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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    Socio-economic assessment of Algae-based PUFA production
    Voort, Marcel van der; Spruijt, Joanneke ; Potters, Jorieke ; Wolf, Pieter de; Elissen, Hellen - \ 2017
    Göttingen : PUFAChain - 84
    bioenergy - biobased economy - biofuels - biomass - algae - fatty acids - bio-energie - biobased economy - biobrandstoffen - biomassa - algen - vetzuren
    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.

    Measurements of transcripts, proteome and metabolite profiles
    Peters, Sander - \ 2017
    Fuel4Me - 7
    biobased economy - biobrandstoffen - algen - algenteelt - oliën - biobased economy - biofuels - algae - algae culture - oils
    The work described for this deliverable was carried out by DLO-PRI, in collaboration with WU, and aim ed to understanding lipid production in Phaeodactylum tricornutum . By means of transcriptome, proteome and metabolome analyses we aimed to provide insight into the one step lipid production performed by partner WU. Cultivation conditions were chosen to steer lipid profile towards most suitable composition for biofuel production.
    Photosynthetic efficiency in microalgal lipid production
    Remmers, Ilse M. - \ 2017
    Wageningen University. Promotor(en): R.H. Wijffels, co-promotor(en): P.P. Lamers. - Wageningen : Wageningen University - ISBN 9789463434607 - 200
    algae - biofuels - light - triacylglycerols - lipids - metabolism - algae culture - cultural methods - algen - biobrandstoffen - licht - triacylglycerolen - lipiden - metabolisme - algenteelt - cultuurmethoden

    Microalgae can contain large amounts of lipids which make them a promising feedstock for sustainable production of food, feed, fuels and chemicals. Various studies, including pilot-scale, have been performed and the knowledge on microalgal processes has advanced quickly. Unfortunately, current production costs for cultivation are still too high for bulk lipid production from microalgae.

    One of the major causes for the high costs of bulk lipid production is the reduced solar-to-lipid conversion efficiency. Current research, however, does not provide sufficient insight to identify optimization targets. Therefore, in this thesis we have studied the lipid production in microalgae in depth.

    Different TAG-accumulation strategies were investigated from a process engineering and metabolic point of view. The combination of all findings were used in the general discussion to thoroughly evaluate the microalgal lipid accumulation strategies. Current phototrophic microalgal lipid yields are still 10 times lower than the theoretical maximum. There is, however, still an enormous potential for further improvements. Future research should focus on (genetically) improved strains and advanced cultivation strategies, including adaptation to fluctuating outdoor weather conditions.

    This thesis was performed within the EU FP7 FUEL4ME project under grand agreement No 308938. Objective of this program is to develop a sustainable and scalable process for biofuels from microalgae and to valorize the by-products.

    Metabolic modeling to understand and redesign microbial systems
    Heck, Ruben G.A. van - \ 2017
    Wageningen University. Promotor(en): V.A.P. Martins dos Santos, co-promotor(en): M. Suárez Diez. - Wageningen : Wageningen University - ISBN 9789463434553 - 239
    micro-organismen - modelleren - kooldioxide - biotechnologie - algen - metabolisme - pseudomonas - microorganisms - modeling - carbon dioxide - biotechnology - algae - metabolism - pseudomonas

    The goals of this thesis are to increase the understanding of microbial metabolism and to functionally (re-)design microbial systems using Genome- Scale Metabolic models (GSMs). GSMs are species-specific knowledge repositories that can be used to predict metabolic activities for wildtype and genetically modified organisms. Chapter 1 describes the assumptions associated with GSMs, the GSM generation process, common GSM analysis methods, and GSM-driven strain design methods. Thereby, chapter 1 provides a background for all other chapters. In this work, there is a focus on the metabolically versatile bacterium Pseudomonas putida (chapters 2,3,4,5,6), but also other model microbes and biotechnologically or societally relevant microbes are considered (chapters 3,4,6,7,8).

    GSMs are reflections of the genome annotation of the corresponding organism. For P. putida, the genome annotation that GSMs have been built on is more than ten years old. In chapter 2, this genome annotation was updated both on a structural and functional level using state-of-the-art annotation tools. A crucial part of the functional annotation relied on the most comprehensive P. putida GSM to date. This GSM was used to identify knowledge gaps in P. putida metabolism by determining the inconsistencies between its growth predictions and experimental measurements. Inconsistencies were found for 120 compounds that could be degraded by P. putida in vitro but not in silico. These compounds formed the basis for a targeted manual annotation process. Ultimately, suitable degradation pathways were identified for 86/120 as part of the functional reannotation of the P. putida genome.

    For P. putida there are 3 independently generated GSMs, which is not uncommon for model organisms. These GSMs differ in generation procedure and represent different and complementary subsets of the knowledge on the metabolism of the organism. However, the differing generation procedures also makes it extremely cumbersome to compare their contents, let alone to combine them into a single consensus GSM. Chapter 3 addresses this issue through the introduction of a computational tool for COnsensus Metabolic Model GENeration (COMMGEN). COMMGEN automatically identifies inconsistencies between independently generated GSMs and semi-automatically resolves them. Thereby, it greatly facilitates a detailed comparison of independently generated GSMs as well as the construction of consensus GSMs that more comprehensively describe the knowledge on the modeled organism.

    GSMs can predict whether or not the corresponding organism and derived mutants can grow in a large variety of different growth conditions. In comparison, experimental data is extremely limited. For example, BIOLOG data describes growth phenotypes for one strain in a few hundred different media, and genome-wide gene essentially data is typically limited to a single growth medium. In chapter 4 GSMs of multiple Pseudomonas species were used to predict growth phenotypes for all possible single-gene-deletion mutants in all possible minimal growth media to determine conditionally and unconditionally essential genes. This simulated data was integrated with genomic data on 432 sequenced Pseudomonas species, which revealed a clear link between the essentiality of a gene function and the persistence of the gene within the Pseudomonas genus.

