Industrial effluent driven lipid induction in marine microalgae under mixotrophic growth: Comparative evaluation of defined carbon sources and non-sterile effluent environments.

The use of marine microalgae as a viable platform for generating renewable fuel through the biomass has sustainable production due to its fast growth rate, lipid content and the ability to assimilate various carbon compounds. The possibility of using unsterilized industrial wastewater as asource of carbon and enhancing microalgal biomass and lipids production is hardly known, especially when contrasted to pure carbon sources and sterilized wastewaters. This study evaluates the mixotrophic growth performance and lipid productivity of two marine microalgae strains, Chlorella vulgaris BDUG 91771 and Picochlorum sp. BDUG 100241, using defined carbon sources (glucose, sucrose, sodium acetate, glycerol, ethanol, sodium bicarbonate) and wastewater-derived effluents (ossein and molasses effluent) diluted with seawater. Among tested carbon sources, glucose yielded the highest biomass in C. vulgaris (1.73 g L-1), while glycerol supported maximum biomass in Picochlorum sp. (6.1 g L-1). However, defined carbon sources showed minimal influence on lipid accumulation, similar to the control. Non-sterile 10% ossein and molasses effluents markedly enhanced lipid yields to 0.570 g L-1 than the control 0.346 g L-1 day-1 in C. vulgaris. Likewise, 1.769 g L-1, 1.159 g L-1 day-1 in Picochlorum sp., representing increased yield over control. These lipid enhancements significantly exceeded those observed with pure carbon sources and sterilized (autoclaved) effluents, indicating that native microbial enzyme-producing communities and heat-sensitive complex carbohydrate substrates are critical for lipid accumulation. The superior performance of non-sterile effluents may contributed to bacterial enzymatic degradation of complex organic polymers into bioavailable simple sugars and volatile fatty acids (acetate, butyrate), coupled with microbial-mediated nutrient transformations that create lipid-inducing conditions. The treatments also maintained robust biomass production, enabling simultaneous growth and lipid induction. This novel integrated approach supports both effective effluent remediation and economically viable microalgal biofuel production, highlighting marine microalgae as promising candidates for next-generation renewable energy systems.