The effect of CO2 ventilation on kinetics and yields of cell-mass and ethanol in batch cultures ofZymomonas mobilis

Summary The effect of CO₂ removal by continuous sparging of N₂ in batch cultures ofZymomonas mobilis (ATCC10988) was examined. N₂ sparging considerably reduces lag times in batch cultures, possibly because of continuous removal of CO₂ from the culture media. Ventilation of CO₂ from culture media results in an increase of about 15% in the average specific growth rate and about 12% in the cell-mass yield with no noticeable trend in the average specific glucose uptake and ethanol production rates. The overall ethanol yield on glucose, however, decreases slightly by 5%. Analysis of ventilated experiments show that the CO₂ production is directly coupled with the ethanol formation but not necessarily with the cell-mass production, indicating a decoupling of growth from ethanol production. Further, comparison of ventilated and non-ventilated experiments rules out the possibility of CO₂ accumulation in the culture media as a factor responsible for increasing growth inhibition and decoupling of growth from ethanol fermentation at increasing initial glucose concentrations in batch cultures.     

The influence of H2, CO2 and dilution rate on the continuous fermentation of acetone-butanol

Summary The effect of product gases, H₂ and CO₂, on solvent production was studied using a continuous culture of alginate-immobilized Clostridium acetobutylicum. Initially, in order to find the optimum dilution rate for aceton--butanol production in this system, fermentations were carried out at various dilution rates. With 10% H₂ and 10% CO₂ in the sparging gas, a dilution rate of 0.07 h^–1 was found to maximize volumetric productivity (0.58 g·l^–1·h^–1), while the maximum specific productivity of 0.27 g^–·h^–1 occured at 0.12 h^–1. Continuous cultures with vigorous sparging of N₂ produced only acids. It was concluded that in the case of continuous fermentation H₂ is essential for good solvent production, although good solvent production is possible in an H₂-absent environment in the case of batch fermentations. When the fermentation was carried out at atmospheric pressure under H₂-enriched conditions, the presence of CO₂ in the sparging gas did not slow down glucose metabolism; rather it changed the direction of the phosphoroclastic reaction and as a result increased the butanol/acetone ratio.     

Improving the yield from fermentative hydrogen production

Efforts to increase H₂ yields from fermentative H₂ production include heat treatment of the inoculum, dissolved gas removal, and varying the organic loading rate. Although heat treatment kills methanogens and selects for spore-forming bacteria, the available evidence indicates H₂ yields are not maximized compared to bromoethanesulfonate, iodopropane, or perchloric acid pre-treatments and spore-forming acetogens are not killed. Operational controls (low pH, short solids retention time) can replace heat treatment. Gas sparging increases H₂ yields compared to un-sparged reactors, but no relationship exists between the sparging rate and H₂ yield. Lower sparging rates may improve the H₂ yield with less energy input and product dilution. The reasons why sparging improves H₂ yields are unknown, but recent measurements of dissolved H₂ concentrations during sparging suggest the assumption of decreased inhibition of the H₂-producing enzymes is unlikely. Significant disagreement exists over the effect of organic loading rate (OLR); some studies show relatively higher OLRs improve H₂ yield while others show the opposite. Discovering the reasons for higher H₂ yields during dissolved gas removal and changes in OLR will help improve H₂ yields.     

Evaluation of photoacoustic infrared spectroscopy for simultaneous measurement of N2O and CO2 gas concentrations and fluxes at the soil surface

Simultaneous measurement of N₂O and CO₂ flux at the soil surface with photoacoustic infrared spectroscopy (PAS) is gaining popularity due to portability, low maintenance, and ease‐of‐operation. However, the ability of PAS to measure N₂O with accuracy and precision similar to gas chromatography (GC) is uncertain due to overlap in N₂O, CO₂, and H₂O absorbance spectra combined with the large range in analyte concentrations. We tested the ability of six PAS units to simultaneously measure N₂O and CO₂ gas concentrations and fluxes with accuracy and precision similar to two GC units. We also evaluated H₂O vapor and CO₂ interferences with N₂O measurement. The accuracy and precision of standard gas concentration measurements with PAS and GC were similar. High water vapor (~26 600 ppm) and CO₂ concentrations (~4500 ppm) did not interfere with N₂O measurement across the concentration range typically observed in static flux chambers at the soil surface (~0.5–3.0 ppm N₂O). On average, N₂O fluxes measured with the six PAS were 4.7% higher than one GC and 9.9% lower than the second GC.     

