Comparison of two-stage thermophilic (68 degrees C/55 degrees C) anaerobic digestion with one-stage thermophilic (55 degrees C) digestion of cattle manure

A two-stage 68 degrees C/55 degrees C anaerobic degradation process for treatment of cattle manure was studied. In batch experiments, an increase of the specific methane yield, ranging from 24% to 56%, was obtained when cattle manure and its fractions (fibers and liquid) were pretreated at 68 degrees C for periods of 36, 108, and 168 h, and subsequently digested at 55 degrees C. In a lab-scale experiment, the performance of a two-stage reactor system, consisting of a digester operating at 68 degrees C with a hydraulic retention time (HRT) of 3 days, connected to a 55 degrees C reactor with 12-day HRT, was compared with a conventional single-stage reactor running at 55 degrees C with 15-days HRT. When an organic loading of 3 g volatile solids (VS) per liter per day was applied, the two-stage setup had a 6% to 8% higher specific methane yield and a 9% more effective VS-removal than the conventional single-stage reactor. The 68 degrees C reactor generated 7% to 9% of the total amount of methane of the two-stage system and maintained a volatile fatty acids (VFA) concentration of 4.0 to 4.4 g acetate per liter. Population size and activity of aceticlastic methanogens, syntrophic bacteria, and hydrolytic/fermentative bacteria were significantly lower in the 68 degrees C reactor than in the 55 degrees C reactors. The density levels of methanogens utilizing H2/CO2 or formate were, however, in the same range for all reactors, although the degradation of these substrates was significantly lower in the 68 degrees C reactor than in the 55 degrees C reactors. Temporal temperature gradient electrophoresis profiles (TTGE) of the 68 degrees C reactor demonstrated a stable bacterial community along with a less divergent community of archaeal species.     

Difference in sporogenous bacterial populations in thermophilic (55 degrees C) and mesophilic (35 degrees C) anaerobic sewage digestion

Spores, sporeforming vegetative cells, and asporogenous populations were enumerated in two semicontinuous anaerobic fermentors digesting municipal primary sludge at 35 and 55 degrees C for more than 87 days. In the 35 degrees C fermentor, the anaerobic total population was 312.5 X 10(6)/ml, with 25.0 X 10(6)/ml being sporogenous. The populations that digest casein, starch, pectin, and cellulose were 23.1 X 10(6), 59.2 X 10(6), 26.2 X 10(6), and 7.3 X 10(6)/ml, respectively, with 2.8 X 10(6), 6.7 X 10(6), 3.4 X 10(6), and 1.5 X 10(6)/ml being sporogenous, respectively. The sporeformers accounted for 8.0 to 20.0% of each of the respective populations. In the 55 degrees C fermentor, the anaerobic total population was 512.5 X 10(6)/ml, with 336.6 X 10(6)/ml being sporogenous. The populations that digest casein, starch, pectin, and cellulose were 97.7 X 10(6), 190.7 X 10(6), 75.8 X 10(6), and 11.2 X 10(6)/ml, respectively, with 47.8 X 10(6), 110.6 X 10(6), 43.3 X 10(6), and 5.1 X 10(6)/ml, respectively, being sporogenous. The sporeformers represented 45.5 to 65.7% of each of the respective populations. The numbers of thermophilic sporeforming vegetative cells in the 55 degrees C fermentor were 9.0 to 19.8 times higher than their counterparts in the 35 degrees C fermentor. Most sporeformers were in the vegetative state in the 35 and 55 degrees C fermentors. After 18 days of fermentation at 55 degrees C, sporeformers carried out most of the digestion; however, the digestion was shared by both sporeformers and asporogenous bacteria after 87 days of fermentation. In the 35 degrees C fermentor, asporogenous bacteria digested most of the sludge. During the 18- and 87-day experimental periods, sporeformers were never predominant.     

