Thermochemical Pretreatment Research Articles

Experimental investigation of impact of torrefaction on the hydrophobic properties of woody biomass using WDPT and moisture uptake test

Torrefaction is the thermo-chemical pretreatment that alters the various physico-chemical properties of the biomass to produce an upgraded solid biofuel (green coal). The study aims to investigate the effect of torrefaction parameters on the hydrophobic characteristics of three woody biomasses derived from Lannea coromandelica, Azadirachta indica, and Leucaena leucocephala. The torrefaction experiment was carried out at 200 ℃, 250 ℃, and 300 ℃ with two residence times of 30 and 60 min. The hydrophobic characteristics of the torrefied biomass were investigated using the Water Drop Penetration Time (WDPT) test and moisture uptake test. The results showed a clear trend across all biomass samples as the temperature and residence time increased, the mass yield consistently decreased. Leucaena leucocephala consistently produced the highest solid yields across all the given conditions, ranging from 84.67 % to 53.33 %. However, as the severity of the torrefaction increases, the HHV increases significantly in all biomass samples. Azadirachta indica showed the greatest improvement, reaching an HHV of 27.51 MJ/kg when torrefied at 300 ℃ for 60 min. Also, as the severity of the torrefaction increases, there is a significant improvement in the hydrophobic characteristics of the biomass, making it more resistant to water absorption. Statistical Analysis (ANOVA) revealed that the torrefaction temperature had a more pronounced impact on biomass hydrophobicity than residence time in all the biomass samples examined in the study. This enhancement in hydrophobicity is critical for increasing the HHV of the biomass fuel, indicating that torrefied biomass can be effectively used for various applications.

Scale sensitivity of ethanol production via consolidated bioprocessing with consideration of feedstock cost

AbstractWe examine feedstock cost and minimum selling price for ethanol production from corn stover as a function of scale, stover yield, participation rate, and price incentives for two conversion technologies: a conventional base case featuring thermochemical pretreatment with added cellulase, and an advanced case featuring consolidated bioprocessing with cotreatment (C‐CBP). Delivered feedstock cost ranged from $85 Mg−1 at small (10 million gallons year−1 or ~38 million L year−1) scale with high yield and participation rates to $124 Mg−1 at large scale (60 million gallons year−1 or 227 million L year−1) and low yield and participation rates. The minimum ethanol selling price (MESP) was approximately twofold lower for the advanced case compared with the base case. The payback period was several times lower for the advanced case compared with the base case, with increasing disparity at smaller scales, and was highly sensitive to ethanol price supports. For both C‐CBP and the conventional processing paradigm, MESP decreased with increasing scale, indicating that the cost penalty due to higher feedstock transport distances was more than outweighed by lower capital costs. However, the cost penalty for operation at small scale, expressed in $ gallon−1 ethanol, is lower for C‐CBP than for the conventional paradigm by roughly twofold. Particularly for initial applications of C‐CBP, we speculate that this cost penalty will likely be modest compared with the anticipated benefits of small‐scale operation such as increased opportunity to use existing infrastructure, easier plant siting and supply chain establishment, and lower total investment required.

Evolution of solid residue composition during inert and oxidative biomass torrefaction

Biomass torrefaction is a thermochemical pretreatment that can be used to improve biomass properties, contributing to the energy densification of biomass or increasing its grindability, burning and gasification characteristics, porous structure, etc. While it is typically carried out under inert conditions, oxygen-lean torrefaction of biomass can reduce the process cost and complexity. This work proposes a novel extended 2-step kinetics mechanism capable of accurately predicting the evolution of the chemical composition of torrefied biomass. The model parameters are obtained from data collected from an extensive experimental campaign in which the chemical composition of torrefied biomass was measured at different temperatures, residence times, and oxygen fractions. The carbon mass fraction of the torrefied products was found to increase by up to 50 % under severe inert torrefaction conditions, i.e., high temperatures and long residence times, whereas the hydrogen fraction decreased. In the presence of oxygen during torrefaction, the carbon and hydrogen contents in the solid residue decrease compared with those produced under inert torrefaction. The extended 2-step model can also be used to determine the high heating value and energy densification of the torrefied biomass, with the latter ranging from 1 to 1.4 for the operating conditions tested.

