Thermochemical Pretreatment Method Research Articles

A Critical Review on Water Overconsumption in Lignocellulosic Biomass Pretreatment for Ethanol Production through Enzymic Hydrolysis and Fermentation

Global demand for renewable and sustainable energy fostered the considerable development of biomass-to-ethanol valorization strategies. Thermochemical pretreatment methods have been proposed to render biomass more amenable to enzymatic and microbial digestion. However, the efforts have not led to its industrial-scale worldwide realization. One of the obstacles to commercialization could be related to water overconsumption, as excessive water washing of the pretreated slurry is often performed to remove inhibitory compounds and residual chemicals after biomass pretreatment. Only increasing solid loading for biomass pretreatment results in ineffective pretreatment performance, more inhibitors formation, and high viscosity, which in turn necessitates the water washing step. A number of physicochemical and biological methods are applied to detoxify the acid-pretreated liquid fraction for enzymatic hydrolysis and fermentation. Among them, alkaline neutralization and liquid–liquid extraction are preferred because of their simple operation and low cost. Seemingly, recycling black liquor for alkali pretreatment offers a pathway to reduce water and chemical consumption, but alkali replenishment and inhibitor accumulation significantly weaken this technology. Interestingly, quite a few studies have removed the water washing and even solid–liquid separation steps after (liquid hot water, Tween 40, and CaO) pretreatment. There is still much room for future studies to render biomass pretreatment more feasible in terms of economic and environmental points of view. This review provides a deep understanding of wastewater generation during biomass upgrading and discusses the solutions to reduce water consumption critically.

Partially Oxidative Torrefaction of Woody Biomass Pellets: Burning Behaviour and Emission Analysis

Non-conventional torrefaction under partially oxidative conditions is an emerging cost-effective thermochemical pre-treatment method to improve the quality of biomass for energy applications. The literature lacks data on the combustion of biomass torrefied under oxygen-deficient atmosphere with actual reactor conditions (inevitable non-uniformities in the thermal environment). In this work, a dual mode fixed-bed biomass (torrefaction) reactor and combustor was operated on Australian biomass pellets, to torrefy the fuels at 275 °C for 30 min using partially oxidative atmosphere (O2: 5 vol%, balance N2) and then to combust them. Combustion behaviour with a particular focus on gaseous emissions of raw, blended (25% torrefied), and torrefied (100%) pellet fuels in a batch-type combustor was investigated. The decomposition behaviour was analysed in a thermogravimetric analyser to understand the impact of biomass constituents on the direct combustion of the tested samples. Results indicate that unlike the combustion of raw biomass, the fuels torrefied under partially oxidative conditions burned 45% faster, attained high packed-bed temperatures (1382 °C) and exhaust gas temperatures (657 °C) then latter (bed: 1128 °C, exhaust: 574 °C) at similar airflow. Additionally, 100% torrefied pellets emitted 38% less NOx compared to raw biomass pellets. However, low CO values for torrefied biomass were attained at higher primary airflows compared to raw. The combustion of 100% torrefied biomass in a fixed-bed was dominated by both flaming and smouldering phases with a modified combustion efficiency (MCE) value of 91%, whereas raw biomass combustion occurred in flaming phase with an MCE value of 98% at same airflow (0.35 kg·m−2·s−1). The outcomes of this work provide useful insights into the viability of using biomass fuels torrefied under partially oxidative conditions alongside other industrial processes generating (waste) heat and flue gases.

Improvement of fermentable sugar extraction from hazelnut shells through microwave assisted dilute acid pretreatment

The most effective method for producing fermentable sugars (FSs) from biomass is thermochemical pretreatment assisted by enzymatic hydrolysis. However, the enzymatic hydrolysis-assisted thermochemical pretreatment method is limited by the formation of fermentation inhibitors, and it is time-consuming. There is growing interest in using a microwave (MW) pretreatment due to its uniform and rapid heating. This study aimed to determine, perform data-driven modeling, and optimize the effect of MW combined with dilute acid pretreatment (MW-DA) on the production of FSs from hazelnut shells. An artificial neural networks (ANNs) model based on Box-Behnken Design (BBD) was the best model described for fermentable sugar extraction (FSE). Optimization via BBD-based ANNs model was carried out for an acid concentration of 0.5 to 2% (w/w), a pretreatment time of 5 to 25 min, a pressure of 5 to 15 bar, and a temperature of 120 to 160 °C. The optimized FSE was estimated at 374 mg/g (81.4% conversion efficiency), with a severity factor of 3.61 under 1.58% H2SO4 for 13 min at 160 °C and 8.5 bar. Using the MW-DA pretreatment process lowered the costs significantly due to the decreases in acid concentration and pretreatment time.

