Hot Compressed Water Pretreatment Research Articles

The influence of thermal treatment on recirculating two phase anaerobic digestion system

Recirculated two-phase anaerobic digestion (RTAD) is a recent technique to improve biogas production. Recirculating the effluent of two-phase anaerobic system has a methanogens invasion risk to dark fermentation. Hot compressed water is possible to reduce the methanogens invasion. The objectives of this study are identifying the effect of hot compressed water pretreatment on RTAD and evaluating the fermentation system during the change of hydraulic retention time and effluent recirculation ratio. The RTAD system was built and operated with 4 different conditions, those are hydraulic retention time 2-day (HRT 2d), HRT 3d, Effluent Ratio 1:5 (R1:5) and R2:5. The result shows that the shorter HRT increase the biogas production. The pH in the reactor is more stable after the recirculation process. In bioreactor performance, the hot compressed water treatment increased the COD removal at all conditions. The highest COD removal achieved at condition of HRT 2-day with removal up to 94.5%. The system that using hot compressed water treatment has the higher energy potential at HRT 2-day, R 1:5 and R 2:5 compared with no hot compressed water treatment.

Effect of Natural Buffer on Biohydrogen Production

Hydrogen is the promising ideal energy carrier with no emission but water on its combustible in the next generation. Hydrogen production using biological methods is greener than other methods using fossil fuel. One of the major factors affecting the operation of biohydrogen production is pH level in bioreactors. Restrain of declining pH is expected to increase hydrogen production. Pretreatment is one key factor in successful biohydrogen fermentation using mixed microbes. This study aims to investigate the natural buffer effect on biohydrogen using hot compressed water pretreatment. This batch fermentation experiment was operated in a 110 mL glass reactor with 3.75 g/L glucose as substrate. Mixed culture was obtained from cow dung compost treated with hot compressed water pretreatment at 150 ºC, 0.5 MPa for 40 minutes. Fine dried eggshell powder and calcinated eggshell were added with 1 g/L, 3 g/L, and 5 g/L concentrations as buffer agents. The result showed that the addition of 1 g/L eggshell obtained the highest hydrogen production rate of 0.92 mol H2/mol glucose. Butyric acid and acetic acid are recognized as an indicator of hydrogen production and the Butyric/Acetic molar ratio over 2.6 as efficient biohydrogen fermentation. The highest B/A ratio in this experiment was 4.62 on 3g/L addition of eggshell powder.

Hot Compressed Water Pretreatment and Surfactant Effect on Enzymatic Hydrolysis Using Agave Bagasse

Agave bagasse is a residual biomass in the production of the alcoholic beverage tequila, and therefore, it is a promising raw material in the development of biorefineries using hot compressed water pretreatment (hydrothermal processing). Surfactants application has been frequently reported as an alternative to enhance monomeric sugars production efficiency and as a possibility to reduce the enzyme loading required. Nevertheless, the surfactant’s action mechanisms in the enzymatic hydrolysis is still not elucidated. In this work, hot compressed water pretreatment was applied on agave bagasse for biomass fractionation at 194 °C in isothermal regime for 30 min, and the effect of non-ionic surfactants (Tween 20, Tween 80, Span 80, and Polyethylene glycol (PEG 400)) was studied as a potential enhancer of enzymatic saccharification of hydrothermally pretreated solids of agave bagasse (AGB). It was found that non-ionic surfactants show an improvement in the conversion yield of cellulose to glucose (100%) and production of glucose (79.76 g/L) at 15 FPU/g glucan, the highest enhancement obtained being 7% regarding the control (no surfactant addition), using PEG 400 as an additive. The use of surfactants allows improving the production of fermentable sugars for the development of second-generation biorefineries.

Biohydrogen production improvement using hot compressed water pretreatment on sake brewery waste

Most hydrogen is derived from fossil fuels. Therefore, more environmentally friendly methods for hydrogen production have been investigated. The present report describes a hot compressed water (HCW) pretreatment to increase hydrogen production using sake lees, which is an industrial waste of sake production. The inoculum is obtained from treated biogas slurry. The temperatures of HCW are 130 (0.3 MPa), 150 (0.5 MPa), and 180 °C (0.8 MPa) for 15–120 min. Gas production was analyzed using gas chromatography; fermentation liquid analyses were performed using HPLC. The modified Gompertz model was used to determine hydrogen potential, lag time, and production rate. Results show an increase in the degradation of sake lees with longer holding time and higher temperature. Total sugar and organic acids also are influenced by HCW pretreatment. The maximum hydrogen yield was obtained at 130 °C for 60 min with the result 112.07 mL H2/g COD. The HCW pretreatment successfully decreased the lag phase of biohydrogen production and increased the degree of acidification. Clostridium butyricum, C. acetobutylicum, and other Clostridium sp. were identified in all samples, while Pantoea agglomerans was detected in two samples.