Enhanced bioethanol production from cassava waste: optimization of thermochemical pretreatment for maximum sugar recovery and characterisation of potential fractions

ABSTRACT Thermochemical pretreatment is an interesting approach for the effective separation of lignocellulosic biomass before fermentation for bioethanol production. This research focused on optimising the thermochemical pretreatment conditions of cassava waste using response surface methodology to predict the glucose yields under the optimal condition. The optimised conditions of 0.045 M of NaOH concentration at 153.59 °C for 48.03 min resulted in the maximum glucose yield of 93.87%. In addition, fermentation process can generate ethanol within a range of solid loading from 10% to 20%. The highest concentration of ethanol was 34.53 ± 0.56 g/L after 72 h, equivalent to ethanol yield of 0.46 g/g. The co-products were also characterised for further utilisation in biorefinery concept. The results of this study confirmed that the thermochemical pretreatment process using the NaOH catalyst could provide high glucose yields, which can be easily converted into bio-based fuels and further valorised of co-products to value-added chemicals.

Anaerobic co-digestion of waste activated oily-biological sludge with sugarcane bagasse using thermo-chemical pre-treatment under thermophilic condition

Anaerobic co-digestion of waste activated oily-biological sludge with sugarcane bagasse using thermo-chemical pre-treatment under thermophilic condition

Synergic effect of thermo-chemical pretreatment of waste-activated sludge on bio-methane enhancement

Sustainable and environmentally friendly energy production is feasible via anaerobic digestion (AD) of organic wastes, such as waste-activated sludge (WAS). However, due to its limited degradation, a pretreatment strategy is applied to WAS to enhance its bio-degradation and, thus, biogas yield. Alkaline (0.5%–9% g NaOH/gTS, 30 min), microwave (MW) (90°C–175°C), and hybrid (0.5% g NaOH/gTS +125°C) pretreatments were applied to WAS. The characterization of untreated and pretreated WAS revealed that with higher alkaline and MW pretreatment, the soluble chemical oxygen demand (sCOD), carbohydrate, and protein increased; however, the readily biodegradable COD (rbCOD) rate was unlike the sCOD. The sCOD was 7%–18%, 8%–23%, and 37% for alkaline, MW, and hybrid pretreatments, respectively. Stronger alkaline and MW pretreatment induced higher turbidity, capillary suction time, and lower average particle size. AD of alkaline-, MW-, and hybrid-pretreated WAS produced 94% (0.5% NaOH), 125% (MW at 125°C), and 199% (0.5% NaOH and MW at 125°C) increased biogas, respectively, compared to the AD of untreated sludge. The AD data on the alkaline-, MW-, and hybrid-pretreated BMP assays fitted well with the modified Gompertz model with a coefficient of determination above 0.95. The PCA analysis showed that biogas production is closely correlated with pretreatment temperature, VFA production, rbCOD, sCOD, and soluble carbohydrates and protein. Microbial genome sequencing analysis showed an improvement in microbial abundance and diversity. Acetoclastic methanogen (Methanothrix) growth was improved by 37% (MW pretreatment). Abundances of Methanosarcina, using all three metabolic pathways for methanogenesis, were 17, 21, 11, and 48% in the control, alkaline-, MW-, and hybrid-pretreated digestate, respectively, corresponding to 186% improvement in hybrid pretreatment when compared to the control.

Evaluation of co-culture of cellulolytic fungi for enhanced cellulase and xylanase activity and saccharification of untreated lignocellulosic material.

