Improved neutral lipid production from Tetradesmus obliquus through fed-batch mixotrophic cultivation at high pH using potato peel hydrolysate

This study investigated the use of potato peel hydrolysate (PPH), obtained through fungal fermentation, as a low-cost organic carbon source to promote the growth and lipid accumulation of Tetradesmus obliquus under initial alkaline conditions (pH 11.0). Mixotrophic growth was investigated by incorporating different volumes of PPH to the culture every two days, resulting in final reducing sugar concentrations of 0.01, 0.02, and 0.03 mg mL− 1. The mixotrophic fed-batch cultivation (0.02 mg mL− 1 PPH) significantly enhanced microalgal biomass and neutral lipid (NL) productivity, reaching 62.73 and 18.70 mg L− 1 day− 1, respectively, which were 1.8 and 2.5 times higher than the autotrophic control. Moreover, the mixotrophic fed-batch system was evaluated under various nutrient conditions. Low nitrogen or sulfur deprivation notably boosted NL productivity to 20.90 and 22.61 mg L− 1 day− 1, respectively. The lipids produced under nutrient-limited mixotrophic fed-batch conditions at pH 11.0 were rich in monounsaturated fatty acids (77.49–80.79%) and saturated fatty acids (15.39–19.23%), with the remaining portion comprising polyunsaturated fatty acids. Additionally, various biodiesel properties were assessed, and the results met international standards. These findings suggest that mixotrophic fed-batch cultivation under extreme alkaline conditions can enhance microalgal productivity and promote cost-effective biofuel production.