Analysis of Microalgal Biorefineries for Bioenergy from an Environmental and Economic Perspective Focus on Algal Biodiesel - Biotechnological Applications of Microalgae - page 134

Supply of nutrients, yield of products from these nutrients, and recycle of unused
nutrients impact GWP and fossil fuel requirements significantly. Opportunities
exist in selecting algal species able to scavenge low nutrient concentrations, having
reduced nitrogen content, as well as to utilize nitrogen and phosphorous resources
efficiently, either by their provision from wastewater or through their recycle.
The typically dilute biomass concentrations required to minimize light limitation
result in the need to process large culture volumes; hence, natural flocculation to
facilitate settling is beneficial. In downstream processing, the most important factors
pertain to the ability to process wet biomass, thereby eliminating the drying process,
as well as the ability to recover product from the algal cell readily, thus minimizing
the requirement for conventional, energy-intensive cell disruption.
As reported by Harding (2009), the production phase typically has the greatest
impact on the overall LCA; hence, its optimization is required in the first instance.
Opportunities to improve the economics correlate well with the environmental
analysis with respect to operating costs. These highlight mass transfer and mixing,
provision of CO 2 , provision of nutrients, biomass recovery, and the avoidance of
rigorous drying. More importantly, the economic studies suggest that algal biofuel
technology requires further enhancement prior to its economic feasibility as a stand-
alone technology. However, opportunity exists to establish a cost-effective algal
biorefinery delivering a combination of products such as biodiesel, biogas, animal
feed, and protein extracts. To this, high-value products may be added. Further, the
predicted cost of algal biomass positions it attractively as a raw material source for
bulk products, including fuels, chemicals, materials feeds, and food supplements.
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