High Methane Concentrations Research Articles

Cruise report CAGE15-3

The cruise had two main objectives: Deployment of the two CAGE ocean floor observatories (OS1 and OS2) at shallow PKF site and deeper PKF site; CAGE ocean floor observatories were designed and build as collaborative work of CAGE scientists with Kongsberg engineers. Observatories have identical set up except that only one of them have side looking multibeam. The set up is: Seabed Platform/seabed lander/mooring frame (x2) – OS1 has black mooring frame, OS2 has grey mooring frame, CTD (x2), Oxygen sensor (x2), CH4 sensor (x2), CO2 sensor (x2), pH sensor (x1), Fluorometer (x2), ADCP (x2), Current profiler (x1), Multibeam echosounder (x1) – grey lander, OS2, Broadband Hydrophone (x2), Flowmeter (x2) For specific description of each lander, please refer to ‘taking over’ documents (WP4 team leader). Landers and sensors arrived to Tromsø with a track from Hamburg, A. Silyakova was a reference person to receive goods and shipping documents. Time period between 24 and 26 of June was the assemblage of observatories and tests of telemetry/communication/camera on a launcher. Pär Jeanson (PhD student WP4) and Reidar Kaasa (substitute engineer instead of Anoop in WP4) from CAGE were assigned to receive training on observatory assemblage/communication. 26 of June – taking over procedure. Sites for the deployment were discussed during preparatory phase. Water depth at the sites could not exceed 500 meters due to restrictions in relation to the recovery rope, which is only 500 meters long. Photographs from the tow cam used during CAGE 15-2 cruise (chief scientist on the cruise G. Panieri) revealed sites with bacterial mats on the ocean floor. Prior each deployment we did echosounder and multibeam survey to know where flares are highly concentrated. Information from the survey was mapped instantly. Target spots for both observatories were chosen based on all this combined information. Oceanographic survey in the area of shallow PKF methane flares; From the “Testing seep fertilization hypothesis” proposal:‘ During cruise CAGE 14-1 the USGS-GAS system detected elevated methane fluxes near the coast and over the shelf seep site in ca. 90m water depth. Methane fluxes above the 240 and 400m site are much less, although slightly elevated with respect to the open ocean (e.g. Vestnesa). Unexpectedly, high methane concentrations (up to 20nM) are often accompanied by low CO2 concentrations. Initial estimates of the total CO2 budget show that under those conditions seep areas are CO2 sinks. What are the biological, geochemical and hydrographic conditions that made these seeps a CO2 sink? Are the observations from CAGE 14-1 repeatable? And ultimately, what are the processes causing the strong CO2 consumption.’It was decided to test seep fertilization hypothesis during CAGE 15-3 cruise by conducting comprehensive water sampling for biogeochemical environment in the entire water column above the area of methane flares. At the same time, USGS-GAS system was onboard allowing to simultaneously measuring surface water/lower atmosphere gas concentrations. This potentially allows calculating vertical gas flux from one realm to another. Depending on available time, collaborators equipment and human resources, water from 64 CTD stations was samples for following parameters: CH4 concentration; discrete sampling to introduce into CDRS system – 13C CH4, CO2; pH; DIC and 13C DIC; DOC; MOx; FISH; DNA; DMSP; CDOM; Nutrients (nitrate, silicate, phosphate). The cruise may be known as: CAGE15_3

