This master thesis project was carried out as a part of the chlorate research conducted at the Process RD&I department for bleaching chemicals at AkzoNobel Pulp and Performance Chemicals AB in Bohus. During the project already implemented filter cloths as well as new types of filters were studied and compared by experimental trials. The results were then examined in an attempt to evaluate existing filtration systems as well as investigate if there are other, better alternatives. The impurities found in a chlorate plant account for an efficiency loss in the process and a reduction of impurities would hence result in an energy reduction and a cleaner product. The trials were conducted at one of AkzoNobel’s chlorate plants. Six filters were studied and evaluated by measuring turbidity of the electrolyte and pressure over the filter during the experiments. Samples of the electrolyte were analyzed to obtain the metal content, and thereby the impurity content, of the electrolyte. The structures of the filters were studied by optical microscopy. The results from the trials show that all filter types except one, a needle felt filter, seem to be suitable for chlorate electrolyte filtration (including the filter types already used in the plants). The other filters all reach turbidity values below 0.1 FNU immediately or within 90 minutes of filtration, which is considered good enough. The results from the metal content analysis show a similar trend where the metal concentrations decrease to levels below the detection limits immediately or within 90 minutes of filtration. Apart from the lab trials performed some measurements were made on the existing filtration equipment in the chlorate plant. The measurements show varying results, partly similar to those achieved during the lab filter trials but also results showing a higher turbidity value and metal content, indicating that full scale operation are more complicated than lab scale operation. The lab trial results obtained with the filter types already used in the plants show that lower impurity content is possible to achieve. However, this would require closer monitoring of the filtration systems in the plants. Apart from the filtration trials, an attempt to determine the sizes of the particles present in the electrolyte using laser diffraction was performed. However, too little was known of the chlorate electrolyte’s optical data for the measurements to be reliable. Further work is needed before a method for size determination of the particles in a chlorate electrolyte can be achieved. Also, an Optical Filtration Test was tried on the electrolyte but was not sensitive enough for utilization on electrolyte with low (below 1 FNU) turbidity values.  The project concluded that a switch to another filtration system is unmotivated, unless a change in the product requirements would occur. Since the impurities have proven to affect the efficiency of the process, it is recommended to make an effort into utilizing the filtration system to its full extent.

In integrated circuit (IC) manufacturing, particulate contamination from hundreds of processe steps is a major cause of yield loss. The removal of particles is typically achieved through liquid chemical formulations aided by a sound field in the MHz frequency range. When liquid is irradiated with megasonic waves, dissolved gases play an important role in particle removal and feature damage. To take the advantage of the beneficial effect of CO₂ (aq.), this thesis describes the development and optimization of a megasonic cleaning process using a chemical system containing NH₄OH and NH₄HCO₃ at an alkaline pH in which a specific amount of aqueous CO₂ can be maintained to minimize feature damage. In addition, certain etching effects at a slightly alkaline pH were supported for achieving high particle removal. Sonoluminescence (SL) data were collected from these cleaning solutions and correlated with the cleaning performance. The intensity of SL is believed to be a sensitive indicator of transient cavitation during megasonic irradiation, which is thought to be responsible for fragile feature damage. To further analyze the SL signal with respect to the emission from hydroxyl radicals, single-band filters were used to collect the SL signal in different wavelength ranges. The study of particle removal and feature damage was performed using a single-wafer cleaning tool, MegPie® (ProSys, Inc.), which provided acoustic irradiation at a frequency of 0.925 MHz. Commercially available SiO₂ slurry with 200 ± 20 nm particles was used for particle contamination. Particle removal was investigated on both blanket SiO₂ samples and patterned samples. Feature damage studies were conducted on patterned samples by examining the number of line breakages per unit area. By adjusting the pH in NH₄OH/NH₄HCO₃ solutions from 7.8 to 8.5, the amount of CO₂ (aq.) was varied. At a pH of 8.2 with ~ 320 ppm CO₂ (aq.) in the cleaning solution, a high particle removal efficiency was achieved (> 90%) at an acoustic power intensity of 1 W/cm² for an exposure time of 60 s, and the feature damage was reduced by > 50%. For SL signal analysis, band filters in the wavelength range of (i) 280 – 305.5 nm, (ii) 300 – 340 nm, (iii) 335 – 375 nm, and (iv) 374.5 – 397.5 nm were used to resolve the SL spectrum in these wavelength ranges. The filters were sandwiched, one at a time, between the optical window and the photomultiplier tube (PMT) in the Cavitation Threshold (CT) cell. Air-, Ar-, and CO₂-containing DI water (at pH 4.53 with ~ 90 ppm aqueous CO₂) was pumped through the cell at a flow rate of 130 ml/min. The acoustic power was ramped from 0.1 to 4 W/cm² at an acoustic frequency of 0.925 MHz. The SL signal intensity showed the highest value in the ranges of 300 – 340 and 335 – 375 nm in air- and Ar-saturated DI water, which is due to the emission from excited hydroxyl radicals. These results are consistent with an SL spectrum analysis performed using expensive optical set-ups. In CO₂-containing DI water, the SL signal intensity was suppressed by a factor of 100. The methodology reported in this work is simple, inexpensive, and capable of capturing SL spectral features due to hydroxyl radicals.

