Staff Publications

Staff Publications

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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.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Description and evaluation of a detailed gas-phase chemistry scheme in the TM5-MP global chemistry transport model (r112)
    Myriokefalitakis, Stelios ; Daskalakis, Nikos ; Gkouvousis, Angelos ; Hilboll, Andreas ; Noije, Twan Van; Williams, Jason E. ; Sager, Philippe Le; Huijnen, Vincent ; Houweling, Sander ; Bergman, Tommi ; Rasmus Nüß, Johann ; Vrekoussis, Mihalis ; Kanakidou, Maria ; Krol, Maarten C. - \ 2020
    Geoscientific Model Development 13 (2020)11. - ISSN 1991-959X - p. 5507 - 5548.

    This work documents and evaluates the tropospheric gas-phase chemical mechanism MOGUNTIA in the three-dimensional chemistry transport model TM5-MP. Compared to the modified CB05 (mCB05) chemical mechanism previously used in the model, MOGUNTIA includes a detailed representation of the light hydrocarbons (C1-C4) and isoprene, along with a simplified chemistry representation of terpenes and aromatics. Another feature implemented in TM5-MP for this work is the use of the Rosenbrock solver in the chemistry code, which can replace the classical Euler backward integration method of the model. Global budgets of ozone (O3), carbon monoxide (CO), hydroxyl radicals (OH), nitrogen oxides (NOx), and volatile organic compounds (VOCs) are analyzed, and their mixing ratios are compared with a series of surface, aircraft, and satellite observations for the year 2006. Both mechanisms appear to be able to satisfactorily represent observed mixing ratios of important trace gases, with the MOGUNTIA chemistry configuration yielding lower biases than mCB05 compared to measurements in most of the cases. However, the two chemical mechanisms fail to reproduce the observed mixing ratios of light VOCs, indicating insufficient primary emission source strengths, oxidation that is too fast, and/or a low bias in the secondary contribution to C2-C3 organics via VOC atmospheric oxidation. Relative computational memory and time requirements of the different model configurations are also compared and discussed. Overall, the MOGUNTIA scheme simulates a large suite of oxygenated VOCs that are observed in the atmosphere at significant levels. This significantly expands the possible applications of TM5-MP.

    Quantifying burning efficiency in megacities using the NO2ĝ•CO ratio from the Tropospheric Monitoring Instrument (TROPOMI)
    Lama, Srijana ; Houweling, Sander ; Boersma, K.F. ; Eskes, Henk ; Aben, Ilse ; Denier Van Der Gon, Hugo A.C. ; C. Krol, Maarten ; Dolman, Han ; Borsdorff, Tobias ; Lorente, Alba - \ 2020
    Atmospheric Chemistry and Physics 20 (2020)17. - ISSN 1680-7316 - p. 10295 - 10310.

    This study investigates the use of co-located nitrogen dioxide (NO2) and carbon monoxide (CO) retrievals from the TROPOMI satellite to improve the quantification of burning efficiency and emission factors (EFs) over the megacities of Tehran, Mexico City, Cairo, Riyadh, Lahore, and Los Angeles. Efficient combustion is characterized by high NOx (NOCNO2) and low CO emissions, making the NO2=CO ratio a useful proxy for combustion efficiency (CE). The local enhancement of CO and NO2 above megacities is well captured by TROPOMI at short averaging times compared with previous satellite missions. In this study, the upwind background and plume rotation methods are used to investigate the accuracy of satellitederived 1NO2=1CO ratios. The column enhancement ratios derived using these two methods vary by 5% to 20% across the selected megacities. TROPOMI-derived column enhancement ratios are compared with emission ratios from the EDGAR v4.3.2 (Emission Database for Global Atmospheric Research v4.3.2) and the MACCity (Monitoring Atmospheric Chemistry and Climate and CityZen) 2018 emission inventories. TROPOMI correlates strongly (r D 0:85 and 0.7) with EDGAR and MACCity, showing the highest emission ratio for Riyadh and lowest emission ratio for Lahore. However, inventory-derived emission ratios are 60% to 85% higher than TROPOMI column enhancement ratios across the six megacities. The short lifetime of NO2 and the different vertical sensitivity of TROPOMI NO2 and CO explain most of this difference. We present a method to translate TROPOMI-retrieved column enhancement ratios into corresponding emission ratios, thereby accounting for these influences. Except for Los Angeles and Lahore, TROPOMI-derived emission ratios are close (within 10% to 25 %) to MACCity values. For EDGAR, however, emission ratios are 65% higher for Cairo and 35% higher for Riyadh. For Los Angeles, EDGAR and MACCity are a factor of 2 and 3 higher than TROPOMI respectively. The air quality monitoring networks in Los Angeles and Mexico City are used to validate the use of TROPOMI. For Mexico City and Los Angeles, these measurements are consistent with TROPOMI-derived emission ratios, demonstrating the potential of TROPOMI with respect to monitoring burning efficiency.

