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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

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Botryococcus braunii for the production of hydrocarbons and exopolysaccharides and the role of associated bacteria
Gouveai, João Diogo Guimarães - \ 2017
Wageningen University. Promotor(en): R.H. Wijffels, co-promotor(en): M.J. Barbosa; D. Sipkema. - Wageningen : Wageningen University - ISBN 9789463436960 - 157
biomass production - algae - algae culture - hydrocarbons - bacteria - biomassa productie - algen - algenteelt - koolwaterstoffen - bacteriën

Microalgae are photosynthetic organisms that are found worldwide in many different aquatic environments and therefore display an immense biological diversity. They are a promising source of many useful polymers that have industrial applications such as food, fuel, material and pharmaceutical. One microalga that has gathered quite a research community is Botryococcus braunii. The reason for its scientific club is the fact it can synthetize long chain hydrocarbons molecules from C20 to C40. These hydrocarbons have been found in oil-shales and tests show that it can be used as aviation fuel. Besides producing hydrocarbons, some strains of B. braunii can produce exopolysaccharides (EPS) composed mainly of galactose and a small fraction of fucose. The EPS has interesting rheological properties for the food industry and potential active compounds that could be used in the pharmaceutical industry .

Like many other microorganisms, microalgae in the natural environment are usually in the presence of bacteria. The presence of bacteria with microalgae can either have a beneficial or an antagonistic effect. For B. braunii little is known about the bacteria community present especially for the EPS producing strain. For that reason, the aim of this thesis was to investigate B. braunii’s associated bacteria with the aim of improving B. braunii’s biomass growth and hydrocarbon and EPS content. In chapter one, we introduced the topic of microalgae as a potential source of sustainable polymers and we introduced the species B. braunii, describing its characteristics and scientific interest. It is also introduced the topic of microalgae and bacteria associations by looking at other studies from literature.

In chapter two, 16 publically available strains of B. braunii were ordered in culture banks and screened for biomass productivity, hydrocarbon and total carbohydrate content. The aim of the study was to identify one or more good strains that displayed high biomass productivity as well as hydrocarbon or total carbohydrate content. In seven strains out of 16 cultivated in 250 mL volume Erlenmeyer flaks, we detected 5 to 42 % content of hydrocarbons of the dry biomass with four strains producing botryococcenes (C30-C34) and three strains producing alkanes (C20-C25). Two strains showed high amounts of EPS content above 50 % per dry biomass. Seven strains comprising of the strains with higher biomass productivity plus the highest hydrocarbons and EPS content, were tested for scalability using bench scale 800 mL volume bubble column reactors. Two strains, AC761 which produces botryococcenes and CCALA778 which produces EPS, were selected as the most promising B. braunii strains for industrial production of hydrocarbon and EPS.

In chapter three, we studied the bacterial community associated with B. braunii. We cultured 12 strains from the initial 16 from chapter 2 and extracted the DNA from samples taken over a time period of 12 days. It was clear from this study that B. braunii hosts a variety of bacterial species and still maintain its growth. The bacteria families Rhizobiaceae, Bradyrhizobiaceae and Comamonadaceae were found in all 12 strains. These families which belong to the phylum Proteobacteria could have an important role regarding B. braunii growth. Each strain displayed a different bacterial community composition but all the strains from the CAEN culture collection clustered near each other suggesting that the algae culture collection could have an influence on the bacterial community composition. Bacteria genus identification based on 16S rRNA gene amplicon similarity showed several genera present including Rhizobium spp. and Variovorax spp.. Two genera were found that are possibly linked to hydrocarbon degradation: Sphingomonas spp. and Rhodobacter spp..