"Aluminum alloy cleanliness has been in the limelight during the last three decades and still remains as one of the top concerns in the aluminum casting industry. In general, cleaning an aluminum alloy refers to minimizing the following contaminants: 1) dissolved gases, especially hydrogen, 2) alkaline elements, such as sodium, lithium, and calcium, and 3) unwanted solid particles, such as oxides, carbides, and a variety of intermetallic compounds. Extensive research has resulted in significant improvements in our understanding of the various aspects of these contaminants, and in many foundries, melt-cleansing practices have been established and are routinely used. However, with the ever-increasing demands for improved casting properties, requirements for molten metal cleanliness has become extremely stringent. Rotary degassing is one of the most efficient ways of cleansing molten metals, thus removal of unwanted particles and dissolved hydrogen from molten aluminum alloys by rotary degassing has become a widely used foundry practice. Rotary degassing involves purging a gas into the molten alloy through holes in a rotating impeller. Monatomic dissolved hydrogen either diffuses into these gas bubbles or it forms diatomic hydrogen gas at the bubbles’ surface; in any case, it is removed from the melt with the rising bubbles. Simultaneously, solid particles in the melt collide with one another due to turbulence created by the impeller and form aggregates. These aggregates either settle to the furnace floor, or are captured by the rising gas bubbles and are also removed from the melt. The objective of this work is to understand the physical mechanisms underlying the removal of dissolved hydrogen and unwanted solid particles from molten aluminum alloys by the rotating impeller degasser, and to develop a methodology for the effective use of the degassing process by providing mathematical models and computer simulations of the process. The models and simulations can be used to optimize the process, design new equipment and determine the cause of specific operational problems."

A series of pilot-scale granular media filtration experiments was conducted to examine the effect of media roughness on filter performance and to evaluate the applicability of spherical, rough engineered ceramic filter media for use in granular media filters used for drinking water treatment. Filter media performance was assessed using turbidity and particle count reductions, Cryptosporidium oocyst and oocyst-sized microsphere removal, head loss and stability of operation. Experiments were designed to allow related facets of current filtration research to be examined. These included: effect of loading rate, coagulant type and dosage, and suitability of latex microspheres as surrogates for Cryptosporidium oocyst removal by granular media filtration. This study indicated that increased filter media roughness consistently improved turbidity and particle count reduction under the conditions investigated. As well, the engineered media also consistently achieved greater stability of operation during non-ideal operational periods (e.g. sudden change in filter influent turbidity).Oocyst removals were generally improved by media roughness, though this improvement was reliant on operating conditions, such as coagulant dose and type of coagulant used. The surrogate relationship between oocyst-sized latex microspheres and oocyst removal by filtration was also dependent on coagulant dose and type of coagulant. During trials with no coagulant addition, contrasts in oocyst removal were not significant, suggesting that neither surface roughness nor the size of media used were significant factors impacting oocyst removal by filtration during those periods of impaired operation. When pre-treating raw water with PACl, the engineered ceramic media achieved up to 1.25 log10 higher oocyst removals than conventional media. This improvement in oocyst removal relative to conventional media was not observed when alum was used as the primary coagulant, however. Future studies should directly compare engineered and conventional media filtration performance, using other raw water sources and different operating conditions. Biologically active filtration should also be included in future performance studies because the rough, highly porous surface of the engineered ceramic media is likely to provide excellent biofilm support.

