Acid pretreatment and fractionation of source-separated organic waste for lignocellulosic saccharification

This study compared two acidic pretreatments on Source-Separated Organic (SSO) waste preprocessed by Aufbereitungs Technology and System thermal-screw, on the basis of fermentable sugars for bioethanol production. The result showed that the SSO contained on average 27% glucan, 5.4% xylan, 1.2% arabinan, 5.7% mannan and 1.2% galactan. Dilute sulfuric acid pretreatment (at 121°C and 16.2 psi) was insufficient to solubilize cellulose and hemicellulose and did not remove much of the lignin. Cellulose-solvent and Organic Solvent-based Lignocellulose Fractionation (COSLIF) (at 50°C and atmospheric pressure) generated high glucose yield (70%). Substituting ethanol for acetone as organic solvent increased the yield to 89.5%. Fermentation using Zymomonas mobilis 8b with this hydrolysate confirmed the pretreatment is promising for the SSO conversion. Amenability of the SSO for biofuel production is validated. Enzymatic hydrolysis of both pretreatments using Accellerase 1500 is preferred over Celluclast 1.5L due to higher activity. Future work includes design of an appropriate batch and/or continuous bioreactor, and further understanding of Zymomonas mobilis 8b.

Acid pretreatment and fractionation of source-separated organic waste for lignocellulosic saccharification

This study compared two acidic pretreatments on Source-Separated Organic (SSO) waste preprocessed by Aufbereitungs Technology and System thermal-screw, on the basis of fermentable sugars for bioethanol production. The result showed that the SSO contained on average 27% glucan, 5.4% xylan, 1.2% arabinan, 5.7% mannan and 1.2% galactan. Dilute sulfuric acid pretreatment (at 121°C and 16.2 psi) was insufficient to solubilize cellulose and hemicellulose and did not remove much of the lignin. Cellulose-solvent and Organic Solvent-based Lignocellulose Fractionation (COSLIF) (at 50°C and atmospheric pressure) generated high glucose yield (70%). Substituting ethanol for acetone as organic solvent increased the yield to 89.5%. Fermentation using Zymomonas mobilis 8b with this hydrolysate confirmed the pretreatment is promising for the SSO conversion. Amenability of the SSO for biofuel production is validated. Enzymatic hydrolysis of both pretreatments using Accellerase 1500 is preferred over Celluclast 1.5L due to higher activity. Future work includes design of an appropriate batch and/or continuous bioreactor, and further understanding of Zymomonas mobilis 8b.

Integration of First- and Second-generation Bioethanol Production from Beet molasses and Distillery Stillage After Dilute Sulfuric Acid Pretreatment

The possibility of using waste distillery stillage (first-generation technology) after dilute acid pretreatment, as a medium for the preparation of beet molasses mash, for ethanol production according to the simultaneous saccharification and fermentation (SSF) technology, was assessed. The combination of lignocellulosic hydrolysates made from acid-pretreated stillage with sugar-rich beet molasses is an effective way of utilizing the first-generation ethanol production by-products in the second-generation ethanol production technology. It was demonstrated that the final ethanol concentration could be as high as 90 g/L. The process yield was over 94% of the theoretical yield when the molasses was diluted using acid-pretreated maize distillery stillage. An attempt to increase the pool of fermentable sugars by using cellulases to hydrolyze cellulose failed due to product inhibition in the fermentation medium with a high glucose concentration. A more than threefold increase in the concentration of ethyl acetate (even up to 924.4±11.8 mg/L) was observed in the distillates obtained from the media incubated with cellulases. The use of beet molasses combined with the hydrolysate of pretreated distillery stillage also changed the concentration of other volatile by-products. An increase in the concentration of aldehydes (mainly acetaldehyde to a concentration of above 1500 mg/L), methanol, 1-propanol, and 1-butanol was observed, while the concentration of higher alcohols (isobutanol, 2-methyl-1-butanol, 3-methyl-1-butanol) decreased. Interestingly, the use of cellulases in fermentation media from molasses and stillage hydrolysates resulted in an average fourfold increase in the concentration of this ester to a maximum level of 924.4±11.8 mg/L. Hydrolysates made from acid-pretreated distillery stillage, combined with sugar-rich beet molasses to boost the efficiency of the conversion process, can be successfully used in the production of second-generation fuel ethanol. However, further optimization of the cellulose enzymatic hydrolysis process is required for efficient use of the raw material.

Water-Soluble Sugars of Pedigreed Sorghum Mutant Stalks and Their Recovery after Pretreatment

Chemical composition of biomass, especially carbohydrate content, is a critical indicator of a biomass source’s potential for biofuel applications. This study characterized physico-chemical properties of stalks from 16 representative pedigreed sorghum mutant lines. The objectives of this study were to evaluate the recovery of sucrose and its hydrolysis products, glucose and fructose, during dilute sulfuric acid pretreatment at conditions typically used for lignocellulosic biomass, and to determine the relationship between water-extractive contents and sugar recovery after pretreatment. Dilute acid-pretreated sorghum stalks had enzymatic saccharification of >82.4% glucose yield for all treated samples with more than 82.3% cellulose recovery and 85% hemicellulose removal. A single-step, one-pot process was recommended for sorghum mutant stalks with low water-extractive content (<35%, w/w) to reduce processing cost and minimize wastewater disposal since the majority of sugars will be recovered after dilute acid pretreatment with minimal degradation products. However, for sorghum mutant stalks with high water-extractive content (>35%, w/w), a pre-washing step is beneficial to recover the water-soluble sugars before subjecting to the pretreatment process in order to avoid sugar losses during the pretreatment stage. Thus, different processing technologies should be applied to lignocellulosic biomass with various water-extractive contents and water-soluble sugar concentrations.