Two-stage Pretreatment Research Articles

Enhancement of sugar recovery and ethanol production from wheat straw through alkaline pre-extraction followed by steam pretreatment

To improve sugar recovery and ethanol production from wheat straw, a sequential two-stage pretreatment process combining alkaline pre-extraction and acid catalyzed steam treatment was investigated. The results showed that alkaline pre-extraction using 8% (w/w) sodium hydroxide at 80 °C for 90 min followed by steam pretreatment with 3% (w/w) sulfur dioxide at 151 °C for 16 min was sufficient to prepare a substrate that could be efficiently hydrolyzed at high solid loadings. Moreover, alkaline pre-extraction reduced the process severity of steam pretreatment and decreased the generation of inhibitory compounds. During enzymatic hydrolysis, increasing solid loading decreased the yield of monomeric sugars. Enzymatic hydrolysis at 25% (w/v) solid loading, the yields of approximately 80% of glucose and 65% of xylose could be reached with an enzyme dosage of 25 mg protein/g glucan. Following fermentation of hydrolysate with sugar concentration of approximately 120 g/L, an ethanol concentration of 54.5 g/L was achieved.

An efficient strategy for enhancing enzymatic saccharification with delignified fungus Myrothecium verrucaria and solid acid

In this work, corn stover was studied as a lignocellulosic material with the potential of serving as a feedstock in the field of bioenergetics. To improve the enzymatic digestibility of carbohydrates in the lignocellulosic biomass, corn stover was pretreated using Myrothecium verrucaria to deplete the lignin, combined with a solid acid pretreatment method to deplete the hemicellulose. The effects of lignin degradation conditions and solid acid concentration on cellulose conversion were investigated. The two-stage pretreatment with M. verrucaria and solid acid under optimal conditions gave 81.54% cellulose conversion yield, 214.22% higher than that of untreated corn stover. Significant lignin and hemicellulose removal rates were observed with the two-stage pretreatment. Scanning electron microscope (SEM), X-ray diffractometer (XRD) and Fourier transform infrared spectroscopy (FTIR) analyses showed major structural changes in the pretreated corn stover. This study provided an efficient strategy to enhance the enzymatic saccharification of cellulose in corn stover.

Evaluation of an organosolv-based biorefinery process to fractionate wheat straw into ethanol and co-products

In this study, organosolv pre-extraction of wheat straw (WS) was conducted to extract lignin for understanding the effect of silica on enzymatic hydrolysis of carbohydrates. The results showed that the presence of silica in the WS substrate was associated with a decreased conversion of carbohydrates into monomeric sugars during enzymatic hydrolysis. Then, a sequential two-stage pretreatment process comprising ethanol pre-extraction and alkaline pretreatment was investigated to convert WS carbohydrates into bioethanol and recover lignin and silica. The results demonstrated that the pre-extraction with ethanol at 160 °C for 50 min followed by alkaline treatment with 11% sodium carbonate (Na2CO3) was sufficient to generate a highly digestible substrate. 85.7% of the original sugars in the raw feedstock was recovered by two-stage pretreatment followed by enzymatic hydrolysis with an enzyme loading of 12 FPU/g glucan. Fermentation with Saccharomyces cerevisiae SR8 u strain consumed 97.8% sugars in the hydrolysate to reach 6.5% w/v ethanol titer. With this proposed process, about 89.1% silica and 62.5% lignin were recovered at high levels of purity.

Efficient conversion of wheat straw into methyl levulinate catalyzed by cheap metal sulfate in a biorefinery concept

Wheat straw can be converted into biofuel candidate-methyl levulinate with copper sulfate as the cheap catalyst. To take advantage of the whole components of wheat straw, a two-stage pretreatment process was developed in this study. In the first-stage process, the hemicellulose component in wheat straw can be converted into biosurfactant at the mild conditions, and the lignin component can be extracted as another value added by-product in the second stage. On the basis, the pretreated wheat straw was used as raw material for methyl levulinate production, and a yield of 20.2 wt% can be obtained under the optimum reaction conditions. Meanwhile, the catalyst recycling experiments showed that copper sulfate was stable and can be reused more than five times. The results of mass balances and preliminary economic analysis further indicated that the production of integrated biorefinery processes producing diversified products offers potential for the sustainable valorization of wheat straw.