Feedstock flexible numerical analysis of sewage sludge gasification

Sewage sludge properties vary with the origin and treatment method of the wastewater. When converting the sewage sludge thermally for material and energy recovery, these properties affect the composition of the products and the efficiency of the process. Rotary kiln gasifiers can handle these variations in the raw materials. For further development, process integration, optimization of the process, upscaling, and industrial application, it is helpful to understand and describe the impact of the sewage sludge properties on operating parameters and product quality. This work analyses the impact of sewage sludge properties numerically using detailed chemistry and the surrogate approach. Sewage sludge is described using woody biomass components, sugars, lipids, proteins, inorganic species, moisture, and ash. The stochastic reactor model (SRM) is used to model the gasification process. In contrast to ideal reactors, stochastic reactors allow for resolving inhomogeneity. Hence, the predicted gas composition results from local temperature and available oxygen. For the analysis, temperature, airflow rate, and fuel properties, i.e., the amount and composition of volatiles, including fuel-bonded nitrogen and sulfur, and the moisture level are varied. Their results are analysed regarding the produced gas composition, emission precursor formation, and cold gas efficiency of the process. The highest efficiencies are found for temperatures of 1223 K and rich conditions. High concentrations of methane and hydrogen accompany this maximum. However, the producer gas’s highest heating value is found at low temperatures thanks to the presence of small hydrocarbons. Furthermore, a high volatile amount and a dry feedstock favour methane and carbon monoxide formation. The hydrogen concentration is found to be sensitive to the moisture content and is the highest at 30%. The cold gas efficiency is predicted to depend strongly on the feedstock and varies for the same operating conditions up to 60%. With increasing fuel-bonded nitrogen and sulfur content, the concentrations of NO and SO2 formation and their precursors increase, respectively. The released ammonia leads to significantly reducing emitted NO through the ThermalDeNOx mechanism. Overall, the generated maps provide a detailed insight in species formation and allows for the prediction of process parameters sensitive to the sewage sludge properties.

THE DISCOVERY OF POGONOPHORES (ANNELIDA, SIBOGLINIDAE) IN THE ST. ANNA TROUGH (KARA SEA) IN THE AREA OF GAS HYDRATES DISSOCIATION

Representatives of pogonophores (Annelida, Siboglinidae), whose vital activity is provided by symbiotic chemoautotrophic bacteria that oxidize methane and hydrogen sulfide, were found in the St. Anna trough at depths of 539 m and 437 m. The discovery of pogonophores indicates high concentrations of methane, which can occur because of dissociation of bottom gas hydrates under the influence of the influx of warm Atlantic water penetrating into the Kara Sea along the St. Anna trough.

Исследование микроструктуры и свойств поликристаллических алмазных покрытий, синтезированных методом HFCVD при высоких концентрациях метана

In this paper we present the results of experimental studies of the dependence of the structure and mechanical properties of diamond films grown by HFCVD method in an H2/CH4 atmosphere on variations in the methane concentration (from 5.6 to 19.3 vol %). Films synthesized at 5.6 vol. % CH4 have a columnar microcrystalline structure. The microstructure of films grown at high methane contents (12.2–19.3 vol. %) contains both individual diamond crystals and dendritic clusters, the calculated values of the crystal sizes of such films are ~5 nm. Depending on the deposition parameters, the hardness and elastic modulus of diamond films varied from 50.4 and 520 GPa to 95.15 and 974.5 GPa, respectively. With an increase in the CH4 concentration during deposition, an increase in residual tensile stresses occurs. In addition, the dependence of residual stresses on the film thickness is presented. Ultrananocrystalline coatings have, on average, order of magnitude lower values of surface roughness than microcrystalline ones; in all films, an increase in roughness is observed with an increase in their thickness.

АНАЛИЗ СВОЙСТВ УГЛЕЙ И ВЫДЕЛИВШЕГОСЯ ГАЗА ПРИ ОПРЕДЕЛЕНИИ ИХ ГАЗОНОСНОСТИ И СКЛОННОСТИ К САМОВОЗГОРАНИЮ

The high methane content in the coals prevents the penetration of oxygen inside and, consequently, their active oxidation and spontaneous combustion. The paper evaluates the composition of the gas released from coal to determine the gas content of coal and to assess the gas components responsible for coal ignition. It is shown, that in order to safely conduct mining operations, it is necessary to comprehensively analyze the composition of gas released from coal. The results can be applied in forecasting and preventing the occurrence of gas dynamic phenomena.

Shallow gas in Holocene sediments of the Pearl River Estuary and the implication for anthropogenic effects on its release

High-resolution seismic and side-scan surveys were conducted to investigate shallow gas accumulation and seepage in the Holocene sediment of the Pearl River Estuary. Extensive shallow gas accumulation and active seepage were detected in the Holocene sediments of the estuary and adjacent shelf regions. Laterally continuous and extremely shallow gas fronts were observed in areas with relatively higher sedimentation rates, whereas shallow gas was absent or discontinuous in regions with the sediment with lower sedimentation rates. Gas accumulation was present at extremely shallow depths in the West Shoal, which is the recent depocentre location. The co-occurrence of shallow gas distributions and variations in the sedimentation rate was related to the role of sediment accumulation in organic carbon burial and preservation, both of which are required for gas generation and accumulation in sediment. In addition, the consistency between the distribution of high water column methane concentrations in the West Shoal, the super shallow gas accumulation pattern in the sediment profile, and active seepage indicate that shallow gas in the Holocene sediment is a methane source in the Pearl River Estuary. Further, considerable evidence of recent or relic seepage is present in areas that have experienced active anthropogenic disturbances, including sand mining, dredging, and bridge building. The disrupted and discontinuous gas fronts at these sites suggest that active shallow gas releases were influenced by anthropogenic activity.

