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.

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Evaluatie zuiveringstechniek voor verwijdering gewasbeschermingsmiddelen III
Ruijven, J.P.M. van; Beerling, E.A.M. ; Staaij, M. van der; Os, E.A. van - \ 2016
Bleiswijk : Wageningen UR Glastuinbouw (Rapport GTB 1414) - 30
afvalwaterbehandeling - waterzuivering - afvalwater - waterverontreiniging - glastuinbouw - kassen - cultuur zonder grond - gewasbescherming - pesticiden - ozon - verwijdering - filtratie - technieken - waste water treatment - water treatment - waste water - water pollution - greenhouse horticulture - greenhouses - soilless culture - plant protection - pesticides - ozone - removal - filtration - techniques
Dutch greenhouse horticulture has to treat all discharged water from soilless cultivations for the removal of plant protection products, to meet the new Dutch Directive Hoofdlijnenakkoord (2015). Building on previous research, (1) the life span of activated carbon filters, (2) the effect of increasing concentrations of plant protection products on the removal efficacy of ozone and the removal efficacy of (3) multimedia filtration and (4) ultrasonic water treatment have been investigated. It turned out to be difficult to design an active carbon based water treatment system capable of durable treatment of greenhouse discharge water: organic and mineral material in the water blocked the pores, thereby clogging the filter system and causing leakage by pressure build-up. Activated carbon filtration (granular activated carbon, 48 min contact time, 50 μm prefiltration with sand filter) achieved a removal efficacy of >95% for up to 430 bed volumes treated. Combination with advanced oxidation improved the removal efficacy, but the removal time of the filter could not be determined due to leakage. The removal efficacy of ozone oxidation remained >98%, even at increased concentrations (factor 10 and 100) of plant protection products in the untreated water. The multimedia filter removed 75% of the plant protection products by adsorption, biological breakdown within the filter was not determined. Treatment of the water with ultrasonic waves hardly had any effect (maximum 30% efficacy) on the breakdown.
Brewing with fractionated barley
Donkelaar, L.H.G. van - \ 2016
University. Promotor(en): Remko Boom; Atze Jan van der Goot. - Wageningen : Wageningen University - ISBN 9789462577343 - 152 p.
brewing - brewing quality - barley - fractionation - endosperm - beers - malt - filtration - industrial wastes - process optimization - food process engineering - bierbereiding - brouwkwaliteit - gerst - fractionering - bieren - mout - filtratie - industrieel afval - procesoptimalisatie - levensmiddelenproceskunde

Brewing with fractionated barley

Beer is a globally consumed beverage, which is produced from malted barley, water, hops and yeast. In recent years, the use of unmalted barley and exogenous enzymes have become more popular because they enable simpler processing and reduced environmental impact. Raw barley, however, contains less endogenous enzymes and more undesired components for the use of beer brewing, compared to malted barley.

The overall aim of this thesis is to investigate how barley can be fractionated to optimize the use of resources for the beer brewing process, while maintaining the quality of the brewed beer. A resource use efficiency analysis was performed to verify the presumed benefits on the environmental sustainability of the proposed process change. The work was based on the hypothesis that fractionation of the unprocessed barley will reduce the amount of undesired components, which leads to improvements in the brewing process based on partial or no malting. Fractionation can be performed by milling and separation, which requires physical disentanglement of the components. This fractionation can be influenced by properties of the components of the material, such as the glass transition temperature (Stuart et al.). Fractionation by abrasive milling, also known as pearling, is another possibility: here one makes use of the spatial distribution of components in the kernels. In case of barley for brewing this technique is especially promising as most of the undesired components are in the outer layer of the kernel. In addition, the removal of bran from the barley reduces the amount of water needed in the process. It will also reduce the volume of spent grains, hence reducing wastes and energy required for drying the spent grains. A disadvantage of pearling is however that it lowers the ability of the barley kernel to produce enzymes. This leads to the need of the addition of exogenous enzymes, as is the case when the malting step is omitted.

Chapter 2 describes the glass-to-rubber transition of protein and starch isolated from the barley endosperm, for different moisture levels. The hypothesis for this chapter is that dry fractionation by milling is facilitated by milling conditions in which the protein is in a rubbery state and the starch in a glassy state. Two methods were used to measure the Tg; differential scanning calorimetry (DSC) and thermo-mechanical compression tests (TMCT). The methods gave different results due to the differences in moisture content range, and heating rates, which may lead to conformational changes of the protein. The value of the Tg of partially crystalline materials, such as starch in barley, was not unambiguous when using TMCT because the mechanical effect of expansion of these materials was smaller. For both results, the Tg lines were modelled using the Gordon-Taylor equation. Based on sorption isotherms, it was concluded that moisture does not distribute evenly over the protein and starch in the kernel. Starch absorbs more moisture than protein at given water activities. This required a correction of the Tg lines. After this correction, the glass transition lines of starch and protein were closer together. The expectation is therefore that achieving good separation between the components based on having one glassy component and one rubbery component is challenging.

For this reason, another dry fractionation technique, pearling, was considered. Chapter 3 describes the chemical composition of the barley and of fractions removed by pearling. Pearling was shown to selectively remove insoluble fibre, ash, protein and polyphenols, while the β-amylase activity and starch content of the remaining kernel was hardly affected. For example, removing the outer 5% of the kernel reduced insoluble arabinoxylans (15%), insoluble fibres (23%), ash (19%), polyphenols (11%) and water holding capacity of the non-starch components (25%), while only lowering starch content by 0.20%. The water holding capacity of the barley fractions was strongly related to the fibre content. This indicates that when the fibre content in the mash was reduced by pearling, the spent grains will take up less water, leading to less wort and sugar losses in this waste stream, and hence better use of the raw materials and less wastes.

