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The mechanism of sludge anaerobic fermentation to produce acid was described. The influencing factors of sludge anaerobic fermentation acid production were summarized, such as C/N, temperature, pH, sludge residence time and pollutants, and it was pointed out that the C/N ratio of sludge anaerobic fermentation system was 20 ~ 30,the temperature was 25 ~ 40 °C, the pH was 10, the sludge residence time was 5 ~ 10 d and the appropriate pollutant concentration was conducive to the accumulation of SC-FAs. The latest research progress of the anaerobic fermentation technology of sludge, co-fermentation and combined pretreatment, was reviewed. Both of the two technologies could significantly increase the yield of SCFAs. At last, the shortcomings of the current research were put forward, and the future research directions were prospected, in order to provide reference for maximizing the resources of sludge treatment and disposal and anaerobic digestion. [ABSTRACT FROM AUTHOR]

Lignocellulosic biomass is a low-cost and environmentally-friendly resource that can be used to produce biofuels such as bioethanol and biogas, which are the leading candidates for the partial substitution of fossil fuels. However, the main challenge of using lignocellulosic materials for biofuel production is the low accessibility to cellulose for hydrolysis of enzymes and microorganisms, which can be overcome by pretreatment. Biological and chemical pretreatments have their own disadvantages, which could be reduced by combining the two methods. In this article, we review biological–chemical combined pretreatment strategies for biogas and bioethanol production. The synergy of fungal/enzyme–NaOH pretreatment is the only biological–chemical combination studied for biogas production and has proven to be effective. The use of enzyme, which is relatively expensive, has the advantage of hydrolysis efficiency compared to fungi. Nonetheless, there is vast scope for research and development of other chemical–biological combinations for biogas production. With respect to ethanol production, fungal–organosolv combination is widely studied and can achieve a maximum of 82% theoretical yield. Order of pretreatment is also important, as fungi may reduce the accessibility of cellulose made available by prior chemical strategies and suppress lignin degradation. The biofuel yield of similarly pretreated biomass can vary depending on the downstream process. Therefore, new strategies, such as bioaugmentation and genetically engineered strains, could help to further intensify biofuel yields. [ABSTRACT FROM AUTHOR]

The bioconversion technique is one of the important methods for producing environmentally friendly bioenergy from lignocellulosic biomass. The objective of this study is to explore the effect of different mechanochemical combined pretreatments on the enzymatic hydrolysis of corn stalks at room temperature. In this study, corn stalk was used as biomass material, lower load of NaOH with mass fractions 0, 1%, 2%, and 3% was used in the groups of NaOH pretreatment alone, the dry NaOH/ball milling combined pretreatment and the wet NaOH/ball milling combined pretreatment, respectively. The following 72 h enzymatic hydrolysis experiments for different pretreated corn stalks were carried out by using the enzyme CellicCtec2 (Novozymes, Denmark). The particle size, crystallinity, surface micromorphology, lignocellulosic composition, and the functional group changes of the pretreated corn stalk samples were systematically characterized. The effects of the different NaOH/ball milling combined pretreatments on samples’ physicochemical properties on enzymatic hydrolysis yield and their correlations were further investigated and discussed in detail. The results showed that both dry and wet NaOH/ball milling combined pretreatment significantly improved the corn stalk glucose yield compared with NaOH pretreatment (P<0.01). And with the increase of NaOH mass fraction (from 1% to 3%), the glucose yield of corn stalk with dry and wet NaOH/ball milling combined pretreatment increased clear (P<0.01). When the mass fraction of NaOH was 3%, the glucose yield of the dry and wet NaOH/ball milling combined pretreatment reached 71.0% and 73.1%, respectively. The dry NaOH/ball milling combined pretreatment effectively reduced the particle size and crystallinity of the corn stalk, compared with the NaOH pretreatment. Once the NaOH mass fraction was 0, the particle size and crystallinity of the corn stalk treated by the dry NaOH/ball milling were the lowest, 15.8 μm and 25.9%, respectively. But, the particle size and crystallinity of the corn stalk pretreated by the wet NaOH/ball milling were higher than those of the dry NaOH/ball milling combined pretreated samples. The cellulose mass fraction of different combined pretreatment samples gradually increased, with the increase of NaOH mass fraction. There was no significant difference in the cellulose mass fraction between the two pretreatment samples under the same NaOH loading conditions. The cellulose mass fraction was up to 48.5% in the wet NaOH/ball milling combined with pretreated samples, when the NaOH mass fraction was 3%. The lignin mass fraction decreased significantly with the increase of NaOH mass fraction (P<0.01). The lignin mass fraction of corn stalk with the wet NaOH/ball milling combined pretreatment was lower than that of dry ones. Once the NaOH mass fraction was 3%, the lignin mass fraction of the wet NaOH/ball milling combined pretreatment was the lowest at 14.9%. Regardless of the dry and wet NaOH/ball milling combined pretreatment, the enzymatic glucose yields were significantly positively correlated with cellulose mass fraction and average particle size D50 (P<0.01), and significantly negatively correlated with lignin mass fraction (P<0.01). The dry NaOH/ball milling combined pretreatment significantly reduced the crystallinity of the corn stalk, thereby enhancing the yield of enzymatic hydrolysis of the corn stalk to a certain extent (P<0.05). This study provides data support to help further reveal the mechanism of biomass mechanochemical combined pretreatment behind. [ABSTRACT FROM AUTHOR]

