Hydrothermal Pretreatment Research Articles

Efficient Enzymatic Hydrolysis and Polyhydroxybutyrate Production from Non-Recyclable Fiber Rejects from Paper Mills by Recombinant Escherichia coli

Non-recyclable fiber rejects from paper mills, particularly those from recycled linerboard mills, contain high levels of structural carbohydrates but are currently landfilled, causing financial and environmental burdens. The aim of this study was to develop efficient and sustainable bioprocess to upcycle these rejects into polyhydroxybutyrate (PHB), a biodegradable alternative to degradation-resistant petroleum-based plastics. To achieve high yields of PHB per unit biomass, the specific objective of the study was to investigate various approaches to enhance the hydrolysis yields of fiber rejects to maximize sugar recovery and evaluate the fermentation performance of these sugars using Escherichia coli LSBJ. The investigated approaches included size reduction, surfactant addition, and a chemical-free hydrothermal pretreatment process. A two-step hydrothermal pretreatment, involving a hot water pretreatment (150 °C and 15% solid loading for 10 min) followed by three cycles of disk refining, was found to be highly effective and resulted in an 83% cellulose conversion during hydrolysis. The hydrolysate obtained from pretreated biomass normally requires a detoxification step to enhance fermentation efficiency. However, the hydrolysate obtained from the pretreated biomass contained minimal to no inhibitory compounds, as indicated by the efficient sugar fermentation and high PHB yields, which were comparable to those from fermenting raw biomass hydrolysate. The structural and thermal properties of the extracted PHB were analyzed using various techniques and consistent with standard PHB.

Harnessing Ulva ohnoi for eco-friendly bioethanol production via hydrothermal pretreatment

BackgroundThe increasing demand for renewable energy sources has sparked interest in biofuels derived from green seaweeds, owing to their abundance and high carbohydrate content. Ulva ohnoi, harvested from Taiwan's shores, presents a promising candidate for bioethanol production due to its favorable characteristics. MethodsIn this study, Ulva ohnoi underwent hydrothermal pretreatment at temperatures of 120 °C, 150 °C, and 180 °C for 20 min. The pretreated slurry obtained at 180 °C was subjected to enzymatic saccharification at pH 4.8 and 50 °C for 72 h. This process resulted in the production of 5.8 g/L of glucose, which was subsequently concentrated to 18.86 g/L. Significant FindingsFermentation of the concentrated sugar fractions using Saccharomyces cerevisiae WLP 300 at 30 °C for 24 h yielded remarkable ethanol yields of 0.39 and 0.43 g/g of sugar. These yields approached the maximum theoretical values of 76.1% and 84.58%, respectively. Additionally, the study reported a maximum ethanol productivity of 0.54 g/L/h in the 12th hour in the concentrated fraction. These findings underscore the potential of Ulva ohnoi as a sustainable biofuel and clean energy source, aligning with Sustainable Development Goal 7 (SDG 7) of ensuring access to affordable, reliable, sustainable, and modern energy for mankind.

Synergistic integration of hydrothermal pretreatment and co-digestion for enhanced biogas production from empty fruit bunches in high solids anaerobic digestion

