High Levels Of H2S Research Articles

Discrimination of the oral microbiota associated with high hydrogen sulfide and methyl mercaptan production

Both hydrogen sulfide (H2S) and methyl mercaptan (CH3SH) are frequently detected in large amounts in malodorous mouth air. We investigated the bacterial composition of saliva of 30 subjects with severe oral malodor exhibiting extreme CH3SH/H2S ratios (high H2S but low CH3SH concentrations, n = 14; high CH3SH but low H2S concentrations, n = 16) and 13 subjects without malodor, using barcoded pyrosequencing analysis of the 16S rRNA gene. Phylogenetic community analysis with the UniFrac distance metric revealed a distinct bacterial community structure in each malodor group. The H2S group showed higher proportions of the genera Neisseria, Fusobacterium, Porphyromonas and SR1 than the other two groups, whereas the CH3SH group had higher proportions of the genera Prevotella, Veillonella, Atopobium, Megasphaera, and Selenomonas. Our results suggested that distinct bacterial populations in the oral microbiota are involved in production of high levels of H2S and CH3SH in the oral cavity.

Community structure and feeding preference of nematodes associated with methane seepage at the Darwin mud volcano (Gulf of Cádiz)

We sampled the Darwin mud volcano (MV) for meiofaunal community and trophic structure in relation to pore-water geochemistry along a 10 m transect from a seep site on the rim of the crater towards the MV slope. Pore-water profiles indicated considerable variation in upward methane (CH4) flow among sediment cores taken along the transect, with highest flux in the seep sediment core, gradually decreasing along the transect, to no CH4 flux in the core taken at a 5 m distance. Low sulphate concentrations and high levels of total alkalinity and sulphide (H2S) suggested that anaerobic oxidation of methane (AOM) occurred close to the sediment surface in the seep sediment core. High H2S levels had a genus- and species-specific impact on meiofaunal densities. Nematode genus composition varied gradually between sediment cores, with the genus Sabatieria dominating almost all sediment cores. However, genus diversity increased with increasing distance from the seep site. These limited data suggest that the community structure of seep meiofauna is highly dependent on local (a)biotic habitat characteristics, and a typical seep meiofaunal community cannot be delineated. Stable isotope values suggested the nematode diet up to 10 m from the seep site included thiotrophic carbon. The thicker hemipelagic sediment layer (photosynthetic carbon), the increased trophic diversity, and the heavier nematode δ13C farther from the seep site suggest a decrease in thiotrophy and an increase in photosynthetic carbon in the nematode diet.

Ongoing Development of Cementing Practices and Technologies for Kuwait Oil Company's Deep HP/HT Exploration and Gas Wells: Case History

Summary Exploration activities in Kuwait have been focused on the search for high-quality oil from the Jurassic formations and gas in the Triassic/Permian series. The wells drilled to these prospects are very challenging because of high-pressure/high-temperature (HP/ HT) conditions, large casing sizes, oil-based mud, the presence of high levels of H2S and CO2, and a narrow pore-/fracture-pressure window. In particular, the cementing of the deep strings in these wells has been extremely challenging. Over the last 8 years, a concentrated effort has been made to introduce new technologies and materials to improve the cementing practices both from operational and safety aspects. In 2003, the success ratio for deep cementations was highly variable. The Kuwait Oil Company (KOC), along with one of their cementing service providers, worked on a series of changes to practices and materials with the aim of improving job quality with high repeatability. This was based primarily on the technologies being developed in HP/HT wells around the globe, especially in the North Sea, and it resulted in a notable improvement in cementing performance. Technologies and practices that had been developed include spacer technology, application of synthetic retarders, fluid-loss and antigas-migration additive improvements, development of finegrained weighting additives, use of HP/HT rheometers, systematic product control, the minimizing of handling, and safer mixing practices at the wellsite. This paper will discuss the application of these technologies, materials, and practices over an 8-year period as a case history to illustrate the improvements made in achieving consistent cement quality and final slurry placement for the deep-casing and liner strings, and will conclude with recommendations and lessons learned during this process.