Bioethanol production from lignocellulosic materials is hindered by the high costs of pretreatment and the enzymes. The present study aimed to evaluate whether co-cultivation of four selected cellulolytic fungi yields higher cellulase and xylanase activities compared to the monocultures and to investigate whether the enzymes from the co-cultures yield higher saccharification on selected plant materials without thermo-chemical pretreatment. The fungal isolates, Trichoderma reesei F118, Penicillium javanicum FS7, Talaromyces sp. F113, and Talaromyces pinophilus FM9, were grown as monocultures and binary co-cultures under submerged conditions for 7days. The cellulase and xylanase activities of the culture filtrates were measured, and the culture filtrates were employed for the saccharification of sugarcane leaves, Guinea grass leaves, and water hyacinth stems and leaves. Total reducing sugars and individual sugars released from each plant material were quantified. The co-culture of Talaromyces sp. F113 with Penicillium javanicum FS7 and of T. reesei F118 with T. pinophilus FM9 produced significantly higher cellulase activities compared to the corresponding monocultures whereas no effect was observed on xylanase activities. Overall, the highest amounts of total reducing sugars and individual sugars were obtained from Guinea grass leaves saccharified with the co-culture of T. reesei F118 with T. pinophilus FM9, yielding 63.5% saccharification. Guinea grass leaves were found to be the most susceptible to enzymatic saccharification without pre-treatment, while water hyacinth stems and leaves were the least. Accordingly, the study suggests that fungal co-cultivation could be a promising approach for the saccharification of lignocellulosic materials for bioethanol production.

Solubilization of sugarcane bagasse by mono and cocultures of thermophilic anaerobes with and without cotreatment

Cotreatment, mechanical disruption of lignocellulosic biomass during microbial fermentation, is a potential alternative to thermochemical pretreatment as a means of increasing the accessibility of lignocellulose to biological attack. Successful implementation of cotreatment requires microbes that can withstand milling, while solubilizing and utilizing carbohydrates from lignocellulose. In this context, cotreatment with thermophilic, lignocellulose-fermenting bacteria has been successfully evaluated for a number of lignocellulosic feedstocks. Here, cotreatment was applied to sugarcane bagasse using monocultures of the cellulose-fermenting Clostridium thermocellum and cocultures with the hemicellulose-fermenting Thermoanaerobacterium thermosaccharolyticum. This resulted in 76 % carbohydrate solubilization (a 1.8-fold increase over non-cotreated controls) on 10 g/L solids loading, having greater effect on the hemicellulose fraction. With cotreatment, fermentation by wild-type cultures at low substrate concentrations increased cumulative product formation by 45 % for the monoculture and 32 % for the coculture. These findings highlight the potential of cotreatment for enhancing deconstruction of sugarcane bagasse using thermophilic bacteria.

Investigation and characterization of changes in potato peels by thermochemical acidic pre-treatment for extraction of various compounds

Potato peel waste (PPW) is an underutilized substrate which is produced in huge amounts by food processing industries. Using PPW a feedstock for production of useful compounds can overcome the problem of waste management as well as cost-effective. In present study, potential of PPW was investigated using chemical and thermochemical treatment processes. Three independent variables i.e., PPW concentration, dilute sulphuric acid concentration and liberation time were selected to optimize the production of fermentable sugars (TS and RS) and phenolic compounds (TP). These three process variables were selected in the range of 5–15 g w/v substrate, 0.8–1.2 v/v acid conc. and 4–6 h. Whole treatment process was optimized by using box-behnken design (BBD) of response surface methodology (RSM). Highest yield of total and reducing sugars and total phenolic compounds obtained after chemical treatment was 188.00, 144.42 and 43.68 mg/gds, respectively. The maximum yield of fermentable sugars attained by acid plus steam treatment were 720.00 and 660.62 mg/gds of TS and RS, respectively w.r.t 5% substrate conc. in 0.8% acid with residence time of 6 h. Results recorded that acid assisted autoclaved treatment could be an effective process for PPW deconstruction. Characterization of substrate before and after treatment was checked by SEM and FTIR. Spectras and micrographs confirmed the topographical variations in treated substrate. The present study was aimed to utilize biowaste and to determine cost-effective conditions for degradation of PWW into value added compounds.