Influence of straw and CO2 on N2-fixation and yield of field-grown soybeans

Straw incorporation at 2 and 4 t/ha with or without CO₂-enrichment at 1000 mg/l from flowering to pod development stage in open top chambers markedly influenced the N₂-fixation and yield of field grown soybeans. N₂-ase activity of soybean root nodules as determined by acetylene reduction technique indicated that (1) straw on average gave significantly 141 and 197% higher N₂-ase activity at 2 and 4 t/ha respectively than controls; (2) CO₂ treatments on average increased the activity by 24% over those without CO₂ and (3) 4 t/ha straw alone or straw at 2 or 4 t/ha in conjunction with CO₂ increased the N₂-ase activity four-fold over the control. High correlations were observed between fresh weights of nodules and N₂-ase activity and between fresh weights of nodules and yield and between N₂-ase activity and yield. This study confirms the earlier investigation that straw could be considered to provide a partial substitute for expensive CO₂-enrichment treatment for improving N₂(C₂H₂) fixation and thereby the general growth and yield of crops.Department of Agronomy, University of Agricultural Sciences, Hebbal, Bangalore, India     

Metabolism of Acetivibrio cellulolyticus during optimized growth on glucose,cellobiose and cellulose

Summary The growth of Acetivibrio cellulolyticus in 2.5 l batch cultures was optimized by controlling the growth pH at 6.7, the dissolved inorganic sulphide concentration at 0.4–0.6 mM, and by constant removal of hydrogen from the cultures by sparging with N₂/CO₂ or N₂ gas. An initial ethanol concentration of 0.15% (w/v) in cellobiose media resulted in specific growth rates which were reduced by about 75% compared to growth rates of 0.17 h^–1 in control cultures. Acetivibrio cellulolyticus had to be adapted for growth on glucose and ¹⁴C-radiotracer studies indicated that glucose was metabolized by the Embden-Meyerhof pathway. The specific growth rate (=0.03h^–1) and molar growth yield (Y_glucose=21.5) were considerably lower than those obtained (=0.17 h^–1, Y_cellobiose=68.9) in cellobiose media. A Y_ATP of 12.8 was obtained during growth on cellobiose. The mol product formed per mol Avicel cellulose fermented (on anhydroglucose equivalent basis) were 3.70 H₂, 2.64 CO₂, 0.73 acetate, 0.39 ethanol and 0.03 total soluble sugars on glucose basis. Maximum cellulase activity was observed in cellulose-grown cultures.National Research council of Canada No. 20826     

Production of acetic acid by Clostridium thermoaceticum in electrodialysis culture using a fermenter equipped with an electrodialyser

Electrodialysis culture of Clostridium thermoaceticum increased the yield of acetate by its continuous removal. In normal batch cultures without pH control the yield was 4.2 g acetic acid/800 ml, while in pH-controlled culture it was 16.8 g/800 ml. Although electrodialysis cultures gave almost the same yield (15.4 g/800 ml) as that in pH-controlled cultures, sparging CO₂ into the broth in electrodialysis culture increased the amount of acetic acid to 22.3 g/800 ml. CO₂ sparging into normal cultures with or without pH control did not significantly increase the amount of acetate produced but yields, in terms of amounts of glucose consumed, were higher than without sparging. The theoretical yield was almost obtained in pH-controlled, electrodialysis cultures with CO₂ sparging.The authors are with the Department of Applied Microbial Technology, Kumamoto Institute of Technology, Ikeda 4-22-1, Kumamoto 860, Japan     

Elevated CO2 concentration enhances the role of the ear to the flag leaf in determining grain yield of wheat

Net photosynthetic rate (P _N) of ear and flag leaf during grain filling stage and grain yield of plants with non-darkened or darkened flag leaf or darkened ear were examined in two different CO₂ concentrations: ambient (AC) and AC+200 μmol mol⁻¹ (EC). Ear showed much higher enhancement (56 %) of P _N than flag leaf (23 %) under EC. Moreover, CO₂ enrichment shortened the photosynthetic duration of flag leaf relative to ear. In this way the ratio of ear to flag leaf contribution to grain yield increased from 1.18 (AC) to 1.39 (EC).     

