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.

    We have a manual that explains all the features 

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    Warmtewisselaars met gekromde buizen
    Kelder, J.D.H. ; Klerk, S. de - \ 2004
    Voedingsmiddelentechnologie 37 (2004)13. - ISSN 0042-7934 - p. 14 - 16.
    warmteuitwisseling - voedseltechnologie - uitrusting - automatisering - thermisch rendement - reologie - vloeistoffen (liquids) - stroming - heat exchange - food technology - equipment - automation - thermal efficiency - rheology - liquids - flow
    Ultra High Temperature (UHT) sterilisation is a commonly applied technique to preserve liquid food products. Stork Food & Dairy Systems has marketed coiled tubular UHT-sterilisers. For viscous and especially for gelatinising foods (e.g. custard and pudding) spiral sterilisers bring superior performance. Heat transfer greatly increases and required temperatures are attained faster, thus reducing processing time. Coiled sterilisers are therefore shorter and more compact, minimising the loss of quality factors due to the heat treatment. Finally, gelatinisation occurs rapidly and uniformly, and de reduced thermo-mechanical stresses enable a potentially lower amount of starch needed to obtain a target consistency
    20 mestverwerkingssystemen op een rij
    Buisonjé, F.E. de - \ 2003
    Praktijkkompas. Varkens 17 (2003)3. - ISSN 1570-8578 - p. 22 - 22.
    mest - dierlijke meststoffen - stalmest - dierlijk afval - afvalverwerking - verwerking - behandeling - systemen - uitrusting - mestverwerking - manures - animal manures - farmyard manure - animal wastes - waste treatment - processing - treatment - systems - equipment - manure treatment
    ASG, divisie Praktijkonderzoek heeft in opdracht van VROM en InfoMil een twintigtal mestverwerkingssystemen beschreven. Zie ook de website van InfoMil (www.infomil.nl). Deze worden regelmatig bijgewerkt aan de hand van nieuwe informatie en mogelijke technische wijzigingen aan de installaties.
    Voorlichting op basis van onderzoek : 1e update en uitbreiding
    Rijssel, E. van; Ploeger, C. - \ 2000
    Aalsmeer : Proefstation voor Bloemisterij en Glasgroente, Vestiging Aalsmeer (Rapport / Proefstation voor Bloemisterij en Glasgroente 272) - 151
    energiebehoud - teelt onder bescherming - kassen - voorlichting - documentatie - overzichten - informatie - uitrusting - landbouwvoorlichting - glastuinbouw - energy conservation - protected cultivation - greenhouses - extension - documentation - reviews - information - equipment - agricultural extension - greenhouse horticulture
    Toepassingsmogelijkheden mestbewerking op varkenshouderijbedrijven
    Verdoes, N. ; Melse, R. - \ 2000
    Praktijkonderzoek varkenshouderij 14 (2000)6. - ISSN 1382-0346 - p. 13 - 13.
    varkenshouderij - varkensmest - mest - verwerking - uitrusting - mestverwerking - pig farming - pig manure - manures - processing - equipment - manure treatment
    Het Praktijkonderzoek Varkenshouderij leidt het project 'Toepassingsmogelijkheden mestbewerking opvarkenshouderijbedrijven', dat mestbewerkingsinstallaties onderzoekt op twaalf praktijkbedrijven.
    Extruder goed toepasbaar voor continue extractie en deegkneden
    Stegeman, D. ; Luyten, H. - \ 2000
    Voedingsmiddelentechnologie 33 (2000)7. - ISSN 0042-7934 - p. 30 - 32.
    uitpersing - verwerking - broodbereiding - brood - vloeistofmechanica - prestatieniveau - kwaliteit - reologie - visco-elasticiteit - uitrusting - voedselindustrie - voedseltechnologie - productieprocessen - machines - extrusion - processing - breadmaking - bread - fluid mechanics - performance - quality - rheology - viscoelasticity - equipment - food industry - food technology - production processes - machines
