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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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.

Biorefinery of proteins from rubber plantation residues
Widyarani, R. - \ 2016
Wageningen University. Promotor(en): Johan Sanders, co-promotor(en): Marieke Bruins; E. Ratnaningsih. - Wageningen : Wageningen University - ISBN 9789462576643 - 236
biorefinery - biomass conversion - rubber - rubber plants - protein extraction - latex - hydrolysis - hydrophobicity - amino acids - wheat gluten - residual streams - biobased economy - bioraffinage - biomassaconversie - rubber - rubberplanten - eiwitextractie - latex - hydrolyse - hydrofobiciteit - aminozuren - tarwegluten - reststromen - biobased economy

Biorefinery of rubber tree side streams could add economic value and income for farmers, who already grow the trees for latex production. The objective of this research was to design a process for the recovery of proteinaceous fractions from rubber tree. The aimed applications were expected to be suitable for local use, particularly in Indonesia, being one of the world’s largest rubber producers. Rubber seed was selected as a model biomass based on its availability (21-144 kg-protein/ha) and its oil content that enables the combination of protein and biodiesel productions within a biorefinery framework. Experimental works were focused on three parts: separation of protein and oil from rubber seed kernel, enzymatic hydrolysis of rubber seed protein into amino acids, and separation of amino acids from hydrolysate. Using alkaline extraction, up to 80% protein from the total original amount of protein in the kernel could be recovered in the extract, comparable to protein recoveries from other oilseeds and oilseed cakes. Seed type and pre-treatment had the most influence on protein recovery. Following protein extraction, the extracted proteins were recovered via isoelectric precipitation, resulting in rubber seed protein concentrate that can be used as such or can be processed further. Different protease combinations were used to hydrolyse rubber seed protein concentrate. After 24 h hydrolysis of rubber seed protein, up to 53% degree of hydrolysis and 35% protein recovery as free amino acids could be achieved. Combination of Pronase + Peptidase R resulted in the highest recovery and concentration of hydrophobic amino acids (phenylalanine, leucine, isoleucine, tyrosine, tryptophan, valine, methionine, and proline) in the hydrolysate. Some hydrophobic amino acids are essential in human and farm animal diets, therefore they can potentially be applied as a group in food and feed. Ethanol was used as an anti-solvent for selective precipitation of amino acids. Ethanol was able to selectively increase the hydrophobic amino acid fraction in rubber seed protein hydrolysate from 59% (mol/mol) in the starting material to 76% in the supernatant. Leucine and valine contributed most to this increase. The results of this study show that rubber seed proteins can be applied locally as animal feed or in industries for technical applications.

Drying and hydration of proteins at high concentration
Bouman, J. - \ 2015
Wageningen University. Promotor(en): Erik van der Linden, co-promotor(en): Renko de Vries. - Wageningen : Wageningen University - ISBN 9789462575509 - 161
eiwit - wei-eiwit - zeïne - drogen - droogmethoden - geneesmiddeltoedieningssystemen - hydratatie - hydrofobiciteit - ph - vacuolen - protein - whey protein - zein - drying - drying methods - drug delivery systems - hydration - hydrophobicity - ph - vacuoles

Proteins are the building blocks of life and serve a wide range of essential functions in organisms. Many metabolic reactions in organisms are catalysed by enzymes, DNA is replicated by proteins and in cells proteins often facilitate active transport of e.g. glucose or ions. Proteins also serve an essential functionality in foods, pharmaceutics, bioplastics and even clothing. Recently, the use of proteins towards higher concentrations is of interest for food, pharmaceutical and medical applications. Nevertheless, the preparation of products with desired product properties can be challenging, when approaching higher protein concentrations. Therefore, in this thesis we investigate proteins at higher concentrations, especially focussing on their drying and hydration behaviour.

In part one of the thesis, the focus is on the dynamics of drying of proteins towards higher concentrations. Dense proteins systems have been scarcely studied compared to proteins at lower concentrations. We address drying behaviour where we focus on the use of whey protein isolate as a model system. In part two of the thesis we focus on the hydration properties of the corn protein zein, where we apply it as a drug excipient. In this part we also investigate the influence of hydration on the release behaviour of drugs into the hydration media.

