Search

[Display omitted] • Autohydrolysis enhanced the delignification of p -TsOH post-treatment of poplar. • Unexpectedly, the glucose yields of combined pretreated poplar decreased. • The intensified surface lignin coverage hindered the enzymatic hydrolysis. • Tween 80 enabled the excellent enzymatic hydrolysis of combined pretreated poplars. In this study, a combined pretreatment involving autohydrolysis and p -toluenesulfonic acid (p -TsOH) was performed on poplar to coproduce xylooligosaccharides (XOSs) and monosaccharides. The autohydrolysis (180 °C, 30 min) yielded 53.2 % XOS and enhanced the delignification efficiency in the subsequent p -TsOH treatment. Furthermore, considerably high glucan contents (64.1 %∼83.1 %) were achieved in the combined pretreated substrates. However, their enzymatic digestibilities were found to be extremely poor (9.6 %∼14.2 %), which were even lower than the single p -TsOH pretreated substrates (10.2 %∼35.8 %). The underlying reasons were revealed by systematically investigating the effects of the single and combined pretreatment strategies on substrate properties. Moreover, the Tween 80 addition successfully reversed the adverse effects of combined pretreatment on the enzymatic hydrolysis, achieving a high glucose yield of 99.3 % at an enzyme loading of 10 filter paper units/g (FPU/g) glucan. These results deepen the understanding of the synergy of combined pretreatment on biomass fractionation and enzymatic saccharification. [ABSTRACT FROM AUTHOR]

To elucidate the effects of lignin repolymerization on the combined pretreatment, the sequential acid and deep eutectic solvent (DES) pretreatment was implemented on Populus (poplar) in this study. Effects of acid pretreatment with or without phenolic additives (2-naphthol (2 N) and resorcinol (RS)) on the DES post-treatment efficiency were examined. The results showed that 2 N inhibited the lignin repolymerization in the first-step pretreatment, and slightly enhanced the lignin removal during DES post-treatment. However, RS intensified the lignin repolymerization, significantly decreasing the delignification of DES post-treatment from 73.6%∼79.4% to 39.0∼43.0%. Moreover, the poorer enzymatic hydrolysis was observed in the combined pretreated substrates as compared to the single DES pretreated ones, due to the higher surface lignin coverage. The addition of 2 N counteracted the adverse effects of acid pretreatment on the hydrolysis yields of combined pretreated substrates, and facilitated the yields from 25.8%∼36.0% to 26.2∼67.3%, while the RS addition further decreased the hydrolysis yields to 8.6∼9.6%. The mechanism for the changes on enzymatic digestibilities of the combined pretreated substrates was elucidated. [Display omitted] • 2-Naphthol inhibited lignin polymerization, while resorcinol intensified it. • Lignin repolymerization hindered the delignification of the DES post-treatment. • 2-Naphthol promoted the hydrolysis of pretreated poplar, but resorcinol impeded it. • 2-Naphthol addition benefited the lignin fractionation and valorization. [ABSTRACT FROM AUTHOR]

• Individual and combined chemical and HTP pretreatments have been investigated. • COD solubilization for combined pretreatment was not notably higher than the HTP. • The highest methane yield was achieved for combined HTP with FNA. • Reaction Curve and First-Order models were applied and found to fit the experimental data. • Preliminary economic analysis indicated that combined HTP with FNA is feasible. This study focused on investigating the effect of combined chemical and hydrothermal pretreatment (HTP) on the anaerobic digestibility of thickened waste activated sludge (TWAS). Three different combined pretreatment conditions of HTP + free nitrous acid (FNA), HTP + Acid, and HTP + Alkaline were applied to TWAS. To control and compare the effect of combined pretreatments and a single pretreatment, Acid, Alkaline, FNA and HTP pretreatments were applied done prior to AD. The results of this study revealed that combined pretreatments have higher potential to improve methane production yield and rate but not in the solubilization of COD. The highest methane yield of 275 mL CH 4 /g TCOD added was achieved for the combined pretreatment with FNA and HTP. HTP + FNA pretreatment was found to produce higher methane yields compared to the combination of other typical acid and alkaline reagents with hydrothermal pretreatment. Methane yields of 594, 527, and 544 L CH 4 /g VSS added, were achieved for HTP + FNA, HTP + ALK, and HTP + ACID pretreatments, respectively. The preliminary economic analysis showed that out of the combined pretreatment, only combining HTP with FNA is economically feasible. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel combined H 2 SO 4 -ChCl/Gly pretreatment of reed stalks was developed. • Synergistic effect of H 2 SO 4 and ChCl/Gly eliminated xylan and lignin effectively. • H 2 SO 4 -ChCl/Gly-treated reed stalk was converted to glucose in a high yield of 91.1%. • High saccharification was due to enhanced accessibility and reduced lignin surface. In this study, an efficient combination of pretreatment solvents involving Choline chloride/Glycerol (ChCl/Gly) and H 2 SO 4 was firstly developed to assess the pretreatment performance and determine optimal pretreatment conditions. The results illustrated that the H 2 SO 4 -[ChCl/Gly] combination efficiently removed lignin (52.6%) and xylan (80.5%) from the pretreated reed stalk, and subsequent enzymatic hydrolysis yielded 91.1% of glucose. Furthermore, several characterizations were conducted to examine the structural and morphological changes of the reed stalk, revealing apparently enhanced accessibility (128.4 to 522.6 mg/g), reduced lignin surface area (357.9 to 229.5 m2/g), and substantial changes on biomass surface. Based on the aforementioned study, possible mechanisms for the H 2 SO 4 -[ChCl/Gly] pretreatment of reed stalks were proposed. The comprehensive understanding of combined H 2 SO 4 -[ChCl/Gly] pretreatment system for enhancing the saccharification of the reed stalk was interpreted in this work. Overall, this novel approach could be efficiently applied to pretreat and saccharify reed stalks, empowering the biomass refining industry. [ABSTRACT FROM AUTHOR]