In chapter four, we investigated further B. braunii CCALA778 which was shown in chapter 2 to accumulate high amounts of EPS. We investigated the effects of antibiotics on algal growth, EPS accumulation and bacterial community composition of CCALA778. Taxonomical identification by 16S rRNA gene analysis indicated that most of the bacteria present with CCALA778 were Gram-negative. Of all antibiotics and antibiotic mixes, only the treatment with Penicillin did not affect the growth of B. braunii. The remaining antibiotics halted the growth of CCALA778 while they were active. The exceptions were with the antibiotics Chloramphenicol, Gentamycin and Linezolid which permanently ceased the growth of CCALA778. The accumulation of EPS seemed to be related to biomass growth, but we did also observe a reduction of EPS with the cultures treated with Penicillin suggesting that bacteria could have an effect on the EPS content. Antibiotics had specific effects on the bacterial community with all treatments showing significant changes over time. The most efficient treatment in removing bacteria were the mixes Metronidazole-Rifampicin-Penicillin and Penicillin-Rifampicin which were the only treatments to show significant changes in the bacterial community when compared to the untreated cultures after 10 days of cultivation. Antibiotics and antibiotic mixes can create changes in the bacterial community but it is unlikely that they alone can lead to axenic B. braunii cultures.

In chapter five, we used Ultra Violet-C light (UVC) to reduce bacteria diversity and abundance present in B. braunii CCALA778. UVC is highly effective in inactivating bacteria and for that reason is being investigated further in medicinal applications. After applying the UVC to B. braunii CCALA778, we were able to reduce the relative abundance of 16S rRNA genes assigned to bacteria to less than 1 % compared to the 70% in the non-treated cultures. With the UVC treated CCALA778 we observed several physiological changes. The UV treated cultures with reduced bacterial load showed nearly double the EPS accumulation when compared to the untreated. To confirm that we did not see an artefact in our results due to the UVC treatment, UVC treated cultures were also inoculated with bacteria from the untreated and we observed a reduction of EPS similar to what we saw with the untreated cultures. There were no changes to the EPS composition after the removal of the bacteria. Other physiological changes were observed, namely that colony size of B. braunii CCALA778 significantly increased when compared to the untreated culture and the UV treated with bacteria. We hypothesise that the increase in colony size was probably due to the fact there was more EPS accumulated which helped with cell aggregation. We also observed an increase on the biomass growth in the UV-treated CCALA778 which we hypothesized being related to the fact that there was none or hardly any competition for essential micronutrients such as phosphate. From this study we concluded that the associated bacteria present with B. braunii CCALA778 were antagonistic. We believe the reason why the bacteria were antagonistic is because of the readily available EPS which is a rich source of organic compounds that bacteria could use for their own proliferation allowing them to compete with B. braunii for essential nutrients.

In chapter 6, we discuss the implications from our previous 4 experimental chapters. The aim of the study was to improve the biomass productivity and hydrocarbon and EPS content of the microalgae B. braunii. In brief, B. braunii displayed a wide range of physiological traits regarding biomass productivity and hydrocarbon and total carbohydrate content. We showed that B. braunii can co-habit with a wide range of bacteria diversity and abundance and that the associated bacteria were antagonistic to CCALA778 by affecting its biomass growth. We also showed that by removing the associated bacteria we can increase the EPS accumulation. Currently most of the research on microalgae and bacteria interactions, focus on the positive side, but we must understand also how bacteria can be antagonistic to microalga growth. Bacteria can be antagonistic to microalgae by competing for nutrients and also being detrimental to industrial process by degrading the product of interest in the case of organic carbons such as EPS. Therefore it is unlikely we can use the benefits that bacteria can provide such as enhancing growth to improve the cultivation of B. braunii and other similar microalgae species that secrete EPS. Since bacteria can be antagonistic to microalgae that secrete large amounts of organic compounds such as EPS, it is imperative to minimize contamination in large scale photobioreactors (PBR). It is important because in large scale PBR, contamination can occur leading to downtime of the reactors. If microalgae industry is to advance, it must develop PBR units that prevent contamination of bacteria from the surrounding environment.

Use of methylene blue uptake for assessing cell viability of colony-forming microalgae
Lemos Bicas, J. ; Kleinegris, D.M.M. ; Barbosa, M.J. - \ 2015
Algal Research 8 (2015). - ISSN 2211-9264 - p. 174 - 180.
botryococcus-braunii - yeast cells - race-b - biomass - hydrocarbons - extraction - chemicals - dyes
During the past few years, interest in microalgae has grown, mainly because of their potential for biofuel production. Botryococcus braunii, a green microalga that can accumulate more than half of its dry weight as hydrocarbons, is one of the most important examples. This microorganism grows in colonies and there has been no reliable viability protocol reported for this species as yet. Knowing the number of dead cells in cultures is essential for the development of efficient bioprocesses such as non-destructive extraction procedures (“milking”) to obtain lipid soluble substances from microalgal biomass. Our study presents a simple colorimetric method to determine the proportion of living to dead cells in cultures, based on the uptake of methylene blue in solution by dead B. braunii cells. The main parameters influencing this process were investigated and used to develop a protocol. This technique was validated using flow cytometry and Neochloris oleoabundans, and appears not to be limited to use with B. braunii.