The drying part (part one) contains two studies. The first study is more fundamental in nature, focussing on the drying of a protein coating. In previous studies mainly the macroscopic properties of protein coatings after drying are investigated, leaving the drying dynamics virtually unexplored. Here we investigate the drying behaviour of the model protein β-lactoglobulin on multiple length scales with an unique combination of in-line techniques. On the microscopic length scale we use dynamic vapour sorption and magnetic resonance imaging while on a smaller length scales, we apply diffusing wave spectroscopy and IR-spectroscopy to monitor the drying process. For all used techniques, the changes in the measured physical properties of the coating as a function of water weight fraction Xw from Xw = 0.8 down to Xw = 0.2 are gradual. However, using dynamic vapour sorption and IR-spectroscopy we measure a sharp change below water weight fractions of Xw = 0.2. We hypothesise that changes in the molecular interactions caused by dehydration of the protein results in a change in the drying kinetics of the film.

In the second study of part one, protein drying is approached on a more applied level, where we study the drying of a spherical droplet. We use single droplet drying as a methods that can model the spray drying process in a simplified and well-controlled way. Sessile droplets are subjected to varying drying conditions such as temperature, initial protein concentration, presence of airflow and droplet rotation. During these experiments the morphological development is monitored by a camera. After drying, scanning electron microscopy and X-ray tomography are used to examine the particles that are formed after complete drying. Irrespective of the conditions used, we observe an initial droplet shrinkage, followed by the nucleation of a hole in the droplet skin, which is followed by the formation of a vacuole. The drying conditions used, strongly influenced the location of the hole and the locking point prior to hole formation. We hypothesise that the location of the hole is caused by local inhomogeneities in protein concentration causing a the nucleation of the hole where the local skin modulus is lowest. Also the locking point of the droplet is found to be due to a inhomogeneity over the whole droplet caused by rapid evaporation. These results can be of importance to understand powder structure and functionality as obtained in spray drying.

In the hydration part (part 2), we investigate the potential of zein as a sole excipient in macroscale caplets obtained by hot melt extrusion (HME) and injection moulding (IM). Zein is good candidate as a sustained release agent, because it is insoluble in two studies. In the first study zein matrices were loaded with the drug paracetamol. Physical mixtures of zein, water and crystalline paracetamol are extruded and injection moulded into caplets. Characterisation of these caplets is performed using differential scanning calorimetry, IR- spectroscopy, scanning electron microscopy and powder X-ray diffraction. The hydration and drug release kinetics from the caplet slices is measured. We find that the drug release kinetics is broadly independent of the dissolution medium and drug loading. The release kinetics is diffusion limited and could be well described by a 2D diffusion model. The results demonstrate that the drug release rate from zein caplet slices can be tuned by its dimensions.

In the second study, a wider range of drugs differing in hydrophobicity is studied. Next to paracetamol, we have used two other model drugs: the hydrophobic indomethacin and the more hydrophilic ranitidine. The zein matrix is capable to stabilize the different dugs in a non-crystalline state, which is promising especially for increasing the bioavailability of poorly water-soluble drugs. Overall crystallinity of the drugs in the caplets increases with its degree of hydrophobicity. For the poorly soluble indomethacin, dissolution rates at low pH were higher from caplet slices, compared to the dissolution rates of indomethacin crystals by themselves. In addition, we found that the electrostatic interactions between zein and drugs can also be used to influence the release kinetics.

Various aspects were found to be of importance both for drying and hydration of concentrated protein systems. The homogeneity during both processes deserves attention as its manipulation can strongly influence final properties if the system. Also the plasticising effect of water on dense proteins is often found essential, when understanding the dynamics of both drying and hydration processes. Finally protein hydrophobicity and its manipulation can provide a window of opportunities in many applications which are involve by drying or hydration.

Listeria monocytogenes repellence by enzymatically modified PES surfaces
Veen, S. van der; Nady, N. ; Franssen, M.C.R. ; Zuilhof, H. ; Boom, R.M. ; Abee, T. ; Schroën, C.G.P.H. - \ 2015
Journal of Applied Polymer Science 132 (2015)10. - ISSN 0021-8995 - 6 p.
stainless-steel - catalyzed modification - biofilm formation - attachment - growth - membranes - water - acid - functionalization - hydrophobicity
: The effect of enzyme-catalyzed modification of poly(ethersulfone) (PES) on the adhesion and biofilm formation of two Listeria monocytogenes strains is evaluated under static and dynamic flow conditions. PES has been modified with gallic acid, ferulic acid and 4-hydroxybenzoic acid. The surfaces modified with any of these compounds show up to 70% reduced adhesion of L. mono-cytogenes under static conditions and up to 95% under dynamic flow conditions compared with unmodified surfaces. Also, under static conditions the formation of biofilms is reduced by 70%. These results indicate that the brush structures that are formed by the polymers on the PES surface directly influence the ability of microorganisms to interact with the surface, thereby reducing attachment and biofilm formation of L. monocytogenes. Based on these results, it is expected that enzyme-catalyzed surface modification is a promising tool to reduce microbial adhesion and biofilm formation
Secretion of elastin-like polypeptides with different transition temperatures by Pichia pastoris
Schipperus, R. ; Eggink, G. ; Wolf, F.A. de - \ 2012
Biotechnology Progress 28 (2012)1. - ISSN 8756-7938 - p. 242 - 247.
