Sulfide Loading Research Articles

Investigating the biodesulfurization potential of isolated microbial consortia: Impact of sulfide loading, pH and oxidation-reduction potential on sulfur recovery

Acid rain is regarded as one of the major concerns due to the release of sulfur-containing wastewaters from petrochemical and other allied industries. Biological desulfurization, an ecofriendly process offers no secondary pollution and allows for the recovery of elemental sulfur as a valuable product in a useable form as fertilizer and can be used as raw material in various industries. Therefore, this work explores the bio desulfurization potential of mixed microbial consortia that was isolated from various sources for the removal of sulfur containing compounds from synthetic wastewater at varying influent sulfide loading rate. Further, this study focused on optimizing the critical process parameters such as influent sulfide loading rate, ORP and pH to achieve maximum sulfur recovery. The experiments were performed at varying sulfide loading of 3000, 4000, 5000 and 6000 mg/L using the isolated mixed consortia at an ORP of −300 ± 20 mV and −360 ± 20 mV for an incubation period of 70 h. Results revealed that the isolated microbial consortia belong to the genera 73% Pseudomonas, 24% Alishewanella and 3% Zobellella. The maximum sulfide conversion efficiency to sulfite 309 mg/L, elemental sulfur 1152 mg/L and sulfate 1813 mg/L was exhibited by microbial consortia at an initial sulfide load of 6000 mg/L and ORP of −360 ± 20 mV.

H2S-Powered Nanomotors for Active Therapy of Tumors by Inducing Ferroptosis and Lactate-Pyruvate Axis Disorders.

Disruption of the symbiosis of extra/intratumoral metabolism is a good strategy for treating tumors that shuttle resources from the tumor microenvironment. Here, we report a precision treatment strategy for enhancing pyruvic acid and intratumoral acidosis to destroy tumoral metabolic symbiosis to eliminate tumors; this approach is based on PEGylated gold and lactate oxidase-modified aminated dendritic mesoporous silica with lonidamine and ferrous sulfide loading (PEG-Au@DMSNs/FeS/LND@LOX). In the tumor microenvironment, LOX oxidizes lactic acid to produce pyruvate, which represses tumor cell proliferation by inhibiting histone gene expression and induces ferroptosis by partial histone monoubiquitination. In acidic tumor conditions, the nanoparticles release H2S gas and Fe2+ ions, which can inhibit catalase activity to promote the Fenton reaction of Fe2+, resulting in massive ·OH production and ferroptosis via Fe3+. More interestingly, the combination of H2S and LND (a monocarboxylic acid transporter inhibitor) can cause intracellular acidosis by lactate, and protons overaccumulate in cells. Multiple intracellular acidosis is caused by lactate-pyruvate axis disorders. Moreover, H2S provides motive power to intensify the shuttling of nanoparticles in the tumor region. The findings confirm that this nanomedicine system can enable precise antitumor effects by disrupting extra/intratumoral metabolic symbiosis and inducing ferroptosis and represents a promising active drug delivery system candidate for tumor treatment.

An investigation of a process for selective biogas desulfurization and autotrophic denitrification in a membrane supported reactor

A lab-scale dense polydimethylsiloxane (PDMS) membrane bioscrubber (MBS) was used for selective removal of highly toxic H2S from biogas under autotrophic conditions for the first time. The performance of MBS was evaluated under the effects of sulfide loadings, pH, and hydraulic retention time (HRT). The results showed that gradual increase in sulfide loading rate from 131 to 316 g/m3.d boost S/N ratios 1.9–4.0, on average sulfide oxidation efficiencies higher than 95% were achieved. The S/N ratios were determinant on the formation of oxidation products, but not on the H2S gas removal efficiency. The transition of HRT significantly affected the denitrification rather than the sulfide oxidation, when HRT reduced from 24 to 12 h the nitrate removal efficiency suddenly dropped from 98% to 70%. Increasing the pH values from 7.0 to 9.0 also decreased the sulfide oxidation efficiency from 97±0.5–92±1.1%. Denitrification efficiency > 96% was observed between pH value of 7.0 and 8.0, whereas at pH 9.0 dropped rapidly to 82%. In the whole experiment time there was no membrane-induced problem that adversely affected the system performance. Over-all the developed anoxic dense MBS successfully employed for selective removal of 10,000 ppm H2S and nitrate concurrently with low chemical consumption, possibility for recovery of elemental sulfur, enhanced CH4 calorific value and eliminating the risks of explosion and dilution of biogas. The current work showed the PDMS MBS system is a promising alternative way in biological nitrogen removal and biogas desulfurization under anoxic conditions. Its application in real scale would have high economic importance.

