Increasing CO2 Partial Pressure Research Articles

Carbonic Anhydrase Mutants in Zea mays Have Altered Stomatal Responses to Environmental Signals.

Stomata regulate transpirational water loss and CO2 uptake for photosynthesis in response to changing environmental conditions. Research investigating stomatal movement has mostly been conducted in C3 eudicot species, which have very different CO2 requirements for photosynthesis relative to C4 grasses. Carbonic anhydrase (CA) catalyzes the hydration of CO2, and its activity has been linked to stomatal aperture regulation in eudicots. The number of Ca genes and their evolutionary history differ between monocots and dicots, and many questions remain unanswered about potential neofunctionalization and subfunctionalization of grass Ca paralogs and their roles in photosynthesis and stomatal conductance. To investigate the roles of different Ca genes in maize (Zea mays), we examined stomatal responses in ca1 and ca2 single mutants as well as a ca1ca2 double mutant. The ca1 and ca2 single mutants had 10% and 87% of the CA activity exhibited by the wild type, respectively, while ca1ca2 had less than 5% of wild-type CA activity. The ca mutants had higher stomatal conductance than the wild type and slower stomatal closure in response to increases in CO2 partial pressure. Contrary to previous reports in eudicots, ca mutants showed slowed stomatal closure in response to the light-dark transition and did not show differences in stomatal density compared with the wild type. These results implicate CA-mediated signaling in the control of stomatal movement but not stomatal development. Drought experiments with ca1ca2 mutant plants suggest a role for CA in water-use efficiency and reveal that Z. mays is not optimized for water-use efficiency under well-watered conditions.

Enhancement of CO2 solubility in a mixture of 40 wt% aqueous N-Methyldiethanolamine solution and diethylenetriamine functionalized graphene oxide

Graphene oxide functionalized by diethylenetriamine (DETA) was prepared and characterized with SEM, XRD, BET, TGA and IR spectroscopy techniques to find out its morphology, crystalline building, porous structure, thermal stability and functional groups. The CO2 solubility in 40 wt% aqueous amine solution, 40 wt% aqueous amine solution +0.1 wt% GO, and 40 wt% aqueous amine solution +0.1 wt% DETA-GO is determined. The solubility measurements were performed at three temperature (303.15, 313.15 and 323.15 K) and CO2 partial pressures up to 2200 kPa. Addition of GO and DETA-GO to MDEA (N-Methyldiethanolamine) solution enhanced the CO2 adsorption capacity of the aqueous amine solution up to 7.5% and 12.5%, respectively. Increasing CO2 partial pressure and decreasing temperature enhanced the CO2 solubility.

Thermodynamic Equilibrium Solubility of Diethanolamine – N-Butyl-1-Methylpyrrolidinium Dicyanamide [DEABMPYRR DCA] Mixtures for Carbon Dioxide Capture

Solubility data of carbon dioxide (CO2) in aqueous Diethanolamine (DEA) blended with pyrrolidinium-based ionic liquid: N-Butyl-1-Methylpyrrolidinium Dıcyanamıde [Bmpyrr][DCA] are presented at various temperatures (313.15K-333.15K) and pressure up to about 700 psi. The concentration of [Bmpyrr][DCA] ranges from 0-10wt% and 30-40wt% for DEA. The solubility of CO2 was evaluated by measuring the pressure drop in high pressure stirred absorption cell reactor. The CO2 loading in all studied mixtures increases with an increase in CO2 partial pressure and decreases with temperature. It was also found that the CO2 loading capacity decrease as the concentration of [Bmpyrr][DCA] increases. The experimental data were correlated as a function of temperature and CO2 partial pressure to predict the solubility of CO2 in the mixtures. It was found that the model predicted results in a good agreement with experimental value.