[Display omitted] • The impacts of water-washing and freeze-drying pretreatment on biochar are studied. • Biochar with combined pretreatments (W-FD-PB) has a large surface area (212.69 m2/g). • Q m of Pb2+ on W-FD-PB is 406.99 mg/g, 1.53-fold of W-PB and 2.19-fold of PB. • Precipitation and ion exchange were enhanced during Pb2+ adsorption by W-FD-PB. • The addition of biochar significantly reduced DTPA-Pb concentrations in soil. This paper examined the impacts of different pretreatments on the characteristics of biochar and its adsorption behavior for Pb2+. Biochar with combined pretreatment of water-washing and freeze-drying (W-FD-PB) performed a maximum adsorption capacity for Pb2+ of 406.99 mg/g, higher than that of 266.02 mg/g on water-washing pretreated biochar (W-PB) and 188.21 mg/g on directly pyrolyzed biochar (PB). This is because the water-washing process partially removed the K and Na, resulting in the relatively enriched Ca and Mg on W-FD-PB. And the freeze-drying pretreatment broke the fiber structure of pomelo peel, favoring the development of a fluffy surface and large specific surface area during pyrolysis. Quantitative mechanism analysis implied that cation ion exchange and precipitation were the driving forces in Pb2+ adsorption on biochar, and both mechanisms were enhanced during Pb2+ adsorption on W-FD-PB. Furthermore, adding W-FD-PB to Pb-contaminated soil increased the soil pH and significantly reduced the availability of Pb. [ABSTRACT FROM AUTHOR]

• Hydrocyclone-induced pretreatment for sludge disintegration was first proposed. • Efficient SCOD release was achieved at specific energy 0.18 W/g TS by hydrocyclone. • Combined pretreatment presents higher SCOD release, VFAs and CH 4 production. • Net profit of 131.73 USD/t TS was achieved for optimal combined pretreated sample. Hydrocyclone-induced pretreatment was first proposed for sludge disintegration to address excess sludge and to be served as a means of sustainable energy production. The effects of hydrocyclone disintegration alone and combination of hydrocyclone and alkaline pretreatments on sludge solubilization followed by anaerobic digestion were investigated. Initially, the flocs were disrupted through hydrocyclone at an optimal specific energy input of 0.18 W/g TS, with 2142 mg/L soluble chemical oxygen demand (SCOD) release. The hydrocyclone induced alkaline pretreatment in different sequence was investigated subsequently, and a maximal SCOD release of 4409 mg/L was observed in combination IV, which included hydrocyclone treatment throughout and alkaline treatment from 50th min to 80th min. Mechanisms of organics release via hydrocyclone-induced sludge pretreatment were also explored, and the sludge disintegration was attributed to its anisotropic flow field as well as common actions of sheared shedding and rotation desorption. The biodegradability analysis exhibited that the optimal combined pretreated sludge also exhibited 23.75% higher levels of VFA accumulation to 1017 mg/L, 32.38% more methane production to 134.29 mL CH 4 /g TS and 5.9% more VSS reduction to 29.3% relative to the hydrocyclone pretreated sludge. An economic of optimal combined sludge pretreatment offers a positive net profit of 130.42 USD/ton of TS, was assessed to be a cost-effective process. [ABSTRACT FROM AUTHOR]

Highlights • Combined ultrasound-acid pretreatment improved H 2 yield of grass by 311.7%. • The combined pretreatment improved the substrate utilization efficiency. • The combined pretreatment induced a more efficient fermentation pathway. • More enrichment of Clostridium contributed to the improvement in H 2 production. Abstract In this study, the dilute acid pretreatment combined with ultrasound was applied to improve fermentative hydrogen production from grass. The experimental results indicated that SCOD and soluble carbohydrate contents of grass was improved by 98.6% and 236.9% after the combined treatment, respectively. Surface morphology (SEM and AFM) and crystallinity analysis revealed that the combined pretreatment process could effectively destroyed the biomass structure and increased their surface area. Owing to the increased soluble organics proportion and better enzymatic accessibility of residual solids, the hydrogen yield reached 42.2 mL/g-dry grass after the combined treatment, which was 311.7%, 190.0% and 35.0% higher in comparison with the control, individual ultrasound and acid pretreated groups, respectively. Meanwhile, the combined treatment also increased the substrate utilization efficiency and induced a more efficient fermentation pathway. Bacterial community analysis revealed that more enrichment of Clostridium and less enrichment of Enterococcus contributed to the improved hydrogen production. [ABSTRACT FROM AUTHOR]

Highlights • Alkali and acid pretreated biomass slurries were mixed for ethanol production. • This approach saved 40–50% alkali/acid use. • This approach improved fermentability. Abstract Alkali and acid pretreatment based processes for lignocellulosic biofuel production typically consume substantial amount of alkali and acid. In addition, alkali pretreatment generates compounds with high toxicity rendering washing/detoxification inevitable. In this work, alkali (AL) and dilute acid (DA) pretreatment based processes were compared side by side for ethanol production from corn stover (CS) using commercial enzymes and Zymomonas mobilis 8b strain. Next, AL and DA pretreated CS slurries (without removing liquid stream) were mixed to neutralize for enzymatic hydrolysis and ethanol fermentation. The digestibility and fermentability of the mixed pretreated biomass were systematically studied and compared to unmixed pretreated biomass. Results showed that mixed biomass process saved 40–50% alkali/acid use and enhanced fermentability compared to AL-CS. This work suggests that it could be beneficial to have both alkali and acid pretreatments operating in a biorefinery, which could accommodate various feedstocks. [ABSTRACT FROM AUTHOR]

