1 Introduction
The increase of world population is associated with the increase of energy consumption to levels that can compromise the economic growth. Energy is mainly
supplied by fossil fuels, which price volatility and sustainable issues (air pollution
and climate change) are the main drawbacks. Concerning climate change, the
desired balance between CO 2 emissions and sinks (controlling the increase of
atmospheric CO 2 concentration) may be achieved through three political strategies
(Pires 2017): (i) energy efficiency enhancement; (ii) renewable energy development; and (iii) forest protection. In this context, biofuels have a huge potential to
reduce CO 2 emissions to atmosphere (clean energy), as they can substitute fossil
fuel energy products without significant technological changes. However, biofuel
must be produced from non-edible feedstocks to avoid competition with human
food market.
Microalgal culture has attracted the attention of the scientific community due to
the high biomass productivity that can be achieved. High growth rates and ability to
fix CO 2 are important characteristics to be considered one of the most promising
alternatives for biofuel production (Chisti 2007). In addition, they can grow in
places that are unsuitable for agriculture, not competing for land with food production practices. However, the cost of microalgal production is still high, being the
industrial-scale microalgal culture limited to high-value products. The increase of
nutrients (nitrogen and phosphorus) price in the last years is one of the significant
contributions to the production cost (Pires et al. 2013). Thus, to obtain microalgal
biomass at low cost (to be used for biofuel production), the integration of processes
must be performed. To reduce nutrients requirements, microalgae can be cultivated
in nutrient-rich wastewater. At the same time, this process integration also reduces
the need of freshwater and promotes the treatment of these effluents. Therefore, this
chapter aims to present technological issues related to the integration of wastewater
treatment and microalgal cultivation for biomass/biofuel production. Recent
advances and challenges are also discussed.
2 Microalgae
Microalgae may be classified as prokaryotic or eukaryote organism (Richmond
2004). With respect to the prokaryotic domain, cyanobacteria (also called
blue-green algae) are the only ones belonging to this group. On the other hand, in
the eukaryotic domain, there are several classes of algae and the most relevant are
the following: green algae (Chlorophyceae), Golden algae (Chrysophyceae) and
diatoms (Bacillariophyceae). Microalgae can be found more often in the water—
freshwater, seawater or brackish water (Lam et al. 2017; Lee 2008). However, they
can also be found in all other terrestrial environments, such as snow or hot springs.
In most habitats, they act as primary producers in the food chain, synthesizing
36
A. P. de Carvalho Lopes et al.
The increase of world population is associated with the increase of energy consumption to levels that can compromise the economic growth. Energy is mainly
supplied by fossil fuels, which price volatility and sustainable issues (air pollution
and climate change) are the main drawbacks. Concerning climate change, the
desired balance between CO 2 emissions and sinks (controlling the increase of
atmospheric CO 2 concentration) may be achieved through three political strategies
(Pires 2017): (i) energy efficiency enhancement; (ii) renewable energy development; and (iii) forest protection. In this context, biofuels have a huge potential to
reduce CO 2 emissions to atmosphere (clean energy), as they can substitute fossil
fuel energy products without significant technological changes. However, biofuel
must be produced from non-edible feedstocks to avoid competition with human
food market.
Microalgal culture has attracted the attention of the scientific community due to
the high biomass productivity that can be achieved. High growth rates and ability to
fix CO 2 are important characteristics to be considered one of the most promising
alternatives for biofuel production (Chisti 2007). In addition, they can grow in
places that are unsuitable for agriculture, not competing for land with food production practices. However, the cost of microalgal production is still high, being the
industrial-scale microalgal culture limited to high-value products. The increase of
nutrients (nitrogen and phosphorus) price in the last years is one of the significant
contributions to the production cost (Pires et al. 2013). Thus, to obtain microalgal
biomass at low cost (to be used for biofuel production), the integration of processes
must be performed. To reduce nutrients requirements, microalgae can be cultivated
in nutrient-rich wastewater. At the same time, this process integration also reduces
the need of freshwater and promotes the treatment of these effluents. Therefore, this
chapter aims to present technological issues related to the integration of wastewater
treatment and microalgal cultivation for biomass/biofuel production. Recent
advances and challenges are also discussed.
2 Microalgae
Microalgae may be classified as prokaryotic or eukaryote organism (Richmond
2004). With respect to the prokaryotic domain, cyanobacteria (also called
blue-green algae) are the only ones belonging to this group. On the other hand, in
the eukaryotic domain, there are several classes of algae and the most relevant are
the following: green algae (Chlorophyceae), Golden algae (Chrysophyceae) and
diatoms (Bacillariophyceae). Microalgae can be found more often in the water—
freshwater, seawater or brackish water (Lam et al. 2017; Lee 2008). However, they
can also be found in all other terrestrial environments, such as snow or hot springs.
In most habitats, they act as primary producers in the food chain, synthesizing
36
A. P. de Carvalho Lopes et al.