3 Bio-liquid Fuels in Industrial Plant Oil
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technologies for processing biomass that extend beyond those that focus on TAGs.
Ideal attributes for algal feedstock for fuels include rapid and dense growth; efficient
use of nutrients, light, and carbon dioxide (CO 2 ) under a range of temperatures; resistance to pests and predators; accumulation of desirable macromolecules that can be
processed into fuels; ease of harvest; and the absence of undesirable by-products.
Commercial and research interest in the United States has focused on microalgae,
and these species are emphasized in this report. Microalgae have been reported to
reach short-term maximum productivities of 50–60 g dry weight per square meter
per day in CO 2 enriched open ponds in Hawaii and California [33]. These and other
data on productivity from laboratory scale experiments have promoted the reputation of microalgae as prime candidates for providing cheap biomass feedstocks
for food, feedstuff, or energy. Some authors have extrapolated values of maximal
biomass productivity and combined them with maximal oil content to predict oil
yields of 100 tons per hectare (ha) per year. Such reports have spurred investment
in intensive research on algal biofuel production. However, such high productivity
projections have yet to be obtained in large-scale, long-term experiments. Serious
barriers remain for reproducing optimal growth and productivity conditions at a commercial scale. They include maintaining the stability of the culture and delivering
the required nutrients and other resources in an efficient manner at such scales. Current yields from large-scale operations range from 40–60 tons dry weight of algal
biomass production per year, and conservative projections anticipate up to 100 tons
dry weight of biomass, or 30 tons of biodiesel per year in subtropical or tropical, sunny
climates [34].
3.2.2 Processing Algal Biomass into Biofuels
Fuel production from algal biomass is most commonly assumed to involve the cultivation of microalgal species that can process the lipid into biodiesel and have high
lipid productivity. In this case, production of biofuel requires the algae to be concentrated and subsequently treated to cause the release of the intracellular lipids.
The concentration or harvest step involves the separation and typically drying of the
algal cells to prepare them for lipid collection. Lipid collection usually is accomplished by rupturing the algal cells. Subsequent extraction of the biomass might be
required for economical oil recovery. Thus, biodiesel production from algae requires
two distinct separation steps—harvest and product collection—regardless of whether
growth occurs in open or closed photobioreactors.
The important feature in harvest and extraction is that the algae and the lipids are
insoluble in water. The technical problem in the production of biodiesel is simply
producing a pure, dry triacylglycerol stream for subsequent processing to biofuels.
Because the algal biomass and the algal oils are immiscible in water, harvest can
be completely spontaneous, and there is no key thermodynamic separation energy
to be overcome. The constraints on the system are purely engineering-related, and
better engineering can reduce the energy expenditure required for separating the algal
95
technologies for processing biomass that extend beyond those that focus on TAGs.
Ideal attributes for algal feedstock for fuels include rapid and dense growth; efficient
use of nutrients, light, and carbon dioxide (CO 2 ) under a range of temperatures; resistance to pests and predators; accumulation of desirable macromolecules that can be
processed into fuels; ease of harvest; and the absence of undesirable by-products.
Commercial and research interest in the United States has focused on microalgae,
and these species are emphasized in this report. Microalgae have been reported to
reach short-term maximum productivities of 50–60 g dry weight per square meter
per day in CO 2 enriched open ponds in Hawaii and California [33]. These and other
data on productivity from laboratory scale experiments have promoted the reputation of microalgae as prime candidates for providing cheap biomass feedstocks
for food, feedstuff, or energy. Some authors have extrapolated values of maximal
biomass productivity and combined them with maximal oil content to predict oil
yields of 100 tons per hectare (ha) per year. Such reports have spurred investment
in intensive research on algal biofuel production. However, such high productivity
projections have yet to be obtained in large-scale, long-term experiments. Serious
barriers remain for reproducing optimal growth and productivity conditions at a commercial scale. They include maintaining the stability of the culture and delivering
the required nutrients and other resources in an efficient manner at such scales. Current yields from large-scale operations range from 40–60 tons dry weight of algal
biomass production per year, and conservative projections anticipate up to 100 tons
dry weight of biomass, or 30 tons of biodiesel per year in subtropical or tropical, sunny
climates [34].
3.2.2 Processing Algal Biomass into Biofuels
Fuel production from algal biomass is most commonly assumed to involve the cultivation of microalgal species that can process the lipid into biodiesel and have high
lipid productivity. In this case, production of biofuel requires the algae to be concentrated and subsequently treated to cause the release of the intracellular lipids.
The concentration or harvest step involves the separation and typically drying of the
algal cells to prepare them for lipid collection. Lipid collection usually is accomplished by rupturing the algal cells. Subsequent extraction of the biomass might be
required for economical oil recovery. Thus, biodiesel production from algae requires
two distinct separation steps—harvest and product collection—regardless of whether
growth occurs in open or closed photobioreactors.
The important feature in harvest and extraction is that the algae and the lipids are
insoluble in water. The technical problem in the production of biodiesel is simply
producing a pure, dry triacylglycerol stream for subsequent processing to biofuels.
Because the algal biomass and the algal oils are immiscible in water, harvest can
be completely spontaneous, and there is no key thermodynamic separation energy
to be overcome. The constraints on the system are purely engineering-related, and
better engineering can reduce the energy expenditure required for separating the algal