To solve the problem of standing wave produced by single-frequency ultrasonic pretreatment, the dual-frequency ultrasound was applied to pretreat the corn stalk. In this paper, the mechanism of dual-frequency ultrasound was studied, and digital simulation results showed that the cavitation of dual-frequency ultrasound was more violent than that of single-frequency ultrasound, and its energy was more efficient. The anaerobic fermentation of corn stalk that was pretreated by dual-frequency ultrasound combined with alkali (Group 1) lasted for 53 days. The results showed that the cumulative biogas yield of Group 1 was 11.1%, 28.2% and 56.6% respectively higher than that of single-frequency ultrasound combined with alkali pretreatment (Group 2), alkali pretreatment (Group 3) and without pretreatment (Group 4). The TS removal rate of Group1 was 9.9%, 25.0% and 71.4% respectively higher than that of other pretreatment samples, and the VS removal rate was 7.4%, 28.9% and 77.1% respectively higher than that of other group samples. The net energy of Group 1 was 32.2%, 114.9% and 19.7% higher than that of Group 2, Group 3 and Group 4. [ABSTRACT FROM AUTHOR]

A thorough assessment of the microstructural changes and synergistic effects of hydrothermal and/or ultrafine grinding pretreatment on the subsequent enzymatic hydrolysis of corn stover was performed in this study. The mechanism of pretreatment was elucidated by characterizing the particle size, specific surface area (SSA), pore volume (PV), average pore size, cellulose crystallinity (CrI) and surface morphology of the pretreated samples. In addition, the underlying relationships between the structural parameters and final glucose yields were elucidated, and the relative significance of the factors influencing enzymatic hydrolyzability were assessed by principal component analysis (PCA). Hydrothermal pretreatment at a lower temperature (170 °C) combined with ultrafine grinding achieved a high glucose yield (80.36%) at a low enzyme loading (5 filter paper unit (FPU)/g substrate) which is favorable. The relative significance of structural parameters in enzymatic hydrolyzability was SSA > PV > average pore size > CrI/cellulose > particle size. PV and SSA exhibited logarithmic correlations with the final enzymatic hydrolysis yield. [ABSTRACT FROM AUTHOR]

In this study, the combined ionizing radiation-acid pretreatment process was firstly applied to enhance hydrogen fermentation of grass waste. Results showed that the combined pretreatment synergistically enhanced hydrogen fermentation of grass waste. The SCOD and soluble polysaccharide contents of grass waste increased by 1.6 and 2.91 times after the combined pretreatment, respectively. SEM observation and crystallinity test showed the combined pretreatment effectively disrupted the grass structure. Owing to the more favorable substrate conditions, the hydrogen yield achieved 68 mL/g-dry grass added after the combined pretreatment, which was 161.5%, 112.5% and 28.3% higher than those from raw, ionizing radiation pretreated and acid pretreated grass waste, respectively. The VS removal also increased from 13.9% to 25.6% by the combined pretreatment. Microbial community analysis showed that the abundance of dominant hydrogen producing genus Clostridium sensu stricto 1 increased from 37.9% to 69.4% after the combined pretreatment, which contributed to more efficient hydrogen fermentation. [ABSTRACT FROM AUTHOR]

An organosolv process using ethanol-water was optimized in order to recover high quality lignin from rice-straw previously pre-treated by autohydrolysis at 210 °C. The results showed a selective and appreciable removal of lignin under very mild conditions and the highest delignification yield occurred at 30 °C. The lignin extracts were characterised using capillary zone electrophoresis (CZE), size exclusion chromatography (SEC), Fourier transform infrared spectroscopy (FT-IR) and 31 P-NMR, and two-dimensional heteronuclear single quantum correlation NMR spectroscopy (2D-HSQC NMR), which enabled the identification of low molecular weight lignins with a syringyl/guaiacyl ratio of about 0.74 containing phenolic compounds with potential bioactive properties. In order to separate the target compounds, membrane technology has been used and an enriched extract containing value-added phenolic compounds such as tricin, vanillin, ferulic acid and p- coumaric acid was obtained. High membrane efficiency (around 80%) was obtained for target compounds. [ABSTRACT FROM AUTHOR]

To enhance the cellulose digestibility of energy grass hybrid Pennisetum ( P. americanum × P. purpureum , HP) with low energy-consumption and high efficiency, a novel combinatorial pretreatment of oxygen-aqueous alkaline ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate ([Emim]Ac) media (OEA) was developed in this work. The combinatorial pretreatment was performed under the relatively low temperature (120 °C), short retention time (30 min), and 12 bar oxygen pressure. The combinatorial pretreatment of OEA was demonstrated effectively for pretreatment of hybrid Pennisetum , which evidenced by the removal of lignin, degradation of carbohydrate, and porosity property of the regenerated biomass. Subsequently, a higher glucose recovery (96.9%) at a low enzyme loading (20 FPU/g substrate) was obtained by the OEA pretreatment, and it was 9.1 times as much as the untreated samples. Overall, the novel OEA combinatorial pretreatment has the advantages of low thermal energy input and enzyme usage, and short retention time. [ABSTRACT FROM AUTHOR]

