Valorization of sorghum distillery residue to produce bioethanol for pollution mitigation and circular economy

• Published in: Environmental pollution (1987) 2021-09, Vol.285, p.117196-117196, Article 117196
• Main Authors: Chen, Wei-Hsin, Lo, Hsiu-Ju, Yu, Kai-Ling, Ong, Hwai-Chyuan, Sheen, Herng-Kuang
• Format: Article
• Language: English
• Subjects: Bioethanol and hydrochar; Optimization; Response surface methodology (RSM); Sorghum distillery residue (SDR); Waste valorization; Wet torrefaction (WT)
• ISSN: 0269-7491; 1873-6424
• DOI: 10.1016/j.envpol.2021.117196

This research aims to study the wet torrefaction (WT) and saccharification of sorghum distillery residue (SDR) towards hydrochar and bioethanol production. The experiments are designed by Box-Behnken design from response surface methodology where the operating conditions include sulfuric acid concentration (0, 0.01, and 0.02 M), amyloglucosidase concentration (36, 51, and 66 IU), and saccharification time (120, 180, and 240 min). Compared to conventional dry torrefaction, the hydrochar yield is between 13.24 and 14.73%, which is much lower than dry torrefaction biochar (yield >50%). The calorific value of the raw SDR is 17.15 MJ/kg, which is significantly enhanced to 22.36–23.37 MJ/kg after WT. When the sulfuric acid concentration increases from 0 to 0.02 M, the glucose concentration in the product increases from 5.59 g/L to 13.05 g/L. The prediction of analysis of variance suggests that the best combination to maximum glucose production is 0.02 M H2SO4, 66 IU enzyme concentration, and 120 min saccharification time, and the glucose concentration is 30.85 g/L. The maximum bioethanol concentration of 19.21 g/L is obtained, which is higher than those from wheat straw (18.1 g/L) and sweet sorghum residue (16.2 g/L). A large amount of SDR is generated in the kaoliang liquor production process, which may cause environmental problems if it is not appropriately treated. This study fulfills SDR valorization for hydrochar and bioenergy to lower environmental pollution and even achieve a circular economy. [Display omitted] •Both hydrochar and bioethanol are produced from sorghum distillery residue (SDR).•The maximum bioethanol concentration from dilute acid pretreatment is 19.21 g/L.•The minimum solid yield from wet torrefaction (WT) is 13.24%.•The maximum higher heating value (HHV) of hydrochar is 23.37 MJ/kg.•WT can increase the HHV of SDR by up to 36.27%. The main finding of the work: Bioethanol and hydrochar produced from sorghum distillery residue with low-concentration sulfuric acid concentrations are achieved, which can mitigate environmental pollution.