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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    Outdoor production of microalgae
    Vree, Jeroen H. de - \ 2016
    Wageningen University. Promotor(en): Rene Wijffels, co-promotor(en): Rouke Bosma; Maria Barbosa. - Wageningen : Wageningen University - ISBN 9789462578784 - 179
    algae - algae culture - design - bioreactors - photobioreactors - modeling - algen - algenteelt - ontwerp - bioreactoren - fotobioreactoren - modelleren

    This thesis describes the production of microalgae under outdoor conditions, for this research was done at pilot scale. Microalgae are an interesting alternative to currently used sources for bulk commodities as food, feed and chemicals. Research activities within the field are shattered; different reactor systems are investigated at different locations while the systems are operated with different species. The shattered activities prevent a consensus to be reached within the scientific community on the reactor system that has the best performance. Selecting the best performing reactor system will bring the algae industry to the next level. In this PhD thesis different reactor designs were compared on a single location while using the same species in all systems. For this purpose the microalgal pilot facility AlgaePARC (Production And Research Centre) was designed and is described within this thesis. Followed by a comparison of the different reactor designs while using for each comparison a different operational strategy. Operational strategies investigated were chemostat operation and turbidostat operation. During chemostat operation a fixed daily dilution rate is applied to the reactor system, biomass concentrations vary as a result of the applied dilution rate and light conditions. During turbidostat operation the biomass concentration within a system is fixed and as a result of the set biomass concentration and light conditions the daily dilution rate varies. Findings from laboratory scale to pilot scale experiments are extrapolated to indicate the potential of microalgae production at a commercial scale. For these extrapolations mathematical models should be used, which require microalgae species specific input parameters. In this thesis input parameters for two industrially relevant microalgae species were obtained and reported. Finally a techno-economic evaluation was developed to indicate the potential of microalgae as a bulk commodity and to pinpoint focal points for future research.

    Antenna size reduction in microalgae mass culture
    Mooij, T. de - \ 2016
    Wageningen University. Promotor(en): Rene Wijffels, co-promotor(en): Marcel Janssen. - Wageningen : Wageningen University - ISBN 9789462578890 - 196
    algae culture - algae - light - photobioreactors - photosynthesis - mutants - algenteelt - algen - licht - fotobioreactoren - fotosynthese - mutanten

    The thesis describes the potential of microalgae with a reduced light harvesting antenna for biomass production under mass culture conditions (high biomass density, high light intensity). Theoretically, the lower chlorophyll content reduces the light harvesting capacity and with that the amount of photosaturation. The result would be an increase of the biomass yield on light energy, which is especially favorable at high light intensities. In practice, it was found that the productivity of several antenna size mutants strains was equal, or even lower than that of wild type microalgae. The genetically modified algae suffered from a reduced fitness, possibly because the antenna alterations led to impaired photoprotection mechanisms. In an alternative approach, it was found that by spectral tuning (applying different light colours) oversaturation was decreased and the productivity of wild type microalgae was increased. Special attention was paid to photoacclimation behavior of wild type microalgae. It was investigated whether ‘natural acclimation’ can be exploited to maximize productivity. In the last chapter, the competition between antenna size mutants and wild type cells is investigated by means of a modeling approach. It became clear that a wild type infection of an antenna size mutant culture should be prevented at all costs, as the mutants have a reduced competitive strength.

    Microalgal triacylglycerides production in outdoor batch-operated tubular PBRs
    Benvenuti, Giulia ; Bosma, Rouke ; Klok, Anne J. ; Ji, Fang ; Lamers, Packo P. ; Barbosa, Maria J. ; Wijffels, René H. - \ 2015
    Biotechnology for Biofuels 8 (2015). - ISSN 1754-6834 - 9 p.
    chlorella-zofingiensis - lipid-accumulation - growth - light - photobioreactors - cultivation - design