Thermophilic (55 degrees C) conversion of methanol in methanogenic-UASB reactors: influence of sulphate on methanol degradation and competition

Two upflow sludge bed reactors (UASB) were operated for 80 days at 55 degrees C with methanol as the substrate with an organic loading rate (OLR) of about 20 g CODl(-1) per day and a hydraulic retention time (HRT) of 10 h. One UASB was operated without sulphate addition (control reactor-R1) whereas the second was fed with sulphate at a COD:SO4(2-) ratio of 10 (sulphate-fed reactor-R2), providing an influent sulphate concentration of 0.6 g l(-1). For both reactors, methanogenesis was the dominant process with no considerable accumulation of acetate. The methanol removal averaged 93% and 83% for R1 and R2, respectively, and total sulphate removal was achieved in the latter. The pathway of methanol conversion for both sludges was investigated by measuring the fate of carbon in the presence and absence of bicarbonate or specific inhibitors for a sludge sample collected at day 72. In both sludges, about 70% of the methanol was syntrophically converted to methane and/or sulphide, via the intermediate H2/CO2. A strong competition between methanogens and sulphidogens took place in the R2 sludge with half of the methanol-COD being used by methane-producing bacteria and the other half by sulphate-reducing bacteria. Acetate was not an important intermediate for both sludges, and played a slightly more important role for the sulphate-adapted sludge (R2), sustained by the higher amount of bicarbonate produced during sulphate-reduction. The pathway study indicates that, although acetate does not represent an important intermediate, the system is susceptible to its accumulation.     

Difference in sporogenous bacterial populations in thermophilic (55 degrees C) and mesophilic (35 degrees C) anaerobic sewage digestion.

Spores, sporeforming vegetative cells, and asporogenous populations were enumerated in two semicontinuous anaerobic fermentors digesting municipal primary sludge at 35 and 55 degrees C for more than 87 days. In the 35 degrees C fermentor, the anaerobic total population was 312.5 X 10(6)/ml, with 25.0 X 10(6)/ml being sporogenous. The populations that digest casein, starch, pectin, and cellulose were 23.1 X 10(6), 59.2 X 10(6), 26.2 X 10(6), and 7.3 X 10(6)/ml, respectively, with 2.8 X 10(6), 6.7 X 10(6), 3.4 X 10(6), and 1.5 X 10(6)/ml being sporogenous, respectively. The sporeformers accounted for 8.0 to 20.0% of each of the respective populations. In the 55 degrees C fermentor, the anaerobic total population was 512.5 X 10(6)/ml, with 336.6 X 10(6)/ml being sporogenous. The populations that digest casein, starch, pectin, and cellulose were 97.7 X 10(6), 190.7 X 10(6), 75.8 X 10(6), and 11.2 X 10(6)/ml, respectively, with 47.8 X 10(6), 110.6 X 10(6), 43.3 X 10(6), and 5.1 X 10(6)/ml, respectively, being sporogenous. The sporeformers represented 45.5 to 65.7% of each of the respective populations. The numbers of thermophilic sporeforming vegetative cells in the 55 degrees C fermentor were 9.0 to 19.8 times higher than their counterparts in the 35 degrees C fermentor. Most sporeformers were in the vegetative state in the 35 and 55 degrees C fermentors. After 18 days of fermentation at 55 degrees C, sporeformers carried out most of the digestion; however, the digestion was shared by both sporeformers and asporogenous bacteria after 87 days of fermentation. In the 35 degrees C fermentor, asporogenous bacteria digested most of the sludge. During the 18- and 87-day experimental periods, sporeformers were never predominant.     

The transformation and toxicity of anthraquinone dyes during thermophilic (55 degrees C) and mesophilic (30 degrees C) anaerobic treatments

We studied in batch assays the transformation and toxicity of anthraquinone dyes during incubations with anaerobic granular sludge under mesophilic (30 degrees C) and thermophilic (55 degrees C) conditions. Additionally, the electron shuttling capacity of the redox mediator anthraquinone-2-sulfonic acid (AQS) and subsequent increase on decolourisation rates was investigated on anthraquinone dyes. Compared with incubations at 30 degrees C, serum bottles at 55 degrees C presented distinctly higher decolourisation rates not only with an industrial wastewater containing anthraquinone dyes, but also with model compounds. Compared with batch assays at 30 degrees C, the first-order rate constant "k" of the Reactive Blue 5 (RB5) was enhanced 11-fold and 6-fold for bottles at 55 degrees C supplemented and free of AQS, respectively. However, the anthraquinone dye Reactive Blue 19 (RB19) demonstrated a very strong toxic effect on volatile fatty acids (VFA) degradation and methanogenesis at both 30 degrees C and 55 degrees C. The apparent inhibitory concentrations of RB19 exerting 50% reduction in methanogenic activity (IC50-value) were 55 mg l(-1) at 30 degrees C and 45 mg l(-1) at 55 degrees C. Further experiments at both temperatures revealed that RB19 was mainly toxic to methanogens, because the glucose oxidizers including acetogens, propionate-forming, butyrate-forming and ethanol-forming microorganisms were not affected by the dye toxicity.     