Chapter 4 compares a traditional brewing process to an enzyme-assisted brewing process with respect to their resource use efficiency, which is one aspect of the sustainability of the processes. The use of exogenous enzymes is found to be more efficient than producing enzymes through the malting process. The exergetic efficiency of the conventional malting process was 77%. The main losses stem from the use of natural gas for removal of moisture from the barley in the kilning process, and from the loss of starch in the germination process. In case of the use of exogenous enzymes, it was concluded that the chemical exergy content of the enzymes was not a good measure for the exergy content of the enzymes. Instead, we proposed to use the cumulative exergetic consumption in the enzyme production rather than just the chemical exergy content of the enzymes. This cumulative exergetic consumption in the production of the enzymes was ± 30 times higher than their standard chemical exergy. This shows that the cumulative exergetic costs of minor components should be taken into account if a process uses them in significant quantities. This can be done by extending the system boundaries to include the production process of the purified components. The exergy efficiency of the enzyme formulation production process ranges between 20% and 42% depending on whether the by-product of the fermentation broth was considered as useful as the enzyme product. Even though the cumulative exergy consumption of the process was 30 times the standard chemical exergy of the dry enzyme, the total exergy input (i.e. both wasted and destroyed) for the production of 100 kg of beer was still larger for the conventional malting process (441 MJ) than for the enzyme-assisted process (354 MJ). In addition, beer produced using exogenous enzymes reduces the use of water by 7%, of raw materials by 14%, and of natural gas by 78%. Thus, the exergy loss of the enzyme production process is more than compensated by the prevention of exergy loss in the total beer brewing process.

Chapter 5 describes brewing tests using malted, unmalted and pearled, unmalted barley kernels. Brewing with unmalted barley saves material, energy and water in the malting stage but may result in complications during processing. Pearling mitigates these problems. Exogenous enzymes were used to compensate for the low enzyme activity in unmalted barley. Lautertun filtration and mash filtration were considered as filtration methods. Principle component analysis was performed on the chemical composition of the wort and the various spent grains, to investigate the effect of the malt-to-barley ratio, the degree of pearling and the filter method. A mash filter is optimal for this type of process, and we identified a window of operation in which optimal use is made of the raw materials while maintaining the end product quality, judged on basis of 4 quality parameters.

The concluding chapter 6 presents a general discussion of all results described in this thesis. In addition, the benefits of pearling over that of milling and fractionation, and the effect of pearling on milling properties were discussed. Furthermore, it explores the advantages in environmental sustainability that can be achieved by pearling. Pearling as a pre-treatment for malting reduces the enzyme activity of germinating barley, and therefore the mash quality.

This thesis provides insights in how pre-treatment of barley can make beer brewing more efficient in the use of resources. It stresses the need to optimally use all material streams in a process, to be able to design an environmentally sustainable process, and it shows that efficient resource use is key for achieving this. Additionally the value of enzymes as processing aids was discussed. A clear result is that one needs to include the resource use in the production of enzymes or other processing aids, when analyzing the environmental sustainability of a process, since this can be significant in the overall process.

Extraction of steviol glycosides from fresh Stevia using acidified water; clarification followed by ultrafiltration and nanofiltration
Kootstra, A.M.J. ; Elissen, H.J.H. ; Huurman, Sander - \ 2016
Lelystad : Wageningen UR, PPO/Acrres (Rapport / PPO-AGV 686) - 38 p.
separation technology - stevia - purification - biorefinery - glycosides - ultrafiltration - filtration - scheidingstechnologie - zuiveren - bioraffinage - glycosiden - ultrafiltratie - filtratie
As part of the PPS Kleinschalige bioraffinage project (WP1b), fresh Stevia material was used in the extraction of steviol glycosides using water acidified through conversion of sugar by microorganisms naturally present on the plant. Two successive harvests from the same plot were used. Previous experiments had resulted in high steviol glycoside extraction rates of 80 % to 90 % but the purity of the final extract was low (15 % to 20 % of steviol glycosides in the dry matter). The first batch of plants was used to test a clarification step by filtration on a small scale. A second batch of plants was used to perform clarification, purification using ultrafiltration, and concentration by nanofiltration on a larger scale.
Sensory quality of drinking water produced by reverse osmosis membrane filtration followed by remineralisation
Vingerhoeds, M.H. ; Nijenhuis, M.A. ; Ruepert, N. ; Bredie, W.L.P. ; Kremer, S. - \ 2016
Water Research 94 (2016). - ISSN 0043-1354 - p. 42 - 51.
drinking water - water quality - sensory evaluation - taste research - reverse osmosis - membranes - filtration - drinkwater - waterkwaliteit - sensorische evaluatie - smaakonderzoek - omgekeerde osmose - membranen - filtratie
Membrane filtration of ground, surface, or sea water by reverse osmosis results in permeate, which is almost free from minerals. Minerals may be added afterwards, not only to comply with (legal) standards and to enhance chemical stability, but also to improve the taste of drinking water made from permeate. Both the nature and the concentrations of added minerals affect the taste of the water and in turn its acceptance by consumers. The aim of this study was to examine differences in taste between various remineralised drinking waters. Samples selected varied in mineral composition, i.e. tap water, permeate, and permeate with added minerals (40 or 120 mg Ca/L, added as CaCO3, and 4 or 24 mg Mg/L added as MgCl2), as well as commercially available bottled drinking waters, to span a relevant product space in which the remineralised samples could be compared. All samples were analysed with respect to their physical–chemical properties. Sensory profiling was done by descriptive analysis using a trained panel. Significant attributes included taste intensity, the tastes bitter, sweet, salt, metal, fresh and dry mouthfeel, bitter and metal aftertaste, and rough afterfeel. Total dissolved solids (TDS) was a major determinant of the taste perception of water. In general, lowering mineral content in drinking water in the range examined (from <5 to 440 mg/L) shifted the sensory perception of water from fresh towards bitter, dry, and rough sensations. In addition, perceived freshness of the waters correlated positively with calcium concentration. The greatest fresh taste was found for water with a TDS between 190 and 350 mg/L. Remineralisation of water after reverse osmosis can improve drinking quality significantly.
Bio-filtration of helminth eggs and coliforms from municipal sewage for agricultural reuse in Peru
Yaya Beas, R.E. - \ 2016
University. Promotor(en): Grietje Zeeman; Jules van Lier; Katarzyna Kujawa. - Wageningen : Wageningen University - ISBN 9789461734945 - 187 p.
waste water treatment - waste water treatment plants - anaerobic treatment - helminth ova - anaerobic conditions - filtration - public health - afvalwaterbehandeling - afvalwaterbehandelingsinstallaties - anaërobe behandeling - wormeneitjes - anaërobe omstandigheden - filtratie - volksgezondheid