Microalgae and Cyanobacteria Biomass Pretreatment Methods: A Comparative Analysis of Chemical and Thermochemical Pretreatment Methods Aimed at Methane Production

Anaerobic digestion of microalgae and cyanobacteria was first proposed as a destination for algal biomass accumulated on stabilization ponds since it could not be disposed of directly in the environment. Now, the versatility of algal biomass makes them a suitable candidate to produce biofuels and other biomolecules in biorefineries. Anaerobic digestion of biomass is advantageous because it does not require the extraction of specific cellular constituents or drying of the biomass. Nevertheless, challenges remain regarding biomass concentration and their resistant cell walls, which are factors that could hamper methane yield. Many pretreatment methods, including chemical and thermochemical, have been proposed to break down the complex polymers present on the cell wall into smaller molecules. Unfortunately, the relationship between biomass solubilization and methane yield is not well defined. This article intends to review the anaerobic digestion of algal biomass and the role of chemical and thermochemical pretreatments in enhancing methane production. Several pretreatment conditions selected from the scientific literature were compared to verify which conditions actually improve methane yield. The severity of the selected pretreatments was also assessed using the combined severity factor. Results suggest that thermochemical pretreatment in less severe conditions is the most efficient, leading to a greater increase in methane yield. Only enzymatic pretreatments and some thermal pretreatments result in a positive energy balance. The large-scale implementation of pretreatment methods requires technological innovations to reduce energy consumption and its integration with other processes in wastewater treatment plants.

Modeling of thermo-chemical pretreatment of yam peel substrate for biogas energy production: RSM, ANN, and ANFIS comparative approach

The modeling and optimization of the substrate treatment process in biogas energy production from yam peel substrates via anaerobic digestion was the purpose of this work. Thermo-chemical pretreatment method was used in the substrate treatment. The instrumental analysis of the substrate was investigated using FTIR and SEM. Central composite design was used in the design of experiment and intelligent modeling of the substrate treatment in the biogas production via adaptive neuro-fuzzy inference systems (ANFIS), artificial neural network (ANN), and response surface methodology (RSM). The kinetics of the anaerobic digestion process was studied using five kinetic models. The result indicated that among the three process parameters investigated, temperature has the most significant effect on the substrate pretreatment. The instrumental analysis showed that the thermo-chemical modification of the substrate resulted in the transformation of its bond structure and the solubilization of the hemicelluloses molecules. ANFIS, ANN, and RSM models were efficient in modeling the anaerobic digestion process with correlation coefficient of 0.9997, 0.9997 and 0.9887, respectively showing good agreement between the experimental and predicted biogas yield. Further statistical error indices involving HYBRID (ANFIS=0.3180, ANN=0.3207, and RSM=11.157), RMSE (ANFIS=0.3359, ANN=0.8235, and RSM=4.969), and ARE (ANFIS=0.3068, ANN=0.3075, and RSM=1.5756) depicted the ANFIS as being marginally better than the ANN in simulating and modeling the anaerobic digestion. Optimization of the ANFIS model yielded a biogas volume of 356.24 ml at concentration, time, and temperature of 0.04 N, 60 s and 80 °C, respectively. The kinetics of the cumulative biogas production was described by the Modified Logistics, Transference and the Logistics models. The purification of the biogas by scrubbing gave about 92% methane gas. The sediments from the digestion with low C/N ratio could be used as manure and soil conditioner in agriculture.

The effect of various thermochemical pretreatment methods on the biomethanisation of hemp (Cannabis sativa) hurd and kinetic analysis

The effect of various thermochemical pretreatment methods on the biomethanisation of hemp (Cannabis sativa) hurd and kinetic analysis

Potential Application of Pin-to-Liquid Dielectric Barrier Discharge Structure in Decomposing Aqueous Phosphorus Compounds for Monitoring Water Quality.

Here, we proposed a pin-to-liquid dielectric barrier discharge (DBD) structure that used a water-containing vessel body as a dielectric barrier for the stable and effective treatment of aqueous solutions in an open atmosphere. To obtain an intense pin-to-liquid alternating current discharge using a dielectric barrier, discharge characteristics, including the area and shape of a ground-plate-type electrode, were investigated after filling the vessel with equivalent amounts of water. Consequently, as the area of the ground electrode increased, the discharge current became stronger, and its timing became faster. Moreover, we proposed that the pin-to-liquid DBD reactor could be used to decompose phosphorus compounds in water in the form of phosphate as a promising pretreatment method for monitoring total phosphorus in water. The decomposition of phosphorus compounds using the pin-to-liquid DBD reactor demonstrated excellent performance—comparable to the thermochemical pretreatment method—which could be a standard pretreatment method for decomposing phosphorus compounds in water.