This study investigates the co-digestion of hydrothermally pretreated empty fruit bunches (EFB) at 190 °C for 5 min (HTP190-EFB) with decanter cake (DC) to improve biogas production in high solid anaerobic digestion (HSAD). The HTP190-EFB exhibited a 67.98 % reduction in total solids, along with the production of 0.89 g/L of sugar, 2.39 g/L of VFA, and 0.56 g/L of furfural in the liquid fraction. Co-digestion of HTP190-EFB with DC at mixing ratios of 5, 10, and 15 %w/v demonstrated improved methane yields and process stability compared to mono-digestion of HTP190-EFB. The highest methane yield of 372.69 mL CH4/g-VS was achieved in the co-digestion with 5 %w/v DC, representing a 15 % increase compared to digestion of HTP190-EFB (324.30 mL CH4/g-VS) alone. Synergistic effects were quantified, with the highest synergistic methane yield of 77.65 mL CH4/g-VS observed in the co-digestion with 5 %w/v DC. Microbial community analysis revealed that co-digestion of hydrothermally pretreated EFB with decanter cake promoted the growth of Clostridium sp., Lactobacillus sp., Fibrobacter sp., Methanoculleus sp., and Methanosarcina sp., contributing to enhanced biogas production compared to mono-digestion of pretreated EFB. Energy balance analysis revealed that co-digestion of HTP190-EFB with DC resulted in a total net energy of 599.95 kW, 52 % higher than mono-digestion of HTP190-EFB (394.62 kW). Economic analysis showed a shorter return on investment for the co-digestion system (0.86 years) compared to the mono-digestion of HTP190-EFB (1.02 years) and raw EFB (2.69 years). The co-digestion of HTP190-EFB with 5 %w/v DC offers a promising approach to optimize methane yield, process stability, and economic feasibility, supporting the palm oil industry for producing renewable energy and sustainable waste management.

Effect of hydrothermal pre-treatment on dehulling and nutritional characteristics of Kodo millet

Effect of hydrothermal pre-treatment on dehulling and nutritional characteristics of Kodo millet

Machine learning facilitated the modeling of plastics hydrothermal pretreatment toward constructing an on-ship marine litter-to-methanol plant

An onboard facility shows promise in efficiently converting floating plastics into valuable products, such as methanol, negating the need for regional transport and land-based treatment. Gasification presents an effective means of processing plastics, requiring their transformation into gasification-compatible feedstock, such as hydrochar. This study explores hydrochar composition modeling, utilizing advanced algorithms and rigorous analyses to unravel the intricacies of elemental composition ratios, identify influential factors, and optimize hydrochar production processes. The investigation begins with decision tree modeling, which successfully captures relationships but encounters overfitting challenges. Nevertheless, the decision tree vote analysis, particularly for the H/C ratio, yielding an impressive R2 of 0.9376. Moreover, the research delves into the economic feasibility of the marine plastics-to-methanol process. Varying payback periods, driven by fluctuating methanol prices observed over a decade (ranging from 3.3 to 7 yr for hydrochar production plants), are revealed. Onboard factories emerge as resilient solutions, capitalizing on marine natural gas resources while striving for near-net-zero emissions. This comprehensive study advances our understanding of hydrochar composition and offers insights into the economic potential of environmentally sustainable marine plastics-to-methanol processes.

Daniel Antorán - Enhancing the performance of waste hemp hurd-based carbons in SIBs through H2SO4-assisted hydrothermal pretreatment

Daniel Antorán - Enhancing the performance of waste hemp hurd-based carbons in SIBs through H2SO4-assisted hydrothermal pretreatment

Cascading Recovery of Added-Value Cocoa Bean Shell Fractions Through Autohydrolysis Treatments

AbstractIn this work, an autohydrolysis treatment was applied to cocoa bean shells (CBS) to obtain different potentially added-value fractions rich in phenolic compounds with antioxidant potential and oligosaccharides with potential prebiotic properties. The final residue was enzymatically treated to deliver sugars that can undergo fermentation-based biotransformation. This hydrothermal pretreatment was assessed for maximum temperatures (Tmax) between 120 to 200 °C and severities (S0) between 1.1 and 3.4. The highest oligosaccharide concentration (5.5 g/L) was achieved at S0 of 3.4. The increase of S0 during the process allowed to increase the recovery of interesting bioactive compounds, achieving a maximum TPC and antioxidant activity of 2.8 g/L and 17178.5 µmol Fe2+/L, respectively, when the Tmax reached 200 °C. However, at this temperature, a significant amount of degradation products such as organic acids and HMF was already formed, and a compromise temperature of 160 °C was chosen for further tests. It was possible to obtain a maximum glucose yield of 71% when the pretreated solids were enzymatically hydrolysed. Hence, the use of autohydrolysis, avoiding the use of toxic chemicals, has proved to be a sustainable alternative to obtain different CBS fractions with interesting composition to be potentially employed in multiple sectors.