Evidence for an unidentified non-photochemical ground-level source of formaldehyde in the Po Valley with potential implications for ozone production
Kaiser, J. ; Wolfe, G.M. ; Bohn, B. ; Ganzeveld, L.N. - \ 2015
Atmospheric Chemistry and Physics 15 (2015). - ISSN 1680-7316 - p. 1289 - 1298.
volatile organic-compounds - exchange cafe model - total oh reactivity - tropospheric degradation - chemical mechanism - gas-phase - part - atmosphere - forest - hydrocarbons
Ozone concentrations in the Po Valley of northern Italy often exceed international regulations. As both a source of radicals and an intermediate in the oxidation of most volatile organic compounds (VOCs), formaldehyde (HCHO) is a useful tracer for the oxidative processing of hydrocarbons that leads to ozone production. We investigate the sources of HCHO in the Po Valley using vertical profile measurements acquired from the airship Zeppelin NT over an agricultural region during the PEGASOS 2012 campaign. Using a 1-D model, the total VOC oxidation rate is examined and discussed in the context of formaldehyde and ozone production in the early morning. While model and measurement discrepancies in OH reactivity are small (on average 3.4 ± 13%), HCHO concentrations are underestimated by as much as 1.5 ppb (45%) in the convective mixed layer. A similar underestimate in HCHO was seen in the 2002–2003 FORMAT Po Valley measurements, though the additional source of HCHO was not identified. Oxidation of unmeasured VOC precursors cannot explain the missing HCHO source, as measured OH reactivity is explained by measured VOCs and their calculated oxidation products. We conclude that local direct emissions from agricultural land are the most likely source of missing HCHO. Model calculations demonstrate that radicals from degradation of this non-photochemical HCHO source increase model ozone production rates by as much as 0.6 ppb h-1 (12%) before noon.
Hydrothermal Deoxygenation of Triglycerides over Pd/C aided by In Situ Hydrogen Production from Glycerol Reforming
Hollak, S.A.W. ; Jong, K.P. de; Es, D.S. van; Ariëns, M.A. - \ 2014
ChemSusChem 7 (2014)4. - ISSN 1864-5631 - p. 1057 - 1062.
catalytic deoxygenation - fatty-acids - supercritical water - reaction pathways - oil - carbon - hydrodeoxygenation - hydrocarbons - derivatives - selectivity
A one-pot catalytic hydrolysis–deoxygenation reaction for the conversion of unsaturated triglycerides and free fatty acids to linear paraffins and olefins is reported. The hydrothermal deoxygenation reactions are performed in hot compressed water at 250¿°C over a Pd/C catalyst in the absence of external H2. We show that aqueous–phase reforming (APR) of glycerol and subsequent water–gas-shift reaction result in the in situ formation of H2. While this has a significant positive effect on the deoxygenation activity, the product selectivity towards high-value, long-chain olefins remains high.
Catalytic Deoxygenation of Fatty Acids: Elucidation of the Inhibition Process
Hollak, S.A.W. ; Jong, K.P. de; Es, D.S. van - \ 2014
ChemCatChem 6 (2014)9. - ISSN 1867-3880 - p. 2648 - 2655.
stearic-acid - mesoporous carbon - vegetable-oils - diesel fuel - continuous decarboxylation - palladium catalysts - reaction pathways - supported nickel - hydrocarbons - adsorption
Catalytic deoxygenation of unsaturated fatty acids in the absence of H2 is known to suffer from significant catalyst inhibition. Thus far, no conclusive results have been reported on the cause of deactivation. Here we show that CC double bonds present in the feed or the products dramatically reduce the deoxygenation activity of supported palladium catalysts. In the case of stearic acid deoxygenation the addition of 0.1 equivalents of a mono-unsaturated fatty acid or olefin already reduces the catalytic deoxygenation activity by 60¿%. This effect becomes more pronounced with an increasing number of double bonds. The inhibition is shown to be reversible in H2 atmosphere, indicating no significant contribution from irreversibly deposited hard coke. Furthermore, the type of support material has no apparent effect on catalyst inhibition. Hence we propose that initial catalyst inhibition proceeds through reversible adsorption of CC double bonds on the palladium active sites.
