Increasing Agitation Rate Research Articles

Expansion of umbilical cord blood derived haematopoietic stem cells under constant dynamic conditions

Background & Aim Umbilical cord blood (UCB) offers a source of haematopoietic stem and progenitor cells (HSPCs) with a proven clinical rack record. However, one major drawback is the relatively low number of HSPCs within one unit, limiting its clinical potential. Due to this, strategies to expand UCB-HSPCs have been developed and involve the use of additional molecules to support expansion, such as SR-1, UM-171, immobilised Notch ligand Delta-like 1 and nicotinamide. As these potential therapeutics reach late stage clinical trials, considerations for manufacturing in order to meet clinical demand are required. In this study we have investigated the impact that constant shaking, at differing magnitudes, during the expansion of UBC-HSPCs has on the overall total nucleated cell expansion, Lin-CD34+ and Lin-CD34+CD38-CD90+ cell expansion, cell viability and colony forming unit (CFU) potential. Methods, Results & Conclusion Method UCB CD34+ cells were seeded at 1 × 104 cells/mL in IMDM+10% FBS supplemented with 100ng/mL SCF, TPO and Flt3-L and 20ng/mL IL-6 and maintained under static (T-flasks) or shaken (125mL Erlenmeyer flasks, with a 10mm shaking diameter) conditions for nine days. Daily cell counts were completed and immunophenotyping, apoptosis detection and CFU potential were performed on day 0 and day 9. Results UCB-HSPCs were successfully expanded for all donors under both conditions, the final viable cell densities achieved were significantly higher in the shaken conditions compared to the static controls, in addition the final viable cell densities increased with an increasing agitation rate, 3.1±0.3 × 104, 6.2±0.1 × 104, 10.2±0.2 × 104 and 12.4±0.4 × 104 cells mL−1 (mean value ± SD) for static, 30rpm, 70rpm and 110rpm respectively. Immunophenotyping of the expanded cells demonstrated an increase in both Lin-CD34+ HSPCs and Lin-CD34+CD38-CD90+ haematopoietic stem cells, this increase was significantly higher in the shaken conditions compared to the static controls. Finally, the fold change in CFU potential was significantly higher for both granulocyte, monocyte colonies and granulocyte, erythrocyte, monocyte, megakaryocyte colonies compared to static controls and with an increasing agitation rate. Conclusion In this study we have shown that expansion of UCB-HSPCs under shaken conditions improves the overall cellular yield that can be achieved, maintains both Lin-CD34+ and the more primitive Lin-CD34+CD38-CD90+ cell populations and enhances CFU potential.

Effect of zoning on mixing and mass transfer in dual agitated gassed vessels

Gas–liquid multi-phase processes are widely used for processes that require reactions. To increase productivity in these reactions one potential method is to increase the gas flow rate into the vessel. This means that it is important to understand how these reactors perform at high gas flow rates, which can create problems such as zones within the vessel. This paper investigates the mixing performance and the mass transfer in dual agitated systems at high gas flow rates. Two configurations have been compared a 6 blade disk turbine (Rushton turbine) below either a 6 Mixed flow Up-pumping or down-pumping agitator. Zoning has been identified by Electrical Resistance Tomography which affects the mixing time within the vessel, with increasing agitation rate potentially increasing the mixing times at high gas flow rates. At these high gas flow rates the zoning also affects the mass transfer meaning that it is not constant within the whole vessel. However, dividing the vessel into the key zones allows the mass transfer rate to be predicted with a single equation.

Alkaline cyanide leaching of refractory gold flotation concentrates and bio-oxidised products: The effect of process variables