Fructose degradation byDesulfovibrio sp. in pure culture and in coculture withMethanospirillum hungatei

In a mineral medium containing sulfate, the sulfate-reducing bacteriumDesulfovibrio sp. strain JJ degraded 1 mol of fructose stoichiometrically to 1 mol of H₂S, 2 mol of acetate, and presumably 2 mol of CO₂. The doubling time was 10 h, and the yield was 41.6 g dry weight/mol fructose degraded. In the absence of sulfate, the hydrogenophilic methanogenMethanospirillum hungatei replaced sulfate as hydrogen sink. In such cocultures, 1 mol of fructose was converted to acetate, methane, succinate, and presumably CO₂ in varying concentrations. The growth yield of the H₂-transferring association was 33 g dry weight/mol fructose. In the absence of sulfate,Desulfovibrio strain JJ slowly fermented 1 mol of fructose to 1 mol of succinate, 0.5 mol of acetate, and 0.5 mol of ethanol. The results are compared with those of other anaerobic hexose-degrading bacteria.     

Land use and season affect fluxes of CO2, CH4, CO,N2O,H2 and isotopic source signatures in Panama: evidence from nocturnal boundary layer profiles

Conversion of tropical rainforests to pastures and plantations is associated with changes in soil properties and biogeochemical cycling, with implications for carbon cycling and trace gas fluxes. The stable isotopic composition of ecosystem respiration (δ¹³C_R and δ¹⁸O_R) is used in inversion models to quantify regional patterns of CO₂ sources and sinks, but models are limited by sparse measurements in tropical regions. We measured soil respiration rates, concentrations of CO₂, CH₄, CO, N₂O and H₂ and the isotopic composition of CO₂, CH₄ and H₂ at four heights in the nocturnal boundary layer (NBL) above three common land‐use types in central Panama, during dry and rainy seasons. Soil respiration rates were lowest in Plantation (average 3.4 μmol m^?2 s^?1), highest in Pasture (8.3 μmol m^?2 s^?1) and intermediate in Rainforest (5.2 μmol m^?2 s^?1). δ¹³C_R closely reflected land use and increased during the dry season where C₃ vegetation was present. δ¹⁸O_R did not differ by land use but was lower during the rainy than the dry season. CO₂ was correlated with other species in approximately half of the NBL profiles, allowing us to estimate trace gas fluxes that were generally within the range of literature values. The Rainforest soil was a sink for CH₄ but emissions were observed in Pasture and Plantation, especially during the wet season. N₂O emissions were higher in Pasture and Plantation than Rainforest, contrary to expectations. Soil H₂ uptake was highest in Rainforest and was not observable in Pasture and Plantation during the wet season. We observed soil CO uptake during the dry season and emissions during the wet season across land‐use types. This study demonstrated that strong impacts of land‐use change on soil–atmosphere trace gas exchange can be detected in the NBL, and provides useful observational constraints for top‐down and bottom‐up biogeochemistry models.     

Gas Exchange Responses to CO2 Concentration Instantaneously Elevated in Flag Leaves of Winter Wheat Cultivars Released in Different Years

Three winter wheat (Triticum aestivum L.) cultivars, representatives of those widely cultivated in Beijing over the past six decades, were grown in the same environmental conditions. Net photosynthetic rate (P _N) per unit leaf area and instantaneous water use efficiency (WUE) of flag leaves increased with elevated CO₂ concentration. With an increase in CO₂ concentration from 360 to 720 µmol mol^–1, P _N and WUE of Jingdong 8 (released in 1990s and having the highest yield) increased by 173 and 81 %, while those of Nongda 139 (released in 1970s) increased by 88 and 66 %, and Yanda 1817 (released in 1945, with lowest yield) by 76 and 65 %. Jingdong 8 had the highest P _N and WUE values under high CO₂ concentration, but Yanda 1817 showed the lowest P _N. Stomatal conductance (g _s) of Nongda 139 and Yanda 1817 declined with increasing CO₂ concentration, but g _s of Jingdong 8 firstly went down and then up as the CO₂ concentration further increased. Intercellular CO₂ concentration (C _i) of Jingdong 8 and Nongda 139 increased when CO₂ concentration elevated, while that of Yanda 139 increased at the first stage and then declined. Jingdong 8 had the lowest C _i of the three wheat cultivars, and Yanda 1817 had the highest C _i value under lower CO₂ concentrations. However, Jingdong 8 had the highest P _N and lowest C _i at the highest CO₂ concentration which indicates that its photosynthetic potential may be high.     