Where fresh water resources are scarce, treated wastewater becomes an attractive alternative for agricultural irrigation. However, the presence of large amounts of pathogens, even in treated wastewater, constraints its productive use, which is aggravated when sanitation and public health are poor. Among pathogenic indicators, helminth eggs are one of the most persistent microorganisms in treated effluents that may survive for several months in the irrigated fields. Application of upflow anaerobic sludge blanket (UASB) reactors could contribute to decrease the pathogenic content in wastewater due to physical and biological interactions with the anaerobic sludge bed, such as filtration and entrapment. In this thesis, the potential of the anaerobic sludge bed to particularly remove helminth eggs, was investigated in four phases. In the first phase, a temperature of 4° C was fixed in the UASB reactors in order to reduce the biological activity of the sludge. Hence, the anaerobic sludge filtration capacity at different upflow velocities was studied. This phase of the research was performed in two experiments. The first one using latex beads, simulating helminth eggs, and the second one using real helminth eggs, predominating in Peruvian wastewater. First experimental results show that increasing the upflow velocity led to a decrease in the removal efficiency of latex beads. At the lowest upflow velocity of 0.3 m·h−1, 100% removal of latex beads was reached. At an upflow velocity higher than 1 m·h−1, the removal efficiency dropped under 90 %. The degree of stabilisation of the sludge nor the sludge bed volume did not have a significant effect. Second experiment's results show that with upflow velocities below 1.5 m·h−1 real helminth eggs removal is greater than 70 %. Simultaneously tested, total and faecal coliforms removal was less than 83 %. The most common helminth eggs species found in the studied wastewater were Ascaris lumbricoides, Trichuris spp. and Strongyloides spp. The second phase was performed using two lab-scale UASB reactors at average ambient temperatures between 16.7 °C and 28.5 °C in the city of Lima (Peru). Ascaris suum eggs originating from infected pigs were selected as model organisms, considering their similarity, in terms of size and morphology, with Ascaris lumbricoides, a human pathogen. The sludge filtration capacity was determined, applying upflow velocities between 0.09 and 0.68 m·h−1. Average helminth eggs removals varied between 26 and 93 %, depending on upflow velocity and sludge bed height. 93 % removal was achieved when applying an upflow velocity of 0.09 m·h−1 and a sludge bed height reaching 19-25 % of the total reactor height. The third phase was conducted to test the effect of lower operational temperatures in the UASB reactor on the pathogen removal from domestic wastewater. Thus, a lab scale UASB reactor in the city of Puno (Peru), treating wastewater with temperatures varying between 11.3 and 14.3 °C for a period of 22 weeks after the start-up of the reactor, was used. Upflow velocities varied between 0.12 and 0.41 m·h−1. Results confirmed outcomes of the first phase of this research concerning helminth eggs removal, and consequently show that the sludge bed filtration capacity varied between 89 and 95 %. Faecal coliform removal varied between 0.9 and 2.1 log10 and E. coli removal between 0.8 and 1.6 log10. In general, removal efficiencies regarding helminth eggs and faecal coliforms, are not sufficient to comply with reuse standards. Finally, the capacity of Down Flow Hanging Sponge (DHS) reactors for removing faecal coliforms from domestic UASB reactor effluent for agricultural reuse in developing countries was investigated. Applied reactors were the cube type DHS (G1) without recirculation, the cube type DHS (G1) with recirculation and the curtain type DHS (G2). Results reveal an average faecal coliform removal of 4.74, 3.42 and 1.25 log10 respectively. These results comply with categories A, B and C of WHO (1989) standards, correspondingly. Therefore, treatment trains consisting of UASB-DHS reactors can possibly be applied when agricultural reuse is contemplated.