A series of pilot-scale granular media filtration experiments was conducted to examine the effect of media roughness on filter performance and to evaluate the applicability of spherical, rough engineered ceramic filter media for use in granular media filters used for drinking water treatment. Filter media performance was assessed using turbidity and particle count reductions, Cryptosporidium oocyst and oocyst-sized microsphere removal, head loss and stability of operation. Experiments were designed to allow related facets of current filtration research to be examined. These included: effect of loading rate, coagulant type and dosage, and suitability of latex microspheres as surrogates for Cryptosporidium oocyst removal by granular media filtration. This study indicated that increased filter media roughness consistently improved turbidity and particle count reduction under the conditions investigated. As well, the engineered media also consistently achieved greater stability of operation during non-ideal operational periods (e.g. sudden change in filter influent turbidity).Oocyst removals were generally improved by media roughness, though this improvement was reliant on operating conditions, such as coagulant dose and type of coagulant used. The surrogate relationship between oocyst-sized latex microspheres and oocyst removal by filtration was also dependent on coagulant dose and type of coagulant. During trials with no coagulant addition, contrasts in oocyst removal were not significant, suggesting that neither surface roughness nor the size of media used were significant factors impacting oocyst removal by filtration during those periods of impaired operation. When pre-treating raw water with PACl, the engineered ceramic media achieved up to 1.25 log10 higher oocyst removals than conventional media. This improvement in oocyst removal relative to conventional media was not observed when alum was used as the primary coagulant, however. Future studies should directly compare engineered and conventional media filtration performance, using other raw water sources and different operating conditions. Biologically active filtration should also be included in future performance studies because the rough, highly porous surface of the engineered ceramic media is likely to provide excellent biofilm support.

Over the years, megasonic energy has been widely used in the semiconductor industry for effective particle removal from surfaces after chemical mechanical planarization (CMP) processes. As a sound wave propagates through a liquid medium, it generates two effects, namely, acoustic streaming and acoustic cavitation. Acoustic streaming refers to time independent motion of liquid due to viscous attenuation, while cavitation arises from the bubble activity generated due to the difference in the pressure field of the propagating wave. Cavitation can be classified into two categories, (1) stable and (2) transient cavitation. When a bubble undergoes continuous oscillations over repeated cycles it is known to exhibit stable cavitation, while a sudden collapse is referred to as transient cavitation. Due to the rapid implosion of the transient cavity, drastic conditions of temperature (5,000-10,000 K) and pressure (hundreds of bars) are generated within and surrounding the bubble. If this phenomenon occurs close to the substrate, it causes damage to the sub-micron features. In this study, emphasis has been laid on understanding acoustic cavitation as it is critical to achieving high cleaning efficiency without any feature damage. The research work described in this dissertation has been divided into three sections. In the first part of the dissertation, the development of a novel sono-electrochemical technique for removal of sub-micron (300 nm) silica particles from conductive surfaces (Ta) has been discussed. The technique employs megasonic field at low pulse time and duty cycle in conjunction with an applied electrical field for achieving superior particle removal efficiency (PRE). In order to demonstrate the effectiveness of the sono-electrochemical technique, cleaning studies were conducted using 300 nm silica particles both in the presence and absence of an applied electrical field in air and argon saturated solutions. In the presence of the megasonic field (0.5 W/cm², 10% duty cycle, 5ms pulse time) alone, about 55% PRE was observed in Ar saturated DI water, while in the presence of the sono-electrochemical field (-1.5V vs Ag/AgCl (sat. KCl)), about 80% PRE was measured. The enhancement in particle removal efficiency was attributed to oscillating hydrogen bubbles formed from water reduction in close vicinity of the tantalum surface, that grow to a resonant size under suitable acoustic conditions and likely cause removal of particles. Interestingly, increasing the applied potential to -2V (vs Ag/AgCl (sat. KCl)) enhanced the particle removal efficiency to about 100%. Investigations were also performed in solutions containing 10 mM potassium chloride (KCl). The results revealed that even at low applied potentials of -1.5V, almost complete particle removal was achieved. This improvement in PRE was attributed to a combined effect of microstreaming and electro-acoustic forces. The results revealed that almost complete removal of particles could be achieved at low power density and duty cycle when a sound field at 1 MHz is used in conjunction with electrochemistry. The second study focuses on the effect of acoustic frequency and transducer power density for the development of a damage-free megasonic cleaning process. Here, an effort was made to characterize cavitation activity at acoustic frequencies of 1, 2 and 3 MHz by means of electrochemical, acoustic emission and fluorescence spectroscopy