3.2.1 Major Factors Affecting the Flat-Plate Photobioreactor
Performance
Light Supply
The flat-plate photobioreactors can be illuminated artificially or through sunlight.
However, as the use of sunlight is much more economically feasible, and these
systems have an excellent setting to capture sunlight, this is the most commonly
used option.
The light absorption is totally dependent on the length of light path. In general,
the biomass productivity is highest at the smallest light path and smallest at the
longest light path PBR (Richmond and Cheng-Wu 2001). Other configuration that
has an influence on light capture is the tilt angle of flat-plate photobioreactor.
Throughout the year, the optimal tilt of the PBR that allows maximal incident light
will change due to the position of the sun (Wang et al. 2012). Hu et al. (1998)
described that as a general rule, the optimal angle for year-round biomass production is equal to the geographic latitude of the location.
Gas Balance and Mixing
A great advantage of flat-panel reactors is that they have a much shorter oxygen
path than tubular reactors, so the accumulation of dissolved oxygen is low (Sierra
et al. 2008; Chang et al. 2017). According to Sierra et al. (2008), in a flat-panel
photobioreactor, an aeration of 0.25 VVM (volume of air per volume of liquid per minute) and a power supply of 53 W/m
3 are sufficient to maintain the
balance of gases, mixing is ideally suited for most microalgal culture. Other authors
reported even much higher aeration rates up to 2.0 VVM with positive effects (Alias
et al. 2004; Wang et al. 2005).
Temperature
Microalgae cultivations in outdoor PBRs are exposed to seasonal and diurnal
variation of temperature. These variations have a direct influence on the cellular
growth and the chemical composition of the biomass, and therefore, for the
development of an efficient and controlled process, the temperature must be
maintained with the least possible variation.
Particularly, flat-plate photobioreactors are very susceptible to overheating due
to its thin layer of cultivation and high light exposure. For this reason, the PBRs
must have an efficient temperature control system. This control is usually done by
water spraying (evaporative cooling) or alternatively, by using internal heat
exchangers (Chang et al. 2017).
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M. M. Maroneze and M. I. Queiroz
Performance
Light Supply
The flat-plate photobioreactors can be illuminated artificially or through sunlight.
However, as the use of sunlight is much more economically feasible, and these
systems have an excellent setting to capture sunlight, this is the most commonly
used option.
The light absorption is totally dependent on the length of light path. In general,
the biomass productivity is highest at the smallest light path and smallest at the
longest light path PBR (Richmond and Cheng-Wu 2001). Other configuration that
has an influence on light capture is the tilt angle of flat-plate photobioreactor.
Throughout the year, the optimal tilt of the PBR that allows maximal incident light
will change due to the position of the sun (Wang et al. 2012). Hu et al. (1998)
described that as a general rule, the optimal angle for year-round biomass production is equal to the geographic latitude of the location.
Gas Balance and Mixing
A great advantage of flat-panel reactors is that they have a much shorter oxygen
path than tubular reactors, so the accumulation of dissolved oxygen is low (Sierra
et al. 2008; Chang et al. 2017). According to Sierra et al. (2008), in a flat-panel
photobioreactor, an aeration of 0.25 VVM (volume of air per volume of liquid per minute) and a power supply of 53 W/m
3 are sufficient to maintain the
balance of gases, mixing is ideally suited for most microalgal culture. Other authors
reported even much higher aeration rates up to 2.0 VVM with positive effects (Alias
et al. 2004; Wang et al. 2005).
Temperature
Microalgae cultivations in outdoor PBRs are exposed to seasonal and diurnal
variation of temperature. These variations have a direct influence on the cellular
growth and the chemical composition of the biomass, and therefore, for the
development of an efficient and controlled process, the temperature must be
maintained with the least possible variation.
Particularly, flat-plate photobioreactors are very susceptible to overheating due
to its thin layer of cultivation and high light exposure. For this reason, the PBRs
must have an efficient temperature control system. This control is usually done by
water spraying (evaporative cooling) or alternatively, by using internal heat
exchangers (Chang et al. 2017).
22
M. M. Maroneze and M. I. Queiroz