protein - fusion - hydrophobicity - expression - hydrogels - purification - length
Like natural tropoelastin, polypeptides based on an elastin-like VPGXG repeat have a characteristic inverse temperature response, which leads to coacervate formation above a certain transition temperature and which could be useful for a variety of applications. The key advantage of elastin-like polypeptides (ELPs) over (tropo)elastin is a full control over this temperature response by adjustment of either the amino acid composition or the chain length, according to insights provided by extensive research. Future application of ELPs will require efficient ELP production systems, and in a previous article, we described the successful use of Pichia pastoris for secreted production of an ELP, with an overall yield of ˜ 200 mg L(-1). In this study, we investigated the influence of changed amino acid composition and chain length on the yield of secreted ELP. We have found that both parameters have a distinct impact on the overall yield, with higher yield for shorter and more hydrophilic ELPs. Because yield and transition temperature (Tt) thus appear to be positively correlated, we hypothesize that good solubility of ELP below the Tt promotes the secreted production and coacervate formation above Tt decreases it.
Natural and fire-induced soil water repellency in a Portugese Shrubland
Stoof, C.R. ; Moore, D. ; Ritsema, C.J. ; Dekker, L.W. - \ 2011
Soil Science Society of America Journal 75 (2011)6. - ISSN 0361-5995 - p. 2283 - 2295.
coarse-textured soils - forest soils - pine forests - hydrological behavior - eucalyptus-globulus - spatial variability - prescribed fire - sandy soil - hydrophobicity - moisture
Post-fire land degradation is often attributed to fire-induced soil water repellency, despite the fact that soil water repellency is a natural phenomenon in many soils and is therefore not necessarily caused by fire. To improve our understanding of the role of soil water repellency in causing fire-induced land degradation, a long-term monitoring study was performed in which the temporal variation of topsoil water repellency (0–2.5-cm depth) was captured in a Portuguese shrubland before and after fire between November 2007 and March 2010. In addition, similarities and dissimilarities between changes following burning and clipping were assessed in a plot experiment. Soil water repellency appeared to be the rule rather than the exception, both before and after fire, and was strongly related to soil moisture and organic matter content. Surprisingly, despite the low soil temperatures during the fire (60°C) and the lack of direct soil moisture changes, fire significantly increased the persistence of soil water repellency (the water drop penetration time). Vegetation removal by burning and clipping played a key role in determining post-fire water repellency in litter and at the soil surface and considerably reduced the time needed to both develop and eliminate water repellency of the litter and surface soil. Where pre-fire (or “natural”) soil water repellency is abundant, an increase in erosion after fire cannot be solely caused by soil water repellency. Nevertheless, fire-induced removal of the protective canopy cover may increase the hydrologic significance of soil water repellency in burned landscapes
Poisson analysis of streptococcal bond strengthening on stainless steel with and without salivary conditioning film
Mei, Li ; Mei, H.C. van der; Ren, Y. ; Norde, W. ; Busscher, H.J. - \ 2009
Langmuir 25 (2009)11. - ISSN 0743-7463 - p. 6227 - 6231.
atomic-force microscopy - bacterial adhesion - surface - hydrophobicity - charge
Poisson analysis of retract force-distance curves in atomic force microscopy (AFM) has yielded a new dimension to the decoupling of individual bond forces into a hydrogen bonding and nonspecific force component. Accordingly, bacterial adhesion forces have been decoupled into a hydrogen bonding and nonspecific Lifshitz-Van der Waals contribution. Due to the forced nature of AFM contact, the nonspecific force contribution has hitherto turned out to be repulsive in the analysis of bacterial adhesion forces on nonconducting surfaces. In this study, we present the results of a Poisson analysis of adhesion forces for streptococci adhering to a conducting surface. Adhesion forces measured between stainless steel, both in the absence and presence of an adsorbed salivary conditioning film, increased with increasing contact time between the streptococcal AFM probe and the surface. Concurrent with the increase in adhesion force, there was an increase in the number of minor force peaks in the retract force-distance curves. Poisson analyses of the adhesion forces indicated repulsive nonspecific Lifshitz-Van der Waals forces for streptococci adhering to saliva-coated stainless steel, but interestingly and for the first time, attractive nonspecific forces were revealed on stainless steel in the absence of a salivary conditioning film. We tentatively attribute this to attraction between the negatively charged streptococci and their positive image charges in the conducting material, which cannot develop in a nonconducting material or in the presence of a nonconductive protein layer on the stainless steel surface.
