Assessment of Coproduction of Ethanol and Methane from Pennisetum purpureum: Effects of Pretreatment, Process Performance, and Mass Balance

To overcome the structural complexity and improve the bioconversion efficiency of Pennisetum purpureum into bioethanol or/and biomethane, the effects of ensiling pretreatment, NaOH pretreatment, and their combination on digestion performance and mass flow were comparatively investigated. The coproduction of bioethanol and biomethane showed that 65.2 g of ethanol and 102.6 g of methane could be obtained from 1 kg of untreated Pennisetum purpureum, and pretreatment had significant impacts on the production; however, there is no significant difference between the results of NaOH pretreatment and ensiling-NaOH pretreatment in terms of production improvement. Among them, 1 kg of ensiling-NaOH treated Pennisetum purpureum could yield 269.4 g of ethanol and 144.5 g of methane, with a respective increase of 313.2% and 40.8% compared to that from the untreated sample; this corresponded to the final energy production of 14.5 MJ, with the energy conversion efficiency of 46.8%. In addition, for the ensiling-NaOH treated Pennisetum purpureum, the energy recovery from coproduction (process III) was 98.9% higher than that from enzymatic hydrolysis and fermentation only (process I) and 53.6% higher than that from anaerobic digestion only (process II). This indicated that coproduction of bioethanol and biomethane from Pennisetum purpureum after ensiling and NaOH pretreatment is an effective method to improve its conversion efficiency and energy output.

Automated summary

After ensiling and NaOH pretreatment, the coproduction of bioethanol and biomethane from Pennisetum purpureum has been shown to significantly increase production output, with higher energy recovery compared to enzymatic hydrolysis and fermentation only or anaerobic digestion only methods.