    Background: Microalgal triacylglycerides (TAGs) are a promising sustainable feedstock for the biofuel, chemical and food industry. However, industrial production of microalgal products for commodity markets is not yet economically viable, largely because of low microalgal productivity. The latter is strictly dependent on initial-biomass-specific (IBS) light availability (i.e. ratio of light impinging on reactor ground area divided by initial biomass concentration per ground area). This study investigates the effect of IBS-light availability on batch TAG production for Nannochloropsis sp. cultivated in two outdoor tubular reactors (i.e. vertical and horizontal) at different initial biomass concentrations for the TAG accumulation phase, during two distinct seasons (i.e. high and low light conditions). Results: Increasing IBS-light availability led to both a higher IBS-TAG production rate and TAG content at the end of the batch, whereas biomass yield on light decreased. As a result, an optimum IBS-light availability was determined for the TAG productivity obtained at the end of the batch and several guidelines could be established. The vertical reactor (VR) should be operated at an initial biomass concentration of 1.5 g L-1 to achieve high TAG productivities (1.9 and 3.2 g m-2 day-1 under low and high light, respectively). Instead, the horizontal reactor (HR) should be operated at 2.5 g L-1 under high light (2.6 g m-2 day-1), and at 1.5 g L-1 under low light (1.4 g m-2 day-1). Conclusions: From this study, the great importance of IBS-light availability on TAG production can be deduced. Although maintaining high light availabilities in the reactor is key to reach high TAG contents at the end of the batch, considerable losses in TAG productivity were observed for the two reactors regardless of light condition, when not operated at optimal initial biomass concentrations (15-40% for VR and 30-60% for HR).