Oxidative stress in the hydrocoral Millepora alcicornis exposed to CO2-driven seawater acidification

Global impacts are affecting negatively coral reefs’ health worldwide. Ocean acidification associated with the increasing CO2 partial pressure in the atmosphere can potentially induce oxidative stress with consequent cellular damage in corals and hydrocorals. In the present study, parameters related to oxidative status were evaluated in the hydrocoral Millepora alcicornis exposed to three different levels of seawater acidification using a mesocosm system. CO2-driven acidification of seawater was performed until reaching 0.3, 0.6 and 0.9 pH units below the current pH of seawater pumped from the coral reef adjacent to the mesocosm. Therefore, treatments corresponded to control (pH 8.1), mild (pH 7.8), intermediate (pH 7.5) and severe (pH 7.2) seawater acidification. After 0, 16 and 30 d of exposure, hydrocorals were collected and the following parameters were analyzed in the holobiont: antioxidant capacity against peroxyl radicals (ACAP), total glutathione (GSHt) concentration, reduced (GSH) and oxidized (GSSG) glutathione ratio (GSH/GSSG), lipid peroxidation (LPO) and protein carbonyl group (PC) levels. ACAP was increased in hydrocorals after 16 d of exposure to intermediate levels of seawater acidification. GSHt and GSH/GSSG did not change over the experimental period. LPO was increased at any level of seawater acidification, while PC content was increased in hydrocorals exposed to intermediate and severe seawater acidification for 30 d. These findings indicate that the antioxidant defense system of M. alcicornis is capable of coping with acidic conditions for a short period of time (16 d). Additionally, they clearly show that a long-term (30 d) exposure to seawater acidification induces oxidative stress with consequent oxidative damage to lipids and proteins, which could compromise hydrocoral health.

Agglomeration mechanism in biomass fluidized bed combustion – Reaction between potassium carbonate and silica sand

Agglomeration is one of the operational problems in fluidized bed combustion of biomass, which is caused by interaction between bed materials (e.g. silica sand) and the biomass ash with a high content of potassium species. However, the contribution of different potassium species to agglomeration is not fully understood yet. In the present work, the reaction between K2CO3 and silica sand has been studied extensively by thermogravimetric analysis. The reacted samples were analyzed by SEM-EDX to reveal the reaction mechanism. The results indicated that the reaction occurs in a solid-solid phase already at temperatures around 700°C. The reaction rate increases with increasing temperature, but decreases with an increase of CO2 partial pressure. Using smaller particle size and well mixed solid reactants results in an increased reaction rate. It is observed that the reaction initiates in the contact area between K2CO3 and silica sand, forming a thin product layer. The layer acted as a reactive media further reacting with K2CO3 and silica sand. The results provide a basis for understanding of potassium induced agglomeration process in fluidized bed biomass combustion.

Satellite Evidence that E. huxleyi Phytoplankton Blooms Weaken Marine Carbon Sinks

AbstractPhytoplankton blooms of the coccolithophore Emiliania huxleyi are known to produce CO2, causing less uptake of atmospheric CO2 by the ocean, but a global assessment of this phenomenon has so far not been quantified. Therefore, here we quantify the increase in CO2 partial pressure (ΔpCO2) at the ocean surface within E. huxleyi blooms for polar and subpolar seas using an 18 year ocean color time series (1998–2015). When normalized to pCO2 in the absence of bloom, the mean and maximum ΔpCO2 values within the bloom areas varied between 21.0%–43.3% and 31.6%–62.5%, respectively. These results might have appreciable implications for climatology, marine chemistry, and ecology.