Biomass fast pyrolysis in a fluidized bed reactor under N2, CO2, CO, CH4 and H2 atmospheres

Biomass fast pyrolysis is one of the most promising technologies for biomass utilization. In order to increase its economic potential, pyrolysis gas is usually recycled to serve as carrier gas. In this study, biomass fast pyrolysis was carried out in a fluidized bed reactor using various main pyrolysis gas components, namely N₂, CO₂, CO, CH₄ and H₂, as carrier gases. The atmosphere effects on product yields and oil fraction compositions were investigated. Results show that CO atmosphere gave the lowest liquid yield (49.6%) compared to highest 58.7% obtained with CH₄. CO and H₂ atmospheres converted more oxygen into CO₂ and H₂O, respectively. GC/MS analysis of the liquid products shows that CO and CO₂ atmospheres produced less methoxy-containing compounds and more monofunctional phenols. The higher heating value of the obtained bio-oil under N₂ atmosphere is only 17.8 MJ/kg, while that under CO and H₂ atmospheres increased to 23.7 and 24.4 MJ/kg, respectively.     

Photosynthesis and transpiration of tomato and CO2 fluxes in a greenhouse under changing environmental conditions in winter

Responses of tomato leaves in a greenhouse to light and CO₂ were examined at the transient stage at the end of winter, when both photoperiod and irradiance gradually increase. Additionally, CO₂ fluxes were calculated for a greenhouse without supplementary lighting and without CO₂ enrichment based on CO₂ sinks (plant photosynthesis) and CO₂ sources (plant and substrate respiration). In January, tomato leaves in the greenhouse showed low photosynthesis with a maximum assimilation of 6–8 μmol CO₂ m⁻² s⁻¹, a quantum yield of 0.06 μmol CO₂ μmol⁻¹ photosynthetic active radiation (PAR) and a low light compensation point of 26 μmol PAR m⁻² s⁻¹, a combination which classifies them as shade leaves. In February, tomato leaves increased their light compensation point to 39 μmol PAR m⁻² s⁻¹ and quantum yield to 0.08, the former indicating the adaptation to increased irradiance and photoperiod. These tomato leaves increased their transpiration from 0.4 to 0.9 in January to ∼2 mmol H₂O m⁻² s⁻¹ in February. Both photosynthesis and transpiration were primarily limited by light but neither by stomatal conductivity nor by CO₂. In January, light response of photosynthesis, dark respiration and transpiration were negligibly affected by increasing CO₂ concentrations from 600 to 900 ppm CO₂ under low light conditions, indicating no benefit of CO₂ enrichment unless light intensity increased. In February, tomato leaves were photoinhibited at inherent greenhouse CO₂ concentrations on the first sunny day; this photoinhibition was further enhanced by an increased CO₂ concentration of 1000 ppm. CO₂ fluxes in the greenhouse appeared strongly dependent on solar radiation. After exceeding the light compensation point in the morning, greenhouse CO₂ concentrations decreased by 58 or by 110 ppm CO₂ h⁻¹ on a sunny day in January or February and by 23 ppm on overcast days in both months. Calculated per overall tomato canopy, plant photosynthesis contributed 42–50% to the morning CO₂ depletion in the greenhouse. Dark respiration of tomato leaves was ∼2 μmol CO₂ m⁻² s⁻¹ in January and ∼3 μmol CO₂ m⁻² s⁻¹ in February. This dark respiration resulted in rises of 15 and 17 ppm CO₂ h⁻¹ at night in the greenhouse compartment and was identified as primary source of CO₂. Respiration of the substrate used to grow the plants, which produced 7.3 ppm CO₂ h⁻¹, was identified as secondary source of CO₂. The combined plant and substrate respiration resulted in peaks of up to 900 ppm CO₂ in the greenhouse before dawn.     

