Algae Crops: Coproduction of Algae Biofuels - Industrial Crops: Breeding for BioEnergy and Bioproducts - page 371

Other limiting factors that impact the growth of algae include the supply of
nutrients—carbon being the most essential [ 4 ]. Temperature is another factor that
may limit algae biofuels production. Optimal biofuel algae production occurs
between 20 and 35 C[ 4 ]. The diurnal temperature, not the average, is more
important because high temperature at night increases metabolism, consuming
some daylight production. Also, cold water temperatures in the early morning
slow down production substantially. Other factors that impact algae biofuel pro-
duction include water quality and water use, the physical mixing of the pond, as
well as the biotic environment.
Large technical barriers to algae biofuel production prevent it from becoming
economically viable. However, coproduction may tip the economics making algae
biofuels profitable. Further, as the conceptual framework suggests, coproduction of
algae with other value-added products using aquaponics, especially when there is a
large gap between the private and social cost of production, may result in algae
biofuels becoming economically profitable.
Discussion and Concluding Remarks: Searching
for Synergies
Production of algae biofuels is expensive, at least at present and in the near term.
Thus, for algae production to become economically viable, additional income
streams are required. One example, presented in [ 4 ], was to combine algae produc-
tion with wastewater treatment. Combining algae biofuels and wastewater treat-
ment produced a net cash flow of $0.21/kWh. Other options discussed in the
literature consider coproduction of animal feed with algae biofuel. However, [ 4 ]
argued that the benefits are at most marginal and it might make more sense
economically to produce animal feed without the biofuel component. Another
option would be to combine biofuel production with high-value coproducts. One
example is Haematococcus pluvialis for production of astaxanthin.
The concept guiding aquaponics is the creation of sustainable aquatic production
systems. The idea is to combine both aquaculture and hydroponics, such that the
effluents that accumulate in the water and increase toxicity for the fish can be
transferred to a hydroponic system that filters out the pollution from the aquaculture
system. The cleansed water is recirculated back to the aquaculture production
system. Algae can be used to treat wastewater and consume the nutrients, and this
system can support large-scale fish production. Furthermore, such production
processes warrant government support because of the pollution they are preventing.
Future research will assess such systems and evaluate their sustainability, as well as
measure the income flows of coproducing fish and algae for biofuels. This research
will derive a threshold price that will determine if algae should go to feed, biofuels,
or both—should it be used within a closed system or sold and used in industrial
processes. Such analysis will compare the proposed aquatic system with alternative
methods as well as alternative fuels.