Abstract
In this study, wastewater was utilized as an inexpensive medium for cultivating microalgae for biodiesel production using SO42−/Fe3O4-Al2O3 as a magnetic nanocatalyst. Next, some parameters affecting the growth of microalgae in a non-sterile medium (municipal wastewater), catalyst activity (sulfate and ferric oxide concentrations), and biodiesel production (transesterification reaction conditions) were assessed. Regarding the weight of cultivated microalgae, the highest growth was obtained after 5 days. The results of the catalyst studies indicated the important role of the sulfate groups in the activity of the alumina with the highest activity obtained at 2 M concentration of sulfuric acid. These groups formed sulfated alumina structures as active phases causing enhanced surface area, acidity, and activity. Further, the addition of ferric oxide to alumina at Fe/Al ratio of 0.25 resulted in production of a catalyst with suitable activity and magnetic properties while the sample with Fe/Al ratio of 0.15 and 0.35 presented negligible magnetic properties and insufficient enhancement in the activity, respectively. Finally, a yield of 87.6% was obtained using the best magnetic nanoparticle under the optimum conditions of 120 °C, catalyst concentration of 8 wt%, 9 mL methanol/g microalgae, and 4 h of reaction time. The best sample also showed appropriate reusability such that its activity declined by around 14.2% after the fifth cycle of use.
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