High Concentrations Of H2S Research Articles

Recent advances in adaptation genomics in fumarole fields, an overlooked extreme environment.

Extreme environments and plants thriving in them, known as extremophytes, offer promising platforms for studying the diverse adaptive mechanisms that have evolved in plants. However, research on adaptation to extreme environments is still limited to those environments where model species or their relative can survive. Fumarole fields, an extreme environment often overlooked, are characterized by multi-hazardous abiotic stressors, including atmospheric contamination (high concentration of H2S, SO2, and CO2), high soil temperature (~60℃), and strong soil acidification (pH=2-3). These conditions make fumarole fields a rich source for studying stress tolerance mechanisms in plants. In this review, we highlight the recent ecological, physiological, and genomic advances involved in fumarole field adaptation, and discuss the forward avenues. The studies outlined in this paper demonstrate that the extreme levels of abiotic stressors found in fumarole fields make them unparalleled field laboratories for studying the unknown stress tolerance mechanisms, warranting further genomic assessments. Some studies succeeded in identifying genes associated with fumarole field adaptation and shedding light on evolutionary implications; however, they have also encountered challenges such as limited genome resources and high genetic differentiation from related species and/or neighboring populations. To overcome such difficulties, we propose integrating ecophysiological and genomic approaches, drawing from the recent studies in other extreme environments. We expect that further studies in the fumarole fields will contribute to broadening our general knowledge of the limits of life.

Hydrogen Sulfide (H2S) Activatable Photodynamic Therapy Against Colon Cancer by Tunable FRET Effect.

Developing activatable photodynamic agents is becoming a promising mode for realizing selective photodynamic therapy (PDT) in cancer treatment. However, till now only a few H2S-activatable photodynamic agents have been involved in this field. Here, we fabricated H2S-activatable nano-assemblies (P@TPPCY) for the treatment of colon cancer containing high concentration H2S. The H2S-activatable photosensitizer (TPPCY) was synthesized by covalent conjugation between tetraphenylporphyrin (TPP) and heptamethine cyanine (Cy7), and then TPPCY was encapsulated by an amphiphilic polymer DSPE-mPEG to form P@TPPCY nano-assemblies. We demonstrated that the photosensitizing effect of TPP was efficiently quenched by Cy7 with strong absorption in the NIR region via fluorescence resonance energy transfer (FRET) effect. Interestingly, the FRET effect between Cy7 and TPP was attenuated by the decrease of absorption of Cy7 in the NIR region after the Cy7 reacted with H2S, and then the photosensitizing effect of TPP in P@TPPCY was activated. Strikingly, the P@TPPCY showed efficient H2S-activatable photodynamic therapy (PDT) in vitro against HCT116 cells (human colon carcinoma cell line), thus this work provides a new method for realizing accurate treatment of colon cancer in virtue of high H2S concentration microenvironment.

Evaluación del riesgo en la salud del personal del Parque Nacional Volcán Poás, Costa Rica, por exposición a los gases SO2 y H2S

[Objective] Verify the levels of exposure to SO2 and H2S of park rangers at the Poás Volcano National Park, using OSHA international standards as a reference. [Methodology] SO2 and H2S concentrations were studied from September 2018 to December 2019 and February 2019 to December 2019, respectively using MultiRae portable detection equipment. Sampling points were placed at the ranger’s house, the entrance station, the visitors' center, and the overlook. The level of chemical risk was determined taking into consideration: the workers’ health, exposure time, safety equipment, training, and TWA and STEL values obtained. [Results] The highest SO2 concentration was 16.0 ppm, which was recorded at the visitor center, while the highest H2S concentration was 45 ppm, which was obtained from the park ranger’s house. The average gas concentration was close to the detection limit for both gasses, suggesting that gasses, in general, are not directed toward visitors’ areas. No measurement station exceeded 2 ppm for SO2 in 8 hours (TWA). However, in the visitors’ center and the overlook, SO2 exceeded 5 ppm in 15 minutes (STEL) with concentrations equal to 10.1 ppm and 7.4 ppm, respectively. [Conclusions] Low levels of chemical hazard were obtained for both gasses at the sampling points, except for the visitors’ center which had a medium level.

