Bulk Feed Research Articles

A Monte Carlo simulation model for vacuum membrane distillation process

Vacuum membrane distillation (VMD) process received a great deal of attention by many investigators because of its promising applications in many separation areas. Theoretical models published in literature describe vapor flux through membrane pores ignoring membrane pore space interconnectivity. Those models, in most cases are restricted to Knudsen type of flow and in a less extent to the combined Knudsen-viscous mechanism also described by the dusty gas model. This paper is one of a series of papers in which a Monte Carlo simulation model is developed to describe the vapor flux across the membrane in association with membrane distillation process. Unlike earlier paper in the series, this paper deals with VMD for the first time. The membrane pore space is described by a three-dimensional network of interconnected cylindrical pores, having a pore size distribution. The model can take into account all related mass transport mechanisms based on the kinetic theory of gases. When this model was applied to VMD process, it was assumed that water vapor is the only permeant, the VMD process is in an isothermal condition and there is no surface effect. The effects of the bulk feed temperature, downstream pressure and membrane pore size on the simulated VMD flux were discussed. The Monte Carlo model predictions were found to be in qualitative agreement with available experimental data when Knudsen type of flow was considered. When viscous type of flow is considered, the simulation results indicate that the higher feed solution temperature and higher pore size do not necessarily increase the vapor flux.

Effects of frequent out-of-feed events on growth performance of nursery and grow-finish pigs1

Two experiments were conducted to evaluate effects of out-of-feed events on nursery and grow-finish pig performance. An out-of-feed event is a period of time that pigs do not have access to feed as a result of late feed delivery or bridging in bulk bins, feed lines, or feeders. In these studies, we created an out-of-feed event by removing the feeders from pens or preventing access to the feeder. In Exp. 1, 190 pigs (initially 6.4 +/- 1.6 kg and 21 +/- 3 d of age) were used in a 35-d growth study. Treatments involved a 20-h feed withdrawal for 1, 2, or 3 randomly selected times or a control treatment where feeders were never withdrawn. Feeders were withdrawn on d 11 for pigs with 1 out-of-feed event, d 8 and 23 for pigs with 2 out-of-feed events, and d 9, 14, and 20 for pigs with 3 out-of-feed events. There was a treatment (P < 0.06) effect only during weeks in which an out-of-feed event occurred. Growth rate was lower (P < 0.05) for pigs with 1 out-of-feed event (d 11) compared with control in the d 8 to 14 period. During the same period, those pigs with the first of 2 (d 8) or 3 (d 9) out-of-feed events had intermediate ADG. In the d 15 to 21 period, only pigs with the second and third of 3 out-of-feed events (d 15 and 20) had lower growth performance compared with control pigs, whereas growth performance was similar to the control for those with 1 or 2 out-of-feed events. Pigs with 3 out-of-feed events had greater ADG and G:F (P < 0.05) compared with the other 3 treatments for the d 22 to 28 period. For the overall study (d 0 to 35), there were no differences (P > 0.86) in growth performance among pigs with 0, 1, 2, or 3 out-of-feed events. In Exp. 2, 479 pigs (initially 41.6 +/- 4 kg) were used in an 85-d growth study. Treatments involved feed withdrawal (20 h) weekly for the duration of the study; feed withdrawn weekly from d 45 to 85; or a control treatment where pigs had access to feed for the duration of the experiment. Feed withdrawal occurred on a randomly selected day with the exception of Saturday, Sunday, or a day before a weigh day (usually a Thursday every other week). From d 0 to 45, 46 to 85, and the overall d 0 to 85 period, there were no differences (P > 0.12) in ADG, ADFI, G:F, or average final BW among treatments. Results suggest that out-of-feed events of 20 h or less have no long-term detrimental effects on growth performance in nursery or grow-finish pigs.