    De voortdurende ontwikkeling van de apparatuur zorgt voor een continue uitbreiding van de toepassingsmogelijkheden van de extrusietechnologie. De werking van het extrusie-extractieproces is behandeld en schematisch weergegeven
    Ex-post evaluatie van een gasmotorwarmtepomp op een glastuinbouwbedrijf
    Haastert, M. van - \ 2000
    Den Haag : LEI - ISBN 9789052426297 - 47
    kassen - verwarming - stookkosten - verwarmingssystemen - uitrusting - warmtepompen - warmtewisselaars - verwarmingsapparatuur - economische analyse - kosten-batenanalyse - greenhouses - heating - heating costs - heating systems - equipment - heat pumps - heat exchangers - heaters - economic analysis - cost benefit analysis
    Hydrometry
    Boiten, W. - \ 2000
    Rotterdam [etc.] : Balkema - ISBN 9789054104193 - 246
    meting - doorstroommeters - vloeistofmechanica - kanalen, klein - waterpassen - ontladingen - instrumenten (meters) - meetopeningen - uitrusting - measurement - flow meters - fluid mechanics - channels - level gauges - discharges - instruments - measuring orifices - equipment
    Met ontvochtiger blijft warmte binnen
    Campen, J.B. - \ 1999
    Groenten en Fruit. Vakdeel glasgroenten (1999)14. - ISSN 1380-3573 - 17
    klimaat - vochtigheid - uitrusting - energiebehoud - technische informatie - glastuinbouw - climate - humidity - equipment - energy conservation - technical information - greenhouse horticulture
    Schematisch ontwerp van ontvochtiger van IMAG-DLO. Gecombineerd stoken en ventileren om de luchtvochtigheid te verlagen kost veel energie. Door een deel van de energie terug te winnen met een ontvochtiger, kan het energieverbruik in kassen verminderen
    Helft veldspuiten vertoont gebreken
    Vries, R.L. de - \ 1998
    Landbouwmechanisatie 49 (1998)3. - ISSN 0023-7795 - p. 24 - 25.
    gewasbescherming - uitrusting - spuitapparaten - componenten - landbouwwerktuigen - boerderij uitrusting - gereedschappen - onderhoud - service - regulatie - wetgeving - beleid - duitsland - plant protection - equipment - sprayers - components - farm machinery - farm equipment - tools - maintenance - servicing - regulation - legislation - policy - germany
    Microorganisms in Foods 6: Microbial Ecology of Food Commodities.
    Schothorst, M. van - \ 1997
    London : Blackie Academic & Professional - ISBN 9780751404302 - 615
    voedselindustrie - voedseltechnologie - micro-organismen - bacteriën - classificatie - taxonomie - dierlijke producten - bacteriologie - kiemgetal - voedselinspectie - microbiologie - voedingsmiddelen - voedselbewaring - groenteproducten - opslag - plantaardige producten - microbiële ecologie - methodologie - biologische technieken - experimenten - uitrusting - voedselmicrobiologie - voedselproducten - landbouwproducten - voedselbesmetting - toxische stoffen - xenobiotica - haccp - food industry - food technology - microorganisms - bacteria - classification - taxonomy - animal products - bacteriology - bacterial count - food inspection - microbiology - foods - food preservation - vegetable products - storage - plant products - microbial ecology - methodology - biological techniques - experiments - equipment - food microbiology - food products - agricultural products - food contamination - toxic substances - xenobiotics - haccp
    Biopreservation in modified atmosphere packaged vegetables
    Bennik, M.H.J. - \ 1997
    Agricultural University. Promotor(en): F.M. Rombouts; L.G.M. Gorris. - S.l. : Bennik - ISBN 9789054858089 - 96
    uitrusting - verpakking - verpakkingsmaterialen - verpakken - planten - dieren - behoud - machines - equipment - packaging - packaging materials - packing - plants - animals - preservation - machines