تاثیر فشار جزئی گاز کاربن دای اکساید بالای ریفورمینگ ایتانول بطریقه خشک برای تولید هایدروجن (Effect of CO <sub>2</sub> Partial Pressure on Dry Reforming of Ethanol for Hydrogen Production)

Persian Abstract: تاثیر فشار جزئی کاربن دای اکساید در ریفورمینگ ایتانول به طریقه خشک باالی کتلست Al2O3/Co%10-Ce%5 در فشار های گاز کاربن دای اکساید از 20 الی 50 کیلو پاسکال، فشار ایتانول 20 کیلوپاسکال، حرارت 973 درجه کلوین وتحت فشار اتمسفیری ارزیابی گردیده است. کتلست بطریقه اشباع سازی مرطوب آماده گردیده و در دستگاه با بستر ثابت امتحان شده است. فاز های اکساید کوبالت Co3O4 ،اسپینل اکساید CoAl2O4 و اکساید سیریم CeO2با استفاده از انالیز XRD در سطح کتلست تشکیل شده است. اکساید های سیریم و کوبالت درجریان پروگرام حرارتی کلسینه g 1 -شدن بدست آمده است. کتلست Al2O3/Co%10-Ce%5 دارای مساحت سطح بلند 2 m 35.137 میباشد. ایتانول و کاربن دای اکساید تبدیل شده با افزایش فشار جزئی گاز کاربن دای اکساید از 20 الی 50 کیلو پاسکال، افزایش نموده درحالیکه مقدار مطلوب محصول هایدروجن و کاربن مونواکساید در فشار 50 کیلو پاسکال بدست آمده است. English Abstract: The effect of CO2 partial pressure on ethanol dry reforming was evaluated over 5%Ce-10%Co/Al2O3 catalyst at = PCO2 = 20-50 kPa, PC2H5OH = 20 kPa, reaction temperature of 973 K under atmospheric pressure. The catalyst was prepared by using impregnation method and tested in a fixed-bed reactor. X-ray diffraction measurements studied the formation of Co3O4, spinel CoAl2O4 and CeO2, phases on surface of 5%Ce-10%Co/Al2O3 catalyst. CeO2, CoO and Co3O4 oxides were obtained during temperature–programmed calcination. Ce-promoted 10%Co/Al2O3 catalyst possessed high BET surface area of 137.35 m2 g-1. C2H5OH and CO2 conversions was improved with increasing CO2 partial pressure from 20-50 kPa whilst the optimal selectivity of H2 and CO was achieved at 50 kPa.

Reduction Kinetics of Ilmenite Ore for Pressurized Chemical Looping Combustion of Simulated Natural Gas

Reduction kinetics of ilmenite ore as an oxygen carrier for the chemical looping combustion of a simulated natural gas mixture under elevated pressure was studied using a pressurized thermogravimetric analyzer (PTGA). The fuel gas is a mixture of hydrocarbon, carbon dioxide, and nitrogen to simulate an actual combustion environment. The oxidation phase of the experiments was carried out in air. Effects of temperature (1023–1223 K), total pressure (0.6–1.6 MPa), fuel partial pressure (0.126–0.34 MPa), and CO2 partial pressure (pFuel/pCO2 = 0.5–1) were studied. The results showed that the presence of small amounts of ethane and propane clearly led to a higher ilmenite reactivity at temperatures below 1123 K, but this effect became less significant as temperature increased and completely disappeared above 1123 K. The results also showed that increasing CO2 partial pressure had little effect on ilmenite conversion rate, though it did have some slightly negative influence on ilmenite oxygen carrying capacity t...

High-pressure absorption study of CO2 in aqueous N-methyldiethanolamine (MDEA) and MDEA-piperazine (PZ)-1-butyl-3-methylimidazolium trifluoromethanesulfonate [bmim][OTf] hybrid solvents