Comparative Study of High-Temperature Anaerobic Digestion of Municipal Sludge Under Acid/Alkali and Low-Temperature Hydrothermal Synergistic Pretreatment

Comparative Study of High-Temperature Anaerobic Digestion of Municipal Sludge Under Acid/Alkali and Low-Temperature Hydrothermal Synergistic Pretreatment

Novel strategy for efficient energy recovery and pollutant control from sewage sludge and food waste treatment

Considering the high organic matter contents and pollutants in sewage sludge (SS) and food waste (FW), seeking green and effective technology for energy recovery and pollutant control is a big challenge. In this study, we proposed a integrated technology combing SS mass separation by hydrothermal pretreatment, methane production from co-digestion of hydrothermally treated sewage sludge (HSS) centrate and FW, and biochar production from co-pyrolysis of HSS cake and digestate with heavy metal immobilization for synergistic utilization of SS and FW. The results showed that the co-digestion of HSS centrate with FW reduced the NH4+-N concentration and promoted volatile fatty acids conversion, leading to a more robust anaerobic system for better methane generation. Among the co-pyrolysis of HSS cake and digestate, digestate addition improved biochar quality with heavy metals immobilization and toxicity reduction. Following the lab-scale investigation, the pilot-scale verification was successfully performed (except the co-digestion process). The mass and energy balance revealed that the produced methane could supply the whole energy consumption of the integrated system with 26.2 t biochar generation for treating 300 t SS and 120 t FW. This study presents a new strategy and technology validation for synergistic treatment of SS and FW with resource recovery and pollutants control.

Recycling and reuse of waste agricultural plastics with hydrothermal pretreatment and low-temperature pyrolysis method

Recycling and reuse of agricultural plastics is an urgent worldwide issue. In this work, it is shown that low-density polyethylene (PE) typically used in mulch films can be converted into high-capacity P and N adsorbents through a two-step method that uses hydrothermal pretreatment (180 °C, 24 h) followed by pyrolysis at 500 °C with Ca(OH)2 additive. CaPE@HC500 materials prepared with the proposed two-step method were found to have high adsorption capacities for phosphate (263.6 mg/g) and nitrogen (200.7 mg/g) over wide ranges of pH (3–11). Dynamic adsorption of phosphate by CaPE@HC500 material in a packed-bed had a half-time breakthrough of 210 min indicating the feasibility of continuous systems. Material stability, cost, environmental-friendliness, and recyclability of the CaPE@HC500 material were determined to be superior to literature-proposed Ca-containing adsorbents. The two-step method for converting waste agricultural plastic mulch films into adsorbents is robust and highly-applicable to industrial settings.

Effect of hydrothermal pretreatment on leachate fed Scenedesmus sp. biomass solubilization and biogas production

The aim of the present study was to assess the effect of hydrothermal pretreatment on the solubilization and anaerobic digestion (AD) of Scenedesmus sp. biomass. At first, the microalgae was cultivated in 5% fresh leachate (FL) to recover nutrients such as nitrogen and phosphorus. Scenedesmus sp. grown in 5% FL obtained 100%, 77% and 97% removal efficiency of ammonium nitrogen (NH4+ - N), total Kjeldahl nitrogen (TKN) and phosphate phosphorous (PO43− -P), respectively. In the following step, the hydrothermal pretreatment of Scenedesmus sp. biomass was carried out at 120, 150 and 170 °C and retention time of 0, 30 and 60 min to evaluate its solubilization and biogas production through AD in batch test. Soluble chemical oxygen demand (sCOD) increased by 260% compared to untreated microalgae at 170 °C for 60 min. In comparison to untreated microalgae, the highest increase in biogas (70%) and methane yield (100%) was observed for 150 °C and 60 min pretreated microalgae as a consequence of hydrothermal pretreatment. Hydrothermal pretreatment has shown effectiveness in enhancing biomass solubilization and increasing biogas yield. Nevertheless, further research at the pilot scale is necessary to thoroughly evaluate the potential and feasibility of hydrothermal pretreatment for full-scale implementation.