Rhodoquinone-dependent electron transport chain is essential for Caenorhabditis elegans survival in hydrogen sulfide environments

Hydrogen sulfide (H2S) has traditionally been considered as an environmental toxin for animal lineages; yet, it plays a signaling role in various processes at low concentrations. Mechanisms controlling H2S in animals, especially in sulfide-rich environments, are not fully understood. The main detoxification pathway involves the conversion of H2S into less harmful forms, through a mitochondrial oxidation pathway. The first step of this pathway oxidizes sulfide and reduces ubiquinone (UQ) through sulfide-quinone oxidoreductase (SQRD/SQOR). Because H2S inhibits cytochrome oxidase and hence UQ regeneration, this pathway becomes compromised at high H2S concentrations. The free-living nematode C. elegans feeds on bacteria and can face high sulfide concentrations in its natural environment. This organism has an alternative ETC that uses rhodoquinone (RQ) as the lipidic electron transporter and fumarate as the final electron acceptor. In this study, we demonstrate that RQ is essential for survival in sulfide. RQ-less animals (kynu-1 and coq-2e KO) cannot survive high H2S concentrations, while UQ-less animals (clk-1 and coq-2a KO) exhibit recovery, even when provided with a UQ-deficient diet. Our findings highlight that sqrd-1 uses both benzoquinones and that RQ-dependent ETC confers a key advantage (RQ regeneration) over UQ in sulfide-rich conditions. C. elegans also faces cyanide, another cytochrome oxidase inhibitor, whose detoxification leads to H2S production, via cysl-2. Our study reveals that RQ delays killing by the HCN-producing bacteria Pseudomonas aeruginosa PAO1. These results underscore the fundamental role that RQ-dependent ETC serves as a biochemical adaptation to H2S environments, and to pathogenic bacteria producing cyanide and H2S toxins.

Effects of exogenous hydrogen sulfide and honokiol intervention on the proliferation, apoptosis, and calcium signaling pathway of rat enteric glial cells

Hydrogen sulfide (H2S) is a gaseous signaling molecule that influences digestive and nervous system functions. Enteric glial cells (EGCs) are integral to the enteric nervous system and play a role in regulating gastrointestinal motility. This study explored the dual effects of exogenous H2S on EGCs and the influence of apoptosis-related pathways and ion channels in EGCs. We also administered honokiol for further interventional studies. The results revealed that low-concentration H2S increased the mitochondrial membrane potential (MMP) of EGCs, decreased the whole-cell membrane potential, downregulated BAX and caspase-3, upregulated Bcl2 expression, reduced apoptosis, and promoted cell proliferation. The Ca2+ concentration, Cx43 mRNA, and protein expression were also increased. A high concentration of H2S had the opposite effect. In addition, GFAP mRNA expression was upregulated in the test-low group, downregulated in the test-high group, and upregulated in the test-high + Hon group. Honokiol treatment increased MMP, reduced whole-cell membrane potential, inhibited BAX and caspase-3 expression, increased Bcl2 expression, decreased cell apoptosis, and increased cell proliferation. The Ca2+ concentration, Cx43 mRNA, and protein expression were also upregulated. In conclusion, our study showed that exogenous H2S can bidirectionally regulate EGC proliferation and apoptosis by affecting MMP and cell membrane potential via the Bcl2/BAX/caspase-3 pathway and modulate Cx43-mediated Ca2+ responses in EGCs to regulate colonic motility bidirectionally. Honokiol can ameliorate the damage to EGCs induced by high H2S concentrations through the Bcl2/BAX/caspase-3 pathway and improve colon motility by increasing Cx43 expression and Ca2+ concentration.

Tungsten-needle intensifies microwave-sustained plasma accelerating direct H2S conversion to H2