In present study, high pressure CO2 absorption performance of aqueous N-methyldiethanolamine (MDEA) and its hybrid solvents with anhydrous perazine (PZ) and ionic liquid (IL) 1-butyl-3-methylimidazolium trifluoromethanesulfonate [bmim][OTf] were investigated. The absorption performance of hybrid solvents were carried out to investigate CO2 loading capacity (mol of CO2/mol of solvent), and apparent absorption rate (CO2 capture efficiency, overall rate constant). The CO2 loading capacity of aqueous MDEA and its hybrid solvents were experimentally investigated for a wide range of compositions between pressure ranges of 2 to 50bar and at three different temperatures (303.15, 313.15, and 333.15K). Furthermore, apparent absorption rate performance of hybrid solvents were determined at 303.15K temperature and 2bar pressure. The effect of temperature, CO2 partial pressure, and ionic liquid (IL) concentrations on CO2 loading of aqueous IL-amines hybrid solvents were also investigated. The results indicated that CO2 loading of hybrid solvents were increased with increase in CO2 partial pressure and IL concentration (up to 10wt%), further increased concentration of IL suppressed CO2 loading capacity. The CO2 loading capacity of hybrid solvents were also reduced with rise in system's temperature. The addition of IL and anhydrous PZ significantly enhanced CO2 capture efficiency (nCO2) and overall absorption rate constant (k) of aqueous MDEA solvent.

Growth and nephrocalcinosis for Atlantic salmon (Salmo salar L.) post-smolt exposed to elevated carbon dioxide partial pressures

Atlantic salmon (Salmo salar L.) post-smolt were reared at six different water CO2 partial pressures (0.6 control, 2.6, 5.5, 8.0, 10.4 and 11.6mmHg) in duplicate 500L tanks for 12weeks in 34‰ sea water at 10°C. Weight samplings divided the experiment into four periods (Periods I–IV). Plasma chloride concentration decreased linearly with increasing CO2 partial pressure in the water and the changes lasted during the four periods (p<0.05). During Period I and II, polynomial models described the significant relationship between PCO2 and specific growth rate (p<0.05). For both these periods, SGR declined between 8 and 10mmHg. No significant relationship between PCO2 and SGR was found during period III (p>0.05), however during period IV SGR decreased linearly as a function of PCO2 in the range 0.6–12mmHg (p<0.05). Condition factor decreased linearly with increasing CO2 concentration on day 19, 36, 65 and 77 (p<0.05), representing all four periods. Nephrocalcinosis was not observed in the control group, in the low group or in the medium group (medians in the range 0.6–5.5mmHg, which corresponds to 2–15mgL−1) at the end of the experiment. At the three highest PCO2 levels (medians in the range 8.0–11.6mmHg or about 21–30mgL−1), 9 of 26 fish (34%) developed nephrocalcinosis (p<0.05).

Effective control of Poterioochromonas malhamensis in pilot-scale culture of Chlorella sorokiniana GT-1 by maintaining CO2-mediated low culture pH

Although predators in microalgal culture can often be protozoa reducing biomass productivity and culture stability, there are few effective approaches to control them. This study investigated the effect of culture pH (i.e., 6.0, 6.5, 7.0 and 7.5) maintained by supply of compressed air bubbles containing various concentrations of CO2 on death of the flagellate Poterioochromonas malhamensis and several other protozoa in the culture of the green microalgae Chlorella sorokiniana GT-1. C. sorokiniana GT-1 grew well at pH6.0 and 6.5 and a sustainable biomass concentration of 1.61gL−1 was obtained from the cultures maintained at pH6.5. The cultures maintained at pH7.0 and 7.5 collapsed on days 7 and 4 of culture, respectively, as a result of contamination by P. malhamensis and to less extent by other protozoa (e.g., ciliates and amoebae). Further experiments revealed that it was the actual dissolved CO2, not the low pH itself, or reduced dissolved oxygen in the culture medium that prevented the occurrence of P. malhamensis. It is speculated that increased CO2 partial pressure in the culture media may enhance diffusion of CO2 into the cytoplasm of P. malhamensis that lowers the intercellular pH, and thus results in cell death. The method developed in this study can be effective in protozoan control in pilot-scale Chlorella culture in an open raceway pond. It is suggested that a low pH maintained temporarily or constantly by supply of CO2 may be a promising approach to control P. malhamensis and alike in microalgal culture.