Isolation of Highly Crystalline Cellulose via Combined Pretreatment/Fractionation and Extraction Procedures within a Biorefinery Concept.

Sustainable production of bio-based materials and chemicals requires integrated approaches which utilize all fractions of lignocellulosic biomass. In this work, highly crystalline cellulose was isolated via combined pretreatment/fractionation and extraction processes from beechwood sawdust. The proposed approach was based on the selective recovery of hemicellulose components in the first step, followed by enhanced delignification in the second step, permitting the efficient recovery of the remaining cellulose via bleaching in the final step. Hydrothermal pretreatment under tailored conditions in neat water or dilute acid resulted in almost complete hemicellulose removal (80-96 wt %) in the liquid fraction. In the second step, the formed surface lignin was isolated via mild extraction while enhanced removal of both native/structural and surface lignin (71 wt %) was achieved by applying the organosolv treatment using dilute sulfuric acid as catalyst. Dilute sulfuric acid pretreatment followed by acid catalyzed organosolv pretreatment proved to be the most efficient combined approach, leading to 80 wt % hemicellulose removal as xylose monomer, and 71 wt % delignification. High crystallinity cellulose (<88%), with an overall cellulose recovery of 68-91 wt % based on native cellulose in parent biomass was isolated in the last step via bleaching of all pretreated biomass solids. The proposed integrated biorefinery procedures that aim to whole "waste" biomass valorization, replacing fossil resources, with the use of green solvents (water, ethanol) at relatively mild temperature/pressure conditions, are in line with the scope of several United Nations Sustainable Development Goals, such as UN SDG 8, 11, 12, and 13.

Response of methanogenic metabolism to polystyrene microplastics at varying concentrations: The trade-off between inhibitory and protective effects in anaerobic digestion

Polystyrene (PS) is an important raw material of food packages, and its induced microplastics (MPs) inevitably enter into the food waste (FW) with mechanical or hydrothermal pretreatment, which may affect the FW anaerobic digestion (AD). However, the different microbial responses to PS MPs in AD system have rarely been reported at varying PS MPs levels. In this study, the trade-off between positive and negative effects of PS MPs on syntrophic methanogenesis in AD for FW treatment was investigated when the dosage varied from 10 to 200 mg/L. The results showed that methane (CH4) yield was upgraded by 4.72% at a lower PS MPs concentration (25 mg/L) compared with the control reactor without PS MPs dosing. In contrast, it would be inhibited by 10.13% when PS MPs concentration increased to 100 mg/L. More secretion of extracellular polymeric substances was the main reason for methanogenic metabolism enhancement at lower dosages of PS MPs due to its characteristics of cell-protection and electron transfer facilitation. Furthermore, the higher abundance of genes regarding superoxide dismutase and catalase in the reactor with PS MPs of 25 mg/L could impede reactive oxygen species formation and alleviate its toxicity. The findings of the study provide a comprehensive understanding of the promotion and inhibition mechamisms of syntrophic metabolism in the AD process by PS MPs and their released substances at varying concentrations.

Development of nickel-based bimetallic catalysts for production of hydrogen-rich syngas via supercritical water gasification of liquid residue from hydrothermal pretreatment of food waste

Hydrothermal carbonization has become increasingly prevalent in the pretreatment of food waste, leading to the generation of substantial volumes of liquid effluent. This hydrothermal liquid effluent from food waste (HLF) contains high content of organic compounds, making it challenging to treat using conventional methods. In this regard, the HLF was considered a potential source for energy production via supercritical water gasification (SCWG). This study aimed to develop effective bimetallic catalysts based on Ni/Al2O3 with four different promoters (Cu, Co, La, and Ce), and investigated their performance in the catalytic SCWG for the treatment of HLF and hydrogen production. Among the tested promoters, the Ce-Ni catalyst was considered the most suitable in terms of its highest H2 yield and H2 selectivity. The optimal Ce content was found to be 5 wt%, with a catalyst dosage of 5 % by weight of HLF. These conditions resulted in the highest H2 selectivity of 1.61 and a relatively high H2 yield of 749.60 mmol/L under SCWG operating conditions of 480 °C and 30 min. Excessive catalyst dosages increased total syngas yield but reduced H2 selectivity. The stability test demonstrated that the Ce promoter contributed to enhancing the catalyst resistance to deactivation by coke deposition. The hydrogen production of 5Ce-Ni decreased by 13.8 % after three reuses, whereas a larger decrease of 26.0 % was observed with Ni/Al2O3. These findings indicate that Ce-Ni catalyst show promise for enhancing H2-rich syngas production in the SCWG of hydrothermal liquid effluent from food waste.