Methods for determining actual soil water repellence
Dekker, L.W. ; Ritsema, C.J. ; Oostindie, K. ; Moore, D. ; Wesseling, J.G. - \ 2009
Water Resources Research 45 (2009). - ISSN 0043-1397 - 6 p.
sandy soils - organic-matter - contact-angle - forest - hydrophobicity - flow - persistence - severity - patterns - molarity
In this paper we describe a simple and quick method for determining the presence of water repellency in a soil by using a small core sampler (1.5 cm in diameter, 25 cm long) and applying the water drop penetration time (WDPT) test at different depths on the sandy soil cores. Obtained results provide spatial distribution patterns of water repellency in a soil profile, demonstrating seasonal changes in repellency. An advantage of the method is that the soil is not disturbed by the sampling. For assessment of the persistence of water repellency in strongly to extremely water repellent soils, and for determination of the critical soil water contents, the WDPT test and volumetric water content determinations should preferably be performed in the laboratory.
Editorial: Water repellence of soils: new insights and emerging research needs
Doerr, S.H. ; Ritsema, C.J. ; Dekker, L.W. ; Scott, D.F. ; Carter, D. - \ 2007
Hydrological Processes 21 (2007)17. - ISSN 0885-6087 - p. 2223 - 2228.
hydrophobicity - portugal - rainfall - dynamics - impact - flow
An increasing awareness of the occurrence and implications of soil water repellence has caused a surge in research activity addressing this phenomenon in recent years. This has involved not only the disciplines of hydrology, soil, and related environmental sciences, but increasingly also biology, chemistry, physics, and surface sciences, which has allowed elucidation of the causes and behaviour of soil water repellence based on first order principles. Furthermore, novel approaches and advances in technology have allowed examination of its causes and implications at increasingly coarse and fine spatial and temporal scales. The 19 papers presented in this special issue exemplify this trend by bringing together studies from diverse disciplines and presenting the latest advances regarding the origin, occurrence, controls, hydrological effects, and amelioration of soil water repellence. Here we aim to summarize, evaluate and set into context some of the new insights arising from these studies and also attempt to identify the key current and likely future research gaps related to water repellence in soils
Biochemical ripening of dredged sediments. Part 2. Degradation of polycyclic aromatic hydrocarbons and total petroleum hydorcarbons in slurried and consolidated sediments
Vermeulen, J. ; Gool, M.P.M. van; Mentink, G.H. ; Joziasse, J. ; Bruning, H. ; Grotenhuis, J.T.C. - \ 2007
Environmental Toxicology and Chemistry 26 (2007)12. - ISSN 0730-7268 - p. 2540 - 2549.
soil organic-matter - contaminated sediments - desorption-kinetics - bioavailability - biodegradation - bioremediation - model - oxygen - hydrophobicity - sequestration
Ripening of polycyclic aromatic hydrocarbons (PAH) and total petroleum hydrocarbons (TPH) polluted dredged sediment can be considered as a bioremediation technique. Aerobic biodegradation of PAH and TPH was studied in five previously anaerobic-slurried sediments during a 350-d laboratory incubation experiment. In addition, oxygen penetration and degradation of PAH and TPH were studied in three consolidated (physically ripened) sediments. All experiments were conducted in the laboratory at 30°C. A double exponential decay model could adequately describe PAH and TPH degradation kinetics in the slurried sediments. First-order degradation rate constants for the rapidly degradable fractions (12¿58%) were approximately 0.13 and 0.058 d¿1 for PAH and TPH, respectively, whereas the rate constants for the slowly degradable fractions were approximately 0.36 × 10¿3 (PAH) and 0.66 × 10¿3 d¿1 (TPH). Rate constants for the rapidly and slowly degrading fractions have the same order of magnitude as the mineralization rate constants of the rapidly and slowly mineralizing organic matter (OM) fractions in the sediments. Oxygen uptake by degradation of PAH and TPH was negligible compared to the oxygen uptake by sulfur oxidation and OM mineralization. In consolidated sediments, PAH and TPH degradation was limited to the oxygenated part. Amounts of PAH and TPH that degraded in the oxygenated parts of the consolidated sediments during 21 d of incubation were similar to the amounts that degraded during 21 d in the slurried sediments.