Fuzzy control of the start-up phase of the food extrusion process

In this paper, a fuzzy control system is proposed to improve the start-up procedure of a food extrusion process generally based on the principle of the inverse relation between the screw speed and the torque. The proposed control structure consists of three control loops connected in a parallel configuration using multiple-input, single-output (MISO) Takagi–Sugeno–Kang (TSK) fuzzy controllers, which monitor the screw speed, the bulk feed rate and the water input rate in a highly coordinated way, such as the start-up is performed quickly and without screw blockage. The fuzzy control system was carried out through experiments on corn starch.

The effects of frequent out-of-feed events on growth performance of nursery, growing, and finishing pigs

An “out-of-feed” event is defined as a period of time that pigs do not have access to feed as a result of late feed delivery (feeders running empty) or bridging of bulk bins, feed lines, or feeders. To determine the effects of these out-of-feed events on pig growth performance, nursery and growing-finishing pig studies were conducted. In Exp. 1, 190 pigs (initial wt 14.0 lb) were allotted to one of four experimental treatments. Treatments included a 20-hour feed withdrawal for 1, 2, or 3 randomly selected times during the 35-d trial or a control treatment in which feeders were never withdrawn. Feeders were withdrawn on d 11 for pigs with 1 out-of-feed event, d 8 and 23 for pigs with 2 out-of-feed events, and d 9, 14, and 20 for pigs with 3 out-of-feed events. Throughout the study, the week in which an out-of-feed event occurred, ADG and ADFI were decreased (P<0.06), compared with those of control pigs. In some instances, if the out-of-feed event occurred early in the week, pig growth performance was intermediate to that of control pigs and the other pigs with an out-of-feed event later in the week. In the following week, however, pigs that had an outof- feed event in the previous week had improved ADG and F/G, compared with performance of the others. For the overall study, there were no differences in growth performance among pigs with 0, 1, 2, or 3 out-of-feed events. In Exp. 2, 479 growing-finishing pigs were used in an 85-d trial in a commercial finishing barn to determine the effects of frequency and timing of out-of-feed events on pig performance. Treatments included feed withdrawal (20 h) weekly for the duration of the trial, feed withdrawn weekly from d 45 to 85 (market wt), or a control treatment in which pigs had access to feed for the duration of the trial. Feed withdrawal occurred on a randomly selected day, with the exception of Saturday, Sunday, or a day before a weigh day (usually a Wednesday every other week). There were no differences (P>0.13) in growth performance throughout the 85-d trial. With weekly out-of-feed events in the finishing phase, there is a possibility that pigs may quickly learn to adjust their feed intake for the out-of-feed event. In this study, however, results suggest that out-of-feed events (20 h or less) will have no long-term effects on growth performance in nursery or

Adsorption of glutamicum onto polysulphone membrane

A systematic study on the influence of solution chemistry (pH, ionic strength) and bulk cell concentration on static and dynamic glutamicum adsorption onto polysulphone membrane, cell adsorption isotherms, and the rate of adsorption was performed. The interaction between cells and membrane surface in the absence of salt was dominated by electrostatic interaction due to the charges on the cell surface. The maximum adsorption occurred at isoelectric point (IEP) of cells, suggesting complementary electrostatically driven adsorption. At pH values below the IEP, adsorption increased as pH increased, but above the IEP, adsorption decreased as pH increased. Increased salt concentration reduces electrostatic repulsion between like-charged material (increasing adsorption) and decreases electrostatic attraction between oppositely charged material (decreased adsorption). Isotherms were performed to determine equilibrium adsorption behavior. Adsorption isotherms follow Langmuir laws, the parameters of which were determined. By taking into account electrostatic interactions, it has been possible to explain the evolution in the adsorption isotherms of the cell on the membrane surface with the solution chemical conditions. Rate of adsorption was determined by measuring adsorbed mass as a function of time at different pH values, ionic strength, and bulk feed concentration. In order to determine the effect of convective flow and electrostatic interactions on the cell adsorption behavior, static and dynamic adsorption were compared. Although convective forces tend to increase the amount of cell accumulated near the membrane surface, electrostatic interactions played a stronger role, as evident in the irreversible adsorption results for the static and dynamic cases. Controlling electrostatic interactions could reduce adsorption of cells onto the membrane, consequently reducing long-term membrane fouling.

