Butanol production from sweet sorghum bagasse with high solids content: Part I-comparison of liquid hot water pretreatment with dilute sulfuric acid

In these studies, we pretreated sweet sorghum bagasse (SSB) using liquid hot water (LHW) or dilute H₂ SO₄ (2 g L^-1 ) at 190°C for zero min (as soon as temperature reached 190°C, cooling was started) to reduce generation of sugar degradation fermentation inhibiting products such as furfural and hydroxymethyl furfural (HMF). The solids loading were 250-300 g L^-1 . This was followed by enzymatic hydrolysis. After hydrolysis, 89.0 g L^-1 sugars, 7.60 g L^-1 acetic acid, 0.33 g L^-1 furfural, and 0.07 g L^-1 HMF were released. This pretreatment and hydrolysis resulted in the release of 57.9% sugars. This was followed by second hydrolysis of the fibrous biomass which resulted in the release of 43.64 g L^-1 additional sugars, 2.40 g L^-1 acetic acid, zero g L^-1 furfural, and zero g L^-1 HMF. In both the hydrolyzates, 86.3% sugars present in SSB were released. Fermentation of the hydrolyzate I resulted in poor acetone-butanol-ethanol (ABE) fermentation. However, fermentation of the hydrolyzate II was successful and produced 13.43 g L^-1 ABE of which butanol was the main product. Use of 2 g L^-1 H₂ SO₄ as a pretreatment medium followed by enzymatic hydrolysis resulted in the release of 100.6-93.8% (w/w) sugars from 250 to 300 g L^-1 SSB, respectively. LHW or dilute H₂ SO₄ were used to economize production of cellulosic sugars from SSB. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 34:960-966, 2018.

Using Co-Culture to Functionalize Clostridium Fermentation

Clostridium fermentations have been developed for producing butanol and other value-added chemicals, but their development is constrained by some limitations, such as relatively high substrate cost and the need to maintain an anaerobic condition. Recently, co-culture is emerging as a popular way to address these limitations by introducing a partner strain with Clostridium. Generally speaking, the co-culture strategy enables the use of a cheaper substrate, maintains the growth of Clostridium without any anaerobic treatment, improves product yields, and/or widens the product spectrum. Herein, we review recent developments of co-culture strategies involving Clostridium species according to their partner stains' functions with representative examples. We also discuss research challenges that need to be addressed for the future development of Clostridium co-cultures.