Rice straw is an abundant lignocellulosic biomass used to produce biogas. However, its resistant structure hinders biogas production. In this study, three pretreatments, microwave, ammoniation, and microwave-assisted ammoniation (MAA), were evaluated for their use in improving biogas production from rice straw. After an 18-day digestion, methane production by rice straw pretreated with MAA was 281.56 mL/g (volatile solids of substrate), which was 25.43%, 7.96%, and 18.18% more than that produced following the control, microwave, and ammoniation pretreatments, respectively. These increases were mainly attributed to the change in the resistant structure of rice straw following the MAA pretreatment and a more stable anaerobic digestion system. The degradation rate for the volatile solids of the rice straw pretreated with MAA during anaerobic digestion was 71.20%, which was 4.71%, and 4.86% higher than the rates observed using microwave and ammoniation pretreatments, respectively. In addition, the MAA method had a T90 fermentation cycle of 6 days, which was 33.3%, 25.0%, and 33.3% shorter than those for the control, microwave, and ammoniation methods, respectively. This technology shows the potential to enhance biogas production from the anaerobic digestion of rice straw. [ABSTRACT FROM AUTHOR]

The effects of CH3COOH and Na2SO3 pretreatment on the structural properties and hydrolyzability of fast-growing Paulownia elongate were investigated. Acetic acid increased cellulose's crystallinity and hydrolyzability when combined with alkaline sodium sulfite and sodium hydroxide. The cellulose content increased by 21%, the lignin content decreased by 6%, and the product showed better enzymatic digestibility. With a cellulase dose of 30 FPU/g DM, after 72 h hydrolysis, the hydrolysis yields of glucose and xylose were 78% and 83%, respectively, which were 51% and 69% higher than those of untreated materials. When the enzyme dosage was 20 FPU/g DM, after 72 h hydrolysis, the hydrolysis yields of glucose and xylose were 74% and 79%, respectively. The high hydrolyzability, low enzyme loading, and high hydrolysis yield demonstrate the potential of the proposed system for producing platform sugars from fast-growing Paulownia elongate. [ABSTRACT FROM AUTHOR]