    RNA-seq analysis of Clostridium beijerinckii DSM 6423 at early exponential, acetogenic, and solventogenic growth phase on rhamnose compared to glucose
    Diallo, M. ; Simons, Andre ; Wal, H. van der; Collas, Florent ; Houweling-Tan, G.B.N. ; Kengen, S.W.M. ; Lopez Contreras, A.M. - \ 2019
    Wageningen Food and Biobased Research
    E-MTAB-7487 - ERP112812 - PRJEB30358 - Clostridium beijerinckii
    This experiment aim was to characterize the catabolism of L-rhamnose of Clostridium beijerinckii DSM 6423 by transcriptomic analysis, generating new insights and knowledge on utilization of L-rhamnose for production of chemicals, including Isopropanol, Butanol, Ethanol (IBE) and 1,2-propandiol. These analysis on cultures grown on L-rhamnose compared to D-glucose grown cultures showed upregulation of the L-rhamnose-related clusters and genes, and lower expression of the solventogenic genes, which was reflected in the products formed.
    What caused the extreme CO concentrations during the 2017 high-pollution episode in India?
    Dekker, Iris N. ; Houweling, Sander ; Pandey, Sudhanshu ; Krol, Maarten ; Röckmann, Thomas ; Borsdorff, Tobias ; Landgraf, Jochen ; Aben, Ilse - \ 2019
    Atmospheric Chemistry and Physics 19 (2019)6. - ISSN 1680-7316 - p. 3433 - 3445.

    The TROPOspheric Monitoring Instrument (TROPOMI), launched 13 October 2017, has been measuring carbon monoxide (CO) concentrations in the Earth's atmosphere since early November 2017. In the first measurements, TROPOMI was able to measure CO concentrations of the high-pollution event in India of November 2017. In this paper, we studied the extent of the pollution in India, comparing the TROPOMI CO with modeled data from the Weather Research and Forecasting model (WRF) to identify the most important sources contributing to the high pollution, both at ground level and in the total column. We investigated the period 11-19 November 2017. We found that residential and commercial combustion was a much more important source of CO pollution than the post-monsoon crop burning during this period, which is in contrast to what media suggested and some studies on aerosol emissions found. Also, the high pollution was not limited to Delhi and its direct neighborhood but the accumulation of pollution extended over the whole Indo-Gangetic Plain (IGP) due to the unfavorable weather conditions in combination with extensive emissions. From the TROPOMI data and WRF simulations, we observed a buildup of CO during 11-14 November and a decline in CO after 15 November. The meteorological conditions, characterized by low wind speeds and shallow atmospheric boundary layers, were most likely the primary explanation for the temporal accumulation and subsequent dispersion of regionally emitted CO in the atmosphere. This emphasizes the important role of atmospheric dynamics in determining the air quality conditions at ground level and in the total column. Due to its rapidly growing population and economy, India is expected to encounter similar pollution events more often in future post-monsoon and winter seasons unless significant policy measures are taken to reduce residential and commercial emissions.

