Optimization of Pre-treatment Using RSM on Wheat Straw and Production of Lactic Acid Using Thermotolerant, Inhibitor Tolerant and Xylose Utilizing Bacillus Sonorenesis Strain DGS15

Thermotolerant lactic acid producing bacteria, isolated from red soil of brick kiln was identified by 16S rRNA sequencing as Bacillus sonorenesis , which showed remarkable capability to ferment sugars of lignocellulosic biomass after pre-treatment, yielding 0.97 g/g lactic acid with overall productivity of 0.38 g L -1/ h. RSM was employed to optimize the sulphuric acid pre-treatment combined with dilute NaOH and hot water pre-treatment. Pretreated wheat straw biomass had 40.4% cellulose, 18.4% hemicellulose, 12.4% lignin and 28.2 g L -1 reducing sugar, while native wheat straw biomass had 36% cellulose, 25% hemicellulose, 20% total lignin, and 0.94 g L -1 reducing sugar. Scanning electron microscopy (SEM) revealed that the ordered and compact structure of wheat straw was destroyed upon pre-treatment. X-ray diffractogram (XRD) revealed 9.71% increase in crystallinity index ( CrI ) in pretreated biomass. FTIR spectrogram showed removal of lignin due to reduction of peak at 1640 cm -1 in pretreated biomass. Bacillus sonorenesis DGS15 is inhibitor tolerant (furfural (1.2 g L -1 ) and HMF (2.4 g L -1 )). Furfural was consumed after 72 h of fermentation and HMF got accumulated with 3.75-fold increase in concentration in the fermentation broth. In terms of final concentration, yield, and fermentation duration, this is the best performance of DGS15 for lactic acid production utilizing xylose, glucose as the carbon source. All of these findings showed that the thermotolerant Bacillus sonorenesis strain DGS15 is a novel, attractive candidate for producing lactic acid from lignocellulosic biomass.

Ultrasound Assisted Pretreatments Applied to Cupuaçu Husk (Theobroma grandiflorum) from Brazilian Legal Amazon for Biorefinery Concept

Cupuaçu husk (CH) is the waste of a common fruit from a native species of the Brazilian Legal Amazon. The current study investigated the influence of ultrasound (US) combined with aqueous, acid, alkaline, and ionic liquid (IL) pretreatments on the chemical and physical aspects of CH and the yield of chemical platforms production, 5-hydroxymethylfurfural (HMF) and furfural (FF), using IL. Scanning electron microscopy, X-ray diffraction (XRD) and Fourier transform infrared spectroscopy were used to feature the raw and pretreated biomass. The highest levels of glucose (9.90 g L-1) were observed in the liquid fraction resulting from the acid + US pretreatment followed by acid hydrolysis. The IL + US pretreatment recorded the best performance in removing lignin. Based on XRD analyses, ultrasound increased crystallinity of all pretreated samples as a result of the removal of cellulose’s amorphous fraction. However, it promoted accessibility to adopted reagents by increasing biomass exposure due to cavitation. The best yields of HMF and FF were recorded from hydrolysis of the solid fraction resulting from the acid + US (12.94%) and alkaline + US (48.84%) pretreatment, respectively. These results indicate satisfactory performance of ultrasound assisted pretreatments to the simplified and economic conversion of biomass into value-added products.

Assessment of the effectiveness of liquid hot water and steam explosion pretreatments of fast-growing poplar (Populus trichocarpa) wood

