Enhanced Production of Green Tide Algal Biomass through Additional Carbon Supply

Intensive algal cultivation usually requires a high flux of dissolved inorganic carbon (Ci) to support productivity, particularly for high density algal cultures. Carbon dioxide (CO(2)) 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 (HCO(3) (−)) as a carbon source for photosynthesis will benefit from CO(2) enrichment. This study quantified the HCO(3) (−) 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 CO(2) enrichment. All three species had similar high pH compensation points (9.7–9.9), and grew at similar rates up to pH 9, demonstrating HCO(3) (−) utilization. Algal cultures enriched with CO(2) as a carbon source had 30% more total Ci available, supplying twenty five times more CO(2) 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 CO(2) can enhance the productivity of targeted green tide algal species under intensive culture, despite their clear ability to utilise HCO(3) (−).