Photobioreactor operation

Rochatte V, Dauchet J, Cornet JF Experimental validation and modelling of a photobioreactor operating with diluted and controlled light flux, 2015 (to be published in Journal of Physics Conference Series, Proceedings of Eurotherm Conference 105 Computational Thermal Radiation in Participating Media V, France) (in press). 

Doucha J, Livansky K Productivity, C02/02 exchange and hydrauhcs in outdoor open high density microalgal (ChloreUa sp.) photobioreactors operated in a Middle and Southern European climate, Phycol 18 811-826, 2006. 

Metis161 reported a preliminary cost study on a 500-L scaled-up modular photobioreactor, and outlined the following cost distribution for the unit based on operating it for a period of 6 months photobioreactor materials, 45% mineral nutrients, 39% labor 4% water supply, 4% land lease, 2% power, 1% and miscellaneous expenses, 5%. He reported the actual cost of the materials for the pilot photobioreactor unit as 0.75 m 2, but the material used and the lifetime of the unit was not stated. This cost is much lower that the often quoted estimates of up to 100 per meter square using glass covered structures. Glass does not appear to be a realistic material to use in a commercial photobioreactor system because of both initial and replacement costs. 

Many operating costs are the same as those for any conventional chemical production process, such as operating labor, raw materials, and equipment maintenance. However, some expenses, such as cleaning optical surfaces or preventing biofilm growth on the photobioreactor surfaces, are unique to photobiological processes. 

Along with concerns of lost production during cloudy periods, the amount of downtime associated with maintenance will also affect the overall economics. Ideally, the photobioreactor would operate continuously. If operated in batch mode, there would be a period of limited H2 production while the cell density increased at the start of a new batch. If the system needs to be emptied for maintenance purposes, or if the cell culture is lost due to equipment failure or contamination, lost production will significantly affect the economics. The length of time required to build up cell mass in a wastewater treatment plant during start-up can be weeks, for example. 

An early system designed for the sulfur-deprived process required several days to poise the cells for Hj production. This transition period represented lost production compared to continuous operation. Daily start-up of the photobioreactor at sunrise may also decrease production if it extends into the daylight hours. Some other operations, for example, H2 liquefaction processes, would not be a logical choice for a diurnal cycle because of the losses and inefficiencies of starting up and shutting... 

Table 1. Maximum daily growth yield and photosynthetic efficiency of CWoreWa sp. strain HA-1 in the cone-shaped helical tubular photobioreactor under field culture operation. ...

Miyamoto, K. and Benemann, J. R. (1988). Vertical Tubular Photobioreactor Design and Operation. Biotechnology Letters 10, 703-710. 

This study demonstrates the principal possibility of hydrogen production in an outdoor photobioreactor (PhBR) incorporating a cyanobacterial mutant of Anabaena variabilis (PK84) under aerobic conditions. A computer-controlled helical tubular PhBR was operated over 4 summer months. A maximum rate of 80 mL H2 per hr per reactor volume (4.35 L) was obtained on a bright day (400 W m 2) from a batch culture. Also the culture was grown in chemostat mode at dilution rate D of 0.02 h 1. The maximum efficiency of conversion of light to chemical energy of H2 in the PhBR was 0.33% and 0.14% on a cloudy and a sunny day, respectively. 

As discussed above, an ideal photobioreactor for hydrogen production by a biophotolysis process must be uniformly illuminated (no photoinhibition and dark zones) and must have higji mass transfer capacity for efficient C02 supply and, most importantly, for 02 removal. Good mass transfer will also facilitate pH and temperature control when necessary. Also operation under sterile conditions is desirable for long term contamination-free operation. 

Complete a feasibility study on the operation of a new photobioreactor that produces H2 for longer periods of time as an alternative to significantly increasing H2-production rates. 

Initially, we will focus on the mesoscopic description associated with the radiative transfer equation. Then, we will introduce the single-scattering approximation and two macroscopic approximations the PI approximation and two-flux approximation. AH of these discussions are based on the configuration shown in Fig. 6. Collimated emission and Lambertian emission wiU also be considered in the discussion later they correspond to the direct component and the diffuse component of solar radiation, respectively. Throughout our study, the biomass concentration Cx is homogeneous in the reaction volume V (assumption of perfect mixing), and the emission phenomena in V are negligible. The concentration Cx is selected close to the optimum for the operation of the photobioreactor the local photon absorption rate. 4 at the rear of the photobioreactor is close to the compensation point A.C (see Section 5 and chapter Industrial Photobioreactors and Scale-up Concepts by Pruvost et al.). 

Contrary to Section 3.3, where we addressed the equivalent transport problem, ballistic photons here are in the minority, except close to = 0, for 0 G [0, r/2]. It is possible to take into account all the ballistic photons in our calculations (Eqs. (75) and (76)) because the mesoscopic solution for is obtained easily, even in the present case, with Lambertian emission and reflection 2Lt z = E. Nonetheless, except for the term that we used in Eq. (84), their contribution to the boundary conditions is negligible for most photobioreactor configurations during operation close to the optimum biomass growth rate. 

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