Effect of post-pretreatment washing on saccharification and co-fermentation from bagasse pretreated with biocompatible cholinium ionic liquid

Minimizing water consumption for sugar and lignin recovery via the integration of acid and alkali pretreated biomass and their mixed filtrate without post-washing

Excessive post-washing of pretreated biomass leads to huge water consumption and chemical loss. To address this issue, parallel HOAc and NaOH pretreatments of biomass followed by integration of their biomass and filtrate were investigated. Pretreatment effectiveness including morphology, crystallinity, and component recovery, were elucidated. Results showed that HOAc and NaOH in the mixed filtrate were neutralized to achieve a pH of around 4.80 prompting the alkali lignin precipitation. Lignin (46.01 and 48.38 g/kg-biomass for hemp and poplar, respectively) exhibiting comparable FTIR characteristics with the commercial alkali lignin was recovered. Compared to sodium acetate buffer as a control, integrating HOAc and NaOH pretreated biomass and their mixed filtrate for enzymatic hydrolysis boosted total sugar concentration (hemp: 42.90 vs. 38.27 g/L; poplar: 43.18 vs. 38.76 g/L) without compromising glucose yield (hemp: 70.86 vs. 70.69%; poplar: 66.48 vs. 69.48%) but improving xylose yield (hemp: 60.10 vs. 35.92%; poplar: 56.90 vs. 29.39%).

Enhancing the Thermostability of Papain by Immobilizing on Deep Eutectic Solvents-Treated Chitosan With Optimal Microporous Structure and Catalytic Microenvironment

Deep eutectic solvents (DESs) have attracted an increasing attention in the fields of biocatalysis and biopolymer processing. In this study, papain immobilized on choline chloride- lactic acid (ChCl-Lac) DES-treated chitosan exhibited excellent thermostability as compared to the free enzyme. The properties of native or DES-treated chitosan and immobilized enzyme were characterized by FT-IR, SEM, surface area and pore property analysis. Like the common enzyme immobilization, papain immobilized on DES-treated chitosan resulted in a lower catalytic efficiency and a higher thermostability than the free enzyme due to the restricted diffusion. The results also revealed that DES could control the active group content, thus achieving the appropriate microporous structure of immobilized enzyme. Meanwhile, it could also help to construct the optimal microenvironment by hydrogen-bonding interaction between enzyme, chitosan, and residual DES, which are benefit for maintaining an active conformation and subsequently a high thermostability of papain. Moreover, it was found that trace DES (10 mM) significantly promoted the activity of free papain (145%). Deactivation thermodynamics study showed that the DES could enhance the thermostability of papain especially at high temperature (half-life of 7.4 vs. 3.5 h) because of the increased Gibbs free energy of denaturation. Secondary structure analysis by circular dichroism spectroscopy (CD) agreed well with the activity and thermostability data, further confirming the formation of rigid conformation induced by a specific amount of DES. This work provides a new way of enzyme immobilization synergistically intensified by solvents and supporting materials to achieve better microporous structure and catalytic microenvironment.

Ultrasound and surfactant assisted ionic liquid pretreatment of sugarcane bagasse for enhancing saccharification using enzymes from an ionic liquid tolerant Aspergillus assiutensis VS34

Ionic liquid (IL) pretreatment represents an effective strategy for effective fractionation of lignocellulosic biomass (LB) to fermentable sugars in a biorefinery. Optimization of combinatorial pretreatment of sugarcane bagasse (SCB) with IL (1-butyl-3-methylimidazolium chloride [Bmim]Cl) and surfactant (PEG-8000) resulted in enhanced sugar yield (16.5%) upon enzymatic saccharification. The saccharification enzymes (cellulase and xylanase) used in the current study were in-house produced from a novel IL-tolerant fungal strain Aspergillus assiutensis VS34, isolated from chemically polluted soil, which produced adequately IL-stable enzymes. This is the first ever report of IL-stable cellulase/xylanase enzyme from Aspergillus assiutensis. To get the mechanistic insights of combinatorial pretreatment physicochemical analysis of variously pretreated biomass was executed using SEM, FT-IR, XRD, and ¹H NMR studies. The combined action of IL, surfactant and ultrasound had very severe and distinct effects on the ultrastructure of biomass that subsequently resulted in enhanced accessibility of saccharification enzymes to biomass, and increased sugar yield.