Waterefficiënte Emissieloze Kas : optimaal telen
Beerling, E.A.M. ; Blok, C. ; Os, E.A. van; Ruijven, J.P.M. van - \ 2015
glastuinbouw - emissiereductie - emissie - bemesting - druppelbevloeiing - steenwol - substraten - recirculatiesystemen - filtratie - greenhouse horticulture - emission reduction - emission - fertilizer application - trickle irrigation - rockwool - substrates - recirculating systems - filtration
Aanpassen recept van bemesting bij emissieloos telen per element. Interval tussen analyses zo kort mogelijk houden.
Flow-induced particle migration in microchannels for improved microfiltration processes
Dinther, A.M.C. van; Schroen, C.G.P.H. ; Imhof, A. ; Vollebregt, H.M. ; Boom, R.M. - \ 2013
Microfluidics and Nanofluidics 15 (2013)4. - ISSN 1613-4982 - p. 451 - 465.
2-dimensional channel flow - shear-induced diffusion - pressure-driven flow - concentrated suspensions - couette-flow - poiseuille flow - reynolds-number - self-diffusion - microfluidics - filtration
Microchannels can be used to induce migration phenomena of micron sized particles in a fluid. Separation processes, like microfiltration, could benefit from particle migration phenomena. Currently, microfiltration is designed around maximum flux, resulting in accumulation of particles in and on the membrane. In this paper it is shown that starting the design at the particle level will result in a new microfiltration process. The behaviour of suspensions between 9 and 38 volume% was studied by confocal scanning laser microscopy; migration as a result of shear-induced diffusion was observed in a rectangular microchannel with nonporous walls. Particles segregated on size within the first 10 cm of the channel. To illustrate this, at 20 volume% of small (1.53 µm) and large (2.65 µm) particles each, the larger particles migrated to the middle of the channel, while the small particles had high concentrations near the walls. The small particles could then be collected from their position close to the permeable walls, e.g. membranes, where the pore size of the membrane is no longer the determining factor for separation. Guidelines for using this phenomenon in a microfiltration process were derived and the selectivity of the process was experimentally evaluated. The small droplets could be removed from the mixtures with a membrane having pores 3.7 times larger than the droplets, thereby minimizing accumulation of droplets in and on the membrane. As long as the process conditions are chosen appropriately, no droplet deposition takes place and high fluxes (1.7 × 103 L h-1 m-² bar-1) can be maintained.
Transient critical flux due to coupling of fouling mechanisms during crossflow microfiltration of beer
Sman, R.G.M. van der; Vollebregt, H.M. - \ 2013
Journal of Membrane Science 435 (2013). - ISSN 0376-7388 - p. 21 - 37.
pressure-driven flow - concentration polarization - concentrated suspensions - colloidal suspensions - particle migration - yeast suspensions - model - filtration - shear - simulations
Models of fouling during beer clarification, previously validated for dead-end filtration, are combined with a model describing the build-up of the cake layer of yeast cells via shear-induced diffusion induced by crossflow. For describing shear-induced diffusion, we have taken the most recent model, which is based on the effective temperature concept. Via scale analysis we show that (1) effects of polydispersity are negligible and (2) the cake layer growth model still be reduced to the earlier model of Romero and Davis, albeit with different parameter values. The adapted Romero and Davis model has been coupled to the earlier reviewed models of fouling by aggregates and macromolecules, for which we have performed computer simulations. In this paper we report on striking results on the downstream movement of the critical point, xcr, where the cake layer starts building up. We show that this is due to strong coupling between the cake layer build-up and the other fouling modes. Hence, this means that the concept of critical flux can not be viewed any more as a time-invariant value. This finding has implications beyond the application of beer, and especially for biotechnological broths which have similar composition of beer.
Effect of algae- and silt concentration on clearance- and growth rate of the razor clam Ensis directus, Conrad
Kamermans, P. ; Brummelhuis, E.B.M. ; Dedert, M. - \ 2013
Journal of Experimental Marine Biology and Ecology 446 (2013). - ISSN 0022-0981 - p. 102 - 109.
acclimated digestive responses - suspended bottom material - cerastoderma-edule l. - mytilus-edulis - particle selection - feeding bivalves - food quality - absorption - filtration - mussel
Laboratory experiments were carried out with Ensis directus to estimate clearance rate and growth rate as a function of the amount of food and presence of silt. Two food levels were tested: low food availability (6.5 µg chla/l) and high food availability (16.5 µg chla/l) at four silt concentrations (0, 50, 150 and 300 mg/l). Clearance rates of E. directus varied between 0.7 and 5.9 l/h/g DW. At a silt concentration of 300 mg/l clearance rates were significantly lower (16–56%) than rates at 150 mg/l, 50 mg/l and 0 mg/l silt. This indicates that only the highest silt concentration induced a reduction in clearance rate. The tested food levels did not influence the clearance rate of E. directus. Maximum growth rate of E. directus was 0.24 mm increase in shell length and 2% increase in wet weight per day. Long-term (10 weeks) exposure to silt concentrations of 300 mg/l showed significantly higher growth than the 150 mg/l treatment. This indicates that exposure to a high silt concentration did not induce a reduction in growth, but stimulated growth. Long-term (10 weeks) exposure to a food level of 6.5 µg chla per litre reduced the shell growth of E. directus with 40% compared to growth at 16.5 µg chla per litre. The laboratory experiments suggest that E. directus is more sensitive to a reduction in algal concentration than to an increase in silt concentration.
Separation process for very concentrated emulsions and suspensions in the food industry
Dinther, A.M.C. van; Schroën, C.G.P.H. ; Boom, R.M. - \ 2013
Innovative Food Science and Emerging Technologies 18 (2013). - ISSN 1466-8564 - p. 177 - 182.
induced particle migration - cross-flow microfiltration - shear-induced diffusion - flux decline - couette-flow - ultrafiltration - filtration - deposition
Separation of concentrated food suspensions and emulsions by e.g. microfiltration is currently not possible and therefore preceded by dilution, wasting energy and water. A new approach is shown, with sieves having pores much larger than the micron-sized droplets, low cross-flow velocities and a non-porous channel before the sieve. The complex behavior of concentrated emulsions under laminar flow in a non-porous channel causes depletion of large droplets and higher concentrations of small droplets near the wall. When the liquid flow through the pores relative to the channel flow is below a certain value, the liquid from the pores is completely devoid of larger droplets and has higher concentrations of small droplets than in the channel. This effect was caused by a combination of shear-induced migration in the channel and the interaction of droplets with the pores. Industrial separation processes can operate at high concentrations under mild conditions, potentially saving water and energy. Industrial relevance: Separation of suspensions, essential in processing any harvested agricultural material, is usually done by membrane separation or centrifugation, which is based on size exclusion by a membrane or a difference in density between particles and fluid, and this places intrinsic boundaries on the concentrations that can be processed, typically b5%. The sieve filtration process for micron-sized particles introduced here operates best at very high volume fractions and much lower cross-flow velocities than currently used. Industrial application of our finding could therefore have major benefits: no water is needed for dilution and waste is minimized. Besides energy used for dehydration and the separation process is reduced.
Filtratie van pirimifos-methyl uit condensvocht : Filtratie van condensvocht van bewaarcellen behandeld met Actellic
Lans, A.M. van der; Bisseling, E. - \ 2012
Lisse : Praktijkonderzoek Plant & Omgeving BBF - 25
bloembollen - pirimifos-methyl - filtratie - verontreinigingsbeheersing - milieubescherming - oppervlaktewater - opslagloodsen - ornamental bulbs - pirimiphos-methyl - filtration - pollution control - environmental protection - surface water - stores
Tijdens de warme bewaring van tulpenbollen in klimaatcellen wordt het middel Actellic (werkzame stof pirimifos - methyl pirimifos - methyl ) ingezet voor de bestrijding van galmijten. Het middel ‘plakt’ niet alleen aan de bollen maar ook aan de wanden, de vloer, het fust en de klimaatapparatuur en blijft op deze wijze gedurende vele maanden in de cel aanwezig. Als er na de warme bewaring vervolgens in deze cellen producten gekoeld worden, kan condensvorming optreden. Uit eerder onderzoek van PPO bleek dat in condenswater uit deze klimaatcellen pirimifos - methyl ruim boven het MTR (Maximaal Toelaatbaar Risico voor waterleven ) van 0.002 μg l voor kan komen . Het condens water komt vervolgens via de condens afvoerpijp in het riool of op het (on)verharde gedeelte van het erf terecht. Deze emissieroute via condenswater vormt een grote bedreiging voor het lokale aquatische milieu doordat pirimifos - methyl op deze manier in het oppervlaktewater terecht kan komen.
Understanding flow-induced particle migration for improved microfiltration
Dinther, A.M.C. van - \ 2012
University. Promotor(en): Remko Boom, co-promotor(en): Karin Schroen. - S.l. : s.n. - ISBN 9789461733498 - 207
microfluidics - filtratie - migratie - deeltjes - stroming - suspensies - emulsies - membranen - filtration - migration - particles - flow - suspensions - emulsions - membranes