techniques. Studies conducted with a microelectrode using ferricyanide as an electroactive species showed that at 1 MHz and 2 W/cm², current peaks with a rise and fall time of about 30-50 ms and 80-120 ms were observed, respectively, which were indicative of transient cavitation behavior. Interestingly at higher frequencies (3 MHz), symmetric and oscillatory behavior in the current was observed. The rise and fall times were about 3 orders of magnitude lower at about 50 µs. This oscillatory behavior in the current at 3 MHz was attributed to the presence of stable cavities. Furthermore, hydrophone studies supported the microelectrode studies as they showed a reduction of about two orders of magnitude in the intensity of transient cavitation as frequency was increased from 1 to 3 MHz. Hydroxyl radical (OH*) capture measurements using terephthalate dosimetry corroborated the above results as they illustrated an order of magnitude decrease in OH* generation rate at 3 MHz compared to 1 MHz. These studies suggest that the use of higher megasonic frequencies may be more suitable for damage-free and effective cleaning of patterned surfaces in the semiconductor industry. In the last part of the dissertation, we investigate the effect of solution parameters on cavitation characteristics using a bicarbonate based alkaline chemical cleaning formulation that has been previously demonstrated to be beneficial in achieving effective megasonic cleaning and low damage. The results of this study revealed that in the presence of ammonia (NH₃) or carbonate/bicarbonate ions at concentrations greater than 75 mM or 200 mM respectively, the measured rate of generation of hydroxyl radicals at 1 MHz and 2 W/cm² was significantly reduced. The lower rate of OH· was attributed to scavenging of radicals in these solutions and additionally due to reduced transient cavitation in ammonia solutions. Hydroxyl radical measurements at higher power density of 8 W/cm² showed that carbonate ions were better scavengers of hydroxyl radicals than bicarbonate ions. The study on the effect of bulk solution temperature illustrated that the rate of generation of OH· increased with increase in temperature from 10 to 30 °C suggesting enhanced transient cavitation at higher temperatures (in the investigated range). The use of optimum concentration of ammonia or carbonates ions in cleaning formulation and bulk solution temperature would likely provide desired cleaning with minimum damage.

The use of particle counters in potable water treatment is achieving higher levels of acceptance on an ongoing basis. This is due to its superior sensitivity in terms of water clarity determination in comparison to turbidity meters. However, the ability of the particle counter to distinguish between various particle sizes, arguably its biggest advantage over turbidity measurement, is not being utilised fully, due to the large volumes of data generated and the amount of post-measurement data processing required to unlock some of the information. In many cases it is being used purely as a substitute or parallel measurement for turbidity. Furthermore, in the South African context, where data is being generated, the particle count data holds little value as it cannot be compared to generally available data sets to reveal the entire message contained in the count. No record of counts is available to rate new measurements against. / Prof. J. Haarhoff

Securing water in the right quantities at the right quality for the right price is a major issue around the world. Membranes are making an increasingly important contribution to meeting this need; however their performance is limited by fouling. This thesis reports on an investigation into the fouling of systems related to water treatment using the Direct Observation Through the Membrane (DOTM). The investigation focused on the measurement of critical flux and observation of particle behaviour under a variety of conditions and for a number of different particles. The range of meanings attributed to critical flux in the literature was analysed and several proposals made for the improved use of the concept. In particular, critical flux determination techniques were classified by whether they measure resistance changes or particle deposition; leading to the definition of Critical Resistance and Critical Deposition Fluxes. In this thesis the deposition definition is used exclusively. The effect of Reynolds number and spacer orientation on critical flux was correlated for spacer-filled channels. The heterogeneous deposition patterns observed with regions of heavy deposition next to areas of little or no deposition. This pattern was related to the local hydrodynamics of spacer cells (a few mm2 in size). The correlations developed for critical flux in spacer-filled channels were adjusted for submicron particle size and incorporated into a SpiralWound Module (SWM) leaf model and then used to simulate the fouling of SWM leaves under a range of operating conditions and operating policies. The Mass Balance technique of critical flux determination was also briefly assessed. The applicability of critical flux criteria to SWM arrays was discussed. Fouling, particle behaviour and critical flux were also investigated in air-sparged systems. The post-cleaning water flux was found to be enhanced when the membrane is fouled in the presence of bubbles. The rate of flux decline was reduced by bubbles. Critical flux increased with air flowrate, and decreased with increased liquid flowrate and concentration. Bubbles caused particles to periodically deposit on the membrane. Particles were observed to stream past the membrane under the influence of back-diffusive forces. Video clips of particulate fouling are provided.