    Microalgae for aquaculture
    Michels, M.H.A. - \ 2015
    Wageningen University. Promotor(en): Rene Wijffels, co-promotor(en): Marian Vermue. - Wageningen : Wageningen University - ISBN 9789462572249
    aquacultuur - aquacultuursystemen - algenteelt - visvoeding - fotobioreactoren - biomassa productie - biobased economy - aquaculture - aquaculture systems - algae culture - fish feeding - photobioreactors - biomass production - biobased economy
    In 2007, the project ‘Zeeuwse Tong’ (Zeeland Sole) was founded with support of the province of Zeeland, the Netherlands. The aim of the Zeeuwse Tong project was to establish an innovative land-based integrated multi-trophic aquaculture sector, which is producing sole, ragworms, algae, shellfish and saline crops in close harmony with nature. The project was divided into two sub-projects: The integrated saline aquaculture farm and the integrated nursery. The research described in this thesis resides within the integrated nursery subproject. In this project the rearing of fingerlings of sole would be combined with the cultivation of microalgae as feed for shellfish larvae and spat inside a greenhouse. An integrated nursery in a greenhouse has several advantages: a greenhouse with a multipurpose use of space, sole culture combined with the cultivation of microalgae and shellfish larvae or spat, an integrated thermoregulation and the reuse of nutrients from the wastewater of the fish basins for the production of microalgae in closed photobioreactors (PBRs). For this thesis, a horizontal tubular PBR needed to be designed and constructed to investigate the productivity and yield of microalgae applied as feed for shellfish larvae or spat, within the context of an integrated nursery.
    Microalgae cultivation for nutrient recovery from human urine
    Tuantet, K. - \ 2015
    Wageningen University. Promotor(en): Grietje Zeeman, co-promotor(en): Hardy Temmink; Marcel Janssen. - Wageningen : Wageningen University - ISBN 9789462572676 - 174
    afvalwaterbehandeling - afvalwateraquacultuur - urine - algenteelt - terugwinning - fosfor - stikstof - fotobioreactoren - biomassa productie - biobased economy - nieuwe sanitatie - waste water treatment - wastewater aquaculture - urine - algae culture - recovery - phosphorus - nitrogen - photobioreactors - biomass production - biobased economy - new sanitation
    Nieuwe, brongerichte sanitatieconcepten krijgen meer en meer aandacht en laten een groot potentieel zien voor het terugwinnen van nutriënten, organische stof en water, en voor de productie van energie. Verschillende van deze nieuwe sanitatieconcepten zijn geïmplementeerd in landen zoals Nederland, Duitsland, Zweden en China. Van de beschikbare terugwinningstechnieken voor urine is er geen één die zowel stikstof als fosfor kan terugwinnen. Dat is wel mogelijk door algen te kweken op urine, vanwege de hoge N:P ratio in de algen biomassa. Tot nu toe zijn er maar een beperkt aantal studies uitgevoerd gericht op het gebruik van urine voor het kweken van microalgen. Microalgenkweek heeft een groot potentieel voor de behandeling van urine in vergelijking met de meeste andere technieken die op dit moment al commercieel beschikbaar zijn. Een model system voor Nederlandse omstandigheden werd geëvalueerd, gebruik makend van parameterwaarden uit de experimenten beschreven in dit proefschrift als wel uit de literatuur. Dit heeft aangetoond dat in Nederland microalgenkweek mogelijk is van de late lente tot laat in de zomer.
    Opportunities to improve the areal oil productivity of microalgae
    Breuer, G. ; Lamers, P.P. ; Janssen, M.G.J. ; Wijffels, R.H. ; Martens, D.E. - \ 2015
    Bioresource Technology 186 (2015). - ISSN 0960-8524 - p. 294 - 302.
    triacylglycerol tag accumulation - nitrogen starvation - scenedesmus-obliquus - starchless mutants - photosynthesis - light - photobioreactors - temperature - metabolism - simulation
    Microalgae are often considered as a promising alternative source of vegetable oils. These oils can be used for food and biofuel applications. Productivities that are projected for large-scale microalgal oil production are, however, often poorly supported by scientific evidence and based on too optimistic assumptions. To facilitate the inclusion of the microalgal physiology in these projections, existing knowledge and novel scientific insights were condensed into a mechanistic model that describes photosynthesis and carbon partitioning during nitrogen starvation. The model is validated using experimental data from both wild-type and a starchless mutant of Scenedesmus obliquus. The model is subsequently used to quantify how reactor design, process design, and strain improvement can improve the oil productivity from 2.1 to up to 10.9 g m-2 day-1. These projected productivities are used to reflect on commonly assumed oil productivities and it is concluded that the microalgal oil productivity is often overestimated several folds.
    Antenna size reduction as a strategy to increase biomass productivity: a great potential not yet realized
    Mooij, T. de; Janssen, M.G.J. ; Cerezo-Chinarro, O. ; Mussgnug, J.H. ; Kruse, O. ; Ballottari, M. ; Bassi, R. ; Bujaldon, S. ; Wollman, F.A. ; Wijffels, R.H. - \ 2015
    Journal of Applied Phycology 27 (2015)3. - ISSN 0921-8971 - p. 1063 - 1077.
    harvesting chlorophyll antenna - alga chlamydomonas-reinhardtii - photosynthetic productivity - solar-energy - light - photobioreactors - efficiency - microalgae - protein - phytoplankton
    A major limitation in achieving high photosynthetic efficiency in microalgae mass cultures is the fact that the intensity of direct sunlight greatly exceeds the photosynthetic capacity of the cells. Due to the high pigment content of algal cells, the light absorption rate surpasses the much slower conversion rate to biochemical energy. The excess of light energy is predominantly dissipated as heat, decreasing the light use efficiency of the culture. Algae with a truncated antenna system could substantially increase biomass productivity of mass cultures because oversaturation of the photosystems and concomitant dissipation of light energy are minimized. In this study, we measured the areal biomass productivity of wild-type strain cultures and four promising antenna size mutant cultures of Chlamydomonas reinhardtii. This was performed under simulated mass culture conditions. The strains were cultivated in turbidostat controlled lab-scale panel photobioreactors at an incident light intensity of 1500 µmol photons m-2 s-1. The mutant cultures did not exhibit the expected higher productivity. The greatest mutant culture productivity values were approximate to those of the wild-type productivity of 1.9 g m-2 h-1. The high sensitivity to abrupt light shifts indicated that the mutant cultures experienced reduced fitness and higher susceptibility to photodamage. This can possibly be explained by impaired photoprotection mechanisms induced by the antenna complex alterations, or by unintended side effects of the genetic modifications. Still, if these effects could be eliminated, the principle of antenna size reduction is a promising strategy to increase productivity. Selection criteria for the future creation of antenna size mutants should, therefore, include tolerance to high light conditions.
    Algae: promising new ingredient
    Wijffels, R.H. - \ 2014
    algae - nutrition - biomass production - biorefinery - algae culture - photobioreactors - nutritive value - biobased economy - applications
    Scenario studies for algae production
    Slegers, P.M. - \ 2014
    Wageningen University. Promotor(en): Gerrit van Straten; Rene Wijffels, co-promotor(en): Ton van Boxtel. - Wageningen : Wageningen University - ISBN 9789461738448 - 221
    algen - algenteelt - ontwerp - fotobioreactoren - plassen - biomassa productie - biomassa - energiegebruik - bioproceskunde - algae - algae culture - design - photobioreactors - ponds - biomass production - biomass - energy consumption - bioprocess engineering