Chemical and structural changes of pretreated empty fruit bunch (EFB) in ionic liquid-cellulase compatible system for fermentability to bioethanol

The pretreatment of empty fruit bunch (EFB) was conducted using an integrated system of IL and cellulases (IL-E), with simultaneous fermentation in one vessel. The cellulase mixture (PKC-Cel) was derived from Trichoderma reesei by solid-state fermentation. Choline acetate [Cho]OAc was utilized for the pretreatment due to its biocompatibility and biodegradability. The treated EFB and its hydrolysate were characterized by the Fourier transform infrared spectroscopy, scanning electron microscopy, and chemical analysis. The results showed that there were significant structural changes in EFB after the treatment in IL-E system. The sugar yield after enzymatic hydrolysis by the PKC-Cel was increased from 0.058 g/g of EFB in the crude sample (untreated) to 0.283 and 0.62 ± 06 g/g in IL-E system after 24 and 48 h of treatment, respectively. The EFB hydrolysate showed the eligibility for ethanol production without any supplements where ethanol yield was 0.275 g ethanol/g EFB in the presence of the IL, while lower yield obtained without IL-pretreatment. Moreover, it was demonstrated that furfural and phenolic compounds were not at the level of suppressing the fermentation process.

Dual effect of soluble materials in pretreated lignocellulose on simultaneous saccharification and co-fermentation process for the bioethanol production

In this study, wash liquors isolated from ethylenediamine and dry dilute acid pretreated corn stover were used to evaluate the effect of soluble materials in pretreated biomass on simultaneous saccharification and co-fermentation (SSCF) for ethanol production, respectively. Both of the wash liquors had different impacts on enzymatic hydrolysis and fermentation. Enzymatic conversions of glucan and xylan monotonically decreased as wash liquor concentration increased. Whereas, with low wash liquor concentrations, xylose consumption rate, cell viability and ethanol yield were maximally stimulated in fermentation without nutrient supplementary. Soluble lignins were found as the key composition which promoted sugars utilization and cell viability without nutrient supplementary. The dual effects of soluble materials on enzymatic hydrolysis and fermentation resulted in the reduction of ethanol yield as soluble materials increased in SSCF.

Evaluation of several ionic liquids for in situ hydrolysis of empty fruit bunches by locally-produced cellulase

Lignocellulosic biomasses, exhibit resistance to enzymatic hydrolysis due to the presence of lignin and hemicellulose. Ionic liquids proved their applicability in lignin degradation, however, ionic liquid removal has to be performed to proceed to hydrolysis. Therefore, this study reports an in situ hydrolysis of empty fruit bunches (EFB) that combined an ionic liquid (IL) pretreatment and enzymatic hydrolysis. For enzyme production, palm kernel cake (PKC) was used as the primary media for microbial cellulase (PKC-Cel) from Trichoderma reesei (RUTC30). The obtained enzyme exhibited a promising stability in several ionic liquids. Among few, in choline acetate [Cho]OAc, PKC-Cel retained 63.16 % of the initial activity after 6 h and lost only 10 % of its activity in 10 % IL/buffer mixture. Upon the confirmation of the PKC-Cel stability, EFB was subjected to IL-pretreatment followed by hydrolysis in a single step without further removal of the IL. The findings revealed that choline acetate [Cho]OAc and choline butyrate [Cho]Bu were among the best ILs used in the study since 0.332 ± 0.05 g glucose/g and 0.565 ± 0.08 g total reducing sugar/g EFB were obtained after 24 h of enzymatic hydrolysis. Compared to the untreated EFB, the amount of reducing sugar obtained after enzymatic hydrolysis increased by three-fold in the case of [Cho]OAc and [Cho]Bu, two-fold with [EMIM]OAc and phosphate-based ILs whereas the lowest concentration was obtained in [TBPH]OAc. Pretreatment of EFB with [Cho]OAc and [Cho]Bu showed significant differences in the morphology of EFB samples when observed with SEM. Analysis of the lignin, hemicellulose and hemicellulose showed that the total lignin content from the raw EFB was reduced from 37.8 ± 0.6 to 25.81 ± 0.35 % (w/w) upon employment of [Cho]OAc in the compatible system. The PKC-Cel from T. reesei (RUTC30) exhibited promising characteristics that need to be investigated further towards a single-step process for bioethanol production.