Thesis (MScAgric)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Grinding of feedstuffs prior to in sacco incubation results in fine particles that could escape from dacron bags without being degraded. The objective of this study was to determine the effect of the removal of these fine particles on protein degradation parameters. The feedstuffs that were used were protein feedstuffs that are commonly used in dairy cattle diets in South Africa. Feedstuffs were soybean oilcake, sunflower oilcake, maize gluten 20, maize gluten 60 and fish meal. Treatments were; 1. grinding through a 2 mm screen with no subsequent sieving, 2. grinding through a 2 mm screen followed by sieving through a 106 μm mesh, and 3. grinding through a 2 mm screen followed by sieving through a 150 μm mesh. In the first trial, the material that was lost through sieving and the chemical composition of the different treatments were determined. Protein solubility was also determined. Between 20 and 60% of the material dry matter was lost with the sieving. The chemical composition for the soybean and sunflower oilcake and maize gluten 60 was similar between the three different treatments (or fractions). The CP content of fish meal and maize gluten 20 differed somewhat between the treatments. The 106 μm mesh seemed to be most suitable for fish meal, but a suitable mesh size could not be found for maize gluten 20. In the second trial, the degradability parameters were determined according to the in sacco degradation procedure. Three lactating Holstein cows that were fitted with rumen cannulae were used. The cows received a commercial lactation diet and oat hay that was supplied ad libitum. Samples of all the protein sources were placed in dacron bags and incubated in the rumen. The following removal times were used: 0, 2, 4, 8, 12, 24 or 48 hours. Dry matter and CP disappearances were determined, and the values were used to estimate DM and CP degradability parameters using a non-linear model. Effective CP degradability was also determined. The a-values were affected most of all. On average, the a-values were 39.4 and 40.3% higher for the un-sieved treatments than for the sieved treatments, for DM and CP, respectively. The effective CP degradability was also, on average, 43% higher for the un-sieved treatments. Grinding without the subsequent sieving of samples appears to result in an overestimation of DM and CP degradation in the rumen. It is therefore recommended that after grinding, feedstuffs should be sieved through at least a 106 μm mesh in preparation for in sacco incubations. / AFRIKAANSE OPSOMMING: Die maal van grondstowwe ter voorbereiding van in sacco inkubasies lei tot ‘n potensiële verlies van klein partikels uit die dakronsakkies sonder dat hulle gedegradeer word. Die doel van hierdie studie was om die invloed van die verwydering van fynmateriaal op proteïen-degradeerbaarheidsparameters te bepaal. Die grondstowwe wat in hierdie studie gebruik is, is proteïengrondstowwe wat algemeen in melkbeesdiëte in Suid-Afrika gebruik word. Die grondstowwe was soja-oliekoek, sonneblom-oliekoek, mielie gluten 20, mielie gluten 60 en vismeel. Behandelings was; 1. maal deur ‘n 2 mm sif sonder verdere sifting, 2. maal deur ‘n 2 mm sif gevolg deur sifting deur ‘n 106 μm sif en 3. maal deur ‘n 2 mm sif gevolg deur sifting deur ‘n 150 μm sif. In die eerste proef is die hoeveelheid materiaal wat verlore gaan as gevolg van sifting van die grondstowwe bepaal en die chemiese samestelling van die verskillende behandelings. Proteïenoplosbaarheid is ook bepaal. Tussen 20 en 60% van die materiaal het verlore gegaan as gevolg van sifting. Die chemiese samestelling van die soja- en sonneblom oliekoek, asook dié van die mielie gluten 60 was soortgelyk vir al drie die behandelings. Die ruproteïeninhoud (RP) van die vismeel en mielie gluten 20 het verskil tussen die drie behandelings. Dit wil voorkom asof die 106 μm sif die mees geskikte is vir vismeel, maar ‘n geskikte sif kon nie vir mielie gluten 20 gevind word nie. In die tweede proef is die degradeerbaarheidsparameters bepaal met behulp van die in sacco-metode. Drie lakterende Holsteinkoeie met rumen kannulas is gebruik. Die koeie het ‘n kommersiële melkbeesdieët ontvang en hawerhooi ad libitum. Die monsters is in dakronsakkies in die rumen geïnkubeer. Die sakkies is na die volgende inkubasietye verwyder: 0, 2, 4, 8, 12, 24 of 48 uur. Die DM- en RP-verdwyning is bereken en die waardes is gebruik om die DM- en RP- degradeerbaarheidsparameters te bereken met behulp van ‘n nie-lineêre model. Effektiewe RP- degradeerbaarheid is ook bereken. Die waardes wat die meeste beïnvloed is, is die a-waardes. Die a-waardes was gemiddeld 39.4 en 40.3% hoër vir die ongesifte behandelings as vir die gesifte behandelings, vir DM en RP, onderskeidelik. Die effektiewe RP-degradeerbaarheid was ook gemiddeld 43% hoër vir die ongesifte behandelings. Dit wil voorkom asof DM- en RP-degradeerbaarheid oorskat word wanneer voermonsters slegs gemaal word. Dit word aanbeveel dat grondstowwe ten minste deur ‘n 106 μm sif gesif word ter voorbereiding vir in sacco-studies.