Low-concentration methane removal: what can we learn from high-concentration methane conversion?

Methane (CH4) is the worlds second most potent greenhouse gas after carbon dioxide (CO2).

Stable Isotope Evaluation of Geothermal Gases from the Kızıldere and Tekke Hamam Geothermal Fields, Western Anatolia, Turkey

Volatiles transported from the Earth’s interior to the surface through permeable faults provide insights on the gas composition of deep reservoirs, mixing and migration processes, and can also be applied as gas-geothermometer. Here, we present carbon (δ13C), hydrogen (δ2H) and nitrogen (δ15N) isotopic data of CO2, CH4, and N2 from gas samples collected from the Kızıldere and Tekke Hamam geothermal fields, located along the eastern segment of the Büyük Menderes Graben, Turkey. The stable isotopic composition of carbon (δ13C) ranges from +0.30 to +0.99‰ (PDB) for CO2 from Kızıldere and is slightly more variable (−0.95 to +1.3‰) in samples from Tekke Hamam. Carbon isotope data in combination with CO2/3He data reveal that ~97% (Tekke Hamam) to ~99% (Kızıldere) of CO2 derives from limestone sources, with the residual CO2 being magmatic in origin with no evidence for CO2 from organic sources. The slightly higher contribution of limestone-derived CO2 in Kızıldere, compared to Tekke Hamam can be attributed to the higher temperatures of the Kızıldere reservoir and resulting amplified fluid–limestone interaction, as well as helium depletion during phase separation for Kızıldere samples. In contrast to the carbon isotopic composition of CO2, the δ13C values of methane from Kızıldere and Tekke Hamam are clearly distinct and vary between −23.6 and −20.8‰ for Kızıldere and −34.4 and −31.7‰ for Tekke Hamam, respectively. The δ2H-CH4 composition is also distinct, measured as −126.7‰ for Kızıldere and −143.3‰ for Tekke Hamam. CO2-CH4 carbon isotope geothermometry calculations based on the isotopic fractionation of δ13C between the dominant component CO2 and the minor component CH4 reveals temperatures 20–40 °C and 100–160 °C higher than the bottom–hole temperatures measured for Tekke Hamam and Kızıldere, respectively. Based on the CO2-CH4 carbon isotope disequilibrium, unusual high methane concentrations of ~0.3 to 0.4 vol.-% and CH4/3He-δ13C-CH4 relationships we suggest thermal decomposition of late (Tekke Hamam) to over-mature (Kızıldere) organic matter and, to some extent, also abiogenic processes as principal source of methane. The N2/36Ar ratios of most samples reveal the existence of a non–atmospheric nitrogen component within the gas mixture issuing from both fields, in addition to a constant contribution of atmospheric derived nitrogen accompanied into the system via the meteoric recharge of the geothermal system. Based on the δ15N isotopic ratios (varying between −4.44‰ and 4.54‰), the non–atmospheric component seems to be a mixture of both sedimentary (crustal organic) and mantle nitrogen. The thick Pliocene sedimentary sequence covering the metamorphic basement is the likely major source for the thermogenic content of CH4 and crustal N2 gas content in the samples.

Data Driven Modelling and Control Strategies to Improve Biogas Quality and Production from High Solids Anaerobic Digestion: A Mini Review

Anaerobic Digestion (AD) is one of the oldest processes for producing biofuels from organic waste. Approximately 180 years have passed since the construction of the first modern plant, however, large prospects for improvement are still feasible, especially in regards to the quality and uniformity of the biogas produced. This work focalizes on the main quality issues and the available post-production treatment processes for biogas; subsequently, a mini-review on data-driven models and control strategies for biogas and bio-methane production plants is presented. Attention is focused on High Solids Anaerobic Digesters (HSADs), since these reactors present many interesting advantages, including a high number of operating variables which enable process optimization, high methane concentration in exit, reduced reactor volume and low water requirements. HSADs are the reactors with which Europe is aiming to rapidly increase the production of biogas and bio-methane, in order to carry out de-carbonization and reduce dependence on external methane imports. Crucial points for achieving these objectives include qualitative leaps in process operation and management, which, contrary to current practice in existing plants, require a significant increase in process automation, with control of product quality and reduction of stops due to death of bacteria at changing process parameters (such as temperature and pH). The most significant papers related to biogas quality, data-driven models and control strategies are briefly analyzed.

