozyme-based paper sensor array, which is a user-friendly and reliable platform for probing different alkaloids. In addition, the developed sensing strategy enables the identification of AChE-related diseases, positively contributing to the screening available of AD-associated drugs.

Near-Infrared Dual-Range Methane Sensor Using the OAIC-HC Mode Based on VMD-SG-Assisted Optical Noise Suppression.

Based on tunable diode laser absorption spectroscopy and off-axis integrated cavity output spectroscopy, a dual-range methane hybrid sensor was constructed utilizing the overtone absorption band of CH4 gas molecules at 1653.7 nm. By simultaneously utilizing an off-axis integrated cavity and Herriott cell with an effective absorption path of 11 and 405 m, respectively, the two received photoelectric signals are decomposed into different frequency components by VMD and then reconstructed after SG filtering. Applying the global optimization algorithm DA-ELM to CH4 concentration inversion, the correlation coefficient R2 is as high as 0.9995. Through long-term stability verification, the instrument's standard deviation at 1 ppm is 27 ppb. After Allan-Werle deviation analysis, the sensor's limit of detection is 2.298 ppb at an integration time of 138 s. Using the self-developed sensor, the detection of dual-range trace CH4 gas is achieved, enabling a dynamic detection range of trace CH4 gas ranging from 400 ppb to 1000 ppm. The sensor realizes dual-range methane trace detection and actively controls methane emissions to improve environmental quality while taking into account the safety benefits of reducing production accidents.