Sustainable duckweed biomass valorization for dark fermentative hydrogen production: Process evaluation under meso- and thermophilic operations

Aquatic plants are rich in biomass and contain good amounts of carbohydrates and proteins which are amenable for valorization to generate bioenergy. Duckweed is rich in proteins and carbohydrates that grow abundantly in contaminated waterbodies, which is now tested for as a substrate for biohydrogen production. Dark-fermentative hydrogen production was done by hydrothermal pretreatment of duckweed biomass under 15 lbs pressure, evaluated under three different operating temperatures that cover mesophilic (35 °C) and thermophilic conditions (50 and 55°C). The study resulted in the maximum hydrogen production rate of 0.97 mmol/day in batch culture (160 mL) from 55 °C that was found superior to 50 °C (0.84 mmol/day) and 35 °C (0.38 mmol/day) operations. From the 7 days of operation, under uncontrolled pH conditions, substrate (chemical oxygen demand, COD) utilization was 57.27 %, which is higher than in mesophilic conditions (50.67 %). Efficient hydrolysate conversion was noticed with thermophilic conditions, especially under operation at 55 °C (416 mL H2/g of biomass) than mesophilic conditions (144 mL H2/g of biomass) suggesting that duckweed can be dependable biomass for hydrogen production, and the dark-fermentation can be an appropriate solution of aquatic weed biomass management in a sustainable approach.

Application of Microwave Energy to Biomass: A Comprehensive Review of Microwave-Assisted Technologies, Optimization Parameters, and the Strengths and Weaknesses

This review article focuses on the application of microwave-assisted techniques in various processes, including microwave-assisted extraction, microwave-assisted pyrolysis, microwave-assisted acid hydrolysis, microwave-assisted organosolv, and microwave-assisted hydrothermal pretreatment. This article discusses the mechanisms behind these techniques and their potential for increasing yield, producing more selectivity, and lowering reaction times while reducing energy usage. It also highlights the advantages and disadvantages of each process and emphasizes the need for further research to scale the processes and optimize conditions for industrial applications. A specific case study is presented on the pretreatment of coffee waste, demonstrating how the choice of microwave-assisted processes can lead to different by-products depending on the initial composition of the biomass.

WITHDRAWN: Component Analysis of Corncob after Hydrothermal Treatment

Hydrothermal pretreatment is a green pretreatment technology, which can effectively promote the degradation of biomass without adding any chemical reagent. In this study, hydrothermal pretreatment on improving digestibility of corncobs was investigated and the effect of hydrothermal pretreatment on changes of structure of the corncob lignocellulose was investigated. The composition and amounts of sugar content in hydrolysate and enzymatic hydrolysate were determined. Hydrothermal treatment destroyed the lignocellulose structure of corncob and caused different degrees of degradation. With the increasing temperature of hydrothermal treatment, the degradation of cellulose, hemicellulose and lignin in corncob was detected with increasing the content of reducing sugars in hydrolysate. The hydrolysate of corncob treated by hydrothermal treatment at 190 ℃ for 60min mainly included glucose, xylobiose, xylotriose and xylotetraose. The content of glucose, xylobiose, xylotriose and xylotetraose in the hydrolysate of hydrothermal treatment corncob was at level of 0.001mg·g-1, 16.740mg·g-1, 4.306mg·g-1 and 3.164mg·g-1 respectively. The yield of glucose, xylobiose, xylotriose and xylotetraose in enzymatic hydrolysate were 4.771mg·g-1, 64.437mg·g-1, 6.853mg·g-1 and 1.835mg·g-1, respectively. The understanding will help to improve the conversion and utilization of corncob as an agriculture residue.