    Influence of Atmospheric Transport on Estimates of Variability in the Global Methane Burden
    Pandey, Sudhanshu ; Houweling, Sander ; Krol, Maarten ; Aben, Ilse ; Nechita-Banda, Narcisa ; Thoning, Kirk ; Röckmann, Thomas ; Yin, Yi ; Segers, Arjo ; Dlugokencky, Edward J. - \ 2019
    Geophysical Research Letters 46 (2019)4. - ISSN 0094-8276 - p. 2302 - 2311.
    atmospheric burden - atmospheric transport - CH emissions - interhemispheric difference - methane - TM5

    We quantify the impact of atmospheric transport and limited marine boundary layer sampling on changes in global and regional methane burdens estimate using tracer transport model simulations with annually repeating methane emissions and sinks but varying atmospheric transport patterns. We find the 1σ error due to this transport and sampling effect on annual global methane increases to be 1.11 ppb/year and on zonal growth rates to be 3.8 ppb/year, indicating that it becomes more critical at smaller spatiotemporal scales. We also find that the trends in inter-hemispheric and inter-polar difference of methane are significantly influenced by the effect. Contrary to a negligible trend in the inter-hemispheric difference of measurements, we find, after adjusting for the transport and sampling, a trend of 0.37 ± 0.06 ppb/year. This is consistent with the emission trend from a 3-D inversion of the measurements, suggesting a faster increase in emissions in the Northern Hemisphere than in the Southern Hemisphere.

    l-Rhamnose Metabolism in Clostridium beijerinckii Strain DSM 6423
    Diallo, Mamou ; Simons, Andre D. ; Wal, Hetty van der; Collas, Florent ; Houweling-Tan, Bwee ; Kengen, Servé W.M. ; López-Contreras, Ana M. - \ 2019
    Applied and Environmental Microbiology 85 (2019)5. - ISSN 0099-2240
    1,2-propanediol - IBE fermentation - l-rhamnose - propionic acid - Ulva lactuca

    Macroalgae (or seaweeds) are considered potential biomass feedstocks for the production of renewable fuels and chemicals. Their sugar composition is different from that of lignocellulosic biomasses, and in green species, including Ulva lactuca, the major sugars are l-rhamnose and d-glucose. C. beijerinckii DSM 6423 utilized these sugars in a U. lactuca hydrolysate to produce acetic acid, butyric acid, isopropanol, butanol, and ethanol (IBE), and 1,2-propanediol. d-Glucose was almost completely consumed in diluted hydrolysates, while l-rhamnose or d-xylose was only partially utilized. In this study, the metabolism of l-rhamnose by C. beijerinckii DSM 6423 was investigated to improve its utilization from natural resources. Fermentations on d-glucose, l-rhamnose, and a mixture of d-glucose and l-rhamnose were performed. On l-rhamnose, the cultures showed low growth and sugar consumption and produced 1,2-propanediol, propionic acid, and n-propanol in addition to acetic and butyric acids, whereas on d-glucose, IBE was the major product. On a d-glucose-l-rhamnose mixture, both sugars were converted simultaneously and l-rhamnose consumption was higher, leading to high levels of 1,2-propanediol (78.4 mM), in addition to 59.4 mM butanol and 31.9 mM isopropanol. Genome and transcriptomics analysis of d-glucose- and l-rhamnose-grown cells revealed the presence and transcription of genes involved in l-rhamnose utilization and in bacterial microcompartment (BMC) formation. These data provide useful insights into the metabolic pathways involved in l-rhamnose utilization and the effects on the general metabolism (glycolysis, early sporulation, and stress response) induced by growth on l-rhamnose.IMPORTANCE A prerequisite for a successful biobased economy is the efficient conversion of biomass resources into useful products, such as biofuels and bulk and specialty chemicals. In contrast to other industrial microorganisms, natural solvent-producing clostridia utilize a wide range of sugars, including C5, C6, and deoxy-sugars, for production of long-chain alcohols (butanol and 2,3-butanediol), isopropanol, acetone, n-propanol, and organic acids. Butanol production by clostridia from first-generation sugars is already a commercial process, but for the expansion and diversification of the acetone, butanol, and ethanol (ABE)/IBE process to other substrates, more knowledge is needed on the regulation and physiology of fermentation of sugar mixtures. Green macroalgae, produced in aquaculture systems, harvested from the sea or from tides, can be processed into hydrolysates containing mixtures of d-glucose and l-rhamnose, which can be fermented. The knowledge generated in this study will contribute to the development of more efficient processes for macroalga fermentation and of mixed-sugar fermentation in general.

