Namibia Workshop Presentations

Presenter: John Milledge

There has been considerable interest in the growth of micro-algae to produce renewable biofuels, as they can be cultivated on non-agricultural land and many species grow in brackish or salt water, but the production of micro-algal biofuel appears currently uneconomic. Micro-algae production is economically viable for non-fuel products that may represent only a minor fraction of the total biomass. It is critical for the commercial viability of micro-algae biofuels to; exploit the entire biomass and co-products; and reduced energy consumption of algae cultivation, harvesting and processing.

Biorefinery is a term used in the literature since the 1980s, and is the co-production of a spectrum of high value bio-based products and energy from biomass. Dunaliella salina is grown in highly saline water for the production of β-carotene and could also be a source of glycerol for use as biofuel and a green chemical feedstock. The growth of Dunaliella could provide the biomass for a biorefinery. This type of biorefinery, that produces a variety of products from a single biomass source, may be termed a vertical biorefinery.

Dunaliella is found in open pan salt production ponds and an economic analysis has shown that the costs of growing Dunaliella may be reduced by combining growth of the alga with natural evaporative salt production. The micro-algal species found in open salt pan production systems vary throughout the process with changing salt concentration. Dunaliella from open salt pans could provide the feed stock for a vertical biorefinery, but the variety of micro-algal species in the various stages of salt production might provide additional micro-algal biomass feed stocks that may yield an additional range of high value products. The exploitation of changing micro-algae with increasing salt concentration for a variety of end products may be termed a horizontal biorefinery.