    Recent trends in food preservation are the use of mild preservation techniques, such as modified atmosphere (MA) packaging and refrigeration, to prolong the shelflife of foods without affecting the fresh character of the product. This has resulted in the development of a new generation of chill stored, minimally processed foods, such as vegetables that are packaged under reduced oxygen (0 2 ) and elevated carbon dioxide (C0 2 ) concentrations. These gas atmospheres in combination with refrigerated storage conditions reduce the respiration rates of these products, and can limit the growth of endogenous spoilage bacteria, thereby rendering prolonged shelflives as compared with storage under ambient conditions. Although MA packaged vegetables have a fair safety record, they may incidently harbor foodborne pathogens. Especially the outgrowth of psychrotrophic (cold tolerant) pathogens can be considered a safety concern, but quantitative data on their growth under MA conditions that are suitable for produce are essentially lacking. Detailed information on the outgrowth of both pathogens and vegetable-associated spoilage bacteria under these conditions may give better insight into possible antagonistic action of competing microflora on the growth of pathogens, and the development of adequate countermeasures toward their growth to hazardous levels.

    One of the objectives of the studies that are described in this thesis was to obtain information on the impact of refrigerated MA storage conditions on the growth of microorganisms on minimally processed, MA packaged produce. Since our initial studies substantiated the possible hazard which can be posed by psychrotrophic pathogens, the use of biopreservation for adequate control of these microorganisms was investigated. In this respect, we have focused on lactic acid bacteria (LAB) because they occur naturally on fresh and minimally processed vegetables, and are able to produce a variety of antimicrobial substances, amongst which bacteriocins.

    Chapter 1 gives a short introduction on the technology of MA packaging of minimally processed vegetables and their current microbiological safety and quality status. Furthermore, the possible role of LAB as biopreservation agents in foods is addressed with special emphasis on those strains that are able to produce bacteriocins. The characteristics and mode of action of different bacteriocins that are produced by LAB are described, as well as aspects which are relevant to the application of these antimicrobial compounds or their producing organisms as food preservatives.

    Detailed information on the impact of refrigerated MA storage on the population dynamics of the endogenous microflora on vegetables is limited. Therefore, the prevailing epiphytic microorganisms on model produce ( i.e . chicory endive, and mungbean sprouts) were identified before and after MA storage. Subsequently, the growth characteristics of the predominant spoilage bacteria were determined under MA conditions ( Chapter 2 ). It was found that the major strains on both products were Enterobacteriaceae and Pseudomonas species. There were changes in the prevalent species on chicory endive before and after MA storage, but this was not observed for mungbean sprouts. To quantify the influence of C0 2 and 0 2 on the growth of the individual spoilage bacteria, a model agar system was developed that mimicked the in situ growth of bacteria on the surface of vegetables. The analysis of the growth of the predominant strains under controlled 0 2 and C0 2 concentrations at 8°C indicated that, in general, lag times were not present under the various conditions tested, and that the maximum population sizes were not affected. However, the maximum specific growth rates generally decreased with increasing C0 2 concentrations, which was independent of the 0 2 concentrations applied. This effect was more pronounced for Pseudomonas species than for Enterobacteriaceae. Representatives of the former subpopulation already showed significantly reduced maximum specific growth rates at C0 2 concentrations that are suitable for MA packaged vegetables.

    In Chapter 3 , the effects of different 0 2 and C0 2 concentrations on the growth of Aeromonas hydrophila, Yersinia enterocolitica, L. monocytogenes, and a cold tolerant strain of Bacillus cereus were quantified in the above mentioned model agar system at 8°C. Again, the maximum specific growth rates of the various microorganisms decreased significantly with increasing C0 2 concentration, while the maximum population densities were not affected and lag times were not observed. Extrapolation of the results from the model system to MA packaged vegetables suggested that growth of the above pathogens may occur at 8°C to the same maximum population densities as compared to ambient conditions, but at 10 to 20% lower maximum specific growth rates. Because we have shown that MA packaging can only moderately retard the growth of psychrotrophic pathogens, these bacteria can be considered a safety hazard to which countermeasures need to be developed.

