example, algae-integrated wastewater treatment systems are able to capture CO 2
from power plants and remove N and P from wastewater while cultivating algae for
biofuel production. Inorganic carbon and air from CO 2 and air gas sparging can be
controlled for achieving proper autotrophic cultivation, DO removal, and optimal
pH. Continuous flow of wastewater influent can be applied to PBRs, minimizing
water loss and the need to supply exogenous nutrients. Continuous recycling of the
culture medium could substantially reduce production costs by minimizing the water
and nutrient footprints (Zaimes and Khanna 2013).
3.2 Membrane Integration with Algae Processes
In microalgal biorefineries, 90% of equipment costs are associated with microalgae
dewatering, which is a major burden hindering the development of a microalgaebased fuel industry. Microfiltration (MF), ultrafiltration (UF), and forward osmosis
(FO) are typically used for algae membrane separation. Although membrane filtration for algal bioenergy production is still an infant technology, the integration of
membrane technology with microalgae processes for wastewater treatment can
provide simultaneous nutrient removal and biomass generation for renewable energy
production. There are three types of membrane integration with algae processes for
wastewater treatment: (1) an integration of a traditional activated sludge process
(ASP) with a membrane photobioreactor (MPBR), (2) an integration of membrane
bioreactors (MBRs) with conventional microalgae photobioreactor, and (3) an integration of MBRs with a MPBR. As microalgae are photoautotrophic, in the common
practice of wastewater treatment, abundant organic carbon is oxidized in a MBR or
ASP, and then the effluent is polished using microalgae in a PBR or MPBR as a
posttreatment. Either aerobic or anaerobic MBRs are used for organic carbon
removal in the first stage. Using algae, P can be removed by “luxury uptake”
under P limitation or chemical phosphate precipitate by microalgae-induced flocculation. Algae-induced P precipitation is key to P removal in high-density algae
cultivation of an algae-based membrane bioreactor (A-MBR), which produces
P-rich algal biomass with good settling properties. Low tendency for membrane
fouling is also reported due to the low algal extracellular polymeric substances (EPS)
production.
3.3 Bioenergy Production from Wastewater
3.3.1 Biodiesel Production from Microalgae
Biodiesel is a mixture of fatty acid methyl esters (FAMEs) obtained by
transesterification (ester exchange reaction) of lipid feedstock like algal cells. Esters
in FAMEs can have R1, R2, and R3 as long-chain hydrocarbons, which can be
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from power plants and remove N and P from wastewater while cultivating algae for
biofuel production. Inorganic carbon and air from CO 2 and air gas sparging can be
controlled for achieving proper autotrophic cultivation, DO removal, and optimal
pH. Continuous flow of wastewater influent can be applied to PBRs, minimizing
water loss and the need to supply exogenous nutrients. Continuous recycling of the
culture medium could substantially reduce production costs by minimizing the water
and nutrient footprints (Zaimes and Khanna 2013).
3.2 Membrane Integration with Algae Processes
In microalgal biorefineries, 90% of equipment costs are associated with microalgae
dewatering, which is a major burden hindering the development of a microalgaebased fuel industry. Microfiltration (MF), ultrafiltration (UF), and forward osmosis
(FO) are typically used for algae membrane separation. Although membrane filtration for algal bioenergy production is still an infant technology, the integration of
membrane technology with microalgae processes for wastewater treatment can
provide simultaneous nutrient removal and biomass generation for renewable energy
production. There are three types of membrane integration with algae processes for
wastewater treatment: (1) an integration of a traditional activated sludge process
(ASP) with a membrane photobioreactor (MPBR), (2) an integration of membrane
bioreactors (MBRs) with conventional microalgae photobioreactor, and (3) an integration of MBRs with a MPBR. As microalgae are photoautotrophic, in the common
practice of wastewater treatment, abundant organic carbon is oxidized in a MBR or
ASP, and then the effluent is polished using microalgae in a PBR or MPBR as a
posttreatment. Either aerobic or anaerobic MBRs are used for organic carbon
removal in the first stage. Using algae, P can be removed by “luxury uptake”
under P limitation or chemical phosphate precipitate by microalgae-induced flocculation. Algae-induced P precipitation is key to P removal in high-density algae
cultivation of an algae-based membrane bioreactor (A-MBR), which produces
P-rich algal biomass with good settling properties. Low tendency for membrane
fouling is also reported due to the low algal extracellular polymeric substances (EPS)
production.
3.3 Bioenergy Production from Wastewater
3.3.1 Biodiesel Production from Microalgae
Biodiesel is a mixture of fatty acid methyl esters (FAMEs) obtained by
transesterification (ester exchange reaction) of lipid feedstock like algal cells. Esters
in FAMEs can have R1, R2, and R3 as long-chain hydrocarbons, which can be
290
J.-H. Hwang et al.