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Sweet sorghum bagasse (SSB) provides a raw material rich in polysaccharides that can be converted into biofuel and other high-value-added bioproducts under the biorefinery concept. The aim of this study was to evaluate the effect of hydrothermal pretreatment on the availability of SSB fermentable sugars for bioethanol production, considering the energy balance of the process. For this, the biomass was subjected to one process, pre-saccharification simultaneous and fermentation (PSSF). Previously, the temperature, time, and particle size effect were determined, as well as the enzymatic load for the more significant release of monomeric sugars. It was observed that the increase in the pretreatment severity, defined by the severity factor [log(Ro)], resulted in a more significant release of sugar and energy consumption. In the PSSF, bioethanol production was 22.17 g/L, with a total energy consumption of 2.46 MJ/g of processed biomass, of which 79.14% was by concept of electricity.

Sodium-ion batteries (SIBs) are emerging as a viable alternative to lithium-ion batteries, reducing the reliance on scarce transition metals. Converting agricultural biomass into SIB anodes can remarkably enhance sustainability in both the agriculture and battery industries. However, the complex and costly synthesis and unsatisfactory electrochemical performance of biomass-derived hard carbon have hindered its further development. Herein, we employed a hydrothermally assisted carbonization process that converts switchgrass to battery-grade hard carbon capable of efficient Na-ion storage. The hydrothermal pretreatment effectively removed hemicellulose and impurities (e.g., lipids and ashes), creating thermally stable precursors suitable to produce hard carbon via carbonization. The elimination of hemicellulose and impurities contributes to a reduced surface area and lower oxygen content. With the modifications, the initial Coulombic efficiency (ICE) and cycling stability are improved concurrently. The optimized hard carbon showcased a high reversible specific capacity of 313.4 mAh g -1 at 100 mA g -1 , a commendable ICE of 84.8%, and excellent cycling stability with a capacity retention of 308.4 mAh g -1 after 100 cycles. In short, this research introduces a cost-effective method for producing anode materials for SIBs and highlights a sustainable pathway for biomass utilization, underscoring mutual benefits for the energy and agricultural sectors.

Chinese hickory shell, a by-product of the food industry, is still not utilized and urgent to develop sustainable technologies for its valorization. This research focuses on the systematical evaluation of degraded products and xylooligosaccharide production with high yield from the shell via hydrothermal process. The pretreatment was carried out in a bath pressurized reactor at 140–220 °C for 0.5–2 h. The results indicated that the pretreatment condition strongly affected the chemical structures and compositions of the liquid fraction. The maximum yield of XOS (55.3 wt%) with limitation of by-products formation was achieved at 160 °C for 2 h. High temperature (220 °C) and short time (0.5 h) contributed to hydrolysis of xylooligosaccharide with high DP to yield 37.5 wt% xylooligosaccharide with DP from 2 to 6. Xylooligosaccharide obtained mainly consisted of xylan with branches according to the HSQC NMR analysis. Overall, the production of XOS with a high yield from food waste will facilitate the valorization of food waste in the biorefinery industry. [ABSTRACT FROM AUTHOR]

Increasing application for lignin due to its unique aromatic structures has encouraged the development of pretreatment techniques for lignin separation and recovery. In this work, the integration of microwave-assisted hydrothermal pretreatment (MW-HTP) and alkaline post-treatment was proposed for separating lignin from poplar wood and revealing its structural characteristics. Results showed that the yields of the lignins fractionated via the integrated treatment based on MW-HTP were increased up to 52.6%, and their associated sugars contents were clearly decreased to 0.19–0.09%, as compared to the fractionated lignins without the microwave pretreatment (29.8% and 0.29%). Interestingly, the integrated treatment based on MW-HTP promoted the cracking of β - O -4 ethers in the lignin macromolecules of poplar wood, resulting in the raise of their phenol OH groups up to 2.36 mmol/g. Overall, the fulfillment of this work will be conducive to improve the fractionation and efficient utilization of lignin in biorefinery industry. • Integration of microwave-assisted hydrothermal and alkali treatments was proposed. • High-yield/purity lignin was obtained from poplar by the integrated treatment. • Structural features of the lignin fractions isolated from poplar were investigated. • The β - O -4 linkage of poplar lignin was cleaved during the integrated treatment. • Depolymerization of lignin was the major reaction during the integrated treatment. [ABSTRACT FROM AUTHOR]

In response to this drawback, the system performance of the heat and hydrothermal pretreatment in conjunction with zero-valent iron ( ZVI) to treat food waste in the thermophilic AD process was investigated. Heat pretreatment technology can significantly improve the effect of CH4 production. The result of ( 0. 46 ± 0. 06) U ( g VS · d) was obtained with the addition of ZVI, which is approximately 6% and 48% higher than the specific CH4 production of heat pretreatment and hydrothermal pretreatment of food waste, respectively. [ABSTRACT FROM AUTHOR]

Cow bedding is one of the dominant livestock wastes among agricultural waste in China. The bedding is a good raw material for anaerobic digestion (AD) and produces biogas of sustainable energy. To improve the AD performance of bedding, a two-step pretreatment of hydrothermal with ammonia (TPHA) was used at 100, 150, and 200 °C holding for 5–30 min. The results revealed that the highest volatile fatty acids concentration was 4720.1 mg/L at a TPHA of 200 °C for 5 min. The highest removal rates of cellulose and hemicellulose were 35.4% and 97.4% at a hydrothermal pretreatment (HP) of 100 °C for 30 min and 200 °C for 10 min, respectively. The highest methane yield of cow bedding was 169.1 mL/g VS using the TPHA at 150 °C for 10 min, which was 54.5% higher than that of the untreated group. Kinetic analysis showed that the modified Gompertz model was more suitable for TPHA for cow bedding. Therefore, TPHA could improve pretreatment characteristics and enhance the methane yield of cow bedding. [ABSTRACT FROM AUTHOR]