Bioaugmentation of a two-stage thermophilic (68 degrees C/55 degrees C) anaerobic digestion concept for improvement of the methane yield from cattle manure

The possibility of improving a two-stage (68 degrees C/55 degrees C) anaerobic digestion concept for treatment of cattle manure was studied. In batch experiments, a 10-24% increase of the specific methane yield from cattle manure and its fractions was obtained, when the substrates were inoculated with bacteria of the genus Caldicellusiruptor and Dictyoglomus. In a reactor experiment inoculation of a 68 degrees C pretreatment reactor with Caldicellusiruptor resulted in a 93% increase in the methane yield of the pretreatment reactor for a period of 18 days, but gave only a slight increase in the overall methane yield of the two-stage setup.     

Thermophilic (55-65 degrees C) and extreme thermophilic (70-80 degrees C) sulfate reduction in methanol and formate-fed UASB reactors

The feasibility of thermophilic (55-65 degrees C) and extreme thermophilic (70-80 degrees C) sulfate-reducing processes was investigated in three lab-scale upflow anaerobic sludge bed (UASB) reactors fed with either methanol or formate as the sole substrates and inoculated with mesophilic granular sludge previously not exposed to high temperatures. Full methanol and formate degradation at temperatures up to, respectively, 70 and 75 degrees C, were achieved when operating UASB reactors fed with sulfate rich (COD/SO4(2-)=0.5) synthetic wastewater. Methane-producing archaea (MPA) outcompeted sulfate-reducing bacteria (SRB) in the formate-fed UASB reactor at all temperatures tested (65-75 degrees C). In contrast, SRB outcompeted MPA in methanol-fed UASB reactors at temperatures equal to or exceeding 65 degrees C, whereas strong competition between SRB and MPA was observed in these reactors at 55 degrees C. A short-term (5 days) temperature increase from 55 to 65 degrees C was an effective strategy to suppress methanogenesis in methanol-fed sulfidogenic UASB reactors operated at 55 degrees C. Methanol was found to be a suitable electron donor for sulfate-reducing processes at a maximal temperature of 70 degrees C, with sulfide as the sole mineralization product of methanol degradation at that temperature.     

Neural network prediction of thermophilic (65 degrees C) sulfidogenic fluidized-bed reactor performance for the treatment of metal-containing wastewater

The performance of a fluidized-bed reactor (FBR) based sulfate reducing bioprocess was predicted using artificial neural network (ANN). The FBR was operated at high (65 degrees C) temperature and it was fed with iron (40-90 mg/L) and sulfate (1,000-1,500 mg/L) containing acidic (pH = 3.5-6) synthetic wastewater. Ethanol was supplemented as carbon and electron source for sulfate reducing bacteria (SRB). The wastewater pH of 4.3-4.4 was neutralized by the alkalinity produced in acetate oxidation and the average effluent pH was 7.8 +/- 0.8. The oxidation of acetate is the rate-limiting step in the sulfidogenic ethanol oxidation by thermophilic SRB, which resulted in acetate accumulation. Sulfate reduction and acetate oxidation rates showed variation depending on the operational conditions with the maximum rates of 1 g/L/d (0.2 g/g volatile solids (VS)/d) and 0.3 g/L/d (0.06 g/g VS/d), respectively. This study presents an ANN model predicting the performance of the reactor and determining the optimal architecture of this model; such as best back-propagation (BP) algorithm and neuron numbers. The Levenberg-Marquardt algorithm was selected as the best of 12 BP algorithms and optimal neuron number was determined as 20. The developed ANN model predicted acetate (R=0.91), sulfate (R=0.95), sulfide (R=0.97), and alkalinity (R=0.94) in the FBR effluent. Hence, the ANN based model can be used to predict the FBR performance, to control the operational conditions for improved process performance.     