Membrane microfiltration processes are used in for example the food, biotechnology, chemical and pharmaceutical industry, and more generally in e.g. wastewater treatment. Microfiltration is mostly used to separate components that are greatly different in size, e.g. micro-organisms from water, but rarely to fractionate components that are of similar size. This latter option would be interesting for many applications, since it would lead to enriched starting materials and possibly new products, but is hampered by accumulation of components in and on the membrane due to size exclusion by the pores. This leads to flux reduction and increased retention of components in time, basically the accumulated layer determines which components can pass the membrane (see Figure 1).

Figure 1. Schematic representation of a cross-flow microfiltration process with a decrease in permeate flux over the length of the membrane due to pore blocking and particle adsorption in the pores and on the membrane walls.
Most research focusses on accumulation mechanisms (concentration polarization, cake formation and adsorption) and concepts targeted at controlling particle accumulation. One example is back-pulsing, but this only gives a short term solution leading to extensive cleaning procedures given the way membranes are currently operated in practice. Clearly it would be beneficial if accumulation could be prevented, and through that, more stable operation could be achieved.

This thesis presents how flow-induced particle migration can be used for stable membrane flux and retention of components in time. The particle migration mechanisms that are considered in this thesis, shear-induced diffusion, inertial lift, and fluid skimming, act on particles that are typically between 0.1 and 10 micron. They induce separation of components in the fluid moving (larger) particles away from the membrane, therewith facilitating separation; basically pore size no longer determines particle permeation. In the thesis it will be shown that these effects improve processing of dilute suspensions and make processing of highly concentrated systems possible, which is beyond the scope of current microfiltration processes.

Before the design of these processes, methods to measure velocity and concentration profiles in microfluidic devices are described, compared and evaluated. The small dimensions of these devices will cause particles to migrate; as is used later in the thesis to facilitate segregation and separation. A drawback of the small dimensions is that they make measurement of velocity and concentration gradients difficult. Based on our evaluation, Nuclear Magnetic Resonance (NMR) and Confocal Scanning Laser Microscopy (CSLM), although expensive, are the most promising techniques to investigate flowing suspensions in microfluidic devices, where one may be preferred over the other depending on the size, concentration and nature of the suspension, the dimensions of the channel, and the information that has to be obtained.

