Effect of sonication pretreatment on hydrogen and acetone-butanol-ethanol coproduction from Chlamydomonas mexicana biomass using Clostridium acetobutylicum

Acetone-butanol-ethanol (ABE) fermentation produces acetone, butanol, and ethanol, which are clean and sustainable energy sources with high energy densities. The ABE fermentation encounters butanol toxicity, by-products formation, and generation of lignin-derived inhibitors. The implementation of the low-lignin substrate, effective pretreatment, and biofuel coproduction would enhance the fermentation efficiency. Thus, this study investigated the use of sonication pretreated Chlamydomonas mexicana biomass as a cost-effective substrate to produce biohydrogen (bioH₂) and ABE using Clostridium acetobutylicum to demonstrate effective production of biofuels through ABE fermentation. Sonication enhanced the recovery and bioaccessibility of carbohydrates (74%) and proteins (52.4%), and their efficient utilization for bioH₂ and volatile fatty acid (VFA) production. The bioH₂ yield from sonicated C. mexicana biomass (2.9 mL/g-carbohydrate), was ~1.5 times higher than that attained from non-sonicated biomass (1.97 mL/g-carbohydrate). Subsequently, VFAs generated in the acidogenic phase (1.5 g/L acetate, and 6.05 g/L butyrate) were used to produce 0.54 g-ABE/g-carbohydrate through ABE fermentation. Thus, this study demonstrates that both soluble carbohydrates (28 g/L) and proteins (14 g/L) from pretreated microalgal biomass were efficiently converted to 110.2 mL bioH₂ and 20.84 g/L ABE. These soluble carbohydrates and proteins could be used for high-energy biofuel production through ABE fermentation with minimum waste generation.