A combined cellulosic and starchy ethanol and biomethane production with stillage recycle and respective cost analysis

To minimize waste generation in ethanol production from starchy and cellulosic feedstocks, the feasibility of stillage recycle to fermentation process was studied. For sugarcane bagasse (SCB) and palm empty fruit bunch (EFB), optimal hot-compressed water (HCW) pretreatment and enzyme hydrolysis (10% wt) gave the highest total reducing sugar (TRS) yields of 64.2% and 67.3%, respectively. Ethanol fermentation of SCB, EFB and fresh cassava by Saccharomyces cerevisiae TISTR5606 gave the highest yields of 0.31 g g−1, 0.40 g g−1, and 0.31 g g−1 TRS, respectively. For recycling of SCB and EFB stillage, a slight decline of ethanol yield was found while ethanol yield of cassava significantly increased from 60.8% to 89.9%. The ethanol yields from the 2nd recycle of cassava was still 10% higher than no recycle. Addition of 10%–20% v/v black liquor from lignocellulosic HCW pretreatment into anaerobic digestion system noticeably enhanced the chemical oxygen demand removal and methane production. Analysis of variable operating cost showed that stillage recycles for 20% for fresh cassava and 10% for SCB is cost-effective process for ethanol production.

Chemical-free fractionation of palm empty fruit bunch and palm fiber by hot-compressed water technique for ethanol production

The purpose of this study was to valorize oil palm empty fruit bunch (EFB) and palm fiber (PF) from palm oil mills to produce fuel ethanol. Chemical-free fractionation of EFB and PF using hot-compressed water (HCW) pretreatment at temperatures ranging from 150 to 200ºC at 30 bars and reaction times for 5, 15, 25 min was applied to remove most of hemicellulose and partial lignin fractions into liquid phase. Comparison of the effects of different commercial cellulase enzyme complexes (Accellerase 1500, Cellic® Ctec2, Cellic® Htec2 and Ctec2＋Htec2) on HCW pretreated materials were investigated. Finally, an inhibitory effect of using the whole slurry from HCW pretreatment of EFB and PF on enzyme hydrolysis and ethanol production by Saccharomyces cerevisiae TISTR5606 was studied. The finding suggested using solely solid fraction from HCW pretreatment for ethanol fermentation, otherwise some additional tannic acid, furfural and acetic acid removal steps are required to prevent the inhibition on yeast growth.

3-90-6 水熱および粉砕によるスギの糖化前処理(Session 3 バイオマス等,ポスター発表)

3-90-6 水熱および粉砕によるスギの糖化前処理(Session 3 バイオマス等,ポスター発表)

Kinetics of the Formation of Saccharides and Fermentation Inhibitors during the Hot-compressed Water Pretreatment of Cassava Residue

A mathematical description was developed for production of saccharides and fermentation inhibitors during the hot-compressed water pretreatment of cassava residue. Pretreatment was conducted at 150 °C, 160 °C, 170 °C, and 180 °C, and reaction times ranged from 0 to 70 min. The formation of saccharides and four main inhibitors (furfural (F), hydroxymethylfurfural (HMF), acetic acid, and formic acid) were studied. A model for predicting the concentrations of F and HMF (CF and CHMF, respectively) as functions of H+ concentration was established. Furthermore, kinetic models were built after introducing the hydrogen ion concentration index mi. Hydrogen ion concentration had a dramatic effect on the dissolution of pentosan but did not greatly affect the dissolution of hexosan or the degradation of hexose or pentose. Additionally, the activation energies for the formation of pentose or hexose were lower than the degradation energies. The coefficients of determination (R2) of the kinetic models for predicting the yield of the four compounds (pentose, hexose, furfural, and HMF) were higher than 0.923. These kinetic models provided a theoretical foundation and technical support for controlling the production of the main carbohydrates and fermentation inhibitors.