    Downstream Processing of Isochrysis galbana using Wet Biomass
    Ibañeza, E. ; Gilbert-López, B. ; Mendiola, J.A. ; Houweling-Tan, G.B.N. ; Broek, L.A.M. van den; Sijtsma, L. ; Herrero, M. ; Cifuentes, A. - \ 2018
    In: Downstream Processing of Isochrysis galbana using Wet Biomass. - Valencia, Spain : CSIC - 5 p.
    In the present work, wet Isochrysis galbana biomass has been processed directly after harvesting to obtain high added-value compounds. A three-step sequential process has been designed to extract soluble proteins, lipids and pigments, leaving an exhausted residue. With this process, based on the use of compressed fluids, we were able to lower the energetic requirements, obtain higher extraction efficiency and lower generation of residues (while using environmentally benign solvents), compared to a similar procedure developed using dry microalgae biomass. The three-step sequential process started using subcritical water (employing mainly the residual water contained in the wet biomass) at 10-100 bar and 30-50 ºC to recover soluble proteins; the second step consisted on a pigments extraction using carbon dioxide expanded ethanol (CXE) (pressures between 50-100 bar, 40-60 ºC and ethanol percentages 40-80%); later on, a supercritical fluid extraction using pure CO2 is used to recover lipids (conditions between 250-400 bar and 40-70 ºC). By using this integrated process, we were able to recover around 70-80% of valuable lipids and pigments while proteins and sugars were mainly left in the residue. Life Cycle Assessment (LCA) has been measured and compared with results previously obtained in our research group working with Isochrysis galbana after freeze drying of the biomass. Results obtained demonstrated that energy requirements and associated costs of the developed process were much lower, therefore increasing the possibilities for biorefinery development at large scale.
    Natte herfst nog steeds probleem in bewaring
    Tramper, M. - \ 2018
    Natte herfst nog steeds probleem in bewaring
    Tramper, M. - \ 2018
    Natte herfst nog steeds probleem in bewaring
    Tramper, M. - \ 2018
    Sterk fungicide beschikbaar voor Nederlandse akkerbouwer
    Tramper, M. - \ 2018
    Monascus ruber as cell factory for lactic acid production at low pH
    Weusthuis, R.A. ; Mars, A.E. ; Springer, J. ; Wolbert, E.J.H. ; Wal, H. van der; Vrije, G.J. de; Levisson, M. ; Leprince, A. ; Houweling-Tan, G.B.N. ; Moers, A.P.H.A. ; Hendriks, S.N.A. ; Mendes, O. ; Griekspoor, Y. ; Werten, M.W.T. ; Schaap, P.J. ; Oost, J. van der; Eggink, G. - \ 2017
    PRJEB20852 - ERP023042
    A Monascus ruber strain was isolated that was able to grow on mineral medium at high sugar concentrations and 175 g/l lactic acid at pH 2.8.
    Quantification of CO emissions from the city of madrid using MOPITT satellite retrievals and WRF simulations
    Dekker, Iris N. ; Houweling, Sander ; Aben, Ilse ; Röckmann, Thomas ; Krol, Maarten ; Martínez-Alonso, Sara ; Deeter, Merritt N. ; Worden, Helen M. - \ 2017
    Atmospheric Chemistry and Physics 17 (2017)23. - ISSN 1680-7316 - p. 14675 - 14694.