A novel combined pretreatment strategy, where the hydrophobicity of feedwater is reduced and the morphology of flocs is optimized by varying the sequence of powdered activated carbon (PAC) adsorption and coagulation, is applied to alleviate membrane fouling. To explore the effects of pretreatment sequence and the role of PAC on the membrane fouling, the combined pretreatments of adsorption followed by coagulation (A-C) and coagulation followed by adsorption (C-A) are investigated with various PAC dosages (10, 20, and 50 mg/L). The results reveal that since PAC directly participates in the growth of flocs as the core during A-C pretreatment, the A-C pretreatment is more conducive than the C-A pretreatment to form flocs with a larger size, higher strength, and smaller fractal dimension. Thus, the flocs can accumulate into a porous cake layer to improve the membrane permeability and fouling reversibility. Moreover, the irreversible fouling is highly linearly correlated SUVA values in the early ultrafiltration cycles (R2 SUVA = 0.9536) and with the floc strength in the late cycles (R2 Strength = 0.9348–0.9763). This finding can be used to make a targeted diagnosis of irreversible fouling in different cycles, providing valuable guidance for prolonging the service life of ultrafiltration membranes. [Display omitted] • The sequence of combined pretreatment has significant effects on membrane fouling. • PAC has a higher adsorption efficiency for organic matter in A-C pretreatment. • Flocs with PAC as the core have a larger size, higher strength, and lower D f. • Irreversible fouling (IF) can be selectively predicted by SUVA and floc strength. • A-C pretreatment promotes the formation of a porous cake layer to alleviate IF. [ABSTRACT FROM AUTHOR]

[Display omitted] • Waste activated sludge is an efficient feedstock for biohydrogen production. • Synergetic disintegration were emphasized by thermo-chemo disperser pretreatment. • Solubilization and SS reduction fostered at 2081.82 kJ/kg TS specific energy. • About 116.9 mL H 2 /g COD achieved at TCD pretreated samples. Generation of excess sludge in large quantities from wastewater treatment plant face huge problem in terms of handling and management, whereas it possess higher organic and inorganic constituents and thus it can be used as a feedstock for the generation of biofuel with proper disintegration techniques. In this regard, an effort has been made in this study to combine thermo-chemo-disperser pretreatment for the disintegration of paper mill waste activated sludge for the production of biohydrogen in an energy efficient way. These combinations of thermo-chemo-disperser (TCD) tend to be effective in disintegration and possess 24.3% COD solubilization and higher suspended solid reduction of 18.8% at the specific energy usage of 2081.82 kJ/kg TS. The pretreatment with TCD technique shows the biohydrogen production of 120.2 mLH 2 /gCOD as compared to thermochemically pretreated alone (73.6 mLH 2 /gCOD) sample. Thus, the combined process was considered to be potentially effective in sludge disintegration. [ABSTRACT FROM AUTHOR]

Biofuel production from lignocellulose has recently been gaining much more attention as a result. One major problem of using lignocellulosic materials for the production of biofuel is the low accessibility of cellulose to enzymes and microorganisms. Therefore, pretreatment of lignocellulose is a critical step in biofuel production from such materials. Of the pretreatments, fungal treatment has become an important process due to its low energy demands and selective degradation of lignin and hemicellulose. This capability comes from the unique enzymatic systems, cellulolytic and ligninolytic enzymes, especially in white rot fungi. The low energy demand of fungal pretreatment has generated interest in studying the applicability of fungal pretreatment for biofuel production from woody materials. The most significant drawback of fungal pretreatment is the lengthy time required for the process. Combining fungal pretreatment with other pretreatment methods might reduce the time necessary for the whole process to operate. It can also introduce cost-effectiveness. Thus combining fungal pretreatment with other physical and chemical methods has been recently contemplated. This paper provides a comprehensive review of current fungal pretreatments and feasibility for biofuel production, with a focus on combining fungal pretreatment with other methods. The advantages and disadvantages of all physical and chemical methods were also briefly reviewed. The applicability of the combination of fungal with other pretreatment methods has been considered in a number of recent publications. To be commercially attractive, both energy demand and processing time should be reduced. In terms of energy demand reduction, combined fungal physico-chemical pretreatment has been effective. However, the lengthy time taken for the whole process has not been significantly improved upon. A great deal of work is still required to be done regarding time reduction for the process (combined fungal-physico chemical pretreatment). Therefore, it seems to remain an open field for research and process development. [ABSTRACT FROM AUTHOR]

Combining more than one processes in one-step is an effective approach for economical, ecological and efficient processing of textiles. The most commonly used alpha-amylase enzyme, suitable for desizing woven fabrics, is not compatible for combined desizing-scouring-bleaching process in one step due to lack of stability under high temperature and alkaline condition in the combined process. The aim of this study was to use a novel, non-enzymatic desizer, which is stable under high alkalinity and temperature condition in the combined process. The lab trials showed the effectiveness of non-enzymatic desizer for one-step pretreatment of polyester/cotton blended fabrics. After successful lab trials, the proposed one-step process for combined desizing-scouring-bleaching on polyester/cotton blended fabrics was optimized for industrial-scale application. The concentration parameters for hydrogen peroxide, sodium hydroxide and the desizer were optimized with the help of central composite experimental design (CCD) of response surface methodology. The results obtained in one-step pretreatment method, in terms of the physical properties of the treated fabrics, were comparable with the results obtained by separate desizing, scouring and bleaching processes carried out on the identical fabric. However, the proposed one-step pretreatment process is much more advantageous with respect to saving in chemicals, water and energy as well as reduction in the process time. [ABSTRACT FROM AUTHOR]

Combined pretreatment with hot compressed water and wet disk milling was performed with the aim to reduce the natural recalcitrance of oil palm biomass by opening its structure and provide maximal access to cellulase attack. Oil palm empty fruit bunch and oil palm frond fiber were first hydrothermally pretreated at 150–190 °C and 10–240 min. Further treatment with wet disk milling resulted in nanofibrillation of fiber which caused the loosening of the tight biomass structure, thus increasing the subsequent enzymatic conversion of cellulose to glucose. The effectiveness of the combined pretreatments was evaluated by chemical composition changes, power consumption, morphological alterations by SEM and the enzymatic digestibility of treated samples. At optimal pretreatment process, approximately 88.5% and 100.0% of total sugar yields were obtained from oil palm empty fruit bunch and oil palm frond fiber samples, which only consumed about 15.1 and 23.5 MJ/kg of biomass, respectively. [ABSTRACT FROM AUTHOR]