Experimental investigation of CO2 removal using Piperazine solution in a stirrer bubble column

In the present work, absorption of carbon dioxide into Piperazine solution was investigated experimentally in a pilot scale stirrer bubble column. In the experiments, mass transfer and hydrodynamics parameters including loading, removal efficiency, absorption flux and mass transfer coefficients at various volumetric liquid and CO2 flow rate, absorbent concentration, and stirrer speed were studied. The experiments were carried out at 295.15K temperature and atmospheric pressure under the Piperazine concentration in range of 0.1–0.5moll−1, CO2 partial pressure range 16.0–35.2kPa, stirrer speed range in range of 0–300rpm and liquid flow rate in range of 0.5–2.0lh−1.The results showed that mass transfer flux, overall mass transfer coefficient, driving force and CO2removal efficiency were varied in the range of (6.18–15.99)×10−6 kmolm−2s−1, (2.39–2.58)×10−6 kmolm−2s−1kPa−1, 200–1400Pa, and 65.5–82.1%, respectively. The hydrodynamics studies indicate that the gas holdups and the Sauter mean diameter in the bubble column increase with increasing CO2 partial pressure. CO2 partial pressure influence depends on the Piperazine concentration. This positive influence of partial pressure emanates from the smaller bubbles formation. Also increasing the CO2 partial pressure in the range of 16.0–35.2kPa, increases the gas holdup and Sauter mean diameter up to about 48%.

Investigation of solubility of carbon dioxide in anhydrous milk fat by lab-scale manometric method

This study aims to examine the solubility of CO2 in anhydrous milk fat (AMF) as functions of partial pressure, temperature, chemical composition and physical state of AMF. AMF was fractionated at 21°C to obtain stearin and olein fractions. The CO2 solubility was measured using a home-made experimental apparatus based on changes of CO2 partial pressures. The apparatus was found to be reliable as the measured and theoretical values based on the ideal gas law were comparable. The dissolved CO2 concentration in AMF increased with an increase in CO2 partial pressure (0–101kPa). The apparent CO2 solubility coefficients (molkg−1Pa−1) in the AMF were 5.75±0.16×10−7, 3.9±0.19×10−7 and 1.19±0.14×10−7 at 35, 24 and 4°C, respectively. Higher liquid oil proportions resulted in higher CO2 solubility in the AMF. There was insignificant difference in the dissolved CO2 concentration among the AMF, stearin and olein fractions in their liquid state at 40°C.

Changes in Physiological Variables During Slow‐ and Rapid‐Onset Airway Obstruction in Swine

Airway compromise is a significant cause of death in emergency and battlefield settings. While novel airway management devices are available, there is no reproducible animal model of airway obstruction for testing these new product solutions. The goals of this study were to develop a slow‐ and rapid‐onset model of airway obstruction and compare changes in blood gas and cardiovascular parameters. Female swine were anesthetized, intubated, and instrumented for blood sampling and arterial blood pressure and heart rate recordings. Pigs were allowed to breathe spontaneously and a hemostatic clamp on the endotracheal tube was either slowly ratcheted closed over 30 minutes (slow‐onset) or fully clamped immediately (rapid‐onset) until a real‐time pulse oximeter reading of 70% or below was attained. Maximal decreases in blood oxygen saturation (Slow: −66±10% vs Fast: −49±5%) and oxygen partial pressure (Slow: −70±14 mmHg vs Fast: −96±12 mmHg) did not differ (P&gt;0.05) between slow and rapid‐onset obstructions. In contrast, the increase in CO2 partial pressure was significantly greater during slow (23±1 mmHg) vs rapid (13±2 mmHg, P&lt;0.001) obstruction. Surprisingly, mean arterial pressure did not change significantly from baseline during either slow‐(Baseline: 109±8 mmHg vs Obstruction: 112±12 mmHg) or fast‐onset (Baseline: 105±7 mmHg vs Obstruction: 104±8 mmHg) obstruction. Heart rate significantly increased during slow‐onset obstruction (Baseline: 70 ± 8 bpm vs Obstruction: 88±11 bpm, P&lt;0.05) but was unchanged during fast‐onset obstruction (Baseline: 72±7 bpm vs Obstruction: 80±5 bpm). The changes in mean arterial pressure (Slow: 3±9 mmHg vs Fast: −1±5 mmHg) and heart rate (Slow: 19±5 vs Fast: 8±6 mmHg, p=0.09) were not significantly different between groups. In conclusion, our model of slow‐ and fast‐onset airway obstruction induced significant hypoxemia and hypercapnia similar to what is expected during airway compromise and shows promise for use in testing components of airway management devices. Further studies are needed to determine whether obstruction for longer time periods (to induce a greater reduction in real‐time pulse oximetry blood oxygen levels) will cause greater cardiovascular changes.