Being a lignocellulose-rich biomass, pineapple leaves waste (PL) could be a potential raw material for the production of biofuel, biochemicals, and other value-added products. The main aim of this study was to investigate the potential of pineapple leaves in the sustainable production of bioethanol via stepwise saccharification and fermentation. For this purpose, PL was subjected to hydrothermal pretreatment in a high-pressure reactor at 150 °C for 20 min without any catalyst, resulting in a maximum reducing sugar yield of 38.1 g/L in the liquid fraction after solid-liquid separation of the pretreated hydrolysate. Inhibitors (phenolics, furans) and oligomers production were also monitored during the pretreatment in the liquid fraction of pretreated PL. Enzymatic hydrolysis (EH) of both pretreated biomass slurry and cellulose-rich solid fraction maintained at a solid loading (dry basis) of 5% wt. was performed at 50 °C and 150 rpm using commercial cellulase at an enzyme dose of 10 FPU/gds. EH resulted in a glucose yield of 13.7 and 18.4 g/L from pretreated slurry and solid fractions, respectively. Fermentation of the sugar syrup obtained by EH of pretreated slurry and the solid fraction was performed at 30 °C for 72 h using Saccharomyces cerevisiae WLP300, resulting in significant ethanol production with more than 91% fermentation efficiency. This study reveals the potential of pineapple leaves waste for biorefinery application, and the role of inhibitors in the overall efficiency of the process when using whole biomass slurry as a substrate.

• 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]

Flotation is the common method for fine low rank coal upgrading while it is always inefficient due to the rough surface morphology and rich oxygen-containing functional groups. Hydrothermal pretreatment is widely used in dewatering for low rank coal. The physicochemical properties of coal surface considerably vary following the hydrothermal pretreatment. In this study, hydrothermal pretreatments at different temperatures for different times were applied to enhance lignite flotation. The hydrothermal pretreatment at 200 °C can significantly improve the flotation efficiency, while the temperature raised to 300 °C, the flotation recovery did not increase or even decrease. Scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Zeta potential, Brunauer–Emmett–Teller, and particle size distribution analysis were conducted to explain the underlying mechanism. The contents of pore and crack on coal surface considerably decreased and more fresh and smooth surfaces exposed following hydrothermal pretreatment, according to SEM analysis. The FTIR spectroscopy and XPS showed that the contents of oxygen-containing functional groups were decreased, while the hydrophobicity of lignite was increased following pretreatment. The decrease of Zeta potential also indicated the decrease of oxygen-containing functional groups and increase of hydrophobicity on coal surface. However, excessive temperature of hydrothermal pretreatment could increase the pore diameter and fine particle fraction, leading to a higher collector consumption and lower bubble–particle collision efficiency. Consequently, the flotation recovery was not improved or even decreased at the hydrothermal pretreatment temperature of 300 °C. [Display omitted] • Hydrothermal pretreatment was applied to enhance lignite flotation. • New fresh and smooth surface is exposed after proper hydrothermal pretreatment. • Surface hydrophobicity of lignite was enhanced after hydrothermal pretreatment. • Excessive hydrothermal pretreatment increase the pore diameter and fine size fractions. [ABSTRACT FROM AUTHOR]

Malaysia is the second largest palm oil producer and exporter globally. When crude palm oil is produced in both plantations and oil processing mills, a large amount of oil palm empty fruit bunch (OPEFB) is simultaneously produced as a waste product. Here, we describe the preparation of hydrolysate from OPEFB. After OPEFB was hydrothermally treated at 180–200 °C, the resultant liquid phase was subjected to high-performance liquid chromatography analysis, while the solid phase was used for acidic and enzymatic hydrolysis. Hemicellulose yield from the acid-treated solid phase decreased from 153 mg/g-OPEFB to 27.5 mg/g-OPEFB by increasing the hydrothermal treatment temperature from 180 to 200 °C. Glucose yield from the enzyme-treated solid phase obtained after hydrothermal treatment at 200 °C was the highest (234 ± 1.90 mg/g-OPEFB, 61.7% production efficiency). In contrast, xylose, mannose, galactose, and arabinose yields in the hydrolysate prepared from the solid phase hydrothermally treated at 200 °C were the lowest. Thus, we concluded that the optimum temperature for hydrothermal pretreatment was 200 °C, which was caused by the low hemicellulose yield. Based on these results, we have established an effective method for preparing OPEFB hydrolysates with high glucose content. [ABSTRACT FROM AUTHOR]

The restricted bioavailability of structurally complex carbohydrates for digestion has hitherto resulted in a low methane potential from rubber wood waste (RW). The effects of hydrothermal (HT) and ethanol organosolv (OS) pretreatments on the methane produced by anaerobic digestion of RW were investigated in the study reported. HT with temperatures above 190 °C significantly enhanced the anaerobic digestibility of RW mainly due to the degradation of hemicellulose. On the other hand, OS with 75% ethanol provided a potential methane gas yield of 165.1 L CH4/kg-VS, which was higher than that for HT at 210 and 230 °C by 39 and 7%, respectively. This was due to intensive delignification during OS pretreatment which led to a reduction in the non-productive adsorption of cellulolytic enzymes by lignin. A first-order kinetic model showed that OS had a higher hydrolysis rate (k = 0.073 ± 0.003 day−1) resulting in a higher methane yield when lower pretreatment temperatures were applied. The anaerobic degradation of the pretreated RW in this study was a result of simultaneous CH4 production through the symbiosis of anaerobic bacteria and methanogens using a combination of the aceticlastic and hydrogenothrophic bioconversion pathways. The recovery and use of the phenolic compounds remaining in the process water would be a way of adding value to this process and the feasibility of producing methane from RW should be further investigated. [ABSTRACT FROM AUTHOR]