The less predictive nature of alkaline cyanide leaching, owing to its complex functional relationships, render most processing plants unproductive and subsequent shutdown. In this work, the mechanism and kinetics of alkaline cyanide leaching of the two refractory flotation gold concentrates and their bio-oxidised products, taken as surrogates, have been investigated under isothermal, batch conditions, together with a review of the cognate literature. Specifically, the influence of ore mineralogy, pH modifier (caustic soda and quicklime), agitation rate (600–1000 rpm) and time on the leaching behaviour has been studied at 30 °C and pH 10.5 ± 0.2 over 8 h period. The results showed that cyanide leaching of the refractory flotation concentrates did not significantly alter the ore mineralogy, regardless of the pH modifier deployed. In case of jarosite-free bio-oxidised product, gypsum and bassanite phases present were leached out completely whilst only bassanite was leached out from jarosite-bearing bio-oxidised product upon deploying caustic soda as pH modifier. Unlike the caustic soda, bassanite was not leached from the jarosite-free and jarosite-bearing bio-oxidised products when quicklime was used to modify the pulp pH. In addition, increasing the agitation rate did not show any impact on the rate and yield of leaching the flotation concentrates. On the other hand, the rate and yield of leaching the bio-oxidised products increased with increasing agitation rate in an ore-type dependent manner. The gold leaching rates were greater within the initial 60 min than the later 420 min. The use of quicklime generally reduced the gold leaching rates compared with the caustic soda, however, certain variations, dependent on the ore mineralogy were observed within the initial 30 min. The leaching kinetics and mechanism of the flotation concentrates followed a chemical reaction controlled, shrinking core model whilst their corresponding bio-oxidised products followed a porous layer diffusion controlled, shrinking core model, both in a two-stage manner. The observed gold leaching rates were ~ 3–4 orders of magnitude lower than those reported for some sulphidic and oxidised gold ores, reflecting the refractoriness of the ores under investigation. The findings highlight the pivotal role complex, refractory ore mineralogy and its variation, pretreatment, process chemistry and applied mechanical action play in judicious manipulation and control of gold leach behaviour and extraction efficacy.

Research on sulphur conversion and acid balance from marmatite in pressure acid leaching

In this paper, the kinetics of oxygen pressure acid leaching of marmatite was studied in the low-temperature region (383–413 K). The effects of agitation rate, particle size, temperature, H2SO4 concentration and oxygen partial pressure on the conversion of sulphur (S2− → S0) were investigated. The results showed that the conversion ratio increased with increasing agitation rate, temperature and oxygen partial pressure, and with decreasing particle size and H2SO4 concentration. Moreover, the results demonstrated that sulphur conversion was controlled by an interfacial chemical reaction, with an apparent activation energy of 51.17 kJ mol−1. The calculated reaction orders of sulphuric acid and oxygen were 0.48 and 1.01, respectively. The leaching reaction followed an unreacted shrinking core model. A model kinetic equation was established for sulphur conversion. Orthogonal experiments regarding the acid balance () of the oxygen pressure leaching residue were carried out. Variance analysis showed that temperature had the largest influence on this, so the effect of the temperature region (383–443 K) on acid balance was further investigated. When the temperature exceeded 443 K, the increase in the sulphur oxidation ratio was too large, which tended to increase the acidity of the system.

Influence of Agitation on Primary Nucleation in Stirred Tank Crystallizers

The influence of agitation on nucleation of butyl paraben and m-hydroxybenzoic acid polymorphs has been investigated through 330 cooling crystallization experiments. The induction time has been measured at different supersaturations and temperatures in three parallel jacketed vessels equipped with different overhead stirring agitators. In each case, the nucleating polymorph of m-hydroxybenzoic acid has been identified by infrared spectroscopy. The influences of agitation rate, impeller type, impeller diameter, impeller to bottom clearance, and the use of baffles have been investigated. A general trend in all of the experiments is that the induction time decreases with increasing agitation rate. Across all experiments with different fluid mechanics for the butyl paraben system, the induction time is correlated to the average energy dissipation rate raised to the power −0.3. It is shown that this dependence is consistent with a turbulent flow enhanced cluster coalescence mechanism. In experiments with m-hyd...

Solubility and Crystal Nucleation in Organic Solvents of Two Polymorphs of Curcumin

Two crystal polymorphs of 1,7-bis-(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione (curcumin) have been obtained by crystallization from ethanol (EtOH) solution. The polymorphs have been characterized by differential scanning calorimetry, infrared spectroscopy, and X-ray powder diffraction and shown to be the previously described forms I and III. The solubility of both polymorphs in EtOH and of one polymorph in ethyl acetate (EA) has been measured between 10°C and 50°C with a gravimetric method. Primary nucleation of curcumin from EtOH solution has been investigated in 520 constant temperature crystallization experiments in sealed, magnetically stirred vials under different conditions of supersaturation, temperature, and agitation rate. By a thermodynamic analysis of the melting data and solubility of form I, the solid-state activity is estimated from 10°C up to the melting point. The solubility is lower in EtOH than in EA, and in both solvents, a positive deviation from Raoult's law is observed. Form I has lower solubility than form III and is accordingly thermodynamically more stable over the investigated temperature interval. Extrapolation of solubility regression models indicates that there should be a low-temperature enantiotropic transition point, below which form I will be metastable. By slurry conversion experiments, it is established that this temperature is below -30°C. All nucleation experiments resulted in the stable form I. The induction time is observed to decrease with increasing agitation rate up to a certain point, and then increase with further increasing agitation rate; a trend previously observed for other compounds. By correlating the induction time data obtained at different supersaturation and temperature, the interfacial energy of form I in EtOH is estimated to be 3.0 mJ/m(2) .

