The effects of limiting nighttime aeration on productivity and lipid accumulation in Scenedesmus dimorphous

As algal research strives for economic viability of algal biomass as a resource for biofuels and bioproducts there are two key foci that need continued research: reducing energy consumption and utilizing ammonium as nitrogen source. One of the largest concerns in utilizing ammonium as a nitrogen source for algal cultivation is the volatility and toxicity associated with pH values greater than 8.0. In cultures aerated with increased CO₂ concentrations pH becomes problematic at night when the CO₂ supply is removed and the pH of the cultivation medium re-equilibrates with the atmosphere (typically) above a pH of 8.0. In photobioreactors, one of the ways to eliminate energy consumption is to minimize aeration and mixing at night, which also prevents the pH of the medium from increasing. However, by eliminating nighttime aeration cultures show a significant lag in lipid accumulation attributable to anoxic conditions. To minimize oxygen limitations, cultures were either periodically sparged or supplied with low aeration (less than 10% of daytime aeration) to minimize pH increase. The results showed similar productivities to highly aerated cultures with a decrease of more than 95% of nightly aeration requirements and concomitant energy consumption.