Kinetic study of sulfide leaching by galvanic interaction between chalcopyrite, pyrite, and sphalerite in the presence of T. ferrooxidans (30 degrees C) and a thermophilic microorganism (55 degrees C)

A systematic, kinetic study and comparison of the leaching of mixed metal sulfides by galvanic conversion and in the presence of bacteria has been carried out for the first time using both powder (-100 to -400 mesh) and larger (bulk) specimen systems. The rates of dissolution of copper from chalcopyrite and zinc from sphalerite as single, electrically isolated (separate) systems were compared with electrically contacting (galvanically coupled) systems involving CuFeS(2)/FeS(2) and ZnS/FeS(2), with and without bacteria and at temperatures of 30 and 55 degrees C. The dissolution of Cu was observed to increase by a factor of 4.6 when the galvanic leaching of CuFeS(2)/FeS(2) was compared to CuFeS(2) leaching at 30 degrees C. When bacteria were present, Cu dissolution increased by an additional factor of 2.1 in the CuFeS(2)/FeS(2) system. At 55 degrees C, the corresponding ratios for Cu were 4.3 and 2.7, respectively. The galvanic leaching of Zn in the ZnS/FeS(2) system compared to ZnS leaching increased by a factor of 2 at 30 degrees C; in the presence of bacteria the dissolution of Zn from the ZnS/FeS(2) system increased by an additional factor of 1.3 at the same temperature. By comparison, the ratio of Cu dissolution from CuFeS(2) in acid-bacterial medium and sterile controls (without bacteria) was 5.5. The corresponding ratio for Zn from ZnS was 2.2 at both 30 and 55 degrees C. The order of reaction was found to be essentially first order for the leaching of powder systems at both 30 and 55 degrees C (with T. Ferrooxidans and thermophilic microorganisms, respectively). The corresponding reaction rate constants were observed to be 12.6 and 22.9 for T. ferrooxidans and the thermophilic microorganisms, respectively. Activation energies for the various systems were also determined.     

Potential for thermophilic (50 degrees C) anaerobic dechlorination of pentachlorophenol in different ecosystems

Thermophilic (50 degrees C) anaerobic biodegradation of pentachlorophenol (PCP) was investigated by using different inocula from natural ecosystems and anaerobic digesters. The inocula tested were three freshwater sediments, four anaerobic sewage sludge samples from digesters treating sludge from wastewater plants with various industrial inputs, and digested manure from an anaerobic reactor. Only one digested-sludge sample and the manure sample were from thermophilic environments. The initial PCP concentration was 7.5 or 37.5 microM. After 8 months, PCP had disappeared from the sediment samples and various, less chlorinated intermediates were present. Additions of extra PCP were degraded within 4 weeks, and a maximal observed dechlorination rate of 1.61 mumol/liter/day in the vials with addition of 7.5 microM PCP and 7.50 mumol/liter/day in the vials with addition of 37.5 microM PCP were measured for a freshwater sediment. In contrast, only 2.8 to 17.5% of the initial PCP added had disappeared from the sludge samples after 8 months of incubation. The complex pattern of intermediates formed indicated that the dechlorination of PCP proceeded via different pathways, involving at least two different populations in the dechlorination processes.     