Enhancement of bio-S0 recovery and revealing the inhibitory effect on microorganisms under high sulfide loading

Biodesulfurization is a mature technology, but obtaining biosulfur (S0) that can be easily settled naturally is still a challenge. Increasing the sulfide load is one of the known methods to obtain better settling of S0. However, the inhibitory effect of high levels of sulfide on microbes has also not been well studied. We constructed a high loading sulfide (1.55–10.86 kg S/m3/d) biological removal system. 100% sulfide removal and 0.56–2.53 kg S/m3/d S0 (7.0 ± 0.09–16.4 ± 0.25 μm) recovery were achieved at loads of 1.55–7.75 kg S/m3/d. Under the same load, S0 in the reflux sedimentation tank, which produced larger S0 particles (24.2 ± 0.73–53.8 ± 0.70 μm), increased the natural settling capacity and 45% recovery. For high level sulfide inhibitory effect, we used metagenomics and metatranscriptomics analyses. The increased sulfide load significantly inhibited the expression of flavin cytochrome c sulfide dehydrogenase subunit B (fccB) (Decreased from 615 ± 75 to 30 ± 5 TPM). At this time sulfide quinone reductase (SQR) (324 ± 185–1197 ± 51 TPM) was mainly responsible for sulfide oxidation and S0 production. When the sulfide load reached 2800 mg S/L, the SQR (730 ± 100 TPM) was also suppressed. This resulted in the accumulation of sulfide, causing suppression of carbon sequestration genes (Decreased from 3437 ± 842 to 665 ± 175 TPM). Other inhibitory effects included inhibition of microbial respiration, production of reactive oxygen species, and DNA damage. More sulfide-oxidizing bacteria (SOB) and newly identified potential SOB (99.1%) showed some activity (77.6%) upon sulfide accumulation. The main microorganisms in the sulfide accumulation environment were Thiomicrospiracea and Burkholderiaceae, whose sulfide oxidation capacity and respiration were not significantly inhibited. This study provides a new approach to enhance the natural sedimentation of S0 and describes new microbial mechanisms for the inhibitory effects of sulfide.

Evaluation of commercial moving bed media and sugarcane bagasse as packing material in biotrickling filter for hydrogen sulfide removal

This study compared two biotrickling filter packing materials for hydrogen sulfide removal. Inlet H2S concentrations and empty-bed retention time were tested on the two biotrickling filters. First reactor (BT1) had immobilized sulfur-oxidizing bacteria on commercial moving-bed media, whereas second reactor (BT2) had sulfur-oxidizing bacteria on sugarcane bagasse. The study found that BT1 performed best at 120 s empty-bed retention time, 422.39 g/m3·h hydrogen sulfide loading rate, resulted in 416 g/m3·h hydrogen sulfide elimination capacity. In contrast, BT2 performed best at 180 s empty-bed retention time, 278.77 g/m3·h hydrogen sulfide loading rate, and 273 g/m3·h elimination capacity was achieved. High-throughput sequencing showed Acidithobacillus spp. dominated the sulfur-oxidizing bacteria consortium. Sugarcane bagasse may receive less hydrogen sulfide loading than moving bed medium under optimal conditions, but its low cost and reasonable removal capacity of hydrogen sulfide -containing industrial gases in a biotrickling filter system make it an excellent alternative packing material.