Retrospective characterization of Newcastle Disease Virus Antrim '73 in relation to other epidemics, past and present.

In November 1973 Newcastle disease suddenly appeared in Northern Ireland, where the viscerotropic disease had not been seen in 3 1/2 years and the two Irelands had been regarded as largely disease free for 30 years. It was successfully controlled with only 36 confirmed affected layer flocks, plus 10 more slaughtered as 'dangerous contacts'. Contemporary investigations failed to reveal the source of the Irish epidemic. Using archival virus samples from most of the affected flocks, RT PCR was conducted with primers selected for all six NDV genes. Phylogenetic analyses of three genes, HN, M and F, confirmed vaccine as the cause of one of the outbreaks. The other six samples were identical and closely related to previous outbreaks in the United States and western Europe initiated by infected imported Latin American parrots. The probable cause of the epidemic followed from the importation from The Netherlands of bulk feed grains contaminated with infected pigeon faeces.

Experimental studies in the dead-end ultrafiltration of dextran: analysis of concentration polarization

Considerable theoretical and experimental work has been published to explain the cause of flux decline in the ultrafiltration (UF) of dextran. However, an experimental determination of resistance contributions due to polarization to the overall filtration resistance has not been addressed. Also, the effects of feed concentration and applied pressure on membrane concentration and boundary layer thickness and unsteady-state flux response to a step change in trans-membrane pressure have not been reported. This work reports experimental results of the ultrafiltration of dextran with a fully retentive membrane along with a procedure to determine the contributions of various resistances to filtration. It was observed that the ultrafiltration of dextran was osmotically limited in our work. The contribution of polarization resistance was found to be dependent on applied pressures and initial bulk feed concentrations whereas the boundary layer thickness of polarization was affected by feed concentration alone.

Evaluation of herd sampling for Salmonella isolation on midwest and northeast US dairy farms

Epidemiologic investigations of Salmonella infections in dairy cattle often rely on testing fecal samples from individual animals or samples from other farm sources to determine herd infection status. The objectives of this project were to evaluate the effect of sampling frequency on Salmonella isolation and to compare Salmonella isolation and serogroup classification among sample sources on 12 US dairy farms sampled weekly for 7–8 weeks. Three herds per state were enrolled from Michigan, Minnesota, New York and Wisconsin based upon predefined herd-size criteria. Weekly samples were obtained from cattle, bulk tank milk, milk filters, water and feed sources and environmental sites. Samples were submitted to a central laboratory for isolation of Salmonella using standard laboratory procedures. The herd average number of cattle fecal samples collected ranged from 26 to 58 per week. Salmonella was isolated from 9.3% of 4049 fecal samples collected from cattle and 12.9% of 811 samples from other sources. Serogroup C1 was found in more than half of the samples and multiple serogroups were identified among isolates from the same samples and farms. The percentage of herd visits with at least one Salmonella isolate from cattle fecal samples increased with overall herd prevalence of fecal shedding. Only the three herds with an average fecal shedding prevalence of more than 15% had over 85% of weekly visits with at least one positive fecal sample. The prevalence of fecal shedding from different groups of cattle varied widely among herds showing that herds with infected cattle may be classified incorrectly if only one age group is tested. Testing environmental sample sources was more efficient for identifying infected premises than using individual cattle fecal samples.