Computational screening of ZIFs for CO2 separations

Using molecular simulations, we studied a diverse collection of zeolite–imidazolate frameworks (ZIFs) to evaluate their performances in adsorption- and membrane-based gas separations. Molecular simulations were performed for both single-component gases (CH₄, CO₂, H₂ and N₂) and binary gas mixtures (CO₂/CH₄, CO₂/N₂, CO₂/H₂ and CH₄/H₂) to predict the intrinsic and mixture selectivities of ZIFs. These two selectivities were compared to discuss the importance of multi-component mixture effects on making predictions about the separation performance of a material. Gas separation performances of ZIFs were compared with other nanoporous materials and our results showed that several ZIFs can outperform well-known zeolites and metal–organic frameworks in CO₂ separations. Several other properties of ZIFs such as gas permeability, working capacity and sorbent selection parameter were computed to identify the most promising materials in adsorption- and membrane-based separation of CO₂/CH₄, CO₂/N₂, CO₂/H₂ and CH₄/H₂.     

Effect of nitrogen and phosphorus availability on the growth response of Eucalyptus grandis to high CO2

The response of Eucalyptus grandis seedlings to elevated atmospheric CO₂ concentrations was examined by growing seedlings at either 340 or 660 n mol CO₂ mol^-1 for 6 weeks. Graded increments of phosphorus and nitrogen fertilizers were added to a soil deficient in these nutrients to establish if the growth response to increasing nutrient availability was affected by CO₂ concentration. At 660 μmol CO₂ mol^-1, seedling dry weight was up to five times greater than at 340 μmol CO₂ mol^-1. The absolute response was largest when both nitrogen and phosphorus availability was high but the relative increase in dry weight was greatest at low phosphorus availability. At 340 μmol CO₂ mol^-1 and high nitrogen availability, growth was stimulated by addition of phosphorus up to 76 mg kg 1 soil. Further additions of phosphorus had little effect. However, at 660 μmol CO₂ mol^-1, growth only began to plateau at a phosphorus addition rate of 920mg kg^-1 soil. At 340 μmol CO₂ mol^-1 and high phosphorus availability, increasing nitrogen from 40 to 160mg kg^-1 soil had little effect on plant growth. At high CO₂, growth reached a maximum at between 80 and 160mg nitrogen kg^-1 soil. Total uptake of phosphorus was greater at high CO₂ concentration at all fertilizer addition rates, but nitrogen uptake was either lower or unchanged at high CO₂ concentration except at the highest nitrogen fertilizer rate. The shoot to root ratio was increased by CO₂ enrichment, primarily because the specific leaf weight was greater. The nitrogen and phosphorus concentration in the foliage was lower at elevated CO₂ concentration partly because of the higher specific leaf weight. These results indicate that critical foliar concentrations currently used to define nutritional status and fertilizer management may need to be reassessed as the atmospheric CO₂ concentration rises.     

The influence of elevated CO2 and temperature on biomass production of continuously defoliated white clover

Clonal plants of white clover (Trifolium repens L.), grown singly in pots of Perlite and solely dependent for nitrogen on root nodule N₂ fixation, were maintained in controlled environments which provided four environments: 18/13 °C day/night temperature at 340 and 680 μmol mol^?1 CO₂ and 20·5/15·5°C day/night temperature at 340 and 680 μmol mol^?1 CO₂. The daylength was 12 h and the photon flux density 500±25 μmol m^?2 s^?1 (PFD). All plants were defoliated for about 80d, nominally every alternate day, to leave the youngest expanded leaf intact on 50% of stolons, plus expanding leaves (simulated grazing). Elevated CO₂ increased the yield of biomass removed at defoliation by a constant 45% during the second 40d of the experiment and by a varying amount in the first half of the experiment. Elevated temperature had little effect on biomass yield. Nitrogen, as a proportion of the harvested biomass, was only fractionally affected by elevated CO₂ or temperature. In contrast, N₂ fixation increased in concert with the promoting effect of elevated CO₂ on biomass production. The increased yield of biomass harvested in 680 μmol mol^?1 CO₂ was primarily due to the early development and continued maintenance of more stolons. However, the stolons of plants grown in elevated CO₂ also developed leaves which were heavier and slightly larger in area than their counterparts in ambient CO₂. The conclusion is that, when white clover plants are maintained at constant mass by simulated grazing, they continue to respond to elevated CO₂ in terms of a sustained increase in biomass production.     

