Municipal solid waste as a suitable substrate for butanol production as an advanced biofuel

Abstract

The biodegradable fraction of municipal solid waste (BMSW), dominantly composed of starchy and lignocellulosic materials, has high potential to be used for liquid biofuel production. Hot water or dilute acid treatment at high temperature was utilized for the solubilization or hydrolysis of the starch fraction and pretreatment of the lignocellulosic fraction. The treatment liquor, which was rich in sugars and starch, was evaluated for acetone, butanol, and ethanol (ABE) production by Clostridium acetobutylicum, and it was found that phenolic compounds, especially tannins, critically inhibited the butanol production. To improve ABE production, the extraction of phenolic compounds prior to hot water or dilute acid treatment was evaluated. Among the evaluated extractants, i.e., acetone, ethanol, butanol, and water, ethanol showed the highest amount of tannin extraction, resulting in an 87% reduction in tannin content. Dilute acid treatment of the ethanol extracted BMSW at 140 °C for 60 min resulted in a liquor containing 23 g/L glucose and 41 g/L soluble starch, which was fermented to the highest ABE concentration of 17 g/L with productivity of 0.24 g/L/h. The fermentation of liquor obtained by dilute acid treatment of butanol, acetone, and water-extracted BMSW was accompanied by 9, 6, and 4 g/L ABE production. Even by hot water treatment, the liquor obtained from ethanol extracted BMSW was fermented to the highest ABE concentration of 8 g/L. In addition to the liquor, the pretreated lignocellulosic material was subjected to enzymatic hydrolysis and ABE fermentation, leading to production of 5–6 g/L ABE. This process resulted in the production of 83.9 g butanol, 36.6 g acetone, and 20.8 g ethanol from each kg of BMSW. Moreover, the co-production of ethanol by ABE fermentation reduced concerns about organic extractor loss in the extraction process, which was inescapable in the tannin extraction process.