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Flocculant Zetag-47 (polyacrylamide-based) in dose 1/50 LD50 increased the number of metaphases in rat marrow. These results were used in hygienic standardization of this substance.
New flocculants SMMA-Na and PMAK-Na slightly accumulate in animal organism and are low toxic (4th class of danger). These substances influence water taste and water self-purification.
Alcoholic fermentation of cheese whey permeate was investigated using a recombinant flocculating Saccharomyces cerevisiae, expressing the LAC4 (coding for beta-galactosidase) and LAC12 (coding for lactose permease) genes of Kluyveromyces marxianus enabling for lactose metabolization. Data on yeast fermentation and growth on cheese whey permeate from a Portuguese dairy industry is presented. For cheese whey permeate having a lactose concentration of 50 gL(-1), total lactose consumption was observed with a conversion yield of ethanol close to the expected theoretical value. Using a continuously operating 5.5-L bioreactor, ethanol productivity near 10 g L(-1) h(-1) (corresponding to 0.45 h(-1) dilution rate) was obtained, which raises new perspectives for the economic feasibility of whey alcoholic fermentation. The use of 2-times concentrated cheese whey permeate, corresponding to 100 gL(-1) of lactose concentration, was also considered allowing for obtaining a fermentation product with 5% (w/v) alcohol.
Both intrinsic and observed kinetic investigations for those ethanol fermentations using self-flocculated yeast strains have been hindered by the lack of real online monitoring techniques and proper characterization methods for the flocs. An optical detecting technique, the focused beam reflectance measurement probe developed by Lasentec (Redmond, WA) was inserted into a fermentor to monitor the floc chord length distributions. Using a simulating system composed of the floc-buffer suspensions, the total floc chord length counts per second were directly correlated with the floc biomass concentrations so that the floc biomass concentrations can be in situ detected. Furthermore, a characterization method of the flocs was established by properly weighted treatments of the detected floc chord length distributions. When a real yeast floc ethanol fermentation system was detected during its intrinsic kinetic investigations in which the floc size needed to be controlled at a level of micrometer scale to eliminate inner mass transfer limitations, it was found and validated that CO(2) produced during fermentation exerted significant disturbances. By applying 1/length-weighted treatment, these disturbances were effectively overcome.
A novel continuously stirred anaerobic bioreactor (CSABR) seeded with silicone-immobilized sludge was developed for high-rate fermentative H2 production using sucrose as the limiting substrate. The CSABR system was operated at a hydraulic retention time (HRT) of 0.5-6 h and an influent sucrose concentration of 10-40 g COD/L. With a high feeding sucrose concentration (i.e., 30-40 g COD/L) and a short HRT (0.5 h), the CSABR reactor produced H2 more efficiently with the highest volumetric rate (VH2) of 15 L/h/L (i.e., 14.7 mol/d/L) and an optimal yield of ca. 3.5 mol H2/mol sucrose. The maximum VH2 value obtained from this work is much higher than any other VH2 values ever documented. Formation of self-flocculated granular sludge occurred during operation at a short HRT. The granule formation is thought to play a pivotal role in the dramatic enhancement of H2 production rate, because it led to more efficient biomass retention. A high biomass concentration of up to 35.4 g VSS/L was achieved even though the reactor was operated at an extremely low HRT (i.e., 0.5 h). In addition to gaining high biomass concentrations, formation of granular sludge also triggered a transition in bacterial community structure, resulting in a nearly twofold increase in the specific H2 production rate. According to denatured-gradient-gel-electrophoresis analysis, operations at a progressively decreasing HRT resulted in a decrease in bacterial population diversity. The culture with the best H2 production performance (at HRT = 0.5 h and sucrose concentration = 30 g COD/L) was eventually dominated by a presumably excellent H2-producing bacterial species identified as Clostridium pasteurianum.
The effect of impeller type and shear rate on the evolution of floc size and structure during shear-induced flocculation of polystyrene particles with aluminum sulfate is investigated by image analysis. One radial flow (six-blade Rushton turbine) and two axial flow (three-blade fluid foil, four-blade 45° pitch) impeller configurations are examined. The steady state average floc size is shown to depend on the frequency of recirculation to the impeller zone and its characteristic velocity gradient. The concepts of fractal geometry are used to characterize the floc structure. For all impellers, the two-dimensional floc fractal dimension, Dpf, increases during floc growth, indicating formation of more open structures. Later on, Dpf levels off at a steady state value as breakage becomes significant and the floc size distribution approaches steady state. The shear rate does not affect the steady state Dpf of the flocs within experimental uncertainty.