    L. monocytogenes is a relevant psychrotrophic pathogen on minimally processed vegetables that requires adequate control measures. This Gram-positive bacterium can be inhibited by a number of bacteriocins that are produced by LAB. Thus, biopreservation using bacteriocin producing LAB strains may effectively prevent the growth of this bacterium, and possibly other psychrotrophic pathogens. With respect to practical application, an effort was made to obtain bacteriocinogenic LAB from minimally processed vegetables since these strains might be best adapted to the specific conditions under which their antimicrobial activity is required. Out of a total of 890 LAB isolates from mungbean sprouts and chicory endive, only nine strains were found to produce bacteriocins ( Chapter 4 ). Three of these strains exhibited antimicrobial activity towards a wide variety of Gram- positive bacteria, including the foodborne pathogens L.monocytogenes, and nonproteolytic Clostridium botulinum. Two of these bacteriocinogenic isolates were identified as Pediococcus parvulus on the basis of fermentation patterns and ribotyping. Recombinant DNA experiments revealed the presence of the pediocin PA-1 gene in both LAB strains, and further biochemical analysis confirmed the production of pediocin PA-1 in absence of other bacteriocins.

    The third broad spectrum bacteriocin-producing strain was identified as Enterococcus mundtii ( Chapter 5 ). Its bacteriocin was purified to homogeneity and characterized. Elucidation of the complete primary amino acid sequence revealed a novel bacteriocin of 43 amino acids (M r 4287.2), designated as mundticin, that belongs to the class IIa bacteriocins of LAB. Other LAB that produce this class of antimicrobial peptides have previously been isolated from a wide variety of meat and dairy products, and their apparent wide-spread occurrence in foods may allow for the selection of strains that are ecologically adapted to specific food environments.

    As further described in Chapter 5 , mundticin exhibited bactericidal activity towards L.monocytogenes, and was shown to dissipate the membrane potential of whole cells, and to deplete their intracellular ATP pools. Mundticin was selected as a prototype of class IIa bacteriocins to investigate the biophysical properties of this peptide by molecular computer analysis. It was found that mundticin and related bacteriocins, contain a central α-helical region that was predicted to insert at an angle of 30 to 50° in a simulated hydrophobic/hydrophilic interface. This oblique insertion is proposed to cause a destabilisation of the phospholipid bilayer and facilitate the insertion and/or aggregation of monomers into functional pores in the cytoplasmic membrane. This concept is of interest for the rational design of bacteriocins with, for example, better biopreservation properties.

    For the effective application of bacteriocins as biopreservation agents, it is essential to gain more insight into the variation in the susceptibility of Gram-positive bacteriocins towards bacteriocins. The comprehensive study that is described in Chapter 6 addresses several factors which are associated with the natural variability in the bacteriocin-sensitivity of closely related non- bacteriocinogenic LAB. Two sets of strains for which the minimal inhibitory concentrations for nisin and pediocin PA-1 differed 100 to 1000-fold were compared. Our data provide evidence that the association of bacteriocins with the cell membrane and their subsequent insertion into the membrane take place in a similar way for cells that have a high or a low natural bacteriocin tolerance. For insensitive strains, the overall constitution of the membrane, rather than the mere membrane fluidity, may preclude the formation of pores with sufficient diameters and lifetimes to ultimately cause cell death. Further analysis of this phenomena may require more attention for the structural role of proteins in biological membranes.

    The last part of this dissertation comprises a study on the potential of the vegetable- associated bacteriocin-producing bacteria and mundticin to act as biopreservation agents on refrigerated, MA-stored vegetables ( Chapter 7 ). Both P. parvulus strains were found to be unsuitable for this purpose, due to the lack of bacteriocin production at 4 and 8°C. By contrast, E. mundtii displayed a number of characteristics that favor an application as a biopreservative agent, such as limited acid production, production of a bacteriocin with anti-listeria activity at low temperatures, and high growth rates under MA conditions. Despite these properties, this strain failed to effectively inhibit the growth of L. monocytogenes on fresh mungbean sprouts. This is probably not due to a lack of in situ bacteriocin production, but rather the result of proteolytic degradation of mundticin or the growth of L. monocytogenes cells that are resistant to mundticin. Experiments with mundticin in a washing step and as a component of a coating were successful and warrant further research on the potential of this compound as a natural preservative agent for minimally processed vegetables.