Hydrolysis kinetics of tulip tree xylan in hot compressed water

Lignocellulosic biomass, a promising renewable resource, can be converted into numerous valuable chemicals post enzymatic saccharification. However, the efficacy of enzymatic saccharification of lignocellulosic biomass is low; therefore, pretreatment is necessary to improve the efficiency. Here, a kinetic analysis was carried out on xylan hydrolysis, after hot compressed water pretreatment of the lignocellulosic biomass conducted at 180–220°C for 5–30min, and on subsequent xylooligosaccharide hydrolysis. The weight ratio of fast-reacting xylan to slow-reacting xylan was 5.25 in tulip tree. Our kinetic results were applied to three different reaction systems to improve the pretreatment efficiency. We found that semi-continuous reactor is promising. Lower reaction temperatures and shorter space times in semi-continuous reactor are recommended for improving xylan conversion and xylooligosaccharide yield. In the theoretical calculation, 95% of xylooligosaccharide yield and xylan conversion were achieved simultaneously with high selectivity (desired product/undesired product) of 100 or more.

Investigation of organosolv and hot-compressed water pretreatments of rice straw

Ethanol organosolv pretreatments followed by hot-compressed water pretreatments of rice straw have been investigated. The formation of monomeric and oligomeric sugar productions, degradation products, and soluble lignin in liquid fraction was analyzed. A solid to liquid ratio of 1:10 (w/w) was used for pretreatments. The organosolv pretreatment was carried out at the temperatures (170, 190, 210 °C) for (0, 30, and 60 min). Hot-compressed water pretreatment was performed at 220 °C for 15 min starting from dried solid residues recovered from organosolv pretreatments. The highest amount of dissolved lignin and xylan (oligosaccharides) in liquor was 64.6 mg/g and 0.07 % at 190 °C for 60 min, respectively. The production of sugar and dissolved lignin in liquor in hot-compressed water pretreatment was decreased with increase temperature and time, but degradation products increased. The crystallinity index of untreated and treated rice straws was calculated based on X-ray diffraction (XRD) data. The structural feature of untreated and treated rice straws was characterized by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM).

Changes in plant cell-wall structure of corn stover due to hot compressed water pretreatment and enhanced enzymatic hydrolysis.

Corn stover is a potential feedstock for biofuel production. This work investigated physical and chemical changes in plant cell-wall structure of corn stover due to hot compressed water (HCW) pretreatment at 170-190 °C in a tube reactor. Chemical composition analysis showed the soluble hemicellulose content increased with pretreatment temperature, whereas the hemicellulose content decreased from 29 to 7 % in pretreated solids. Scanning electron microscopy revealed the parenchyma-type second cell-wall structure of the plant was almost completely removed at 185 °C, and the sclerenchyma-type second cell wall was greatly damaged upon addition of 5 mmol/L ammonium sulfate during HCW pretreatment. These changes favored accessibility for enzymatic action. Enzyme saccharification of solids by optimized pretreatment with HCW at 185 °C resulted in an enzymatic hydrolysis yield of 87 %, an enhancement of 77 % compared to the yield from untreated corn stover.

Optimization of hot-compressed water pretreatment of bagasse and characterization of extracted hemicelluloses

Developing optimum treatment and separation procedures for hemicellulose components of lignocellulosic biomass could be useful in ethanol fermentation processes and obtaining pure hemicelluloses as biopolymers. Sugarcane bagasse analyses indicate that xylose is the major hemicellulose component constituting 17.7% of dry bagasse weight. In this study the effects of treatment conditions such as time, temperature and pressure on the yields of extracted hemicelluloses were studied. The optimum conditions were achieved at 180°C for 30min and 1MPa pressure, with the yield of xylose reaching to 85% and the concentrations of sugar degradation products such as HMF and furfural remaining minimal at 0.95 and 0.07g/L, respectively. Further, isolation of hemicelluloses from extracted hemicelluloses solutions was performed using Alfa Laval M20 membrane filtration system in two steps: (1) concentration of high molar mass hemicelluloses by ultrafiltration; and (2) separation of low molar mass hemicelluloses and oligomeric sugars by nanofiltration. The isolated hemicelluloses with the optimum pretreatment conditions were characterized by FT-IR and 13C NMR techniques, resulting in agreement with typical spectra of xylan-type hemicelluloses.

