Enhanced FAME production using green catalyst with superior profile from the isolated halophilic Aphanothece halophytica grown in raceway ponds

The unprecedented use of fossil fuels necessitates the research community to find clean, safe, renewable and sustainable energy source. One such promising source is microalgal biofuel, which can mitigate the environmental concerns and energy crisis due to its closed carbon cycle. Selection of proper strain and optimization of the culture conditions to maximize the lipid productivity is very important for successful economical biodiesel conversion process. One such robust halophilic species identified was Aphanothece halophytica with rich lipid productivity. They were cultivated in different media and optimized on lab scale as well as in large scale using raceway ponds to produce sufficient biomass for algal oil extraction. The biodiesel conversion process parameters were then optimized by multi-variant response surface methodology (RSM). The free fatty acid (FFA) content of the raw algal oil was only 0.51% which enables direct conversion by transesterification. Eco-friendly, natural white clam shell was calcinated to obtain CaO, which was recovered and reused for three times effectively. The maximum biodiesel yield of around 99 vol% was obtained for the oil/methanol ratio of 0.32(v/v) using calcinated CaO for 6 wt% of raw feed while stirring at 400 rpm at a temperature of 70 °C for 85 min. The GC-MS analysis of the algal biodiesel confirmed the presence of saturated and unsaturated fatty acids in balanced proportion to provide better oxidation stability and good combustion characteristics. Other biodiesel properties were analyzed and found to be within the standards specified by EN and ASTM for automotive application without any engine modification.