Bioleaching of chalcopyrite concentrate by a moderately thermophilic culture in a stirred tank reactor

A mixed culture of moderately thermophilic microorganisms was enriched from acid mine drainage samples collected from several chalcopyrite mines in China. Such mixed culture can be used to effectively extract copper from chalcopyrite. Furthermore, after being adapted to gradually increased concentration of chalcopyrite concentrate, the tolerance of the mixed culture to chalcopyrite concentrate was brought up to 80 g/L. The effects of several leaching parameters on copper recovery in stirred tank reactor also had been investigated. The results of the investigation show that it was possible to achieve a copper extraction rate of 75% in 44 days at a pulp density of 8%. The leaching rate of chalcopyrite concentrate tended to increase with dissolved total iron concentration. At low pH ranges, more microscopic counts of microorganisms were found in the solution. Furthermore, the analysis of leached residues indicates that the passivation of chalcopyrite concentrate was mainly due to a mass of jarosite and PbSO(4) on the mineral surface, other than the elemental sulphur layer. The bacterial community composition was analyzed by using Amplified Ribosomal DNA Restriction Analysis. Two moderately thermophilic bacteria species were identified as Leptospirillum ferriphilum and Acidithiobacillus caldus with abundance of 67% and 33% in the bio-pulp, respectively.     

Synthesis and characterisation of the carboxylate linked osmium clusters [{Os3H(CO)10}2(CO2CH2CO2)], [{Os3H(CO)10}2(CO2C2H4CO2)], [{Os3H(CO)10}2(C4O4)] and [{Os3H(CO)10}2(C4O4){Co2(CO)6}]

Reactions between the activated cluster [Os₃(CO)₁₀(NCMe)₂] and malonic acid, succinic acid and dicarboxylic acetylene, respectively, lead to the formation of the linked cluster complexes [{Os₃H(CO)₁₀}₂(CO₂CH₂CO₂)] (1), [{Os₃H(CO)₁₀}₂(CO₂C₂H₄CO₂)] (2), and [{Os₃H(CO)₁₀}₂(C₄O₄)] (3) in good yield. Cluster 3 was subsequently treated with [Co₂(CO)₈] and this results in the addition of a “Co₂(CO)₆” group giving [{Os₃H(CO)₁₀}₂(C₂O₄){Co₂(CO)₆}] (4). The X-ray crystal structures are reported for 2–4. In each structure the two triangular triosmium units are linked by the carboxylate groups and within each complex the carboxylate groups are chelating and bridge two osmium atoms.     

Potential for thermophilic (50 degrees C) anaerobic dechlorination of pentachlorophenol in different ecosystems.

Thermophilic (50 degrees C) anaerobic biodegradation of pentachlorophenol (PCP) was investigated by using different inocula from natural ecosystems and anaerobic digesters. The inocula tested were three freshwater sediments, four anaerobic sewage sludge samples from digesters treating sludge from wastewater plants with various industrial inputs, and digested manure from an anaerobic reactor. Only one digested-sludge sample and the manure sample were from thermophilic environments. The initial PCP concentration was 7.5 or 37.5 microM. After 8 months, PCP had disappeared from the sediment samples and various, less chlorinated intermediates were present. Additions of extra PCP were degraded within 4 weeks, and a maximal observed dechlorination rate of 1.61 mumol/liter/day in the vials with addition of 7.5 microM PCP and 7.50 mumol/liter/day in the vials with addition of 37.5 microM PCP were measured for a freshwater sediment. In contrast, only 2.8 to 17.5% of the initial PCP added had disappeared from the sludge samples after 8 months of incubation. The complex pattern of intermediates formed indicated that the dechlorination of PCP proceeded via different pathways, involving at least two different populations in the dechlorination processes.     

Synthesis and characterization of two isomers of Os3(CO)10(C5H4N-2-C(H)NR) and the conversion to ortho-metallated HOs3(C5H3N-2-C(H)NR)(CO)9. Part III. X-ray Structure of HOs3(C5H3N-2-C(H)Ni-Pr)(CO)9