Structure elucidation of female-specific volatiles released by the parasitoid wasp Trichogramma turkestanica (Hymenoptera: Trichogrammatidae)
Tröger, A. ; Beek, T.A. van; Huigens, M.E. ; Silva, I.M.M.S. ; Posthumus, M.A. ; Francke, W. - \ 2014
Beilstein Journal of Organic Chemistry 10 (2014). - ISSN 1860-5397 - p. 767 - 773.
sex-pheromone - aggregation pheromone - beetle - stereochemistry - identification - hydrocarbons - esters - acid
Females of the parasitoid wasp Trichogramma turkestanica produce the putative polydeoxypropionates (2E,4E,6S,8S,10S)-4,6,8,10-tetramethyltrideca-2,4-diene and (2E,4E,6S,8S,10S)-4,6,8,10-tetramethyltrideca-2,4-dien-1-ol or their enantiomers as sex specific volatiles. The structures were assigned on the basis of GC–MS investigations using synthetic reference compounds.
Data from: Stable isotope labeled n-alkanes to assess digesta passage kinetics through the digestive tract of ruminants
Warner, D. ; Ferreira, L.M.M. ; Breuer, M.J.H. ; Dijkstra, J. ; Pellikaan, W.F. - \ 2013
digesta passage - hydrocarbons - herbivores - ruminants
We describe the use of carbon stable isotope (13C) labeled n-alkanes as a potential internal tracer to assess passage kinetics of ingested nutrients in ruminants. Plant cuticular n-alkanes originating from intrinsically 13C labeled ryegrass plants were pulse dosed intraruminally in four rumen-cannulated lactating dairy cows receiving four contrasting ryegrass silage treatments that differed in nitrogen fertilization level (45 or 90 kg nitrogen ha−1) and maturity (early or late). Passage kinetics through the gastrointestinal tract were derived from the δ13C (i.e. the ratio 13C:12C) in apparently undigested fecal material. Isotopic enrichment was observed in a wide range of long-chain n-alkanes (C27–C36) and passage kinetics were determined for the most abundant C29, C31 and C33 n-alkanes, for which a sufficiently high response signal was detected by combustion isotope ratio mass spectrometry. Basal diet treatment and carbon chain length of n-alkanes did not affect fractional passage rates from the rumen (K1) among individual n-alkanes (3.71–3.95%/h). Peak concentration time and transit time showed a quantitatively small, significant (p≤0.002) increase with carbon chain length. K1 estimates were comparable to those of the 13C labeled digestible dry matter fraction (3.38%/h; r = 0.61 to 0.71; p≤0.012). A literature review has shown that n-alkanes are not fermented by microorganisms in the rumen and affirms no preferential depletion of 13C versus 12C. Our results suggest that 13C labeled n-alkanes can be used as nutrient passage tracers and support the reliability of the δ13C signature of digestible feed nutrients as a tool to measure nutrient-specific passage kinetics.
Tolerance of Four Tropical Tree Species to Heavy Petroleum Contamination
Perez-Hernandez, I. ; Ochoa-Gaona, S. ; Schroeder, R.H.A. ; Rivera-Cruz, M.C. ; Geissen, V. - \ 2013
Water Air and Soil Pollution 224 (2013)8. - ISSN 0049-6979
soil-water relations - oxidative stress - bioremediated soils - seed-germination - end-point - phytoremediation - oil - hydrocarbons - growth - plants
Four species of trees were selected to evaluate the tolerance to heavy crude oil contamination by means of a tolerance index integrating germination, height, biomass and survival as variables. Fresh seeds to Cedrela odorata (tropical cedar), Haematoxylum campechianum (tinto bush), Swietenia macrophylla (mahogany) and Tabebuia rosea (macuilis) were planted in a Vertisol to which heavy crude petroleum was added at four different treatments (C0, 0; C1, 18,940; C2, 44,000; and C3, 57,000 mg kg(-1)), with the control being uncontaminated soil. The experiment was carried out in a greenhouse during 203 days with a completely random design. The presence of petroleum in soil stimulated and increased germination of S. macrophylla and C. odorata, accelerated the germination of T. rosea and did not affect the germination of H. campechianum. The height and biomass of all species was reduced in the presence of petroleum in the soil. The survival of S. macrophylla and H. campechianum was not affected by petroleum at any concentration studied. On the other hand, C. odorata and T. rosea showed high mortality at all concentrations. The tolerance index showed that S. macrophylla was best at tolerating petroleum in soil and could be employed as a productive alternative for the advantageous use of contaminated sites. The use of tree species could be important because of the great potential of trees for phytoremediation due to their long life, biomass and deep roots that can penetrate and remediate deeper soil layers.