    Chapters 5 and 6 describe the use of GSMs to (re-)design microbial systems. P. putida is, despite its acknowledged versatile metabolism, an obligate aerobe. As the oxygen-requirement limits the potential applications of P. putida, there have been several experimental attempts to enable it to grow anaerobically, which have so far not succeeded. Chapter 5 describes an in silico effort to determine why P. putida cannot grow anaerobically using a combination of GSM analyses and comparative genomics. These analyses resulted in a shortlist of several essential and oxygen-dependent processes in P. putida. The identification of these processes has enabled the design of P. putida strains that can grow anaerobically based on the current understanding of P. putida metabolism as represented in GSMs.

    Efficient microbial CO2 fixation is a requirement for the biobased community, but the natural CO2 fixation pathways are rather inefficient, while the synthetic CO2 fixation pathways have been designed without considering the metabolic context of a target organism. Chapter 6 introduces a computational tool, CO2FIX, that designs species-specific CO2 fixation pathways based on GSMs and biochemical reaction databases. The designed pathways are evaluated for their ATP efficiency, thermodynamic feasibility, and kinetic rates. CO2FIX is applied to eight different organisms, which has led to the identification of both species-specific and general CO2 fixation pathways that have promising features while requiring surprisingly few non-native reactions. Three of these pathways are described in detail.

    In all previous chapters GSMs of relatively well-understood microbes have been used to gain further insight into their metabolism and to functionally (re-)design them. For complex microbial systems, such as algae (chapter 7) and gut microbial communities (chapter 8), GSMs are similarly useful, but substantially more difficult to create and analyze. Algae are widely considered as potential centerpieces of a biobased economy. Chapter 7 reviews the current challenges in algal genome annotation, modeling and synthetic biology. The gut microbiota is an incredibly complex microbial system that is crucial to our well-being. Chapter 8 reviews the ongoing developments in the modeling of both single gut microbes and gut microbial communities, and discusses how these developments will enable the move from studying correlation to causation, and ultimately the rational steering of gut microbial activity.

    Chapter 9 discusses how the previous chapters contribute to the research goals of this thesis. In addition, it provides an extensive discussion on current GSM practices, the issues associated therewith, and how these issues can be tackled. In particular, the discussion focuses on issues related to: (i) The inability to distinguish between biological difference and GSM generation artifacts when using multiple GSMs, (ii) The lack of continuous GSM updates, (iii) The mismatch between what GSM predictions and experimental data represent, (iv) The need for standardization in GSM evaluation, and (v) The lack of experimental validation of GSM-driven strain design for metabolic engineering.

    A blooming business : Identifying limits to Lake Taihu's nutrient input
    Janssen, Annette B.G. - \ 2017
    Wageningen University. Promotor(en): Wolf Mooij, co-promotor(en): J.H. Janse; A.A. van Dam. - Wageningen : Wageningen University - ISBN 9789463431897 - 268
    lakes - freshwater ecology - aquatic ecosystems - nutrients - cycling - nutrient flows - biodiversity - algae - models - critical loads - limnology - spatial variation - ecological restoration - china - meren - zoetwaterecologie - aquatische ecosystemen - voedingsstoffen - kringlopen - nutriëntenstromen - biodiversiteit - algen - modellen - critical loads - limnologie - ruimtelijke variatie - ecologisch herstel - china

    Last century, Lake Taihu (China) became serious eutrophic due to excessive nutrient input. During the 1980s, the first algal blooms emerged in the lake, reaching disastrous proportions in 2007. During that year, the intake of drinking water had to be shut down and millions of people had to look for an alternative source of drinking water. This raises the question whether such problems can be avoided. Of crucial importance in avoiding and reducing toxic algal blooms is the identification of the maximum nutrient load ecosystems can absorb, while remaining in a good ecological state. In this thesis, I aim to determine the critical nutrient load for Lake Taihu. I approach the search for critical nutrient loads of Lake Taihu in five steps with diversity as an overarching topic throughout this thesis: diversity in lakes, diversity in models, diversity in spatial distribution of nutrient and water sources, diversity in the development of lakes around the earth and finally diversity within specific lakes. From the long list of available models I chose the model PCLake to use in my analysis because it is the most extensively used food web model applied for bifurcation analysis of shallow aquatic ecosystems. The approach has resulted in a range of critical nutrient loads for different parts of Lake Taihu. Furthermore, critical nutrient loads depend on management goals, i.e. the maximum allowable chlorophyll-a concentration. According to the model results, total nutrient loads need to be more than halved to reach chlorophyll-a concentrations of 30-40 μg.L-1 in most sections of the lake. To prevent phytoplankton blooms with 20 μg.L-1 chlorophyll-a throughout Lake Taihu, both phosphorus and nitrogen loads need a nearly 90% reduction. This range contrasts to the single point of recovery that is often found for small shallow lakes. The range in critical nutrient loads found for Lake Taihu can be interpreted as providing a path of recovery for which each step leads to water quality improvement in certain parts of the lake. To reach total recovery, nutrient reduction seems to be the most promising management option.

    Harvesting and cell disruption of microalgae
    Lam, Gerard Pieter 't - \ 2017
    Wageningen University. Promotor(en): R.H. Wijffels; M.H.M. Eppink, co-promotor(en): M.H. Vermuë. - Wageningen : Wageningen University - ISBN 9789463431736 - 206
    algae - harvesting - flocculation - polymers - chlorella vulgaris - biorefinery - electric field - organelles - algen - oogsten - uitvlokking - polymeren - chlorella vulgaris - bioraffinage - elektrisch veld - organellen

    Microalgae are a potential feedstock for various products. At the moment, they are already used as feedstock for high-valuable products (e.g. aquaculture and pigments).

