Phycoremediation by High-Rate Algal Ponds (HRAPs) - Biotechnological Applications of Microalgae - page 195

biorefinery process, including lipid extraction for biodiesel, utilization of residual
biomass for combustion, and anaerobic digestion of biosolids, has the poten-
tial to provide a significant amount of energy in the region of 4,610 kW-h d −1
to 48,000 kW-h d −1 (Sheehan et al . , 1998; Sturm and Lamer, 2011). The energy
requirement of conventional wastewater treatment is significantly higher than
that of high-rate algal ponds. The Advanced Integrated Wastewater Ponds System
(AIWPS), designed by Oswald and Green, LLC, requires up to 91% less energy
(kW-h kg −1 BOD removed) than conventional systems (Olguın, 2003; Rawat
et al . , 2011).
Microalgal oxygen release provides the oxygen required for the proliferation
of heterotrophic bacteria, thus negating the requirement for mechanical aera-
tion as in conventional wastewater treatment. Conventional wastewater treatment
costs approximately four times more than the use of HRAPs (Rawat et al . , 2011).
The AIWPS consists of advanced facultative ponds with anaerobic digestion pits,
HRAPs, algal settling ponds, and maturation ponds in series (Craggs, 2005). This
system requires 50 times more land area than conventional wastewater treatment
viz. activated sludge, not taking into account the land area required for waste
activated sludge disposal. Capital costs and operational costs of the AIWPS are
half and less than one-fifth that of activated sludge, respectively (Park et al . ,
2011a). The supply of nutrients, water, and CO 2 contributes from 10% to 30%
of the total cost of commercial algal production (Benemann, 2008). Much of
the cost of wastewater HRAPs is covered by the cost of wastewater treatment
(Table 12.2). The costs of algal production and harvesting using wastewater
treatment HRAPs have less environmental impact in terms of water footprint,
energy, and fertilizer use. Recycling of growth media is used as a method of
minimizing costs. Recycling can, however, cause a reduction in algal productiv-
ity due to the increase in contamination and/or the accumulation of inhibitory
metabolites (Park et al . , 2011a).
12.8 CONCLUSION
Researchers are in general agreement that the use of wastewater treatment HRAPs
is the only economical method currently available for algal production of biofuels.
There are significant benefits to the use of wastewater HRAPs for the effective, low-
cost treatment of wastewaters and algal biomass production for biofuels generation.
There is, however, still a great need to optimize conditions for algal growth and
nutrient removal under prevailing climatic conditions. Large-scale lipid optimiza-
tion and harvesting of algal biomass still remains a challenge, and improvements in
this area will subsequently decrease the overall cost of algae production and reme-
diation of wastewater.
ACKNOWLEDGMENTS
The authors hereby acknowledge the National Research Foundation (South Africa)
for financial contribution.