Direct sustainable conversion of hydrogen sulfide (H2S) enables collaborative recovery of H and S resources via a metal-enhanced microwave plasma strategy, avoiding the hydrogen waste in the traditional Claus process. However, the metal size effect on microwave plasma property, the optimal process parameters, and the enhancement mechanism remain unclear in H2S conversion. Herein, the optimal tungsten needle (diameter: 1 mm, length: 60 mm, and tip angle: 10°) is experimentally proven for intensifying microwave discharge in multi-mode cavities. Theoretical calculations and plasma distribution reveal that the optimized tungsten needle achieves the ideal coupling with the microwave field, exhibiting extreme electric field augmentation around the needle tip. Tungsten-needle intensifies microwave-sustained plasma, realizing 40.2 % (90.1 %) conversion of 100 % (10 %) concentration H2S to H2 at a low microwave power of 300 W with a good stability of 30 hrs. Low power, large flow rate, and high H2S concentration are beneficial for improving energy efficiency. The excitation of microwave plasma is accompanied by a massive generation of highly energetic electrons. The direct high-energy electron-H2S collision contributes a lot to H2S splitting, especially for high-concentration H2S. In-situ optical emission spectroscopy confirms the vital S and H radicals in the plasma. The free radical reactions triggered by electron collisions are responsible for the production of H2 and S. This work opens an avenue to sustainable and low-carbon hydrogen production from the direct conversion and utilization of H2S.

Nomograph derivation for underwater sour gas releases in shallow waters based on computational fluid dynamics simulations

Ruptured underwater pipelines releasing sour gas (i.e., natural gas with high concentrations of H2S) pose significant threats to environmental safety due to their toxic and contaminative properties. This study suggests a transient Eulerian-Eulerian multiphase computational fluid dynamics (CFD) model for assessing the environmental impact of sour gas releases in shallow, ecologically sensitive waters. Employing the Realizable k-ε turbulence model and additional bubble plume mechanisms, the model was rigorously validated against well-documented experimental data, showing high levels of agreement across multiple metrics. Key environmental safety parameters—such as rise time and H2S surface gas concentration, indicative of toxic exposure risk to aquatic life and human health—were extracted for multiple release scenarios. To present generalized and easily accessible data, these parameters were nondimensionalized and incorporated into a nomograph, enabling environmental risk assessments to be conducted four orders of magnitude faster than with high-fidelity simulations. The study emphasizes the nomograph's utility in rapid, environmentally relevant risk assessment and emergency planning for mitigating the impact of sour gas spills. An error and sensitivity analysis revealed uncertainties of ±7 % for rise time and ±58 % for surface gas concentration, pinpointing avenues for future research.

Exposure to sublethal levels of H2S does not influence the short-term growth or feed utilization in post-smolt Atlantic salmon (Salmo salar) during restrictive feeding

Hydrogen sulfide (H2S) related mass mortality events in land-based recirculating aquaculture systems (RAS) are associated with the sudden release of substantial amounts of H2S, resulting in acutely toxic exposure. However, the production and release of H2S can also occur at slower constant rates, leading to continuous exposure to sublethal H2S concentrations, the effects of which are unknown. Here, we examined growth rates, feed conversion ratios, and apparent nutrient digestibility in post-smolt Atlantic salmon, following a 10-day exposure to one of two sublethal concentrations of H2S, compared against a control group. The H2S concentrations of the low exposure (LE) and moderate exposure (ME) groups throughout the trial were 1.8 ± 0.8 μg/L and 4.1 ± 1.9 μg/L, respectively. Neither exposure regime affected growth, feed utilization, or the apparent nutrient digestibility. The results suggest that Atlantic salmon tolerate exposure to sublethal H2S concentrations for 10 days, without a discernible effect on the production performance. For aquaculture systems, specifically RAS, this means that while higher concentrations of H2S should be strictly avoided, the presence of low H2S concentrations for a limited period might not be detrimental to fish welfare or production. The RAS environment is complex, and the potential combined effects of H2S and factors pertinent to RAS may influence fish performance differently in a production setting.

Sulphate removal by membrane filtration minimizes the risk of hydrogen sulphide formation in fixed bed biofilters