Free Air CO2 Enrichment of potato (Solanum tuberosum L.): development, growth and yield

A FACE (Free Air CO₂ Enrichment) experiment was carried out on Potato (Solanum tuberosum L., cv. Primura) in 1995 in Italy. Three FACE rings were used to fumigate circular field plots of 8 m diameter while two rings were used as controls at ambient CO₂ concentrations. Four CO₂ exposure levels were used in the rings (ambient, 460, 560 and 660 μmol mol^–1). Phenology and crop development, canopy surface temperature, above- and below-ground biomass were monitored during the growing season. Crop phenology was affected by elevated CO₂, as the date of flowering was progressively anticipated in the 660, 560, 460 μmol mol^–1 treatments. Crop development was not affected significantly as plant height, leaf area and the number of leaves per plant were the same in the four treatments. Elevated atmospheric CO₂ levels had, instead, a significant effect on the accumulation of total nonstructural carbohydrates (TNC = soluble sugars + starch) in the leaves during a sunny day. Specific leaf area was decreased under elevated CO₂ with a response that paralleled that of TNC concentrations. This reflected the occurrence of a progressive increase of photosynthetic rates and carbon assimilation in plants exposed to increasingly higher levels of atmospheric CO₂. Tuber growth and final tuber yield were also stimulated by rising CO₂ levels. When calculated by regression of tuber yield vs. the imposed levels of CO₂concentration, yield stimulation was as large as 10% every 100 μmol mol^–1 increase, which translated into over 40% enhancement in yield under 660 μmol mol^–1. This was related to a higher number of tubers rather than greater mean tuber mass or size. Leaf senescence was accelerated under elevated CO₂ and a linear relationship was found between atmospheric CO₂ levels and leaf reflectance measured at 0.55 μm wavelength. We conclude that significant CO₂ stimulation of yield has to be expected for potato under future climate scenarios, and that crop phenology will be affected as well.     

The effects of gas sparging on growth and glucose utilization of Zymomonas mobilis at low glucose concentrations

Summary In a batch culture of Zymomonas mobilis the specific growth and specific glucose uptake rates and the molar growth yields were similar under CO₂ and N₂ sparging. The use of N₂ or N₂ with nucleation agents to strip dissolved CO₂ from the medium did not improve growth rates or yields or enhance glucose consumption rates. Carbon dioxide produced no direct feedback inhibition on metabolic rates. The catabolic enzymes of Z. mobilis are not allosterically controlled by CO₂.     

Novel synthetic co-culture of Acetobacterium woodii and Clostridium drakei using CO2 and in situ generated H2 for the production of caproic acid via lactic acid

Acetobacterium woodii is known to produce mainly acetate from CO₂ and H₂, but the production of higher value chemicals is desired for the bioeconomy. Using chain-elongating bacteria, synthetic co-cultures have the potential to produce longer-chained products such as caproic acid. In this study, we present first results for a successful autotrophic co-cultivation of A. woodii mutants and a Clostridium drakei wild-type strain in a stirred-tank bioreactor for the production of caproic acid from CO₂ and H₂ via the intermediate lactic acid. For autotrophic lactate production, a recombinant A. woodii strain with a deleted Lct-dehydrogenase complex, which is encoded by the lctBCD genes, and an inserted D-lactate dehydrogenase (LdhD) originating from Leuconostoc mesenteroides, was used. Hydrogen for the process was supplied using an All-in-One electrode for in situ water electrolysis. Lactate concentrations as high as 0.5 g L^–1 were achieved with the AiO-electrode, whereas 8.1 g L^–1 lactate were produced with direct H₂ sparging in a stirred-tank bioreactor. Hydrogen limitation was identified in the AiO process. However, with cathode surface area enlargement or numbering-up of the electrode and on-demand hydrogen generation, this process has great potential for a true carbon-negative production of value chemicals from CO₂.