Ectopic Production of 3,4-Dihydroxybenzoate in Planta Affects Cellulose Structure and Organization.

Lignocellulosic biomass is a highly sustainable and largely carbon dioxide neutral feedstock for the production of biofuels and advanced biomaterials. Although thermochemical pretreatment is typically used to increase the efficiency of cell wall deconstruction, genetic engineering of the major plant cell wall polymers, especially lignin, has shown promise as an alternative approach to reduce biomass recalcitrance. Poplar trees with reduced lignin content and altered composition were previously developed by overexpressing bacterial 3-dehydroshikimate dehydratase (QsuB) enzyme to divert carbon flux from the shikimate pathway. In this work, three transgenic poplar lines with increasing QsuB expression levels and different lignin contents were studied using small-angle neutron scattering (SANS) and wide-angle X-ray scattering (WAXS). SANS showed that although the cellulose microfibril cross-sectional dimension remained unchanged, the ordered organization of the microfibrils progressively decreased with increased QsuB expression. This was correlated with decreasing total lignin content in the QsuB lines. WAXS showed that the crystallite dimensions of cellulose microfibrils transverse to the growth direction were not affected by the QsuB expression, but the crystallite dimensions parallel to the growth direction were decreased by ∼20%. Cellulose crystallinity was also decreased with increased QsuB expression, which could be related to high levels of 3,4-dihydroxybenzoate, the product of QsuB expression, disrupting microfibril crystallization. In addition, the cellulose microfibril orientation angle showed a bimodal distribution at higher QsuB expression levels. Overall, this study provides new structural insights into the impact of ectopic synthesis of small-molecule metabolites on cellulose organization and structure that can be used for future efforts aimed at reducing biomass recalcitrance.

Enhanced Production of Clean Fermentable Sugars by Acid Pretreatment and Enzymatic Saccharification of Sugarcane Bagasse

Sugarcane bagasse (SCB), an agro-industrial byproduct generated by a sugar mill, holds a substantial carbohydrate content of around 70 wt.%, comprising cellulose and hemicellulose. Saccharification plays a pivotal role in the conversion of SCB into second-generation (2G)-ethanol and valuable compounds, which is significantly aided by thermochemical pretreatments. In this study, SCB underwent diluted sulfuric acid pretreatment (2% H2SO4, 80 rpm, 200 °C, 20 min), resulting in the removal of 77.3% of the xylan. The hemicellulosic hydrolysate was analyzed to identify the sugars and degraded products acting as microbial inhibitors. The acid hydrolysate showed a xylose yield of 68.0% (16.4 g/L) and a yield of 3.8 g/L of acetic acid. Afterward, the hemicellulosic hydrolysate was concentrated 2.37 times to obtain a xylose-rich stream (39.87 g/L). The sequential detoxification, employing calcium oxide and activated carbon, removed the inhibitory compounds, including acetic acid, while preserving the xylose at 38.10 g/L. The enzymatic saccharification of cellulignin at 5% and 10% of the total solids (TSs) yielded comparable reducing sugar (RS) yields of 47.3% (15.2 g/L) and 47.4% (30.4 g/L), respectively, after 96 h, employing a 10 FPU/g enzyme loading of Cellic® CTec3 (Novozymes Inc. Parana, Brazil). In summary, these findings outline an integrated green chemistry approach aimed at addressing the key challenges associated with pretreatment, concentration, detoxification, and enzymatic hydrolysis to produce fermentable sugars.

Alkali, thermal, or thermo-alkali pre-treatment to improve the anaerobic digestion of poly(lactic acid)?