Hydrogen sulphide (H2S) is one of the suspected reasons behind sudden mass fish mortalities in recirculating aquaculture systems (RAS) in recent years. H2S production in aquaculture systems depends on sulphate and organic matter availability, presence of specific microbial groups, and local anoxic conditions. Specific potential H2S production hotspots in RAS have been identified within biofilters and in accumulated sludge. Current H2S control methods have been identified, such as improved hydrodynamics, increasing degassing efficiency, chemical addition of hydrogen peroxide or ozone, but have not been efficient or widespread applied. In this study, a nanomembrane filtration system was installed at a brackish water (mixture of seawater and freshwater to 15 ppt) smolt production site in Norway to remove sulphate ions from the seawater intake line (15 times reduction). The hydrogen sulphide production potential of the nanofiltered seawater mixed with freshwater (n = 3) was compared to an unfiltered seawater and freshwater mixture (15 ppt, n = 3) for 42 days in experimental scale biofilters using industrial fixed bed media. In both treatments, the linear production of H2S started around the time that bulk water measurements of oxidation-reduction potential (ORP) and dissolved oxygen (DO) dropped below 0 mV and 1 mg/L, respectively. As expected, the highest H2S concentration was observed in unfiltered water reactors, which also reached the highest concentration faster than filtered-water reactors. A 15 times reduction in initial sulphate levels by the nanofiltration membrane led to overall three times lower H2S production and delayed the onset of production by two days. Hence, membrane-filtering intake water decreased the risk of H2S production. A limitation in this study, however, was that sulphate was not completely removed from the intake water, and the next steps should evaluate how increasing the effort of membrane operation to completely remove sulphate affect the dynamics of H2S production in RAS.

Comparison of Techniques for the Quantitation of Reductive Aroma Compounds in White Wine: Links to Sensory Analysis and Cu Fractions.

Multiple analytical methodologies allow quantitation of H2S and methanethiol (MeSH) in wine, but confirmation that the determined concentrations are related to perceived off-aromas, or "reductive" faults, is yet to be provided. Fifty white wines underwent sensory evaluation and measurement of free and salt-treated H2S and MeSH concentrations by gas chromatography with sulfur chemiluminescence detection and/or gas detection tubes. The determined concentrations were compared across techniques and different analysis laboratories. Sulfhydryl off-odors in the wines were best described by boiled and rotten egg and natural gas/sewerage/durian aroma attributes. The wines with the highest ratings for both aromas had high concentrations of free H2S, free MeSH, and/or salt-treated MeSH but were unrelated to salt-treated H2S. The free sulfhydryl concentrations and their associated aromas appeared to be suppressed by specific Cu fractions in the wines. This study provides evidence of the relevant measures of reductive aroma compounds and their relation to off-odors and Cu fractions.

Hydrogen embrittlement susceptibility of AISI 4140 alloy-steel under cathodic protection and in H2S and CO2 environment

The susceptibility to hydrogen embrittlement (HE) of AISI 4140 steel when subjected to environments such as those found in offshore oil and gas fields is investigated. Hydrogen charging was carried out for 15 days using two different hydrogen sources, cathodic protection (CP) and corrosion in a saline solution containing high concentrations of H2S and CO2 (SC-sour corrosion). The steel specimens were austenitized at 850 °C, oil-quenched at ambient temperature, followed by tempering for 18 min at 350, 450, and 600 °C. The effect of tempering temperatures on hydrogen embrittlement susceptibility was also investigated. Tensile strength testing, scanning electron microscopy (SEM), and fractography analysis were used to correlate the HE with microstructural and environmental conditions. The results revealed that both hydrogen charging conditions increased the steel hardness and decreased ductility, with this effect being more pronounced at lower tempering temperatures and SC-hydrogen charging. Fracture surfaces of the steel tempered at 600 °C with hydrogen charged exhibited predominantly ductile behavior with the presence of dimples, while at 350 and 450 °C surface fractures showed cleavage facets as a consequence of brittle behavior. In general, the AISI 4140 steel hydrogen embrittlement index (%EI) was higher for hydrogen charging induced by SC compared to CP.

Unveiling the Air Quality Impacts of Municipal Solid Waste Disposal: An Integrative Study of On-Site Measurements and Community Perceptions

