aeration, and sunlight. Photosynthetically produced oxygen by algae induces nitrification by nitrifying bacteria under autotrophic condition. In this system, inhibiting
factors for scale-up could be removed by utilizing heterotrophic bacterial growth in
the denitrifying biofilter system. Supported aeration could induce a sustainable
wastewater treatment and prohibit algae-based system from changing into activated
sludge even when the amount of sunshine is insufficient. Additionally, supported
aeration enhances the growth of both algal and nitrifying bacteria by decreasing
competitive inhibition and decreases the required land area. Under an optimized
operational condition of EANP (i.e., 4 days of solids retention time (SRT) and 8.6 h
of HRT), the oxygen consumption was below 50% compared to the traditional A2O
(anaerobic/anoxic/oxic) process, and the removal efficiency of BOD, total nitrogen
(TN), and total phosphorus (TP) was improved to 98%, 73%, and 52%, respectively.
Considering the water retention time of HRAP (4~10 days) and WSPs (2~3 weeks)
(Santhanam 2009), EANP reduced required HRT dramatically. Although decreased
efficiency at low temperature is still one of the drawbacks, EANP is definitely a
highly possible technology for scale-up of algae-integrated wastewater treatment
processes by reducing required land area with short HRT.
3.5 Sustainability Benefits of Microalgal Products
3.5.1 Environmental Sustainability
Life cycle assessment (LCA) is a method used to quantify and measure the environmental impacts of a material, product, system, or service. More specifically, LCA
is a systems-based process of assessing and calculating the human health, energy,
and environmental burdens of those commodities from “cradle to grave.” This is
done by compiling and evaluating the input water, energy, and materials; output
by-products, pollutants, emissions, and waste; and the potential environmental
impacts, resource use, and waste generation throughout the life cycle. LCA provides
a method to (1) collect and manage materials and energy information for a life cycle
and (2) assess the potential energy and environmental impacts of materials and
energy flows.
Since existing LCAs on wastewater treatment have focused on biofuel production, the focus on the section will be on sustainability aspects of biofuels. To better
assess the costs and benefits of commercialization of algal biofuels, one would need
to evaluate their life cycle sustainability. Due to the difficulty of assessing sustainability using independent metrics, LCA is a favorable method to systemically
integrate these metrics to ultimately determine the energy and environmental impacts
of algal biofuels. Mu et al. (2014) surveyed the environmental impacts of
wastewater-based algal biofuels, as it is proposed to be a more commercial sustainable option. Four nutrient sources were examined – municipal wastewater influent to
the activated sludge process, centrate from the sludge drying process, swine manure,
and freshwater with synthetic fertilizers. Four algae conversion technologies were
12 Microalgae: An Eco-friendly Tool for the Treatment of Wastewaters for. . .
295
factors for scale-up could be removed by utilizing heterotrophic bacterial growth in
the denitrifying biofilter system. Supported aeration could induce a sustainable
wastewater treatment and prohibit algae-based system from changing into activated
sludge even when the amount of sunshine is insufficient. Additionally, supported
aeration enhances the growth of both algal and nitrifying bacteria by decreasing
competitive inhibition and decreases the required land area. Under an optimized
operational condition of EANP (i.e., 4 days of solids retention time (SRT) and 8.6 h
of HRT), the oxygen consumption was below 50% compared to the traditional A2O
(anaerobic/anoxic/oxic) process, and the removal efficiency of BOD, total nitrogen
(TN), and total phosphorus (TP) was improved to 98%, 73%, and 52%, respectively.
Considering the water retention time of HRAP (4~10 days) and WSPs (2~3 weeks)
(Santhanam 2009), EANP reduced required HRT dramatically. Although decreased
efficiency at low temperature is still one of the drawbacks, EANP is definitely a
highly possible technology for scale-up of algae-integrated wastewater treatment
processes by reducing required land area with short HRT.
3.5 Sustainability Benefits of Microalgal Products
3.5.1 Environmental Sustainability
Life cycle assessment (LCA) is a method used to quantify and measure the environmental impacts of a material, product, system, or service. More specifically, LCA
is a systems-based process of assessing and calculating the human health, energy,
and environmental burdens of those commodities from “cradle to grave.” This is
done by compiling and evaluating the input water, energy, and materials; output
by-products, pollutants, emissions, and waste; and the potential environmental
impacts, resource use, and waste generation throughout the life cycle. LCA provides
a method to (1) collect and manage materials and energy information for a life cycle
and (2) assess the potential energy and environmental impacts of materials and
energy flows.
Since existing LCAs on wastewater treatment have focused on biofuel production, the focus on the section will be on sustainability aspects of biofuels. To better
assess the costs and benefits of commercialization of algal biofuels, one would need
to evaluate their life cycle sustainability. Due to the difficulty of assessing sustainability using independent metrics, LCA is a favorable method to systemically
integrate these metrics to ultimately determine the energy and environmental impacts
of algal biofuels. Mu et al. (2014) surveyed the environmental impacts of
wastewater-based algal biofuels, as it is proposed to be a more commercial sustainable option. Four nutrient sources were examined – municipal wastewater influent to
the activated sludge process, centrate from the sludge drying process, swine manure,
and freshwater with synthetic fertilizers. Four algae conversion technologies were
12 Microalgae: An Eco-friendly Tool for the Treatment of Wastewaters for. . .
295