Semibatch reaction crystallization of salicylic acid

Reaction crystallization of salicylic acid has been investigated by experiments and modeling. In the experimental work, dilute hydrochloric acid has been added to an agitated aqueous solution of sodium salicylate in 1L scale, and product crystals have been characterized by image analysis. The results show that the product crystal number mean size at first increases with increasing agitation rate but then gradually decreases again at further increase in stirring rate. At lower stirring rate, larger crystals are obtained when the feeding point is located close to the agitator instead of being located out in the bulk solution. The mean crystal size increases with decreasing feeding rate and with decreasing reactant concentrations. There is a decrease in mean size with increasing feed pipe diameter. These trends in the experimental results show great similarity with previous results on benzoic acid. The experimental results have been examined by a population balance model accounting for meso and micro mixing, and crystal nucleation and growth rate dispersion. It is found that the crystallization kinetic parameter estimation is quite complex, and the objective function hyper surface contains many different minima. Hence, parameter estimation has to rely on a combination of mathematical optimization strategies and a scientific understanding of the physical meaning of the parameters and their relation to current theories. As opposed to our previous work on benzoic acid, it has not been possible to find a set of kinetic parameters that provides for a good description of all experimental data.

Solubility and metastable zone width of DL‐tartaric acid in aqueous solution

AbstractSolubility and metastable zone width (MSZW) of DL‐tartaric acid (DL‐TA) in aqueous solution have been determined. Solubility of DL‐TA was measured in the temperature range from 0 to 50 °C at atmospheric pressure by means of the conventional polythermal method using Turbidity Monitoring Technique, which was verified by a gravimetric method. The dissolution enthalpy and entropy of DL‐TA were then calculated from the solubility data using van't Hoff equation. Two approaches was used to estimate the nucleation kinetics from the measured metastable zone width data, the self‐consistent approach and the approach based on 3D nucleation. In addition, the metastable zone width slightly decreases with increasing agitation rate and was independent of working volume.

Poly(urea-formaldehyde)에 의한 페닐아세테이트의 미세캡슐화

본 연구에서는 페닐아세테이트를 core 물질로 하고 poly(urea-formaldehyde)를 캡슐막 구성물질로 하는 미세캡슐의 제조에 있어서, 교반속도, core/shell 질량비, 계면활성제 농도, 반응시간 등의 공정변수가 캡슐의 크기, 막두께, 표면형태 등의 특성에 미치는 영향을 조사하였다. FTIR 및 TGA에 의하여 원하는 미세캡슐이 제조되었음을 확인하였다. 캡슐의 특성은 광학현미경과 FE-SEM을 사용하여 분석하였다. 교반속도의 증가에 따라 캡슐의 크기와 막두께가 감소하는 것으로 나타났다. 캡슐막 구성물질 질량의 증가는 캡슐막의 두께와 막표면에 부착되는 나노입자의 양을 증가시키는 것으로 나타났다. 계면활성제 농도의 증가에 의하여 캡슐크기와 캡슐막 두께가 감소하는 것으로 확인되었다. 반응시간을 증가시키면 캡슐의 수율과 막두께가 증가하는 것이 관찰되었다.

Effect of impeller type and agitation on the performance of pilot scale ASBR and AnSBBR applied to sanitary wastewater treatment

The objective of this work was to assess the effect of agitation rate and impeller type in two mechanically stirred sequencing batch reactors: one containing granulated biomass (denominated ASBR) and the other immobilized biomass on polyurethane foam (denominated AnSBBR). Each configuration, with total volume of 1 m(3), treated 0.65 m(3) sanitary wastewater at ambient temperature in 8-h cycles. Three impeller types were assessed for each reactor configuration: flat-blade turbine impeller, 45 degrees -inclined-blade turbine impeller and helix impeller, as well as two agitation rates: 40 and 80 rpm, resulting in a combination of six experimental conditions. In addition, the ASBR was also operated at 20 rpm with a flat-blade turbine impeller and the AnSBBR was operated with a draft tube and helix impeller at 80 and 120 rpm. To quantify how impeller type and agitation rate relate to substrate consumption rate, results obtained during monitoring at the end of the cycle, as well as the time profiles during a cycle were analyzed. Increasing agitation rate from 40 rpm to 80 rpm in the AnSBBR improved substrate consumption rate whereas in the ASBR this increase destabilized the system, likely due to granule rupture caused by the higher agitation. The AnSBBR showed highest solids and substrate removal, highest kinetic constant and highest alkalinity production when using a helix impeller, 80 rpm, and no draft tube. The best condition for the ASBR was achieved with a flat-blade turbine impeller at 20 rpm. The presence of the draft tube in the AnSBBR did not show significant improvement in reactor efficiency. Furthermore, power consumption studies in these pilot scale reactors showed that power transfer required to improve mass transfer might be technically and economically feasible.