Supported La2O3 and MgO nanoparticles as solid base catalysts for aldol reaction while suppressing dehydration at room temperaure
Frey, A.M. ; Kumar Karmee, S. ; Jong, K.P. de; Bitter, J.H. ; Hanefeld, U. - \ 2013
ChemCatChem 5 (2013). - ISSN 1867-3880 - p. 594 - 600.
platinum catalysts - carbon nanofibers - liquid - hydrotalcites - oxide - hydrogenation - condensation - hydrocarbons - chemicals - basicity
La2O3 and MgO nanoparticles (3–4 nm) supported on carbon nanofibers were evaluated as solid base catalysts for the aldol reaction of benzaldehyde and acetone at room temperature. Both catalysts were found to be highly active and selective with respect to 4-hydroxy-4-phenylbutan-2-one, thus suppressing the elimination of H2O, which is a challenge for this reaction. La2O3 nanoparticles were more stable towards water, which makes them more applicable than MgO nanoparticles as a solid base catalyst for this reaction.
Comparison of Tungsten and Molybdenum Carbide Catalysts for the Hydrodeoxygenation of Oleic Acid
Hollak, S.A.W. ; Gosselink, R.J.A. ; Es, D.S. van; Bitter, J.H. - \ 2013
ACS Catalysis 3 (2013)12. - ISSN 2155-5435 - p. 2837 - 2844.
stearic-acid - fatty-acids - ruthenium catalysts - diesel production - reaction pathways - deoxygenation - biodiesel - hydrocarbons - adsorption - oils
Group 6 (W, Mo) metal carbide catalysts are promising alternatives to hydrodesulfurization (NiMo, CoMo) catalysts and group 10 (Pd) type catalysts in the deoxygenation of vegetable fats/oils. Herein, we report a comparison of carbon nanofiber-supported W2C and Mo2C catalysts on activity, selectivity, and stability for the hydrodeoxygenation of oleic acid to evaluate the catalytic potential for the upgrading of fat/oil feeds. W2C/CNF was more selective toward olefins, whereas Mo2C/CNF was more selective toward paraffins. This was related to the hydrogenation activities of the respective metal carbides. Mo2C/CNF showed higher activity and stability compared with W2C/CNF.
Biodegradation of aged diesel in diverse soil matrixes: impact of environmental conditions and bioavailability on microbial remediation capacity
Sutton, N.B. ; Gaans, P. van; Langenhoff, A.A.M. ; Maphosa, F. ; Smidt, H. ; Grotenhuis, J.T.C. ; Rijnaarts, H.H.M. - \ 2013
Biodegradation 24 (2013)4. - ISSN 0923-9820 - p. 487 - 498.
oil-contaminated soil - real-time pcr - crude-oil - bioremediation - community - sediments - hydrocarbons - degradation - scale - site
While bioremediation of total petroleum hydrocarbons (TPH) is in general a robust technique, heterogeneity in terms of contaminant and environmental characteristics can impact the extent of biodegradation. The current study investigates the implications of different soil matrix types (anthropogenic fill layer, peat, clay, and sand) and bioavailability on bioremediation of an aged diesel contamination from a heterogeneous site. In addition to an uncontaminated sample for each soil type, samples representing two levels of contamination (high and low) were also used; initial TPH concentrations varied between 1.6 and 26.6 g TPH/kg and bioavailability between 36 and 100 %. While significant biodegradation occurred during 100 days of incubation under biostimulating conditions (64.4-100 % remediation efficiency), low bioavailability restricted full biodegradation, yielding a residual TPH concentration. Respiration levels, as well as the abundance of alkB, encoding mono-oxygenases pivotal for hydrocarbon metabolism, were positively correlated with TPH degradation, demonstrating their usefulness as a proxy for hydrocarbon biodegradation. However, absolute respiration and alkB presence were dependent on soil matrix type, indicating the sensitivity of results to initial environmental conditions. Through investigating biodegradation potential across a heterogeneous site, this research illuminates the interplay between soil matrix type, bioavailability, and bioremediation and the implications of these parameters for the effectiveness of an in situ treatment
Chemical oxidation of cable insulating oil contaminated soil
Jinlan Xu, ; Pancras, T. ; Grotenhuis, J.T.C. - \ 2011
Chemosphere 84 (2011)2. - ISSN 0045-6535 - p. 272 - 277.