Replacing petroleum-based plastics with biodegradable polymers is a major challenge for modern society especially for food packaging applications. To date, poly(lactic acid) represents 25 % of the total biodegradable plastics and it is estimated that, in the future, it could become the main contributor to the biodegradable plastics industry. Anaerobic digestion is an interesting way for the poly(lactic acid) end of life, even if its biodegradability is limited in mesophilic conditions. The aims of this study were to identify the best pre-treatment for maximizing the methane yield, minimizing the anaerobic digestion duration and limiting residual plastic fragments in the digestate. A systematic comparison was carried out between thermal, chemical, and thermo-chemical pre-treatment. Pre-treatment with 4 M KOH for 48 h at 35°C was effective in improving the mesophilic anaerobic digestion of the poly(lactic acid). Such pre-treatment allows obtaining 90 % of the theoretical methane potential, in 24 - 30 days. Importantly, such pre-treatment completely solubilized the poly(lactic acid), leaving no solid residues in the digestate. In addition, using KOH permits to avoid the sodication of the soil due to the digestate application as fertilizer.

Maximizing fermentable feedstocks from Camellia oleifera seed oil extraction residues: Green pretreatment and enzymatic hydrolysis for effective valorization

This study aimed to convert wastes generated during the extraction of oil from Camellia oleifera seeds, including the fruit shell (COFS) and seed cake (COSC), into fermentable feedstocks using pretreatment and enzymatic hydrolysis processes. The application of a green acid catalyst in the thermochemical pretreatment of the COFS and COSC mixture yielded the highest sugar of 28 g/L. Solid-state fermentation (SSF) was conducted on-site using various waste biomass substrates to produce enzymes for the saccharification process. This study found that COFS was the ideal substrate for generating SSF enzymes capable of breaking down lignocellulosic biomass. A novel enzymatic hydrolysis strategy was developed to minimize water consumption and enhance substrate utilization efficiency. By fine-tuning the enzymatic hydrolysis process, an additional sugar of 20.58 g/L was achieved using thermochemically pretreated solid residues and SSF enzymes. Standard techniques were used to analyze the raw materials, residual solids, and hydrolysates to assess the efficiency of each processing step. In general, the use of SSF enzymes and green pretreatment methods, reduction of water consumption in the process, and implementation of an efficient biomass utilization approach, enhance the overall efficiency and eco-friendliness of this study.

Statistical optimization of thermo-chemical pretreatment of elephant grass for efficient delignification and enzymatic saccharification

Statistical optimization of thermo-chemical pretreatment of elephant grass for efficient delignification and enzymatic saccharification

Thermochemical Pretreatment for Improving the Psychrophilic Anaerobic Digestion of Coffee Husks

Psychrophilic anaerobic digestion emerges as an appealing integrated solution for the management of agricultural waste, particularly for farmers in regions where the average temperature does not exceed 26 °C, as seen in coffee cultivation. Therefore, this study seeks to assess the biomethane potential of thermochemical-treated coffee husk through psychrophilic anaerobic digestion (C3-20 °C-w/pretreatment). To examine its viability, outcomes were compared with reactors operating at both mesophilic (C1-35 °C) and psychrophilic (C2-20 °C) conditions, albeit without the use of pretreated coffee husk. The C3-20 °C-w/pretreatment test demonstrated a 36.89% increase (150.47 NmL CH4/g VS; 161.04 NmL CH4/g COD), while the C1-35 °C test exhibited a 24.03% increase (124.99 NmL CH4/g VS; 133.77 NmL CH4/g COD), both in comparison to the C2-20 °C test (94.96 NmL CH4/g VS; 101.63 NmL CH4/g COD). Notably, the C3-20 °C-w/pretreatment trial yielded superior outcomes, accompanied by an associated energy output of 3199.25 GWh/year, sufficient to meet the annual energy demands of 494 residences. This marks an increase of 83 and 182 million residences compared to the mesophilic and psychrophilic AD of CH without pretreatment, respectively.