Two-stage pretreatment of excess sludge for electricity generation in microbial fuel cell

ABSTRACTThermophiles hydrolysis and acidogens fermentation were sequentially adopted to pretreat excess sludge for microbial fuel cell (MFC) electricity production. The results indicated that MFC fed with the thermophiles-acidogens pretreated sludge (MFC AB), reached a higher removal of ammonia nitrogen than the MFC fed with the heating hydrolysis and acidogens fermentation pretreated sludge (MFC NB). However, compared with the MFC AB, MFC NB presented a better performance for removal of soluble chemical oxygen demand (SCOD) (90.08%) and protein (82.42%). As for the electricity production, MFC NB obtained higher voltage of 0.632 V and maximum power density with 1.05 W/m3 while MFC AB reached maximum voltage of 0.373 V and maximum power density of 0.58 W/m3. Bacterial 16S rRNA-based molecular microbial techniques showed that microbial communities on both MFC anode biofilms was diverse and different. The cooperation of fermentation bacteria and electricigen Shewanella baltica in the MFC NB may have contributed towards the improvement of electricity generation.

Novel dihydrogen-bonding deep eutectic solvents: Pretreatment of rice straw for butanol fermentation featuring enzyme recycling and high solvent yield

Rice straw (RS) is one of the most abundant lignocellulosic biomasses in China, which contains mainly of cellulose, hemicellulose and lignin. In this study, a novel deep eutectic solvent (DES), foraceline, was prepared with choline chloride and double hydrogen bond donors (formic acid and acetic acid). By combining foraceline and sodium carbonate (1%), a two-stage pretreatment method was developed and applied in RS pretreatment to improve the biodegradability of lignocellulose. The highest glucose and total sugar of 37.3 g·L−1 and 42.8 g·L−1 were obtained after hydrolysis of 24 h using 50 FPU·gtotal solid-1 of cellulase. The cellulase attached to RS was reutilized for five continuous cycles in which enzyme loading was reduced from 50 FPU·gtotal solid-1 (Cycle I) to 30 FPU·gtotal solid-1 (Cycle V), resulting in total sugar of 41.3–42.6 g·L−1 for each cycle. RS hydrolysates (Cycle I and V) was utilized in butanol fermentation by Clostridium saccharobutylicum DSM 13864, achieving butanol titer and yield of 9.5 g·L−1 and 0.25 g·gtotal sugar-1, similar to those of glucose medium. This study demonstrated the feasibility of this newly developed biomass pretreatment by dihydrogen bonding DES featuring cellulase recycling and high butanol yield.

Ethanol production from bamboo using mild alkaline pre-extraction followed by alkaline hydrogen peroxide pretreatment

A sequential two-stage pretreatment process comprising alkaline pre-extraction and alkaline hydrogen peroxide pretreatment (AHP) was investigated to convert bamboo carbohydrates into bioethanol. The results showed that mild alkaline pre-extraction using 8% (w/w) sodium hydroxide (NaOH) at 100°C for 180min followed by AHP pretreatment with 4% (w/w) hydrogen peroxide (H2O2) was sufficient to generate a substrate that could be efficiently digested with low enzyme loadings. Moreover, alkali pre-extraction enabled the use of lower H2O2 charges in AHP treatment. Two-stage pretreatment followed by enzymatic hydrolysis with only 9FPU/g cellulose led to the recovery of 87% of the original sugars in the raw feedstock. The use of the pentose-hexose fermenting Saccharomyces cerevisiae SR8u strain enabled the utilization of 95.7% sugars in the hydrolysate to reach 4.6%w/v ethanol titer. The overall process also enabled the recovery of 62.9% lignin and 93.8% silica at high levels of purity.

