treatments have no capacity to carry out the CO 2 capture and thus prevent its release
to the atmosphere.
3.3 Benefits of Microalgae in WWTPs
In the activated sludge treatment, it is estimated that 1 kg of BOD removal consumes about 1 kWh of electricity for aeration (implying 1 kg of CO 2 emissions in
the electricity production) and produces about 0.45 kg of biomass residues (Oswald
2003). On the other hand, the removal of 1 kg of BOD by microalgae (photosynthetic pathway), in mixotrophic systems, does not require energy input and it
can produce enough biomass to generate methane, which will produce 1 kWh of
electricity. The wastewater treatment based on microalgae is an ecological process,
without secondary pollution, and it allows the efficient recycling of nutrients
(Mulbry et al. 2008; Muñoz and Guieysse 2006; Pizarro et al. 2006).
The microalgae biomass resulting from wastewater treatment systems can give
rise to products with commercial interest, such as fertilizer, animal feed, fine
chemicals, biofuels, among others, thereby reducing the total cost of the treatment
plant (De La Noüe et al. 1992).
Finally, the CO 2 biofixation by microalgae is an environmentally friendly
method to remove carbon from the atmosphere (Singh and Yadav 2015).
Microalgae have been described as having high capacity to fix CO 2 when compared
with land plants (Chen et al. 2013). They may fix the CO 2 released by the activated
sludge, avoiding its release to the atmosphere.
The interest in the cultures of microalgae is that conventional treatment processes present some important disadvantages, such as: (i) variable efficiency
depending on the nutrient to be removed; (ii) expensive treatment; (iii) chemical
processes leading to secondary pollution; and (iv) nutrient loss with possible value
(N and P) (De La Noüe et al. 1992).
Thus, the increase in global warming, scarcity of fossil fuels and the need to
mitigate emissions of greenhouse gases, the study of the feasibility of biological
wastewater treatment based on microalgae (associated with the production of biofuels) is of utmost importance (Rawat et al. 2011).
3.4 Reduction of Operating Costs
The introduction of microalgae in wastewater treatment processes can reduce the
costs associated to aeration and coagulation and at the same time can obtain biomass with high commercial value (Christenson and Sims 2011). The
microalgae-based treatment system is a less expensive and ecologically safer
technology when compared with physical and chemical processes, with the additional benefits of resources recovery and recycling. The biological nitrification/
46
A. P. de Carvalho Lopes et al.
to the atmosphere.
3.3 Benefits of Microalgae in WWTPs
In the activated sludge treatment, it is estimated that 1 kg of BOD removal consumes about 1 kWh of electricity for aeration (implying 1 kg of CO 2 emissions in
the electricity production) and produces about 0.45 kg of biomass residues (Oswald
2003). On the other hand, the removal of 1 kg of BOD by microalgae (photosynthetic pathway), in mixotrophic systems, does not require energy input and it
can produce enough biomass to generate methane, which will produce 1 kWh of
electricity. The wastewater treatment based on microalgae is an ecological process,
without secondary pollution, and it allows the efficient recycling of nutrients
(Mulbry et al. 2008; Muñoz and Guieysse 2006; Pizarro et al. 2006).
The microalgae biomass resulting from wastewater treatment systems can give
rise to products with commercial interest, such as fertilizer, animal feed, fine
chemicals, biofuels, among others, thereby reducing the total cost of the treatment
plant (De La Noüe et al. 1992).
Finally, the CO 2 biofixation by microalgae is an environmentally friendly
method to remove carbon from the atmosphere (Singh and Yadav 2015).
Microalgae have been described as having high capacity to fix CO 2 when compared
with land plants (Chen et al. 2013). They may fix the CO 2 released by the activated
sludge, avoiding its release to the atmosphere.
The interest in the cultures of microalgae is that conventional treatment processes present some important disadvantages, such as: (i) variable efficiency
depending on the nutrient to be removed; (ii) expensive treatment; (iii) chemical
processes leading to secondary pollution; and (iv) nutrient loss with possible value
(N and P) (De La Noüe et al. 1992).
Thus, the increase in global warming, scarcity of fossil fuels and the need to
mitigate emissions of greenhouse gases, the study of the feasibility of biological
wastewater treatment based on microalgae (associated with the production of biofuels) is of utmost importance (Rawat et al. 2011).
3.4 Reduction of Operating Costs
The introduction of microalgae in wastewater treatment processes can reduce the
costs associated to aeration and coagulation and at the same time can obtain biomass with high commercial value (Christenson and Sims 2011). The
microalgae-based treatment system is a less expensive and ecologically safer
technology when compared with physical and chemical processes, with the additional benefits of resources recovery and recycling. The biological nitrification/
46
A. P. de Carvalho Lopes et al.