Preparation and characterization of polyethyleneglycolmethacrylate (PEGMA)- co-vinylimidazole (VI) microspheres to use in heavy metal removal

Polyethyleneglycolmethacrylate (PEGMA) and vinylimidazole (VI) were used in order to obtain microspheres of PEGMA-VI copolymers that can be used in heavy metal removal applications. The obtained copolymers were characterized and their use as sorbents in heavy metal removal was investigated. In the first part of the study, PEGMA-VI microspheres were prepared by suspension polymerization method. The obtained swellable microspheres with 10–50 μm average diameter did not have permanent porosity according to the morphological and physicochemical determinations. The sizes of microspheres became smaller with increasing VI and cross-linker ethyleneglycoldimethacrylate (EGDMA) contents and increasing agitation rate. The VI content, EGDMA ratio, pH and ionic strength were determined as the effective parameters on the swelling behavior of PEGMA-VI microspheres. In the second part of the study, Cu(II) ions were used as a model species in order to investigate the usability of the obtained PEGMA-VI microspheres in heavy metal removal. Adsorption capacities under optimum conditions were determined. The Cu(II) ion adsorption capacity increased by increasing the initial Cu(II) ion concentration, and it reached the maximum value (i.e., 30 mg Cu(II)/g PEGMA-VI microspheres) at 400 mg Cu(II)/L initial Cu(II) ion concentration under the determined optimum conditions. Microspheres were found to be reusable after desorption for several times.

Studies on production of gentamicin from Micromonosporas purpurea using crude vegetable oils

Crude vegetable oils and natural nitrogen sources were investigated to evaluate their potential as energy sources for the efficient production of gentamicin from Micromonosporas purpurea. Of the various crude vegetable oils, soybean oil was found to be the most suitable carbon source for efficient gentamicin production. An initial concentration of 40 g/l gave the highest gentamicin concentration and lipase activity, at 0.75 g/l and 298.1 U/ml, respectively. However, with more than 60 g/l oil, both of these values deceased. When 0.4 g/l of linoleic acid was added to the culture broth, the maximum gentamicin concentration was 0.82 g/l, which was about 3.0-fold higher than that obtained without the addition of linoleic acid. Soybean meal and corn steep liquor (CSL) appeared to be the most important nitrogen sources for the production of gentamicin. Especially, with a mixture of 15 g/l soybean meal and 15 g/l CSL, the gentamicin production was higher than with the use of a sole nitrogen source. The oil consumption increased with increasing agitation rate of the jar fermentor. However, the maximum gentamicin concentration of 1.45 g/l was achieved after 5 days in the culture agitated at 400 rpm. Using these basic results, fed-batch cultures were performed for 8 days in a jar fermentor. When soybean oil was used, the extracellular protease activity was 920.5 U/ml, which was 3.6-fold higher than that of the glucose medium. The maximum gentamicin concentration was 3.5 g/l, which was about 4.9-fold higher than that of the glucose medium. The product yield of the consumed soybean oil was about 12.8-fold higher than that of the glucose medium.

Swelling and erosion properties of hydroxypropylmethylcellulose (Hypromellose) matrices—influence of agitation rate and dissolution medium composition

The effect of dissolution medium variables, such as medium composition, ionic strength and agitation rate, on the swelling and erosion of Hypromellose (hydroxypropylmethylcellulose, HPMC) matrices of different molecular weights was examined. Swelling and erosion of HPMC polymers was determined by measuring the wet and subsequent dry weights of matrices. It was possible to describe the rate of dissolution medium uptake in terms of a square root relationship and the erosion of the polymer in terms of the cube root law. The extent of swelling increased with increasing molecular weight, and decreased with increasing agitation rate. The erosion rate was seen to increase with decrease in polymer molecular weight, with a decrease in ionic strength and with increasing agitation rate. The sensitivity of polymer erosion to the degree of agitation may influence the ability of these polymers to give reproducible, agitation-independent release, compared to more rigid non-eroding matrix materials, in the complex hydrodynamic environment of the gastrointestinal tract.