    Microalgae pre-dominantly consist out of proteins, lipids and carbohydrates. This makes algae an interesting feedstock for various bulk-commodities. To successfully produce bulk-commodities, a multi-product biorefinery should be adopted that aims on production of both bulk- and high value co-products. In the downstream process, however, harvesting- and cell disruption are technological hurdles for cost effective multi-product biorefinery.

    Flocculation is considered as a low-cost harvesting process. Flocculating microalgae at high salinities used to be not feasible We demonstrated that marine microalgae can successfully be flocculated and harvested by using cationic polymers.

    In the second part of this thesis we studied Pulsed Electric Field (PEF) as potential cheap and non-disruptive technology to open microalgae. PEF-treatment evokes openings/’holes’ in micro-organisms. PEF in combination with a pre-treatment to weaken the cell wall resulted in release of proteins from microalgae at low energy consumption.

    Recent advances in technology development learned that harvesting of micro-algae is no longer a bottleneck. Future research and development should focus on cell disruption and mild extraction technologies. Costs for the biorefinery will decrease by process simplification. For that unit operations for cell disruption and extraction need to be integrated.

    This project was part of a large public private partnership program AlgaePARC biorefinery (www.AlgaePARC.com). Objective of this program is to develop a more sustainable and economically feasible microalgae production process. For that all biomass components (e.g. proteins, lipids, carbohydrates) should be used at minimal energy requirements and minimal costs while keeping the functionality of the different biomass components. Biorefining of microalgae is very important for the selective separation and use of the different functional biomass components.

    Algen: onze oorspronkelijke omega-3 bron
    Spruijt, J. - \ 2017
    Wageningen University & Research - 6
    algen - omega-3 vetzuren - voedseltechnologie - plantaardige oliën - algae - omega-3 fatty acids - food technology - plant oils
    Brochure over de marktkansen voor omega-3 uit algen voor PUFAChain.
    From harmful to useful algae
    Blaas, Harry - \ 2017
    Wageningen University. Promotor(en): Carolien Kroeze. - Wageningen : Wageningen University - ISBN 9789463430357 - 117
    algae - algae culture - adverse effects - nitrogen - phosphorus - rivers - eutrophication - waste water treatment - europe - algen - algenteelt - nadelige gevolgen - stikstof - fosfor - rivieren - eutrofiëring - afvalwaterbehandeling - europa

    Eutrophication of coastal waters is a worldwide phenomenon. This study focuses on eutrophication in the coastal waters of Europe. Eutrophication is mainly a result of the increased transport of nutrients from watersheds by rivers to the coastal waters. Nutrient losses from watersheds are generally from agriculture, sewage, atmospheric deposition and from natural sources. In case of an overload of nutrients in the coastal waters, algal blooms may develop which increase the risk of hypoxia, fish mortality, and loss of biodiversity.

    Algae can also be useful. They are increasingly considered an interesting product. For instance, micro-algae can be grow on land to produce proteins, lipids and fatty acids. Some studies indicate that micro-algae can be an important feedstock in the future for, for instance, the production of biodiesel. Moreover, macro-algae can be produced in seawater in sea farms. Macro-algae can be edible, or be used as a feedstock. By yielding macro-algae, nutrients are removed from the water, reducing coastal eutrophication.

    The objective of this study is to analyse past and future trends in nutrient export by rivers to European seas with a focus on the role of algae. Three types of algae will be distinguished: (1) harmful algal blooms in coastal seas, (2) cultivation of micro-algae on land for the production of proteins, lipids and fatty acids, and (3) cultivation of multi cellular algae in seaweed farms for human consumption or other products.

    To meet the objective the following research questions are addressed:

    RQ1 To what extent do N and P loads exceed levels that minimize the risk of harmful algal blooms, and what are the relative shares of sources of N and P in rivers of the European Union?

    RQ2 What are the potential consequences of large-scale land-based production of biodiesel from cultivated micro-algae in Europe for coastal eutrophication?

    RQ3 Would it possible to cultivate and process micro-algae in a factory, and what is the environmental performance?

    RQ4 To what extent can seaweed farming in combination with nutrient management in agriculture and waste water treatment reduce the potential for coastal eutrophication?

    These questions are answered through model analyses. The Global NEWS (Nutrient Export from WaterSheds) model simulates river export of nutrients as function of human activities on land. It includes more than 6000 rivers worldwide. It can be used to quantify nutrient flows from land to sea for the years 1970, 2000, 2030 and 2050. For future years four scenarios have been implemented. One of these scenarios is named Global Orchestration and mostly used as a reference in this thesis. This scenario assumes a globalised world, with a reactive approach towards environmental problems. The model was released in 2010, has been validated for the years 1970 and 2000. The nutrients considered in the model are nitrogen (N) and phosphorus (P). In this thesis Global NEWS is used to calculate transport of nutrients to the coastal waters of Europe. The model uses ICEP (Indicator for Coastal Eutrophication Potential) values at the river mouths as an indicator for potentially harmful effects of nutrient enrichment. These ICEP values reflect the ratio of nitrogen and phosphorus to silica in coastal seas. A positive ICEP value indicates that nitrogen or phosphorus levels are too high, favouring conditions for potentially harmful algae to bloom.