CSLM is used to study the behaviour of suspensions, between 9 and 38 volume%, at the particle level. Under Poiseuille flow in a closed microchannel, shear-induced diffusion causes migration in these suspensions. Under all measured process conditions, particles segregate on size within an entrance length of around 1000 times the channel height. Mostly, the larger particles migrate to the middle of the channel, while the small particles have high concentrations near the walls. This indicates that the small particles could be collected from their position close to the wall and that this principle can be applied to microfiltration (see Figure 2).

Figure 2. Schematic representation of a cross-flow microfiltration process with a constant permeate flux over the length of the membrane due to shear-induced particle migration in combination with the use of a closed entrance length and large pores.
Microfiltration of emulsions proves that the small particles can be removed without accumulation of particles in and on the membrane, as long as the process conditions are chosen appropriate. The membrane cross-flow module consists of a closed channel to allow particles to migrate due to shear-induced diffusion followed by a membrane with 20 micron pores, being much larger than the particles, where fractions of these emulsions can be removed. The emulsions consist of small droplets (~2.0 micron) and large droplets (~5.5 micron), with total concentrations between 10 and 47% and different ratios between small and large particles. As expected, the size of the emulsion droplets in the permeate is a function of trans-membrane pressure, membrane design and oil volume fraction (i.e., of the total, the small and the large particles). The guidelines for appropriate process conditions are described and application of the right process conditions leads to very high selectivity. This means that the permeate only consists of small droplets, and on top of that their concentration is higher than in the original emulsion. Especially at high droplet concentration (which is known to cause severe fouling in regular membrane filtration), these effects are occurring as a result of shear-induced diffusion. If only small particles are targeted in the permeate, the module can be operated at fluxes of 40 L/(h•m²); if fractionation is targeted the fluxes can be maintained considerably higher (2-10 fold higher).

Separation of concentrated suspensions is currently done by dilution and since the process based on shear-induced diffusion works well at low velocities and high concentrations, industrial application could have major benefits in terms of energy and water use. An outlook is given on how current industrial processes can be designed and improved in terms of energy consumption by making use of particle migration. It is shown that return of investment of installation of these new membrane modules is short compared to the membrane life time, due to high energy savings. In order to reach this, it will be necessary to take unconventional process conditions that target particle migration and membrane designs as a starting point.

Besides concentrated suspensions, also dilute suspensions benefit from particle migration. Migration phenomena can induce fractionation of yeast cells from water in dilute suspensions, using micro-engineered membranes having pores that are typically five times larger than the cells. The observed effects are similar to fluid skimming (in combination with inertial lift), and the separation performance can be linked to the ratio between cross-flow and trans-membrane flux, which is captured in a dimensionless number that can predict size of transmitted cells. For sufficiently high cross-flow velocity, the particles pass the pore and become part of the retentate; the separation factor can simply be changed by changing the ratio between cross-flow velocity and trans-membrane flux. Since the membranes have very large pores, fouling does not play a role and constant high trans-membrane flux values of 200–2200 L/(h•m2) are reached for trans-membrane pressures ranging from 0.02 to 0.4 bar.

In conclusion, particle migration can improve (membrane) separation processes and even has the potential to lead to totally new separation processes. Particle migration can be advantageous in both dilute as well as concentrated systems, leading to reduced fouling, reduced energy and water consumption and a reduction in waste. This can all be achieved at production capacity similar or better than currently available in microfiltration processes.

