Bioremediation of restaurant wastewater using extremophilic Galdieria sulphuraria: An approach contributing to circular bioeconomy and environmental sustainability

Recently, some applied sciences have focused on the biorefinery of wastewater because of its intrinsic composition. Algal-based wastewater treatment was explored for its potent bioremediation ability and biomass production, which can be used in various applications. When considering microalgae cultivation’s role in integrated production systems, especially when using wastewater and gaseous effluents, the hunt for new potential strains is crucial. This research explored the potential of microalga Galdieria sulphuraria (G. sulphuraria) 074 W (NIES-3638) to bioremediate raw restaurant wastewater owing to its distinct characteristics, including high temperature and acidic pH settings. The cultivation conditions were subjected to three cultivation modes (i.e., mixotrophic, heterotrophic, and autotrophic) for 14 days. During the cultivation of G. sulphuraria, various evaluations, including optical density, specific growth rate, and biomass productivity, were examined. Furthermore, the bioremediation efficiency of G. sulphuraria was examined for the removal of pollutants, including chemical oxygen demand (COD), biochemical oxygen demand (BOD), fats, oil, grease (FOG), and uptake of nutrient such as ammoniacal-nitrogen (NH₄⁺-N), total-nitrogen (TN), total-phosphorus (TP), and potassium (K). G. sulphuraria grown with restaurant wastewater scored 0.15 day⁻¹ for specific growth rate and 39 mg L^-1 d^-1 biomass productivity. The maximum removal efficiencies for COD, BOD, FOG, NH₄⁺-N, TN, TP, and K were 71%, 80%, 66%, 96%, 93%, 99%, and 75%, respectively. Overall, this study revealed that using G. sulphuraria is a promising approach for treating restaurant wastewater by removing pollutants, uptaking nutrients, and producing enriched biomass that can be further utilized to generate secondary metabolites.