Both the efficiency values and PQ show the ability of these photosynthetic
microorganisms to convert the solar energy and, consequently, the water photolysis.
However, these quantitative relations can only be considered if parameters such as
photobioreactor configuration, light incidence, mixing, and ecological aspects are
properly determined.
5 Volatile Organic Compounds as Energy Source
Besides the biological oxygen generation, other products are biotransformed by
microalgae photosynthetic cultures, being the volatile organic compounds (VOCs)
of great relevance. These compounds correspond to the larger fraction (gas phase)
of carbon bioconverted in photobioreactors that satisfy the global mass balance in
the system, in addition to biomass (solid phase), carbonates, bicarbonates, and
extracellular polymers (liquid phase) (Jacob-Lopes and Franco 2013).
The VOCs are organic chemical molecules with high vapor pressure and low
boiling point, passing freely through biological membranes, which causes them to
easily evaporate into the atmosphere (Dudareva et al. 2013). Additionally, VOCs
are among the fastest growing molecules in aquatic ecosystems, and many of these
compounds with specific biological activity are generated and released from the
metabolism of photosynthetic microorganisms, both in marine and in freshwater
phytoplankton (Goldstein and Galbally 2007).
According to Zepka et al. (2015), the VOCs produced by microalgae can be
divided into terpenoids, phenylpropanoids/benzenoids, carbohydrate derivates, fatty
acids derivates, and amino acid derivates, besides specific compounds not represented in those major classes. Microalgae are able to generate and release substantial amounts of VOCs belonging to different classes of compounds, such as
alcohol, aldehydes, ketones, hydrocarbons, esters, terpenes, carboxylic acids,
Table 4 Photosynthetic quotients (PQ) found by different species of microalgae
Microalgal species
Bioreactor type PQ
References
Arthrospira platensis
Membranes
1.38
Cogne et al. (2005)
Chlamydomonas reinhardtii
Bubble column 1.00
Eriksen et al. (2007)
Chlorella sp.
1.30
Aphanothece microscopica Nägeli Bubble column 0.74
Jacob-Lopes et al. (2010)
Chlorella sorokiniana
Bubble column 1.40
Kliphuis et al. (2010)
Tetraselmis striata
Bubble column 1.50
Holdt et al. (2013)
Synechococcus PCC7002
Bubble column 1.30–1.40 Bernal et al. (2014)
Synechocystis sp.
Anabaena PCC7120
Chaetoceros wighamii
Bubble column 1.26
Spilling et al. (2015)
13 Biofuels from Microalgae …
281
microorganisms to convert the solar energy and, consequently, the water photolysis.
However, these quantitative relations can only be considered if parameters such as
photobioreactor configuration, light incidence, mixing, and ecological aspects are
properly determined.
5 Volatile Organic Compounds as Energy Source
Besides the biological oxygen generation, other products are biotransformed by
microalgae photosynthetic cultures, being the volatile organic compounds (VOCs)
of great relevance. These compounds correspond to the larger fraction (gas phase)
of carbon bioconverted in photobioreactors that satisfy the global mass balance in
the system, in addition to biomass (solid phase), carbonates, bicarbonates, and
extracellular polymers (liquid phase) (Jacob-Lopes and Franco 2013).
The VOCs are organic chemical molecules with high vapor pressure and low
boiling point, passing freely through biological membranes, which causes them to
easily evaporate into the atmosphere (Dudareva et al. 2013). Additionally, VOCs
are among the fastest growing molecules in aquatic ecosystems, and many of these
compounds with specific biological activity are generated and released from the
metabolism of photosynthetic microorganisms, both in marine and in freshwater
phytoplankton (Goldstein and Galbally 2007).
According to Zepka et al. (2015), the VOCs produced by microalgae can be
divided into terpenoids, phenylpropanoids/benzenoids, carbohydrate derivates, fatty
acids derivates, and amino acid derivates, besides specific compounds not represented in those major classes. Microalgae are able to generate and release substantial amounts of VOCs belonging to different classes of compounds, such as
alcohol, aldehydes, ketones, hydrocarbons, esters, terpenes, carboxylic acids,
Table 4 Photosynthetic quotients (PQ) found by different species of microalgae
Microalgal species
Bioreactor type PQ
References
Arthrospira platensis
Membranes
1.38
Cogne et al. (2005)
Chlamydomonas reinhardtii
Bubble column 1.00
Eriksen et al. (2007)
Chlorella sp.
1.30
Aphanothece microscopica Nägeli Bubble column 0.74
Jacob-Lopes et al. (2010)
Chlorella sorokiniana
Bubble column 1.40
Kliphuis et al. (2010)
Tetraselmis striata
Bubble column 1.50
Holdt et al. (2013)
Synechococcus PCC7002
Bubble column 1.30–1.40 Bernal et al. (2014)
Synechocystis sp.
Anabaena PCC7120
Chaetoceros wighamii
Bubble column 1.26
Spilling et al. (2015)
13 Biofuels from Microalgae …
281