Effect of variations in concentration of algae and silt on filtration and growth of the razor clam (Ensis directus, Conrad)
Kamermans, P. ; Dedert, M. - \ 2012
Yerseke : IMARES (Report / IMARES Wageningen UR C017/11) - 69
ensis - voedselopname - algen - silt - groeitempo - filtratie - kustwateren - noordzee - food intake - algae - growth rate - filtration - coastal water - north sea
As part of a collaboration between the research programme Knowledge for Primary Processes Silt of Rijkswaterstaat Waterdienst NWOB (department of Infrastructure and Environment, MinIenM, RWS) and the Monitoring programme Sand extraction RWS and the LaMER Foundation, RWS-WD NWOB requested further research into the relation between food availability and Ensis production. The aim is to better understand the effect of different algae and silt concentrations on filtration and growth rates and improve prediction of effects. Laboratory experiments were carried out with Ensis directus to estimate food intake rate and growth rate as a function of food density and clam size. Growth experiments carried out in 2010 showed that the species seems to be very fragile as shown by the low growth rates and high mortality rates. Improvements designed to optimize the experimental conditions, survival rates and experimental set-up were implemented in 2011. These were: experimental animals were collected with a box corer instead of a suction dredge; animals were kept in cylinders without sediment, but their shells were closed with elastic bands during the filtration experiments; circular tanks were used with increased water movement; the diet during the growth experiment consisted of two species of algae. Two food levels were tested: low food availability (6.5 μg Chla/l) and high food availability (16.5 μg Chla/l) at four silt concentrations (0, 50, 150 and 300 mg/l). Only the highest silt concentration induced a reduction in filtration rate. Food level did not influence filtration rate of Ensis, but intake rate is higher at the high food concentration, because more algal cells are present in a certain volume of water. Longterm (10 weeks) exposure to silt concentrations of 300 mg/l showed significantly higher growth than the 150 mg/l treatment indicating that exposure to a high silt concentration did not induce a reduction in growth. Long-term (10 weeks) exposure to a food level of 6.5 ug chla per liter reduced shell growth of Ensis compared to growth at 16.5 ug chla per liter. The filtration and growth rate results are used in a modelling study on growth and condition of Ensis during sand extraction 2013-2017 (Schellekens, in prep). The conclusions of this study give more notion of the effects of sand extraction in the coastal zone of the North Sea on the viability of the razor clam Ensis directus. Sand extraction always goes together with an increase of silt concentration in the water column. This reduces the light conditions for algal growth which reduces the food availability for Ensis. The laboratory experiments suggest that Ensis is more sensitive to a reduction in algal concentration than to an increase in silt concentration. Some discussion is given on the implications of the results for the management of sand extraction.
Low concentration of powdered activated carbon decreases fouling in membrane bioreactors
Remy, M.J.J. - \ 2012
University. Promotor(en): Wim Rulkens, co-promotor(en): Hardy Temmink. - S.l. : s.n. - ISBN 9789461732309 - 163
afvalwaterbehandeling - geactiveerd slib - membranen - bioreactoren - filtratie - waste water treatment - activated sludge - membranes - bioreactors - filtration
Het doel van deze studie was te onderzoeken welke slibeigenschappen verantwoordelijk zijn voor de membraanvervuiling in MBR systemen, en om een methode te vinden om deze eigenschappen dusdanig te manipuleren dat de membraanvervuiling drastisch kan worden gereduceerd.
Determination of prey capture rates in the stony coral Galaxea fascicularis: a critical reconsideration of the clearance rate concept
Osinga, R. ; Delft, S. van; Lewaru, M.W. ; Janse, M. ; Verreth, J.A.J. - \ 2012
Journal of the Marine Biological Association of The United Kingdom 92 (2012)4. - ISSN 0025-3154 - p. 713 - 719.
stylophora-pistillata - scleractinian corals - skeletal growth - flow - heterotrophy - filtration
In order to determine optimal feeding regimes for captive corals, prey capture by the scleractinian coral Galaxea fascicularis was determined by measuring clearance of prey items from the surrounding water. Colonies of G. fascicularis (sized between 200 and 400 polyps) were incubated in 1300 ml incubation chambers. Nauplii of the brine shrimp Artemia sp. were used as the prey item. A series of incubation experiments was conducted to determine the maximal capture per feeding event and per day. To determine maximal capture per feeding event, total uptake of nauplii after one hour was determined for different prey item availabilities ranging from 50 to 4000 nauplii per polyp. To determine maximal capture per day, the corals were subjected to four repetitive feeding events at three different prey item densities (50, 100 and 150 nauplii per polyp). Alongside these quantitative experiments, it was tested to what extent the feeding response of corals is triggered by chemical cues. One hour after food addition, extract of Artemia nauplii was added to the incubation chambers to test its effect on subsequent prey capture rates. In all experiments, prey capture was expressed as the number of nauplii consumed per coral polyp. Total capture of Artemia nauplii by G. fascicularis after a single feeding event increased linearly up till a prey item availability of 2000 nauplii per polyp. Maximal capture per feeding event was estimated at 1200 nauplii per polyp, which is higher than rates reported in previous studies. It became apparent that at high densities of Artemia nauplii, the clearance rate method does not discriminate between active capture and passive sedimentation. Repetitive feeding with 50 nauplii per polyp resulted in a constant total prey capture per feeding event. At a supply of 100 nauplii per polyp, total capture decreased after the first feeding event, and remained constant during the subsequent feeding events at a level comparable to the lower food availability. However, at a supply of 150 nauplii per polyp, total capture per event was higher throughout the entire four-hour incubation period, which obfuscates an accurate estimation of the maximal daily food uptake. In all incubations, a decrease in capture efficiency was observed within the course of the feeding event. In all repetitive feeding experiments, capture efficiency increased immediately upon addition of a new batch of food. This increase in efficiency was not caused by a priming effect of extract of Artemia. The inconsistencies in the data show that estimates of prey capture based on clearance rates should be interpreted with caution, because this method does not take into account potential dynamics of prey capture and release.
First pioneering laboratory experiments on filtration, respiration and growth of the razor clam (Ensis directus, Conrad)
Kamermans, P. ; Brummelhuis, E.B.M. ; Wijsman, J.W.M. - \ 2011
Yerseke : IMARES (Report / IMARES Wageningen UR C115/11) - 48
ensis - voedsel - ademhaling - filtratie - groeitempo - mariene ecologie - noordzee - food - respiration - filtration - growth rate - marine ecology - north sea