Pautas de comportamiento alimentario y adaptaciones progresivas en los apéndices auxiliares en Agostocaris bozanici y Barbouria yanezi (Crustacea: Decapoda: Caridea: Agostocarididae, Hyppolitidae)

There are several adaptations shown by crustaceans to cave life; namely: vision loss, lack of pigmentation, specialization of sensory structures and elongation of ambulatory appendages. Since it has been mentioned in the literature that food scarcity is the evolutionary force and that in anchialine caves the main energy source is produced by bacteria, an scanning electron microscopy analysis was conducted to identify the adaptations in the appendages that these crustaceans use for feeding, chelate pereopods and maxillipeds, considering those species that live exclusively in zones that have high levels of H2S. The results show that Agostocaris bozanici has more setae on the propodus of the third maxilliped whilst Barbouria yanezi has stronger setae in this appendage. But along the inner margin of the chelipeds of A. bozanici is an interesting specialization with a series of long setae possibly used as a tool to separate microorganisms, maybe ciliates, from the sediment. The conclusions are that Barbouria yanezi eats large particulate material in degradation coming from the nearby tropical forest, while Agostocaris bozanici has a specialized seta to eat the microorganisms that decompose this material.

Impact of Oxygen Dissolved at Bottling and Transmitted through Closures on the Composition and Sensory Properties of a Sauvignon Blanc Wine during Bottle Storage

This work outlines the results from an investigation to determine the effect of the oxygen dissolved at bottling and the specific oxygen barrier properties of commercially available closures on the composition, color and sensory properties of a Bordeaux Sauvignon Blanc wine during two years of storage. The importance of oxygen for wine development after bottling was also assessed using an airtight bottle ampule. Wines were assessed for the antioxidants (SO(2) and ascorbic acid), varietal thiols (4-mercapto-4-methylpentan-2-one, 3-mercaptohexan-1-ol), hydrogen sulfide and sotolon content, and color throughout 24 months of storage. In addition, the aroma and palate properties of wines were also assessed. The combination of oxygen dissolved at bottling and the oxygen transferred through closures has a significant effect on Sauvignon Blanc development after bottling. Wines highly exposed to oxygen at bottling and those sealed with a synthetic, Nomacorc classic closure, highly permeable to oxygen, were relatively oxidized in aroma, brown in color, and low in antioxidants and volatile compounds compared to wines sealed with other closures. Conversely, wines sealed under more airtight conditions, bottle ampule and screw cap Saran-tin, have the slowest rate of browning, and displayed the greatest contents of antioxidants and varietal thiols, but also high levels of H(2)S, which were responsible for the reduced dominating character found in these wines, while wines sealed with cork stoppers and screw cap Saranex presented negligible reduced and oxidized characters.

Tail-Gas Cleanup by Simultaneous SO2and H2S Removal

Tail-gas streams from refinery processes such as Claus units often contain and emit SO2 and H2S at levels exceeding permissible emission limits, which are currently set at 10 ppm H2S and 250 ppm SO2 (U.S.). Gas compositions vary widely depending on the application, with some containing high levels of SO2, H2S, and moisture. This publication describes the simultaneous removal of these sulfur-containing contaminants utilizing a regenerable catalytic sorbent. A simplified process with the potential to reduce a four-stage process to a two-stage process is presented. The new process would compete with currently established technologies such as amine scrubbers or Cansolv units (property of Cansolv Technologies Inc., Montreal, Quebec, Canada H2M 2N9).

