Potential of microalgae for phytoremediation of various wastewaters for nutrient removal and biodiesel production through nanocatalytic transesterification

Tetraselmis indica, a strain of microalgae, was cultivated in four distinct wastewaters in a photobioreactor of 1000 ml in a 16:8 light/dark period beneath the light intensity of 94.5 mu mol m(-2) s(-1) for 14 days. The maximum biomass growth of 1125 mg/L was attained in the sewage wastewater (SWW). The T. indica eliminated the maximum pollution load from the primary wastewater of the paper mill (PWW), which was 94.95% nitrate, 96.625% phosphate, 99.5% ammonia, 72.8% COD, 94.14% BOD, and 98.9% TDS and heavy metals (94.84% Pb, 93.83% Mg, 99.78% Cu, 81.25% Mn, 94% Cd, 70.34% Zn, 99.84% Fe). The effectiveness of a lithium-impregnated calcium oxide 1.75-Li-CaO nanocatalyst in the transesterification of microalgae was evaluated after growing an appropriate amount of microalgae on all four wastewaters. The nanocatalyst 1.75-Li-CaO was prepared by the wet impregnation method and characterized by various structural and spectral techniques. The scanning electron microscopy study shows the structure of nanocatalyst, which is in the shape of oval and hexagonal with a particle size of 20 nm. The Fourier transform infrared spectroscopy spectrum confirms that the nanocatalyst contains necessary functional groups, which were visible at 1470 cm(-1). Because of its highest basic strength, 1.75-Li-CaO exhibits the highest activity for trans-esterifying microalgal oil. The FAME profile of PWW-based microalgae through nanocatalytic transesterification shows the existence of myristic acid (2.81%), stearic acid (5.28%), palmitic acid (38.74%), oleic acid (16.43%), linoleic acid (21.19%), and arachidic acid (5.85%). Thus, this research work validates that microalgae grown on SWW have the highest biomass output, and microalgae cultivated on PWW have the highest FAME yield when used to make biodiesel using nanocatalytic transesterification.