This study examines air quality conditions in and around a classroom located in the Sarıçam/Adana region of Türkiye, near the campus of Adana Alparslan Türkeş Science and Technology University and the Sofulu municipal solid waste (MSW) facility. This academic setting was strategically chosen due to its proximity to the waste facility. The study aims to provide a comprehensive view of the environmental and social impacts of solid waste management through a methodological approach that combines quantitative on-site measurements and qualitative survey studies. Findings from measurements and surveys underline the significant and measurable impacts of MSW facilities on the ambient air quality of university residents. The analysis revealed a marked increase in concentrations of key pollutants, including carbon monoxide (CO), hydrogen sulfide (H2S), dust, and methane (CH4). At sampling point N1, H2S levels rose from 0 ppm in July to 13 ppm in November. Methane increased from 0.2% to 2.5% of the Lower Explosive Limit (LEL) at the same point, although it remained within safety limits. Additionally, CO levels showed a 40% increase, and dust concentration levels rose from 0.21 mg/m3 to 2.36 mg/m3 from summer to winter, indicating a seasonal variation likely influenced by the landfill’s operational dynamics, as well as changes in temperature and relative humidity. In particular, the results indicate high concentrations of CO, H2S and dust, which are directly related to air quality degradation. The study also sheds light on the impacts of these waste disposal facilities on the general well-being and health of the university community, particularly on students and staff. In addition to these findings, the study highlights a general lack of awareness in the university community about the impacts of MSW facilities on air quality. This highlights the need for increased education and information dissemination. The results support the development of comprehensive and effective strategies, including technical solutions and public awareness initiatives, to mitigate the impacts of these facilities on residential areas. In conclusion, the impacts of MSW facilities on air quality should be seen as a multidimensional issue that requires a holistic approach addressing environmental, health, social, and educational dimensions.

Emission Characteristics of Odorous Compounds from a Swine Farm on Jeju Island, Korea

This study investigated 26 malodorous substances emitted from a swine farm on Jeju Island, South Korea, to discern their specific emission characteristics and potential implications for workers’ health and environmental management. A detailed analysis of emissions from livestock buildings, the compost facility, and the manure storage tank was conducted. Accurate quantification involved rigorous collection methods measuring concentrations of NH3, hydrogen sulfide (H2S), trimethylamine (TMA), aldehyde compounds, volatile organic compounds (VOCs), volatile fatty acids (VFAs), p-cresol, indole, and skatole. High concentrations of NH3 and H2S, particularly in the manure storage tank, raised concerns about the health of workers. TMA levels were notably elevated in the livestock building, whereas aldehydes and VOCs remained within limits. VFAs were prevalent in the livestock building, with p-cresol, indole, and skatole in the manure storage tank. Distinct emission profiles across farm facilities highlight the need for tailored odor management strategies, ensuring worker well-being and effective environmental practices. These findings offer valuable insights for implementing targeted mitigation measures in similar agricultural settings.

Manganese diagenesis in different geochemical environments of the ria de Vigo (Galicia, NW Iberian Peninsula)

Manganese is one of the most abundant elements in marine sediments and plays an essential role in sediment redox processes. However, unlike Fe or S, the Mn cycle has not received the same attention. Mn is a ubiquitous redox-active metal in marine systems; however, its influence on C and S cycling is still poorly understood. In particular, we hypothesize that conditions that favor high H2S production can lead to high Mn pyritization. In the Ria de Vigo, large methane fields have been identified at different depths within sediments, ranging from the surface to 2 m below the surface. Four sediment cores from different locations (outermost, middle, and innermost) within the Ria de Vigo were analyzed. Samples were subjected to a general characterization and a five-step Mn sequential extraction procedure, and analyses were complemented with X-ray absorption spectroscopy (EXAS). The results showed that the main geochemical forms of Mn undergo intense spatial and depth-related variations in sediments. Two geochemical scenarios were identified: one corresponding to the innermost section and another one to the middle and outermost sections of the ria. The former was characterized by intense Mn pyritization and by the absence of the Mn‑carbonate fraction due to the high production of H2S because of anaerobic oxidation of methane. The formation of MnS bonds was only identified by EXAS. Conversely, in the middle and outermost part of the ria, with or without the presence of methanogenesis in deep sediment layers, the Mn‑carbonate fraction was dominant even at depth, along with the presence of methane, high concentrations of H2S and, therefore, high degrees of Fe pyritization. These results suggest that, once Mn‑carbonate is formed under suboxic conditions (with low or no presence of H2S) at or near the surface, it remains stable after burial, even under conditions of high H2S concentration.

High conversion of H2S to H2 and S via a robust microwave-induced discharge plasma

Direct conversion of H2S could achieve the co-production of hydrogen and sulfur, avoiding hydrogen waste in the traditional Claus process. Herein, we propose a robust SiC-mediated microwave-induced discharge plasma, achieving H2S conversion of 98.8% to H2 and S with the inlet H2S of 2% (volume concentration) at 600 W. We realize efficient excitation and stable maintenance of microwave plasma in the multimode cavity via optimizing large SiC particles at the waveguide port. In addition, the introduction of tungsten sheets enhances discharge plasma. The H2S conversion of 52.8% was realized for the high inlet H2S concentration (30%) at 600 W. In-situ optical emission spectroscopy reveals that atomic S and H are the key reactive intermediates in the overall H2S decomposition. Direct electron-H2S collision coupling excited Ar atom-H2S collision contributes to H2S direct conversion. This work paves a path to hydrogen production toward sustainable energy applications from the direct conversion and utilization of H2S.