    In chapter 2 Global NEWS is used to calculate the transport of nutrients and ICEP values for 48 European rivers for the years 2000 and 2050. The model calculates a positive ICEP for 38 rivers in the year 2000, and for 34 rivers in the year 2050. This indicates that current policies are not so effective in reducing the river transport of nutrients. For polluted rivers the anthropogenic sources of the nutrients are investigated. For most rivers the dominant polluting sources are agriculture or sewage. The results indicate that a basin-specific policy is needed to reduce the risks of coastal eutrophication.

    In chapter 3 the focus is on useful algae: micro-algae cultivation on land for, for instance, biodiesel production. The consequences of large-scale production of biodiesel on nutrient export by rivers to the European coastal waters are investigated. A scenario is developed assuming that a production of 0.4 billion m3 diesel from cultivated micro-algae. The cultivation is assumed to be in the open air, for instance in ponds or in closed tube systems. Such production levels would need a land surface area as large as Portugal. The Global NEWS model is used to calculate the amount of waste water from micro-algae production that will be transported to the coastal waters in this scenario. The results indicate that large-scale cultivation of micro-algae on land can become a source of nutrient pollution in rivers. In the scenario with large-scale micro-algae cultivation the future transport of nitrogen and phosphorus is considerably higher than in the reference scenario. To ensure sustainable production of biodiesel from micro-algae it is important to develop cultivation systems with low nutrient losses to the environment.

    Chapter 4 presents a design of a factory for the cultivation and processing of micro-algae in an environmentally sound way. The factory does not use fossil fuels and applies maximum recycling of water and nutrients. In this factory it is possible to produce lipids, carbohydrates, proteins and minerals. The factory can be built on any piece of land, so there is no need to use arable land. The factory is independent of weather and climate. Energy can be delivered by wind mills. In this chapter an example of producing diesel in the factory is shown. In the 12 stories factory with a cultivation area of 1 hectare, 810 ton micro-algae can be cultivated per year. This is enough for the production of 386 ton diesel per year.

    Chapter 5 focuses on mitigation of eutrophication in European coastal waters. A scenario is presented assuming different types of measures. The scenario first assumes that nutrient use efficiencies in agriculture are higher than today, and that waste water treatment in sewage systems is improved. In addition, it assumes that all excess N and P in coastal waters is harvested in seaweed farms producing edible macro-algae. In our scenario for 2050 there is seaweed farming in the coastal waters of 34 rivers mouths in Europe .NEWS The areas needed to ensure that ICEP values remain below 0 (low potential for coastal eutrophication) range between 0 and 952 km2 per river mouth.

    This thesis shows that algae can be both harmful and useful. River export of nutrients can lead to coastal eutrophication increasing the risks of harmful algal blooms. On the other hand, micro-algae can be produced without environmental harm on land, and macro-algae can be useful in reducing pollution levels in coastal seas. This thesis could serve as a basis for environmental policies to stimulate the production of these useful algae. The methods to mitigate algal blooms and to use algae in a sustainable way in this thesis are also useful for other parts of the world.

    Groen proceswater: zuivering brouwerijprocesafvalwater met microalgen
    Dijk, W. van; Weide, R.Y. van der; Kroon, A. - \ 2016
    Lelystad : ACRRES - Wageningen UR (PPO 721) - 42
    brouwerij-industrie - brouwerijafvalwater - afvalwater - afvalwaterbehandeling - waterzuivering - algen - biomassa - biomassa productie - afvoerwater - flotatie - algenteelt - brewing industry - brewery effluent - waste water - waste water treatment - water treatment - algae - biomass - biomass production - effluents - flotation - algae culture
    In 2012 is het project Groen Proceswater gestart. Hierin worden de mogelijkheden van zuivering van brouwerijprocesafvalwater met behulp van microalgen onderzocht. Dit is gedaan in een samenwerkingsverband van Heineken Nederland BV, Algae Food & Fuel en WUR-ACRRES. De resultaten behaald in 2012 en 2013 zijn beschreven in afzonderlijke rapporten. In dit rapport zijn de resultaten van 2014 en 2015 beschreven. In 2014 is onderzocht of een voorbehandeling van het proceswater via cavitatie-flotatie het zuiveringsresultaat kan verbeteren en in 2015 of de energie-input van de LEDbelichting kan worden verminderd door te flashen (afwisselende licht-donker periodes op microseconde tijdschaal). Verder is in 2015 en 2016 via een literatuurstudie gekeken naar de verwaarding van de geproduceerde algenbiomassa en zijn de conclusies van het gehele project samengevat.
    Biobased Economy: Algen, het groene goud
    Barbosa, M.J. - \ 2016
    Wageningen : Wageningen University & Research
    algenteelt - algen - biomassa productie - teeltsystemen - cultuurmethoden - biobased economy - algae culture - algae - biomass production - cropping systems - cultural methods - biobased economy
    De wereldbevolking groeit en daarmee ook de behoefte aan energie, chemicaliën, en producten zoals plastic, zeep, schoonmaakmiddelen, verf en lijm. Om daarin te kunnen voorzien, moeten we overstappen naar een economie, waarin we de grondstoffen voor deze producten uit duurzame, hernieuwbare bronnen halen. Een voorbeeld van een van de meest duurzame oplossingen zijn micro-algen. Maria Barbosa van Wageningen University & Research vertelt er alles over.
    Mild disintegration of green microalgae and macroalgae
    Postma, Richard - \ 2016
    Wageningen University. Promotor(en): Michel Eppink; Rene Wijffels, co-promotor(en): Giuseppe Olivieri. - Wageningen : Wageningen University - ISBN 9789462579477 - 181
    algae - chlorella vulgaris - bioprocess engineering - biorefinery - proteins - milling - carbohydrates - biobased economy - disintegrators - technology - extraction - algen - chlorella vulgaris - bioproceskunde - bioraffinage - eiwitten - maling - koolhydraten - biobased economy - desintegrators - technologie - extractie

    An increased worldwide protein demand for food and feed and the necessity to release the water soluble proteins in the first stage of the cascade biorefinery require the development of mild protein extraction technologies. Cell disintegration is the first hurdle and is considered as one of the most energy consuming steps. Therefore, this thesis focused on the development of a mild, scalable and energy efficient disintegration technology for green microalgae and macroalgae (seaweed) aimed on extraction of water soluble components (like proteins and carbohydrates).