Thesis (MScAgric (Animal Sciences))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: In vitro and in situ methods using the in sacco technique have a wide application in ruminant nutrition as they allow the degradability and quality of forages and ruminant diets to be determined quicker and at a lower cost than in vivo methods. These trials make use of artificial fibre bags, made of polyester (dacron) or nylon which are available in variable pore sizes. Results from such degradability trials are of great value to feed formulation programs such as AMTS.cattle and CPM Dairy and the more accurate the results are obtained from such trials the more accurate feed formulation models are enabling the ruminant nutritionist to formulate the best diet possible to reach the genetic potential of ruminants. The accepted method for in sacco trials (NRC, 2001) requires that the feed samples are ground through a 2 mm screen. This usually results in a variety of particle sizes, including a significant amount of extremely fine particles. Research has, however, shown that these fine particles can potentially be washed out of the dacron bags that are used in in sacco degradability trials. This would result in an overestimation of the soluble and rapidly fermentable nutrient fractions. The objective of this study was to determine the effect of fine particle removal from ground forage samples on the chemical composition and in vitro dry matter (DM) and neutral detergent fibre (NDF) degradability of forages. Lucerne hay, oat hay and wheat straw samples were sourced from seven different locations in the Western Cape. Samples were milled through a 2 mm screen and then sieved through either 150 μm, 125 μm or 106 μm. All fractions were analysed for DM, crude protein (CP), NDF, fat and ash. Based on the NDF content of the original samples, four samples from each forage type were selected for in vitro trials to determine DM and NDF disappearance over time. Samples were incubated for 0, 6, 24 and 48 hours in an ANKOM Daisy II incubator. Significant variation occurred within forage types in terms of chemical composition. Fine particle removal had no effect on the NDF content of lucerne hay and wheat straw, but sieved oat hay fractions had a higher NDF content than the un-sieved samples. The NDF content was on average 635.9 for the sieved OH fractions, whereas the NDF content of the un-sieved samples was 606.8. The CP content of sieved oat hay (61.4 on average) and wheat straw fractions (47.7 on average) were lower than the un-sieved fractions (65.7 for OH and 55.4 for WS), whereas for lucerne hay, sieving had no effect on CP content. Dry matter and NDF disappearances were significantly higher for the un-sieved samples than for the sieved fractions for all three forage types at all incubation times, which indicates an overestimation of the soluble and readily digestible forage fractions. Compared to sieved samples, DMD values at 0 hours (washing only) of the un-sieved samples were, on average, 13.8% higher for lucerne hay, 27.3% for oat hay and 44.7% for wheat straw. At 48 h, the overestimation of lucerne DMD for the un-sieved samples was between 4.0% (compared to 106 μm sieve) and 7.3% (compared to 150 μm sieve). This over-estimation in the un-sieved samples was carried over to all four time points. No significant differences between the fractions (150, 125 and 106) were found within a forage type at all incubation times. The estimated degradation rates and the predicted digested proportions were also significantly higher for the un-sieved fractions compared to the sieved fractions. It was concluded that fine particle removal from forage samples would result in more accurate estimations of in sacco nutrient degradability. / AFRIKAANSE