In this paper, the influence of physicochemical pretreatment methods on the chemical composition, enzymatic hydrolysis efficiency and porosity of fast-growing Populus trichocarpa wood was compared. Among the pretreatment methods, the liquid hot water (LHW) and steam explosion (SE) were used, which were performed at three different temperatures (160 °C, 175 °C and 190 °C) and two residence times (15 min and 1 h). The chemical composition, enzymatic hydrolysis and porosity analysis were done for native wood and solid fraction obtained after LHW and SE pretreatments. The porosity analysis was performed by inverse size exclusion chromatography method. Additionally, inhibitors of hydrolysis and fermentation processes in the liquid and solid fractions obtained after pretreatments were examined. Based on the results, it was found that the tested pretreatments caused the greatest changes in the chemical content of hemicelluloses. It was found that after LHW and SE pretreatments up to 99.1% or 94.0%, respectively, of hemicelluloses were removed from the obtained solid fraction. Moreover, the LHW and SE processes greatly enhanced the enzymatic digestibility of fast-growing poplar wood. The highest glucose yield was achieved after 15 min of SE pretreatment at 190 °C and was 676.4 mg/g pretreated biomass, while in the case of xylose the highest value (119.3 mg/g pretreated biomass) was obtained after 15 min of LHW pretreatment at 160 °C. Generally, after SE pretreatment process, more inhibitors were formed, and a greater effect of porous structure development was noticed than after LHW pretreatment. Despite this difference, the average glucose contents and yields after enzymatic hydrolysis of pretreated biomass were generally similar regardless of the pretreatment used.

Organosolv Fractionation of Birch Sawdust: Establishing a Lignin-First Biorefinery

The use of residual biomass for bioconversions makes it possible to decrease the output of fossil-based chemicals and pursue a greener economy. While the use of lignocellulosic material as sustainable feedstock has been tried at pilot scale, industrial production is not yet economically feasible, requiring further technology and feedstock optimization. The aim of this study was to examine the feasibility of replacing woodchips with residual sawdust in biorefinery applications. Woodchips can be used in value-added processes such as paper pulp production, whereas sawdust is currently used mainly for combustion. The main advantages of sawdust are its large supply and a particle size sufficiently small for the pretreatment process. Whereas, the main challenge is the higher complexity of the lignocellulosic biomass, as it can contain small amounts of bark and cambium. Here, we studied the fractionation of birch sawdust by organosolv pretreatment at two different temperatures and for two different durations. We evaluated the efficiency of fractionation into the three main fractions: lignin, cellulose, and hemicellulose. The cellulose content in pretreated biomass was as high as 69.2%, which was nearly double the amount in untreated biomass. The obtained lignin was of high purity, with a maximum 4.5% of contaminating sugars. Subsequent evaluation of the susceptibility of pretreated solids to enzymatic saccharification revealed glucose yields ranging from 75% to 90% after 48 h but reaching 100.0% under the best conditions. In summary, birch sawdust can be successfully utilized as a feedstock for organosolv fractionation and replace woodchips to simplify and lower the costs of biorefinery processes.

The effect of microwave power on lignocellulose content, physical and chemical characteristics of biomass: A review

Bioethanol is alternative energy derived from biomass that can be obtained from the agricultural industry to replace fossil fuels. The issue with biomass to energy conversion is the presence of lignin in lignocellulose biomass which inhibits the hydrolysis process. Microwave-acid pre-treatment is a method that combines microwaves and H2SO4 to break down lignin. In other studies, various microwave power is studied. The aim of this review is to provide insight and novelty into the effect of microwave power that is used on the lignocellulose content of rape straw and the physical and chemical characteristics of biomass after pre-treatment. Various microwave powers on delignification processes were presented, while the physical and chemical characteristics of pretreated biomass and also the prospect of future applications of microwave-assisted pretreatment were also discussed.

Effect of neutralizing agents in the preparation of succinic acid from oil palm trunk

Neutralization is an important process to control the pH required for enzymatic saccharification of pretreated biomass followed by fermentation for biochemical conversion. In this study, the production of succinic acid as a potential C4 building block was investigated by utilizing lignocellulosic biomass in the form of oil palm trunk (OPT). The effect of different neutralizing agents (NaOH, KOH and NH4OH) on the enzymatic saccharification of oxalic acid-pretreated OPT and subsequent succinic acid fermentation by Actinobacillus succinogenes ATCC 55618 was investigated. The results showed that all neutralizing agents tested were able to assist in the recovery of fermentable sugars with concentrations ranging from 38.1 to 39.6 g/L. However, during succinic acid fermentation, it was found that the soluble NH4-oxalate salt formed severely inhibited succinic acid fermentation compared to Na and K, thereby decreasing the succinic acid production from 14.0 g/L (using NaOH) to 1.0 g/L (using NH4OH). In particular, Na-and K-oxalate did not exhibit apparent inhibition for both the saccharification and fermentation processes. Hence, the choice of neutralizing reagent is essential to prevent inhibition in the preparation of succinic acid from lignocellulosic biomass.