    For microalgae disintegration, two main technologies were investigated. First of all the conventional technology bead milling and second a novel approach using Pulsed Electric Field (PEF). In Chapter 2 a benchmark was set by means of bead milling for the release of water soluble protein from the green microalgae Chlorella vulgaris. Overall, protein yields between 32 and 42% were achieved, while the energy consumption was reduced with 85% by selective protein extraction to values as low as 0.81 kWh kgDW-1. Remarkably, the benchmark was much better than expected.

    In Chapter 3 the bead mill was further optimized by decreasing the applied bead size, furthermore the applicability of bead milling on two additional microalgae species (Neochloris oleoabundans, Tetraselmis suecica) was shown. In addition, to be able to better understand the disintegration mechanism, the so-called stress model was applied. This model describes the comminution process in a bead mill as function of the amount of bead contacts and the force of each impact. The release kinetics could be improved and thereby the specific energy consumption could be reduced to 0.45‒0.47 kWh kgDW-1 by using 0.3 mm beads for all algae.

    Chapter 4 describes a screening on the applicability of PEF, over a broad range of operating conditions, for the extraction of water soluble proteins from the microalgae C. vulgaris and N. oleoabundans. No substantial protein yields were observed under the investigated conditions. This led to the conclusion that PEF is not suitable to release water soluble proteins, not even at specific energy consumptions much higher than those for the benchmark, bead milling.

    In Chapter 5 it was attempted to improve the performance of PEF by investigating the synergistic effect with the processing temperature. The PEF experiments were performed using a pilot scale continuous flow electroporation unit in which the processing temperature was controlled between 25 – 65 °C. The results showed that under the tested conditions, the combined PEF-Temperature treatment did not cause substantial disintegration of the algal cells to effectively release water soluble proteins.

    In addition to the microalgae, macroalgae were subject of investigation in the search for new protein sources in Chapter 6. Four batch technologies were used to disintegrate the green macroalgae Ulva lactuca, being; osmotic shock, enzyme incubation, PEF and High Shear Homogenization (HSH). In descending order the highest protein yields per treatment; HSH (~40%) > enzyme degradation (~25%) > osmotic shock (~20%) > PEF (~15%).

    In the final chapter the main results and remaining bottlenecks are discussed and a future outlook on microalgae disintegration is presented. To date, bead milling is the only technology able to disintegrate fresh microalgae at specific energy consumptions below 10% of the total energy available from the algae and release substantial amounts of water soluble protein. The future outlook was based on a techno-economic evaluation, which showed that the cultivation costs are limiting the economic feasibility of microalgae biorefinery. Future focus should be on the cultivation.

    Ionic liquid pre-treatment of microalgae and extraction of biomolecules
    Desai, Rupali K. - \ 2016
    Wageningen University. Promotor(en): Michel Eppink; Rene Wijffels. - Wageningen : Wageningen University - ISBN 9789462579804 - 126
    salts - liquids - fractionation - extraction - hydrophobicity - algae - biomass production - zouten - vloeistoffen (liquids) - fractionering - extractie - hydrofobiciteit - algen - biomassa productie

    Liquid-liquid extraction (LLE) techniques are widely used in separation primarily due to ease of scale up. Conventional (LLE) systems based on organic solvents are not suitable for extraction of fragile molecules such as proteins as it would result in denaturation. On the other hand aqueous biphasic system though suitable for extraction of proteins they are restricted by limited polarity range. Ionic liquids are salts which are liquid at room temperature. Ionic liquids have gained interest in extraction over the past years due to its non-volatility and tunable property. In this thesis we explored the feasibility of using two ionic liquid based systems for extraction: 1) Ionic liquid based aqueous two phase system for extraction of microalgae proteins and 2) ionic liquid based emulsions for separation of hydrophilic (e.g. proteins) and hydrophobic (e.g. pigments) components from complex biomass such as microalgae. Additionally the influence of IL pre-treatment on microalgae cell walls and subsequent fractionation of its components (e.g. proteins, pigments, lipids) was also investigated.

    The fatter the better : selecting microalgae cells for outdoor lipid production
    Dominguez Teles, I. - \ 2016
    Wageningen University. Promotor(en): Rene Wijffels, co-promotor(en): Maria Barbosa; Dorinde Kleinegris. - Wageningen : Wageningen University - ISBN 9789462578821 - 164
    algae - chlorococcum - lipids - lipogenesis - fat - production - phenotypes - inoculum - diameter - cells - sorting - algen - chlorococcum - lipiden - lipogenese - vet - productie - fenotypen - entstof - diameter - cellen - sorteren

    In chapter 1 we introduce microalgae, photosynthetic microorganisms with potential to replace commodities (such as food, feed, chemicals and fuels). Production costs are still high, reason why microalgae are still only economically feasible for niche markets. We suggest to borrow the concept of plant domestication to select industrial microalgae cells. Two approaches can be successfully used to domesticate microalgae: adaptive laboratory evolution (ALE) and fluorescence assisted cell sorting (FACS). ALE takes advantage of the natural adaptability of microorganisms to different environments, while FACS actually select cells with specific phenotypes. This thesis aimed to select cells of Chlorococcum littorale with improved phenotypes, assuming that these cells could establish new populations with increased industrial performance.