Decomposition of microplastics: Emission of harmful substances and greenhouse gases in the environment

Few reports have been reported on the conditions of the decomposition of plastics in the environment and their threats, while the influence of the decomposition of plastics as a potential factor in increasing greenhouse gas emissions has not been investigated. Greenhouse gases from the decomposition of plastics have so far not been considered in the development of models that show the likely climate change in the future. The work described here examined the presence and possibility of emission of phthalic acid esters and greenhouse gases from various plastic materials in daily use in the aquatic environment. The article presents, inter alia, research on the influence of temperature (20, 60, and 90 °C), pH (3, 7, and 10), plastic material, time (1, 3, 5, 7, and 14 d), and ultraviolet radiation on the migration of components present in various types of plastics, such as poly(vinyl chloride) (with high and low content of plasticizers) and polypropylene. No significant effect of pH on the migration of the plasticizers from the polymer matrix was observed. In turn, the influence of temperature on the emission of these susceptibilities was determined by the type of polymer. The highest emission level of plasticizers made of poly(vinyl chloride) was recorded for 60 °C, while from polypropylene for 20 °C. Depending on environmental conditions, the degradation of microplastics leads to a reduction in the mass of the material and conversion to methane and carbon dioxide. Each material was degraded, which resulted in the observed migration of components and methane and carbon dioxide emissions from the analysed materials. The highest degree of bis(2-ethylhexyl) phthalate migration was observed for the material made of poly(vinyl chloride). The amount of greenhouse gas emissions depended on the insolation conditions, and the poly(vinyl chloride) material showed the highest emission of methane and carbon dioxide. The highest concentration of methane at the level of 94 ppm after 360 days was observed for poly(vinyl chloride) with a large amount of plasticizers without access to light.

Bioenergy recovery from two-stage mesophilic-thermophilic anaerobic digestion of cheese whey

Among renewable energy sources, hydrogen and methane are gaseous fuels that have a higher energy density than petroleum-derived gasoline and diesel. In recent years, there has been increasing interest in converting existing anaerobic digestion systems to a two-stage process that produces hydrogen in the first stage and then methane in the second stage and is characterized by increased recovery of biofuels and bioenergy. In this study, an assessment of the energy recovery from two-stage mesophilic-thermophilic anaerobic digestion of cheese whey (CW) was carried out. After appropriate dilution, CW was fed at three COD levels of 6.8, 9.2 and 13.8 g O 2 /L to a mesophilic acidogenic reactor with a hydraulic retention time (HRT) of 10 h. The acidogenic reactor effluent was then fed to three thermophilic methanogenic reactors, which operated at different HRTs: 72, 48, and 24 h. Polyurethane foam was used to immobilize the anaerobic acidogenic and methanogenic sludge. The heating value (HV) was determined according to the experimental method using a bomb calorimeter for modes with the highest methane content and with the highest hydrogen content, as well as a calculation method based on the content of combustible gases in biohythane. The obtained deviations of the calculated from the experimentally determined HV of biohythane (4.84–7.60%) may be due to the fact that the HV of biohythane is probably not equal to the sum of the HV of pure hydrogen and methane. While an increase in the hydrogen content in biohythane leads to a decrease in the deviation of the calculated HV of biohythane from the experimental one. The maximum energy production rate was 53.2 kJ/(L d) at a COD level of 13.8 g O 2 /L, HRT in an acidogenic reactor of 10 h, and HRT in a methanogenic reactor of 48 h. The maximum energy yield of 14.42 kJ/g COD was obtained at a COD level of 9.2 g O 2 /L, HRT in an acidogenic reactor of 10 h and HRT in a methanogenic reactor of 72 h.