Economic simulation modeling of reprocessing alternatives for corn masa byproducts

Increasing production of corn masa for tortillas, chips, and related snack foods is resulting in large quantities of organic residuals requiring environmentally sound management. These byproduct streams appear suitable for use as livestock feed material, thus eliminating landfilling costs. Possibilities for developing livestock feed include direct shipping to livestock feeding facilities, blending prior to shipping, extrusion processing, pellet mill processing, and dehydration. To assess the viability of these options for reprocessing masa byproducts as livestock feed materials, an economic model was developed and applied to each of these alternatives. Through a series of simulation runs with this model, it was determined that direct shipping was by far the most inexpensive means of recycling masa processing residuals (10–57 $/Mg). Other alternatives examined in increasing order of costs included blending prior to shipping, extrusion, pellet mill processing (3–15, 5–18, and 4–18 times greater than direct shipping, respectively), while dehydration was clearly cost-prohibitive (33–81 times greater). Bagged feed was slightly more expensive to produce than bulk feed (1.1 times greater), and reprocessing costs increased as delivery distance increased, due to increased labor, equipment, and fuel costs, but decreased as byproduct generation rate increased, due to the development of the economies of scale. Alternately, based on a tipping fee of 50 $/Mg, the total estimated cost to landfill ranged from 65 to 112 $/Mg. Based on this cost analysis, direct shipping and feeding to livestock is the recycling option of choice for masa processing byproducts. Although specific details of process configurations and associated costs will vary, similar results are likely for other high moisture food processing residuals destined for utilization as livestock feed or components thereof.

Extractive Separation of Zinc from Oxidic Solid Bulk Feed

Dust from steel processing is a heterogeneous, multicomponent mixture of metal oxides of zinc, lead, and iron, and several trace elements such as cadmium, nickel, cobalt, and copper. The hydrometallurgical separation and downstream processing of nonferrous metals from dust of electric arc furnaces (EAF) was investigated. Solid–liquid extraction was carried out with aqueous acetic acid. In a next step, isolation of metals from the solvent phase and solvent recovery was tested. Besides isolation of intermediates, the electrochemical deposition of the metallic substances was investigated. Electrochemical deposition of zinc from aqueous feed needs high-grade purity of the feed electrolyte due to sensitivity of the hydrogen overvoltage. The effect of nickel on the break down of the hydrogen overvoltage is a major concern in electrochemical deposition of zinc from sulfate-based feed. Nickel contamination has to be kept at minimum concentration level. In contrast to sulfate-based electrolytes, the hydrogen overvoltage in acetic acid can be kept high, even when electrolyzing the extract phase without pretreatment of the extract phase.

‘Flash pasteurization’ of contaminated streams using a direct contact gas-fired water heater

A commercial direct contact gas-fired water heater was modified for in-lab evaluation of microbial reduction and temperature consistency at various water flow rates. The water heater was modified so that a contaminated input stream could be treated using 50-gal (189.3-l) bulk feed tanks. A final reservoir tank was bypassed using six sampling ports placed in pairs along three locations in the vertical heating column with which to test the efficacy of a single pass at different positions in the heating zone. Temperature probes were utilized to follow water temperature at 8, 10, and 12 gal min −1 (30.3, 37.9, and 45.4 l min −1). When using inoculated water streams, we obtained 4–7 log 10 cycle reductions of various micro-organisms tested suggesting that this may have potential use in situations where water recycling is of interest in food processing environments.

Application of fuzzy control to start-up of twin screw extruder

For the improvement of existing control method which used a simple method of comparison of torque with main screw rpm in start-up of extruder, the fuzzy control algorithm was applied based on the expert principles of extrusion. The first step of the start-up in extrusion of corn grits was that water input rate is maintained at three times higher than an operating set point. Then, as bulk feed rate increases to its set point stepwise, the main screw rpm is controlled by fuzzy reasoning to prevent a blockage phenomena. In the fuzzy reasoning, input variables were torque% and main screw rpm ( n)%, and the main screw rpm was estimated to keep the main screw rpm% at higher level than the torque% in excess of about 18% and 26%, respectively. After the bulk feed rate reaches at its set point, the water input rate sequentially decreases back to its set point, during which the main screw rpm is also controlled by fuzzy reasoning in the same manner. Finally, the main screw rpm is also adjusted to its set point after the water input rate reaches at its set point. To manipulate the temperatures of the barrel and the die, PID algorithm for heating and on/off control for cooling were used. Consequently, the successful automation was achieved reproducibly without blockage.