Application potential of a carbocation scavenger in autohydrolysis and dilute acid pretreatment to overcome high softwood recalcitrance

Both autohydrolysis and acidic pretreatments have already been commercialised to allow for the bioconversion of lignocellulosic biomass to valuable products. Recent fundamental research has shown that the pretreatment of lignocellulosic biomass can be enhanced by the suppression of lignin repolymerisation. This work evaluates the application potential of a carbocation scavenger additive that prevents lignin repolymerisation for the autohydrolysis and acidic pretreatment of woody biomass. The results show that the enhancing effect of the scavenger is strongly dependent on the type of biomass. While it proved hardly beneficial in the pretreatment of hardwoods, the pretreatment of recalcitrant softwoods could be greatly enhanced. Softwood has an exceptionally high recalcitrance to biochemical conversion compared to other biomass types, though the reasons for this behaviour have hardly been understood so far. Our study revealed that lignin repolymerisation is a major factor accounting for the exceptional softwood recalcitrance. A sensitivity analysis of pretreatment temperature and time showed that the scavenger can enhance the enzymatic digestibility of softwood cellulose by up to 113% in autohydrolysis and up to 142% in dilute acid pretreatments. The scavenger proved effective for both softwood sawdust and wood chips. Its mode of action in pretreatment was shown to be particularly suitable for the implementation in two-stage pretreatments, which are of high commercial relevance.

Comparison of a two-stage and a combined single stage salt-acid based lignocellulosic pretreatment for enhancing enzymatic saccharification

This study compares the optimization of combined and two-stage salt-acid pretreatment technique for efficient delignification, hemicellulose removal and enhancement of sugar yield from sugarcane leaf waste. The effect of process parameters ZnCl2 concentration (1M–5M), H2SO4 concentration (0.10–2.0%, v/v) and solid loading (5–15%, w/v) on the reducing sugar yield were investigated. The developed models showed coefficients of determination (R2) >0.94. The two-stage pretreatment under optimal conditions of 3.32M ZnCl2, 1.84% (v/v) H2SO4, and 9.26% (w/v) solid loading gave 0.293g/g reducing sugar, a 9% improvement compared to the optimized combined pretreatment. SEM and FTIR analysis showed major structural changes in the pretreated biomass. Significant lignin and hemicellulose removal was observed with the two-stage pretreatment. The optimized two-stage pretreatment also showed 66% and 194% yield improvement on sorghum leaves and Napier grass respectively. These results indicate that a two-stage ZnCl2-H2SO4 pretreatment can significantly enhance enzymatic saccharification of lignocellulosic waste.

A comparison of various lignin-extraction methods to enhance the accessibility and ease of enzymatic hydrolysis of the cellulosic component of steam-pretreated poplar

BackgroundCurrent single-stage delignification-pretreatment technologies to overcome lignocellulosic biomass recalcitrance are usually achieved at the expense of compromising the recovery of the polysaccharide components, particularly the hemicellulose fraction. One way to enhance overall sugar recovery is to tailor an efficient two-stage pretreatment that can pre-extract the more labile hemicellulose component before subjecting the cellulose-rich residual material to a second-stage delignification process. Previous work had shown that a mild steam pretreatment could recover >65% of the hemicellulose from poplar while limiting the acid-catalysed condensation of lignin. This potentially allowed for subsequent lignin extraction using various lignin solvents to produce a more accessible cellulosic substrate.ResultsA two-stage approach using steam and/or solvent pretreatment was assessed for its ability to separate hemicellulose and lignin from poplar wood chips while providing a cellulose-rich fraction that could be readily hydrolysed by cellulase enzymes. An initial steam-pretreatment stage was performed over a range of temperatures (160–200 °C) using an equivalent severity factor of 3.6. A higher steam temperature of 190 °C applied over a shorter residence time of 10 min effectively solubilized and recovered 75% of the hemicellulose while enhancing the ability of various solvents [deep eutectic solvent (DES), ethanol organosolv, soda/anthraquinone (soda/AQ) or a hydrotrope] to extract lignin in a second stage. When the second-stage treatments were compared, the mild DES treatment (lactic acid and betaine) at 130 °C, removed comparable amounts of lignin with higher selectivity than did the soda/AQ and organosolv pretreatments at 170 °C. However, the cellulose-rich substrates obtained after the second-stage organosolv and soda/AQ pretreatments showed the highest cellulose accessibility, as measured by the Simon’s staining technique. They were also the most susceptible to subsequent enzymatic hydrolysis.ConclusionsThe second-stage pretreatments varied in their ability to solubilize and extract the lignin component of steam-pretreated poplar while enhancing the enzymatic hydrolysis of the resulting cellulose-rich residual fractions. Although DES extraction was more selective in extracting lignin from the steam-pretreated substrates, the organosolv and soda/AQ post treatments disrupted the cellulose structure to a greater extent while enhancing the ease of enzymatic hydrolysis. Graphical abstractEffective hemicellulose removal via steam pretreatment followed by subsequent lignin extraction under acidic, alkaline or solvolytic conditions results in a highly accessible, more readily hydrolysed cellulose fraction.