Pretreatment was the essential step for industrial application of lignocellulosic biomass. Combination of steam explosion and fungal treatment was conducted, and synergistic mechanism of the combined pretreatment was evaluated in terms of pore size distribution, crystallinity index, chemical compositions and enzymatic hydrolysis. The results showed that steam explosion destroyed the rigid structure of corn stalk, increased pore size and porosity, and exposed crystalline component of cellulose. Steam explosion broke the lignin-carbohydrate-complex structure of lignocellulosic biomass and facilitated the fungal treatment.Phellinus baumii could selectively degrade 34.7% and 36.58% of lignin for 1.4 MPa and 1.7 MPa steam-exploded corn stalk, respectively. As a result, the highest glucose yield of corn stalk pretreated by the condition of 1.7 MPa steam explosion associated with 21 d P. baumii reached 313.31 g kg-1, which was 2.88 and 1.32 times higher than that of the untreated corn stalk and the 1.7 MPa steam-exploded corn stalk, respectively. The combined pretreatment enhanced the enzymatic hydrolysis, which was a promising technology that might be explored as alternative to the existing pretreatment. [ABSTRACT FROM AUTHOR]

[Display omitted] • Additives in pretreatment notably raised fermentable sugars and bioethanol yields. • Mechanisms of reducing lignin repolymerization by additives were investigated. • −OH groups of additives suppressed lignin repolymerization by forming a new reaction. • More hydrophilic groups of lignin reduced non-specific binding into enzymes. • Enlarged biomass porosity and lower surface coverage reduced surface lignin barrier. Pretreatment is the key factor for producing fermentable sugars and biofuels from lignocellulosic biomass. However, during pretreatment lignin repolymerization occurs which reduces the efficiency of carbohydrates hydrolysis. In the present study, three additives (2-naphthol-7-sulfonate, 2-naphthol, and mannitol) were evaluated for boosting the effectiveness of combined pretreatment (liquid hot water + green liquor) of pine-wood biomass. The results revealed that supplied additives into combined pretreatment changed the physicochemical structure of lignin, therefore, alleviating the inhibitory effect of lignin repolymerization and notably raised sugars yield (glucose, xylose) ranging from 85% to 93%. XPS and FTIR analyses confirmed that −OH groups of additives led to lower formation of phenolic hydroxyl (PhOH) and higher hydrophilic groups of lignin, accounting for reduced non-specific binding of lignin into cellulase enzymes. Furthermore, additives increased surface lignin coverage, biomass porosity, and fiber swelling by 1.96–2.59, 1.66–1.86, and 1.13–1.29 folds respectively, comparing to corresponding sample without additives caused more liquified and extractable lignin, which notably reduced the surface lignin barrier. Hence, both factors including non-specific binding effect and surface lignin barrier, contributed to reducing lignin repolymerization, thereby increased cellulose accessibility for high production of fermentable sugars and bioethanol in softwood biomass. [ABSTRACT FROM AUTHOR]

Abstract: In this study, individual pretreatments (acid and ultrasonic) and a combination of these pretreatments were optimized to enhance the efficiency of dark fermentative hydrogen production (DFHP) from microalgal biomass. The experimental results show that the maximum H2 production performance of 42.1mL H2/g dry cell weight (dcw) was predicted at 0.79% (v/w) HCl and at a specific energy input (SEI) of 49,600kJ/kg dcw in the combined pretreatment, while it was limited in both individual pretreatments. Repeated batch testing of the predicted optimal conditions revealed that the combined pretreatment conditions for DFHP from microalgal biomass were successfully optimized by increasing the solubilization of the feedstock and by reducing the formation of the toxic 5-hydroxymethylfurfural (HMF). [Copyright &y& Elsevier]

The synergetic effect of ultrafine grinding coupled with the incorporation of an appropriate amount of nanomaterials (NMs) on biohydrogen (bioH 2) production from corn stover (CS) was studied. The changes in the physicochemical and optical characteristics of CS pretreated with various ultrafine grinding times were comprehensively studied. High-quality SnO 2 NMs with high defect concentrations (e.g., oxygen vacancies (OVs)) were successfully synthesised. The physio-optical structures of pretreated CS and synthesised NMs were analysed using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy, and diffuse reflectance spectroscopy. SEM measurements confirmed that the morphology of the CS changed with the increase in grinding time and the particle size was reduced to the submicron range with increased surface roughness. The biomass particle size changed considerably from micron to submicron with an increase in grinding time. The intensities of the diffracted peak 22° decreased and the full width at half maximum increased with the increase in grinding time, which confirmed the considerable modification of biomass crystalline structure. The SEM analysis revealed that the synthesised SnO 2 NMs were spherical in nature with a uniform size distribution. XRD analysis confirmed that the synthesised NMs had a stable rutile structure without any secondary phases. Hydrogen production tests were performed by utilising a mixed consortium of photosynthetic bacteria HAU-M1 as the inoculum. Hydrogen production rates of 120, 123, and 145 mL/h were observed for samples pretreated with 2, 4, and 6 h of ultrafine grinding, respectively. Owing to the synergetic effect of ultrafine grinding and nanomaterial loading, the hydrogen production rate increased considerably to 143, 144, and 163 mL/h after 2, 4, and 6 h of ultrafine grinding and nanomaterial loadings of 200, 150, and 150 mg/L, respectively. The highest cumulative bioH 2 production of 425 mL was recorded after ultrafine grinding for 6 h and nanomaterial loading of 150 mg/L, 49% higher than that achieved with the standard sample (285 mL). Furthermore, the synergetic effect reduced not only the lag time (from 36 to 24 h) but also the amount of SnO 2 NMs loading required to achieve the highest hydrogen production rate (150 mg/L) as compared with the standard sample (200 mg/L). Our results highlight that an appropriate combination of pretreatments can present a potential roadmap to enhance bioH 2 production from lignocellulosic biomass, which can be a prospective sustainable energy supply. [Display omitted] • SEM images showed 6 h ultrafine grinding has particle size in the range of micron. • High quality SnO 2 NMs with size variation of 5–15 nm were fabricated. • Highest HPR of 163 mL/h was observed at 6 h of ultrafine grinding and 150 mg/L NMs. • In comparison to SS, the total bioH 2 yield is 49% higher with synergetic effect. • The synergetic effect helped to reduce the lag time (24 h from 36 h). [ABSTRACT FROM AUTHOR]