Response surface methodology (RSM) for optimization of thermochemical pretreatment method and enzymatic hydrolysis of deodar sawdust (DS) for bioethanol production using separate hydrolysis and co-fermentation (SHCF)

In the present work, Cedrus deodara (deodar) sawdust abbreviated as DS was subjected to thermochemical pretreatment followed by enzymatic hydrolysis and fermentation for bioethanol production. Response surface methodology (RSM) based on central composite design (CCD) tool was employed to optimize dilute acid pretreatment method (at 121 °C temperature and 1-bar pressure) and enzymatic hydrolysis processes. Factorial design of experiments used chemical concentration, incubation time, and biomass loading to optimize thermochemical pretreatment method using dilute acid concentration. Maximum total reducing sugar (TRS) concentration (13.62 g/L) was obtained using optimized conditions (1.5% HCl concentration, 10% biomass loading and 30-min incubation time). These significant studies were subjected to optimize enzymatic hydrolysis process using the CCD tool of the RSM where cellulase loading, xylanase loading, pH, and temperature were taken into consideration. TRS concentration obtained was 29.20 g/L after 48 h with enzyme loading of 9 U/g biomass, each for cellulase and xylanase enzyme at pH 5.0 and 30 °C temperature. Fermentation conditions for enzymatically hydrolyzed DS revealed that at 10% (v/v) yeast inoculum concentrations (Saccharomyces cerevisiae (MTCC-36) and Pichia stipitis (NCIM-3498)) after 24-h fermentation time and pH 5.0, bioethanol concentration was 14.25 g/L with 95.68% conversion efficiency. Characterization studies for native and pretreated DS by Fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction (PXRD), and scanning electron microscopy (SEM) analyses revealed delignification rate of 30.93% of DS biomass under optimized thermochemical pretreatment conditions. Statistical studies for optimization of pretreatment and enzymatic hydrolysis for bioethanol production stated DS sawdust (a furniture industry waste) as a potential substrate for biofuel production.

Dilute acid pretreatment of pine needles of Pinus roxburghii by response surface methodology for bioethanol production by separate hydrolysis and fermentation

Bioethanol from lignocellulosic biomass is environment friendly and a renewable source of energy which can serve as alternative to fossil fuels particularly in transport sector. The present study investigates the efficiency of bioethanol production from pine needles of Pinus roxburghii (PNPR) using thermochemical pretreatment method. The PNPR biomass was subjected to thermochemical pretreatment using dilute concentrations (0.5%, 1%, 1.5%, and 2%) of HCl at a biomass loading of 5%, 10%, and 15%. Maximum reducing sugar (RS) yield of 96 mg/g biomass using one variable at a time (OVAT) approach was achieved using 1% HCl and a biomass loading of 5% (w/v). Central composite design (CCD) tool of response surface methodology (RSM) enhanced the RS yield to 0.2 g/g biomass under the optimized conditions. FTIR analysis revealed reduction in the lignin, cellulose, and hemicellulose content of PNPR biomass during the pretreatment process. Enzymatic hydrolysis was attempted using combinations of cellulase, xylanase, and pectinase commercial enzymes and the highest RS yield obtained was 0.43 g/g biomass. The hydrolysate was then fermented by Saccharomyces cerevisiae (MTCC-36) as well as by a combination of Saccharomyces cerevisiae (MTCC-36) and Pichia stipitis (NCIM-3498) to produce bioethanol. With a conversion efficiency of 90%, maximum bioethanol yield of 0.144 g/g biomass after 24 h was obtained from separate hydrolysis and fermentation (SHF) using combined cultures of S. cerevisiae (MTCC-36) and P. stipitis (NCIM-3498).

Evaluation of chemical, thermobaric and thermochemical pre-treatment on anaerobic digestion of high-fat cattle slaughterhouse waste

This work aimed to enhance the anaerobic digestion of fat-rich dissolved air flotation (DAF) sludge through chemical, thermobaric, and thermochemical pre-treatment methods. Soluble chemical oxygen demand was enhanced from 16.3% in the control to 20.84% (thermobaric), 40.82% (chemical), and 50.7% (thermochemical). Pre-treatment altered volatile fatty acid concentration by −64% (thermobaric), 127% (chemical) and 228% (thermochemical). Early inhibition was reduced by 20% in the thermochemical group, and 100% in the thermobaric group. Specific methane production was enhanced by 3.28% (chemical), 8.32% (thermobaric), and 8.49% (thermochemical) as a result of pre-treatment. Under batch digestion, thermobaric pre-treatment demonstrated the greatest improvement in methane yield with respect to degree of pre-treatment applied. Thermobaric pre-treatment was also the most viable for implementation at slaughterhouses, with potential for heat-exchange to reduce pre-treatment cost. Further investigation into long-term impact of pre-treatments in semi-continuous digestion experiments will provide additional evaluation of appropriate pre-treatment options for high-fat slaughterhouse wastewater.