catalyzed hydrogen-peroxide - modified fentons reactions - remediation - reagent - bioremediation - hydrocarbons - degradation - systems
Leaking cable insulating oil is a common source of soil contamination of high-voltage underground electricity cables in many European countries. In situ remediation of these contaminations is very difficult, due to the nature of the contamination and the high concentrations present. Chemical oxidation leads to partial removal of highly contaminated soil, therefore chemical oxidation was investigated and optimized aiming at a subsequent bioremediation treatment. Chemical oxidation of cable oil was studied with liquid H2O2 and solid CaO2 as well as permanganate at pH 1.8, 3.0 and 7.5. Liquid H2O2 most effectively removed cable oil at pH 7.5 (24%). At pH 7.5 poor oil removal of below 5% was observed with solid CaO2 and permanganate within 2 d contact time, whereas 18% and 29% was removed at pH 1.8, respectively. A prolonged contact time of 7 d showed an increased oil removal for permanganate to 19%, such improvement was not observed for CaO2. Liquid H2O2 treatment at pH 7.5 was most effective with a low acid use and was best fit to a subsequent bioremediation treatment. To further optimize in situ chemical oxidation with subsequent bioremediation the effect of the addition of the iron catalyst and a stepwise liquid H2O2 addition was performed. Optimization led to a maximum of 46% cable oil removal with 1469 mM of H2O2, and 6.98 mM Fe(II) chelated with citric acid (H2O2:FeSO4 = 210:1 (mol mol-1). The optimum delivery method was a one step addition of the iron catalyst followed by step wise addition of H2O2
The role of boundary layer dynamics on the diurnal evolution of isoprene and the hydroxyl radical over tropical forests
Vilà-Guerau de Arellano, J. ; Patton, E.G. ; Karl, T. ; Dries, K. van den; Barth, M.C. ; Orlando, J.J. - \ 2011
Journal of Geophysical Research: Atmospheres 116 (2011)D7. - ISSN 2169-897X - 16 p.
large-eddy simulation - atmospheric chemistry - stiff odes - fluxes - entrainment - emissions - scalars - model - hydrocarbons - inversion
We investigate diurnal variability of isoprene and related chemical species in the Amazonian region. The dynamics and chemistry of an atmospheric boundary layer are studied with a large-eddy simulation code and a mixed-layer model which are guided by observations available for the same area. The main features of isoprene and related species are reproduced well, but their evolution raises questions regarding the physical and chemical processes responsible for the observed diurnal behaviors. To address these questions, we systematically examine the role of (1) the exchange of chemical species between the free troposphere and the atmospheric boundary layer (entrainment), (2) surface isoprene and nitric oxide emissions, and (3) new chemical pathways to recycle the hydroxyl radical. The entrainment flux of isoprene is shown to be equally important as surface isoprene emissions in determining the isoprene temporal evolution. Varying the relationship between the initial isoprene mixing ratio in the boundary layer and that in the overlying free troposphere in the early morning results in an 50% increase/decrease in isoprene mixing ratio or more within the atmospheric boundary layer at noon. Entrainment of free tropospheric nitrogen oxides creates changes of similar magnitude to the boundary layer isoprene mixing ratio. These effects of entrainment and surface emissions on isoprene are found for two different chemical regimes. The introduction of an OH recycling pathway in the chemical mechanism increases midday OH. Our findings show that atmospheric dynamics and chemistry are equally important for interpreting the diurnal observation of reactants and for including in regional-scale modeling efforts where turbulence is parameterized.
