Abstract
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.
Highlights
IntroductionThe addition of sulfate as a source of sulfur has been shown to increase microalgal biomass production as well as nitrogen and phosphorus removal efficiencies (Mera et al 2016; Lv et al 2017)
The highest biomass concentration of Chlamydomonas moewusii was obtained in a medium with ammonium as the nitrogen source when sulfur concentrations were between 3.2– 96 mg L−1 (Mera et al 2016), while the final Chlorococcum sp. biomass concentration and specific growth rates were similar in a synthetic wastewater with nitrate as nitrogen source when sulfur concentration was 6, 15, 25.7, 45.3, and 90.3 mg L−1 (Lv et al 2017)
The different iron and sulfur concentrations resulted in varied ash-free dry weight (AFDW) with both NO3− and NH4+
Summary
The addition of sulfate as a source of sulfur has been shown to increase microalgal biomass production as well as nitrogen and phosphorus removal efficiencies (Mera et al 2016; Lv et al 2017). The highest biomass concentration of Chlamydomonas moewusii was obtained in a medium with ammonium as the nitrogen source when sulfur concentrations were between 3.2– 96 mg L−1 (Mera et al 2016), while the final Chlorococcum sp. Tao et al (2017) observed different microalgal biomass concentration and ammonium removal efficiencies were obtained when Scenedesmus acuminatus was grown in two kinds of liquid digestates from pulp and paper industry and one potential reason for the difference was different initial sulfur concentration of the digestates
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