Abstract: In the present work, a combined (acid + thermal) pretreatment was applied for the enhanced fermentative H2 production (FHP) from Laminaria japonica. Various pretreatment conditions including HCl concentrations, heating temperatures, and reaction times were optimized via response surface methodology (RSM) with a Box-Behnken design (BBD). Through regression analysis, it was found that H2 yield was well fitted by a quadratic polynomial equation (R 2 = 0.97), and the HCl concentration was the most significant factor influencing FHP. The desirable pretreatment conditions found were HCl concentration of 4.8%, temperature of 93 °C, and reaction time of 23 min, under which H2 yield reached to 159.6 mL H2/g dry cell weight (dcw). The main organic acids produced were acetic and butyric acids that related closely with H2 production. The concentration of hydroxymethylfurfural (HMF), a byproduct formed during the pretreatment process, showed an inverse relationship with H2 yield, indicating that pretreatment conditions for the H2 production from L. japonica were successfully optimized, by increasing the hydrolysis rate of the feedstock and also reducing the formation of HMF. [Copyright &y& Elsevier]

Abstract: Pretreatment technology is a prerequisite to facilitate the release of sugars from a lignocellulosic biomass prior to fermentation. Recently, some pretreatment methods have been tried with ionic liquids, but they were still expensive and unpractical. In this study, an efficient pretreatment method using ammonia and ionic liquid was developed for the recovery of bio-digestible cellulose from a lignocellulosic byproduct, rice straw, and the increase of ionic liquid utilization. The combined use of ammonia and ionic liquid ([Emim]Ac) treatment exhibited a synergy effect for rice straw with 82% of the cellulose recovery and 97% of the enzymatic glucose conversion. This cooperative effect showed over 90% of the glucose conversion even with a reduced enzyme usage and incubation time. The ionic liquid was successfully recycled more than 20 times. The 20th-recycled ([Emim]Ac) showed 74% of the cellulose recovery and 78% of the glucose conversion to rice straw. Compared with the conventional pretreatment, our combined method for lignocellulosic biomass pretreatment was an economical and eco-friendly. [Copyright &y& Elsevier]

Abstract: The individual effects of alkaline (pH 8-13) and ultrasonic (3750–45,000kJ/kg TS) pretreatments on the disintegration of sewage sludge were separately tested, and then the effect of combining these two methods at different intensity levels was investigated using response surface methodology (RSM). In the combined pretreatment, ultrasonic treatment was applied to the alkali-pretreated sludge. While the solubilization (SCOD/TCOD) increase was limited to 50% in individual pretreatments, it reached 70% in combined pretreatment, and the results clearly showed that preconditioning of sludge at high pH levels played a crucial role in enhancing the disintegration efficiency of the subsequent ultrasonic pretreatment. By applying regression analysis, the disintegration degree (DD) was fitted based on the actual value to a second order polynomial equation: Y =−172.44+29.82X 1 +5.30×10−3 X 2 −7.53×10−5 X 1 X 2 −1.10X 1 2 −1.043×10−7 X 2 2, where X 1, X 2, and Y are pH, specific energy input (kJ/kg TS), and DD, respectively. In a 2D contour plot describing the tendency of DD with respect to pH and specific energy input, it was clear that DD increased as pH increased, but it seemed that DD decreased when the specific energy input exceeded about 20,000kJ/kg TS. This phenomenon tells us that there exists a certain point where additional energy input is ineffective in achieving further disintegration. A synergetic disintegration effect was also found in the combined pretreatment, with lower specific energy input in ultrasonic pretreatment yielding higher synergetic effect. Finally, in order to see the combined pretreatment effect in continuous operation, the sludge pretreated with low intensity alkaline (pH 9)/ultrasonic (7500kJ/kg TS) treatment was fed to a 3 L of anaerobic sequencing batch reactor after 70 days of control operation. CH4 production yield significantly increased from 81.9±4.5mL CH4/g CODadded to 127.3±5.0mL CH4/g CODadded by pretreatment, and this enhanced performance was closely related to the solubilization increase of the sludge by pretreatment. However, enhanced anaerobic digestion resulted in 20% higher soluble N concentration in the reactor, which would be an additional burden in the subsequent nitrogen removal system. [Copyright &y& Elsevier]