Solar Torrefaction of Solid Olive Mill Residue

Torrefaction is a thermochemical pretreatment method for improving fuel characteristics of biomass. The process is conducted between 200 and 300 °C under inert atmosphere. The relatively low process temperature of torrefaction makes the use of solar energy suitable with low costs. In this study, solid olive mill residue (SOMR) was used to test the feasibility of using solar energy in the torrefaction process. SOMR is an agricultural waste obtained from olive oil extraction, and it is mainly produced in the Mediterranean region, which has high solar energy potential. In this study, the torrefaction of SOMR was conducted by concentrating solar energy with a parabolic dish concentrator, at 250 °C for 10 min. The fuel properties of solar torrefaction products were compared with raw SOMR. Solar torrefaction yielded a deoxygenated solid fuel with increased carbon content and higher heating value (HHV), similar to torrefaction.

Wet Explosion: a Universal and Efficient Pretreatment Process for Lignocellulosic Biorefineries

Lignocellulosic biomass resources especially agricultural and forests residues, perennial crops, farm wastes, and the organic fraction of municipal solid waste hold significant potential for the widespread production of sustainable fuels, chemicals, and bioproducts worldwide. For biochemical conversion processes, deconstruction of lignocellulosic biomass into its components (cellulose, hemicellulose, and lignin) for further microbial conversion has been a major challenge due to the recalcitrant nature of lignocellulose. Thus pretreatment is prerequisite for efficient hydrolysis of lignocellulose and cost for such treatment is currently about one third of the overall processing costs in a cellulosic biorefinery. Thus, the development of a more efficient and cost-effective pretreatment method is crucial for the commercialization of lignocellulosic biorefineries. Wet explosion (WEx), a thermochemical pretreatment method with additional features of oxygen addition and explosive decompression, can be adjusted to different biomass feedstock and to subsequent bio-catalytic and microbial processes. The WEx pretreatment method has been successfully applied in combination with both microbial fermentation and anaerobic digestion processes using both agricultural and forest residues as well as manure fibers. Steam explosion, represents a related process to WEx pretreatment where high pressure is used but no oxygen is added. This process has been tested in demonstration scale while WEx is on its way to commercialization. Presented here is a summary of the basic concepts and parameters involved in WEx pretreatment.

The pretreatment of corn stover with Gloeophyllum trabeum KU-41 for enzymatic hydrolysis.

BackgroundPretreatment is an essential step in the enzymatic hydrolysis of biomass for bio-ethanol production. The dominant concern in this step is how to decrease the high cost of pretreatment while achieving a high sugar yield. Fungal pretreatment of biomass was previously reported to be effective, with the advantage of having a low energy requirement and requiring no application of additional chemicals. In this work, Gloeophyllum trabeum KU-41 was chosen for corn stover pretreatment through screening with 40 strains of wood-rot fungi. The objective of the current work is to find out which characteristics of corn stover pretreated with G. trabeum KU-41 determine the pretreatment method to be successful and worthwhile to apply. This will be done by determining the lignin content, structural carbohydrate, cellulose crystallinity, initial adsorption capacity of cellulase and specific surface area of pretreated corn stover.ResultsThe content of xylan in pretreated corn stover was decreased by 43% in comparison to the untreated corn stover. The initial cellulase adsorption capacity and the specific surface area of corn stover pretreated with G. trabeum were increased by 7.0- and 2.5-fold, respectively. Also there was little increase in the cellulose crystallinity of pretreated corn stover.ConclusionG. trabeum has an efficient degradation system, and the results indicated that the conversion of cellulose to glucose increases as the accessibility of cellulose increases due to the partial removal of xylan and the structure breakage of the cell wall. This pretreatment method can be further explored as an alternative to the thermochemical pretreatment method.

Effects of thermo-chemical pre-treatment on anaerobic biodegradability and hydrolysis of lignocellulosic biomass

The effects of different thermo-chemical pre-treatment methods were determined on the biodegradability and hydrolysis rate of lignocellulosic biomass. Three plant species, hay, straw and bracken were thermo-chemically pre-treated with calcium hydroxide, ammonium carbonate and maleic acid. After pre-treatment, the plant material was anaerobically digested in batch bottles under mesophilic conditions for 40 days. From the pre-treatment and subsequent anaerobic digestion experiments, it was concluded that when the lignin content of the plant material is high, thermo-chemical pre-treatments have a positive effect on the biodegradability of the substrate. Calcium hydroxide pre-treatment improves the biodegradability of lignocellulosic biomass, especially for high lignin content substrates, like bracken. Maleic acid generates the highest percentage of dissolved COD during pre-treatment. Ammonium pre-treatment only showed a clear effect on biodegradability for straw.