In Dutch marine circumstances, sand extraction releases silt into the water column. The extra silt can reduce light penetration into the water and consequently algal growth. To predict potential effects of an expansion of sand extraction activities it is necessary to know possible impacts on the environment. Ensis directus, a dominant species web of the North Sea coastal zone, has a key position in the food web. Therefore, it was selected as model species in this study to predict the effects of the reduced food conditions due to sand extraction on the growth of E. directus. A DEB (Dynamic Energy Budget) model is in development. This study describes the basic experiments that have been done to determine empirical relations between clam size or food concentration and filtration, respiration and growth rates necessary for the DEB modelling. Also, the basic values on physiology itself have their value because little is known on this species. Filtration and respiration rates were measured at four food levels (2, 5, 20 and 40 μg chlorophyll a/l). Clam shell length varied from 42 to 135 mm. Filtration rate decreased with an increase in clam size from maximally 3.3 lh-1 g-1 ash-free dry weight (ADW) to 0. lh-1 g-1 ADW. There was no relation between food concentration on filtration rate. Respiration rates showed a similar decrease with clam size from maximally 5000 mg O2 lh-1 g-1 ADW to 1500 mg O2 lh-1 g-1 ADW. In addition, an increase in respiration rate was found with an increase in food concentration. In the growth experiment five food levels were tested (0, 2, 5, 20 and 40 μg chlorophyll a/l).Clams smaller than 75 mm shell length showed more growth (up to 1% increase in wet weight (WW) per day or 0.3% shell length per day) than larger clams (maximally 0.16% increase in WW per day or 0.01% shell length per day). Growth rates showed an increase with increased food concentration.
High-flux membrane separation using fluid skimming dominated convective fluid flow
Dinther, A.M.C. van; Schroën, C.G.P.H. ; Boom, R.M. - \ 2011
Journal of Membrane Science 371 (2011)1-2. - ISSN 0376-7388 - p. 20 - 27.
particle trajectories - spherical-particle - laminar-flow - porous wall - microfiltration - suspensions - filtration - deposition - system - mechanics
We here report on the separation of yeast cells, with micro-engineered membranes having pores that are typically five times larger than the cells. The separation is due to neither shear-induced diffusion, nor initial lift, but to an effect similar to fluid skimming. The separation performance is linked to the ratio between cross-flow and transmembrane flux, and could be captured with a dimensionless number relating those. On the basis of this dimensionless number, flux and transmission of the cells could be predicted. The mechanism rests on having a sufficiently high cross-flow velocity, such that particles are not dragged too deep in the pore, but are dragged with the cross-flow back into the feed stream. The separation factor can simply be changed by changing the ratio between crossflow velocity and transmembrane flux. Since the membranes have very large pores, fouling does not play a role. Constant high transmembrane flux values of 200–2200 L/m2 h were reached for transmembrane pressures ranging from 0.02 to 0.4 bar (typical industrial fluxes are 150 L/m2 h bar with a maximum of 2000 L/m2 h bar for short periods of time, comparable to 50–400 L/m2 h [1] and [2]). Although the effect is strongest with monodispersed pores, it will be possible to exploit the mechanism with conventional membranes. As such, it may open up a new route towards non-fouling crossflow microfiltration
Influence of membrane properties on fouling in submerged membrane bioreactors
Marel, P. van der; Zwijnenburg, A. ; Kemperman, A. ; Wessling, M. ; Temmink, B.G. ; Meer, W. van der - \ 2010
Journal of Membrane Science 348 (2010)1-2. - ISSN 0376-7388 - p. 66 - 74.
waste-water treatment - cross-flow microfiltration - subcritical flux operation - activated-sludge - step method - filtration - ultrafiltration - deposition - morphology - colloids
Polymeric flat-sheet membranes with different properties were used in filtration experiments with activated sludge from a pilot-scale MBR to investigate the influence of membrane pore size, surface porosity, pore morphology, and hydrophobicity on membrane fouling. An improved flux-step method was used to measure both the critical flux and critical flux for irreversibility. Long term experiments were performed to evaluate if influences of membrane properties on short term could be translated to long term fouling behavior. The results showed that a hydrophilic asymmetric membrane with an interconnected pore structure, a nominal pore size of 0.3 µm, and large surface porosity of 27%, provided the best membrane performance with respect to critical flux and critical flux for irreversibility. The dominant fouling mechanism in long term filtration experiments was gel layer formation, which for this membrane was the least severe, and therefore extended the sustainable time.
Maatregelen ter vermindering van fijnstofemissie uit de pluimveehouderij: indicatieve evaluatie van biofiltratie als potentiële fijnstofreductietechniek = Measures to reduce fine dust emission from poultry: indicative evaluation of biofiltration as potential fine dust reduction technique
Winkel, A. ; Ogink, N. ; Hol, J.M.G. - \ 2010
Lelystad : Wageningen UR Livestock Research (Rapport / Wageningen UR Livestock Research 313) - 13
biologische filtratie - filtratie - emissie - pluimvee - pluimveehouderij - zuiveren - innovaties - landbouwtechniek - luchtkwaliteit - fijn stof - biological filtration - filtration - emission - poultry - poultry farming - purification - innovations - agricultural engineering - air quality - particulate matter
In this study biofiltration is indicatively evaluated for its potential to remove fine dust from exhaust air of poultry houses. From this study it is concluded that biofiltration can be effective and applicable.
In situ quantification of membrane foulant accumulation by reflectometry
Schroën, C.G.P.H. ; Roosjen, A. ; Tang, K. ; Norde, W. ; Boom, R.M. - \ 2010
Journal of Membrane Science 362 (2010)1-2. - ISSN 0376-7388 - p. 453 - 459.
cross-flow microfiltration - ultrafiltration membranes - protein adsorption - skim milk - performance - filtration - polymer - bioreactors - inhibition - modules
In this paper, we present laser light reflectometry [1] (not to be mistaken with ultrasound reflectometry [2] that uses ultrasound waves) as a tool for quantitative investigation of (the initial stages of) fouling on membrane-like surfaces. Reflectometry allows in situ investigation of adsorption and accumulation of components near a surface However, before the method can be applied, a membrane-resembling layer should be attached to a reflecting surface and this layer should have minimal roughness. This was investigated for the widely used membrane materials polyethersulfone (PES), polyvinylpyrrolidone (PVP), and a blend of both The adsorption of typical foulants, such as BSA, dextrin, and tannin was followed in time Both unmodified and modified surfaces, obtained through pre-adsorption of Tween components were investigated The interactions responsible for adsorption of foulants could be charted, and surface modifications could be proposed that specifically target these interactions (C) 2010 Elsevier B.V All rights reserved
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