Abstract: Two novel two-step pretreatments for enzymatic hydrolysis of rice hull (RH) were proposed to lower the severity requirement of fungal pretreatment time. They consisted of a mild physical or chemical step (ultrasonic and H2O2) and a subsequent biological treatment (Pleurotus ostreatus). The combined pretreatments led to significant increases of the lignin degradation than those of one step pretreatments. After enzymatic hydrolysis of the pretreated RH, the net yields of total soluble sugar (TS) and glucose (G) increased greatly. The combined pretreatment of H2O2 (2%, 48h) and P. ostreatus (18d) was more effective than sole pretreatment of P. ostreatus for 60d. It could remarkably shorten the residence time and reduce the losses of carbohydrates. Ligninase analyses and SEM observations indicated that the enhancing of the efficiency could possibly attribute to the structure disruption of the RH during the first pretreatment step. So, the combined pretreatment could be recommended to different lignocellulosic materials for enzyme based conversions. [Copyright &y& Elsevier]

Biohydrogen production from sewage sludge through anaerobic fermentation is a cleaner production process. However, the complex sludge structure, especially the outer-layer extracellular polymeric substances, significantly restricts the utilization of available organics in the inner-layer sludge cells for hydrogen production. In view of this, this study firstly adopted a cation-binding agent, sodium citrate (SC), to strip the outer-layer extracellular polymeric substances from the sludge floc, followed by thermal disintegration of microbial cells, which aimed to promote the disintegration performance and biohydrogen productivity. The results showed that the sludge with the combined SC-Thermal pretreatment (0.3 g SC/g-SS + 121 °C for 30 min) achieved the maximum biohydrogen yield of 28.6 mL/g-VS added , which was 346.9%, 73.3% and 148.7% higher that of the control, sole SC pretreated system, and sole thermal pretreated system, respectively. The mechanism study revealed that the combined SC-Thermal pretreatment synergistically disintegrated the sludge floc and promoted the soluble organics content by 107.5 times. Meanwhile, the combined pretreatment also shortened the lag time of hydrogen formation, accelerated the hydrolysis, and improved the organics utilization, thus contributing to the improvement of hydrogen yield. The bacterial community analysis demonstrated that the combined pretreatment promoted the abundances of hydrolytic genera (Bacteroides , Proteocatella and Proteiniclasticum) and hydrogen-producing genera (Clostridium sensu stricto , Citrobacter , Paraclostridium and Escherichia-Shigella), which might be fundamentally responsible for the improvement of biohydrogen productivity. [Display omitted] • Combined sodium citrate-thermal pretreatment evidently disrupted the sludge flocs • Pretreatment promoted the SCOD content by 107.5 times and accelerated the hydrolysis • Pretreatment improved the bioH 2 yield by 346.9% and shortened the lag phase • Pretreated sludge exhibited the mixed acid type fermentation • Pretreatment improved the abundance of hydrogen-producing bacteria in the reactor [ABSTRACT FROM AUTHOR]

• Pretreatment is an essential step for the breakdown of lignocellulosic biomass. • Combining pretreatment helps to lower the severity of the drawbacks of a single step. • Biological-chemical/physicochemical combined pretreatment strategies were reviewed. • The order of pretreatment in the combined studies affects the overall efficiency. Sustainable biorefinery concepts based on lignocellulosic biomass are gaining worldwide research interest because of their inexpensiveness and abundance. The recalcitrance of lignocellulosic biomass poses a major hindrance to enhance biofuel production. Therefore, a pretreatment step is critical to prepare the substrates for the downstream process. Combining pretreatment steps help to lower the severity of the drawbacks of a single pretreatment step. This paper systematically reviews the combined biological and chemical/physicochemical pretreatment based on fiber degradation and sugar yield. An energy-efficient biological pretreatment method combined with a chemical pretreatment that accelerates the pretreatment times has been seen to be efficient for fiber degradation and sugar yields. However, fungal species, culture conditions, biomass type, the severity of chemical pretreatment and the order of sequential pretreatment influences the relative component contents and sugar yield. Even the same biomass from different sources undergoing similar pretreatment conditions could result in a varying amount of digestibility. [ABSTRACT FROM AUTHOR]

• Sodium citrate-ultrasonic pretreatment was applied to enhance bioH 2 yield of sludge. • Pretreatment obviously disrupted the sludge flocs and promoted soluble COD. • Pretreatment improved the H 2 yield by 604.2% and shortened the lag phase. • Energy conversion efficiency increased from 7.4% to 32.8% through pretreatment. • Pretreatment promoted the abundance of H 2 -producing bacteria in the fermenter. Proper pretreatment of waste activated sludge is commonly needed before biohydrogen fermentation due to its complex floc structure. Considering that the outer-layer extracellular polymeric substances (EPS) could restrict the disintegration of inner-layer microbial cells during the pretreatment of sludge, this study firstly applied sodium citrate pretreatment (0.3 g/g-TSS) for removing EPS from sludge flocs, followed by ultrasonic pretreatment (2 W/mL, 15 min), which aimed to enhance the disintegration efficiency. The subsequent hydrogen fermentation performance was tested in batch mode at 37 °C and initial pH 7.0. Results showed that the combined sodium citrate-ultrasonic pretreatment significantly disrupted the sludge floc structure and promoted soluble COD concentration by 157.5 times, which synergistically enhanced the biohydrogen fermentation performance. The maximum hydrogen yield of 38.8 mL/g-VS added was achieved with the combined pretreatment, which was 604.2%, 155.1%, and 92.6% higher compared to the control, individual ultrasonic pretreatment, and individual sodium citrate pretreatment, respectively. Correspondingly, the energy conversion efficiency increased from 7.4% to 32.8% through the combined pretreatment. The combined pretreatment also enhanced the organics utilization, induced a more efficient fermentative pathway, and shortened the hydrogen-generating lag phase. More enrichment of hydrogen-producing bacteria, especially the genera Clostridium sensu stricto and Paraclostridium , was responsible for the synergistic enhancement in hydrogen yield and energy conversion efficiency. The present work puts forward an effective and eco-friendly pretreatment approach for enhancing bioenergy recovery from waste activated sludge. [ABSTRACT FROM AUTHOR]