Using experimental data of AgI sol and poly(2-methyl-5-vinylpyridine) chloride, we show that there is good agreement between the developed mathematical model of suspension flocculation by polyelectrolytes and the experimental data. The rate constants of bridging and nonbridging aggregation of particles and of floc breakup, as well as their ratios, have been determined. It has been shown that the role of the nonbridging mechanism, as compared with that of the bridging one, diminishes when molecular mass of polyelectrolyte increases from 1.4 x 10(5) to 9.3 x 10(5).
The aim of this paper is to show that the ESA (electrokinetic sonic amplitude) technique can be used to study the flocculation between cationic polyelectrolytes and negatively charged silica particles. The ESA signal was measured when cationic polyacrylamide (CPAM) or cationic polyamine (POL) was mixed with silica particles. The dynamic mobility of the formed flocs was calculated from the corrected ESA signal. The amount of nonadsorbed polyelectrolyte was determined by viscosity. The floc sediment volume was also measured. It was found that the polyacrylamide molecule was more efficient than the polyamine molecule in neutralizing the charges on the silica particles due to the longer CPAM molecules and the larger distance between the CPAM charges which was in better accordance with the distance between the silica charges compared to POL. Copyright 1999 Academic Press.
The kinetics of the adsorption of diethylene-triaminomethylated polyacrylamide on kaolin dispersed in water has been investigated. An influence of the flocculation of kaolin dispersion on polymer adsorption has been found. The kinetics of particle aggregation under the influence of dissolved polymer has been studied. Polymer adsorption and particle aggregation proceed simultaneously, accompanied by a steady decrease in the amount of adsorbed polymer per unit mass of kaolin. A mathematical model of the adsorption process, consistent with the experimental data, is described. The rate constants and their ratios have been determined. Copyright 1999 Academic Press.
The feasibility of a high-gradient magnetic separation process, utilizing magnetite as the energizable element in lieu of stainless steel wool, is evaluated by means of an equilibrium, two-particle, magnetic hetero-flocculation model. The model calculates the net force, defined as the sum of the magnetic, electrostatic, and van der Waals forces, exerted on a paramagnetic nanoparticle that is in the proximity of a fixed magnetite particle. Since the nanoparticle-magnetite system is assumed to be in direct contact with the moving fluid, the influence of the hydrodynamic force on the magnetic attractive force between the two particles is also explored. This model clearly reveals the ranges and conditions over which each of these various forces contributes to the net force relative to Brownian (thermal) motion. The model also reveals the feasibility of using magnetite particles instead of stainless steel as the energizable element for high-gradient magnetic separation. Important variables investigated include the size and surface charge of the particles, the magnetic field, the flow velocity, the electrolyte concentration, and the magnetic susceptibility of the nanoparticle. Copyright 2000 Academic Press.
Discrimination between different rival models for describing the inhibitory effect of ethanol both on yeast growth and on fermentation was studied for a continuous process of alcoholic fermentation in a tower reactor with recycling of flocculating cells. Models tested include linear, parabolic, hyperbolic, exponential, and generalized nonlinear power-law types. The best expressions were identified under the criteria that all the kinetic parameters should assume acceptable values in a feasible range and should result in the best fit of the experimental data. The kinetic parameters were estimated from steady-state data of several sugar concentrations in feeding stream (S0 = 160, 170, 180, 190, 200 g/L), constant dilution rate (D = 0.2 h-1), recycle ratio (alpha = 13.6), and temperature (T = 30 degrees C). The best model for the yeast growth was of power-law type, whereas for the product formation the best model was of linear type. These models were able to reproduce the trends of the process variables satisfactorily.
Variations in residual sugar composition have been observed during Jerusalem artichoke extract fermentations by using Saccharomyces diastaticus NCYC 625, a flocculating yeast strain. In batch cultures, these differences were due to the inulin polymer size distribution of the extracts: measurements of enzymatic activities on different polymerized substrates have shown that the hydrolysis and fermentation yield decreased when the fructose/glucose ratio of the extract increased. Inulin hydrolysis appeared to be the limiting factor of the fermentation rate. A comparison of continuous and batch cultures with the same extract showed that fermentability differences were related to the structure and size of the yeast flocs. This led to an hydrolysis selectivity of the inulin polymers according to their size: the chemostat culture in which the floc average size was larger gave longer chained residual sugars.