    In conclusion, this dissertation has contributed to a better understanding of the microbiological characteristics of minimally processed vegetables that are stored under MA conditions. A general concern for the possible outgrowth of psychrotrophic pathogens on MA stored vegetables was substantiated by our investigations, which stresses that hygienic cultivation and processing conditions of this type of products remain indispensable. Although bacteriocins cannot be used as the sole preservatives to enhance the safety of refrigerated MA-stored minimally processed vegetables, they can contribute to tackle safety problems that may arise from certain cold tolerant, Grampositive pathogens.

    Benutting van het afvalwater van een melkveebedrijf voor het spoelen van de mestgangen : een orienterend onderzoek = Use of waste water from a dairy farm for flushing alleys : a preliminary research
    Kroodsma, W. ; Bleijenberg, R. ; Lent, A.J.H. van - \ 1996
    Wageningen : IMAG-DLO (Rapport / Dienst Landbouwkundig Onderzoek, Instituut voor Milieu- en Agritechniek 96-09) - ISBN 9789054061458 - 16
    landbouw - schoonmaken - schoonmaakgereedschap - melkvee - melkveehouderij - uitrusting - rioolwater - scheren - stallen - wassen (activiteit) - afvalwater - agriculture - cleaning - cleaning equipment - dairy cattle - dairy farming - equipment - sewage - shearing - stalls - washing - waste water
    Desinfectie van bedrijfsvreemd materiaal door blootstelling aan UV-C
    Roelofs, P.F.M.M. - \ 1996
    Rosmalen : Praktijkonderzoek varkenshouderij (Proefverslag / Praktijkonderzoek Varkenshouderij P1.166) - 28
    uitrusting - schoonmaken - wassen (activiteit) - scheren - stallen - varkensstallen - woningen - desinfectie - ontsmettingsmiddelen - steriliseren - ultraviolette straling - equipment - cleaning - washing - shearing - stalls - pig housing - dwellings - disinfection - disinfectants - sterilizing - ultraviolet radiation
    Waterverbruik schoonspuiten melkstallen
    Verstappen-Boerekamp, J.A.M. ; Wolters, G.M.V.H. - \ 1996
    Lelystad : Praktijkonderzoek Rundvee, Schapen en Paarden (Publicatie / Praktijkonderzoek Rundvee, Schapen en Paarden (PR) 114) - 17
    melkmachines - melkstandinrichtingen - uitrusting - schoonmaken - wassen (activiteit) - scheren - hergebruik van water - schadepreventie - milking machines - milking parlours - equipment - cleaning - washing - shearing - water reuse - loss prevention
    In deze publicatie wordt het onderzoek naar het waterverbruik en de gebruikte methodiek voor het schoonspuiten van de melkstal beschreven en de mogelijkheden die er zijn om het waterverbruik te verminderen.
    Reductie ammoniakemissie door stalen roostervloer
    Kant, P.P.H. - \ 1996
    Lelystad : Praktijkonderzoek Rundvee, Schapen en Paarden (Publicatie / Praktijkonderzoek Rundvee, Schapen en Paarden (PR) 110) - 20
    luchtverontreiniging - ammoniak - emissie - vervluchtiging - rundvee - uitrusting - schoonmaken - wassen (activiteit) - scheren - air pollution - ammonia - emission - volatilization - cattle - equipment - cleaning - washing - shearing
    De roosterelementen hadden een doorlaat van 52,5 %. De dieren liepen voorzichtiger dan normaal op de betonnen roosters. De stalen roosters reduceerden de ammoniak-emissie met 52 % in vergelijking met de betonnen roosters.
    Rubber trekker zorgt voor minder water bij schoonspuiten melkstal
    Verstappen-Boerekamp, J.A.M. - \ 1996
    Praktijkonderzoek Rundvee, Schapen en Paarden. Praktijkonderzoek 9 (1996)3. - ISSN 1386-8470 - p. 26 - 28.
    schoonmaken - uitrusting - schadepreventie - melkstandinrichtingen - scheren - wassen (activiteit) - watergebruik - cleaning - equipment - loss prevention - milking parlours - shearing - washing - water use
    Een eenvoudige manier om water te besparen is gebruik van een rubber trekker vóórdat wordt schoongespoten.
    Performance indicators for the statistical evaluation of digital image classifications
    Urso, G. D'; Menenti, M. - \ 1996
    ISPRS Journal of Photogrammetry and Remote Sensing 51 (1996)2. - ISSN 0924-2716 - p. 78 - 90.
    uitrusting - afbeelden - fotointerpretatie - remote sensing - equipment - imagery - photointerpretation - remote sensing
    A statistical procedure is proposed to evaluate the algorithms for the numerical classification of images. The approach is based on the derivation of performance indicators from measurements of signature separability and thresholding analysis. Although these measurements are not new in image processing techniques, they are used in this study in an original way for the comparison of outputs resulting from different classification criteria. The theoretical description of the method suggested is followed by its practical application to a case-study for mapping crop coefficients in an irrigation district.
    Growth and death of animal cells in bioreactors
    Martens, D.E. - \ 1996
    Agricultural University. Promotor(en): J. Tramper; C.D. de Gooijer. - S.l. : Martens - ISBN 9789054855934 - 222
    weefselkweek - celkweek - meristemen - zoölogie - chemische reacties - uitrusting - biotechnologie - chemische industrie - biochemie - tissue culture - cell culture - meristems - zoology - chemical reactions - equipment - biotechnology - chemical industry - biochemistry - cum laude