Syngas production from methane dry reforming over Ni/SBA-15 catalyst: Effect of operating parameters

The influence of operating conditions including reactant partial pressure and reaction temperature on the catalytic performance of 10%Ni/SBA-15 catalyst for methane dry reforming (MDR) reaction has been investigated in this study. MDR reaction was carried out under atmospheric pressure at varying CH4/CO2 volume ratios of 3:1 to 1:3 and 923–1023 K in a tubular fixed-bed reactor. SBA-15 supported Ni catalyst exhibited high specific surface area of 444.96 m2 g−1 and NiO phase with average crystallite size of 27 nm was detected on catalyst surface by X-ray diffraction and Raman measurements. H2 temperature-programmed reaction shows that NiO particles were reduced to metallic Ni0 phase with degree of reduction of about 90.1% and the reduction temperature depended on the extent of metal-support interaction and confinement effect of mesoporous silica support. Catalytic activity appeared to be stable for 4 h on-stream at 973–1023 K whilst a slight drop in activity was observed at 923 K probably due to deposited carbon formed by thermodynamically favored CH4 decomposition reaction. Both CH4 and CO2 conversions increased with rising reaction temperature and reaching about 91% and 94%, respectively at 1023 K with CO2 and CH4 partial pressure of 20 kPa. CH4 conversion improved with increasing CO2 partial pressure, PCO2 and exhibited an optimum at PCO2 of 30–50 kPa depending on reaction temperature whilst a substantial decline in CO2 conversion was observed with growing PCO2. Additionally, CH4 and CO2 conversions decreased significantly with rising CH4 partial pressure because of increasing carbon formation rate via CH4 cracking in CH4-rich feed. Post-reaction characterization shows that active Ni metal phase was not re-oxidized to inactive metal oxide during MDR reaction. The heterogeneous nature of deposited carbons including carbon nanofilament and graphite was detected on catalyst surface by Raman measurement.

Inhibition Behavior of an Imidazoline Inhibitor for Carbon Steel in a Supercritical CO2/H2O System

The inhibition effect of a synthesized imidazoline inhibitor on carbon steel in a supercritical CO2-H2O system was investigated using weight loss measurement, electrochemical tests, and surface analyses. In the presence of the imidazoline inhibitor, the corrosion rate and corrosion process showed minimal change with increasing CO2 partial pressure under non-supercritical CO2 conditions, whereas the corrosion rate clearly increased and the corrosion process greatly differed when the supercritical CO2 condition was reached. The introduction of KI substantially decreased the corrosion rate in the supercritical CO2 condition. The excess surface charge of the carbon steel changed from negative to positive as the partial pressure of CO2 increased to the supercritical condition, thereby hindering the adsorption of imidazoline inhibitor, which in turn decreased the inhibition efficiency.

Carbonation Performance of NaNO3 Modified MgO Sorbents

NaNO3 modified MgO sorbents have a large theoretical CO2 capture capacity, but their practical capture performance at medium temperatures (350–400 °C) is poor for the high thermodynamic equilibrium partial pressure of CO2 at these temperatures. The thermodynamic limitations for NaNO3 modified MgO sorbents can be relaxed by adding alkali or alkaline earth carbonates, and the effective carbonation temperature can be shifted to the higher temperatures (350–400 °C) to satisfy the requirement of fast kinetic reactions. In this paper, the CO2 absorption characteristics of NaNO3 modified MgO with or without CaCO3 are compared experimentally to verify the promoting effects of CaCO3. Based on the CaCO3 promoting theory, the methods of stage heating during carbonation and partial decomposition during regeneration were adopted to improve the CO2 absorption ability of NaNO3 modified MgO sorbents at 350 °C. Combined with the composition of fuel gas, effects of increasing CO2 partial pressure and H2O were tested, and t...