Algorithm of multi-criterion green process assessment for renewable raw materials bioconversion

Green Chemistry is one of the most important and practically used tools to integrate principles of sustainable development and green economy in the field of chemistry and the chemical industry in various countries. There is a number of metrics in the field of green chemistry. The research presented is an original algorithm of multi-criterion green process assessment for renewable raw materials bioconversion. The algorithm is used when the process of obtaining the same target substance N is possible to be carried out in many ways (or under different conditions). In this case, the researcher task is to choose the best process in compliance with the principles of green chemistry. The multiple-factor complex assessment is to be used to choose the optimum process conditions. The algorithm designed was tested for efficiency in choosing the optimal processes of acid hydrolysis of deproteinized meals. The deproteinized sunflower meal preprocessing efficiency analysis was carried out during the course of its microbiological conversion into a vegetable protein and carbohydrate feed supplement taking into account the principles of green chemistry. The methodology testing was based on the experimental data obtained by chemical hydrolysis of deproteinized residues, and two-stage pretreatment process of deproteinized residues processing comprising the steps of chemical and enzymatic hydrolysis. The combination of chemical and enzymatic hydrolysis in two-stage deproteinized sunflower meal processing was justified. The proposed algorithm allowed not only to determine the effective ranges of parameters of deproteinized sunflower meal processing, but also allowed to justify the possibility of its optimization due to the both processes combined.

Intensification of steam explosion and structural intricacies impacting sugar recovery

Dilute acid (DA) pretreatment at pilot level failed for cotton stalk (CS) due to the technical issues posed by its inherent nature. Reasonable glucan conversion has been reported via two-stage pretreatment but adds on to the process cost. Proposed herewith is a single-stage steam explosion (SE) process preceded by water extraction resulting in high sugar recovery from CS. Raising the extraction temperature to 80°C increased the glucan conversion from 37.9 to 52.4%. Further improvement up to 68.4% was achieved when DA was incorporated during the room temperature extraction. LC-MS revealed the formation of xylo-oligomers limiting the glucan conversion in proportion to the length of xylo-oligomers. Varying extraction conditions induced structural alterations in biomass after SE evident by compositional analysis, Infrared Spectroscopy, X-Ray Diffraction and Scanning Electron Microscopy. Overall glucose recovery, i.e. 75.8–76.7% with and without DA extraction respectively was achieved.

Enhancing lignin degradation by Mn2+ ion supplementation to assist enzymatic hydrolysis of cellulose in a two-stage pretreatment of bamboo