    Microalgae are a promising biomass for the biobased economy to produce food, feed, fuel, chemicals and materials. So far, large-scale production of algae is limited and as a result estimates on the performance of such large systems are scarce. There is a need to estimate large-scale biomass productivity and energy consumption, while considering the uncertainty and complexity in such large-scale systems.

    In this thesis frameworks are developed to assess 1) the productivity during algae cultivation, 2) energy consumption during the transport of resources and processing biomass to biodiesel, and 3) the frameworks are applied to estimate the impact of algae cultivation in the production of algae-based food commodities. Design, location and future scenario are applied to deal with the complexity and uncertainty arising in the various data and models used.

    The first part of this thesis focuses on the development of a productivity framework for biomass production for flat panels (Chapter 2), horizontal and vertical tubular photobioreactors (Chapter 3) and raceway ponds (Chapter 4). The framework uses bio-physics-based models to simulate the light input on the reactor surface and the light gradient inside the reactor systems. The internal light gradient depends on the reactor geometry and dimensions, and the penetration of diffuse light between parallel reactors, which includes the canyon effect, and the reflection of light from the ground surface to the reactors are incorporated as well. Specific growth rates are derived from this internal light gradient based on species-specific growth characteristics. In raceway ponds the effect of the dynamic water temperature on the specific growth rate is included.

    The productivity framework enables to study cultivation under a wide range of process conditions and reactor designs, even those which have not been yet developed or tested under outdoor conditions. The results show that regional weather conditions, solar angles and algae species are key factors in making the best choice for the specific reactor design. The productivity framework allows to optimise the reactor design (e.g. geometry, light path, distances between parallel units and height) to the regional light conditions and growth characteristics of the algae species of interest. The best biomass concentration for cultivation varies between the reactor design, location and algae species. We recommend to select species suited to growth well at the regional light angles and weather conditions. An initial global sensitivity analysis shows that the absorption coefficient, maximum specific growth rate and functional cross section of the photosynthetic apparatus are the essential parameters of the model for single flat panels. An important next step is to validate and calibrate the productivity framework using data from outdoor experiments in various reactor designs, at different locations and with several algae species.

    Algae production is strongly connected to regional weather conditions, but also to the infrastructure for resource supply and to the processing of biomass. The energy consumption for resource supply has not been quantified yet and the energy consumption of biomass processing is mostly based on fixed values. These elements are tackled in part 2 of this thesis.

    In Chapter 5the productivity framework is combined with logistic models to optimise the supply network for algae cultivation. The results show that the availability, supply and demand of resources has a dominant effect on the feasibility of regions for algae cultivation. Not all locations achieve a positive energy balance for transport and the supply logistics is essential for planning algae cultivation locations. In the Benelux many locations are feasible for algae production due to the availability of large amounts of resources, while the limited supply of CO2in southern France and the Sahara demands for plants which are scattered over the regions. For the Sahara the distance for water transport should be minimal. Still, the average transport distances are higher than commonly assumed and algae cultivation does not necessarily need to take place in proximity of CO2supply. The transport energy consumption is found to be low compared to the energy contained in algae biomass (mostly below 3%).

    Chapter 6 describesa model-based combinatorial optimisation approach for the energy-efficientprocessing of algae biomass. In this approach, mass and energy balances and additional relations are used to relate the product yield and energy consumption of process units and process routes to the processing conditions. Process routes with the highest net energy ratios are derived by optimising the process conditions of each process unit in a given superstructure. This optimisation leads to 5-38% improvement of the net energy ratio compared to fixed process conditions. The approach moreover allows a bottleneck analysis for each process route. The results show that process design should be tailor-made. The model-based approach proves to be a versatile tool for the design of efficient microalgae processing systems.