Ecology of tree roots in substrates of The Hague
Arhipova, L. ; Spijker, J.H. ; Kopinga, J. - \ 2007
Wageningen : Alterra (Alterra-rapport 1590) - 111
wortels - straatbomen - stedelijke gebieden - groeimedia - rizosfeer - substraten - bodemdegradatie - kationenuitwisselingcapaciteit - waterafstotende gronden - hydrofobiciteit - nederland - zuid-holland - roots - street trees - urban areas - growing media - rhizosphere - substrates - soil degradation - cation exchange capacity - water repellent soils - hydrophobicity - netherlands - zuid-holland
The ecology of uniformly and non-uniformly distributed roots in layered and/or heterogeneous substrates, especially sand-peat-clay mixes, have been studied from literature and through a case study. There is a strong interaction between soil layering and/or heterogeneity and local root growth and local branching rate. In principle, the minimum area of root surface that a plant needs is very low. Real situations have much higher root surface areas for several reasons, one being the absence of synchronisation and synlocation of supply and demand of nutrients and water
Aggregation of -Lactoglobulin Regulated by Glucosylation
Broersen, K. ; Elshof, E. ; Groot, J. de; Voragen, A.G.J. ; Hamer, R.J. ; Jongh, H.H.J. de - \ 2007
Journal of Agricultural and Food Chemistry 55 (2007)6. - ISSN 0021-8561 - p. 2431 - 2437.
heat-induced aggregation - amyloid formation - fibril formation - protein - glycoprotein - stability - hydrophobicity - glycosylation - calreticulin - denaturation
A large number of proteins are glycosylated, either in vivo or as a result of industrial processing. Even though the effect of glycosylation on the aggregation of proteins has been studied extensively in the past, some reports show that the aggregation process is accelerated, whereas others found that the process is inhibited by glycosylation. This paper investigates the reasons behind these controversial results as well as the potential mechanism of the effect of glucosylation on aggregation using bovine -lactoglobulin as a model. Glucosylation was found to inhibit denaturant-induced aggregation, whereas heat-induced aggregation was accelerated. It was also found that the kinetic partitioning from an unfolded state was driven toward refolding for glucosylated protein, whereas aggregation was the preferred route for the nonglucosylated protein. Keywords: Aggregation; glucosylation; -lactoglobulin; hydrophobicity; electrostatic repulsion; unfolding/refolding
Germination of Bacillus cereus spores adhered to stainless steel
Hornstra, L.M. ; Leeuw, P.P.L.A. de; Moezelaar, R. ; Wolbert, E.J.H. ; Vries, Y.P. de; Vos, W.M. de; Abee, T. - \ 2007
International Journal of Food Microbiology 116 (2007)3. - ISSN 0168-1605 - p. 367 - 371.
l-alanine - surface - hydrophobicity - removal - milk - inactivation - sporulation - resistance - sanitizer - adhesion
Adhered spores of Bacillus cereus represent a significant part of the surface-derived contamination in processing equipment used in the dairy industry. As germinated spores lose their resistance capacities instantaneously, efficient germination prior to a cleaning in place treatment could aid to the disinfecting effect of such a treatment. Therefore, spores of B. cereus ATCC 14579 and that of the environmental isolate B. cereus CMCC 3328 were assessed for their germination behaviour when adhered to a stainless steel surface. A mixture of l-alanine and inosine initiated germination of adhered spores efficiently, resulting in 3.2 decimal logarithms of germination. Notably, implementation of a germination-inducing step prior to a representative cleaning in place procedure reduced the number of survivors with over 3 decimal log units, while an alkali treatment alone, as part of the cleaning in place procedure, did not show any effect on B. cereus spore viability. These results show that implementation of a germination step enhances the disinfection effect of currently used cleaning in place procedures.