Purification and upgrading biogas from anaerobic digestion using chemical asborption of CO2 with amines in order to produce biomethane as biofuel for vehicles: a pilot-scale study

ABSTRACT Methane from biogas is a promising option for the transition to a circular economic system based on renewable and sustainable energy. Currently, there is a wide variety of technologies capable of efficiently extracting the impurities contained in biogas in order to produce biomethane. In the present study, work was carried out in a pilot plant for cleaning and upgrading real biogas from anaerobic digestion by means of the chemical absorption method. In contrast to other technologies, chemical absorption stands out for having the lowest CH4 losses, which was crucial for this study. The objective was to purify and upgrade the biogas from anaerobic digestion of a WWTP to achieve a high concentration of methane and use it as biofuel in vehicles. The two aqueous solutions used as absorbents were mono-ethanolamine (MEA) and N-methyldiethanolamine (MDEA), both at 20% and 40% concentrations. It was found that the most effective solution was the MEA at 20% concentration, since it has the highest CO2 removal efficiency (94%) and, therefore, CH4 richness (96%). Finally, for every 100 m3 of biomethane generated after the chemical absorption process, 62 Nm3 of biofuel were obtained.

Performance of an Innovative Low-Cost Recycled Filling (LCRF) in Anaerobic Treatment of Dairy Effluent-A Pilot-Scale Study.

The rapid growth in dairy production leads to increasing outputs of high-load effluent, necessitating new methods of treating such waste. Anaerobic processes have been increasingly popular but are hamstrung by limited nutrient removal efficiency. The aim of the present study was to investigate whether low-cost recycled filling (LCRF) improves the anaerobic treatment of dairy effluent. The addition of LCRF was found to increase both COD removal (86.1 ± 2.6%-92.8 ± 1.6%) and Ptot. removal (22.1 ± 3.5% to 36.9 ± 4.6%) from the wastewater. The LCRF ensured near-neutral pH and stabilized the structure of the anaerobic microbe community (including Archaea) across all pollutant loads tested. This translated to efficient biogas production and high methane content in the LCRF reactors, peaking at 0.35 ± 0.01 m3/kg CODremoved and 68.2 ± 0.6% (respectively) in the best-performing variant.

Highest methane concentrations in an Arctic river linked to local terrestrial inputs

Abstract. Large amounts of methane (CH4) could be released as a result of the gradual or abrupt thawing of Arctic permafrost due to global warming. Once available, this potent greenhouse gas is emitted into the atmosphere or transported laterally into aquatic ecosystems via hydrologic connectivity at the surface or via groundwaters. While high northern latitudes contribute up to 5 % of total global CH4 emissions, the specific contribution of Arctic rivers and streams is largely unknown. We analyzed high-resolution continuous CH4 concentrations measured between 15 and 17 June 2019 (late freshet) in a ∼120 km transect of the Kolyma River in northeast Siberia. The average partial pressure of CH4 (pCH4) in tributaries (66.8–206.8 µatm) was 2–7 times higher than in the main river channel (28.3 µatm). In the main channel, CH4 was up to 1600 % supersaturated with respect to atmospheric equilibrium. Key sites along the riverbank and at tributary confluences accounted for 10 % of the navigated transect and had the highest pCH4 (41 ± 7 µatm) and CH4 emissions (0.03 ± 0.004 mmolm-2d-1) compared to other sites in the main channel, contributing between 14 % to 17 % of the total CH4 flux in the transect. These key sites were characterized by warm waters (T>14.5 ∘C) and low specific conductivities (κ<88 µS cm−1). The distribution of CH4 in the river could be linked statistically to T and κ of the water and to their proximity to the shore z, and these parameters served as predictors of CH4 concentrations in unsampled river areas. The abundance of CH4-consuming bacteria and CH4-producing archaea in the river was similar to those previously detected in nearby soils and was also strongly correlated to T and κ. These findings imply that the source of riverine CH4 is closely related with sites near land. The average total CH4 flux density in the river section was 0.02 ± 0.006 mmolm-2d-1, equivalent to an annual CH4 flux of 1.24×107 g CH4 yr−1 emitted during a 146 d open water season. Our study highlights the importance of high-resolution continuous CH4 measurements in Arctic rivers for identifying spatial and temporal variations, as well as providing a glimpse of the magnitude of riverine CH4 emissions in the Arctic and their potential relevance to regional CH4 budgets.