    The developed frameworks combined with scenario studies are a powerful tool to assess algae production. The presented approaches help to reduce the uncertainty in the interpretation of data and are thereby an appropriate basis to use in impact analysis. In Chapter 7this is illustrated for the production of algae protein and oil as food commodities. The design scenarios show the implications of various reactor designs, two algae species and at two locations on biomass productivity, production cost and environmental life cycle indicators.

    The achievements of this work and the new horizons from this work are discussed in Chapter 8. The results of the developed frameworks demonstrate the power of the scenario approach and show that sensible predictions and projections of biomass productivity and energy consumption for logistics and biomass processing follow from the models.

    A techno-economic analysis of biodiesel production from microalgae
    Olivieri, G. ; Guida, T. ; Salatino, P. ; Marzocchella, A. - \ 2013
    Environmental Engineering and Management Journal (EEMJ) 12 (2013)8. - ISSN 1582-9596 - p. 1563 - 1573.
    stichococcus-bacillaris - photobioreactors - biomass - oil - efficiency - recovery
    The preliminary assessment of a cost-effective flow-sheet for the production of biodiesel from microalgae lipid fraction was carried out. The study was based on approximated cost-estimation methods integrated with the simulation software Aspen Plus (R). Several scenarios were investigated to compare costs regarding the main steps of the biodiesel production process. Ranges of input variables from downstream literature and experimental data were used to simulate the sections that define concrete process routes for production of algal biofuels: the extraction of the lipid fraction from aqueous solution, the lipid transesterification, and the methyl esters (FAMEs) and glycerol recover. The design variables were selected so as to correspond to the main degrees of freedom of the process: number of equilibrium stages, solvent recycle flow rate, transesterification time, methanol to triacylglycerols ratio, plate number and reflux ratio of the distillation unit for methanol recovery. The cost estimation for the conceptual design of the flowsheet dedicated to the FAMEs production from microalgae was carried out according to Happel's method. Data were worked out to assess the venture profit and the selling price (s) for mass unit of FAMEs. The minimization of s was adopted as the objective function. A preliminary determination of plausible values of the cost for unit of mass of biodiesel was attempted as a function of operating conditions.
    Algenteelt in fotobioreactoren in kas in Bleiswijk: ervaringen na een jaar
    Voogt, W. ; Hemming, S. ; Sapounas, A. ; Scheffers, C.P. ; Winkel, A. van - \ 2013
    teeltsystemen - algenteelt - algen - fotobioreactoren - proeven op proefstations - glastuinbouw - biobased economy - cropping systems - algae culture - algae - photobioreactors - station tests - greenhouse horticulture - biobased economy
    Poster met onderzoeksinfgormatie. Doel van dit onderzoek is het leren telen van algen in een kas, verzamelen van meetgegevens en kengetallen en ervaring opdoen met het effect van groeifactoren op de groei en ontwikkeling van algen.
    Effects of oxygen concentration on the growth of Nannochloropsis sp.
    Raso, S. - \ 2013
    Wageningen University. Promotor(en): Rene Wijffels, co-promotor(en): Marian Vermue. - S.l. : s.n. - ISBN 9789461737472 - 157
    algen - voer - aquacultuur - visvoeding - fotobioreactoren - eicosapentaeenzuur - zuurstof - algae - feeds - aquaculture - fish feeding - photobioreactors - eicosapentaenoic acid - oxygen

    ANannochloropsissp. is a promising microalgal resource for production of food, feed and bio-based commodities, as it can grow relatively fast and combines high lipid content with high content of poly-unsaturated fatty acids. High productivity with constant product quality can be achieved in fully controlled closed photobioreactors. In these closed photobioreactors, however, oxygen accumulation occurs and causes inhibition of the growth by photorespiration combined with photoinhibition.

    The inhibitory effects of photorespiration and photoinhibition can be partly dealt with via the carbon concentration mechanism of the cells and by activation of the water-water cycle. At constant high oxygen concentration and high light intensity, however, the growth of the cells ceases. To our surprise, the accumulating oxygen did not affect the growth rate of the algae if the oxygen was removed regularly. In large scale production in closed photobioreactors, it is thus crucial apply degassing to achieve high algal productivity.

