Biological particle

Pollutant Distribution. Of particular importance for the aquatic ecosystem is the distribution of volatile substances, eg, gases and volatile organic compounds, between the atmosphere and water, and the sorption of compounds at soHd surfaces, eg, settling suspended matter, biological particles, sediments, and soils (41,42). 

The main part of the report describes the results of systematic investigations into the hydrodynamic stress on particles in stirred tanks, reactors with dominating boundary-layer flow, shake flasks, viscosimeters, bubble columns and gas-operated loop reactors. These results for model and biological particle systems permit fundamental conclusions on particle stress and the dimensions and selection of suitable bioreactors according to the criterion of particle stress. 

In addition to true bioreactors which are used to carry out biological reactions, many authors have used special model apparatuses to study the stress on cells and organisms, and also non-biological particles, in models. 

The results provided in the literature for stress with biological particle systems, whereby gas distributors with small hole diameters, i.e. with smaller bubble sizes, have a more negative effect on cells (see e.g. [4, 30,31]), are frequently not comparable, as in these studies there was differing stress during bubble formation at the gas distributor due to different hole velocities. 

Since in the case of turbulent stress the ratio of particle diameter dp to length scale of turbulence qp is decisive for the stress regime (see Fig. 1) the model particle systems must have properties which guarantee dp/qp values which are in the same range as for the biological particle systems. 

Fig. 2. Properties of model and biological particle systems Micro scale related particle diameter dp/riL versus maximum energy dissipation e , in stirred reactors explanations see Table 3 and Table 4...

Table 4. Conditions for the investigations with biological particle systems ...

It could be shown (see Sect. 6) that in stirred vessels with baffles and under the condition of fully developed turbulence, particle stress can be described by Eqs. (2) and (4) alone. The turbulent eddys in the dissipation range are decisive for the model particle systems used here and many biological particle systems (see Fig. 2), so that the following equation applies to effective stress ... 

Many results with model systems and also biological particle systems indicate that the stress in technical bioreactors, in which turbulent flow conditions exist, could not be simulated by model studies in small bioreactors, where no fully turbulent flow exists, and especially with laminar flow devices such as viscosimeters, tubes or channels. 

Fig. 5. Estimated characteristic strength of typical biological particles of interest to biotechnology data are based on in-situ measurements of the minimum stresses necessary to cause permanent breakage of particles. For comparison data are shown based on Van der Waals and pendular liquid bridges between two 10-pm particles, 0.01 pm apart...

The sorptive nature of bacterial or algal exterior membranes is well-documented [118-122]. Biological particles can influence the distribution of heavy metals in natural waters because the functional groups on the cell surfaces are able to bind certain metal ions [124]. 

The biggest difference between biological particles and ceramic particles in the application of Eq. (4.20) is that while most ceramic particles are spherical ( Ch = 2.5), most biological particles can be modeled as either prolate ellipsoids or oblate spheroids (or ellipsoids). Ellipsoids are characterized according to their shape factor, ajb, for which a and b are the dimensions of the semimajor and semiminor axes, respectively (see Eigure 4.17). In a prolate ellipsoid, a > b, whereas in an oblate ellipsoid, b > a.ln the extremes, b approximates a cylinder, and b a approximates a disk, or platelet. 

The hydrodynamic shape factor and axial ratio are related (see Eigure 4.18), but are not generally used interchangeably in the literature. The axial ratio is used almost exclusively to characterize the shape of biological particles, so this is what we will utilize here. As the ellipsoidal particle becomes less and less spherical, the viscosity deviates further and further from the Einstein equation (see Eigure 4.19). Note that in the limit of a = b, both the prolate and oblate ellipsoid give an intrinsic viscosity of 2.5, as predicted for spheres by the Einstein equation. 

Additional measurements of the 34 matrix element for biological particles (red blood cells) have been reported by Kilkson et al. (1979). 

Bickel, W. S., and M. E. Stafford, 1980. Biological particles as irregularly shaped particles, in Light Scattering by Irregularly Shaped Particles, D. Schuerman (Ed.), Plenum, New York, pp. 299-305. 

Morris, S. J., H. A. Shultens, M. A. Hellweg, G. Striker, and T. M. Jovin, 1979. Dynamics of structural changes in biological particles from rapid light scattering measurements, Appl. Opt., 18, 303-311. 

For biological particles, for example, cells which have a semi-permeable membrane and semi-permeable microcapsules, their mechanical integrity can be characterised by exposuring them to media with different osmotic pressures (Van Raamsdonk and Chang, 2001). 

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