Interpretation of role of methane in low-temperature oxidation processes of methane/n-heptane mixtures

• Nonlinear suppression of methane added on low-temperature oxidation of n -heptane. • Physical and chemical roles of methane in methane/ n -heptane oxidation process. • Channels for added methane influencing low-temperature oxidation of n -heptane. • Competition for radicals between methane and n -heptane during oxidation process. To understand the function of methane in low-temperature oxidation processes of methane/ n -heptane mixtures, mole fractions of various species in oxidation processes occurring in an atmospheric-pressure jet-stirred reactor were quantified at different methane contents over the temperature range of 500–750 K and equivalence ratios of 0.5, 1.0 and 2.0 with a residence time of 1.4 s. After examining the capability of the NUI model in reproducing the experimental data, physical and chemical roles of methane were separated from each other. Chemical kinetic characteristics behind the action of methane were revealed through analyses of reaction pathways and competition for radicals between methane and n -heptane. The result shows that the addition of methane inhibits nonlinearly the low-temperature oxidation of n -heptane. The physical effect of methane is equivalent to that of nitrogen under the high-dilution condition, and as the methane content reaches 50%, methane starts to show the chemical effect, leading to the decrease of the maximum conversion ratio of n -heptane. The reaction pathway analysis shows that under the studied conditions, the stable oxygenated species and olefins will be left, and the added methane mainly affects the reaction pathways of small-molecule intermediates with OH and HO 2 . At higher methane content, less ketohydroperoxides and hydroperoxyl cyclic ethers will be consumed, and the negative effect of the reaction R46 CH 4 + OH <=> CH 3 + H 2 O on the consumption of n -heptane strengthens gradually. In addition, it is found that contributions of elementary reactions related to C 7 species to generation and consumption of OH and HO 2 remain unchanged under different methane additions, and methane suppresses the low-temperature oxidation of n -heptane mainly through its subsequent reactions to compete for OH and HO 2 with small-molecule intermediates.

Dynamics of the Great Oxidation Event from a 3D photochemical–climate model

Abstract. From the Archean toward the Proterozoic, the Earth's atmosphere underwent a major shift from anoxic to oxic conditions at around 2.4 to 2.1 Ga known as the Great Oxidation Event (GOE). This rapid transition may be related to an atmospheric instability caused by the formation of the ozone layer. Previous works were all based on 1D photochemical models. Here, we revisit the GOE with a 3D photochemical–climate model to investigate the possible impact of the atmospheric circulation and the coupling between the climate and the dynamics of the oxidation. We show that the diurnal, seasonal and transport variations do not bring significant changes compared to 1D models. Nevertheless, we highlight a temperature dependence for atmospheric photochemical losses. A cooling during the late Archean could then have favored the triggering of the oxygenation. In addition, we show that the Huronian glaciations, which took place during the GOE, could have introduced a fluctuation in the evolution of the oxygen level. Finally, we show that the oxygen overshoot, which is expected to have occurred just after the GOE, was likely accompanied by a methane overshoot. Such high methane concentrations could have had climatic consequences and could have played a role in the dynamics of the Huronian glaciations.

Elucidation of microbial interactions, dynamics, and keystone microbes in high pressure anaerobic digestion

High-pressure anaerobic digestion (HPAD) is a promising technology for producing biogas enriched with high methane content in a single-step process. To enhance HPAD performance, a comprehensive understanding of microbial community dynamics and their interactions is essential. For this, mesophilic batch high-pressurized anaerobic reactors were operated under 3 bars (H3) and 6 bars (H6). The experimental results showed that the effect of high-pressure (up to 6 bar) on acidification was negligible while methanogenesis was significantly delayed. Microbial analysis showed the predominance of Defluviitoga affiliated with the phylum Thermotogae and the reduction of Thiopseudomonas under high-pressure conditions. In addition, the microbial cluster pattern in H3 and H6 was significantly different compared to the CR, indicating a clear shift in microbial community structure. Moreover, Methanobacterium, Methanomicrobiaceae, Alkaliphilus, and Petrimonas were strongly correlated in network analysis, and they could be identified as keystone microbes in the HPAD reactor.