    Oxygen accumulation in photobioreactors
    Fonseca e Sousa, C.A. da - \ 2013
    Wageningen University. Promotor(en): Rene Wijffels, co-promotor(en): Marian Vermue. - S.l. : s.n. - ISBN 9789461735546 - 121
    fotobioreactoren - zuurstof - algen - algenteelt - ontgassing - photobioreactors - oxygen - algae - algae culture - degassing

    Phototropic microalgae are regarded as a promising feedstock for sustainable biodiesel production, as microalgae can use natural sunlight as light source and are able to utilize CO2from flue gases and nutrients (P, N) from waste streams. To make large-scale outdoor microalgae production in closed photobioreactors economically feasible and sustainable, the costs for mixing and degassing should be reduced and the overall energy balance should become positive. This thesis focused on the effect of the accumulation of oxygen on the growth of the oleaginous microalga Neochloris oleoabundansat different light intensities. This study showed at what concentrations oxygen becomes toxic for the algae at the different light conditions encountered during outdoor cultivation and different strategies to overcome the inhibiting factor. The implementations of the main findings of this thesis wereevaluated using an economic model. The model was used to calculatethe energy and costs associated to microalgal biomass production in The Netherlands.The two methods adopted to overcome the negative effect of oxygen in microalgal cultures did result in a decrease in biomass production costs. Moreover, it showed that using the findings of this thesis, a positive energy balance for outdoor production of Neochloris oleoabundans in closed photobioreactors can be reached.