Beer clarification by cross-flow microfiltration — effect of surface hydrodynamics and reversed membrane morphology

The separation characteristics in beer microfiltration is based on a fine balanced retention of particles (yeast cells, debris, and coagulated protein–polyphenol complexes) and transmission of dissolved macromolecules (proteins, carbohydrates, colour and flavour compounds) to achieve beer clarification whilst preserving the ‘wholesome’ quality of the filtered beer. The required porous transmission of large amount of macromolecular species led to an unavoidable and complex membrane fouling in terms of fouling constituents, formation and structure, which are the major obstacles to obtaining an economically viable flux and consistent permeate quality. This paper describes an experimental study of beer clarification by cross-flow microfiltration with the aim of increasing a low permeation rate to an economically acceptable level by employing and optimising some flux-enhancement techniques. These include, (i) modification of bulk feed flow hydrodynamic conditions by superimposing a helical-flow pattern and a two-way reversing flow pulsation; (ii) application of an automated high frequency backflush programme with controllable frequency and backpulse strength; and (iii) filtration at reversed membrane morphology to allow the open substructure of the asymmetric ceramic membrane (Ceramem) to face the feed flow and thereby a reversed transmembrane pressure (TMP) gradient. The increased bulk-flow turbulence generated by flow pulsation was found disappointingly ineffective, and the superimposed helical flow pattern was only marginally better. The backflush technique was a more effective method and application of an optimised backflush programme at normal cross-flow conditions achieved 410% flux increase. The most dramatic flux improvement was achieved when the filtration was carried out with high frequency backflush at a reversed membrane mounting configuration. The author attributed the large flux increase to a mechanism of reversible ‘particle holding and releasing’ by the open sub-structure of the membrane under the influence of high frequency backflush, which greatly reduced fouling in the critical membrane phase.

Non-destructive automated sampling of mycotoxins in bulk food and feed — A new tool for required harmonization

Mycotoxins contamination is highly non-uniformly distributed as is well recog-nized by the EC, by not only setting legal limits in a series of commodities, but also schedule a sampling plan that takes this heterogeneity into account. In practice however, it turns out that it is very difficult to carry out this sampling plan in a harmonised way. Applying the sampling plan to a container filled with pallets of bags (i.e. with nuts or coffee beans) varies from very laborious to almost impossible. The presented non-destructive automated method to sample bulk food could help to overcome these practical problems and to enforcing of EC directives. It is derived from a tested and approved technology for detection of illicit substances in security applications. It has capability to collect and iden-tify ultra trace contaminants, i.e. from a fingerprint of chemical substance in a bulk of goods, a cargo pallet load (~ 1000 kg) with boxes and commodities.The technology, patented for explosives detection, uses physical and chemistry processes for excitation and remote rapid enhanced release of contaminant residues, vapours and particulate, of the inner/outer surfaces of inspected bulk and collect them on selective probes. The process is automated, takes only 10 minutes, is non-destructive and the bulk itself remains unharmed. The system design is based on applicable international regulations for shipped cargo hand-ling and transportation by road, sea and air. After this process the pallet can be loaded on a truck, ship or plane. Analysis can be carried out before the cargo leaves the place of shipping. The potent application of this technology for myco-toxins detection, has been demonstrated by preliminary feasibility experiments. Aflatoxins were detected in pistachios and ochratoxin A in green coffee beans bulk. Both commodities were naturally contaminated, priory found and confirm-ed by common methods as used at routine inspections. Once the contaminants are extracted from a bulk shipment, an appropriate existing analytical method, i.e. a CEN method, can be used to measure the mycotoxins.The system, routinely in use for explosives detection, was able to screen bulk food and feed for mycotoxins, through non-destructive automated sampling of a whole batch/lot/sublot of commodities. The opportunity to sample a whole bulk would provide more effective tools for inspection at seaports, production facili-ties and distri-bution points. It will advance the current process of myco-toxins check because: (i) Checks will be automated and harmonized, (ii) Checks will be non-destructive, (iii) Checks will be faster and allow a greater amount of bulk commodities to be inspected and (iv) The ability to check, with automated equipment, larger portions of lots of a shipment will increase the probability to detect the heterogeneous mycotoxins contamination in bulk foods. The poster provides some results of feasibility experiments indicating the capability of this technology for inspection of commodities bulks for the detection of mycotoxins, at legal limits, in naturally contaminated food.