    The growth of mega-cities leads to air quality problems directly affecting the citizens. Satellite measurements are becoming of higher quality and quantity, which leads to more accurate satellite retrievals of enhanced air pollutant concentrations over large cities. In this paper, we compare and discuss both an existing and a new method for estimating urban-scale trends in CO emissions using multiyear retrievals from the MOPITT satellite instrument. The first method is mainly based on satellite data, and has the advantage of fewer assumptions, but also comes with uncertainties and limitations as shown in this paper. To improve the reliability of urban-To-regional scale emission trend estimation, we simulate MOPITT retrievals using the Weather Research and Forecast model with chemistry core (WRFChem). The difference between model and retrieval is used to optimize CO emissions in WRF-Chem, focusing on the city of Madrid, Spain. This method has the advantage over the existing method in that it allows both a trend analysis of CO concentrations and a quantification of CO emissions. Our analysis confirms that MOPITT is capable of detecting CO enhancements over Madrid, although significant differences remain between the yearly averaged model output and satellite measurements (R2 D0.75) over the city. After optimization, we find Madrid CO emissions to be lower by 48% for 2002 and by 17% for 2006 compared with the EdgarV4.2 emission inventory. The MOPITT-derived emission adjustments lead to better agreement with the European emission inventory TNO-MAC-III for both years. This suggests that the downward trend in CO emissions over Madrid is overestimated in EdgarV4.2 and more realistically represented in TNO-MACC-III. However, our satellite and model based emission estimates have large uncertainties, around 20% for 2002 and 50% for 2006.

    Monascus ruber as cell factory for lactic acid production at low pH
    Weusthuis, Ruud A. ; Mars, Astrid E. ; Springer, Jan ; Wolbert, Emil J.H. ; Wal, Hetty van der; Vrije, Truus G. de; Levisson, Mark ; Leprince, Audrey ; Houweling-Tan, Bwee ; Moers, Antoine ; Hendriks, Sjon N.A. ; Mendes, Odette ; Griekspoor, Yvonne ; Werten, Marc W.T. ; Schaap, Peter J. ; Oost, John van der; Eggink, Gerrit - \ 2017
    Metabolic Engineering 42 (2017). - ISSN 1096-7176 - p. 66 - 73.
    Evolutionary engineering - Genetic engineering - Lactic acid production at low pH - Monascus ruber - Strain isolation
    A Monascus ruber strain was isolated that was able to grow on mineral medium at high sugar concentrations and 175 g/l lactic acid at pH 2.8. Its genome and transcriptomes were sequenced and annotated. Genes encoding lactate dehydrogenase (LDH) were introduced to accomplish lactic acid production and two genes encoding pyruvate decarboxylase (PDC) were knocked out to subdue ethanol formation. The strain preferred lactic acid to glucose as carbon source, which hampered glucose consumption and therefore also lactic acid production. Lactic acid consumption was stopped by knocking out 4 cytochrome-dependent LDH (CLDH) genes, and evolutionary engineering was used to increase the glucose consumption rate. Application of this strain in a fed-batch fermentation resulted in a maximum lactic acid titer of 190 g/l at pH 3.8 and 129 g/l at pH 2.8, respectively 1.7 and 2.2 times higher than reported in literature before. Yield and productivity were on par with the best strains described in literature for lactic acid production at low pH.
    Enhanced methane emissions from tropical wetlands during the 2011 la Niña
    Pandey, Sudhanshu ; Houweling, Sander ; Krol, Maarten ; Aben, Ilse ; Monteil, Guillaume ; Nechita-Banda, Narcisa ; Dlugokencky, Edward J. ; Detmers, Rob ; Hasekamp, Otto ; Xu, Xiyan ; Riley, William J. ; Poulter, Benjamin ; Zhang, Zhen ; McDonald, Kyle C. ; White, James W.C. ; Bousquet, Philippe ; Röckmann, Thomas - \ 2017
    Scientific Reports 7 (2017). - ISSN 2045-2322
    Year-to-year variations in the atmospheric methane (CH4) growth rate show significant correlation with climatic drivers. The second half of 2010 and the first half of 2011 experienced the strongest La Niña since the early 1980s, when global surface networks started monitoring atmospheric CH4 mole fractions. We use these surface measurements, retrievals of column-averaged CH4 mole fractions from GOSAT, new wetland inundation estimates, and atmospheric δ13C-CH4 measurements to estimate the impact of this strong La Niña on the global atmospheric CH4 budget. By performing atmospheric inversions, we find evidence of an increase in tropical CH4 emissions of ∼6-9 TgCH4 yr-1 during this event. Stable isotope data suggest that biogenic sources are the cause of this emission increase. We find a simultaneous expansion of wetland area, driven by the excess precipitation over the Tropical continents during the La Niña. Two process-based wetland models predict increases in wetland area consistent with observationally-constrained values, but substantially smaller per-area CH4 emissions, highlighting the need for improvements in such models. Overall, tropical wetland emissions during the strong La Niña were at least by 5% larger than the long-term mean.
    Global methane emission estimates for 2000-2012 from CarbonTracker Europe-CH4 v1.0
    Tsuruta, Aki ; Aalto, Tuula ; Backman, Leif ; Hakkarainen, Janne ; Laan-Luijkx, Ingrid T. Van Der; Krol, Maarten C. ; Spahni, Renato ; Houweling, Sander ; Laine, Marko ; Dlugokencky, Ed ; Gomez-Pelaez, Angel J. ; Schoot, Marcel Van Der; Langenfelds, Ray ; Ellul, Raymond ; Arduini, Jgor ; Apadula, Francesco ; Gerbig, Christoph ; Feist, D.G. ; Kivi, Rigel ; Yoshida, Yukio ; Peters, Wouter - \ 2017
    Geoscientific Model Development 10 (2017)3. - ISSN 1991-959X - p. 1261 - 1289.