Technology Focus: Casing and Cementing (May 2009)

Technology Focus The current trend in well construction technology is focused on reducing the risk associated with capital-intensive wells in deeper and/or increasingly hostile environments. With a water depth between 4,000 and 11,000 ft, total depth approaching 30,000 ft, and a total cost per well of USD 200 million to 300 million, the deepwater projects being developed around the world are a prime example. One significant design error or oversight can lead to well failure and have serious effect on a company's bottom line. With mudline temperatures as low as 34°F and production temperatures as high as 250°F, annular temperatures may increase by more than 100°F during production cycles. As the annular fluid heats up, it expands. If that fluid is in a confined section of casing/casing annulus, the annular pressure can exceed 10,000 psi. This phenomenon has led to rupture or collapse of casing strings and loss of some wells. One approach to mitigating this phenomenon is to use vacuum-insulated tubing to limit heat transfer to the trapped fluid. Another is the novel use of a new annular fluid that shrinks rather than expands as the annular temperature increases. A greater proportion of our future energy will come from more-hostile environments as we increase the pursuit in deepwater, high-pressure/high-temperature, geothermal projects while using CO2-storage wells to reduce CO2 emissions. These wells may contain high levels of H2S, CO2, and/or chlorides and have temperatures in excess of 350°F. Proper selection of tubulars, anatomic seals, and cement will be critical to reducing total well cost and environment and commercial risk. I asked one of Chevron's cementing experts (Robert Carpenter) for help with current cementing technology. With the growing concern about "carbon emissions" and "carbon capture," CO2 injection for geological storage is our next big area of activity. The success of this industry segment is predicated on very-long-term isolation of injected CO2. We are in the investigational stage of this rapidly growing industry segment, and the primary issue is ensuring the long-term integrity. There is extensive debate and conflicting laboratory and field investigations into the suitability of Portland cement for a CO2-rich environment. Recent investigations indicate identifying and preventing existing cement defects as the primary concern, and the CO2 attack on Portland cement as less of an issue. Casing and Cementing additional reading available at the SPE eLibrary: www.spe.org SPE 115638 • "Advanced Cement Systems Used to Improve Geothermal-Well Reliability in Java" by K. Ravi, Halliburton, et al. SPE 119504 • "The Effect of Carbonic Acid on Well Cements as Identified Through Lab and Field Studies" by A. Duguid, SPE, Schlumberger. SPE 112624 • "Analysis of Control Lines Strapped to Tubing" by Robert F. Mitchell, Halliburton, et al.

Characterization of Cysteine‐Degrading and H2S‐Releasing Enzymes of Higher Plants ‐ From the Field to the Test Tube and Back

Due to the clean air acts and subsequent reduction of emission of gaseous sulfur compounds sulfur deficiency became one of the major nutrient disorders in Northern Europe. Typical sulfur deficiency symptoms can be diagnosed. Especially plants of the Cruciferae family are more susceptible against pathogen attack. Sulfur fertilization can in part recover or even increase resistance against pathogens in comparison to sulfur-deficient plants. The term sulfur-induced resistance (SIR) was introduced, however, the molecular basis for SIR is largely unknown. There are several sulfur-containing compounds in plants which might be involved in SIR, such as high levels of thiols, glucosinolates, cysteine-rich proteins, phytoalexins, elemental sulfur, or H2S. Probably more than one strategy is used by plants. Species- or even variety-dependent differences in the development of SIR are probably used. Our research focussed mainly on the release of H2S as defence strategy. In field experiments using different BRASSICA NAPUS genotypes it was shown that the genetic differences among BRASSICA genotypes lead to differences in sulfur content and L-cysteine desulfhydrase activity. Another field experiment demonstrated that sulfur supply and infection with PYRENOPEZIZA BRASSICA influenced L-cysteine desulfhydrase activity in BRASSICA NAPUS. Cysteine-degrading enzymes such as cysteine desulfhydrases are hypothesized to be involved in H2S release. Several L- and D-cysteine-specific desulfhydrase candidates have been isolated and partially analyzed from the model plant ARABIDOPSIS THALIANA. However, it cannot be excluded that H2S is also released in a partial back reaction of O-acetyl-L-serine(thiol)lyase or enzymes not yet characterized. For the exact determination of the H2S concentration in the cell a H2S-specific microsensor was used the first time for plant cells. The transfer of the results obtained for application back on BRASSICA was initiated.