Response to "Comment on Halogenated Contaminants in Farmed Salmon, Trout Tilapia, Pangasius, and Shrimp"
Leeuwen, S.P.J. van; Velzen, M.J.M. van; Swart, C.P. ; Veen, I. van der; Traag, W.A. ; Boer, J. de - \ 2009
Environmental Science and Technology 43 (2009)19. - ISSN 0013-936X - p. 7586 - 7587.
polybrominated diphenyl ethers - pearl river delta - health-risk assessment - fresh-water fish - south china - organochlorine pesticides - seafood products - hong-kong - exposure - hydrocarbons
On inferring isoprene emission surface flux from atmospheric boundary layer concentration measurements
Vilà-Guerau de Arellano, J. ; Dries, K. van den; Pino, D. - \ 2009
Atmospheric Chemistry and Physics 9 (2009). - ISSN 1680-7316 - p. 3629 - 3640.
model - hydrocarbons - entrainment - inversion - forest - parameterization - dynamics - cumulus - amazon - site
We examine the dependence of the inferred isoprene surface emission flux from atmospheric concentration on the diurnal variability of the convective boundary layer (CBL). A series of systematic numerical experiments carried out using the mixed-layer technique enabled us to study the sensitivity of isoprene fluxes to the entrainment process, the partition of surface fluxes, the horizontal advection of warm/cold air masses and subsidence. Our findings demonstrate the key role played by the evolution of boundary layer height in modulating the retrieved isoprene flux. More specifically, inaccurate values of the potential temperature lapse rate lead to changes in the dilution capacity of the CBL and as a result the isoprene flux may be overestimated or underestimated by as much as 20%. The inferred emission flux estimated in the early morning hours is highly dependent on the accurate estimation of the discontinuity of the thermodynamic values between the residual layer and the rapidly forming CBL. Uncertainties associated with the partition of the sensible and latent heat flux also yield large deviations in the calculation of the isoprene surface flux. Similar results are obtained if we neglect the influence of warm or cold advection in the development of the CBL.We show that all the above-mentioned processes are non-linear, for which reason the dynamic and chemical evolutions of the CBL must be solved simultaneously. Based on the discussion of our results, we suggest the measurements needed to correctly apply the mixed-layer technique in order to minimize the uncertainties associated with the diurnal variability of the convective boundary layer.
Atmospheric oxidation capacity sustained by a tropical forest
Lelieveld, J. ; Butler, T. ; Crowley, J.N. ; Dillon, T.J. ; Fischer, H. ; Ganzeveld, L.N. ; Harder, H. ; Lawrence, M.G. ; Martinez, M. ; Taraborelli, D. ; Williams, J. - \ 2008
Nature 452 (2008)7188. - ISSN 0028-0836 - p. 737 - 740.
volatile organic-compounds - isoprene - chemistry - hydrocarbons - emission - model - thermotolerance - terrestrial - simulation - budget
Terrestrial vegetation, especially tropical rain forest, releases vast quantities of volatile organic compounds (VOCs) to the atmosphere1, 2, 3, which are removed by oxidation reactions and deposition of reaction products4, 5, 6. The oxidation is mainly initiated by hydroxyl radicals (OH), primarily formed through the photodissociation of ozone4. Previously it was thought that, in unpolluted air, biogenic VOCs deplete OH and reduce the atmospheric oxidation capacity5, 6, 7, 8, 9, 10. Conversely, in polluted air VOC oxidation leads to noxious oxidant build-up by the catalytic action of nitrogen oxides5, 6, 7, 8, 9, 10 (NOx = NO + NO2). Here we report aircraft measurements of atmospheric trace gases performed over the pristine Amazon forest. Our data reveal unexpectedly high OH concentrations. We propose that natural VOC oxidation, notably of isoprene, recycles OH efficiently in low-NOx air through reactions of organic peroxy radicals. Computations with an atmospheric chemistry model and the results of laboratory experiments suggest that an OH recycling efficiency of 40¿80 per cent in isoprene oxidation may be able to explain the high OH levels we observed in the field. Although further laboratory studies are necessary to explore the chemical mechanism responsible for OH recycling in more detail, our results demonstrate that the biosphere maintains a remarkable balance with the atmospheric environment
Thermodynamic analysis of direct internal reforming of methane and butane in proton and oxygen conducting fuel cells
Biesheuvel, P.M. ; Geerlings, J.J.C. - \ 2008
Journal of Power Sources 185 (2008)2. - ISSN 0378-7753 - p. 1162 - 1167.