Abstract: It is of great significance to reveal a key agent to improve the efficiency of conversion of lignocellulosic biomass to fermentable sugars for the production of bioethanol. This study investigated a two-stage pretreatment of bamboo comprising a microbial treatment using Ceriporiopsis sp. followed by a hydrothermal treatment to facilitate the process with Mn2+ as an accelerator. The effects of Mn2+ nutritional addition on ligninolytic activity, lignin degradation, total weight loss, pulp yield, sugar yield and sugars in the soluble fraction were examined. The results showed that the time required for the incubations supplemented with Mn2+ to achieve sufficient lignin degradation and sugar yield from both the pulp and soluble fractions was significantly shortened, whereas all three ligninolytic activities were significantly decreased. The enzyme activity varied according to the presence of Mn2+, although the amount and species of the expressed protein are similar. Considering the cost, microbial treatment with a one-time fed-batch supply of metal nutrition (MnSO4) was the most preferable contribution to hydrothermal pretreatment, resulting in 19.7% lignin degradation, 66.7% pulp yield and 26.1% sugar yield over a period of 21 d. It was proven that microbial treatment by solid state incubation with Mn2+ nutrition has the potential to be a low-cost, environmentally friendly alternative to chemical approaches. Keywords: hydrolysis, fungi, Mn2+ ion, pretreatment, bamboo, Ceriporiopsis sp. DOI: 10.3965/j.ijabe.20171003.2991 Citation: Liu J, Gan L H, Long M N. Enhancing lignin degradation by Mn2+ ion supplementation to assist enzymatic hydrolysis of cellulose in a two-stage pretreatment of bamboo. Int J Agric & Biol Eng, 2017; 10(3): 175–184.

Evaluation of an integrated process to fully utilize bamboo biomass during the production of bioethanol

Aiming for the complete utilization of bamboo biomass, an integrated process which combines ethanol production with the recovery of silica and lignin was proposed. To reduce chemical charge required for the fractionation of silica and lignin from bamboo and improve the digestibility of the obtained substrate, a sequentially two-stage pretreatment process of autohydrolysis and alkaline extraction was carried out. From the view of enhancing enzymatic hydrolysis and recovery of silica and lignin, a two-stage treatment of autohydrolysis at 180°C for 90min followed by alkaline extraction at 100°C with 6% NaOH (based on pretreated chips) for 120min was optimized. About 93.7% of original silica and 75.7% of original lignin could be recovered from bamboo. Enzymatic hydrolysis and fermentation of carbohydrates showed that an overall sugar yield of 88.6% of original sugar content and an ethanol recovery of 0.467g/g sugar were achieved based on the proposed scheme.

Optimization of ethylenediamine pretreatment and enzymatic hydrolysis to produce fermentable sugars from corn stover

Ethylenediamine (EDA) pretreatment is an effective pretreatment technology to improve enzymatic digestibility of corn stover for the production of fermentable sugars. In this study, key pretreatment parameters were identified and optimized to improve enzymatic digestibility of corn stover. We found that agitation and biomass stack height during pretreatment had significant impacts on enzymatic digestibility. Response surface experiment showed that optimal condition to achieve maximum total sugar enzymatic yield was 150°C and 80mL EDA/100g corn stover. Under this condition, glucose yield was greater than 90% in enzymatic hydrolysis at 1% glucan loading. Optimized temperature to minimize residual EDA in pretreated corn stover was 200°C. Two-stage pretreatment was carried out to maximize both sugar yields and EDA removal, in which glucose and xylose enzymatic yields reached 92% and 70% respectively at 1% glucan loading, and EDA residue reduced to 27g/kg corn stover. With the optimal enzyme loadings (both enzymes of Ctec2 and Htec2 were loaded at 30mg protein/g glucan), glucose and xylose yields at 6% glucan loading reached 81% and 58%, respectively.

A novel integrated biorefinery process for diesel fuel blendstock production using lipids from the methanotroph, Methylomicrobium buryatense

In light of the availability of low-cost methane (CH4) derived from natural gas and biogas along with increasing concerns of the greenhouse gas emissions, the production of alternative liquid biofuels directly from CH4 is a promising approach to capturing wasted energy. A novel biorefinery concept integrating biological conversion of CH4 to microbial lipids together with lipid extraction and generation of hydrocarbon fuels is demonstrated in this study for the first time. An aerobic methanotrophic bacterium, Methylomicrobium buryatense capable of using CH4 as the sole carbon source was selected on the basis of genetic tractability, cultivation robustness, and ability to accumulate phospholipids in membranes. A maximum fatty acid content of 10% of dry cell weight was obtained in batch cultures grown in a continuous gas sparging fermentation system. Although phospholipids are not typically considered as a good feedstock for upgrading to hydrocarbon fuels, we set out to demonstrate that using a combination of novel lipid extraction methodology with advanced catalyst design, we could prove the feasibility of this approach. Up to 95% of the total fatty acids from membrane-bound phospholipids were recovered by a two-stage pretreatment method followed by hexane extraction of the aqueous hydrolysate. The upgrading of extracted lipids was then demonstrated in a hydrodeoxygeation process using palladium on silica as a catalyst. Lipid conversion in excess of 99% was achieved, with a full selectivity to hydrocarbons. The final hydrocarbon mixture is dominated by 88% pentadecane (C15H32) based on decarbonylation/decarboxylation and hydrogenation of C16 fatty acids, indicating that a biological gas-to-liquid fuel (Bio-GTL) process is technically feasible.

