While re-use of CO2 would be desirable and some water requirements could be met with wastewater or saline water, the increased demand for fertilizer and electricity could have negative economic impacts. Depend­ing on the scale of production, this electricity input requirement could impact electricity prices and yield a significant, unintended increase in carbon emissions.

5.3.6.1 CARBON DIOXIDE

Under ideal conditions, algae require roughly 2 kg of CO2 for each kg of algal biomass produced [2,15,17]. However, in the experiments, most of the CO2 delivered to the growth volumes was not retained in biomass (and released as outgas). As a result, 9.35 g of CO2 were consumed per liter of pond water processed, which only contained 0.26 g of algae, on average. Based on this consumption, 3.7 Mg of CO2 were consumed per L of bio-oil. For the Highly Productive Case (with 1 kg algal biomass/kL of processed volume, 8 kg of CO2 per kL of processed volume, and 0.26 L of bio-oil per kL of processed volume) 31 kg of CO2 would be required for each L of bio-oil produced. For 19 GL/yr of bio-oil (5 Bgal/yr), this equates to 5.8 x 1011 kg of CO2 consumed per year, which is ~11% of the total CO2 emissions from the U. S. [42].