High contents of hypotaurine and thiotaurine in hydrothermal-vent gastropods without thiotrophic endosymbionts

Invertebrates at hydrothermal vents and cold seeps must cope with high levels of toxic H2S. In addition, these and all marine invertebrates must balance internal osmotic pressure with that of the ocean. Cells usually do so with organic osmolytes, primarily free amino acids (e.g., taurine, glycine) and methylamines (e.g., betaine). At vents and seeps, clams, mussels, and vestimentiferans with thiotrophic endosymbionts have high levels of hypotaurine and thiotaurine (a product of hypotaurine and HS-). These serve as osmolytes but their primary function may be to transport and/or detoxify sulfide; indeed, thiotaurine has been proposed to be a marker of thiotrophic symbiosis. To test this, we analyzed Depressigyra globulus snails and Lepetodrilus fucensis limpets from Juan de Fuca Ridge vents (1,530 m). Neither has endosymbionts, though the latter has thiotrophic ectosymbionts. Some specimens were rapidly frozen, while other live ones were kept in laboratory chambers, some with and others without sulfide. Non-vent gastropods from a variety of depths (2-3,000 m) were also collected. Tissues were analyzed for major osmolytes and taurine derivatives. The dominant osmolytes of non-vent snails were betaine in all species, and either taurine in shallow-living species or scyllo-inositol, glycerophosphorylcholine, and other amino acids in deep-sea species. In contrast, the dominant osmolytes were hypotaurine and betaine in D. globulus, and hypotaurine in L. fucensis. Both species had thiotaurine (as well as hypotaurine) at levels much greater than previously reported for vent and seep animals without endosymbionts. The ratio of thio- to thio- plus hypotaurine, a possible indicator of sulfide exposure, decreased in both species when kept in laboratory chambers with low or no sulfide, but stayed at high levels in snails kept with 3-5 mM sulfide. Thus, in some vent animals without endosymbionts, sulfide may be detoxified via conversion of hypotaurine to thiotaurine. The latter may be a marker of high sulfide exposure but not of thiotrophic endosymbionts.

Chemosynthetic communities as fingerprints of submarine sliding-linked hydrocarbon seepage, Miocene deep-sea strata of the Tuscan–Romagna Apennines, Italy

A specialised low-diversity bivalve assemblage dominated by chemosymbiotic vesicomyid bivalves (?Calyptogena sp.) is associated with a large submarine landslide (Casaglia-M. della Colonna slide) within the turbiditic Miocene Marnoso-arenacea Formation in the northern Apennines. This macrofossiliferous horizon is located just at the top of the slide close to the boundary between intrabasinal deformed sediments and extrabasinal sediments. There is a causal relationship between the emplacement of this large submarine slide and fluid expulsion promoting the localised and ephemeral establishment of specialised communities. The occurrence of exclusively sulphur-based biota and the concomitant absence of 13C-depleted authigenic carbonates from the host sediment are likely an indication that hydrocarbons within subsurface fluids were consumed through sulphate reduction processes. As a result, high levels of shallow-seated H2S were produced and then exploited by chemosymbiotic bivalves.

Massive release of hydrogen sulfide to the surface ocean and atmosphere during intervals of oceanic anoxia

Simple calculations show that if deep-water H2S concentrations increased beyond a critical threshold during oceanic anoxic intervals of Earth history, the chemocline separating sulfidic deep waters from oxygenated surface waters could have risen abruptly to the ocean surface (a chemocline upward excursion). Atmospheric photochemical modeling indicates that resulting fluxes of H 2S to the atmosphere (.2000 times the small modern flux from volcanoes) would likely have led to toxic levels of H 2S in the atmosphere. Moreover, the ozone shield would have been destroyed, and methane levels would have risen to .100 ppm. We thus propose (1) chemocline upward excursion as a kill mechanism during the end-Permian, Late Devonian, and Cenomanian‐Turonian extinctions, and (2) persistently high atmospheric H2S levels as a factor that impeded evolution of eukaryotic life on land during the Proterozoic.

