Effect of CO 2 and metal-rich waste water on bioproduct potential of the diazotrophic freshwater cyanobacterium, Tolypothrix sp.

Continued economic growth is reliant on stable, affordable energy, requiring at present fossil fuel-derived energy production. Coal-fired power stations produce metal-rich but macro-nutrient-poor waste waters and emit flue gas, containing ∼10% CO ₂ . Algae and cyanobacteria remediate metals and CO ₂ , but use of N ₂ -fixing (diazotrophic)cyanobacteria can reduce nitrogen-fertilization costs. The resulting biomass represents a promising source for biofuel and bio-product development. This study investigated the effect of CO ₂ - and trace metals on growth performance, biochemical profiles and metal content of the freshwater diazotrophic cyanobacterium Tolypothrix sp. to assess bioproduct potential. Aerated 2 L batch cultures were grown in simulated ash-dam water (SADW)and BG11 without nitrogen (BG11(-N)controls). Supplied air was supplemented with either 15% CO ₂ or not (non-CO ₂ controls). CO ₂ supplementation resulted in 2.4 and 3.3-fold higher biomass productivities and 1.3 and 1.2-fold higher phycocyanin and phycoerythrin contents, whilst metals (media)had no effect. Al, Cu, Ni and V were more efficiently removed (50–90%)with CO ₂ -addition, while As, Mo, Se and Sr removal was higher (30–87%)for non-CO ₂ controls. No significant effect on Zn and Fe removal was evident. Calculated biomass metal concentrations, at quantities required to meet N-requirements of wheat, suggests no metal toxicity when applied as a mineral-nitrogen biofertilizer. With a carbohydrate content of 50%, the biomass is also suitable for bioethanol production. In summary, Tolypothrix sp. raised in ash dam waste water supplemented with flue gas CO ₂ could yield high-value phycobiliproteins, bioethanol or biogas, and mineral-rich nitrogen fertilizer which would offset remediation costs and improve agricultural productivity.