BIOETHANOL FROM PEARL MILLET STALK, MAIZE STALK AND SPIRULINA PLANTESIS: A COMPARATIVE REVIEW OF PRETREATMENT, ENZYMATIC HYDROLYSIS AND FERMENTATION

Maize stalk, pearl millet stalk and Spirulina offer different routes to non-food bioethanol. •                  The two stalks are available as crop residues and hold 71–75% carbohydrate. However, they need acid pretreatment at 121 °C, carry 17.5–19.35% lignin, and have much of their sugar in pentose form. The best reported concentrations were 44.24 g/L for pearl millet (with added glucose) and 25.88 g/L for a lignin-reduced maize mutant. •                  Spirulina holds less carbohydrate (46.34%), but it is a lignin-free α-glucan. It hydrolysed to 70.45 g/L of reducing sugar in 10 h and fermented at 83% efficiency without detoxification or added nutrients, and its residues can be converted to biomethane. The choice between the feedstocks depends on whether carbohydrate quantity or ease and speed of conversion matters more. A controlled comparison under a single framework is the most pressing need.

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