    In Chapter 2 we wanted to know what happened during time to biomass and lipid productivities of Chlorococcum littorale repeatedly subjected to N-starvation. We tested 2 different cycles of N-starvation, short (6 days) and long (12 days). Short cycles didn’t affect lipid productivity, highlighting the potential of C. littorale to be produced in semi-continuous cultivation. Repeated cycles of N-starvation could have caused adaptations of the strain. Hence, we also discussed the implications of using repeated N-starvation for adaptive laboratory evolution (ALE) experiments. Chapter 3 introduces a method to detect and to select microalgae cells with increased lipid content. The method requires only the fluorescence dye Bodipy505/515 dissolved in ethanol, and the method was designed to maintain cellular viability so the cells could be used to produce new inoculum. In chapter 4 we evaluated a question that emerged while deciding which criteria to use to sort lipid-rich cells: does cellular size affects lipid productivity of C. littorale? We hypothesized that cells with different diameters have different division rates, which could affect lipid productivity. Therefore, we assessed the influence of cell diameter, as a sorting parameter, on both biomass and lipid productivity of Chlorococcum littorale (comparing populations before and after sorting, based on different diameters). Results showed that the size of vegetative cells doesn’t affect the lipid productivity of C. littorale. In chapter 5 we present a strategy to sort cells of C. littorale with increased TAG productivity using the method developed at chapter 3. Both the original and the sorted population with the highest lipid productivity (namely, S5) were compared under simulated Dutch summer conditions. The results confirmed our data from experiments done under continuous light: S5 showed a double TAG productivity. Our results showed also that the selected phenotype was stable (1.5 year after sorting) and with potential to be used under industrial conditions. In chapter 6 we extrapolated our results (indoor and outdoor) to other climate conditions. We ran simulations changing the light conditions to four different locations worldwide (the Netherlands, Norway, Brazil and Spain) to estimate both biomass and TAG productivities. Results indicated that biomass yields were reduced at locations with higher light intensities (Brazil/Spain) when compared with locations with lower light intensities (Norway/Netherlands). Hence, the choice of location should not be based on light intensity, but on how stable irradiation is. Chapter 7 is the general discussion of the thesis, demonstrating that both ALE and FACS are effective approaches to select industrial microalgae cells. We also present our view on how ALE and FACS could further improve microalgae strains for industry.

    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.

    Microalgae production in a biofilm photobioreactor
    Blanken, Ward - \ 2016
    Wageningen University. Promotor(en): Rene Wijffels, co-promotor(en): Marcel Janssen. - Wageningen : Wageningen University - ISBN 9789462578425 - 234
    algae - algae culture - biofilms - bioreactors - growth - production costs - biomass - artificial lighting - photosynthesis - carbon dioxide - algen - algenteelt - biofilms - bioreactoren - groei - productiekosten - biomassa - kunstmatige verlichting - fotosynthese - kooldioxide

    Microalgae can be used to produce high-value compounds, such as pigments or high value fatty acids, or as a feedstock for lower value products such as food and feed compounds, biochemicals, and biofuels. In order to produce these bulk products competitively, it is required to lower microalgae production cost. Production costs could be reduced by employing microalgae biofilms as a production platform. The main advantages of microalgae biofilms are a direct harvest of concentrated microalgae paste, and the uncoupling of the hydraulic retention time from the microalgal retention time. The latter allows to decrease the liquid volume or to employ dilute waste streams. To successfully employ biofilms, however, it is required that microalgal biofilms can be cultivated at high productivity and high photosynthetic efficiency. The aim of this thesis was to optimize the productivity of microalgal biofilms.

    Light energy drives microalgal growth. Sunlight is free and abundant, but sunlight intensity varies over the day and the seasons. This makes it impossible to maintain optimal production conditions throughout the day. These fluctuations in irradiance can be prevented by applying artificial lighting. Although, artificial lighting will supply a constant light intensity and thus increase productivity and simplify process control, it will also increase microalgae production cost. A quantitative evaluation of lighting costs and energy requirement was still missing and this was the topic of Chapter 2. The costs related to artificial lighting were identified as 25.3 $ per kilogram of dry-weight biomass, with only 4% to 6% of the electrical energy required to power the lamps eventually stored as chemical energy in microalgal biomass. Energy loss and increased production cost may be acceptable for the production of high value products, but in general they should be avoided.

    In Chapter 3, a photobioreactor design based on a rotating biological contactor (RBC) was introduced and used as a production platform for microalgal biomass cultivated in a biofilm. In the photobioreactor, referred to as the Algadisk, microalgae grow in biofilm on vertical rotating disks partially submerged in water with dissolved nutrients. The objective was to evaluate the potential of the Algadisk photobioreactor, and identify the window of operation of the process with respect to the effects of disk roughness, disk rotation speed and CO2 concentration. These parameters were evaluated in relation to biomass productivity, photosynthetic efficiency, and the long-term cultivation stability of the production process.

    The mesophilic green microalga Chlorella sorokiniana was used as a model organism. In the lab-scale Algadisk reactor, a productivity of 20.1 ±0.7 gram per m2 disk surface per day and a biomass yield on light of 0.9 ±0.04 gram dry weight biomass per mol photons were obtained. This productivity could be retained over 21 weeks without re-inoculation. To obtain maximal and stable productivity it was important that the disk surface provides a structure that allows biomass retention on the disk after harvest. The retained biomass acts as inoculum for the new biofilm and is therefore essential for quick biofilm regrowth. Most important process parameters were CO2­ supply, temperature, and pH. Although deviations of these parameters from the optimal conditions resulted in productivity loss, the system quickly recovered when optimal conditions were restored. These results exhibit an apparent opportunity to employ the Algadisk photobioreactor and biofilm systems in general at large scale for microalgae biomass production provided CO2 supply is adequate.