Confinement-induced symmetry breaking of interfacial surfactant layers
Leermakers, F.A.M. ; Koopal, L.K. ; Goloub, T.P. ; Vermeer, A.W.P. ; Kijlstra, J. - \ 2006
The Journal of Physical Chemistry Part B: Condensed Matter, Materials, Surfaces, Interfaces & Biophysical 110 (2006)17. - ISSN 1520-6106 - p. 8756 - 8763.
field lattice model - nonionic surfactants - ionic surfactants - statistical thermodynamics - adsorption regulation - adsorbed layer - phase-behavior - aqueous film - association - hydrophobicity
Interaction forces between mesoscopic objects are fundamental to soft-condensed matter and are among the prime targets of investigation in colloidal systems. Surfactant molecules are often used to tailor these interactions. The forces are experimentally accessible and for a first theoretical analysis one can make use of a parallel-plate geometry. We present molecularly realistic self-consistent field calculations for an aqueous nonionic surfactant solution near the critical micellization concentration, in contact with two hydrophobic surfaces. The surfactants adsorb cooperatively, and form a monolayer onto each surface. At weak overlap the force increases with increasing compression of the monolayers until suddenly a symmetry braking takes place. One of the monolayers is removed jump-like and as the remaining monolayer can relax, some attraction is observed, which gives way to repulsion at further confinement. The restoring of symmetry at strong confinement occurs as a second-order transition and the force jumps once again from repulsion to attraction. It is anticipated that the metastable branch of the interaction curve will be probed in a typical force experiment. Under normal conditions pronounced hysteresis in the surface force is predicted, without the need to change the adsorbed amount jump-like
Near-surface distributions of soil water and water repellency under three effluent irrigation scemes in a blue gum (Eucalyptus globulus) plantation
Thwaites, L.A. ; Rooij, G.H. de; Salzman, S. ; Allinson, G. ; Stagnitti, F. ; Carr, R. ; Versace, V. ; Struck, S. ; March, T. - \ 2006
Agricultural Water Management 86 (2006)1-2. - ISSN 0378-3774 - p. 212 - 219.
spatial variability - preferential flow - wetting patterns - pinus-radiata - sandy soils - portugal - hydrophobicity - management - australia - moisture
Water repellent soils are difficult to irrigate and susceptible to preferential flow, which enhances the potential for accelerated leaching to groundwater of hazardous substances. Over 5 Mha of Australian soil is water repellent, while treated municipal sewage is increasingly used for irrigation. Only if a critical water content is exceeded will repellent soils become wettable. To avoid excessive loss of water from the root zone via preferential flow paths, irrigation schemes should therefore aim to keep the soil wet enough to maintain soil wettability. Our objective was to monitor the near-surface water content and water repellency in a blue gum (Eucalyptus globulus) plantation irrigated with treated sewage. The plantation's sandy soil surface was strongly water repellent when dry. For 4 months, three rows of 15 blue gum trees each received no irrigation, three other rows received 50% of the estimated potential water use minus rainfall, and three more rows received 100%. During this period, 162 soil samples were obtained in three sampling rounds, and their water content (% dry mass) and degree of water repellency determined. Both high and low irrigation effectively wetted up the soil and eliminated water repellency after 2 (high) or 4 (low) months. A single-peaked distribution of water contents was observed in the soil samples, but the water repellency distribution was dichotomous, with 44% extremely water-repellent and 36% wettable. This is consistent with a threshold water content at which a soil sample changes from water repellent to wettable, with spatial variability of this threshold creating a much wider transition zone at the field scale. We characterized this transition zone by expressing the fraction of wettable samples as a function of water content, and demonstrated a way to estimate from this the wettable portion of a field from a number of water content measurements. To keep the plantation soil wettable, the water content must be maintained at a level at which a significant downward flux is likely, with the associated enhanced leaching. At water contents with negligible downward flux, the field is water repellent, and leaching through preferential flow paths is likely. Careful management is needed to resolve these conflicting requirements.
Bioflocculation of mesophilic and thermophilic activated sludge
Vogelaar, J.C.T. ; Keizer, A. de; Spijker, S. ; Lettinga, G. - \ 2005
Water Research 39 (2005)1. - ISSN 0043-1354 - p. 37 - 46.