    We present a global distribution of surface methane (CH4) emission estimates for 2000-2012 derived using the CarbonTracker Europe-CH4 (CTE-CH4) data assimilation system. In CTE-CH4, anthropogenic and biospheric CH4 emissions are simultaneously estimated based on constraints of global atmospheric in situ CH4 observations. The system was configured to either estimate only anthropogenic or biospheric sources per region, or to estimate both categories simultaneously. The latter increased the number of optimizable parameters from 62 to 78. In addition, the differences between two numerical schemes available to perform turbulent vertical mixing in the atmospheric transport model TM5 were examined. Together, the system configurations encompass important axes of uncertainty in inversions and allow us to examine the robustness of the flux estimates. The posterior emission estimates are further evaluated by comparing simulated atmospheric CH4 to surface in situ observations, vertical profiles of CH4 made by aircraft, remotely sensed dry-air total column-averaged mole fraction (XCH4) from the Total Carbon Column Observing Network (TCCON), and XCH4 from the Greenhouse gases Observing Satellite (GOSAT). The evaluation with non-assimilated observations shows that posterior XCH4 is better matched with the retrievals when the vertical mixing scheme with faster interhemispheric exchange is used. Estimated posterior mean total global emissions during 2000-2012 are 516 ± 51 Tg CH4 yr-1, with an increase of 18 Tg CH4 yr-1 from 2000-2006 to 2007-2012. The increase is mainly driven by an increase in emissions from South American temperate, Asian temperate and Asian tropical TransCom regions. In addition, the increase is hardly sensitive to different model configurations ( < 2 Tg CH4 yr-1 difference), and much smaller than suggested by EDGAR v4.2 FT2010 inventory (33 Tg CH4 yr-1), which was used for prior anthropogenic emission estimates. The result is in good agreement with other published estimates from inverse modelling studies (16-20 Tg CH4 yr-1). However, this study could not conclusively separate a small trend in biospheric emissions (-5 to +6.9 Tg CH4 yr-1) from the much larger trend in anthropogenic emissions (15-27 Tg CH4 yr-1). Finally, we find that the global and North American CH4 balance could be closed over this time period without the previously suggested need to strongly increase anthropogenic CH4 emissions in the United States. With further developments, especially on the treatment of the atmospheric CH4 sink, we expect the data assimilation system presented here will be able to contribute to the ongoing interpretation of changes in this important greenhouse gas budget.

