3.2.4 Scaling-up in Flat-Plate Photobioreactors
The scale-up in flat-plate photobioreactors presents some challenges, which are
usually caused by the large surface area of the photobioreactor. This type of design
requires many modules and supports materials, shows difficulty in controlling
culture temperature and is very susceptible to the fouling, which is the phenomena
that occur when cells attach to the plastic walls, causing a reduction in light
availability and an increased risk of contamination (Carvalho et al. 2014; Chang
et al. 2017).
Despite the limitations, several commercial large-scale flat-plate photobioreactors have been developed. One example is the Green Wall Panel (GWP
® ) that has a
concept of ‘disposable panels’ for large-scale applications. This system commercialized by Fotosintetica & Microbiologica S.r.l consists of vertical PBRs of
100-litre bags, made of a polyethylene foil enclosed in a rigid framework (Tredici
et al. 2016). Other systems available commercially are the flat-plate airlift patented
and produced by Subitec GmbH, in Germany. In this case, the photobioreactors are
produced on scales varying from 6 to 180 L per unit.
4 Recent Developments in Microalgae Cultivation Systems
Recently, biofilm cultivation of microalgae emerged as a new biomass production
strategy. These systems consist of a densely packed layer of microalgae that grow
attached to a solid surface, which should be illuminated and should be frequently
exposed to water containing nutrients. Among the advantages of the biofilm-based
microalgae cultivation are the cost reduction related to microalgae harvesting,
reduced light limitation, low footprint, low water consumption, and efficient CO 2
mass transfer. In contrast, the limitations of the system are the formation of gradients
over the biofilm for pH, nutrients, and light (Gross et al. 2015; Hoh et al. 2015).
Another photobioreactor configuration that has attracted attention in recent years
is the membrane photobioreactor, mainly for the cultivation of microalgae using
wastewater. The membrane photobioreactor is a technology that integrates a conventional enclosed PBR with a submerged or side-stream membrane filtration
process using microfiltration or ultrafiltration membranes for solid–liquid separation. These systems can operate in continuous mode, which increases the microalgal
biomass production, they produce a high quality treated effluent with low levels of
organic substances, pathogen, and suspended solids and are easy to operate and
scale-up. However, only limited studies exist about these techniques and for a
large-scale implementation, techno-economic analyses and environmental performance assessment are required to assess their viability (Billad et al. 2015; Luo et al.
2016).
Finally, hybrid photobioreactors have proved to be a promising technology for
the mass production of microalgae compared with single PBRs. Hybrid photobioreactors are systems that combine different growth stages in two types of PBRs,
24
M. M. Maroneze and M. I. Queiroz
The scale-up in flat-plate photobioreactors presents some challenges, which are
usually caused by the large surface area of the photobioreactor. This type of design
requires many modules and supports materials, shows difficulty in controlling
culture temperature and is very susceptible to the fouling, which is the phenomena
that occur when cells attach to the plastic walls, causing a reduction in light
availability and an increased risk of contamination (Carvalho et al. 2014; Chang
et al. 2017).
Despite the limitations, several commercial large-scale flat-plate photobioreactors have been developed. One example is the Green Wall Panel (GWP
® ) that has a
concept of ‘disposable panels’ for large-scale applications. This system commercialized by Fotosintetica & Microbiologica S.r.l consists of vertical PBRs of
100-litre bags, made of a polyethylene foil enclosed in a rigid framework (Tredici
et al. 2016). Other systems available commercially are the flat-plate airlift patented
and produced by Subitec GmbH, in Germany. In this case, the photobioreactors are
produced on scales varying from 6 to 180 L per unit.
4 Recent Developments in Microalgae Cultivation Systems
Recently, biofilm cultivation of microalgae emerged as a new biomass production
strategy. These systems consist of a densely packed layer of microalgae that grow
attached to a solid surface, which should be illuminated and should be frequently
exposed to water containing nutrients. Among the advantages of the biofilm-based
microalgae cultivation are the cost reduction related to microalgae harvesting,
reduced light limitation, low footprint, low water consumption, and efficient CO 2
mass transfer. In contrast, the limitations of the system are the formation of gradients
over the biofilm for pH, nutrients, and light (Gross et al. 2015; Hoh et al. 2015).
Another photobioreactor configuration that has attracted attention in recent years
is the membrane photobioreactor, mainly for the cultivation of microalgae using
wastewater. The membrane photobioreactor is a technology that integrates a conventional enclosed PBR with a submerged or side-stream membrane filtration
process using microfiltration or ultrafiltration membranes for solid–liquid separation. These systems can operate in continuous mode, which increases the microalgal
biomass production, they produce a high quality treated effluent with low levels of
organic substances, pathogen, and suspended solids and are easy to operate and
scale-up. However, only limited studies exist about these techniques and for a
large-scale implementation, techno-economic analyses and environmental performance assessment are required to assess their viability (Billad et al. 2015; Luo et al.
2016).
Finally, hybrid photobioreactors have proved to be a promising technology for
the mass production of microalgae compared with single PBRs. Hybrid photobioreactors are systems that combine different growth stages in two types of PBRs,
24
M. M. Maroneze and M. I. Queiroz