Dissecting the role of heterogeneity and hydrothermal pretreatment of sugarcane bagasse in metabolic pathways for biofuels production

In order to evaluate the effect of sugarcane bagasse (SCB) heterogeneity and hydrothermal (HT) pretreatment on biofuels production, industrial and laboratorial, rind and pith, hydrothermally pretreated (200 degrees C for 10 min at 16 bar and 10 g of SCB mixed with 100 mL of water) and untreated sugarcane bagasse (SCB) were used as substrate (10 g/L) in batch reactors at thermophilic condition (55 degrees C) and initial pH of 6.0. High cellulose content in the hydrothermally (HT) pretreated sugarcane bagasse (SCB) results in hydrogen production (33.7 mmol/L), while lactic acid was the main metabolite produced using laboratorial untreated SCB rind and pith (1.5 and 1.3 g/L, respectively), which caused a decrease in the pH and no hydrogen production. Methane was only observed when industrial untreated SCB pith and rind (5.5 and 3.1 mmol/L), respectively, was used. 16S rRNA sequencing was carried out and at the end of the operation the reactors were fed with untreated laboratorial rind, hydrothermally pretreated industrial rind and untreated industrial pith. Hydrogen-producing bacteria, such as Acetomicrobium (74.4 %) was favored using the HT pretreated fiber, while lactic acid bacteria such as Lactococcus (6.3 %) had a potentially negative effect on the hydrogen-producing bacteria like Thermoanaerobacterium (75.0 %) using laboratorial untreated SCB, since no hydrogen was obtained in this condition. Microorganisms involved in all the anaerobic digestion steps, such as Clostridium (34.4 %), Acetomicrobium (33.4 %), and Methanoculleus (14.8 %) lead to hydrogen, volatile fatty acids (VFA), ethanol, and methane production using industrial untreated SCB. Therefore, this study successfully dissected the detailed microbial community structure and the shift on metabolic pathways as a response of SCB heterogeneity and hydrothermal pretreatment.

Automated summary

The study showed that under high temperature conditions, hydrothermally pretreated sugarcane bagasse with high cellulose content can produce hydrogen; while laboratorial untreated sugarcane bagasse rind and pith mainly produce lactic acid and industrial untreated sugarcane bagasse pith and rind only produce methane.