Kinetic study of methane reforming with carbon dioxide over NiCeMgAl bimodal pore catalyst

The kinetic behavior of NiCeMgAl bimodal pore catalyst for methane reforming with CO2 was investigated after the elimination of external and internal diffusion effects in a fixed‐bed reactor as a function of temperature and partial pressures of reactants and products. Increase in CO2 partial pressure favors the consumptions of CH4 and CO2 but inhibits the formation of H2 due to the existence of reverse water gas shift (RWGS) reaction. The reforming rate increased first and then reached a horizontal stage with the rise of CH4 partial pressure. A Langmuir–Hinshelwood model was developed assuming that the carbon deposition is ignorable but the RWGS reaction is non‐ignorable and the removal of adsorbed carbon intermediate is the rate‐determining step. A nonlinear least‐square method was applied to solve the kinetic parameters. The derived kinetic expression fits the experimental data very well with a R2 above 0.97, and also predicts the products flow rate satisfactorily. © 2016 American Institute of Chemical Engineers AIChE J, 63: 2019–2029, 2017

Thermodynamic and Kinetic Response of Microbial Reactions to High CO2.

Geological carbon sequestration captures CO2 from industrial sources and stores the CO2 in subsurface reservoirs, a viable strategy for mitigating global climate change. In assessing the environmental impact of the strategy, a key question is how microbial reactions respond to the elevated CO2 concentration. This study uses biogeochemical modeling to explore the influence of CO2 on the thermodynamics and kinetics of common microbial reactions in subsurface environments, including syntrophic oxidation, iron reduction, sulfate reduction, and methanogenesis. The results show that increasing CO2 levels decreases groundwater pH and modulates chemical speciation of weak acids in groundwater, which in turn affect microbial reactions in different ways and to different extents. Specifically, a thermodynamic analysis shows that increasing CO2 partial pressure lowers the energy available from syntrophic oxidation and acetoclastic methanogenesis, but raises the available energy of microbial iron reduction, hydrogenotrophic sulfate reduction and methanogenesis. Kinetic modeling suggests that high CO2 has the potential of inhibiting microbial sulfate reduction while promoting iron reduction. These results are consistent with the observations of previous laboratory and field studies, and highlight the complexity in microbiological responses to elevated CO2 abundance, and the potential power of biogeochemical modeling in evaluating and quantifying these responses.

Comparative Analysis of Carbon Monoxide Tolerance among Thermoanaerobacter Species.

An anaerobic thermophilic strain (strain PCO) was isolated from a syngas-converting enrichment culture. Syngas components cannot be used by strain PCO, but the new strain is very tolerant to carbon monoxide (pCO = 1.7 × 105 Pa, 100% CO). 16S rRNA gene analysis and DNA-DNA hybridization revealed that strain PCO is a strain of Thermoanaerobacter thermohydrosulfuricus. The physiology of strain PCO and other Thermoanaerobacter species was compared, focusing on their tolerance to carbon monoxide. T. thermohydrosulfuricus, T. brockii subsp. finnii, T. pseudethanolicus, and T. wiegelii were exposed to increased CO concentrations in the headspace, while growth, glucose consumption and product formation were monitored. Remarkably, glucose conversion rates by Thermoanaerobacter species were not affected by CO. All the tested strains fermented glucose to mainly lactate, ethanol, acetate, and hydrogen, but final product concentrations differed. In the presence of CO, ethanol production was generally less affected, but H2 production decreased with increasing CO partial pressure. This study highlights the CO resistance of Thermoanaerobacter species.