• In-situ lignin modification improved enzymatic hydrolysis of acid-pretreated larch. • Lignin modification with 2-naphthol suppressed lignin repolymerization. • Lignin modification with PEGDE lowered the enzyme non-productive binding on lignins. • 2-Naphthol and PEGDE modification synergistically facilitated enzymatic hydrolysis. To overcome the recalcitrance of residual lignins in acid-pretreated larch (AL), a combined acid and alkali pretreatment with in-situ lignin modification was developed in this study. The results showed that introducing in-situ lignin modification with 2-naphthol to acid pretreatment (160 and 180 oC) improved the enzymatic digestibility of AL by 12.7-14.4%, through suppressing lignin repolymerization. The obviously higher improvement (57.8-88.3%) was achieved by applying alkali post-treatment (90 oC) with poly (ethylene glycol) diglycidyl ether (PEGDE) on AL, mainly due to the function of in-situ lignin modification with PEGDE for reducing enzyme non-productive binding on lignins. More importantly, the synergism of 2-naphthol and PEGDE modification facilitated the enzymatic hydrolysis of AL more significantly. Its beneficial mechanism was explored by investigating the effects of in-situ lignin modification on lignin properties, including extraction yields, functional groups, and enzyme affinity of lignins. Results will give insights into establishing an efficient pretreatment of softwood biomass. [ABSTRACT FROM AUTHOR]

• The individual or dual effect of ultrasound/ozone pretreatment on microalgae were studied. • Ultrasound, released proteins to the aqueous phase and increased lipids viability. • Ozone, induced carbohydrates and phosphorus depolymerization. • Dual ultrasound and ozone intensified microalgae biocompounds fractionation. • Dual pretreatment reduced 95 % the solvent waste and 80 % the extraction time. This study applies individual and combined application of ultrasound and ozone pretreatments for the tandem recovery of microalgae biocompounds (lipids, proteins, and, carbohydrates) and phosphorus from Scenedesmus obliquus cultivated in wastewater. Results of individual application showed that ultrasound released protein to the aqueous phase (99 ± 3 %), and increased microalgal lipid viability from 11 to 90 ± 2 %. Whilst ozone pretreatment induced carbohydrate release to the aqueous phase 28 ± 1 %. Combined ultrasound and ozone pretreatment were studied in sequence mode. Ultrasound was first applied to release proteins and expose lipids, followed by ozone to induce carbohydrates and phosphorus release. The maximum yields of recovered lipids, proteins, carbohydrates and phosphorus by the combined pretreatment were 89 ± 1 %, 91 ± 8 %, 63 ± 1 %, and 75 ± 1 % respectively. In the dual pretreatment best experimental parameters applied for ultrasound were: biomass concentration of 25 g/L and applied energy of 200 kW h/kg dry biomass. Ozone pretreatment used 27 mg O 3 /L, contact time 25 min and pH of 11. The combined pretreatment intensified microalgae fractionation achieving high biocompounds and phosphorus recovery yields; reducing solvent waste by 95 % and extraction time by 90 %, in comparison to biocompounds extraction without pretreatment. [ABSTRACT FROM AUTHOR]

• The first report on bioethanol production from sesame plant residues. • Three combined pretreatments including physical, microbial, and chemical were done. • Kinetic modeling of pretreatment and bioethanol production process was done. • The maximum bioethanol yield was 1.90 g·L−1 in the finest (400 µm) particle size. This study explored the potential of sesame (Sesamum indicum L.) plant residue (SPR) for bioethanol production. Three particle sizes, including 400, 850 and 1300 µm of SPR, were subjected to microbial degradation by Phanerochaete chrysosporium followed by 1% H 2 SO 4 pretreatments. FTIR and HPLC analyses showed that the combined pretreatment which begins with microbial followed up by acid degraded SPR in the finest particle size (400 µm) resulted in the maximum contents of reducing sugars (370.23 mg·g−1). Kinetics studies of the pretreatment process also confirmed the maximized rate of hemicellulose and lignin reduction with reducing sugars production. The logistic model had better fitness as compared to the modified Gompertz model to predict bioethanol production. SPR gave a maximum of 1.90 g·L−1 bioethanol yield after 60 h of fermentation using Saccharomyces cerevisiae. This study is the first report on bioethanol production from SPR, which proposed its suitability for sustainable energy production. [ABSTRACT FROM AUTHOR]

• A combined pretreatment was established based on acetic acid and alkali treatment. • The combined pretreatment coproduced XOS and fermentable sugars from poplar sawdust. • Cellulose accessibility was significantly increased during the combined pretreatment. • In-situ lignin modification with PEGDE reduced the enzyme non-productive binding. A novel combined pretreatment process of poplar sawdust was established in this study based on the sequential acetic acid and alkali treatment with poly (ethylene glycol) diglycidyl ether (PEGDE). Effects of each treatment step on chemical composition, cellulose accessibility, and enzymatic digestibility of poplar sawdust was investigated. Acetic acid pretreatment remarkably increased cellulose accessibility while also producing a relatively high quantity of xylooligosaccharides (XOS) (37.6% of raw xylan). However, enzymatic digestibility remained low (28.3%) despite hemicellulose disruption. Post alkali treatment was next applied, leading to improvement on cellulose accessibility and enzymatic hydrolysis. Enzymatic hydrolysis was improved more significantly by successive alkali treatment with PEGDE. Its potential mechanisms attributable to enzymatic hydrolysis improvement were explored by revealing the changes to lignin properties. This work successfully demonstrated that recalcitrant waste woody biomass can be biorefined into both high-value XOS as well as relatively high yield of fermentable sugars. [ABSTRACT FROM AUTHOR]