Polysulfide Concentration and Chain Length in the Biological Desulfurization Process: Effect of Biomass Concentration and the Sulfide Loading Rate.

Removal of hydrogen sulfide (H2S) can be achieved using the sustainable biological desulfurization process, where H2S is converted to elemental sulfur using sulfide-oxidizing bacteria (SOB). A dual-bioreactor process was recently developed where an anaerobic (sulfidic) bioreactor was used between the absorber column and micro-oxic bioreactor. In the absorber column and sulfidic bioreactor, polysulfides (Sx2-) are formed due to the chemical equilibrium between H2S and sulfur (S8). Sx2- is thought to be the intermediate for SOB to produce sulfur via H2S oxidation. In this study, we quantify Sx2-, determine their chain-length distribution under high H2S loading rates, and elucidate the relationship between biomass and the observed biological removal of sulfides under anaerobic conditions. A linear relationship was observed between Sx2- concentration and H2S loading rates at a constant biomass concentration. Increasing biomass concentrations resulted in a lower measured Sx2- concentration at similar H2S loading rates in the sulfidic bioreactor. Sx2- of chain length 6 (S62-) showed a substantial decrease at higher biomass concentrations. Identifying Sx2- concentrations and their chain lengths as a function of biomass concentration and the sulfide loading rate is key in understanding and controlling sulfide uptake by the SOB. This knowledge will contribute to a better understanding of how to reach and maintain a high selectivity for S8 formation in the dual-reactor biological desulfurization process.

Photoelectrochemical water oxidation properties of Mo-doped CuWO4: Effect of p-type sulfide loading and annealing

Photoelectrochemical water splitting has received much attention from the perspective of the production of hydrogen as a next-generation source of energy. Herein, we focus on CuWO4 as a photoanode for water splitting because it is highly responsive to visible light. Mo doping led to longer wavelength shift of absorption edge in UV–vis absorption spectrum. Linear sweep voltammetry revealed that Mo-doped CuWO4 showed a 47-times higher photo-current density than pristine CuWO4 due to enhanced visible light absorption efficiency. The photo-current density of the Mo-doped sample also doubled when loaded with p-type MoS2.

Transformations of Ferrihydrite-Extracellular Polymeric Substance Coprecipitates Driven by Dissolved Sulfide: Interrelated Effects of Carbon and Sulfur Loadings.

The association of poorly crystalline iron (hydr)oxides with organic matter (OM), such as extracellular polymeric substances (EPS), exerts a profound effect on Fe and C cycles in soils and sediments, and their behaviors under sulfate-reducing conditions involve complicated mineralogical transformations. However, how different loadings and types of EPS and water chemistry conditions affect the sulfidation still lacks quantitative and systematic investigation. We here synthesized a set of ferrihydrite-organic matter (Fh-OM) coprecipitates with various model compounds for plant and microbial exopolysaccharides (polygalacturonic acids, alginic acid, and xanthan gum) and bacteriogenic EPS (extracted from Bacillus subtilis). Combining wet chemical analysis, X-ray diffraction, and X-ray absorption spectroscopic techniques, we systematically studied the impacts of C and S loadings by tracing the temporal evolution of Fe mineralogy and speciation in aqueous and solid phases. Our results showed that the effect of added OM on sulfidation of Fh-OM coprecipitates is interrelated with the amount of loaded sulfide. Under low sulfide loadings (S(-II)/Fe < 0.5), transformation to goethite and lepidocrocite was the main pathway of ferrihydrite sulfidation, which occurs more strongly at pH 6 compared to that at pH 7.5, and it was promoted and inhibited at low and high C/Fe ratios, respectively. While under high sulfide loadings (S(-II)/Fe > 0.5), the formation of secondary Fe-S minerals such as mackinawite and pyrite dominated ferrihydrite sulfidation, and it was inhibited with increasing C/Fe ratios. Furthermore, all three synthetic EPS proxies unanimously inhibited mineral transformation, while the microbiogenic EPS has a more potent inhibitory effect than synthetic EPS proxies compared at equivalent C/Fe loadings. Collectively, our results suggest that the quantity and chemical characteristics of the associated OM have a strong and nonlinear influence on the extent and pathways of mineralogical transformations of Fh-OM sulfidation.

