Cultivation of microalgae Chlorella sp. in municipal sewage for biofuel production and utilization of biochar derived from residue for the conversion of hematite iron ore (Fe₂O₃) to iron (Fe) – Integrated algal biorefinery

This study demonstrated the utilization of municipal sewage for high biomass production at large scale and achieved highest biomass yield of 46.3 tons and the lipid yield of 13.7 metric tons per acre in a year. The extracted crude lipid was analyzed for biodiesel production, and the yield attained was 92.5 wt% with respect to initial lipid weight. Furthermore, the lipid extracted residue obtained from two different algal biomass such as Chlorella sp. and Sargassum sp. were explored for biochar production through a slow pyrolysis technique at 400 °C. The hematite iron ore reduction with algal biochar was performed non-isothermally at 1100 °C under nitrogen atmosphere. The metallic iron synthesis from hematite iron ore involves three major steps, and they were as follows (1) in this step the Fe₃O₄ was synthesized from Fe₂O₃ at the temperature of 350–450 °C; (2) this step contain the formation of FeO from Fe₃O₄ at the temperature of 700–850 °C; (3) finally the formation of metallic iron (Fe) was observed at higher temperature of 850–1100 °C. Herein, we established a novel low-cost microalgae-based biorefinery approach for the production of bioenergy and residue for metallic iron production from municipal waste.