Hybrid Filtration Process for Gas Desulfurization

A hybrid desulfurization process combining a physical filtration stage on cellular concrete (CC abiotic filter, called CCAF) and a biotrickling filter (called BTF) filled with expanded schist as packing material was used to remove high H2S concentrations from a synthetic gas containing dinitrogen (N2), dioxygen (O2) and H2S without the addition of a nutritive solution. Provided that small amounts of oxygen are present in the gas (1.2 ± 0.1% in volume), the global removal efficiency was 100%, and the global removal capacity reached 35 ± 2 gH2S m−3 h−1 for a total empty bed residence time (EBRT) of 120 s (CCAF + BTF). The resilience of the desulfurization process was demonstrated by applying severe changes in the H2S concentrations, from 160 to 1150 ± 20 mg m−3 for an EBRT = 120 s. According to the performances of the abiotic filter, which can decline over time due to the lifetime of the cellular concrete (137 days), the biotrickling filter reacted either as a refining system or as an efficient system able to treat significant H2S loading rates (up to 45 ± 3 gH2S m−3 h−1). Depending on the operating conditions, the increase in the pressure drops of the biotrickling filter (from 45 ± 3 to 234 ± 8 Pa m−1) highlighted biomass accumulation, especially extremophilic Acidithiobacillus sp. Considering the cellular concrete abiotic filter alone, removal capacities of up to 56 ± 3 gH2S m−3 h−1 were recorded for an EBRT of 60 s, demonstrating that gases such as landfill biogas or household biogas could be efficiently treated using this simple technique.

Analysis of Air Pollutants for a Small Paintshop by Means of a Mobile Platform and Geostatistical Methods

Air pollution, in terms of particulate matter (PM10, PM2.5, PM1.0) and gaseous pollutants (H2S and VOC), has serious health effects, particularly in cities. The evaluation of outdoor air quality was carried out in the vicinity of a small paintshop operating in the city of Łódź, Poland. The concentrations of pollutants in the vertical profiles (up to 47 m a.g.l.) of ambient air were measured using a mobile platform (unmanned aerial vehicle with measuring equipment) during three measurement campaigns in September 2021. The vertical structure of the pollutant concentrations indicated the occurrence of different types of layers with an almost constant concentration near the land surface, a strong decrease (up to ca. 10–15 m a.g.l.), and significant fluctuations in concentrations to higher levels (above 25 m a.g.l.). Particulate matter concentrations (PM10, PM2.5, PM1.0) did not exceed 39 µg m−3, with stable levels on the surface. The maximum value of particulate matter concentrations (up to 38.5 µg m−3) in the vertical profiles was recorded at ca. 35–40 m a.g.l. The average concentrations of H2S and VOC varied between 0.07 and 0.12 ppm and 0.01 and 0.27 ppm, respectively. The highest H2S concentrations were observed at ca. 18–23 m a.g.l., reaching 0.14 ppm. A rapid increase in VOC concentrations, reaching 0.29 ppm, was measured in vertical profiles from 20 m a.g.l. and up to about 40 m a.g.l. In situ measurement approaches were combined with interpolation methods in the GIS system to investigate the spatial variability of pollution levels from a specified source in the urban atmosphere. Based on the survey results, the kriging interpolation method was well suited for generating spatially distributed pollution maps for individual measurement campaigns.