Recovery of bio‑sulfur and metal resources from mine wastewater by sulfide biological oxidation-alkali flocculation: A pilot-scale study

Mine wastewater treatment using bio-sulfate reduction technology forms sulfur-containing wastewater that comprises sulfides (HS− and S2−) and metal ions. Bio‑sulfur generated by sulfur-oxidizing bacteria in such wastewater is usually negatively charged hydrocolloidal particles. However, bio‑sulfur and metal resource recovery are difficult using traditional methods. In this study, the sulfide biological oxidation-alkali flocculation (SBO-AF) method was investigated to recover the above resources, and to provide a technical reference for mine wastewater resource recovery and heavy metal pollution control. Specifically, the performance of SBO in forming bio‑sulfur and the key parameters of SBO-AF were explored and then applied in a pilot-scale process to recover resources from wastewater. Results show that partial sulfide oxidation was achieved under a sulfide loading rate of 5.08 ± 0.39 kg/m3·d, dissolved oxygen of 2.9–3.5 mg/L and temperature of 27–30 °C. The average sulfide oxidation rate and sulfur selectivity ratio were 92.86 % and 90.22 %, respectively. At pH 10, metal hydroxide and bio‑sulfur colloids co-precipitated through the precipitation catching and adsorption charge neutralization effect. The average manganese, magnesium and aluminum concentrations and turbidity in the wastewater were 53.93 mg/L, 522.97 mg/L, 34.20 mg/L and 505 NTU, respectively, and decreased to 0.49 mg/L, 80.65 mg/L, 1.00 mg/L and 23.33 NTU, respectively, after treatment. The recovered precipitate mainly contained sulfur, along with metal hydroxides. The average sulfur, manganese, magnesium and aluminum contents were 45.6 %, 29.5 %, 15.1 % and 6.5 %, respectively. Economic feasibility analysis and the above results show that SBO-AF has obvious technical and economic advantages in the recovery resources from mine wastewater.

Desulfurization of hydrophilic and hydrophobic volatile reduced sulfur with elemental sulfur production in denitrifying bioscrubber

Volatile reduced sulfur compounds were odor and irritating toxic gas, which were commonly produced during waste and wastewater treatment. The autotrophic sulfide denitrifiers converted sulfide as alternative electron acceptor to reduce nitrate, which achieved simultaneous denitrification and sulfur oxidation. In this study, to investigate the effect of sulfur compounds solubility, S/N and oxygen on sulfur and nitrogen removal, a bioscrubber was studied for treatment of hydrophilic H2S and hydrophobic CS2. Both H2S and CS2 could be efficiently removed (99%), with the highest sulfide loading of 46.9 gS/m3·d. The elemental sulfur production was strongly correlated to S/N ratio (r = 0.969, p = 0.03), the highest elemental sulfur production efficiency achieved 92.0% under S/N ratio of 2.0 for treatment of H2S. Thiobacillus sp. bacteria was the pre-dominated sulfide-dependent denitrifiers (78.2%) before exposing to oxygen, while abundance of Cryseobacterium and unclassified Xanthomonadaceae aerobic sulfide oxidizer dramatically increased up to 40% and 7.3% after aeration. Remarkably increasing production of extracellular polymeric substance (197%) was observed after treatment of CS2, which might promote the hydrolysis of CS2 and stabilization of elemental sulfur. This study demonstrated the possibility to apply sulfide-dependent denitrification process for treatment of both hydrophilic and hydrophobic volatile reduced sulfur waste gas with elemental sulfur recovery.