    Photosynthetic efficiency and oxygen evolution of Chlamydomonas reinhardtii under continuous and flashing light
    Vejrazka, C. ; Janssen, M. ; Benvenuti, G. ; Streefland, M. ; Wijffels, R.H. - \ 2013
    Applied Microbiology and Biotechnology 97 (2013)4. - ISSN 0175-7598 - p. 1523 - 1532.
    photobioreactors - phytoplankton - cyanobacteria - irradiance - microalgae - growth
    As a result of mixing and light attenuation in a photobioreactor (PBR), microalgae experience light/dark (L/D) cycles that can enhance PBR efficiency. One parameter which characterizes L/D cycles is the duty cycle; it determines the time fraction algae spend in the light. The objective of this study was to determine the influence of different duty cycles on oxygen yield on absorbed light energy and photosynthetic oxygen evolution. Net oxygen evolution of Chlamydomonas reinhardtii was measured for four duty cycles (0.05, 0.1, 0.2, and 0.5) in a biological oxygen monitor (BOM). Oversaturating light flashes were applied in a square-wave fashion with four flash frequencies (5, 10, 50, and 100 Hz). Algae were precultivated in a turbidostat and acclimated to a low photon flux density (PFD). A photosynthesis-irradiance (PI) curve was measured under continuous illumination and used to calculate the net oxygen yield, which was maximal between a PFD of 100 and 200 µmol m(-2)¿s(-1). Net oxygen yield under flashing light was duty cycle-dependent: the highest yield was observed at a duty cycle of 0.1 (i.e., time-averaged PFD of 115 µmol m(-2)¿s(-1)). At lower duty cycles, maintenance respiration reduced net oxygen yield. At higher duty cycles, photon absorption rate exceeded the maximal photon utilization rate, and, as a result, surplus light energy was dissipated which led to a reduction in net oxygen yield. This behavior was identical with the observation under continuous light. Based on these data, the optimal balance between oxygen yield and production rate can be determined to maximize PBR productivity.
    Uncertainty and sensitivity analysis of algae production models for flat panel photobioreactors
    Stefanov, M.S. ; Slegers, P.M. ; Boxtel, A.J.B. van - \ 2012
    gewasgroeimodellen - algen - algenteelt - oogstvoorspelling - fotobioreactoren - onderzoeksprojecten - biobased economy - biomassa productie - crop growth models - algae - algae culture - yield forecasting - photobioreactors - research projects - biobased economy - biomass production
    Poster met onderzoeksinformatie.
    Photosynthetic efficiency of Chlamydomonas reinhardtii in attenuated, flashing light
    Vejrazka, C. ; Janssen, M.G.J. ; Streefland, M. ; Wijffels, R.H. - \ 2012
    Biotechnology and Bioengineering 109 (2012)10. - ISSN 0006-3592 - p. 2567 - 2574.
    quantum yield - photobioreactors - cyanobacteria - dependence - microalgae
    As a result of mixing and light attenuation, algae in a photobioreactor (PBR) alternate between light and dark zones and, therefore, experience variations in photon flux density (PFD). These variations in PFD are called light/dark (L/D) cycles. The objective of this study was to determine how these L/D cycles affect biomass yield on light energy in microalgae cultivation. For our work, we used controlled, short light path, laboratory, turbidostat-operated PBRs equipped with a LED light source for square-wave L/D cycles with frequencies from 1 to 100¿Hz. Biomass density was adjusted that the PFD leaving the PBR was equal to the compensation point of photosynthesis. Algae were acclimated to a sub-saturating incident PFD of 220¿µmol¿m(-2) ¿s(-1) for continuous light. Using a duty cycle of 0.5, we observed that L/D cycles of 1 and 10¿Hz resulted on average in a 10% lower biomass yield, but L/D cycles of 100¿Hz resulted on average in a 35% higher biomass yield than the yield obtained in continuous light. Our results show that interaction of L/D cycle frequency, culture density and incident PFD play a role in overall PBR productivity. Hence, appropriate L/D cycle setting by mixing strategy appears as a possible way to reduce the effect that dark zone exposure impinges on biomass yield in microalgae cultivation. The results may find application in optimization of outdoor PBR design to maximize biomass yields.
    Effect of oxygen concentration on the growth of Nannochloropsis sp. at low light intensity
    Raso, S. ; Genugten, B. van; Vermuë, M.H. ; Wijffels, R.H. - \ 2012
    Journal of Applied Phycology 24 (2012)4. - ISSN 0921-8971 - p. 863 - 871.
    eicosapentaenoic acid - inorganic carbon - reactors - mass - photobioreactors - optimization - temperature - metabolism - microalgae - outdoors
    In large-scale microalgal production in tubular photobioreactors, the build-up of O2 along the tubes is one of the major bottlenecks to obtain high productivities. Oxygen inhibits the growth, since it competes with carbon dioxide for the Rubisco enzyme involved in the CO2 fixation to generate biomass. The effect of oxygen on growth of Nannochloropsis sp. was experimentally determined in a fully controlled flat-panel photobioreactor operated in turbidostat mode using an incident photon flux density of 100 µmol photons m-2 s-1 and with only the oxygen concentration as variable parameter. The dissolved oxygen concentration was varied from 20 to 250% air saturation. Results showed that there was no clear effect of oxygen concentration on specific growth rate (mean of 0.48¿±¿0.40 day-1) upon increasing the oxygen concentration from 20% to 75% air saturation. Upon further increasing the oxygen concentration, however, a linear decrease in specific growth rate was observed, ranging from 0.48¿±¿0.40 day-1 at a dissolved oxygen concentration of 75% air saturation to 0.18¿±¿0.01 day-1 at 250% air saturation. In vitro data on isolated Rubisco were used to predict the quantum yield at different oxygen concentrations in the medium. The predicted decrease in quantum yield matches well with the observed decrease that was measured in vivo. These results indicate that the effect of oxygen on growth of Nannochloropsis sp. at low light intensity is only due to competitive inhibition of the Rubisco enzyme. At these sub-saturating light conditions, the presence of high concentrations of oxygen in the medium induced slightly higher carotenoid content, but the increased levels of this protective antioxidant did not diminish the growth-inhibiting effects of oxygen on the Rubisco.