Os₃(CO)₁₀(MeCN)₂ reacts at room temperature in MeCN or toluene with R-Pyca2 to yield two isomers of Os₃(CO)₁₀(R-Pyca) that differ in the bonding of the R-Pyca ligand to the Os₃(CO)₁₀ unit. In all cases Os₃(CO)₁₀(R-Pyca(4e)) (isomer A; 4a: R = c-Pr, 4b: R = i-Pr, 4c: R = neo-Pent, 4d: R = t-Bu), containing a chelating 4e donating R-Pyca ligand and three OsS bonds, could be isolated. In the case of R = c-Pr and R = i-Pr Os₃(CO)₁₀(R-Pyca(6e)) (isomer B; 5a: R = c-Pr, 5b: R = i-Pr), in which only two OsS bonds are present and the R-Pyca ligand is bonded as a 6e donating ligand bridging two non-bonded Os atoms, could be isolated as a minor product.At 70 °C Os₃(CO)₁₀(R-Pyca(4e)) (4b and 4d) loses one carbonyl and the pyridine moiety of the R-Pyca ligand is ortho-metallated to form HOs₃(C₅H₃N-2-C(H)NR)(CO)₉ (6b: R = i-Pr and 6d: R = t-Bu). Under the same conditions Os₃(CO)₁₀(i-Pr-Pyca(6e)) (5b) reacts to Os₂(CO)₆(6e)) (7b) containing a bridging 6e donating ligands. The latter two reactions were followed with FT-IR spectroscopy in a high temperature IR cell.The structure of the complexes in solution have been studied by ¹H and ¹C NMR and IR spectroscopy. The stoichiometries of 4a and 5a were determined by FAB-mass spectrometry while an exact mass determination was carried out for 4a.The crystal structure of 6b has been determined. Crystal of 6b are monoclinic, space group P2₁/n, with a = 7.808(2),b = 17.613(3),c = 16.400(8)Å, β = 94.09(3)° and Z = 4. The structure was refined to R = 0.039. The molecule contains a triangular array of osmium atoms [Os(1)Os(2) = 2.898(2)Å, Os(1)Os(3) = 2.886(2)Åand Os(2)O(3) = 2.911(2)Å] and nine terminally bonded carbonyl ligands. The C₅H₃N-2-C(H)N-i-Pr ligand is chelate bonded to Os(2) with the pyridine and imine nitrogens atoms axially and equatorially coordinated respectively [Os(2)N(1) = 2.00(2)Åand Os(2)N(2) = 2.11(2)Å]. The i-Pr-Pyca ligand is ortho-metallated at C(1) and forms a four membered ring containing Os(2), Os(3), C(1) and N(1), the Os(3)C(1) distance being 2.12(2)Å. The hydride, which could not be located unequivocally from a difference Fourier map is proposed to bridge the Os(2)(3) bond on the basis of stereochemical considerations.     

Growth of Rhodospirillum rubrum on synthesis gas: conversion of CO to H2 and poly-beta-hydroxyalkanoate

To examine the potential use of synthesis gas as a carbon and energy source in fermentation processes, Rhodospirillum rubrum was cultured on synthesis gas generated from discarded seed corn. The growth rates, growth and poly-beta-hydroxyalkanoates (PHA) yields, and CO oxidation/H(2) evolution rates were evaluated in comparison to the rates observed with an artificial synthesis gas mixture. Depending on the gas conditioning system used, synthesis gas either stimulated or inhibited CO-oxidation rates compared to the observations with the artificial synthesis gas mixture. Inhibitory and stimulatory compounds in synthesis gas could be removed by the addition of activated charcoal, char-tar, or char-ash filters (char, tar, and ash are gasification residues). In batch fermentations, approximately 1.4 mol CO was oxidized per day per g cell protein with the production of 0.75 mol H(2) and 340 mg PHA per day per g cell protein. The PHA produced from R. rubrum grown on synthesis gas was composed of 86% beta-hydroxybutyrate and 14% beta-hydroxyvalerate. Mass transfer of CO into the liquid phase was determined as the rate-limiting step in the fermentation.     

Effect of medium composition and sludge removal on the production, composition, and architecture of thermophilic (55 degrees C) acetate-utilizing granules from an upflow anaerobic sludge blanket reactor.