Genleştirilmiş Perlit ile Ham Petrolün Adsorptif Desülfürizasyonu

Crude oil; is a fossil energy source that has become possible to be used by refining processes and has a critical importance for the welfare, economic development, and quality of life of the society. As a result of the use of fossil fuels, carbon dioxide (CO2), sulfur oxide (SOx), and other greenhouse gases are released and these gases are expressed as the main cause of global climate change. For this reason, scientists are making an intense effort to minimize the harmful effects of SOx gases released as a result of combustion reactions in crude oil.&#x0D; In this presented study; the sulfur content of crude oil has been tried to be reduced by an adsorptive desulfurization technique by using expanded perlite, which is a volcanic rock type and expands as a result of heating and takes on a porous structure. For this purpose, 50 mL samples of crude oil were treated separately with 2, 4, 6, 8, and 10 g of expanded perlite and then exposed to an adsorptive desulfurization process by mixing with a magnetic stirrer at 400 rpm for an hour at room temperature. Then, it was separated from the adsorbent with the help of a centrifuge and the amount of sulfur was determined by the LECO 628S device according to ASTM D 1552-03 method.&#x0D; As a result of the study, it was determined that the amount of sulfur in crude oil decreased by 10.82 %. The study's findings showed that the expanded crude perlite had a good capacity for sulfide loading, was renewably good, and had a stable structure for removing sulfur compounds.

Continuous H2S removal from biogas using purple phototrophic bacteria

Biogas from anaerobic digestion requires desulfurisation before its intended use due to the corrosive nature of H2S. Anaerobic digesters produce biogas continuously and require a continuous process for desulfurisation. Commonly, H2S is removed using adsorption to solid media (iron sponge) or absorption and removal through chemical processes (scrubbing), requiring regeneration or replacement of sorbents. As an alternative, a continuous, anaerobic H2S removal process, utilising purple phototrophic bacteria was developed. The removal is driven by light as an energy source and potentially reduces the requirement for caustic. A desulfurisation bubble column was fed continuously with a synthetic biogas mixture (2000/5000 ppmV H2S, 30% CO2, CH4 balance) at sulfide loading rates ranging from 3.06 to 11.88 mg-S d−1. The liquid was inoculated with purple phototrophic bacteria, nutrients supplied via centrate, an anaerobic digestion residue, and externally irradiated with IR-light. The maximum sulfide removal rate was 10.13 ± 0.06 mg-S (Lh)−1 at a loading rate of 11.83 mg-S (Lh)−1, and the biomass oxidised the sulfide to sulfate utilising electrons for growth. Initially, caustic was dosed to control pH, which was replaced by hydraulic flushing (HRT 4 days), resulting in a mean pH of 6.8 at applied sulfide loading rate of 9.44 mg-S (Lh)−1. A reduction in HRT to 2 days resulted in performance loss. Thus, controlling the biomass inventory was found to be the major challenge of the process. Overall, the process can run caustic-free, and integrate with anaerobic digestion using the centrate as a nutrient source, with light supply limiting feasibility for night-time operation in a scaled process.

Preparation and characterization of the dimethyl sulfide-β-cyclodextrin inclusion complex.