    Animal-cell cultivation is becoming increasingly important especially for the area of hunian- health products. The products range from vaccines to therapeutic proteins and the cells themselves. The therapeutic application of proteins puts high demands upon their quality with respect to purity and structure. For example, a correct folding and glycosylation is of importance for the activity, the in vivo clearance rate and the possible immunogenicity of the protein, and can often only be obtained by production in animal cells. An important class of proteins produced by animal cells is formed by monoclonal antibodies. Monoclonal antibodies are produced by hybridoma cells and have the capacity to bind very specifically to a particular molecular structure (epitope), a quality that makes them suitable for application in in vivo and in vitro diagnostics, in separation technology and for the in vivo targeting of drugs.

    The occurrence of substantial cell death and the presence of cell debris is a major problem in animal-cell cultivation. It interferes with the attainment of high volumetric productivities and with a proper functioning of the process. In addition, it may affect the quality of the product and cause problems in down-stream processing. Cell death may follow two different pathways, being apoptosis and necrosis, which have very distinct physiological and morphological features. Necrosis is a passive process generally caused by sudden high levels of environmental stress, whereas apoptosis is an active, genetically controlled process induced by mild stress conditions or specific signals from the environment.

    After the introduction in Chapter 1, the application of a general framework for the construction of segregated models is discussed in Chapter 2 with respect to the behaviour of animal-cell populations. For the construction of segregated models, the physiological state of an animal cell must be specified, which is discussed in this chapter with special attention for the experimental verification of the models. Finally, a number of age-structured, segregated models, which are of importance for animal-cell cultivation are reviewed in this chapter.

    The required amounts of animal-cell products are expected to be in the order of kilograms or even tonnes on a yearly basis. In order to produce these amounts, scale-up is necessary, which is most easily done in conventional reactor systems like the stirred-tank, bubble-column, and air-lift reactor. A main problem in the scale-up of these reactors is the supply of sufficient oxygen to the culture, which often requires sparging. Hydrodynamic forces associated with sparging cause cell death. In Chapters 3, 4, and 5 the specific death rate of hybridoma cells in bubble-column and air-lift reactors is studied with the hypothetical-killing-volume theory as a central theme. The hypothetical killing volume is a hypothetical volume associated with an air bubble during its lifetime in the reactor in which all cells are killed. The first-order death-rate constant in bubble- column and air-lift reactors can then be derived to be the product of this hypothetical killing volume and the number of bubbles introduced into the reactor per unit time and per unit reactor volume. The specific death rate of the hybridoma cells in the bubble-column and air-lift reactors is shown to be proportional to the gas flow rate and the reciprocal reactor height. Furthermore, in bubble columns the specific death rate is shown to be proportional to the square of the reciprocal reactor diameter. These results are in accordance with the hypothetical-killing-volume theory. The main cause of cell death is found to be bubble breakup at the surface, although detrimental effects at the sparger cannot be excluded. In Chapter 6 the specific death rate of Vero cells immobilized on microcarriers is shown to be proportional to the gas flow rate. Since the height of the reactor is not varied, it cannot be excluded that in this case also the rising of the bubbles or the associated liquid flow cause cell damage.