Production of Medium Chain Length Polyhydroxyalkanoate from Waste Cannabis sativa Biomass

This works aims to evaluate a process to convert residual medical Cannabis sativa stalks into medium chain length polyhydroxyalkanoate (mcl-PHA), using chemical pretreatment and enzymatic hydrolysis to obtain sugars as a carbon source for a fermentation process with Pseudomonas aeruginosa. Chemical composition analysis revealed a content of structural polysaccharides of 57.64%. Thermochemical pretreatments with 2% sulfuric acid or 2% sodium hydroxide were capable of partially removing hemicellulose and lignin, as well as increasing cellulose crystallinity. Pretreated biomass was subjected to hydrolysis using commercial cellulase cocktails Celluclast® 1.5 L and Cellic® CTec3. Acid pretreatment showed an adverse effect on hydrolysis yield of holocellulose, decreasing to 39.5%; compared to 44.4% of untreated biomass. Alkaline pretreatment increased degree of hydrolysis up to 73.3%. Shake flask fermentation of hydrolysate with Pseudomonas aeruginosa produced cell growth of 1.65 g/L and a mcl-PHA titer of 0.41 g/L. Extracted polymer presented characteristic FTIR bands for PHAs, glass transition temperature of − 50.8 °C, melting temperature of 48.9 °C, possibly allowing its use in the biomedical industry. The developed process represents a potential way to valorize Cannabis waste stalks, using alkaline pretreatment, enzymatic hydrolysis with Celluclast® 1.5 L and fermentation with Pseudomonas aeruginosa. Further work should focus on improving yield of the obtained polyhydroxyalkanoate in fermentation, in order to improve industrial feasibility of the entire process and, in turn, increasing revenue of the medical Cannabis industry.Graphical

Impact of Waste Cooking Oils Addition on Thermophilic Dry Co-Digestion of Wheat Straw and Horse Manure for Renewable Energy Production in Two Stages.

Anaerobic co-digestion of waste wheat straw and horse manure in two steps was revealed as a promising option for renewable energy production in the form of hydrogen and methane. Addition of waste cooking oils, disposal of which could cause damage to health or the environment, as a third substrate for digestion, is suggested as an approach not only to help handle the increasing volume of food waste worldwide but also to improve process performance. In the present study, waste cooking oil, in a concentration of 5%, appeared to be a positive modulator of anaerobic digestion with the production of hydrogen and did not lead to inhibition of the hydrolysis phase. The overall efficiency of the two-stage anaerobic digestion of the mixture, which contains mainly lignocellulose waste, is positively dependent on thermochemical pretreatment with the alkali reagent (Ca(OH)2), but elevated temperature (55 °C) and cooking oil addition revealed the opportunity to omit the pre-treatment step. Nevertheless, the overall energy production was lower due to the methane production step. However, the addition of waste cooking oils to the process in which lig-nocellulose is not pretreated (V3) led to an increase in the methane production and energy yield compared to V1. The anaerobic digestion of lignocellulosic waste is a complex process and comprises successive degradation pathways and syntrophic microbial associations' activities, so the division in two reactors ensured suitable conditions for the microorganisms residing in each of them. In this study, along with the production of hydrogen and methane and the separation of the hydrolysis and methanogenesis stages, utilization of agriculture- and kitchen-generated wastes was realized in the context of waste-to-energy sustainable production methods.

Effects of different thermal and thermochemical pretreatments on the anaerobic digestion of algal biomass cultivated in urban wastewater and collected with and without chemical coagulants