Dimethyl sulfide has been widely used in flavors and can also be used as a solvent and catalyst. However, dimethyl sulfide is volatile, and its lasting power is weak. Furthermore, dimethyl sulfide is insoluble in water and is unstable in some cases. This study concentrated on the encapsulation of dimethyl sulfide in β-cyclodextrin to form an inclusion complex and to improve the durability, water solubility, and stability of dimethyl sulfide. The product was successfully produced and characterized by scanning electron microscopy, diffraction of X-rays, and thermal analysis. The dimethyl sulfide loading capacity is 6.40±0.08%. Based on the thermal release characteristics of dimethyl sulfide, the kinetic and thermodynamic parameters were obtained. The apparent activation energy, pre-exponential factor, and reaction order of the dimethyl sulfide release reaction were obtained and the values were 95.0±0.1kJ/mol,1.03×1015 s-1 , and 1, respectively. The activation entropy change, activation enthalpy change, and activation Gibbs free energy change were 41.6 J/K, 95.0kJ/mol, and 81.3kJ/mol, respectively, during the process of dimethyl sulfide release at 56.7℃. To make it clear that the dimethyl sulfide molecule interacts with β-cyclodextrin molecule, molecular simulation was used to investigate the formation process of the dimethyl sulfide-β-cyclodextrin inclusion complex. The binding energy and the optimized structure were obtained. When the Z coordinate of the S atom in the dimethyl sulfide molecule is 1.1×10-10 m, the binding energy attained the minimum value, -51.3kJ/mol. These basic data are helpful for understanding the dimethyl sulfide-β-cyclodextrin inclusion complex formation mechanism and the interaction between dimethyl sulfide and β-cyclodextrin. PRACTICAL APPLICATION: By forming an inclusion complex with β-cyclodextrin, the stability, durability, and water solubility of dimethyl sulfide can be improved. Dimethyl sulfide-β-cyclodextrin inclusion complex can be widely used in the food, beverage, flavor, and fragrance industries. The kinetic and thermodynamic parameters, binding energy, and the results of molecular simulation are helpful to understand the dimethyl sulfide-β-cyclodextrin inclusion complex formation mechanism and the interaction between dimethyl sulfide and β-cyclodextrin.

The performance and microbial communities of Anammox and Sulfide-dependent autotrophic denitrification coupling system based on the gel immobilization

Anammox and sulfide-dependent autotrophic denitrification (ASDAD) coupling system can improve the nitrogen removal, but high sulfide concentration will affect the activity of anaerobic ammonia-oxidizing bacteria (AnAOB). Gel immobilization technology can enhance the survivability of microorganisms in unsuitable environments. Therefore, in this investigation, gel immobilization technology was applied into the ASDAD coupling system to explore the removal performance and microbial communities. The results showed that the optimal S2−/NO3– was 0.6, under which the best TN removal efficiency was 85.69%. The removal performance of ASDAD coupling system was stable under rapid variations of nitrogen loading rate and sulfide loading rate. Immobilized sludge cubes could attenuate the effects of temperature on AnAOB and sulfide-oxidizing bacteria. Observations of SEM and stereoscope suggested that AnAOB was more likely to exist on the surface of the sludge cubes. Thiobacillus, Candidatus Brocadia, and Candidatus Kuenenia were the main functional bacteria in the coupling system.

Continuous electron shuttling by sulfide oxidizing bacteria as a novel strategy to produce electric current

Sulfide oxidizing bacteria (SOB) are widely applied in industry to convert toxic H2S into elemental sulfur. Haloalkaliphilic planktonic SOB can remove sulfide from solution under anaerobic conditions (SOB are ‘charged’), and release electrons at an electrode (discharge of SOB). The effect of this electron shuttling on product formation and biomass growth is not known. Here, we study and demonstrate a continuous process in which SOB remove sulfide from solution in an anaerobic ‘uptake chamber’, and shuttle these electrons to the anode of an electrochemical cell, in the absence of dissolved sulfide. Two experiments over 31 and 41 days were performed. At a sulfide loading rate of 1.1 mmolS/day, electricity was produced continuously (3 A/m2) without dissolved sulfide in the anolyte. The main end product was sulfate (56% in experiment 1% and 78% in experiment 2), and 87% and 77% of the electrons in sulfide were recovered as electricity. It was found that the current density was dependent on the sulfide loading rate and not on the anode potential. Biological growth occurred, mainly at the anode as biofilm, in which the deltaproteobacterial genus Desulfurivibrio was dominating. Our results demonstrate a novel strategy to produce electricity from sulfide in an electrochemical system.

