Screening of wastewater Oedogonium oblangum algae for hyper-oil transformation into biodiesel by response surface methodology

Abstract

The algae have gained more significance as a renewable third-generation feedstock for being easily available and a hyper-production source for lipids and biodiesel. Sustainable and cost-effective production of algal biodiesel requires screening and optimization of various culture conditions. Screening of algae on the basis of its lipid content is crucial for exploring its potential for production of biodiesel. In the current study, the screening of six indigenous algal strains was performed based on lipid contents, out of which Oedogonium oblangum (O. oblangum) exhibited hyper-lipid content (15.76%). Bold basal media and wastewater media were compared as culture media to evaluate the growth of O. oblangum; the respective strain showed better growth on wastewater media, therefore, this media was used for further experimentation. A laboratory-based integrated approach was used to enhance production of algal lipids by applying the effects of temperature, pH, and wastewater dilutions. The oil contents were interestingly improved under the optimal culture conditions of temperature (25°C), pH (6.5), wastewater dilution (45%) with oil contents of 18.35%, 17.15%, and 17.95%, respectively. The extracted oil was transformed into biodiesel by alkali-mediated transesterification reactions using four factors (Oil/methanol ratio, temperature, time, and catalyst) by response surface methodology (RSM). The RSM successfully optimized the transesterification reactions with 86.73% of biodiesel under optimal conditions of oil/alcohol ratio (1:7.6 v/v), temperature (60.5°C), time (59 ​min), and catalyst (0.53 ​wt. %). Physical properties of biodiesel (kinematic viscosity; 5.17; acid value; 0.63; flash point; 152; specific gravity; 0.74; calorific value; 42.11; and water contents; 0.03) comply with the ASTM standards and lead to enhance the quality of produced biodiesel. The optimized culture conditions, transesterification reactions, and wastewater medium can be employed for the economically production of biodiesel at commercial scale. Overall, the results showed that biodiesel derived from an indigenous novel algal strain, O. oblangum, has the potential to compete and replace commercially available petro-diesel using wastewater media. It might contribute to resolve the energy challenges being faced by Pakistan and the entire world.