geactiveerd slib - afvalwaterbehandeling - biologische behandeling - temperatuur - uitvlokking - adsorptie - hydrofobiciteit - activated sludge - waste water treatment - biological treatment - temperature - flocculation - adsorption - hydrophobicity - paper-mill - water - effluent - temperatures - whitewater - reactors - flocs
Thermophilic activated sludge treatment is often hampered by a turbid effluent. Reasons for this phenomenon are so far unknown. Here, the hypothesis of the temperature dependency of the hydrophobic interaction as a possible cause for diminished thermophilic activated sludge bioflocculation was tested. Adsorption of wastewater colloidal particles was monitored on different flat surfaces as a function of temperature. Adsorption on a hydrophobic surface varied with temperature between 20 and 60 °C and no upward or downward trend could be observed. This makes the hydrophobic interaction hypothesis unlikely in explaining the differences in mesophilic and thermophilic activated sludge bioflocculation. Both mesophilic and thermophilic biomass did not flocculate with wastewater colloidal particles under anaerobic conditions. Only in the presence of oxygen, with biologically active bacteria, the differences in bioflocculation behavior became evident. Bioflocculation was shown only to occur with the combination of wastewater and viable mesophilic biomass at 30 °C, in the presence of oxygen. Bioflocculation did not occur in case the biomass was inactivated or when oxygen was absent. Thermophilic activated sludge hardly showed any bioflocculation, also under mesophilic conditions. Despite the differences in bioflocculation behavior, sludge hydrophobicity and sludge zetapotentials were almost similar. Theoretical calculations using the DLVO (Derjaguin, Landau, Verweij and Overbeek) theory showed that flocculation is unlikely in all cases due to long-range electrostatic forces. These calculations, combined with the fact that bioflocculation actually did occur at 30 °C and the unlikelyness of the hydrophobic interaction, point in the direction of bacterial exo-polymers governing bridging flocculation. Polymer interactions are not included in the DLVO theory and may vary as a function of temperature.
Extraction of compounds associated with water repellency in sandy soils of different origin
Doerr, S.H. ; Llewellyn, C.T. ; Douglas, P. ; Morley, C.P. ; Mainwaring, K.A. ; Haskins, C. ; Johnsey, L. ; Ritsema, C.J. ; Stagnitti, F. ; Allinson, G. ; Ferreira, A.J.D. ; Keizer, J.J. ; Ziogas, A.K. ; Diamantis, J. - \ 2005
Australian Journal of Soil Research 43 (2005)3. - ISSN 0004-9573 - p. 225 - 237.
organic-matter - hydrophobicity - variability - substances - severity
After an initial evaluation of several solvents, the efficiency of Soxhlet extractions with isopropanol/ammonia (s.g. 0.88) (70 : 30 v : v; 24 h) in extracting compounds associated with water repellency in sandy soils was examined using a range of repellent and wettable control soils (n = 15 and 4) from Australia, Greece, Portugal, The Netherlands, and the UK. Extraction efficiency and the role of the extracts in causing soil water repellency was examined by determining extract mass, sample organic carbon content and water repellency (after drying at 20°C and 105°C) pre- and post-extraction, and amounts of aliphatic C¿H removed using DRIFT, and by assessing the ability of extracts to cause repellency in acid-washed sand (AWS). Key findings are: (i) none of organic carbon content, amount of aliphatic C¿H, or amount of material extracted give any significant correlation with repellency for this diverse range of soils; (ii) sample drying at 105°C is not necessarily useful before extraction, but may provide additional information on extraction effectiveness when used after extraction; (iii) the extraction removed repellency completely from 13 of the 15 repellent samples; (iv) extracts from all repellent and wettable control soils were capable of inducing repellency in AWS. The findings suggest that compounds responsible for repellency represent only a fraction of the extract composition and that their presence does not necessarily always cause repellency.
Relations between macroscopic and microscopic adhesion of Streptococcus mitis strains to surfaces
Vadillo-Rodriguez, V. ; Busscher, H.J. ; Norde, W. ; Vries, J. de; Mei, H.C. van der - \ 2004
Microbiology 150 (2004). - ISSN 1350-0872 - p. 1015 - 1022.
atomic-force microscopy - bacterial adhesion - escherichia-coli - flow chamber - cell - attachment - polymers - hydrophobicity - deposition - sanguis
Application of physico-chemical models to describe bacterial adhesion to surfaces has hitherto only been partly successful due to the structural and chemical heterogeneities of bacterial surfaces, which remain largely unaccounted for in macroscopic physico-chemical characterizations of the cell surfaces. In this study, the authors attempted to correlate microscopic adhesion of a collection of nine Streptococcus mitis strains to the negatively charged, hydrophilic silicon nitride tip of an atomic force microscope (AFM) with macroscopic adhesion of the strains to a negatively charged, hydrophilic glass in a parallel-plate flow chamber. The repulsive force probed by AFM upon approach of the tip to a bacterial cell surface ranged from 1·7 to 7·7 nN depending on the strain considered and was found to correspond to an activation barrier, governing initial, macroscopic adhesion of the organisms to the glass surface. Moreover, maximum distances at which attractive forces were probed by the AFM upon retraction of the tip (120 to 1186 nm) were related to the area blocked by an adhering bacterium, i.e. the distance kept between adhering bacteria. Bacterial desorption could not be related to adhesive forces as probed by the AFM, possibly due to the distinct nature of the desorption process occurring in the parallel-plate flow chamber and the forced detachment in AFM.