Green chemistry for the optimum technology of biological conversion of vegetable waste

Nowadays the development of low-waste and resource-saving technologies of food products based on renewable raw materials and waste products of their processing enriched with protein is one of the priority tasks to be solved in the framework of sustainable development of modern society. The method of assessing the effectiveness of waste pretreatment of deproteinized sunflower meal (DSFM), one of oil and fat industry waste products is proposed for its microbial conversion into vegetable carbohydrate and protein concentrates according to the principles of green chemistry. The methodology proposed includes an assessment of three factors: amount of wastes per unit of the desired product; the amount of hazardous substances used in the pretreatment process, and process efficiency. The methodology testing was based on the experimental data obtained by chemical hydrolysis of DSFM, and also two-stage pretreatment process of DSFM comprising the steps of chemical and enzymatic hydrolysis. The recommendations for selection of optimal DSFM pretreatment conditions based on the calculated assessments of the process efficiency are submitted.

A two-stage pretreatment using acidic dioxane followed by dilute hydrochloric acid on sugar production from corn stover

A two-stage pretreatment method was developed to improve sugar recovery in this study.

Comparison of two-stage acid-alkali and alkali-acid pretreatments on enzymatic saccharification ability of the sweet sorghum fiber and their physicochemical characterizations

Two-stage acid/alkali pretreatment was used to enhance the saccharification efficiency of sweet sorghum fiber. The physicochemical characterizations of the pretreated fibers were evaluated by SEM, FTIR and XRD. The acid and alkali sequence in the two-stage pretreatment process was compared, and their dosage was optimized. The results indicated that the two-stage pretreatment showed better saccharification performance when compared with conventional single stage pretreatment. And compared with the acid-alkali sequence, the alkali-acid sequence achieved higher glucose yield (0.23g·g−1) under the optimized conditions, which was 1.64 and 1.21 times higher than that of the single stage and the acid-alkali pretreatments, respectively. Overall, the two-stage pretreatment process is a promising approach to achieve high fermentable glucose conversion rate of cellulosic material.

Enhanced enzymatic hydrolysis of kenaf core using irradiation and dilute acid

This study was performed to determine the effect of electron beam dose and enzymatic hydrolysis time for production of sugar such as glucose and xylose. After kenaf core was exposed to an irradiation dose that ranged from 0 to 500kGy, the irradiated kenaf core was treated with a 3% (v/v) sulfuric acid solution using an autoclave for 5h at 120°C. The pretreated kenaf core was subsequently subjected to enzymatic hydrolysis at 50°C in a shaking water bath at 150rpm for 12, 24, 48, and 72h. The determined enzyme activity rates were 70 FPU (Celluclast 1.5L) and 40 CBU (Novozyme-188). The crystallinity index decreased from 50.6% in a non-pretreated kenaf core to 27.7% in kenaf core that was subjected to the two-stage pretreatment at dose of 500kGy. The sugar yield of the two-stage pretreated kenaf core increased with an increase in irradiation dose. The sugar yield after 72h of enzymatic hydrolysis was 73.6% at its highest with an irradiation dose of 500kGy. The enhancement of enzymatic hydrolysis by two-stage pretreatment was more effective than non- and single pretreatment (36.9%, 40.6% and 44.0% in non-pretreatment, electron beam and dilute acid, respectively).