To reduce the dependence on chemical inputs during biomass pretreatment, an integrated process on the basis of hydrothermal pretreatment followed by twin-screw extrusion for poplar was proposed. A comparative study was conducted on the pore structure, crystallinity, relative surface lignin concentration, cellulose accessibility, and enzymatic hydrolysis efficiency of the pretreated materials. Results suggested that the relative surface lignin concentration of fibers pretreated by hydrothermal treatment (conducted at 170 ℃ for 90 min) coupled with extrusion (HE) treatment was decreased compared to the sole hydrothermal (H) process, which had a positive impact on the subsequent enzymatic hydrolysis. Additionally, the HE process resulted in an increase in pore size by 34.4%, pore volume by 447.5%, and specific surface area by 93.5%, which enhanced the penetration and interaction of water into the fibers and thus increased cellulose accessibility by 143.2%. SEM and TEM observations revealed that fibers were separated and finely fibrillated, large amounts of fragmentary structure and cracks appeared on the fiber. In addition, the cell wall structure was deformed and damaged, when pretreated by HE process. Overall, this work showed that hydrothermal treatment followed by twin-screw extrusion was an achievable strategy for high fermentable sugar production of hardwood. [Display omitted] • Hydrothermal treatment coupled with twin-screw extrusion treatment was established. • Enzymatic saccharification was significantly improved by the integrated process. • Mechanism of the biomass fractionation in the integrated process was investigated. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hydrothermal pretreatment is a sustainable approach for the recovery of XOS. • XOS and GOS of 23.7 and 18.3% respectively was obtained under best conditions. • Conduritol B epoxide served as inhibitor for controlled hydrolysis to get cellobiose. • After controlled hydrolysis 174 mg of cellobiose was obtained per gram of biomass. Globally, the demands for sustainably sourced functional foods like prebiotic oligosaccharides have been constantly increasing. This study assessed the potential of pineapple leaves (PL) as lignocellulosic feedstock for sustainable production of cellulose and hemicellulose-derived oligosaccharides through its hydrothermal pretreatment (HT) followed by controlled enzymatic hydrolysis. PL was subjected to HT at 160, 175, and 190 °C for 20, 30, 60, and 90 min without any catalyst for xylooligosaccharide (XOS) production, whereas, the resulting solid content after HT was subjected to controlled enzymatic hydrolysis by commercial cellulase using conduritol B epoxide (0.5–5 mM) for glucooligosaccharides (GOS) production. HT at 160 °C for 60 min resulted in maximum yield of XOS and GOS at 23.7 and 18.3 %, respectively, in the liquid phase. Controlled enzymatic hydrolysis of HT treated (160 °C) PL solids for 20 and 30 min yielded ∼ 174 mg cellobiose/g dry biomass within 24 h, indicating overall high oligosaccharide production. [ABSTRACT FROM AUTHOR]

This study investigated the structural changes in oak and larch lignin-carbohydrate complexes (LCCs) during hydrothermal treatment and enzymatic hydrolysis. Hydrothermal treatment caused hemicellulose degradation (degradation rate at 170 ℃: larch 19.40%; oak, 22.26%). The LCC1 (glucan-lignin) fraction was the highest in the raw material of both biomasses. The LCC3 (xylan-lignin) and LCC2 (glucomannan-lignin) fractions were high in oak and larch, respectively; these fractions decreased as the hydrothermal treatment temperature increased (owing to hemicellulose degradation). Both biomasses had phenyl glycoside, benzyl ether (BE), and γ-ester (Est) linkages. The BE and Est linkages decreased as the hydrothermal treatment temperature increased; the Est linkages decrease was more significantly in oak than in larch. The efficiency of enzymatic hydrolysis was higher in oak than that in larch and increased as the hydrothermal treatment temperature increased. Furthermore, enzyme adsorption on the LCC1 sensor was higher in oak than in larch. The chemical compositions and LCC linkages of the biomass were changed by the hydrothermal treatment, which affected the efficiency of enzymatic hydrolysis. Moreover, the efficiency of enzymatic hydrolysis was higher for oak than for larch because of the difference hemicellulose and cellulose contents and LCC linkages. [Display omitted] • Hydrothermal treatment induces structural changes in lignin-carbohydrate complexes. • Hemicellulose is mainly degraded during hydrothermal treatment. • The Est linkages decrease was significantly in oak than in larch. • LCC linkages affecting enzymatic hydrolysis decrease during hydrothermal treatment. • Enzyme adsorptions on the LCC1 sensor was higher in oak than in larch. [ABSTRACT FROM AUTHOR]

Abstract Background Enzyme-aided valorization of lignocellulose represents a green and sustainable alternative to the traditional chemical industry. The recently discovered lytic polysaccharide monooxygenases (LPMOs) are important components of the state-of-the art enzyme cocktails for cellulose conversion. Yet, these monocopper enzymes are poorly characterized in terms of their kinetics, as exemplified by the growing evidence for that H2O2 may be a more efficient co-substrate for LPMOs than O2. LPMOs need external electron donors and one key question of relevance for bioprocess development is whether the required reducing power may be provided by the lignocellulosic substrate. Results Here, we show that the liquid fraction (LF) resulting from hydrothermal pretreatment of wheat straw supports LPMO activity on both chitin and cellulose. The initial, transient activity burst of the LPMO reaction was caused by the H2O2 present in the LF before addition of LPMO, while the steady-state rate of LPMO reaction was limited by the LPMO-independent production of H2O2 in the LF. H2O2 is an intermediate of LF oxidation as evidenced by a slow H2O2 accumulation in LF, despite high H2O2 production rates. This H2O2 scavenging ability of LF is important since high concentrations of H2O2 may lead to irreversible inactivation of LPMOs. Conclusions Our results support the growing understanding that fine-tuned control over the rates of H2O2 production and consumption in different, enzymatic and non-enzymatic reactions is essential for harnessing the full catalytic potential of LPMOs in lignocellulose valorization.

The organic fraction of municipal solid waste (OFMSW) has a high potential for converting to ethanol. Hydrothermal pretreatment was conducted for the solubilization of the starch fraction as well as pretreatment of the lignocellulosic fraction. The treatment liquor, which was rich in starch, was evaluated for ethanol production through simultaneous saccharification and fermentation (SSF) process using Saccharomyces cerevisiae. Solid phase was subjected to a solid-state simultaneous saccharification and fermentation (SSSF) process to obtain high titer of ethanol, leading to several advantages, e.g., lower energy and water consumption as well as lower wastewater effluent. Hydrothermal pretreatment of OFMSW at 160 °C and 20% (w/w) solid loading for 30 min resulted in a liquor containing 124 g/L soluble starch. Both liquor and solid fractions were then subjected to ethanol production and 81 g/L ethanol was obtained.