Simulation study of hydrogen sulfide removal in underground gas storage converted from the multilayered sour gas field

A simulation study was carried out to investigate the temporal evolution of H2S in the Huangcaoxia underground gas storage (UGS), which is converted from a depleted sulfur-containing gas field. Based on the rock and fluid properties of the Huangcaoxia gas field, a multilayered model was built. The upper layer Jia-2 contains a high concentration of H2S (27.2 g/m3), and the lower layer Jia-1 contains a low concentration of H2S (14.0 mg/m3). There is also a low-permeability interlayer between Jia-1 and Jia-2. The multi-component fluid characterizations for Jia-1 and Jia-2 were implemented separately using the Peng-Robinson equation of state in order to perform the compositional simulation. The H2S concentration gradually increased in a single cycle and peaked at the end of the production season. The peak H2S concentration in each cycle showed a decreasing trend when the recovery factor (RF) of the gas field was lower than 70%. When the RF was above 70%, the peak H2S concentration increased first and then decreased. A higher reservoir RF, a higher maximum working pressure, and a higher working gas ratio will lead to a higher H2S removal efficiency. Similar to developing multi-layered petroleum fields, the operation of multilayered gas storage can also be divided into multi-layer commingled operation and independent operation for different layers. When the two layers are combined to build the storage, the sweet gas produced from Jia-1 can spontaneously mix with the sour gas produced from Jia-2 within the wellbore, which can significantly reduce the overall H2S concentration in the wellstream. When the working gas volume is set constant, the allocation ratio between the two layers has little effect on the H2S removal. After nine cycles, the produced gas’s H2S concentration can be lowered to 20 mg/m3. Our study recommends combining the Jia-2 and Jia-1 layers to build the Huangcaoxia underground gas storage. This plan can quickly reduce the H2S concentration of the produced gas to 20 mg/m3, thus meeting the gas export standards as well as the HSE (Health, Safety, and Environment) requirements in the field. This study helps the engineers understand the H2S removal for sulfur-containing UGS as well as provides technical guidelines for converting other multilayered sour gas fields into underground storage sites.

First Chemical–Physical Measurements by Multi-Parameter Probe in the Blue Hole of Faanu Madugau (Ari Atoll, the Maldives)

Blue holes are submarine karst cavities with chemical and physical characteristics of the water column completely different from those in the surrounding environment. In this study a multi-parameter probe was used, for the first time, to characterise the water column of the Blue Hole of Faanu Madugau (Ari Atoll, Maldives, 3°55.799′ E 72°56.469′ N), the only blue hole described in the Indian Ocean up to date. Measurements of the temperature, salinity, dissolved oxygen, turbidity, chlorophyll-α, photosynthetically active radiation, potential density, pH, and H2S were obtained with a high detail. Three distinct physical–chemical layers were identified from the surface up to 70 m depth. An intermediate and turbid layer, located between 40 m and 46 m depth, sharply separates the upper layer displaying water characteristics equal to those of the outside environment from the deep and more characteristic layer of the blue hole, where a unique environment can be observed. Waters are oxygenated, warm, and rich in chlorophyll-α in the upper layer, whilst waters are anoxic, colder, denser, and completely dark, with low pH values and high H2S content in the deep layer. The Blue Hole of the Maldives represents an extreme environment from a geological, oceanographic, biological, and ecological point of view. Further investigations will be thus required to understand the origin of the Blue Hole waters, the mechanisms that keep it isolated from the external environment, the influence of weather and marine forcing on it, and how climate change may impact it.

Chameleon-like Anammox Bacteria for Surface Color Change after Suffering Starvation.

Bacteria are often exposed to long-term starvation during transportation and storage, during which a series of enzymes and metabolic pathways are activated to ensure survival. However, why the surface color of the bacteria changes during starvation is still not well-known. In this study, we found black anammox consortia suffering from long-term starvation contained 0.86 mmol gVSS-1 cytochrome c, which had no significant discrepancy compared with the red anammox consortia (P > 0.05), indicating cytochrome c was not the key issue for chromaticity change. Conversely, we found that under starvation conditions cysteine degradation is an important metabolic pathway for the blackening of the anammox consortia for H2S production. In particular, anammox bacteria contain large amounts of iron-rich nanoparticles, cytochrome c, and other iron-sulfur clusters that are converted to produce free iron. H2S combines with free iron in bacteria to form Fe-S compounds, which eventually exist stably as FeS2, mainly in the extracellular space. Interestingly, FeS2 could be oxidized by air aeration, which makes the consortia turn red again. The unique self-protection mechanism makes the whole consortia appear black, avoiding inhibition by high concentrations of H2S and achieving Fe storage. This study expands the understanding of the metabolites of anammox bacteria as well as the bacterial survival mechanism during starvation.