Control of H2S waste gas emissions with a biological activated carbon filter

AbstractThe removal of high concentrations of H2S from waste gases containing mixtures of H2S and NH3 was studied using the pilot‐scale biofilter. Granular activated carbon (GAC), selected as support material in this study, demonstrated its high adsorption capacity for H2S and good gas distribution. Extensive tests to determine removal characteristics, removal efficiency, and removal capacity of high H2S levels and coexisting NH3 in the system were performed. In seeking the appropriate operating conditions, the response surface methodology (RSM) was employed. H2S removal capacities were evaluated by the inoculated bacteria (biological conversion) and BDST (Bed Depth Service Time) methods (physical adsorption). An average 98% removal efficiency for 0.083–0.167 mg dm−3 of H2S and 0.004–0.021 mg dm−3 of NH3 gases was achieved during the operational period because of rapid physical adsorption by GAC and subsequently an effective biological regeneration of GAC by inoculated Pseudomonas putida CH11 and Arthrobacter oxydans CH8. The results showed that H2S removal efficiency for the system was not affected by inlet NH3 concentrations. In addition, no acidification was observed in the BAC biofilter. High buffer capacity and low moisture demand were also advantages of this system. The maximal inlet loading and critical loading for the system were 18.9 and 7.7 g‐H2S m−3 h−1, respectively. The results of this study could be used as a guide for the further design and operation of industrial‐scale systems. Copyright © 2004 Society of Chemical Industry

The Lennox Oil and Gas Field, Block 110/15, East Irish Sea

Abstract The Lennox Field, located in blocks 110/15 and 110/14, was the second oil field to be developed in the East Irish Sea Basin. It contains 184 MMBBL of oil in-place within a 143 ft thick oil rim overlain by a large gas cap up to 750 ft thick. The GIIP is estimated to be 497 BCF. The field came on stream in February 1996, and it is now being developed with seven horizontal oil producers, including two multi-lateral wells and two crestal gas injectors. Production from the field can be divided into two distinct phases; the oil rim development phase, and the gas cap blow-down phase. The latter phase is currently anticipated to commence in 2004. The field structure consists of a roll-over anticline formed in the hanging wall of the Formby Point Fault during extensional faulting in Triassic-early Jurassic times, and later readjusted by contractional movements during Tertiary inversion. The oil and gas are trapped in the highly productive Triassic Ormskirk Sandstone Formation. The reservoir comprise high porosity aeolian and fluvial sandstones occurring at a shallow depth ( c. 2500 ft) with a maximum gas column of 750 ft above an oil rim of 143 ft. The reservoir quality is principally controlled by primary depositional processes as no significant adverse diagenetic effects are observed. The hydrocarbon filling history was complex, with at least three phases of oil and gas generation. The field contains a light, saturated oil (45° API) with a GOR of 650 SCF/BBL. The crude contains high levels of H 2 S (0.1 mol%) and mercaptans (450 ppm), which are removed during processing at the Douglas complex. Water cut from the field is currently around 2-5%, and no free gas production has been observed to date. Gas production from Lennox is anticipated to start in 2004.

The Douglas Oil Fields, Block 110/13b, East Irish Sea

Abstract The Douglas Field, on stream in February 1996, is the first oil field to be developed in the East Irish Sea Basin, with an estimated STOIIP of 202 MMBBL. The field structure consists of three tilted fault blocks formed during extensional faulting in Triassic-early Jurassic times, and later readjusted by contractional movements during Tertiary inversion. The oil is trapped in the Triassic Ormskirk Sandstone Formation, which comprises moderate to high porosity aeolian and fluvial sandstones. The reservoir depth is shallow (2140 ft) with a maximum oil column of 375 ft. The reservoir can be divided into several laterally extensive units based on vertical facies variations. The reservoir quality is principally controlled by primary depositional processes, and authigenic clay minerals are not important. However, bitumen is formed extensively in specific areas of the field causing significant permeability reduction. The hydrocarbon filling history of the field was complex, with the occurrence of at least two phases of oil generation and migration. The field contains a relatively 'dead' oil with a low GOR (170scf/bbl). Pressure maintenance is achieved through sea water injection, and to date ten production and six injection wells have been drilled. The crude is light (44° API) and contains high levels of H2S (0.5mol%) and mercaptans, which are removed during processing offshore.