Abstract Background The lignocellulosic biomass feedstocks such as empty fruit bunches (EFBs) prove to be potential renewable resources owing to their abundance, low prices, and high carbohydrate contents. Generally, the conversion of lignocellulosic biomass into chemicals, fuels, and materials mainly includes pretreatment, enzymatic hydrolysis, fermentation, and recovery of final products. To increase the economic viability of such processes, the cost of cellulase production and enzymatic hydrolysis should be reduced. For this, recycling cellulase can be considered for reducing the saccharification cost of lignocellulose. In this study, cellulase recycling for high-solids enzymatic hydrolysis (i.e., 20%) was evaluated in saccharification of hydrothermally-pretreated EFBs. Results High-solids (20%) enzymatic hydrolysis of hydrothermally-pretreated empty fruit bunches with 40 FPU of Cellic CTec3/g glucan was carried out for cellulase recycling. In the second round of hydrolysis using a recycled enzyme, only 19.3% of glucose yield was obtained. The most important limiting factors for cellulase recycling of this study were identified as the enzyme inhibition by glucose, the loss of enzyme activities, and the non-productive binding of enzymes to insoluble biomass solids. To overcome these limitations, PEG was added prior to the first-round hydrolysis to reduce non-productive enzyme binding, glucose was removed from the enzyme fraction to be reused in the second-round hydrolysis, and EFB solids from the first-round hydrolysis were used in the second-round hydrolysis. These three additional measures with cellulase recycling resulted in a 3.5 times higher glucose yield (i.e., 68.0%) at the second round than that of the control, the second-round hydrolysis with cellulase recycling but without these measures. Conclusions Because of the high obstacles found in this study in achieving high saccharification yields in the high-solids saccharification of high-lignin lignocellulose with cellulase recycling, effective measures for improving enzymatic saccharification yields need to be accompanied with cellulase recycling.

The development of green technologies and bioprocesses such as solid-state fermentation (SSF) is important for the processing of macroalgae biomass and to reduce the negative effect of Sargassum spp. on marine ecosystems, as well as the production of compounds with high added value such as fungal proteins. In the present study, Sargassum spp. biomass was subjected to hydrothermal pretreatments at different operating temperatures (150, 170, and 190 °C) and pressures (3.75, 6.91, and 11.54 bar) for 50 min, obtaining a glucan-rich substrate (17.99, 23.86, and 25.38 g/100 g d.w., respectively). The results indicate that Sargassum pretreated at a pretreatment temperature of 170 °C was suitable for fungal growth. SSF was performed in packed-bed bioreactors, obtaining the highest protein content at 96 h (6.6%) and the lowest content at 72 h (4.6%). In contrast, it was observed that the production of fungal proteins is related to the concentration of sugars. Furthermore, fermentation results in a reduction in antinutritional elements, such as heavy metals (As, Cd, Pb, Hg, and Sn), and there is a decrease in ash content during fermentation kinetics. Finally, this work shows that Aspergillus oryzae can assimilate nutrients found in the pretreated Sargassum spp. to produce fungal proteins as a strategy for the food industry.

Abstract Background Ensiling cannot be utilized as a stand-alone pretreatment for sugar-based biorefinery processes but, in combination with hydrothermal processing, it can enhance pretreatment while ensuring a stable long-term storage option for abundant but moist biomass. The effectiveness of combining ensiling with hydrothermal pretreatment depends on biomass nature, pretreatment, and silage conditions. Results In the present study, the efficiency of the combined pretreatment was assessed by enzymatic hydrolysis and ethanol fermentation, and it was demonstrated that ensiling of sugarcane bagasse produces organic acids that can partly degrade biomass structure when in combination with hydrothermal treatment, with the consequent improvement of the enzymatic hydrolysis of cellulose and of the overall 2G bioethanol process efficiency. The optimal pretreatment conditions found in this study were those using ensiling and/or hydrothermal pretreatment at 190 °C for 10 min as this yielded the highest overall glucose recovery yield and ethanol yield from the raw material (0.28–0.30 g/g and 0.14 g/g, respectively). Conclusion Ensiling prior to hydrothermal pretreatment offers a controlled solution for wet storage and long-term preservation for sugarcane bagasse, thus avoiding the need for drying. This preservation method combined with long-term storage practice can be an attractive option for integrated 1G/2G bioethanol plants, as it does not require large capital investments or energy inputs and leads to comparable or higher overall sugar recovery and ethanol yields.

Cassava peel is a by-product produced at large amounts in starch-based agro industries and could be a major feedstock for bioethanol in most of the Asian countries. In this work, we aimed to evaluate two fermentation strategies for bioethanol production from alkali-assisted hydrothermal pretreated cassava peel by thermotolerant Kluyveromyces marxianus MTCC 4139 strain. Initially, milled cassava peel was subjected to alkali-assisted hydrothermal pretreatment at different autoclaving temperatures (110°C − 130°C) and residence times (15 − 30 min) in the presence of different NaOH concentrations (0.25%−1.0% w/v NaOH). On subsequent enzymatic hydrolysis of pretreated cassava peel (1% NaOH at 120°C for 30 min) with different optimal enzyme loadings (α-amylase, glucoamylase and cellulase) showed maximum 670.58 ± 10.13 mg/g reducing sugar yield with 81.25% ± 3.20% saccharification efficiency. Furthermore, SHF (separate hydrolysis and fermentation) and SSF (simultaneous saccharification and fermentation) of cassava hydrolyzates were studied for improved ethanol yield and fermentation efficiencies. SSF of hydrothermal pretreated cassava hydrolyzate with K. marxianus strain showed higher ethanol yield (0.44 g/g) with 86.11% fermentation efficiency as compared to SHF process (0.41 g/g; 80.24% fermentation efficiency). [ABSTRACT FROM AUTHOR]

• Biodegradation performance of PLA plastic at both AD conditions were investigated. • Low hydrolysis rate was identified as the limiting step of PLA degradation in AD. • HTT effectively enhanced methane yields of PLA by 1.2–15.3 times. • Hydrolysis kinetic of PLA plastic was improved from 0.001 to 0.004–0.111 day−1. • Cleavage of ester linkage was the mechanism of HTT of PLA plastic. Polylactic acid (PLA) plastic is becoming a popular alternative to traditional petroleum-based plastics, but the biodegradability in engineered biological system is still a matter of concern. In this study, the biodegradability of PLA plastic at mesophilic and thermophilic AD were investigated, and a hydrothermal pretreatment was proposed to enhance the hydrolysis of PLA plastic and subsequent biomethanization. For raw PLA plastic, the biodegradation results indicated that PLA was hardly biodegraded at mesophilic conditions (only 50.5 ± 0.5 mL/g VS after 146 days). Although it was converted into biogas at thermophilic conditions after long incubation period (442.6 ± 1.1 mL/g VS), the long digestion time (T 90 95.8 days) was destined to be infeasible for practical application. In contrast, hydrothermal pretreatment significantly enhanced the hydrolysis rates of PLA plastic in AD process from 0.001 day-1 for raw PLA plastic to 0.004–0.111 day−1. By balancing biogas production efficiency, energy and reagent cost, the conditions of 200 °C, 10 min and no alkali addition were recommended for hydrothermal pretreatment of waste PLA plastic in practice. At the optimized hydrothermal pretreatment conditions, 460.1 ± 25.0 mL/g VS was achieved in less than 30 days, which was comparable for AD of food waste (FW). Furthermore, LC-QEMS analysis proved that cleavages of ester bonds in PLA and its reaction with water molecule was the mechanism of triggering the hydrothermally decomposition of PLA. These results suggested the PLA-plastic waste co-mingled with OFMSW could be efficiently biomethanized into biogas by involving a mild hydrothermal pretreatment in practical application. [ABSTRACT FROM AUTHOR]