    A common method to reduce the detrimental effects of air bubbles is the use of protective additives. In this thesis it is shown that the addition of two such protectants, Pluronic F68 (Chapter 3) and serum (Chapter 4), respectively, reduces the amount of cell death as a consequence of sparging. Furthermore, as demonstrated in Chapter 4, the protective effect of serum has a fast-acting, physical, and a slow-acting, physiological component. In Chapter 5 the effect of the specific growth rate on the specific death rate of cells due to sparging is studied in air-lift loop reactors. Cells with varying specific growth rates are obtained from steady-state continuous cultures run at different dilution rates. Remarkably, the specific death rate of the cells due to sparging decreased as their specific growth rate decreased. Furthermore, in Chapter 6 it is shown that the specific death rate of Vero cells is reduced by immobilisation of the cells inside porous carriers.

    Below a critical dilution rate in continuous culture as well as towards the end of batch cultures, the specific death rate of hybridoma cells increases rapidly. In this case, the cells mainly die through apoptosis as a consequence of substrate depletion and the accumulation of toxic products. In Chapter 7 an age-structured model is developed to describe the rate of apoptosis as a function of the dilution rate in continuous culture. In this model a critical specific growth rate is introduced below which the cells start becoming apoptotic. In addition to the specific deathand growth rate, the average cell volume of the viable cells and the specific consumption and production rates for glucose, glutamine, lactate and ammonia are calculated. The model can reasonably well describe a set of literature data, with respect to the specific growth- and death rate and the concentrations of viable cells, dead cells, glucose, glutamine, lactate, and ammonia. In Chapter 8 the model is extended with equations concerning two hypotheses for the production of monoclonal antibody being:
    (1) Passive release of antibody from dead cells.
    (2) Increased productivity by the apoptotic cells.
    Both hypotheses can describe the increase in productivity at decreasing dilution rates as observed in Chapter 5. Furthermore, the distribution of cells over the different phases of the cell cycle is calculated and the equations for the average cell volume are rewritten in terms of forward scatter as measured by flow cytometry. Model predictions concerning these variables are compared to results obtained in Chapter 5. The G 1 - and G 2 /M-phase fractions are not predicted correctly, which may be caused by a cell-cycle-phase specificity of apoptosis. In addition, a good prediction of all cell-cycle fractions can be obtained if it is assumed that the duration of the G 2 /M phase is not constant, but increases as the specific growth rate decreases from the maximum to its critical value. Furthermore, the calculated fraction of apoptotic cells is shown to be proportional to the forward scatter.

    Cell death associated with sparging may be minimised by:
    (1) Maximizing the amount of oxygen transferred per bubble introduced in the reactor.
    (2) The addition of a shear-protective agent like Pluronic F68 or serum.
    (3) The immobilisation of cells inside porous microcarriers.
    Point one is most easily done by increasing the reactor height and the oxygen tension in the air bubbles. With respect to the second point, it should be mentioned that the additive must be removed from the final product and can cause problems in down-stream processing. This may lead to an increase in the product cost. Finally, in the case of immobilisation of cells inside carriers, transport limitations may occur, which may in turn induce apoptosis. Cell death through apoptosis as caused by low levels of shear, substrate limitation and the presence of toxic products may be reduced through a careful process design and genetic manipulation of the cells.

    Modelling nutrient removal in a sequencing batch reactor with respirometry
    Bernardes, R.S. - \ 1996
    Agricultural University. Promotor(en): W.H. Rulkens; A. Klapwijk. - S.l. : Bernardes - ISBN 9789054854715 - 173
    waterzuivering - verwijdering - chemische reacties - uitrusting - afvalwaterbehandeling - rioolafvalwaterverwijdering - zuiveringsinstallaties - water treatment - removal - chemical reactions - equipment - waste water treatment - sewage effluent disposal - purification plants

    The main objectives of the present thesis can be summarized as: i) the development and validation of simplified mathematical models for activated sludge processes in an SBR treating real domestic wastewater; ii) the application of these simplified models for analysing the respirometric response and for obtaining information about the oxygen uptake for the different processes; iii) the application of the monitored respirometric values for model calibration and determination of parameter values, which are used to predict the processes in the next cycle; iv) the use of models as theoretical background for the development of control strategies for plug-flow systems and for SBR; v) relating the basic time scale for the models to the short term.