A thermophilic upflow anaerobic sludge blanket (UASB) reactor degrading acetate was started by applying published methods (W. M. Wiegant and A. W. A. de Man, Biotechnol. Bioeng. 28:718-77, 1986) for production of granules dominated by Methanothrix spp. The reactor was inoculated with thermophilic digested sludge. No granules were observed during the first 7 months of start-up of the UASB reactor. However, after the concentrations of potassium, phosphate, ammonium, and magnesium in the medium were gradually increased, granules developed, indicating that there was a critical concentration of one or more of the ions required for production of granules from the starting material. After several years of stable operation, the effect of removing 60% of the granular sludge was investigated. Immunologic qualitative and quantitative studies showed that removal of the granular sludge resulted in an increase in the number of the predominant methanogens, antigenically related to Methanosarcina thermophila TM-1 and Methanosarcina mazeii S-6, and Methanobacterium thermoautotrophicum delta H and GC1. These changes were accompanied by modifications of the microanatomy of the granules, as demonstrated histochemically and immunohistochemically. The results indicated that different catabolic pathways dominated in different regions of the granules, i.e., acetate oxidation in the middle of the granules, where there is a low acetate concentration, and an aceticlastic reaction in the outer surfaces, with a high acetate concentration. The results also showed that removal of granules from a UASB reactor which has been under steady-state operation for a long period can improve the reactor's performance via formation of denser and larger granules with improved microbial activities.     

Quantum Yields for CO(2) Uptake in C(3) and C(4) Plants: Dependence on Temperature, CO(2), and O(2) Concentration

The quantum yields of C₃ and C₄ plants from a number of genera and families as well as from ecologically diverse habitats were measured in normal air of 21% O₂ and in 2% O₂. At 30 C, the quantum yields of C₃ plants averaged 0.0524 ± 0.0014 mol CO₂/absorbed einstein and 0.0733 ± 0.0008 mol CO₂/absorbed einstein under 21 and 2% O₂. At 30 C, the quantum yields of C₄ plants averaged 0.0534 ± 0.0009 mol CO₂/absorbed einstein and 0.0538 ± 0.0011 mol CO₂/absorbed einstein under 21 and 2% O₂. At 21% O₂, the quantum yield of a C₃ plant is shown to be strongly dependent on both the intercellular CO₂ concentration and leaf temperature. The quantum yield of a C₄ plant, which is independent of the intercellular CO₂ concentration, is shown to be independent of leaf temperature over the ranges measured. The changes in the quantum yields of C₃ plants are due to changes in the O₂ inhibition. The evolutionary significance of the CO₂ dependence of the quantum yield in C₃ plants and the ecological significance of the temperature effects on the quantum yields of C₃ and C₄ plants are discussed.     

C(2)H(4): its purification for biological studies

A gas chromatographic technique is described for obtaining ultra high purity ¹⁴C₂H₄ for use in biological studies. ¹⁴C₂H₄ purchased from commercial sources contained readily detectable impurities including radioactive acetylene. Following purification on two different columns, no impurities were detected by high sensitivity gas chromatographic analysis. However, shortly thereafter impurities were detected as a result of radiation decomposition. Trapping and immediately regenerating ultra high purity ¹⁴C₂H₄ from dilute, filtered Hg (CIO₄)₂ solutions did not cause the formation of impurities, whereas additional impurities were formed when unpurified ¹⁴C₂H₄ was used. Impurities were also formed when ultra high purity ¹⁴C₂H₄ was stored in such solutions prior to its regeneration or when it was trapped and immediately regenerated from more concentrated Hg(CIO₄)₂ solutions.     

Variation in Quantum Yield for CO(2) Uptake among C(3) and C(4) Plants

The quantum yield for CO₂ uptake was measured on a number of C₃ and C₄ monocot and dicot species. Under normal atmospheric conditions (330 microliters per liter CO₂, 21% O₂) and a leaf temperature of 30°C, the average quantum yields (moles CO₂ per einstein) were as follows: 0.052 for C₃ dicots, 0.053 for C₃ grasses, 0.053 for NAD-malic enzyme type C₄ dicots, 0.060 for NAD-malic enzyme type C₄ grasses, 0.064 for phosphoenolpyruvate carboxykinase type C₄ grasses, 0.061 for NADP-malic enzyme C₄ dicots, and 0.065 for NADP-malic enzyme type C₄ grasses. The quantum yield under normal atmospheric conditions was temperature dependent in C₃ species, but apparently not in C₄ species. Light and temperature conditions during growth appeared not to influence quantum yield. The significance of variation in the quantum yields of C₄ plants was discussed in terms of CO₂ leakage from the bundle sheath cells and suberization of apoplastic regions of the bundle sheath cells.