The Effect of Shear Field on the Hydrolysis of Cellulose

In an attempt to elucidate the effect of mixing in high‐shear regimens on the extent of enzymatic hydrolysis of cellulosic substrates, cellulose was hydrolyzed using a commercial cellulase preparation at various enzyme concentrations and by three agitation regimens. The activity of cellulase decreased with increasing agitation rate and elapsed mixing time. The effect of shear on enzyme denaturation decreased with increasing enzyme concentration.

Effect of agitation rate on biomass and protease production by a marine bacterium Vibrio harveyi cultured in a fermentor

A marine bacterium Vibrio harveyi was adapted to grow and produce extracellular proteases in a seawater/Zobell-based medium, supplemented with skim milk under different hydrodynamic conditions, namely agitation and aeration rates. The addition of skim milk to Zobell medium enhanced fivefold the extracellular enzyme production. Protease production seemed to take place after maximum luminescence had been produced. Specific growth rate increased as a consequence of increasing agitation rates. The maximum activity of 4.28 units mg−1 protein were formed with 700 rev min−1 and 0.5 v/v/m. Protease activity detected has a molecular weight of 34 kDa. Another minor band of protease activity was found at 40 kDa.

Scale-down studies on the hydrodynamics of two-liquid phase biocatalytic reactors.

The maintenance of constant interfacial area per unit volume is a key parameter for the successful scale-up of two-liquid phase bioconversion processes. To date, however, there is little published information on the hydrodynamics of such systems and a suitable basis for scale-up has yet to be defined and verified. Here we report power input and hydrodynamic data for a whole-cell bioconversion process using resting cells of Rhodococcus R312 to catalyse the hydration of a poorly water-soluble substrate 1,3-dicyanobenzene (1,3-DCB). Experiments were performed in geometrically similar 3-L and 75-L reactors, each fitted with a three-stage Rushton turbine impeller system. The two-phase system used comprised of 20% v/v toluene dispersed in 0.1 M aqueous phosphate buffer containing up to 10 g(ww) x L(-1) of resuspended biocatalyst and 20 g x L(-1) 1,3-DCB. The power input to the 3-L reactor was first determined using an air-bearing technique for both single-phase and two-phase mixing. In both cases, the power number attained a constant value of 11 at Re>10,000, while the measured power inputs were in the range 0.15-3.25 kW x m(-3). Drop size distributions and Sauter mean drop diameters (d(32)) were subsequently measured on-line in both reactors, using an in-situ light-backscattering technique, for scale-up on the basis of either constant power input per unit volume or constant tip speed. At both scales d(32) decreased with increasing agitation rate, while the drop size distributions obtained were log-normal. All the measured d(32) values were in the range of 30-50 microm, with the lowest values being obtained in systems with biocatalyst present. In all cases, constant power input per unit volume was found to be the most suitable basis for scale-up. This gave virtually identical d(32) values and drop size distributions at both scales. A number of correlations were also identified that would allow reasonable prediction of d(32) values for various agitation rates at each scale. While the results obtained are for a particular phase system, the scale-down methodology presented here would allow the rapid evaluation of other bioconversion processes in the 3-L reactor with a 25-fold reduction in scale. In this way, potential problems that might be encountered at the larger scale, such as the carryover of antifoam from the fermentation stage, could be quickly and efficiently identified.

Decreasing extracellular pH increases CD13 receptor surface content and alters the metabolism of HL60 cells cultured in stirred tank bioreactors.

Flow cytometry and Northern blotting were used to examine the effects of extracellular pH on CD13 receptor surface content and mRNA levels of HL60 (human promyelocytic leukemia) cells. Decreasing culture pH (7.4, 7.2, and 7.0) increased the CD13 receptor surface content of HL60 cells cultured at low agitation intensity (80 rpm) in 2-L bioreactors. Unlike our earlier findings on the effects of increasing agitation rates and serum concentrations, changes in CD13 receptor content in response to decreasing culture pH did not correlate with changes in CD13 mRNA levels. Decreasing culture pH also decreased the average HL60 cell size. HL60 cells cultured at pH 7.0 and 7.2 exhibited glucose consumption and lactate production rates that were approximately 30-40% and 20-30% lower, respectively, than values of cells cultured at pH 7.4.

