Photobioreactor volumetric

As discussed earlier the average specific sugar production rate of the microalgal culture must be calculated in order to assess photobioreactor volumetric productivity. The following integral therefore must be calculated ... 

The specific volumetric rate of hydrogen photoproduction depends on the rate of hydrogen production by one unit of biomass and on the concentration of the biomass in a photobioreactor. The improvement of a biomass activity is the basic problem for strain selection or construction. The specific volumetric rate might be increased technologically by increase of biomass concentration. 

Direct bubbling with a mixture of air and C02 is used in many closed photobioreactors. The mass transfer capacity (as measured by the volumetric oxygen transfer coefficient, kLa) increases with decrease in the bubble diameters (achieved by using spargers with very small diameter pores) and with increase in the aeration rate. In vertical columns (Fig. 4), the gas transfer from the gas bubbles to the medium is high since the gas bubbles remain submerged in the broth until they exit the reactor. Thus bubble column bioreactors have been used for many biological processes. 

During the past decades, photobioreactors have found promising apphcations, in particular for high-value products, for example, in pharmacy, cosmetics, and aquaculture feeds. Nevertheless, the development of industrial photobioreactors stiU requires optimization efforts, especially for achieving a high volumetric production rate in the context of large-scale... 

Photobioreactor engineering addresses optimization of the volumetric rate of biomass production, the surface rate of biomass production (with respect to the solar-energy collecting surface), and thermodynamic efficiency of the process as well as biomass composition (ie, the biomass quality). Hereafter, we mainly focus on construction of a predictive model for the volumetric rate (eg, expressed in kg, or moles of dry biomass per second and per m of the reaction volume). This is the main difficulty with assessing performance of a photobioreactor because most of the other parameters of interest can be deduced only from the value of < >, in a... 

Our model is based on integral formulation of the photobioreactor s volumetric rate this approach is extremely convenient for analyzing the interaction between the mechanisms involved at different scales of the process ... 

The purpose of a photobioreactor is to absorb incident light in order to convert it into biomass via coupling with photosynthesis. On the one hand, efficient light absorption usually corresponds to heterogeneous radiation fields (x) within the reaction volume (see Section 3). On the other hand, the coupling law (Eq. (4)) is usually a non-linear function of (x) (the law obtained in Section 5 is non-linear, but this is also the case for most of other models reported in the literature). Therefore, the coupling between radiative transfer and photosynthesis must be formulated locally, which implies that determination of the volumetric rate < > requires... 

Figure 26 (A) A 25 L prototype of the solar volumetrically illuminated photobioreactor DiCoFluV (Cornet, 2010). (B) EDStar geometric structure both the reactor 1Z) and the 979 light-diffusing optical fibers [T) are cylinders 1 m high the reactor s diameter is 16.5 cm, the distance between two fiber axes is djr = 4.8 mm, and the fiber radius is ryr = 1.2 mm.Tl and T are diffuse-reflective with uniform reflectivity p and pT, respectively.. is Lambertian emitting with the uniform surface flux density qn,v (Q Two-dimensional hexagonal lattice fiber arrangement an optical-path example in the culture medium V.

In aU the experiments, the experimental mean volumetric growth rates were obtained according to the biomass balance in a well-mixed photobioreactor (defining the so-caUed residence time for continuous culture as r = ilV... 

Table 2 Comparison Between Experimental Biomass Volumetric Growth Rates Obtained in Different Kinds of Photobioreactors Cultivating Artbrospira platensis and the Knowledge Model Presented in this Chapter... 

Finally, if necessary, the mean volumetric biomass growth rate in the photobioreactor < R > is easily obtained by means of a spatial integral of the specific rate of net oxygen production < J02 > and again by means of... 

Now, the proposed kinetic coupling law (Eq. (163)), already used for example by Takache et al. (2012) for C. reinhardtii cultivation in a simple rectangular photobioreactor, is discussed in the text later as illustration of the whole methodology developed throughout this chapter, especially the use of the integral Monte Carlo formulation for easy calculation of the radiation field, volumetric biomass growth rate < Rx>, standard deviation of the results, and all the desired types of sensitivity (with the same calculation time). 

Comet JP, Dussap CG A simple and reliable formula for assessment of maximum volumetric productivities in photobioreactors, Biotechnol Prog 25(2) 424-435, 2009. 

Cx = biomass concentration in photobioreactor (moix m Cx,in/Cx,out = biomass concentration in inflow or outflow (moix rx = volumetric biomass production rate (moix m s )... 

With respect to the design and operation of photobioreactors the production term tx is of major importance. Parameter represents the volumetric biomass production rate of a cultivation system and it is the product of the biomass concentration in the system and the average specific growth rate of the microalgae ... 

In order to assess the volumetric productivity of the system the micro-algal biomass concentration and average specific growth rate need to be known. For the moment it will be assumed that the biomass concentration can be set at any desired level by means of a turbidostat mode of operation. Consequently, only the average specific growth rate of the microalgae in the photobioreactor needs to be calculated. 

When adopting the Blackman model a simple but useful expression for the volumetric productivity of photobioreactors can be derived. In the Blackman model a constant specific Hght absorption coefficient is used. In other words, the change of light spectrum by preferential absorption within a microaigai culture is not included. 

Ultimately a single expression for the volumetric productivity of a microalgal culture in a photobioreactors can be derived ... 

Figure 26 Volumetric productivity of a photobioreactor Tx as a function of biomass concentration Cx according to Blackman red (dark gray in the print version) lines) and Jassby and Platt blue dark gray in the print version) lines). Solid lines represent resuits for /pi,(0) = 0.75 X 10 molph m s - dashed lines represent resuits for /ph(0) = 1.5 x 1 molph m s Photobioreactor d=0.03 m. Parameter values are based on high-light acclimated Chlorella sorokiniana and a sunlight spectrum Ox=3.33 m moixfor sunlight Vs/ph,m = 0.10 mols molph <7s,m = 1-25 x 10 mols moix s V x/s=0.625 moix mol i ms=3.0 x 10 mols moix" s .

This relation can be used, for example, to calculate volumetric productivity of a photobioreactor at different biomass concentrations when assuming a constant incident photon flux density Iph(O)- In Fig. 26 results are shown for a photobioreactor with an optical depth of 3 cm. The shape of this relation will be discussed later after having introduced a similar approach based on the model of Jassby and Platt. 

In Fig. 26 the volumetric productivity is presented as a function of the biomass concentration for a photobioreactor with a 3-cm optical path. Results are shown both for the approach based on Blackman without spectral resolution and Jassby and Platt including spectral resolution. 

The outcome shows that at the point of maximal volumetric productivity the photon flux density at the backside of the photobioreactor /ph(d) is equal to the compensation point of photosynthesis fph,c which was derived earlier ... 

Also when employing more realistic and more complex models, such as Jassby and Platt with spectral resolution the same rule applies volumetric productivity of a photobioreactor is maximal when the biomass density is such that the photon flux density at the darkest zone of the reactor is equal to the compensation point of photoautotrophic growth. In practice it has also been confirmed that photobioreactors can be operated at maximal productivity when the biomass concentration is maintained at those levels that almost aU light is absorbed within the microalgal culture but at the back still a minimal amount of light is left to compensate for maintenance purposes (Barbera et al, 2015 Takache et al, 2012 Zijffers et al, 2010). 

When operating photobioreactors or raceway ponds in batch mode a compromise must be found between achieving a high volumetric... 

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