carbon formation - hydrocarbons - efficiency - operation - model
We present results of a thermodynamic analysis of direct internal reforming fuel cells, based on either a proton conducting fuel cell (FC-H+) or an oxygen ion conducting fuel cell (FC-O2-). We analyze the option of methane as fuel as well as butane. The model self-consistently combines all chemical equilibria in both the anode and cathode compartments with the proton or oxygen transfer rates through the membrane without predefining fuel utilization. The highest efficiency for generating electricity is obtained in a FC-H+ at a steam-to-carbon (SCR) ratio of around 2.5. In this case, the efficiency is 88% at 600 degrees C and 1 bar and increases when the temperature is decreased, or pressure increased. For an FC-O2- the highest efficiency is obtained when no steam is added, and is always several %-points lower than for the FC-H+. Important is that at the optimum SCR, coke formation is thermodynamically predicted not to occur in a FC-H*, irrespective of the rate of proton transfer through the membrane, down to operating temperatures of 500 degrees C, both for methane and for butane as fuel. Likewise, in an FC-O2- coke formation is thermodynamically not predicted to occur at the optimum oxygen ion transport rate (that is required for the highest efficiency). However, when the oxygen ion transport rate decreases, both for methane and for butane as fuel, we at some point enter the coke-forming regime. Thus, for direct internal reforming of methane or butane, we argue on thermodynamic grounds that a proton conducting fuel cell can be advantageous over an oxygen ion conducting fuel cell with respect to fuel cell efficiency and risk of coke formation. (C) 2008 Elsevier B.V. All rights reserved.
Assessment of chronic effects of n-undecane on plants
Dueck, T.A. ; Dijk, C.J. van - \ 2008
Wageningen : Plant Research International (Report / Plant Research International 204) - 24
gewassen - risicoschatting - koolwaterstoffen - fumigatie - phaseolus - brassica - solanum - plantago - fytotoxiciteit - bomen - crops - risk assessment - hydrocarbons - fumigation - phytotoxicity - trees
This report describes a study that was performed to quantify the effects of undecane on plants in order to derive no-observed-effect-concentrations (NOECs) for each plant species.
Assessment of chronic effects of 1,3,5-trimethyl-benzene (mesitylene) on plants
Dueck, T.A. ; Dijk, C.J. van - \ 2008
Wageningen : Plant Research International (Report / Plant Research International 203) - 24
fytotoxiciteit - koolwaterstoffen - fumigatie - gewassen - phaseolus - brassica - picea - trifolium - solanum - holcus - plantago - bomen - risicoschatting - phytotoxicity - hydrocarbons - fumigation - crops - trees - risk assessment
This report describes a study that was performed to quantify the effects of mesitylene on plants in order to derive no-observed-effect-concentrations (NOECs) for each plant species.
Chromium-incorporated TUD-1 as a new visible light-sensitive photo-catalyst for selective oxidation of propane
Hamdy Mohamed Saad, M.S. ; Berg, O. ; Jansen, J.C. ; Maschmeyer, T. ; Arafat, A. ; Moulijn, J.A. ; Mul, G. - \ 2006
Catalysis today 117 (2006)1-3. - ISSN 0920-5861 - p. 337 - 342.
containing mesoporous silica - metal-oxide surfaces - photocatalytic reaction - irradiation - combustion - no - dehydrogenation - hydrocarbons - reduction - zeolite
Chromium was incorporated in the framework of TUD-1 mesoporous silica by a one-pot synthesis procedure, using triethanolamine as a bi-functional template. The Cr-TUD-1 catalyst was characterized by means of X-ray diffraction, high-resolution transmission electron microscopy, UV¿vis and Raman spectroscopy, as well as elemental analysis and N2 sorption measurements. The results indicate that chromium is incorporated as tetrahedrally co-ordinated Cr6+ in the framework of TUD-1. When tested as a catalyst for the photo-oxidation of propane, Cr-TUD-1 showed high activity and high selectivity towards acetone under visible light irradiation (¿ = 435 nm).
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