Role of cultural variables in augmenting carbohydrate accumulation in the green microalga Scenedesmus acuminatus for bioethanol production

Abstract

Microalgal biomass is regarded as quintessential feedstock for bioethanol production owing to its rapid growth and high carbohydrate content. The present study investigates the effects of nitrate and phosphate starvation, magnesium and lysine supplementation, and initial pH of culture medium on the growth and carbohydrate accumulation in the green microalga, Scenedesmus acuminatus. Under nitrate- and phosphate-starved conditions, the biomass and carbohydrate yield registered a negative trend, whereas magnesium and lysine supplementations showed significant stimulation in both the parameters. Moreover, for lysine-supplemented cultures, the time-period required for maximum carbohydrate accumulation was reduced profoundly. In the test microalga, initial culture pH showed strong effects on biomass and carbohydrate accumulation. The carbohydrate productivity increased from 13.4 ± 1.8 mg L−1d−1 (control) to 38.4 ± 2.4 mg L−1d−1 for pH 9.0+lysine (0.5 g L−1)-supplemented cultures, registering a ~3-fold rise. Correspondingly, bioethanol productivity boosted ~4.3-fold, i.e., from 4.1 ± 0.3 mg L−1d−1 (control) to 17.2 ± 1.2 mg L−1d−1. Conclusively, initial culture pH 9.0 with lysine supplementation was evident as a suitable condition for enhancing the carbohydrate accumulation vis-a-vis bioethanol production in test microalgae. This study thus opened up new avenues towards the exploration of potato-peel waste and soya-meal as low-cost lysine sources to enhance carbohydrate productivity in microalgae for cost-effective bioethanol production.