    In order to better understand the process conditions inside the biofilm a model was developed in the further chapters. These mathematical models were calibrated and validated with dedicated experiments. In Chapter 4 first a general applicable kinetic model was developed able to predict light limited microalgal growth. This model combines a mathematical description for photoautotrophic sugar production with a description for aerobic chemoheterotrophic biomass growth. The model is based on five measurable biological parameters which were obtained from literature for the purpose of this study. The model was validated on experiments described in literature for both Chlorella sorokiniana and Chlamydomonas reinhardtii. The specific growth rate was initially predicted with a low accuracy, which was most likely caused by simplifications in the light model and inaccurate parameter estimations. When optimizing the light model and input parameters the model accuracy was improved and validated. With this model a reliable engineering tool became available to predict microalgal growth in photobioreactors. This microalgal growth model was included in the biofilm growth models introduced in Chapters 5 and 6.

    In Chapter 5 microalgal biofilms of Chlorella sorokiniana were grown under simulated day-night cycles at high productivity and high photosynthetic efficiency. The experimental data under day/night cycles were used to validate a microalgal biofilm growth model. For this purpose the light limited microalgal growth model from Chapter 4 was extended to include diurnal carbon-partitioning and maintenance under prolonged dark conditions. This new biofilm growth model was then calibrated and validated experimentally. Based on these experiments and model simulations no differences in the light utilization efficiency between diurnal and continuous light conditions were identified. Indirectly this shows that biomass lost overnight represents sugar consumption for synthesis of new functional biomass and maintenance related respiration. This is advantageous, as this result shows that it is possible to cultivate microalgae at high photosynthetic efficiencies on sunlight and that the night does not negatively impact overall daily productivity. Long periods of darkness resulted in reduced maintenance related respiration.

    Based on simulations with the validated biofilm growth model it could be determined that the photosynthetic efficiency of biofilm growth is higher than that of suspension growth. This is related to the fact that the maintenance rate in the dark zones of the biofilm is lower compared to that in the dark zones of suspension cultures, which are continuously mixed with the photic zone.

    In Chapter 3 it was identified that concentrated CO2 streams are required to obtain high productivities. However, over-supplying CO2 results into loss of CO2 to the environment and is undesirable for both environmental and economic reasons. In Chapter 6 the phototrophic biofilm growth model from Chapter 5 was extended to include CO2 and O2 consumption, production, and diffusion. The extended model was validated in growth experiments with CO2 as limiting substrate. Based on the validated model the CO2 utilization and productivity in biofilm photobioreactors were optimized by changing the gas flow rate, the number of biofilm reactors in series, and the gas composition. This resulted in a maximum CO2 utilization efficiency of 96% by employing flue gas, while the productivity only dropped 2% compared to non-CO2 limited growth. In order to achieve this 25 biofilm reactors units, or more, must be operated in series. Based on these results we conclude that concentrated CO2 streams and plug flow behaviour of the gaseous phase over the biofilm surface are essential for high CO2 utilization efficiencies and high biofilm productivity.

    In Chapter 7 the implications of these studies for the further development of biofilm photobioreactors was discussed in the light of current biofilm photobioreactor designs. Design elements of state of the art biofilm photobioreactors, were combined into a new conceptual biofilm photobioreactor design. This new design combines all advantages of phototrophic biofilms minimizing the amount of material required. Further improvements by means of process control strategies were suggested that aim for maximal productivity and maximal nutrient utilization efficiency. These strategies include: control of the biofilm thickness, control of the temperature, and optimized nutrient supply strategies.

    Kansen voor toepassing van microalgen in landbouwgewassen
    Spruijt, J. ; Weide, R.Y. van der - \ 2016
    Lelystad : ACRRES - Wageningen UR (Rapport / PPO-AGV 691) - 62
    akkerbouw - tuinbouw - bemesting - algen - algenteelt - duurzame landbouw - duurzame ontwikkeling - gewasbescherming - plantgezondheid - bacteriën - biologische bestrijding - arable farming - horticulture - fertilizer application - algae - algae culture - sustainable agriculture - sustainable development - plant protection - plant health - bacteria - biological control
    Op basis van internationaal literatuuronderzoek blijken er interessante kansen voor toepassing van microalgen producten in landbouwgewassen te zijn. In dit rapport worden zowel groene algen als cyanobacteriën gedefinieerd als microalgen. Stoffen uit microalgen (met name uit cyanobacteriën) blijken in diverse onderzoeken uit de literatuur een goede bestrijding te geven van verschillende schimmels en aaltjes die in landbouwgewassen schade aanrichten. Verder is er (buiten de landbouw) insecticide-, molluscicide-, herbicide- en algacidewerking met stoffen uit cyanobacteriën aangetoond. In Nederland zijn zeewier- en algenextracten krachtens de Verordening gewasbescherming als werkzame stof goedgekeurd voor de groeiregulatie van planten. Het gebruik als bodemverbeteraar of als plantenstimulator is vooralsnog veel minder gereguleerd dan als gewasbeschermingsmiddel. Om de kansen met microalgen te benutten zou er verder geïnvesteerd moeten worden in onderzoek. Het zou duidelijk moeten worden welke werkzame stoffen uit micro algen of welke algenpreparaten andere organismen bestrijden, in welke formulering en met welke dosering. De bestrijdende, bemestende, bodem verbeterende, plantweerstand verhogende en milieueffecten van algentoepassingen zouden vergeleken moeten worden met conventionele methoden.
    Further improvements in water quality of the Dutch Borderlakes : two types of clear states at different nutrient levels
    Noordhuis, Ruurd ; Zuidam, B.G. van; Peeters, E.T.H.M. ; Geest, G.J. van - \ 2016
    Aquatic Ecology 50 (2016)3. - ISSN 1386-2588 - p. 521 - 539.
    Abramis brama - Alternative stable states - Biomanipulation - Cyanobacteria - Dreissena - Macro-algae - Quagga Mussel - Regime shift - randmeren - mussels - algae - water quality - aquatic ecology - eutrophication - randmeren - abramis brama - mossels - cyanobacteriën - algen - waterkwaliteit - aquatische ecologie - eutrofiëring