    Green compressed fluid technologies for downstream processing of Scenedesmus obliquus in a biorefinery approach
    Gilbert-López, Bienvenida ; Mendiola, José A. ; Broek, Lambertus A.M. van den; Houweling-Tan, Bwee ; Sijtsma, Lolke ; Cifuentes, Alejandro ; Herrero, Miguel ; Ibáñez, Elena - \ 2017
    Algal Research 24 (2017). - ISSN 2211-9264 - p. 111 - 121.
    Algae - Biorefinery - Carotenoid - Lipid - Pressurized liquid extraction - Supercritical fluid extraction

    The fractionation of algae biomass in several high-value compounds that can be used as ingredients in other applications sets the basis of the algae biorefinery approach. The present study aimed at the extraction and fractionation of bioactive compounds from the microalga Scenedesmus obliquus, by means of applying a sequential process without the manipulation of the biomass in the extraction cell. This integrated platform of compressed fluid extraction technologies of low-environmental impact was designed in order to produce increases of solvent polarity using non-toxic solvents. The process involved the following steps:(1) supercritical fluid extraction (SFE) using supercritical carbon dioxide (ScCO2); (2) gas expanded liquids (GXL) using 75% ethanol and 25% ScCO2 (v/v) and; (3) pressurized liquid extraction (PLE) using water. Extraction conditions were optimized using response surface methodology (RSM) and kinetic studies. Extraction yield, antioxidant activity as well as contents of total phenols, carotenoids, proteins and sugars were the studied response variables. High performance liquid chromatography coupled to evaporative light-scattering detector (HPLC-ELSD) analyses of the fractions revealed that triacylglycerols were mainly extracted by SFE. Lutein and β-carotene were the main pigments identified in the extracts by HPLC coupled to diode array and mass spectrometry detectors (HPLC-DAD-MS/MS), which were preferentially extracted in the GXL step. Polar compounds such as proteins and sugars remained predominantly in the residue. Therefore, the green downstream platform developed in this study for valorization of the microalgae biomass, is able to produce different fractions with potential application in the food, pharmaceutical and cosmetic industries.

    Global inverse modeling of CH4 sources and sinks : An overview of methods
    Houweling, Sander ; Bergamaschi, Peter ; Chevallier, Frederic ; Heimann, Martin ; Kaminski, Thomas ; Krol, Maarten ; Michalak, Anna M. ; Patra, Prabir - \ 2017
    Atmospheric Chemistry and Physics 17 (2017)1. - ISSN 1680-7316 - p. 235 - 256.

    The aim of this paper is to present an overview of inverse modeling methods that have been developed over the years for estimating the global sources and sinks of CH4. It provides insight into how techniques and estimates have evolved over time and what the remaining shortcomings are. As such, it serves a didactical purpose of introducing apprentices to the field, but it also takes stock of developments so far and reflects on promising new directions. The main focus is on methodological aspects that are particularly relevant for CH4, such as its atmospheric oxidation, the use of methane isotopologues, and specific challenges in atmospheric transport modeling of CH4. The use of satellite retrievals receives special attention as it is an active field of methodological development, with special requirements on the sampling of the model and the treatment of data uncertainty. Regional scale flux estimation and attribution is still a grand challenge, which calls for new methods capable of combining information from multiple data streams of different measured parameters. A process model representation of sources and sinks in atmospheric transport inversion schemes allows the integrated use of such data. These new developments are needed not only to improve our understanding of the main processes driving the observed global trend but also to support international efforts to reduce greenhouse gas emissions.