[Display omitted] Fast pyrolysis of the mixed plastics (PE: PP: PS: PVC = 0.5: 0.3: 0.15: 0.05) with and without hydrothermal dechlorination pretreatment were investigated in a fixed bed reactor to determine the effects of pyrolysis parameters (temperature, carrier gas flow rate and particle size) on the distribution and the quality of the products. The results showed that high pyrolysis temperature, high carrier gas flow rate and small particle size promoted the migration of organic chlorine in condensable products to inorganic chlorine in gas products. And the optimal conditions for fast pyrolysis of mixed plastics to produce oil were the pyrolysis temperature of 500 °C, carrier gas flow rate of 40 ml/min and particle size of 0.1–0.15 mm with the maximum oil yield of 67.88 wt%. Hydrothermal pretreatment of mixed plastics has shown an excellent dechlorination efficiency of 99.9 %. Furthermore, the total yield of oil and wax was increased by 7.06 wt%, meanwhile the content of C 5 -C 9 components in the pyrolysis oil showed an upward trend when compared with fast pyrolysis without pretreatment. Besides, the concentration of methane achieved 50.68 % due to the possible weakening effect of hydrothermal pretreatment on C C bond energy of β-position. [ABSTRACT FROM AUTHOR]

Summary: The objective of this study is to explore the feasibility of sequential hydrothermal and alkaline pretreatment in improving enzymatic hydrolysis and sugar production of coconut pulp residue for bioethanol production. Hydrothermal pretreatment with the different heating duration of 20, 40, 60 minutes yielded 32.27, 27.51, and 26.72 g/L of total sugar, respectively. After posttreatment with 1%, 2%, and 3% alkaline treatment, the further increment of almost 90% on sugar production was observed. Compared to the single pretreatment, the combination of hydrothermal and alkaline pretreatment significantly affected the enzymatic hydrolysis. The optimum condition for efficient hydrolysis was 40 minutes hydrothermal pretreatment, followed by 1% NaOH posttreatment. At these conditions, the total and reducing sugar was 257.14 ± 0.92 and 102.86 ± 0.82 g/L and the maximum ethanol achieved was 27.19 g/L on the 48 hours of fermentation with efficiency and ethanol productivity of 51.83% and 0.57 g/L/h, respectively. [ABSTRACT FROM AUTHOR]

Background: Cocksfoot grass (Dactylis glomerata L.) with high biomass yield and rich cellulose can be used to produce bioethanol as fuel additive. In view of this, ultrasonic and hydrothermal pretreatments followed by successive alkali extractions were assembled into an integrated biorefinery process applied on cocksfoot grass to improve its enzymatic hydrolysis. In this work, the effects of ultrasonic and hydrothermal pretreatments followed by sequential alkali extractions on the enzymatic hydrolysis of cocksfoot grass were investigated. In addition, since large amount of hemicelluloses were released during the hydrothermal pretreatment and alkali extraction process, the yields, structural characteristics and differentials of water- and alkali-soluble hemicellulosic fractions isolated from different treatments were also comparatively explored. Results: The integrated treatment significantly removed amorphous hemicelluloses and lignin, resulting in increased crystallinity of the treated residues. A maximum saccharification rate of 95.1% was obtained from the cellulose-rich substrate after the integrated treatment. In addition, the considerable hemicelluloses (31.4% water-soluble hemicelluloses and 53.4% alkali-soluble hemicelluloses) were isolated during the integrated treatment. The released water-soluble hemicellulosic fractions were found to be more branched as compared with the alkali-soluble hemicellulosic fractions and all hemicellulosic fractions were mixed polysaccharides mainly composed of branched xylans and β-glucans. Conclusion: The combination of ultrasonic and hydrothermal pretreatments followed by successive alkali extractions can dramatically increase the enzymatic saccharification rate of the substrates and produce considerable amounts of hemicelluloses. Detailed information about the enzymatic hydrolysis rates of the treated substrates and the structural characteristics of the co-produced hemicelluloses will help the synergistic utilization of cellulose and hemicellulose in cocksfoot grass. [ABSTRACT FROM AUTHOR]

• Oligogalacturonic acids were prepared by hydrothermal and enzymatic coupling. • Hydrothermal pretreatment had a positive effect on enzymatic kinetics. • The highest yield of oligogalacturonic acids could reach 75.3 %. • The selectivity of endo-polygalacturonase to oligogalacturonic acids was up to 84.8 %. Di-galacturonic acid (Di-GalA) and tri-galacturonic acid (tri-GalA) are emerging as new prebiotics. A novel biorefining strategy was established to prepare di-GalA and tri-GalA (oligogalacturonic acids) from commercial pectin, which utilized a two-stage process consisting of a hydrothermal pretreatment of low-esterification pectin (LP) followed by enzymatic hydrolysis with endo-polygalacturonase. Hydrothermal pretreatment at 140 °C for 35 min significantly decreased molecular weight, esterification degree and viscosity of LP. The pretreatment process was found to greatly enhance subsequent enzymatic hydrolysis by increasing the accessibility of substrate to enzyme and weakening the steric hindrance effect of enzymatic hydrolysis. The oligogalacturonic acids yield of 75.3 % and 84.8 % of the selectivity of endo-polygalacturonase to oligogalacturonic acids after enzymatic hydrolysis of hydrothermal pretreated LP at enzyme loading of 10 U/g pectin for 24 h were obtained. [ABSTRACT FROM AUTHOR]

