Use of factorial experimental design to study the effects of iron and sulfur on growth of Scenedesmus acuminatus with different nitrogen sources

The aim of this study was to determine the combined effects of iron and sulfur on microalgal biomass concentration and removal efficiency of nitrogenous compounds using factorial design. Scenedesmus acuminatus (currently accepted name Tetradesmus lagerheimii) was separately cultivated in batch photobioreactors using modified N-8 media with two nitrogen sources, nitrate, and ammonium. To study the interaction effect between iron and sulfur and to reduce the total number of experimentally studied combinations, a factorial design was used. Three iron (0.1, 1, and 1.9 mg L⁻¹) and three sulfur concentrations (3.7, 20, and 35.8 mg L⁻¹) were employed to the modified N-8 media in this study. The results show that the final microalgal biomass concentration and nitrogen removal efficiency were more sensitive to the changes in iron and sulfur concentrations in the media with nitrate than with ammonium possibly because of the different assimilation mechanisms used by microalgae for these two nitrogen sources. The created models demonstrated that iron had a statistically significant effect on the microalgal biomass concentration and nitrate removal efficiency while sulfur did not. In addition, the interaction effect between iron and sulfur was not significant on microalgal biomass concentration and nitrogen removal. In synthetic medium with nitrate as nitrogen source, the highest microalgal biomass concentration was obtained with 1.0 mg L⁻¹ iron and 35.8 mg L⁻¹ sulfur.