The presence of hemicellulose inhibits the enzymatic hydrolysis of lignocellulosic biomass. The purpose of this study is to investigate the effect of different hemicellulose fractions on the enzymatic hydrolysis and the way to eliminate the inhibiting effect caused by hemicellulose. Four kinds of hemicelluloses, namely, HXF, H15, H30, and H60, were first extracted from corn stover by ethanol fractional precipitation. The structures of hemicellulose samples were analyzed using Fourier transform infrared spectroscopy, 1H and 13C nuclear magnetic resonance, and high-performance ion chromatography. The results show that H30 has the strongest inhibition on the enzymatic hydrolysis of Avicel and corn stover, presenting inhibition ratio of 13.35% and 9.98%, respectively. The inhibition ratios of other hemicelluloses in Avicel and corn stover are 8–12% and 5–9%, respectively. However, the inhibiting effect caused by H30 is removed by adding hemicellulase, which even presents a 4.99% increase in the efficiency of enzymatic hydrolysis of corn stover. The corresponding glucose concentration reached 68.11 g/L. This research could help design effective processes to promote the enzymatic hydrolysis of lignocellulosic biomass. [ABSTRACT FROM AUTHOR]

[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]

Agricultural crops and forest residues are of valuable resources to produce biofuel due to anaerobic digestion. But, the recalcitrance nature of these lignocellulose residues limits its enzymatic degradation. Therefore, efficient pretreatments prior to anaerobic digestion are essential. Hydrothermal-chemical pretreatments using Phenol (Ph), Sodium Hydroxide (SH), and Phosphoric Acid (PA), and combined pretreatments included Ph+SH and Ph+PA as chemical pretreatments were used for spruce wood. The samples were put into the autoclave at 134ºC for 20 min. Acid hydrolysis, FTIR and SEM analyses were carried out. The results indicated that all pretreatments were effective lignin removal having the highest value for Ph (42.362%). Adding Ph to PA increased lignin removal from 1.580% to 6.112%. Mixing Ph to SH represented the same trend in changing structure of spruce wood as compared to individually SH. All results proposed that when Ph contributed in binary pretreatment with SH and PA, it could be more effective on the morphological changes of spruce wood. In general, Ph was more effective on changing the crystalline structure of spruce wood than the others. After that, Ph+SH was more effective compared to Ph+PA on structural changes. In comparison between alkali and acidic pretreatments, SH represented more structural change in spruce wood than PA one. To decreased toxicity of Ph, it is recommended to use the combination of Ph with SH as infectious pretreatment instead of individually Ph. Because, this increases the biodegradation power of SH while the toxicity of Ph decreases. The results are very important in biogas production systems. [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]

Corn stover (CS) is a promising feedstock for producing biomethane, that can replace diminishing fossil fuels. However, the recalcitrant structure of CS resulted in low degradability in anaerobic digestion (AD). Numerous studies investigated the pretreatment of CS before AD, but the insight mechanism of biomethanation enhancement is not fully revealed. Therefore, this study advanced low-temperature urea-hydrothermal pretreatment of CS, and the biomethane production, substance bioconversion, hydrolase activity, and metagenomic analysis were conducted to unravel the intrinsic mechanisms of pretreatment for the enhanced biomethanation. The results showed that the pretreatment improved 11.5% of the specific surface area of CS, providing 111.5% higher total volatile fatty acids and 19.9% higher reducing sugars than the control, potentially enriching more anaerobic microorganisms. As a result, the pretreated CS achieved 19.1% higher biomethane yield, 9.1% higher volatile solid removal rate, and 3 days shorter digestion time. The mass balance and microbial community succession analysis indicated that the pretreatment reinforced the biomethane conversion from carbohydrate, which was attributed to the rapid enrichment of hydrolytic acidification bacteria (g__unclassified_o__Bacteroidales) (33.2%) and mixotrophic archaea (Methanosarcina) (72.3%). Meanwhile, the activity of cellulase and xylanase was enhanced up to 23.7% and 66.7%. Metagenomic analysis revealed that the combined pretreatment of CS promoted methanogenesis by enhancing various CAZymes secretion (such as oligosaccharide-degrading enzymes), and functional genes expression of hydrolytic, acidification and acetate-methane pathways at days 1–5. The study indicated that the combined pretreatment could influence microbial composition and function by changing the physicochemical properties of the CS, thereby improving methanogenic performance. [Display omitted] • Effect of urea-hydrothermal pretreatment of corn stover was investigated on anaerobic digestion. • Microbial community succession rate was enhanced by the combined pretreatment. • The effect of pretreatment on the hydrolases activity and functional genes were examined. • AcEtate-methane pathway was largely activated by the combined pretreatment. [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]