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A two-step process using colloid milling (CM) and hot water (HW) treatment was evaluated for its ability to improve xylose recovery and the enzymatic digestibility of oak wood. In the first step, CM pretreatment was applied at a milling (feeding) speed of 100 mL/min with four different milling times (3, 6, 9, and 12 h), and the enzymatic digestibility and physical properties of each substrate were measured. In the second-step, the HW pretreatment was applied to enhance the enzymatic digestibility and xylan recovery at various reaction severities (Log R0) from 2.07 to 4.43 using 12 h colloid-milled (CM-treated) oak wood. Compared with untreated oak wood, CM not only significantly disrupted the structure of oak wood but also increased its Brunauer–Emmett–Teller surface area (42-fold) and pore volume (28-fold). The crystallinity of two-step-treated oak wood was decreased to 34.8, while the enzymatic digestibility of 12 h CM-treated oak wood was increased to 58.1% at enzyme loading of 30 filter paper units (FPU)/g glucan for 96 h. After HW treatment of CM-treated oak wood at Log R0 = 3.83, 80.7% of xylan recovery yield and 91.1% of enzymatic digestibility (with 15 FPU/g glucan at 96 h) was obtained, which was 84.2% higher than the enzymatic digestibility of untreated oak wood (6.9%).

Lignocellulosic plant material implies an untouched source of fermentable sugars for significant ethanol produc- tion. Pearl millet is potentially a viable feedstock for bioethanol production. The efficiency of Ortho-phosphoric acid, alkaline hydrogen peroxide, lime, and hydrothermal pretreatment as a potential chemical pretreatment on pearl millet was investigated in the present study. Based on the experimental results a mathematical model was developed for each pretreatment. Among the different pretreatment acid pretreated biomass showed highest sugar yield of 41.8 g /100g of biomass and inhibitor yield of 4.02 %. The raw biomass showed (34.76 %) the lowest crystallinity index (CrI) because it has a higher content of hemicellulose and lignin, which are amorphous in nature. The specific surface area of acid pretreated biomass increased significantly and the CrI of the pretreated biomass apparently increased (75.79 %) after the pretreatment. The main aim of pretreatment is to separate the hemicel- lulose and lignin for maximum recovery of fermentable sugars. Pretreated biomass was characterised by scanning electron microscope SEM and X-ray diffraction. [ABSTRACT FROM AUTHOR]

Abstract Background Plants and in particular grasses benefit from a high uptake of silicon (Si) which improves their growth and productivity by alleviating adverse effects of biotic and abiotic stress. However, the silicon present in plant tissues may have a negative impact on the processing and degradation of lignocellulosic biomass. Solutions to reduce the silicon content either by biomass engineering or development of downstream separation methods are therefore targeted. Different cell wall components have been proposed to interact with the silica pool in plant shoots, but the understanding of the underlying processes is still limited. Results In the present study, we have characterized silicon deposition and cell wall composition in Brachypodium distachyon wild-type and low-silicon 1 (Bdlsi1-1) mutant plants. Our analyses included different organs and plant developmental stages. In the mutant defective in silicon uptake, low silicon availability favoured deposition of this element in the amorphous form or bound to cell wall polymers rather than as silicified structures. Several alterations in non-cellulosic polysaccharides and lignin were recorded in the mutant plants, indicating differences in the types of linkages and in the three-dimensional organization of the cell wall network. Enzymatic saccharification assays showed that straw from mutant plants was marginally more degradable following a 190 °C hydrothermal pretreatment, while there were no differences without or after a 120 °C hydrothermal pretreatment. Conclusions We conclude that silicon affects the composition of plant cell walls, mostly by altering linkages of non-cellulosic polymers and lignin. The modifications of the cell wall network and the reduced silicon concentration appear to have little or no implications on biomass recalcitrance to enzymatic saccharification.

Hydrothermal pretreatment (HP) is an eco-friendly process for deconstructing lignocellulosic biomass (LCB) that plays a key role in ensuring the profitability of producing biofuels or bioproducts in a biorefinery. At the laboratory scale, HP is usually carried out under non-isothermal regimes with poor temperature control. In contrast, HP is usually carried out under isothermal conditions at the commercial scale. Consequently, significant discrepancies in the values of polysaccharide releases are found in the literature. Therefore, laboratory-scale HP data are not trustworthy if scale-up or retrofitting of HP at larger scales is required. This contribution presents the results of laboratory-scale batch HP for wheat straw in terms of xylan and glucan release that were obtained with rigorous temperature control under isothermal conditions during the reaction stage. The heating and cooling stages were carried out with fast rates (43 and −40 °C/min, respectively), minimizing non-isothermal reaction periods. Therefore, the polysaccharide release results can be associated exclusively with the isothermic reaction stage and can be considered as a reliable source of information for HP at commercial scales. The highest amount of xylan release was 4.8 g/L or 43% obtained at 180 °C and 20 min, while the glucan release exhibited a maximum of 1.2 g/L or 5.5%. at 160 °C/180 °C and 30 min.

Copyright of China Pulp & Paper is the property of China Pulp & Paper Magazines Publisher and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Three typical waste furniture boards, including fiberboard, chipboard, and blockboard, were pretreated with conventional hydrothermal method. The responses of chemical composition, physicochemical morphology, and performances of enzymatic hydrolysis were evaluated. Results indicated the almost complete hemicellulose removal at higher pretreatment temperatures, the enhanced crystallinity index, and disordered morphology of the pretreated substrates indicated that the hydrothermal pretreatment deconstructed these boards well. However, the very low enzymatic hydrolysis (< 8% after 72 h) of the pretreated substrates showed the poor biological conversion. Three hypotheses for the weakened enzymatic hydrolysis were investigated, and results indicated that the residual adhesives and their degraded fractions were mainly responsible for poor hydrolysis. When NaOH post-pretreatment was attempted, cellulose-glucose conversion of the hydrothermally pretreated fiberboard, chipboard and blockboard can be improved to 28.5%, 24.1%, and 37.5%. Herein, the process of NaOH hydrothermal pretreatment was integrated, by which the hydrolysis of pretreated fiberboard, chipboard and blockboard was greatly promoted to 47.1%, 37.3%, and 53.8%, suggesting a possible way to pretreat these unconventional recalcitrant biomasses. [ABSTRACT FROM AUTHOR]