Algal biomass cultivated in wastewater treatment systems is a promising feedstock for biogas production through anaerobic digestion. However, its rigid cell wall inhibits the hydrolysis of intracellular substances and limits its anaerobic digestibility. To improve anaerobic biodegradability, this study investigated the effects of different thermal and thermochemical pretreatments on the performance of anaerobic digestion of the obtained biomass. High-rate algal ponds fed with UASB effluent treating domestic sewage were used to grow algal biomass. Two methods were used for biomass harvesting: a physical method, through filtration, and a physico-chemical method, using coagulants, Tanfloc SL and Aluminum Sulfate (Al2(SO4)3). Three types of biomasses were obtained, one without coagulant (AB-P), one with Tanfloc (AB-T), and one with Al2(SO4)3 (AB-AS), which were subjected to different thermal and thermochemical pretreatments. Fourier-transform infrared spectroscopy analysis confirmed the effectiveness of the pretreatment methods, showing modifications in the structures of proteins, carbohydrates, and lipids in the microalgae cells. The alkaline thermochemical pretreatment (90 °C-3 h-pH 11) of AB-AS resulted in higher organic matter solubilization, with a 32 % increase in soluble COD. This pretreatment also resulted in the highest biogas yield, producing 460.64 mL CH4.gVS−1, with a 229 % increase, and the highest maximum production rate, with Rmax = 78.98 mL CH4.gVS−1.day−1. Acidic thermochemical pretreatments that resulted in biomass with pH ≤ 4.2 inhibited biogas production. In terms of energy, the best pretreatment was 78 °C-7 h on AB-P, with an EROI of 2.20, which demonstrates a surplus of energy. These findings underscore the potential for optimizing the anaerobic digestibility of algal biomass, thus contributing to more efficient and sustainable biogas production.

Comparative study of chemical and enzymatic pre-treatments of Kitchen waste (KW) to generate fermentable sugars for the production of polyhydroxyalkanoates (PHA)

Kitchen waste (KW) production is anticipated to rise because of accelerated urban and economic growth, particularly in Asian nations. Therefore, applications/recycling of KW should be explored for its effective utilization to generate a sustainable source of energy that will ultimately avoid massive economic and energy losses. The main goal of this study was to investigate the combinational effect of thermochemical and enzymatic pre-treatment on synthetic KW to enhance the release of fermentable sugars for the synthesis of value-added products such as polyhydroxyalkanoates (PHAs). The thermochemical pre-treatment of KW samples was performed using 4 N HCl, 4 N H2SO4, and 4 N NaOH at a concentration of 0–30% (v/v), 30–100 °C for 0–120 min. Furthermore, to enhance the total fermentable sugars, variable enzyme dosages were added after acidic or alkaline pre-treatments (0–1% v/v α-amylase and 0–1% v/v amyloglucosidase-AMG) while maintaining a constant pH 5, temperature 50 °C, and time 30 min. Pre-treatment of KW with acid (15% v/v 4 N HCl in water) at temperature 100 °C, followed by enzymatic hydrolysis, i.e., 0.6% (v/v) α-amylase and 0.4% (v/v) amyloglucosidase (at pH 5, 50 0C and 60 min) resulted in the maximum concentration of fermentable reducing sugars (46.13 g/L) in the hydrolysate.

Dry and Hydrothermal Co-Carbonization of Mixed Refuse-Derived Fuel (RDF) for Solid Fuel Production

The present study aims to test several conditions of the thermochemical pretreatment of torrefaction and carbonization to improve the physical and combustible properties of the Portuguese RDF. Therefore, two different types of RDF were submitted alone or mixed in 25%, 50%, and 75% proportions to dry carbonization processes in a range of temperatures between 250 to 350 °C and residence time between 15 and 60 min. Hydrothermal carbonization was also carried out with RDF samples and their 50% mixture at temperatures of 250 and 300 °C for 30 min. The properties of the 51 chars and hydrochars produced were analyzed. Mass yield, apparent density, proximate and elemental analysis, ash mineral composition, and higher heating value (HHV), among others, were determined to evaluate the combustion behavior improvement of the chars. The results show that after carbonization, the homogeneity and apparent density of the chars were increased compared to the raw RDF wastes. The chars and hydrochars produced present higher HHV and lower moisture and chlorine content. In the case of chars, a washing step seems to be essential to reduce the chlorine content to allow them to be used as an alternative fuel. In conclusion, both dry and wet carbonization demonstrated to be important pretreatments of the RDF to produce chars with improved physical and combustion properties.