In this study fungal pretreatment of willow sawdust (WSD) via the white rot fungi Leiotrametes menziesii and Abortiporus biennis was studied and the effect on fractionation of lignocellulosic biomass and biochemical methane potential (BMP), was evaluated. Scanning electron microscopy (SEM) and IR spectroscopy were used to investigate the changes in the structural characteristics of the pretreated WSD. Fungal pretreatment results revealed that A. biennis is more attractive, since it resulted in higher lignin degradation and lower holocellulose uptake. Samples of the 14th and 30th d of cultivation (i.e. the middle and the end of the pretreatment experiment) with both fungi were used for BMP tests and the effect of pretreatment duration was also evaluated. BMP increase by 31 and 43% was obtained due to the cultivation of WSD with A. biennis , for 14 and 30 d, respectively. In addition, combination of biological (after 30 d of cultivation) with alkaline (NaOH 20 g/100 gTS) pretreatment was performed, in order to assess the effect of the chemical agent on biologically pretreated WSD, in terms of lignocellulosic content and BMP. Combination of alkaline with fungal pretreatment led to high lignin degradation for both fungi, while the cellulose and hemicellulose removal efficiencies were higher for combined alkaline and L. menziesii pretreatment. The maximum BMP was observed for the combined alkaline and A. biennis pretreatment and was 12.5 and 50.1% higher than the respective alkaline and fungal pretreatment alone and 115% higher than the respective BMP of raw WSD. [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]

A combination of steam explosion (SE) and chemical pretreatments, such as acid sulfite (AS), alkali (AL), and alkaline sulfite (ALS), were evaluated using bamboo. Low pressure steam explosion at 1.25 MPa for 4 min was first applied to the bamboo. Then, the pretreated bamboo was delignified using three chemical pretreatments. Enzymatic hydrolysis was also compared among the pretreated bamboo samples. It was found that SE-ALS could be a potential method for bamboo pretreatment, which led to the reduction of lignin from 25.15% to 1.74% at 165 °C for 2 h in 5% (w/v) Na2SO3 and 0.7% (w/v) NaOH; however, little cellulose was solubilized during ALS pretreatment. A maximum glucose yield of 99.35% was achieved during the enzymatic hydrolysis process when combined with the SE-ALS pretreatment. The SE-ALS method resulted in a lower degree of lignin condensation and increased delignification compared to the SE-AS method. In addition, the SE-ALS pretreatment protected carbohydrates from degradation better than the SE-AL methods. [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]

Background Ensiling may act as a pretreatment of fresh grass biomass and increase the enzymatic conversion of structural carbohydrates to fermentable sugars. However, ensiling does not provide sufficient severity to be a standalone pretreatment method. Here, ensiling of grass is combined with hydrothermal treatment (HTT) with the aim of improving the enzymatic biomass convertibility and decrease the required temperature of the HTT. Results Grass silage (Festulolium Hykor) was hydrothermally treated at temperatures of 170, 180, and 190°C for 10 minutes. Relative to HTT treated dry grass, ensiling increased the solubilization of dry matter (DM) during HTT and gave increased glucan content, but lower lignin in the insoluble fiber fraction. Ensiling improved glucose yields in the enzymatic hydrolysis of the washed solid fiber fraction at the lower HTT temperatures. At 170°C glucose yield improved from 17 to 24 (w/w)% (45 to 57% cellulose convertibility), and at 180°C glucose yield improved from 22 to 29 (w/w)% (54 to 69% cellulose convertibility). Direct HTT of grass at 190°C gave the same high glucose yield as for grass silage (35 (w/w)% (77% cellulose convertibility)) and improved xylan yields (27% xylan convertibility). The effect of ensiling of grass prior to HTT improved the enzymatic conversion of cellulose for HTT at 170 and 180°C, but the increased glucose release did not make up for the loss of water soluble carbohydrates (WSC) during ensiling. Overall, sugar yields (C6 + C5) were similar for HTT of grass and grass silage at both 170 and 180°C, but at 190°C the overall sugar yield was better for HTT of dry grass. Conclusions This study unequivocally establishes that ensiling of grass as a biomass pretreatment method comes with a loss of WSC. The loss of WSC by ensiling is not necessarily compensated for by providing a lower temperature requirement for HTT for high enzymatic monosaccharide release. However, ensiling can be an advantageous storage method prior to grass processing. [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]