Coconut pulp residue is the waste generated after the extraction of milk and oil. This material became an interest as feedstock for the production of biofuels and other bioproducts in a biorefinery context. The present study aimed to improve the release of sugar from coconut pulp residue through the optimization of sequential hydrothermal and acid pretreatment. An experimental design was constructed with the central composite design (CCD) response surface method using factors of the hydrothermal residence time of 20, 40, 60 min and post-acid treatment concentration of 1%, 2% and 3% (v/v) in constant temperature and time of 121 °C and 20 min. Total sugar yields of 32.47, 27.51 and 26.72 g/L were observed after hydrothermal pretreatment time of 20, 40 and 60 min, respectively. Furthermore, when the pretreated solid residues were subjected to acid pretreatment, the results revealed an increment of 90% on reducing sugars after reaction with 1%, 2% and 3% H2SO4. Statistically, the optimum condition for the two-stage hydrolysis of coconut pulp residue was 60 min hydrothermal pretreatment followed by 3% H2SO4 acid hydrolysis with maximal reducing sugar release of 120.71 g/L. In addition, the degree of polymerization achieved was 1.2, indicating no further hydrolysis required. The current study demonstrates that two-stage pretreatment improves saccharification and provide sufficient sugars for the fermentation process. [ABSTRACT FROM AUTHOR]

The complex structure and biochemical composition of the cell wall of microalgae impede their anaerobic digestion. To enhance the microalgae anaerobic biodegradability, various pretreatment approaches have been utilized. In this study, the enzyme and hydrothermal pretreatment methods were evaluated for microalgal biomass pretreatment and biogas yield. The optical and scanning electron microscopy along with Fourier transform infrared spectroscopy analysis confirmed the efficient action of both the pretreatment methods. The hydrothermal pretreatment resulted in more structural changes, though the increase in enzymatic concentration was also found to have a pronounced effect on both structural and chemical changes. The FTIR spectra determined that mostly the protein and carbohydrate structures of the microalgal cells were affected. Further upon quantitative analysis, it was observed that 10% dose (w/w) for 24 h of exposure time released significantly more soluble chemical oxygen demand compared to others. The multi-enzyme 10% dose for 24 h resulted in significantly higher biogas production potential (P) of 768.92 mL g−1 VS at a maximum biogas production rate (Rm) of 32.16 mL g−1 d−1 with a very short lag phase (λ) of 0.09 days at the end of 30 days, in comparison to untreated and other pretretment conditions in this study. Both the pretreatment approaches in the present study enhanced the microalgal biomass disintegration, digestibility and biogas production. However, more research is required to optimize the process parameters of these pretreatment approaches to make them more reasonable and applicable. [ABSTRACT FROM AUTHOR]

Investigating the impact of hydrothermal pretreatment (HTP) on organic solubilization and anaerobic acidification of thickened waste activated sludge (TWAS) was the objective of this study. For this purpose, 15 different hydrothermal pretreatment scenarios were investigated. The HTP temperature, retention time, and pressure for this study extended from 150 to 240 °C, 5 to 30 min, and 69 to 488 psi respectively. Mesophilic batch acidification tests were conducted for all pretreated and raw samples. The highest solubilization percentage after HTP and acidification was observed at HTP condition of "200 °C–10 min–225 psi" and "180 °C–15 min–145 psi" accounting for 48% and 40% respectively. Moreover, The HTP condition of "190 °C–10 min–181 psi" indicated the highest volatile fatty acid (VFA) production yield of 5.38 g/L or 1076.6 mgVFAs/gVSSadded. For all hydrothermally pretreated samples, acetic acid was determined to be the most abundant VFA. There was no significant hydrogen produced during the acidification process. [ABSTRACT FROM AUTHOR]

Biogas production from microalgae biomass via anaerobic digestion can be enhanced by hydrothermal pretreatment. The process of hydrothermal pretreatment has a significant impact on the energy gain, greenhouse gas emissions, and levelized cost of energy in biogas production from microalgae biomass, which has not been reported until now. In this study, life cycle and economic assessments of biogas production from microalgae biomass with hydrothermal pretreatment and with solar-driven hydrothermal pretreatment were conducted. The results showed that both types of pretreatment methods improved the biogas yield, promoted the energy gain, and reduced the levelized cost of energy. In biogas production through hydrothermal pretreatment, the net energy ratio (Energy input/Energy output), greenhouse gas emissions, and levelized cost of energy were 0.54, −129.94 g CO 2-eq /(kWh biogas), and 0.22 $/m3, respectively, whereas in biogas production through solar-driven hydrothermal pretreatment, the corresponding values were 0.69, −166.13 g CO 2-eq /(kWh biogas), and 0.17 $/m3, respectively. The biogas yield had the maximum effect on the net energy ratio and economic benefit. The efficiency in nitrogen recovery from the biogas residual had the maximum effect on greenhouse gas emissions. This work provides a theoretical guide to promote the environmental and economic benefits of biogas production from microalgae biomass. • Biogas production from microalgae with solar-driven HTP obtained the lowest LCOE. • The biogas yield from microalgae had the maximum impact on net energy ratio. • The biogas yield from microalgae had the maximum impact on economic benefit. • The efficiency of nitrogen recovery had the maximum impact on GHGs. [ABSTRACT FROM AUTHOR]

The effects of the briquetting temperature, briquetting pressure and hydrothermal pretreatment (HT) on the physicochemical properties of the resulted briquettes prepared from one herbaceous biomass, cotton stalk (CS) and one woody biomass, Chinese pine wood sawdust (WS) were mainly addressed in the paper. The apparent density, compressive strength and combustion characteristics of the resulted briquettes (CS/WS-Bs and CS/WS-HT-Bs) were investigated to evaluate their feasibility as the biomass briquette fuels. The results showed that the increase of briquetting temperature and pressure was beneficial to the densification of CS/WS-Bs. Compared with CS/WS-B, the hydrothermal pretreatment significantly improved the physical properties of the resulted biomass briquettes. As the hydrothermal pretreatment temperature increased, the heating values of the resulted CS/WS-HT-Bs increased, the content of fixed carbon increased and the yields of volatiles decreased. Furthermore, HT promoted the combustion characteristics. In addition, the M ad and heating values of all CS/WS-HT-Bs meet the Sweden Standard (SS18 7120). The most cost effective CS/WS-HT200/230-Bs were prepared from the cotton stalk and wood sawdust hydrothermal pretreated at 200 °C and 230 °C under the briquetting conditions of 75 °C and 80 MPa. However, the changes in the physical and chemical properties of the briquettes prepared from CS and WS followed different trends. • Increasing briquetting temperature and pressure promote biomass densification. • CS briquette has the better compressive strength than WS briquettes. • Appropriate hydrothermal pretreatment improved bio-briquette properties. • Biomass type affects greatly the physicochemical properties of bio-briquette. • Higher quality bio-briquette fuel can be produced without any additives. [ABSTRACT FROM AUTHOR]