Unsteady state flux response: a method to determine the nature of the solute and gel layer in membrane filtration

The unsteady-state permeate flux response to a step change in transmembrane pressure is shown to result in unique flux–pressure profiles for the three types of solutes common in membrane ultrafiltration (UF): (a) solutes which exert an osmotic pressure but do not form a ‘gel’; (b) solutes which do not exert an osmotic pressure but form a ‘gel’ and (c) solutes which exert an osmotic pressure and also form a ‘gel’. It is also shown that for stirred cell UF, changes in the bulk feed solution properties (concentration, volume) are negligible on the time scale needed to attain a stable permeate flux. Unsteady-state permeate flux measurements could therefore be made at short filtration times so that the results would not be masked by changes in bulk properties.

Protein and humic acid adsorption onto hydrophilic membrane surfaces: effects of pH and ionic strength

The effects of solution chemistry on the rate and extent of adsorption of a protein (BSA) and humic acid (Suwannee River humic acid) onto a regenerated cellulose ultrafiltration membrane were studied. Isotherms were performed to determine equilibrium adsorption behavior. Rate of adsorption was determined by measuring adsorbed mass as a function of time. Experiments were performed at differing conditions of pH, ionic strength and bulk feed concentration. For both compounds, adsorption was higher at lower pH values. Adsorption decreased as pH increased. Increased salt concentration reduces electrostatic repulsion between like-charged material (increasing adsorption) and decreases electrostatic attraction between oppositely charged material (decreasing adsorption). These interactions between the adsorbing material and the membrane surface affect the adsorption rate, which was evaluated using two mechanistic models. The modeling was designed to determine the governing mechanism in adsorption onto the hydrophilic membrane surface. These models confirmed that, under conditions of this study, the transport rate to the membrane surface is fast compared to the reactions at the membrane surface, thus electrostatic interactions are very important in determining adsorption of this material onto the membrane. Controlling electrostatic interactions could reduce adsorption of protein and humic material onto the membrane, consequently reducing long-term membrane fouling. Parameters from the models developed in this study can be used to determine the “fouling potential” of a given feed stream.

Simulation of Solute Diffusion through Porous Media

Simulation of solute diffusion through porous media (membrane) was carried out by a random walk procedure. The porous media used were three kinds of two-dimensional square networks of channels with almost the same average pore diameters and porosities, but with different pore size distributions. In the simulation the partition equilibrium of solute between the bulk feed phase and the membrane phase was established, and the apparent permeability in the steady state was evaluated. First, only the steric interaction between the solute and the pore wall was considered. In spite of the similar average pore diameters and porosities of the networks, the apparent permeability and selectivity were dependent on the kinds of networks. The network with more small pores showed the smaller permeability and the higher selectivity. When the diameter of solute which can be actually transported is fairly smaller than the average pore diameter, the network with broad pore distribution and with more small pores is found to be useful for obtaining higher selectivity. Next, the electrostatic and dispersion (van der Waals) interactions between the solute and the pore wall were introduced in this simulation. By such long-range interactions the selectivity increased while the apparent permeability decreased. This result showed that the introduction of the repulsive electrostatic interaction between membrane and solute is one useful method for enhancing the selectivity. The effects of the kinds of networks on transport properties in the presence of long-range interactions were similar to those in the absence of such interactions.