Mutagenic activity in Salmonella typhimurium strains TA 100, TA 98 and TA 97 has been determined for humic water and alum flocculated humic water, treated with the alternative disinfectants chlorine, ozone, chlorine dioxide, ozone/chlorine and chlorine/chlorine dioxide. The most pronounced activity was found for chlorine treated water tested on strain TA 100 without metabolic activation (S9 mix). Ozone treatment prior to chlorination did not alter the activity, while treatment with chlorine in combination with chlorine dioxide reduced the activity to a level somewhat over the background. No mutagenic response was detected in waters treated with ozone or chlorine dioxide alone. In presence of S9 mix all water extracts studied were non-mutagenic.
The chymosin-induced flocculation of casein micelles of bovine milk can be explained and calculated in terms of three relationships, which are (i) the action of chymosin upon the kappa-casein of the micelles; (ii) the probability that a micelle, with a given proportion of its kappa-casein destroyed, will aggregate, and (iii) the aggregation of micelles by a Smoluchowski mechanism. Details of the calculations are given, and the theory is shown to be in good agreement with experimental observations of the dependence of the clotting time with variations in enzyme and substrate concentrations.
Weakly flocculated, thixotropic suspensions have been investigated by means of fast stress jump experiments. With a suitable procedure, reliable stress relaxation data could be collected starting 20 ms after cessation of flow. This technique has been used to determine the elastic and hydrodynamic contributions to the shear stress. Steady state as well as transient flows have been studied for suspensions containing either fumed silica or carbon black particles in a Newtonian medium. In both systems, the elastic stress totally dominates the response at low shear rates and consequently also the apparent yield stress. This stress contribution becomes negligibly small at high shear rates. The hydrodynamic contribution to the viscosity has finite limits at both the low and high shear rate ends. The data are relevant for testing rheological models. As an illustration, it is shown that the data agree qualitatively with the model proposed by Potanin et al. (J. Chem. Phys. 102 (14) (1995) 5845-5853).
Weakly flocculated aqueous anatase suspensions were prepared in situ by hydrothermally treating amorphous titania particles peptized with different amounts of tetraethylammonium hydroxide (TENOH). The simultaneous formation of hydrous TiO2 polyanions in the presence of OH- and tetraethylammonium cations are two essential conditions for the peptization process to occur. The absence of either of these conditions will cause reprecipitation. Transmission electron microscopy (TEM) revealed that the morphology of the particles formed at low TENOH concentrations consisted of well-dispersed anatase crystals, changing to asterisk-like structured particles with increasing concentrations of TENOH. Because of the extremely high absolute zeta potential (over -70 mV in all the samples) and ionic strength values, nontouching particle networks may be formed in situ in the mother solution in all samples, as predicted by DLVO theory. A trend to coagulation was observed in the suspensions with increasing concentrations of TENOH due to a more pronounced secondary minimum in the particle pair potential curves. Assuming the particles remained in the secondary minimum throughout the hydrothermal treatment may lead to the formation of the asterisk-like hard agglomerates. This may arise from the condensation of the -OH-rich TiO2 particles or from the deposition of material in the interparticle gap during the particle growth process. The green packing density of slip-cast bodies from a suspension containing 20 wt% solids was around 46%.
This study investigated the impact of turbulent heterogeneity in a flocculation reactor on particle aggregation and breakup. In particular, the influence of average characteristic velocity gradient (G), particle concentration, and coagulation mechanism (sweep floc vs charge neutralization) on the floc growth, steady-state size, and variance was analyzed. Experiments were performed in a bench-scale reactor with a low-shear axial-flow impeller using a photometric dispersion analyzer (PDA). Results indicated that as G increased, floc growth increased while the mean size and variance in the floc size distribution decreased. In addition, floc growth, mean size, and variance increased with increasing primary particle concentration and when the coagulation mechanism was switched from charge neutralization to sweep floc. Lastly, floc growth, mean size, and variance were found to vary spatially in the reactor at low G values with larger floc size and growth rate in the bulk region and a larger variance in the impeller discharge region.
Diffusing-wave spectroscopy (DWS) has been used to study the stability of sodium-caseinate-stabilized emulsions. The emulsions underwent creaming as a result of depletion flocculation when excess sodium caseinate was added. The creaming process was monitored over a 3-h period and each autocorrelation function was collected for 2 min to ensure adequate signal-to-noise ratio. The temporal variation of average particle size times the coefficient of viscosity of the continuous phase was derived from the backscattering measurements, and the variation of the scattering mean free path length with time was found from the backscattering and transmission measurements. It was confirmed that the creaming process was delayed at high oil concentrations, presumably due to the formation of oil droplet networks.