Anaerobic Co-Digestion to Enhance Waste Management Sustainability at Yosemite National Park

This study evaluated the co-digestion of domestic wastewater solids (WWS) and food waste (FW) at the bench-scale for Yosemite National Park, California, which operates a 1900 m3/d wastewater treatment plant in El Portal, California. A 35-day biochemical methane potential test was performed on varying amounts of FW as a percentage of total waste (WWS plus FW) on a volatile solids basis (%FW). Specific methane yield and volumetric methane yield increased substantially with increasing %FW. A higher %FW was also associated with slower degradation kinetics but higher methane content in biogas. The 75 %FW treatment had relatively rapid kinetics, a high cumulative specific methane yield (453 mL CH4/g VS), and an elevated methane content in biogas, and is suggested as an upper limit %FW mixture for full-scale co-digestion. This, coincidently, is near the estimated ratio of WWS and FW production at the Park (70 %FW). Co-digesting the Park’s feedstock of FW with WWS in existing anaerobic digestion facilities could increase methane production five-fold. Combusting this methane in a combined heat and power system would produce about twice the energy needed to heat anaerobic digestors and power the treatment plant.

Horizontal and vertical heterogeneity of sediment microbial community in Site F cold seep, the South China Sea

Site F is the most vigorous cold seep known on the continental slope of the northern South China Sea. Up to now, the microbial community structures in sediments of Site F based on the high-throughput sequencing of the 16S rRNA genes have been studied extensively. However, few studies investigated the microbial community structures at fine vertical scales of Site F and control stations outside Site F. In this study, a comprehensive investigation of microbial communities in sediments of Site F along the depths varying from 0 to 24 cm below sea floor (cmbsf) of four sampling sites—SRS (Southern Reduced Sediment), NRS (Northern Reduced Sediment), Control 1 (close to Site F), and Control 2 (far from Site F)—was carried out. The high relative abundances of anaerobic methanotrophic archaea (ANME),Desulfobacterota[sulfate-reducing bacteria (SRB)], andCampylobacteria[sulfur-oxidizing bacteria (SOB)] in SRS and NRS indicated that these two sites were newborn cold seep sites compared with non-seep sites, Control 1, and Control 2. A positive correlation between ANME-1b, ANME-2, and SEEP-SRB and an enrichment ofSulfurovumandMethlomonadaceaewere found in the surface sediments of both SRS and NRS, indicating that the processes of anaerobic oxidation of methane (AOM), sulfur oxidation, and sulfate reduction might occur in seep sites. SRS was enriched with ANME-1b and SEEP-SRB2 with a proposed sulfate-methane transition zone (SMTZ) approximately located at 8 cmbsf. The high abundance of ANME in SRS may due to the high concentration of methane. NRS was enriched with ANME-2,Desulfatiglans,Sulfurovum, andMethanosarcinaceaewith a proposed SMTZ at about 10 cmbsf. According to the analyses of microbial community structure and environmental factors, NRS could be described as a notable cold seep reduced sediment site with low sulfate and high H2S that nourished abundant SEEP-SRB1, ANME-2,Methanosarcinales, andSulfurovum, which showed similar distribution pattern. Our study expands the current knowledge on the differences of microbial communities in cold seep sites and non-seep sites and sheds light on the horizontal and vertical heterogeneity of sediment microbial community in Site F.

Potential for the valorization of carbon dioxide from biogas production in Sweden

Biogas solutions offer many advantages to improve sustainable development, but there is still untapped potential in its environmental performance. During biogas upgrading, CO2 is separated from the gas to deliver a flow with high methane concentration and thus high energy content. In this practice, CO2 is commonly emitted to the atmosphere without contributing to a net addition of climate gases because of its biological origin, being a missed opportunity for carbon capture. In this paper, CO2 valorization is an option that has been evaluated using a qualitative and quantitative approach, taking Sweden as an example. Results showed that around 140 kt of CO2 can potentially be captured and utilized from biogas upgrading, which can significantly increase in future scenarios. If CO2 were turned into methane using power-to-gas technology, an additional 35% of biogas could be produced in the short term, meaning up to additional 0.7 TWh in 2020. By 2050, around 600 to 1600 kt of CO2 could be available, depending on how well the biogas production develops and how much of the biogas is upgraded, resulting in up to 6.2 TWh of biomethane. The qualitative assessment suggested that only minor modifications in the upgrading process are required for this practice. Biogas actors are interested in getting involved in valorization projects that enhance their circular business and avoid carbon lock-in mainly to improve the environmental performance of biomethane. Moreover, the application of CO2 valorization requires collaboration with different actors to integrate current CO2 demand or innovative transformation technologies.