denitrification system, the most common process used for nitrogen removal, has as
end product the nitrogen gas (N 2 ), while the treatment with microalgae retains the
nitrogen compounds on biomass, adding value.
The aerobic photosynthetic pathway is especially interesting, as it allows to
reduce the operating costs associated with the aeration of the biological treatment
(Borowitzka and Borowitzka 1988), which represents more than 50% of the energy
needs in a WWTP (EPA Office of Water 2006). Recent studies have shown that
microalgae may also support the aerobic degradation of several hazardous contaminants (Muñoz and Guieysse 2006; Safonova et al. 2004).
4 Microalgal Limitations in Wastewater Treatment
As in all treatment systems, microalgal culture also presents some disadvantages/
limitations in wastewater treatment.
4.1 Temperature Variability
The productivity of microalgae increases with increasing temperature up to an
optimum value, above which the respiration and photorespiration of microalgae
reduce overall productivity (Park et al. 2011). Thus, water temperature too high or
too low can have a negative effect on the growth of microalgae and it can cause
growth inhibition. The ideal temperature, measured under maximum growth conditions (optimal conditions of nutrients and light), varies from species to species;
however, for many species it is between 28 and 35 °C. The optimum temperature
changes when the growth is limited by nutrients and/or light. Moreover, microalgal
growth decreases when they are subject to sudden changes of temperature
(Larsdotter 2006). For example, the exposure of a species at a temperature of 10 °C,
when they were adapted to higher values, resulted in a reduction of about 50% of
the chlorophyll a in 15 h. In addition, a high luminous intensity associated with low
temperatures is also another factor that causes growth inhibition.
Taking into account the variability of temperature during the day and the year, it
is expected that the efficiency of wastewater treatment based on microalgae can be
substantially affected. Therefore, the seasonal temperature variability is one of the
main limitations in the introduction of microalgae in WWTPs, since it will be
difficult to keep the cultures within a range of acceptable temperatures throughout
the year.
3 Process Integration Applied to Microalgal Biofuels Production
47
end product the nitrogen gas (N 2 ), while the treatment with microalgae retains the
nitrogen compounds on biomass, adding value.
The aerobic photosynthetic pathway is especially interesting, as it allows to
reduce the operating costs associated with the aeration of the biological treatment
(Borowitzka and Borowitzka 1988), which represents more than 50% of the energy
needs in a WWTP (EPA Office of Water 2006). Recent studies have shown that
microalgae may also support the aerobic degradation of several hazardous contaminants (Muñoz and Guieysse 2006; Safonova et al. 2004).
4 Microalgal Limitations in Wastewater Treatment
As in all treatment systems, microalgal culture also presents some disadvantages/
limitations in wastewater treatment.
4.1 Temperature Variability
The productivity of microalgae increases with increasing temperature up to an
optimum value, above which the respiration and photorespiration of microalgae
reduce overall productivity (Park et al. 2011). Thus, water temperature too high or
too low can have a negative effect on the growth of microalgae and it can cause
growth inhibition. The ideal temperature, measured under maximum growth conditions (optimal conditions of nutrients and light), varies from species to species;
however, for many species it is between 28 and 35 °C. The optimum temperature
changes when the growth is limited by nutrients and/or light. Moreover, microalgal
growth decreases when they are subject to sudden changes of temperature
(Larsdotter 2006). For example, the exposure of a species at a temperature of 10 °C,
when they were adapted to higher values, resulted in a reduction of about 50% of
the chlorophyll a in 15 h. In addition, a high luminous intensity associated with low
temperatures is also another factor that causes growth inhibition.
Taking into account the variability of temperature during the day and the year, it
is expected that the efficiency of wastewater treatment based on microalgae can be
substantially affected. Therefore, the seasonal temperature variability is one of the
main limitations in the introduction of microalgae in WWTPs, since it will be
difficult to keep the cultures within a range of acceptable temperatures throughout
the year.
3 Process Integration Applied to Microalgal Biofuels Production
47