    Combinatorial Life Cycle Assessment to Inform Process Design of Industrial Production of Algal Biodiesel
    Brentner, L.B. ; Eckelman, M.J. ; Zimmerman, J.B. - \ 2011
    Environmental Science and Technology 45 (2011). - ISSN 0013-936X - p. 7060 - 7067.
    supercritical co2 - microalgae - bioreactors - extraction - chitosan - energy - gas - photobioreactors - flocculation - cultivation
    The use of algae as a feedstock for biodiesel production is a rapidly growing industry, in the United States and globally. A life cycle assessment (LCA) is presented that compares various methods, either proposed or under development, for algal biodiesel to inform the most promising pathways for sustainable full-scale production. For this analysis, the system is divided into five distinct process steps: (1) microalgae cultivation, (2) harvesting and/or dewatering, (3) lipid extraction, (4) conversion (transesterification) into biodiesel, and (5) byproduct management. A number of technology options are considered for each process step and various technology combinations are assessed for their life cycle environmental impacts. The optimal option for each process step is selected yielding a best case scenario, comprised of a flat panel enclosed photobioreactor and direct transesterification of algal cells with supercritical methanol. For a functional unit of 10 GJ biodiesel, the best case production system yields a cumulative energy demand savings of more than 65 GJ, reduces water consumption by 585 m3 and decreases greenhouse gas emissions by 86% compared to a base case scenario typical of early industrial practices, highlighting the importance of technological innovation in algae processing and providing guidance on promising production pathways.
    Photosynthetic efficiency of Chlamydomonas reinhardtii in flashing light
    Vejrazka, C. ; Janssen, M.G.J. ; Streefland, M. ; Wijffels, R.H. - \ 2011
    Biotechnology and Bioengineering 108 (2011)12. - ISSN 0006-3592 - p. 2905 - 2913.
    quantum yield - photobioreactors - microalgae - cyanobacteria - cultivation - dependence - intensity
    Efficient light to biomass conversion in photobioreactors is crucial for economically feasible microalgae production processes. It has been suggested that photosynthesis is enhanced in short light path photobioreactors by mixing-induced flashing light regimes. In this study, photosynthetic efficiency and growth of the green microalga Chlamydomonas reinhardtii were measured using LED light to simulate light/dark cycles ranging from 5 to 100¿Hz at a light-dark ratio of 0.1 and a flash intensity of 1000¿µmol¿m-2¿s-1. Light flashing at 100¿Hz yielded the same photosynthetic efficiency and specific growth rate as cultivation under continuous illumination with the same time-averaged light intensity (i.e., 100¿µmol¿m-2¿s-1). The efficiency and growth rate decreased with decreasing flash frequency. Even at 5¿Hz flashing, the rate of linear electron transport during the flash was still 2.5 times higher than during maximal growth under continuous light, suggesting storage of reducing equivalents during the flash which are available during the dark period. In this way the dark reaction of photosynthesis can continue during the dark time of a light/dark cycle. Understanding photosynthetic growth in dynamic light regimes is crucial for model development to predict microalgal photobioreactor productivities. Biotechnol. Bioeng. 2011;108: 2905–2913. © 2011 Wiley Periodicals, Inc
    Effect of O2:CO2 Ratio on the Primary Metabolism of Chlamydomonas reinhardtii
    Kliphuis, A.M.J. ; Martens, D.E. ; Janssen, M.G.J. ; Wijffels, R.H. - \ 2011
    Biotechnology and Bioengineering 108 (2011)10. - ISSN 0006-3592 - p. 2390 - 2402.
    quantum requirement - energy-production - escherichia-coli - photosynthesis - light - microalgae - growth - pathways - yield - photobioreactors
    High oxygen:carbon dioxide ratios may have a negative effect on growth and productivity of microalgae. To investigate the effect of O2 and CO2 concentrations and the ratio between these on the metabolism of Chlamydomonas reinhardtii we performed turbidostat experiments at different O2:CO2 ratios. These experiments showed that elevated O2 concentrations and the corresponding increase in the ratio of O2:CO2 common in photobioreactors led to a reduction of growth and biomass yield on light with 20–30%. This is most probably related to the oxygenase activity of Rubisco and the resulting process of photorespiration. Using metabolic flux modeling with measured rates for each experiment we were able to quantify the ratio of the oxygenase reaction to the carboxylase reaction of Rubisco and could demonstrate that photorespiration indeed can cause the reduction in biomass yield on light. The calculated ratio of the oxygenase reaction to the carboxylase reaction was 16.6% and 20.5% for air with 2% CO2 and 1% CO2, respectively. Thus photorespiration has a significant impact on the biomass yield on light already at conditions common in photobioreactors (air with 2% CO2).
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