• Hydrothermal pretreatment improves the anaerobic digestion of pepper plant and eggplant. • The highest solubilization of C and N is obtained at 40 min of pretreatment. • Hydrothermal treatment improves methane production with an optimum of 84.5 mL STP CH 4 /g VS. Plant residues are an important source of organic matter that can be degraded by aerobic or anaerobic biological processes. However, due to the presence of lignocellulosic material, these residues are not easily biodegradable. Greenhouse crops, such as pepper and eggplant, generate large amounts of this type of waste after harvesting. In this study, a hydrothermal pretreatment was applied at 120 °C and different times to evaluate the enhancement of C and N solubilization in these residues. The highest solubilization of C was obtained at 40 min, as no significant increases were observed at higher times (100% and 68% for pepper plant [PP] and eggplant [EP], respectively). The solubilization of N shows a linear behavior (PP r2 = 0.9670 and EP r2 = 0.9395). Aerobic and anaerobic biodegradability were also evaluated, with better results found for the anaerobic digestion of the pretreated substrates. The nutrients balance with anaerobic co-digestion of both pretreated substrates (50:50% wt) improved methane production by 1.4 and 1.8 with respect to the substrates individually. [ABSTRACT FROM AUTHOR]

The genera Dysgonomonas, Coprococcus, Sporomusa, Bacteroides, Sedimentibacter, Pseudomonas, Ruminococcus, and Clostridium predominate in compost residue, and vadimCA02, Anaerobaculum, Tatlockia, Caloramator, and Syntrophus prevail in soil used as inoculum in batch rectors. This mixed consortium was used as inoculum for biogas production using different concentrations of sugarcane bagasse (SCB) (from 1.58 to 4.42 g/L) and yeast extract (YE) (from 0.58 to 3.42 g/L) according to a composite central design. The maximum ethanol production (20.11 mg L−1) was observed using 2.0 and 3.0 g L−1 of YE and SCB, respectively (C6). Likewise, the highest hydrogen production (0.60 mmol L−1) was observed using 3.0 and 4.0 g L−1 of YE and SCB, respectively (C1). Methane was also observed, reaching the maximum production (1.44 mmol L−1) using 1.0 and 4.0 g L−1 of YE and SCB, respectively (C2). The archaeal similarity between these conditions was above 90%; however, the richness and diversity were higher in the C2 (12 and 2.42, respectively) than in C1 (5 and 1.43, respectively) and C6 (11 and 2.29, respectively). Equally, the bacterial similarity between C1 and C6 was 60% while richness of 24 and 17 and diversity of 3.13 and 2.81 were observed in C1 and C6, respectively. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel mesoporous biochar was prepared from biogas residue through facile method. • The maximum adsorption capacity of TC on HBRBC reached 289.1 mg⋅g−1. • Hydrothermal pretreatment intensified the pore filling, π–π interaction, and hydrogen bonding. • HBRBC exhibited a high adsorption performance under pH and coexisting ion interference. Biochar preparation is a promising strategy for the application of biogas residue. Modification of biochar to enhance its adsorption performance is worthy of consideration. In this work, the biogas residue was hydrothermally pretreated first, and then directly pyrolyzed to biochar (HBRBC). Pristine biochar and hydrochar were also prepared as controls. The adsorption characteristic of biochars toward tetracycline (TC) were explored. A predominantly mesoporous structure was observed in HBRBC. Furthermore, hydrothermal pretreatment enhanced the carbon defects and the polarity of biochar. Moreover, hydrothermal pretreatment caused the change of composition and functional groups in biochar. Sorption kinetics for HBRBC could be well described with both two-compartment and pseudo-second-order models. Meanwhile, the Freundlich and Temkin models were suitable for the isotherm data of TC sorption onto HBRBC. The maximum adsorption capacity of HBRBC toward TC reached 289.1 mg⋅g−1, which was ascribed to the joint contribution of pore filling, π–π interaction, hydrogen bonding, and electrostatic interaction. Hydrothermal pretreatment mainly intensified the pore filling, π–π interaction, and hydrogen bonding due to the developed mesoporous structure, more functional groups, and high polarity. HBRBC exhibited a high adsorption performance toward TC with a wide pH range and coexisting ion interference. Thus, hydrothermal pretreatment combined with pyrolytic conversion was a feasible pathway for biogas residue utilization. [ABSTRACT FROM AUTHOR]

[Display omitted] • Decision-tree models stand out in predictive accuracy for methane yield. • Pre-treatment methods exhibit negligible impact on sludge solubilization and AD. • Total heating time's significance rivals holding time for enhanced solubilization. • HTP parameters overcome feedstock and AD parameters, influencing performance. • ANN models exhibit superior fitting accuracy for solubilization prediction. This study utilizes decision-tree-based models, including Random Forest, XGBoost, artificial neural networks (ANNs), support vector machine regressors, and K nearest neighbors algorithms, to predict sludge solubilization and methane yield in hydrothermal pretreatment (HTP) coupled with anaerobic digestion (AD) processes. Analyzing two decades of published research, we find that ANN models exhibit superior fitting accuracy for solubilization prediction, while decision-tree models excel in methane yield prediction. Pretreatment temperature is identified as pivotal among various variables, and heating time surprisingly emerges as equally significant as holding time for solubilization and surpasses it for methane yield. Contrary to prior expectations, the HTP method's impact on sludge solubilization and AD performance is minimal. This study underscores data-driven models' potential as resource-efficient tools for optimizing advanced AD processes with HTP. Notably, our research spans nearly two decades of lab, pilot, and full-scale studies, offering novel insights not previously explored. [ABSTRACT FROM AUTHOR]