Mechanistic interpretation of solute permeation through a fully aromatic polyamide reverse osmosis membrane

The objective of this study was to assess the contribution of various mass transfer steps (concentration polarization, partitioning, and diffusive and convective transport) toward overall permeation of major solute sodium chloride (NaCl), and trace component nitrobenzene across the fully aromatic polyamide FT-30 ® membrane. Experiments were performed with a closed-loop flat-leaf reverse osmosis apparatus. Feed solutions tested contained 2000, 4000 or 6000 mg/l NaCl, and 10 mg/l nitrobenzene at pH 6 and 25°C. Solute rejection ranged from 95 to 99.2% for NaCl and from 20 to 60% for nitrobenzene. The overall permeation of both NaCl and nitrobenzene appeared to be primarily by partitioning at water/membrane interfaces and diffusion across the membrane phase. Convection accounting for less than 25 and 0.4% of the overall NaCl and nitrobenzene permeation, respectively, appeared to be the result of a small leakage of feed solution through membrane imperfections estimated at 0.14% of the overall product water flux. Solute permeation was affected by concentration polarization taking place primarily within a fouling film of corrosion products. Concentration polarization levels corresponded to solute concentrations next to the feed water/membrane interface ranging from 5 to 70% (NaCl), and from 8 to 140% (nitrobenzene) higher than bulk feed concentrations.

SOURCES OF VARIANCE IN FEED DISTRIBUTION SYSTEMS

Geometric mean diameter (GMD), by mass, and by protein, calcium and phosphorus concentrations of mashpoultry feed were measured throughout a state-of-the-art feed distribution system. Data was taken from the post-mixermash to the point of consumption. The change in GMD of the feed particles was determined for each of the four primarycomponents of the system: (1) post-mixer and mill tank; (2) transport bulk feed truck; (3) four on-farm storage bins; and(4) two in-house feed distribution systems. The protein, calcium and phosphorus concentrations were measured and thevariances in GMD and nutrient contents were calculated for the bins and the in-house distribution systems. The resultsdefined the effects of various bin device configurations such as an electric hopper unloading aid (EHUA), a bin filldeflection device (BFDD), the combination of both devices and no devices on particle size and nutrient variance. Inhousedistribution was via a drag auger or a drag chain.<br><br>GMD was not significantly changed (p<0.05) by the post-mixer and mill tank, transport bulk feed truck, or the four onfarmstorage bin treatments. However, GMD significantly decreased (p<0.05) as a result of the combination of the postmixerand mill tank, transport bulk feed truck and the on-farm storage; and as a result of the in-house distributionsystems. The bin devices had no significant (p<0.05) effects on GMD, GMD variance, nutrient variance, or day-to-dayvariances of the feed introduced to the in-house distribution system.<br><br>Residual feed remaining in the feeder troughs had significant effects (p<0.05) on the change in GMD and samplenutrient concentrations from the first sampling location inside both production houses (prior to entering the drag augeror drag chain) and the first (of five) sampling locations in each in-house distribution system. In addition, there weresignificant (p<0.05) spatial differences only within the drag chain system; however, there were no significant (p<0.05)temporal differences between systems.

Membrane distillation. II. Direct contact MD

Pure water direct contact membrane distillation (DCMD) experiments were used to measure the permeability parameter associated with the molecular diffusion in membrane distillation (MD). The fluxes given by a recently reported MD model, which is based on the dusty-gas model of gas transport through porous media, showed good agreement with the experimental results over the entire range of feed temperatures studied. The model was also capable of predicting flux as a function of the difference between bulk feed and permeate temperatures for the limiting case in which only molecular diffusion contributes to flow. The DCMD experiments were performed in this work with a new laboratory-scale module that does not require a support for flat-sheet membranes. The resulting DCMD fluxes were two to three times higher than those reported in the literature for either DCMD or reverse osmosis. The MD model was also used to predict the performance of DCMD desalination, and the results were compared to those of reverse osmosis, in terms of both water production rates and NaCl rejection.