Microbial interaction promotes desulfurization efficiency under high pH condition

The existence of H2S in biogas may cause equipment corrosion and considerable SO2 emission. Commonly used biotrickling filters may cause biogas dilution or generation of explosive mixtures. Compared with biotrickling filters, two-step process such as bioscrubber filters can overcome these shortages. However, its removal efficiency was still limited due to low microbial activity under high pH condition. Here, a bioreactor filter was carried out under pH 9.0. Removal efficiency higher than 99% was achieved under sulfide loading rate reaching 4.24 kg S m−3d−1. Results of network and high throughput sequencing showed that Thiobacillus acted as both dominant species (accounting for 75%) and unique kinless hub in this bioreactor. Other bacteria (accounting for 25%) contributed 75% to the network, which implied the intensive interaction between Thiobacillus and others. Sulfide removal ability and pH tolerance of pure bacteria and mixed culture were considered to verify how microbial interaction influenced them. Compared with pure bacteria, mixed culture had better performance under high pH condition, which confirmed that microbial interaction promoted desulfurization efficiency under high pH condition. These results showed that intensive microbial interaction might be the key to enhance sulfide removal efficiency under high pH condition.

A simple model for estimating hydrogen sulfide solubility in aqueous alkanolamines in the high pressure-high gas loading region

Hydrogen sulfide is essentially removed from the raw natural gas to meet the process, health, safety and environmental standards. Alkanolamine based absorption process remains the prevalent technique for hydrogen sulfide removal due to ease of operation and economic considerations. The design of such gas separation systems is a critical factor in meeting the stringent process requirements and optimizing operations. To achieve precise design, determination of vapor–liqid equilibrium for the system is indispensable while maintaining efficacy and simplicity. This study presents a simple model for estimating hydrogen sulfide solubility in aqueous alkanolamines and their blends in the high pressure-high gas loading region. The model equation is developed by considering and combining amine protonation and bi-sulfide formation reactions, assuming ideal liquid properties. Satisfactory correlated values of hydrogen sulfide loadings (0.21–3.15 mol gas/mole solvent) are obtained over a wide range of temperature (298.15–393.15 K), pressure (60–7027 kPa) and alkanolamine concentration (1.12–14.27 molal). Parameters are given for the hydrogen sulfide solubility in aqueous solutions of monoethanolamine, diethanolamine, N-methyldiethanolamine, 2-amino-2-methyl-1-propanol, piperazine, diglycolamine, di-isopropylamine, 1-amino-2-propanol and their selected blends. The model shall be useful for the design of alkanolamine based natural gas sweetening systems, operating at high pressure and high hydrogen sulfide gas loadings.

Model-Based Analysis of Feedback Control Strategies in Aerobic Biotrickling Filters for Biogas Desulfurization

Biotrickling filters are one of the most widely used biological technologies to perform biogas desulfurization. Their industrial application has been hampered due to the difficulty to achieve a robust and reliable operation of this bioreactor. Specifically, biotrickling filters process performance is affected mostly by fluctuations in the hydrogen sulfide (H2S) loading rate due to changes in the gas inlet concentration or in the volumetric gas flowrate. The process can be controlled by means of the regulation of the air flowrate (AFR) to control the oxygen (O2) gas outlet concentration ([O2]out) and the trickling liquid velocity (TLV) to control the H2S gas outlet concentration ([H2S]out). In this work, efforts were placed towards the understanding and development of control strategies in biological H2S removal in a biotrickling filter under aerobic conditions. Classical proportional and proportional-integral feedback controllers were applied in a model of an aerobic biotrickling filter for biogas desulfurization. Two different control loops were studied: (i) AFR Closed-Loop based on AFR regulation to control the [O2]out, and (ii) TLV Closed-Loop based on TLV regulation to control the [H2S]out. AFR regulation span was limited to values so that corresponds to biogas dilution factors that would give a biogas mixture with a minimum methane content in air, far from those values required to obtain an explosive mixture. A minimum TLV of 5.9 m h−1 was applied to provide the nutrients and moisture to the packed bed and a maximum TLV of 28.3 m h−1 was set to prevent biotrickling filter (BTF) flooding. Control loops were evaluated with a stepwise increase from 2000 ppmv until 6000 ppmv and with changes in the biogas flowrate using stepwise increments from 61.5 L h−1 (EBRT = 118 s) to 184.5 L h−1 (EBRT = 48.4 s). Controller parameters were determined based on time-integral criteria and simple criteria such as stability and oscillatory controller response. Before implementing the control strategies, two different mass transfer correlations were evaluated to study the effect of the manipulable variables. Open-loop behavior was also studied to determine the impact of control strategies on process performance variables such as removal efficiency, sulfate and sulfur selectivity, and oxygen consumption. AFR regulation efficiently controlled [O2]out; however, the impact on process performance parameters was not as great as when TLV was regulated to control [H2S]out. This model-based analysis provided valuable information about the controllability limits of each strategy and the impact that each strategy can have on the process performance.

