Abstract
Intensive algal cultivation usually requires a high flux of dissolved inorganic carbon (Ci) to support productivity, particularly for high density algal cultures. Carbon dioxide (CO2) enrichment can be used to overcome Ci limitation and enhance productivity of algae in intensive culture, however, it is unclear whether algal species with the ability to utilise bicarbonate (HCO3 −) as a carbon source for photosynthesis will benefit from CO2 enrichment. This study quantified the HCO3 − affinity of three green tide algal species, Cladophora coelothrix, Cladophora patentiramea and Chaetomorpha linum, targeted for biomass and bioenergy production. Subsequently, we quantified productivity and carbon, nitrogen and ash content in response to CO2 enrichment. All three species had similar high pH compensation points (9.7–9.9), and grew at similar rates up to pH 9, demonstrating HCO3 − utilization. Algal cultures enriched with CO2 as a carbon source had 30% more total Ci available, supplying twenty five times more CO2 than the control. This higher Ci significantly enhanced the productivity of Cladophora coelothrix (26%), Chaetomorpha linum (24%) and to a lesser extent for Cladophora patentiramea (11%), compared to controls. We demonstrated that supplying carbon as CO2 can enhance the productivity of targeted green tide algal species under intensive culture, despite their clear ability to utilise HCO3 −.
Highlights
Macroalgal biomass is an emerging resource for sustainable bioenergy [1] and advanced biofuels [2,3]
There was a significant interaction between the species and the pH levels in which they were cultured (P,0.001, Table 1, Fig. 2), driven by different optimal pH ranges for growth
This study demonstrates that three green tide algal species, C. coelothrix, C. linum and C. patentiramea, have the ability to use HCO32 as a complementary carbon source to CO2 for photosynthesis
Summary
Macroalgal biomass is an emerging resource for sustainable bioenergy [1] and advanced biofuels [2,3]. Bioenergy applications rely on the production of a high volume/low value biomass opening opportunities to develop the culture of new commercial species. Green tide algae have the potential to meet these criteria as they are fast growing species [4] with a tolerance to a broad range of environmental conditions [5]. They are highly suitable as a bioenergy feedstock for ethanol [6], biogas [7,8] and thermo-chemical conversion to biocrude [3,9]. They can be cultured intensively in land-based ponds and tanks integrated into nutrient-rich aquaculture [12,13,14] and municipal [15] waste streams for bioremediation
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