OPSOMMING: In sacco in vitro- en in situ-metodes word dikwels toegepas in die studie van herkouervoeding aangesien hierdie metodes vinniger, meer effektief en meer ekonomies is as in vivo-metodes. Hierdie studies maak gebruik van kunsveselsakkies, gemaak van poliëster (dacron) of nylon wat beskikbaar is in verskeie poriegroottes. Resultate van sulke verteringsproewe is belangrik vir toepassing in voerformuleringsprogramme soos AMTS.cattle en CPM Dairy. Die resultate wat deur hierdie studies verkry word, is belangrik vir akkurate voerformulering deur formuleringsmodelle en stel die herkouervoedingkundige in staat om die ideale voer te formuleer vir die manifestering van die dier se genetiese potensieaal. Die aanvaarde in sacco-metode (NRC, 2001) vereis dat voermonsters deur ‘n 2 mm sif gemaal word wat ‘n groot verskeidenheid partikelgroottes tot gevolg het met ‘n beduidende hoeveelheid baie fyn materiaal. Navorsing het getoon dat hierdie baie fyn partikels uit die dacronsakkies gewas kan word tydens in sacco verteringstudies, met die gevolg dat die oplosbare en vinnig-verteerbare fraksie oorskat kan word. Die doel van die huidige studie was om die invloed van die verwydering van fyn partikels op die chemiese samestelling van ruvoermonsters te bepaal, asook die in vitro droë materiaal (DM) en neutraal-onoplosbaare vesel (NDF) verteerbaarheid daarvan. Monsters van lusernhooi, hawerhooi en koringstrooi, afkomstig van sewe verskillende lokaliteite in die Wes-Kaap, is deur 'n 2 mm sif gemaal en sub-monsters is deur ‘n reeks siwwe met poriegroottes van 150 μm, 125 μm of 106 μm gesif. Al die fraksies is geanaliseer vir DM, ruproteïen (RP), NDF, vet en as. Vier monsters van elke voertipe is op grond van die NDF-inhoud geselekteer vir in vitro-studies om die DM- en NDF- verteerbaarheid oor tyd te bepaal. Monsters is vir 0, 6, 24 of 48 uur geïnkubeer. Die resultate het getoon dat daar betekenisvolle variasie in chemiese samestelling binne ruvoertipes voorgekom het. Die verwydering van die fyn partikels het geen invloed die NDF-inhoud van lusernhooi en koringstrooi gehad nie. Wat hawerhooi betref, was die NDFinhoud van die gesifte monsters egter betekenisvol hoër in vergelyking met die ongesifte monsters. Die NDF inhoud was gemiddeld 635.9 vir die gesifte monsters en vir die ongesifte monsters 606.8. Sifting het geen invloed op die RP-inhoud van lusernhooi gehad nie, maar vir hawerhooi (61.4 gemiddeld) en koringstrooi (47.7 gemiddeld) was die RP-inhoud van die gesifte monsters betekenisvol laer as dié van die ongesifte monsters (65.7 vir hawerhooi en 55.4 vir koringstrooi). In vergelyking met die gesifte monsters, was die in vitro DM- en NDF-verteerbaarhede betekenisvol hoër vir die ongesifte monsters vir al drie ruvoertipes by alle inkubasietye. Hierdie resultate bevestig ‘n oorskatting van oplosbare en maklik verteerbare fraksies in gemaalde voermonsters. In vergelyking met die gesifte monsters, was die DMV-waardes van die ongesifte monsters by 0 ure (slegs gewas) gemiddeld 13.8% hoër vir lusernhooi, 27.3% vir hawerhooi en 44.7% vir koringstrooi. Na 48 h inkubasie was die oorskatting van lusern DMV vir die ongesifte monsters tussen 4.0% (vergeleke met die 106 μm sif) en 7.3% (vergeleke met 150 μm sif). Die oorskatting is oorgedra na al vier inkubasietye. Die resultate het geen noemenswaardige verskille tussen die fraksies (150 μm, 125 μm en 106 μm poriegroottes) van ‘n ruvoertipe by enige inkubasietyd aangedui nie. Die beraamde verteringstempo’s en verteerde fraksies was ook aansienlik hoër vir die ongesifte monsters in vergelyking met die gesifte monsters. Die gevolgtrekking is gemaak dat die verwydering van fyn partikels uit gemaalde ruvoermonsters die akkurate bepaling van in sacco verteerbaarheidswaardes verhoog.