Performance and characteristic of a haloalkaliphilic bio-desulfurizing system using Thioalkalivibrio verustus D301 for efficient removal of H2S

Haloalkaliphilic biological desulfurization is attracting people's attention due to its remarkable economy and good performance. In this study, a bio-desulfurizing system was developed based on a sulfur-oxidizing bacterium Thioalkalivibrio versutus D301 to treat H2S under haloalkaliphilic conditions. Results showed the optimum performance of the system was obtained under sulfide load of 3.27 g/L/d and oxidization-reduction potential (ORP) value of −395 mV. The selection of elemental sulfur and sulfate reached 86.19 % ± 3.02 % and 8.6 ± 0.28 % under these conditions. Then, the obvious linear relationships between sulfide load and ORP as well as aeration rate were revealed. The gradient variations of ORP and sulfurous compounds concentration with bioreactor depth were revealed, which proved the existence of spatial and temporal heterogeneity in the bioreactor. The morphology difference of sulfur particles from bioreactor and shake flask implied the key role of operating conditions in shaping particle morphology, and it was found that 56.3 % of total S° particles were harvested within 2 h by gravity settling. This study will provide a valuable reference for the design of bio-desulfurizing equipment and the optimization of operational conditions in the industrial process in the future.

Oxidoreductase Activities in Oxyphilic Tissues of the Black Sea Ruff Scorpaena porcus under Short-term Hydrogen Sulfide Loading

Hydrogen sulfide can both exert a toxic effect and function as a signaling molecule in various physiological processes. Under conditions of experimental short-term hydrogen sulfide loading (HSL), activities of oxidoreductases (enzymes of energy metabolism and antioxidant defense)—malate dehydrogenase (MDH, 1.1.1.37), lactate dehydrogenase (LDH, 1.1.1.27) and catalase (1.11.1.6) were analyzed in oxyphilic tissues (brain, heart, gills) of the Black Sea sea ruff Scorpaena porcus Linnaeus, 1758. Two groups of fish were exposed for 5 min to different concentrations of sodium sulfide (37 and 75 µM Na2S) used as a hydrogen sulfide donor. High MDH and LDH activities were simultaneously detected in the brain structures and heart chambers, reflecting a similar potential of energy metabolism in these tissues, while enhanced LDH activity in the brain indicated anaerobization of the energy metabolism pathways. Differences in oxydoreductase activities were found between the first and fourth branchial arches, heart atrium and ventricle, as well as between different brain compartments. Under HSL, the gills exhibited some signs of hypoxemia (increasing darkening of the lamellae as the Na2S concentration moved upward) and metabolic depression. At a low Na2S concentration, HSL did not cause significant changes in oxidoreductase activities in the brain and heart, while upon a 2-fold increase in the Na2S concentration these changes became more pronounced. In the key oxyphilic structures (anterior brain compartments, heart ventricle) intense HSL led to a simultaneous increase in LDH and MDH activities, which was due to the ability of MDH to participate in anaerobic processes. The less O2-sensitive structures (medulla oblongata and heart atrium) exhibited almost no changes in MDH and LDH activities even in response to high-intensity HSL, suggesting a different mode of energy metabolism in these tissues. Under intense HSL, the oxidoreductases in the heart ventricles and anterior brain compartments demonstrated responses, which were similar to those under hypoxia/anoxia.