Bioprocess parameters and oxygen transfer effects in the growth of Pseudomonas dacunhae for L-alanine production

Because alanine produced by most micro-organisms through fermentation is of the DL-racemate form and because it is too difficult to obtain L-alanine by fermentation, industrial production of L-alanine is accomplished by using L-aspartic acid as the reactant and L-aspartate β -decarboxylase (ADL) enzyme of resting Pseudomonas dacunhae cells as the biocatalyst. This work reports on the optimum growth conditions, i.e. optimum pH, temperature, agitation rate, substrate concentration and growth kinetics, of P. dacunhae investigated in shake flask cultures, as well as oxygen transfer kinetics studied in laboratory-scale bioreactors. Values of pH 7.0–7.5 and T = 229 K were optimal for both the growth and the enzyme activity. Although the specific growth rate μ . increased with increasing agitation rate between 50 and 300 min −1 , the enzyme activity showed a maximum at an agitation rate of 150 min −1 . Substrate inhibition was observed for high glutamic acid concentrations, i.e. C gGo > 10 kg m −3 which is used as the carbon source for the cultivation. The oxygen transfer kinetics were investigated under optimum conditions in a bioreactor of working volume 4 × 10 −3 m 3 with temperature, pH, dissolved oxygen, stirring rate and foam control. The micro-organism concentration reached a plateau and the enzyme activity reached a maximum at a residence time of t = 15 h. The oxygen transfer coefficient K L a and oxygen uptake rate r o , were maximum at residence times of t = 10 h and t = 7 h respectively. Increases in both the agitation rate and the oxygen feed rate increased the K L a values, with the agitation rate increase being much more effective.

Efficient tylosin production from Streptomyces fradiae using rapeseed oil

Tylosin production in flask and jar fermentor culture of Streptomyces fradiae using seven different vegetable oils as sole carbon sources was investigated. Among the vegetable oils, rapeseed oil was the best carbon source for tylosin production. When the initial rapeseed oil concentration was 60 g/ l, the maximum tylosin concentration reached was 7.0 g/ l, which was about 1.6- and 7-fold that reached using starch and glucose, respectively, at the same initial concentration. Although oil consumption increased with increasing agitation rate, the highest tylosin yield was obtained using an agitation rate of 400 rpm. This indicates that in the case of using an insoluble carbon source, use of an appropriate agitation rate is important for efficient production of tylosin.

Formation and disruption of animal cell aggregates in stirred vessels: Mechanisms and kinetic studies

The kinetics and mechanisms of aggregate formation and disruption have been investigated for BHK natural aggregates grown in 250 cm 3 Corning spinner flasks. The cells were cultivated as continuous cultures with a dilution rate of 0.005 day −1. Hydrodynamics were manipulated varying the agitation rate in a single step, and aggregate characteristics were evaluated until a new stationary state was achieved. Steps increasing agitation rate from 30 to 90 and 100 rpm (for disruption studies) and decreasing from 100 to 30, 45 and 60 rpm (for formation studies) were performed. The initial and final size distributions are essentially monomodal, with bimodal size distributions being observed during the transition phase. Comparing the 30 and 100 and 100 to 30 rpm tests, almost complete reversibility in aggregate size was observed. Aggregates are hydrodynamically controlled, with a power dependence of aggregate size on the energy dissipated per unit of mass close to 0.25. Having dimensions smaller than the Kolmogoroff's eddy size, aggregates are controlled by the action of viscous stresses in the viscous dissipation subrange. The variation in aggregate diameter and concentration with time has been mathematically described, based on kinetic models (first-order for diameter, first- and second-order for concentration), derived from several theories and correlations previously applied to the formation and disruption in different aggregate systems. Aggregate formation is a faster process than disruption; disruption is occurring with two main mechanisms: breakage and cell shedding from the large aggregates, leading to smaller aggregates and an increase in the fraction of single cells. The breakage of large aggregates into smaller ones can occur due to the collisions between aggregates or due to the stress caused by fluid motion. The increase on the agitation step leads to an increase on hydrodynamic stress, and thus the collisional fragmentation mechanism becomes less relevant. Formation is occurring by aggregate-aggregate collisions and, with a smaller relevance, single cell addition into the aggregates. Nevertheless reduced in number, more efficient collisions are occurring between aggregates, leading to an increase in the rate of aggregate formation.