Crystal structure of cystalysin from Treponema denticola: a pyridoxal 5'-phosphate-dependent protein acting as a haemolytic enzyme.

Cystalysin is a C(beta)-S(gamma) lyase from the oral pathogen Treponema denticola catabolyzing L-cysteine to produce pyruvate, ammonia and H(2)S. With its ability to induce cell lysis, cystalysin represents a new class of pyridoxal 5'-phosphate (PLP)-dependent virulence factors. The crystal structure of cystalysin was solved at 1.9 A resolution and revealed a folding and quaternary arrangement similar to aminotransferases. Based on the active site architecture, a detailed catalytic mechanism is proposed for the catabolism of S-containing amino acid substrates yielding H(2)S and cysteine persulfide. Since no homologies were observed with known haemolysins the cytotoxicity of cystalysin is attributed to this chemical reaction. Analysis of the cystalysin-L-aminoethoxyvinylglycine (AVG) complex revealed a 'dead end' ketimine PLP derivative, resulting in a total loss of enzyme activity. Cystalysin represents an essential factor of adult periodontitis, therefore the structure of the cystalysin-AVG complex may provide the chemical basis for rational drug design.

Biological prevention and removal of hydrogen sulphide in sludge at Lillehammer Wastewater Treatment Plant

Formation of H2S and other odorous compounds in sludge can be prevented efficiently by controlled dosage of nitrate. Lillehammer WWTP (N) had problems with malodour that originated mainly from the sludge treatment. Highlevels of H2S caused poor working conditions, and resulted in an overloaded hypochlorite scrubber. In addition, neighbours were complaining. Controlled dosing was necessary to avoid increased loads on the nitrogen removal process and floating sludge in the thickener, and to keep the H2S concentration and chemical costs low. This resulted in considerably better working environment and eliminated complaints from neighbours. A cost-benefit for Nutriox® Septicity Control has been performed.

Anomalous enrichments of iron monosulfide in euxinic marine sediments and the role of H 2 S in iron sulfide transformations; examples from Effingham Inlet, Orca Basin, and the Black Sea

It is well documented that sedimentary pyrite formation proceeds through an iron monosulfide (FeS) precursor. Laboratory studies have tradition- ally indicated that intermediate S species such as elemental sulfur (S 0 ) or polysul- fides (Sx 2 ) are responsible for the transformation of FeS to pyrite (FeS2). Recent experimental work, however, has suggested that H2S may also be responsible for the transformation. The present study extrapolates reaction pathways respon- sible for pyrite formation in the laboratory to two fundamentally different modern anoxic marine systems. We hypothesize that on decadal timescales, H2S (or HS) is responsible for transformations of FeS into FeS2 in natural systems where intermediate S species are isolated from FeS production. The possibility of prolonged coexistence of high levels of H2S and FeS, however, challenges recent experimental predictions of extremely rapid transformations (that is, timescales of hours or less) of FeS to FeS2 via the H2S pathway. Sediments of Effingham Inlet (a fjord on Vancouver Island) and the Orca Basin (an intraslope brine pool in the northern Gulf of Mexico) are both charac- terized by atypically high concentrations of FeS but contrasting levels of H2S and FeS2 production. In both systems, FeS formation is spatially decoupled from intermediate S species as a consequence of either rapid deposition/burial or extreme water-column stratification. Within settings that promote this separa- tion, H2S may be the principal species responsible for pyrite formation. FeS to FeS2 transformations are favored by the high concentrations of H2S in sediments of Effingham Inlet. Additional results from the margin of the anoxic Black Sea corroborate the Effingham model for iron sulfide transformation. H2S concentrations are controlled by the amount of bacterial sulfate reduc- tion and the availability of reactive Fe. H2S concentrations will be buffered to low levels via the production of FeS in systems with appreciable amounts of reactive Fe and therefore be unavailable to transform FeS to FeS2. Under conditions where H2S is the only species available for FeS to FeS2 transformations, some degree of Fe limitation may promote pyrite formation by allowing H2 St o accumulate in the pore waters. Ultimately, this balance between H2S production and reactive Fe availability may strongly influence the amount of pyrite formed in anoxic systems.