Comprehensive hydrothermal pretreatment of municipal sewage sludge: A systematic approach

This study provides a comprehensive analysis of the potential impact of hydrothermal pretreatment (HTP) on municipal thickened waste-activated sludge (TWAS) and its integration with anaerobic digestion (AD). The research demonstrates that HTP conditions (170 °C, 3 bars for 30 min) can increase the solubilization of macromolecular organic compounds by 41%, which enhances biodegradability in semicontinuous bioreactors. This treatment also results in a 50% reduction in chemical oxygen demand (COD) and a 63% increase in the destruction of volatile solids (VS). The combination of HTP with AD significantly boosts methane yields by 51%, reaching 176 ml/g COD, and improves the digestate dewaterability, doubling the solid content in the dewatered cake. However, a higher polymer dose is required compared to conventional AD. Microbial community analysis correlates the observed performance and alterations; it indicates that HTP enhances resilience to stress conditions such as ammonia toxicity. This comprehensive study provides valuable insights into the transition from wastewater treatment plants (WWTPs) to resource recovery facilities (RRF) in line with circular economy principles.

Novel pectins extracted from Euryale ferox fruit peel by combined hydrothermal pretreatment and enzymatic hydrolysis exhibit potential as aqueous gels and antioxidant activities

SummaryThe present study provided new alternatives for recycling of Euryale ferox fruit peel to develop application of pectins in food industry. In this work, the physicochemical characteristics, thermal properties, rheological properties and antioxidant activities of novel pectins (Pectin Hp, Pectin Eh and Pectin Hp‐Eh) extracted from E. ferox fruit peel were explored. The results indicated that Pectin Hp‐Eh had the highest yield (122.48 mg g−1). Pectin HP, Pectin Eh and Pectin HP‐Eh, with strip, polygonal and irregular shaped structures, respectively, exhibited dominant elastic characteristics as aqueous gels. Compared to Pectin HP and Pectin HP‐Eh, Pectin Eh possessed better rheological properties. Moreover, Pectin Eh exhibited stronger scavenging activities of hydroxyl and 1,1‐diphenyl‐2‐picrylhydrazyl (DPPH) radicals than those of Pectin HP and Pectin HP‐Eh. The IC50 values of Pectin Eh for hydroxyl and DPPH radicals were determined to be 11.81 and 14.07 mg mL−1, respectively.

Structural characterization and bioactivities of maize bran feruloylated arabinoxylan and oligosaccharides obtained by a combined hydrothermal and enzymatic pre-treatment

Feruloylated arabinoxylans (F-AX) are gaining importance due to their immense health benefits as nutraceuticals. In the current study, we extracted F-AX from maize bran by a combination of hydrothermal pre-treatment and xylanase and cellulase double enzymatic digestion and studied them in detail. The F-AX composition included carbohydrate (533.74 ± 7.59 mg/g), and phenolic acid (153.71 ± 3.55 mg/g) with an arabinoxylan percentage of 74.17% and degree of substitution of 0.99. Ferulic acid was the major phenolic acid found esterified to arabinose. The GC, FTIR, UPLC, and methylation analysis revealed the typical structure of arabinoxylan with bound ferulic acid and a highly substituted xylopyranose backbone. The LC-MS/MS analysis revealed the structure of F-AXOS, which were the predominant oligosaccharides in the purified fraction. The F-AX showed potent antioxidant activity (DPPH, ABTS, and FRAP) and could effectively inhibit the formation of advanced glycation end products (argpyrimidine, pentosidine, and vesperlysine) and protein oxidation products (dityrosine and N′-formylkynurenine). F-AX also showed potent antiproliferative activity against the human colon cancer cells - Colo 205 and HCT 116. The current study revealed that the combined extraction method has yielded a unique blend of F-AX with bioactivities and these molecules have the potential to be used in the development of innovative functional foods.