    Barley Distillers Dried Grains with Solubles (DDGS) as Feedstock for Production of Acetone, Butanol and Ethanol
    Houweling-Tan, G.B.N. ; Sperber, B.L.H.M. ; Wal, H. van der; Bakker, R.R.C. ; Lopez Contreras, A.M. - \ 2016
    BAOJ Microbiology 2 (2016)3. - 8 p.
    Distillers dried grains with solubles (DDGS) represent important co-product from commercial yeast fermentations, including bioethanol, from grains. In view of the current expansion of the bioethanol fermentation process, with the concomitant increase in production of DDGS, alternative applications to their main current use as animal feed are being explored. In this study, DDGS from a bioethanol facility which uses barley as feedstock have been characterized and used as feedstock for biobutanol production. These DDGS contained, per kg of dry matter, 250 grams of protein and 390 grams of sugars, being glucose, xylose and arabinose the main sugar components. DDGS were hydrolyzed by alkaline pre-treatment followed by enzymatic hydrolysis resulting in the solubilization of approx. 80 % of the sugars in the feedstock and contained 57 g/L total sugars. The fermentation of 20 % (w/v) DDGS suspensions and of the hydrolysate of DDGS by two acetone, butanol and ethanol (ABE)-producing bacterial strains is described. Both strains utilized the sugars in these suspensions and in the hydrolysate to produce ABE. In these cultures, the strains only utilized soluble mono- or oligosaccharides. The hydrolysate was fermentable without addition of extra nutrients, being C. acetobutylicum the best-performing strain, producing 8.3 g/L ABE. In addition, DDGS were used as nutrient for the fermentation of wheat straw hemicellulosic syrup (C5-syrup) with low nutrient content. This C-5 syrup was a side stream obtained from steam-exploded wheat straw, and was subjected to overliming to make it fermentable. The supplementation of the C5-syrup with DDGS eliminated the need for addition of nutrients for the fermentation
    Inverse modeling of GOSAT-retrieved ratios of total column CH4 and CO2 for 2009 and 2010
    Pandey, Sudhanshu ; Houweling, Sander ; Krol, Maarten ; Aben, Ilse ; Chevallier, Frédéric ; Dlugokencky, Edward J. ; Gatti, Luciana V. ; Gloor, Emanuel ; Miller, John B. ; Detmers, Rob ; Machida, Toshinobu ; Röckmann, Thomas - \ 2016
    Atmospheric Chemistry and Physics 16 (2016)8. - ISSN 1680-7316 - p. 5043 - 5062.

    This study investigates the constraint provided by greenhouse gas measurements from space on surface fluxes. Imperfect knowledge of the light path through the atmosphere, arising from scattering by clouds and aerosols, can create biases in column measurements retrieved from space. To minimize the impact of such biases, ratios of total column retrieved CH4 and CO2 (Xratio) have been used. We apply the ratio inversion method described in Pandey et al. (2015) to retrievals from the Greenhouse Gases Observing SATellite (GOSAT). The ratio inversion method uses the measured Xratio as a weak constraint on CO2 fluxes. In contrast, the more common approach of inverting proxy CH4 retrievals (Frankenberg et al., 2005) prescribes atmospheric CO2 fields and optimizes only CH4 fluxes. The TM5-4DVAR (Tracer Transport Model version 5-variational data assimilation system) inverse modeling system is used to simultaneously optimize the fluxes of CH4 and CO2 for 2009 and 2010. The results are compared to proxy inversions using model-derived CO2 mixing ratios (XCO2model) from CarbonTracker and the Monitoring Atmospheric Composition and Climate (MACC) Reanalysis CO2 product. The performance of the inverse models is evaluated using measurements from three aircraft measurement projects. Xratio and XCO2model are compared with TCCON retrievals to quantify the relative importance of errors in these components of the proxy XCH4 retrieval (XCH4proxy). We find that the retrieval errors in Xratio (mean Combining double low line 0.61%) are generally larger than the errors in XCO2model (mean Combining double low line 0.24 and 0.01% for CarbonTracker and MACC, respectively). On the annual timescale, the CH4 fluxes from the different satellite inversions are generally in agreement with each other, suggesting that errors in XCO2model do not limit the overall accuracy of the CH4 flux estimates. On the seasonal timescale, however, larger differences are found due to uncertainties in XCO2model, particularly over Australia and in the tropics. The ratio method stays closer to the a priori CH4 flux in these regions, because it is capable of simultaneously adjusting the CO2 fluxes. Over tropical South America, comparison to independent measurements shows that CO2 fields derived from the ratio method are less realistic than those used in the proxy method. However, the CH4 fluxes are more realistic, because the impact of unaccounted systematic uncertainties is more evenly distributed between CO2 and CH4. The ratio inversion estimates an enhanced CO2 release from tropical South America during the dry season of 2010, which is in accordance with the findings of Gatti et al. (2014) and Van der Laan et al. (2015). The performance of the ratio method is encouraging, because despite the added nonlinearity due to the assimilation of Xratio and the significant increase in the degree of freedom by optimizing CO2 fluxes, still consistent results are obtained with respect to other CH4 inversions.

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