Lignocellulosic Corn Stover Biomass Pre-Treatment by Deep Eutectic Solvents (DES) for Biomethane Production Process by Bioresource Anaerobic Digestion

The valorization study of the largely available corn stover waste biomass after pretreatment with deep eutectic solvent (DES) for biomethane production in one-liter glass bioreactors by anaerobic digestion for 21 days was presented. Ammonium thiocyanate and urea deep eutectic solvent pretreatments under different conditions in terms of the components ratio and temperature were examined on corn stover waste biomass. The lignocellulose biomass was characterized in detail for its chemistry and morphology to determine the effect of the pretreatment on the natural biocomposite. Furthermore, the implications on biomethane production through anaerobic digestion with different loadings of corn stover biomass at 35 g/L and 50 g/L were tested. The results showed an increase of 48% for a cumulative biomethane production for a DES-pretreated biomass, using a solid-to-liquid ratio of 1:2 at 100 °C for 60 min, which is a strong indication that DES-pretreatment significantly enhanced biomethane production.

Comparison of Efficiency and Cost of Methods for Conditioning of Slurries of Steam-Pretreated Softwood

Inhibitors formed during pretreatment impair lignocellulose bioconversion by making enzymatic saccharification and microbial fermentation less efficient, but conditioning of slurries and hydrolysates can improve fermentability and sometimes also enzymatic digestibility. Conditioning of pretreated softwood using four industrial reducing agents (sodium sulfite, sodium dithionite, sodium borohydride, and hydrogen) was compared with standard methods, such as overliming and treatment with activated charcoal. A dosage of approx. 1 mM sulfur oxyanion (sulfite or dithionite) per percent water-insoluble solids (WIS) in the slurry was found to result in good fermentability. Treatment of 10–20% WIS slurries with 15 mM sulfur oxyanion under mild reaction conditions (23°C, pH 5.5) resulted in sulfonation of the solid phase and saccharification improvements of 18–24% for dithionite and 13–16% for sulfite. Among the different conditioning methods studied, treatment of slurries with sodium sulfite was superior with respect to cost-efficient improvement of fermentability. Treatments of slurry or pretreatment liquid with 15 mM sulfite or dithionite resulted in 58–76% reduction of the content of formaldehyde. The comparison indicates that conditioning of pretreated biomass using sulfur oxyanions warrants further attention.

Influence of Sulfuric Acid Pretreatment and Inhibitor of Sugarcane Bagasse on the Production of Fermentable Sugar and Ethanol

Improper disposal of agricultural waste after harvesting season has posed serious health and environmental issues. Alternative methods to utilize agricultural waste to produce a value-added product, especially biofuel, have become the focus of research and industrial stakeholders. To make the process feasible, the maximum conversion should be achieved with the optimum operational condition. This research applied Response Surface Methodology (RSM) with the Box-Behnken design (BBD) to optimize sulfuric acid pretreatment of sugarcane bagasse by varying three pretreatment factors namely, acid concentration (0.5–3.5%), temperature (60–140℃), and time (20–100 min). Pretreated biomass was enzymatically hydrolyzed, and the effectiveness of pretreatment was examined according to the reducing sugar concentration. However, inhibitors namely, acetic acid, 5-hydroxymethylfurfural (5-HMF), and furfural were produced during pretreatment, which was analyzed through GC-MS analysis. The Box-Behnken design could optimize and correlate the effect of pretreatment parameters on the hydrolysis of sugarcane bagasse. The optimum pretreatment condition was predicted at an acid concentration of 3.50%, the temperature of 136.08℃, and the time of 75.36 min to obtain the maximum sugar production. Sugarcane bagasse pretreatment at optimum condition could produce a reducing sugar of 180.15 mg/g-sugarcane bagasse, which is 3.06 folds higher than untreated sugarcane bagasse. However, ethanol yield from pretreated biomass was less than unpretreated biomass because of the inhibitor formation. This study provides a new insight into utilizing agricultural waste in a more efficient and eco-friendly manner.