**5. Case studies in environmental and biological systems**

This section presents a short review of the recent studies on the applications of turbulence or hydrodynamics in the environmental and biological systems (**Table 2**). Water purification, irrigation, water quality assessment, sludge dewatering, bioflocculation, and bio-clogging are some of the technical areas of application identified. *The Role of Micro Vortex in the Environmental and Biological Processes DOI: http://dx.doi.org/10.5772/intechopen.93531*


**Table 2.**

*Vortex Dynamics Theories and Applications*

hydrodynamic stress.

the hydrodynamic breaking force FH. While the binding force is determined by the aggregate structure and physicochemical attributes discussed Section 2, flow turbulence is the principal factor in the case of the hydrodynamic force. Therefore, the dynamics of particle behavior depends on an interplay of collision-induced particle aggregation and cohesive force and the rate of aggregate breakage due to the

The aggregate cohesive strength τ is a function of the physicochemical and biological conditions as well as the aggregate properties, while the hydrodynamic stress σ depends on the design of the aggregation unit and the prevailing process conditions. Several empirical and theoretical formulations are available for predicting the aggregate cohesive force and the maximum hydrodynamic breaking force. The global hydrodynamic stress σ due to the shearing action of the fluid motion on the aggregate as well as the overall cohesive strength τ of the aggregate resisting the hydrodynamic loading assuming a uniform shape and constant porosity can be expressed mathematically in Eqs. (10) and (11) [25, 26]. An equilibrium of particle dynamics is reached at the steady-state condition. In this state, a continued particle or micro flocs/aggregate attachment to the larger flocs/aggregate is prevented, or

the breakup kinetics is equal to the turbulence-induced collision rates.

In assessing aggregate strength and resistance to hydrodynamic-induced breakup, two common approaches are normally followed namely: limiting growth and limiting strength. The former relies on the determination of the maximum floc size before rupture, while the latter is based on the micromechanical analysis of aggregate strength. Many empirical and theoretical formulations based on the mentioned approaches are available in literature (Eqs. (12) and (13)). Liu et al. [27] presented the yield stress approach for calculating maximum aggregate tensile strength τ*y* at which breakage is likely to occur in the inertia range of turbulence (Eq. (12)). Similarly, Attia [28] presented a model for predicting the critical fluid velocity above which there will be aggregate disruption by estimating floc yield stress σ*y* resulting from the dynamic pressure acting on the floc (Eq. (13)).

σ=µ =µ G

( <sup>−</sup> ) τ = <sup>B</sup> 2 p 1 pF

B y 2

F

ε

(10)

(13)

v

<sup>0</sup> λ τ = 

p F

σ= ρ <sup>2</sup> y f 1 v 2

This section presents a short review of the recent studies on the applications of turbulence or hydrodynamics in the environmental and biological systems (**Table 2**). Water purification, irrigation, water quality assessment, sludge dewatering, bioflocculation, and bio-clogging are some of the technical areas of application identified.

**5. Case studies in environmental and biological systems**

k

pd (11)

d d (12)

**10**

*Selected studies on computational and experimental studies of turbulence applications in environmental and biological processes.*

It should be noted that improvements in the performance of the engineered processes (e.g., stirred tanks, shear reactors and photobioreactors etc.) in the identified areas of applications continue to shape the research focus in the field of environmental process engineering [29]. In this respect, studies have been conducted to determine how to accurately quantify the impact of hydrodynamic characteristics on the infectivity of bacteriophage MS2, a norovirus surrogate. Several studies also involved the development of bioreactors for testing the effect of hydrodynamic characteristics on microalgae and human enteric viruses [29–33]. The results obtained from the studies indicated that the hydrodynamic cavitation could trigger the inactivation waterborne viruses to levels defined in water quality directives. This was reportedly due to OH-radicals that form an AOP during the cavitation process and high shear forces inside the cavitation structure. Also, flow structures in a hydrodynamic filter have been numerically investigated [34]. In this study, tangential component of velocity was defined, and the three-dimensional pattern of the flow current/streamlines was obtained using their two-dimensional projection in the meridian cross-section of the filter, which allows one to discover the vortex structures. It was concluded that the optimal flow regime can be implemented by selecting the optimal correlation between the flow of liquid regime to be processed and the rotation frequency of the filtering baffle in the hydrodynamic filter. The remaining sub-sections describe how hydrodynamics, turbulence, and vortex dynamics are applied to achieve the desired process efficiency in other identified areas of applications—water purification, sludge dewatering, food processing, and self-purification of the water bodies.