    The starting points for the model development and simplification were: i) the Activated Sludge Model No. 1, for carbon oxidation, nitrification and denitrification; and ii) the Activated Sludge Model No. 2, for biological phosphorus removal .

    In this study an SBR pilot plant was used and seen as a model for a plug-flow system. During the two and a half years of operation, the plant underwent three different technological phases. The first phase began with the removal of organics and nitrification. Denitrification was incorporated in the second phase. The last phase included biological phosphorus removal.

    In the first phase, two simplified mathematical activated sludge models are presented. The first model gives the response of the respiration rate in an SBR with nitrification, the oxidation of readily biodegradable matter, and endogenous respiration during one cycle. This model is used to predict the respiration rate during a complete SBR cycle. For this, it uses parameter values calibrated during the previous cycle, some default values and information about the ammonia concentration in the influent. The endogenous respiration rate is described with an exponential equation. The second model is used to predict the changes in nitrification capacity after a change in the loading rate and/or sludge wastage rate. For model calibration and validation, an SBR pilot plant receiving domestic wastewater was operated for nine weeks.

    In the second phase, a mathematical model is presented for the behaviour of the respiration rate and nitrate removal in an SBR with nitrification, denitrification and carbon oxidation. This model is based on the response of the respiration rate measured during nitrification and carbon oxidation and the nitrate removal rate during the post-denitrification period. For model calibration and validation, an SBR pilot plant receiving domestic wastewater was operated for three months. The respiration rate was used to calibrate several parameters of the model.

    In the third phase, a mathematical model for an activated sludge SBR with nitrification, denitrification, carbon oxidation and phosphate removal is presented. This model is based on the response of the respiration rate measured during nitrification, carbon oxidation and phosphate removal, together with the behaviour of phosphate and acetate as proposed in the Activated Sludge Model No. 2. For model calibration and validation, an SBR pilot plant receiving settled domestic wastewater plus acetic acid solution was operated for five months.

    In all the three phases the model for the respiration rate ( r ) in an SBR during one cycle, including nitrification, oxidation of readily biodegradable matter, endogenous respiration and a fraction for the respiration rate for phosphorus uptake, gives a good simulation of the measured respiration rate. A good prediction of the total oxygen consumption and distribution during one cycle is found from a simulation, using parameters calculated from the previous cycle together with the variables from the influent. Therefor this model can be used in control strategies as long as it is used for a short time- scale. During long-term operation, parameter variation is significant and too complex to be predicted. In the particular case of nitrification capacity variation in an SBR during long-term operation, the model can explain the variation trend but cannot explain the abrupt changes.

    Simplified mathematical models for the activated sludge process on the bases of the respiration rate are validated. On short-time scale, the models give a good response prediction of the activated sludge process feed with wastewater. The models are good tools for control strategies, however periodical parameter calibration is needed.

    De urease - activiteit en de ammoniakemissie in varkensstallen met een mestschuifsysteem onder de roostervloer = Urease activity and ammonia emission in piggeries with a manure-scraper system below the slatted floor
    Elzing, A. ; Commissaris, A.C.H.M. ; Oosthoek, J. - \ 1995
    Wageningen : IMAG-DLO (Rapport / Instituut voor Milieu- en Agritechniek 94-34) - ISBN 9789054061007 - 48
    luchtverontreiniging - ammoniak - schoonmaken - schoonmaakgereedschap - emissie - enzymen - uitrusting - fermentatie - vloeren - roostervloeren - varkensstallen - scheren - stallen - vervluchtiging - wassen (activiteit) - air pollution - ammonia - cleaning - cleaning equipment - emission - enzymes - equipment - fermentation - floors - grid floors - pig housing - shearing - stalls - volatilization - washing
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