    The Borderlakes are a chain of ten shallow, largely artificial, interconnected lakes in the Netherlands. The ecological recovery of the central Borderlakes (viz. lake Veluwe and Wolderwijd) has been well documented. These lakes shifted from a eutrophic, Planktothrix dominated state in the 1970s to a clear state in 1996. Around 2010, the formerly hypertrophic, southern Borderlake Eem also reached a clear state, but at considerably higher nutrient levels. In this paper, monitoring data are used to compare these changes and identify the differences in driving processes and their consequences. The 1996 shift in Lake Veluwe was linked to increased fishery for benthivorous Bream, followed and stabilized by increase in Zebra Mussels and charophytes. Nutrients in Lake Eem decreased as well and Planktothrix disappeared here too in 1996, despite relatively high TP concentrations which remained stable over time. The start of the change into the clear state in this case also involved a decrease in the Bream population, but with a stronger additional role for dreissenids, particularly of Quagga Mussels. Remaining blooms of cyanobacteria almost disappeared, but the current situation in Lake Eem represents a different type of clear water state than in the central Borderlakes. This type is characterized by the combination of a relatively high phosphorus load, intense dreissenid filtration and filamentous macro-algae instead of either blooms of cyanobacteria or dominance of charophytes. With the dominant role of the River Eem, the relatively short residence time and increasing difficulty to bring down nutrient loading any further, the stability of this clear state depends on high densities (and filtration rates) of dreissenids.

    Batch and repeated-batch oil production by microalgae
    Benvenuti, G. - \ 2016
    Wageningen University. Promotor(en): Rene Wijffels, co-promotor(en): Rouke Bosma; Maria Barbosa. - Wageningen : Wageningen University - ISBN 9789462576582 - 149
    algae - chlorella - arthrospira - dunaliella - nostoc - triacylglycerols - light - lipogenesis - photosynthesis - oil products - productivity - biomass conversion - economic analysis - algen - chlorella - arthrospira - dunaliella - nostoc - triacylglycerolen - licht - lipogenese - fotosynthese - olieproducten - productiviteit - biomassaconversie - economische analyse

    Microalgal triglycerides (TAGs) are promising feedstocks for the commodity markets (i.e. food, chemical and biofuel). Nevertheless, microalgal TAGs are not yet economically feasible due to the high production costs. To reduce these costs, TAG productivity needs to be maximized.

    The aim of this thesis was to increase microalgal TAG productivity by investigating the effects of biological and engineering parameters (i.e. production strain and operational strategy).

    We first screened seven marine species on their TAG productivity under nitrogen (N) starvation. Nannochloropsis sp. was identified as the most suitable species as it retained its photosynthetic activity while accumulating large amounts of TAGs ensuring the highest TAG productivity. Therefore, Nannochloropsis sp. was used in all following studies.

    Next, we aimed at optimizing TAG productivity by investigating the effect of initial-biomass-specific (IBS) light availability (i.e. ratio of light impinging on reactor ground area divided by initial biomass concentration per ground area) in batch outdoor cultivations carried out in horizontal and vertically stacked tubular reactors at different initial biomass concentrations at the start of the TAG accumulation phase, over different seasons. Based on the observed trends of TAG productivity for the Dutch climate, optimal initial biomass concentrations were suggested to achieve high areal TAG productivities for each reactor configuration and season.

    Subsequently, repeated-batch processes were investigated to further increase TAG productivity compared to batch processes. For this, repeated-batch cultivations were tested and compared to batch cultivations both at lab-scale under day/night cycles and in two identical, simultaneously operated, outdoor vertically stacked tubular reactors over different seasons. Although at lab-scale, batch and repeated-batch cultivations led to similar TAG productivities, outdoor repeated-batch processes were always outcompeted by the batch. It was concluded that repeated-batch processes require further optimization.

    For this, the physiological responses of Nannochloropsis sp. to N-starvation and N-replenishment were determined under continuous light in lab-scale batch and repeated-batch cultivations and condensed into a mechanistic model describing both cultivation strategies. Scenarios for improved TAG yields on light were simulated and, based on the optimized yields, a comparison of the two processes was performed. It was concluded that under continuous light, an optimized batch process will always result in higher TAG productivities than an optimized repeated-batch process.

    Finally, a techno-economic analysis for a two-step-continuous TAG production process (i.e. growth reactors are operated in continuous mode such that multiple batch-operated stress reactors are inoculated and sequentially harvested) is performed for a hypothetical 100 ha-scale plant in southern Spain using vertically stacked tubular reactors. Photosynthetic efficiencies based on outdoor pilot data were used as model input. By optimizing both photosynthetic efficiency and process technology, the production cost could be decreased from 7.4 to 3.0 €·kg-1 of TAG-enriched biomass. We believe to be on the right track to achieve an economically feasible TAG production platform provided that photosynthetic efficiency is further improved, the whole biomass is valorized and cheaper reactors are designed.

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