Low-pressure steam explosion (LPSE) combined with alkaline peroxide (AP) pretreatment was first employed to separate hemicellulose from Lespedeza stalks. The monosaccharide composition and molecular weight distribution of the obtained hemicellulose fractions were characterized in this study. The results show that the hemicellulose extracted from Lespedeza stalks consisted of xylose, glucose, galactose, and mannose, which was a mixture of arabinoxylans and xyloglucans or β-glucans. The yield of hemicellulose fractions after AP pretreatment ranged from 11.2% (2.5% hydrogen peroxide (H2O2), w/v for 12 h) to 12.2% (3.3% H2O2, w/v for 72 h). The molecular weight of hemicellulose decreased from 2,458 g/mol to 1,984 g/mol after AP pretreatment, indicating its degradation reaction. The structure of hemicellulose was analyzed by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance, and heteronuclear single quantum coherence. The AP pretreatment partially cleaved the backbone and the ether linkage between lignin and hemicelluloses. Also, branched-chain α-Darabinofuranosyl in which β-D-xylose substituted at the C-3 position (monosubstituted) was removed, illustrating a partial debranching reaction. Therefore, the combination of low-pressure steam explosion and alkaline peroxide pretreatment (LPSE-AP) is an effective pretreatment method to separate hemicellulose from Lespedeza stalk. [ABSTRACT FROM AUTHOR]

A combination of steam explosion (SE) and alkaline peroxide (AP) used to pretreat bamboo was investigated. Steam explosion at 224 °C for 4 min was applied to bamboo, and the pretreated bamboo was delignified by alkaline peroxide. Enzymatic hydrolysis was compared in the pretreated samples. Steam pretreatment led to remarkable hemicellulose solubilization (63.2%). Lignin solubilization (93.1%) was achieved by alkaline peroxide treatment of steam-pretreated bamboo at 80 °C for 1 h in 0.88% (v/v) H2O2, whereas only 33.4% of lignin was solubilized when using raw bamboo. Pretreatment methods resulted in a low degree of polymerization and increased hydrolysis of cellulose. A maximum glucose yield of 90.5% was achieved with a combined steam explosion and alkaline peroxide pretreatment. The surface structure of treated bamboo and the adsorption of enzyme on the substrate were characterized by X-ray photoelectron spectroscopy. Delignification decreased enzyme adsorption and increased enzymatic conversion. SEM analyses indicated that SE-AP pretreatment disrupted lignin networks and exposed crystalline cellulose in bamboo more effectively than SE or AP pretreatment alone. [ABSTRACT FROM AUTHOR]

Corn stover is the most abundant agricultural residue in China and a valuable reservoir for bioethanol production. In this study, we proposed a process for producing bioethanol from corn stover; the pretreatment prior to presaccharification, followed by simultaneous saccharification and fermentation (SSF) by using a flocculating Saccharomyces cerevisiae strain, was optimized. Pretreatment with acid–alkali combination (1% H2SO4, 150°C, 10 min, followed by 1% NaOH, 80°C, 60 min) resulted in efficient lignin removal and excellent recovery of xylose and glucose. A glucose recovery efficiency of 92.3% was obtained by enzymatic saccharification, when the pretreated solid load was 15%. SSF was carried out at 35°C for 36 hr after presaccharification at 50°C for 24 hr, and an ethanol yield of 88.2% was achieved at a solid load of 15% and an enzyme dosage of 15 FPU/g pretreated corn stover. [ABSTRACT FROM AUTHOR]