Anaerobic sludge granulation
Hulshoff Pol, L.W. ; Castro Lopes, S.I. de; Lettinga, G. ; Lens, P.N.L. - \ 2004
Water Research 38 (2004)6. - ISSN 0043-1354 - p. 1376 - 1389.
rioolslib - anaërobe behandeling - korrels - afvalwaterbehandeling - sewage sludge - anaerobic treatment - granules - waste water treatment - uasb reactors - start-up - molecular-mechanism - blanket reactors - bed reactors - hydrophobicity - pelletization - architecture - performance
This paper reviews different theories on anaerobic sludge granulation in UASB-reactors that have been proposed during the past two decades
This paper reviews different theories on anaerobic sludge granulation in UASB-reactors that have been proposed during the past two decades. The initial stages of the formation of anaerobic granules follow the same principles as biofilm formation of bacteria on solid surfaces. There exist strong evidence that inert carriers play an important positive role in granulation. Most researchers conclude that Methanosaeta concilii is a key organism in granulation. Only the Cape Town Hypothesis presumes that an autotrophic hydrogenotrophic organism, i.e., Methanobacterium strain AZ, growing under conditions of high H-2-pressures, is the key organism in granulation. Many authors focus on the initial stage of granulation, and only a few contributions discuss the latter stages in granulation: granule maturation and multiplication. Granule enhancing factors in the latter stages predominantly rely on manipulation of the selection pressure, through which selectively heavier sludge particles are retained in the UASB reactor. (C) 2003 Elsevier Ltd. All rights reserved.
Modelling maximum adsorption capacities of soot and soot-like materials for PAHs and PCBs
Noort, P.C.M. van; Jonker, M.T.O. ; Koelmans, A.A. - \ 2004
Environmental Science and Technology 38 (2004)12. - ISSN 0013-936X - p. 3305 - 3309.
aromatische koolwaterstoffen - polycyclische koolwaterstoffen - adsorptie - sorbaten - hydrofobiciteit - organische verbindingen - monitoring - waterkwaliteit - waterbodems - aromatic hydrocarbons - polycyclic hydrocarbons - adsorption - sorbates - hydrophobicity - organic compounds - monitoring - water quality - water bottoms - polycyclic aromatic-hydrocarbons - hydrophobic organic-chemicals - partition-coefficients - aqueous solubilities - black carbon - sorption - water - sediment - extraction - biphenyls
Recent studies have shown that not partitioning but adsorption is the main mechanism for sorption of hydrophobic organic compounds to soot and soot-like materials. For compounds that adsorb by van der Waals forces only, variation in soot-water distribution coefficients will result from differences in these forces for adsorption, as well as the maximum number of accessible sites. This maximum number of accessible sites may a priori be expected to vary due to differences in both sorbent characteristics and sorbate dimensions. In this modeling study, variation in maximum adsorption capacities is explained from sorbent and sorbate properties. Maximum adsorption capacities were calculated using (a) literature values for soot-water distribution coefficients for polycyclic aromatic hydrocarbons and polycholorobiphenyls on 10 different soot and soot-like materials and (b) Langmuir affinities for adsorption at a carbonaceous surface estimated using a recently reported method
Recent studies have shown that not partitioning but adsorption is the main mechanism for sorption of hydrophobic organic compounds to soot and soot-like materials. For compounds that adsorb by van der Waals forces only, variation in soot-water distribution coefficients will result from differences in these forces for adsorption, as well as the maximum number of accessible sites. This maximum number of accessible sites may a priori be expected to vary due to differences in both sorbent characteristics and sorbate dimensions. In this modeling study, variation in maximum adsorption capacities is explained from sorbent and sorbate properties. Maximum adsorption capacities were calculated using (a) literature values for soot-water distribution coefficients for polycyclic aromatic hydrocarbons and polychlorobiphenyls on 10 different soot and soot-like materials and (b) Langmuir affinities for adsorption at a carbonaceous surface estimated using a recently reported method. The variation in maximum adsorption capacities could be explained by the variation in sorbent specific surface area, sorbent organic carbon content, and the sorbent-sorbate contact area. Furthermore, increasing sorbate thickness was related to a decrease in maximum adsorption capacities, which points to adsorption in micropores. Maximum adsorption capacities decreased by 1-2 orders of magnitude as the contact area increased by 50%. This points to adsorption sites being hardly larger than sorbates.
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