Sulfide Removal and Prevention in Gas Wells

Summary Major problems in oil and gas operations result from the biogenic formation of H2S in the reservoir. The presence of H2S results in increased corrosion, iron sulfide formation, higher operating costs, reduced revenue, and constitutes a serious environmental and health hazard. A new technology that removes and prevents the formation of biogenic H2S has been developed. The technology is based on the addition of low concentrations of a water-soluble nutrient solution, which selectively stimulates the growth of an indigenous microbial population, thereby inhibiting the detrimental sulfate-reducing bacteria (SRB) population, which causes the generation of H2S. This deliberate and controlled modification of the microflora and reservoir ecology has been termed biocompetitive exclusion. This directed alteration of the microbial ecology is achieved by the introduction of a nutrient formulation that favorably influences the dynamics of the reservoir microflora. The treatment system does not require the addition of microbial cultures. Periodic well treatments have been shown to dramatically reduce or completely eliminate sulfide levels and establish control of the system in diverse field demonstrations supported by the U.S. Dept. of Energy. Field data in a variety of reservoirs will be presented that demonstrate the effectiveness of this new approach to treating and remediating wells with high levels of H2S. The versatility and low cost of this novel technology offers the petroleum industry a practical and cost effective methodology for the control of H2S in oil and gas wells.

Polioencephalomalacia.

Polioencephalomalacia (PEM) is a neuropathologic condition of ruminants that can be induced by a variety of neural metabolic disruptions. These include altered thiamine status, water deprivation-sodium ion toxicosis, lead poisoning, and high sulfur intake. Investigations of sulfur-related PEM have demonstrated that the onset of the clinical signs coincides with excessive ruminal sulfide production. A number of ruminal factors could modulate the production and absorption of ruminal sulfide. The development of a convenient method to estimate ruminal gas cap H2S has made it possible to identify cattle with high levels of ruminal H2S and evaluate their risk of developing PEM.

Theoretical limiting prediction of H2S removal efficiency from coal gasification streams using an intermediate temperature electrochemical separation process

A mathematical model has been developed to predict the theoretical limiting H2S removal efficiency of an electrochemical membrane separator (EMS) in the presence of overwhelming levels of H2O and CO2 (as would be found in syn-gas). Thermodynamic principles gave the minimum potential requirements for cell operation. Factors including electrokinetics, mass transfer, chemical equilibria and internal resistance, occuring with application of current, were incorporated into the prediction. Theoretical predictions, which represent a limiting value, show achievable current efficiencies close to 100% for high H2S levels (1000ppm) at 90% removal. At this same removal level with 100 or 10ppm inlet gas, the predicted maximum current efficiencies dropped, due to concentration effects, to 93% and 40%, respectively. This solidifies the economic importance of obtaining close to 100% current efficiencies at sour gas levels compared to polishing applications where the removal, not the current efficiency, is more important. Predicted cell potentials were consistently in the same range, −0.450 to −0.550V, for all concentration levels at 90% removal. Comparison with experimental data gave good agreement; actual current efficiencies were consistently within 15% of the maximum predicted values at coinciding removal levels. However, actual potentials were lower (less negative) because of hydrogen leakage through the cell membrane. While lower potentials require less power, sulfur production at the anode was reduced.