Background: Ensiling is a well-known method for preserving green biomasses through anaerobic production of organic acids by lactic acid bacteria. In this study, wheat straw is subjected to ensiling in combination with hydrothermal treatment as a combined pretreatment method, taking advantage of the produced organic acids. Results: Ensiling for 4 weeks was accomplished in a vacuum bag system after addition of an inoculum of Lactobacillus buchneri and 7% w/w xylose to wheat straw biomass at 35% final dry matter. Both glucan and xylan were preserved, and the DM loss after ensiling was less than 0.5%. When comparing hydrothermally treated wheat straw (170, 180 and 190°C) with hydrothermally treated ensiled wheat straw (same temperatures), several positive effects of ensiling were revealed. Glucan was up-concentrated in the solid fraction and the solubilisation of hemicellulose was significantly increased. Subsequent enzymatic hydrolysis of the solid fractions showed that ensiling significantly improved the effect of pretreatment, especially at the lower temperatures of 170 and 180°C. The overall glucose yields after pretreatments of ensiled wheat straw were higher than for non-ensiled wheat straw hydrothermally treated at 190°C, namely 74-81% of the theoretical maximum glucose in the raw material, which was ∼1.8 times better than the corresponding yields for the non-ensiled straw pretreated at 170 or 180°C. The highest overall conversion of combined glucose and xylose was achieved for ensiled wheat straw hydrothermally treated at 180°C, with overall glucose yield of 78% and overall conversion yield of xylose of 87%. Conclusions: Ensiling of wheat straw is shown to be an effective pre-step to hydrothermal treatment, and can give rise to a welcomed decrease of process temperature in hydrothermal treatments, thereby potentially having a positive effect on large scale pretreatment costs. [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]

Although biological pretreatment has the advantages of being environmentally friendly and having low-energy consumption, it usually requires a relatively long incubation time. In this study, a novel combined pretreatment with white-rot fungus and alkali at near room-temperature for saccharification of corn stalks was investigated to speed up the biological process. Biological pretreatment with Irpex lacteus or Echinodontium taxodii can improve enzymatic hydrolysis of corn stalk greatly, but the process requires a long time (60 days) to achieve a satisfactory sugar yield. The combination processes with the fungi were compared with the sole pretreatments. The results showed that the time of the biological process could be shortened to 15 days when the bio-treatment with I. lacteus was combined with alkali pretreatment. The efficiency of alkali pretreatment can be also enhanced significantly by biological treatment. 271.1mg/g of final glucose yield was obtained for the combination pretreatment, which was an improvement of 50.4% and 28.3% in comparison with the sole alkali pretreatment at the same and optimum reaction time, respectively. In conclusion, the combination of biological pretreatment with alkali processes not only speeded up the biological process, but also improved the sugar yield in comparison to the sole pretreatment and is favorable for the development of biological pretreatment. [ABSTRACT FROM AUTHOR]

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]

Various pretreatment methods have been combined and employed for maximizing the solubilization of waste-activated sludge (WAS). However, the question "by changing the series of applied combined pretreatments (CPs), can the solubilization efficiency of WAS be affected?" has never been addressed. In this study, firstly, thermal (T), alkaline (A), and ultrasonic (U) pretreatments were individually applied at broad strengths (T = 80–120 °C for 30 min, A = pH 9–12, and U = 5–60 min at 300 W). Then, pretreatment conditions that caused similar solubilization (13.0%) (120 °C, pH 11, and 30 min for T, A, and U, respectively), were adopted for CP with reverse sequences of T&A, U&A, and T&U. A similar disintegration degree was observed in U→A and A→U, while a meaningful difference was found in T&A and T&U: T→A (28.3%), A→T (42.9%), T→U (22.9%), and U→T (27.1%). The difference in pretreatment series also affected the characteristics of soluble matters, which was analyzed by excitation emission matrix and molecular weight distribution. Due to these differences, the highest methane yield of 68.8% (based on (chemical oxygen demand) CODinput) was achieved at A→T, compared to T→A (62.3%). Our results suggested a simple strategy for increasing solubilization, at the same expense of energy, which might be beneficial in the following treatment process, such as dewatering and transportation. [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]