Coupling simultaneous bioremediation with high lipid production for quality biodiesel via mixotrophic cultivation of Scenedesmus obliquus in fed-batch.

Sustainable biofuels and the remediation of complex industrial effluents present a critical challenge in the global water-energy nexus. The present work explores a novel strategy for mixotrophic fed-batch cultivation utilizing pre-acclimatized Scenedesmus obliquus to achieve simultaneous bioremediation and high-quality biodiesel production. A constant specific growth rate regime designed to maintain a pseudo-steady-state with a constant biomass-to-substrate ratio was evaluated against the linear feeding model and the traditional continuous chemostat cultivation. To simulate extreme environmental conditions, a 10-fold concentrated cultivation feed was formulated, incorporating continuous CO2 with air, glucose, and glycerol supplementation alongside heavy metal, bicarbonates, synthetic seawater and Najafgarh-drain-wastewater. The developed fed-batch strategy achieved a maximum dry cell weight of 81.53 ± 0.08 g/L and total lipid content of 88.70 ± 0.08 % (g/g), within an improved timeframe of 152-192 h, demonstrating high-quality lipid production with the highest lipid productivity of 0.495 g/L/h in fed-batch and 0.181 g/L/h in chemostat. The system exhibited bioremediation efficiencies of more than 97 % for heavy metals and bicarbonates. GC-MS profiling of the transesterified lipids revealed a FAME composition dominated by C16:0 and C18:1. The biodiesel properties revealed cetane number as 60.024, higher heating value as 39.933 MJ/kg, specific gravity as 0.877 kg/L, kinematic viscosity as 4.399 cSt, iodine value 68.141 (g I2/100 g oil), and cloud point as 9.379 °C, confirmed strict compliance with EN-14214 and ASTM-D6751 international biodiesel standards. By coupling simultaneous bioremediation with high lipid production, this integrated approach presents a highly scalable, sustainable paradigm that directly advances UN-SDGs 6, 7, 9, 12, and 13.