Rapid Recovery of Fermentable Sugars for Biofuel Production from Enzymatic Hydrolysis of Microcrystalline Cellulose by Hot-Compressed Water Pretreatment

Enzymatic hydrolysis of microcrystalline cellulose is a multistep heterogeneous reaction limited by the initial action of enzyme to produce short glucose chains, due to the presence of strong intermolecular and intramolecular hydrogen bonding networks in cellulose chains. The results in this study show that enzymatic hydrolysis of the liquid product from hot-compressed water (HCW) pretreatment of microcrystalline cellulose can be immediately converted into glucose oligomers with DPs up to 5 without incubation even at a low enzyme loading (i.e., ∼8.6 FPU/g glucan-equivalent). A high enzyme loading (i.e., ∼140 FPU/g glucan-equivalent) is able to convert all the glucose oligomers into glucose and cellobiose after 1 h incubation. Overall, the sugar recovery after HCW pretreatment can be drastically increased by up to 2 orders of magnitude, depending on enzyme loading and incubation time. Therefore, HCW pretreatment of microcrystalline cellulose is an effective pretreatment method to break hydrogen bonding net...

Evaluation of hot compressed water pretreatment and enzymatic saccharification of tulip tree sawdust using severity factors

Tulip tree sawdust was pretreated using hot compressed water with different pretreatment severities (LogR0, 3.05-5.01) by varying reaction temperatures (180-220°C) and residence time (1-30 min). It is found that the chemical composition and physicochemical properties of the pretreated products can be characterized and correlated with severity. Removal of most of the xylan and other hemicellulosic sugars from the raw material was observed at a severity of 4.5. Thus, the residual solids were recovered with increased cellulose and lignin contents. Nearly complete glucan conversion was achieved after 48 h of hydrolysis with 10 FPU/g of wet residual solid obtained above a severity of 4.8. The characteristics of the pretreated solids according to the pretreatment severity were strongly related with the glucose yield. The removal of structural barriers to the enzyme attack was the dominant factor affecting enzyme accessibility to the substrate.

Pretreatment of oil palm frond using hot compressed water: An evaluation of compositional changes and pulp digestibility using severity factors

The influence of reaction temperature (160–200°C), residence time (45–90min), and liquid–solid ratio (8–16v/w) on oil palm frond (OPF) pre-treated with hot compressed water (HCW) was evaluated using severity factors. Effect of the process parameters studied on pulps composition and digestibility were found to be complex. The results revealed that digestibility could not be predicted merely according to composition. Severity factor was correlated with compositional changes and digestibility with good R-squared values at varied liquid–solid ratios (8–16v/w), but not with overall glucose yield. HCW pretreatment significantly improved the overall glucose yield up to 83.72% with severity of 3.31 and liquid–solid ratio of 8.0 compared to untreated raw OPF which only recorded an overall glucose yield of 30.97%. HCW is therefore an effective method for pretreatment of OPF for glucose recovery.

Impact of hot compressed water pretreatment on the structural changes of woody biomass for bioethanol production

As an initial step in an alternative use of woody biomass to produce bioethanol, this work was aimed at investigating the effect of hot compressed water (HCW) pretreatment within the temperature range 100 to 200 °C in a batch-type reactor on the structural changes of Tamarix ramosissima. The untreated and pretreated solid residues were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), r transform infrared spectroscopy (FT-IR), solid-state cross polarization/magic angle spinning (CP/MAS), 13C NMR spectroscopy, and thermogravimetric analysis (TGA), as well as chemical methods. The results showed that HCW pretreatment solubilized mainly hemicelluloses and resulted in enriched cellulose and lignin content in the pretreated solids. It was found that the deposition of lignin droplets on the residual surfaces was produced during pretreatment under the hot water conditions above 140 °C. In addition, the removal of hemicelluloses and lignin re-localisation as a result of condensation reactions under the severe pretreatment condition may lead to an increase in cellulose crystallinity and thermal stability of biomass solid residues, thus consequently influencing the downstream digestibility of biomass for sugars and bioethanol production.

Hot compressed water pretreatment of oil palm fronds to enhance glucose recovery for production of second generation bio-ethanol

This work presents the pretreatment of oil palm fronds (OPF) using hot compressed water (HCW) to enhance sugar recovery in enzymatic hydrolysis. A central, composite rotatable design was used to optimize the effect of reaction temperature, reaction time and liquid–solid ratio on the pretreatment process. All variables were found to significantly affect the glucose yield. A quadratic polynomial equation was used to model glucose yield by multiple regression analysis, using response surface methodology (RSM). Using a 10 bar pressurized reactor, the optimum conditions for pretreatment of OPF were found at 178 °C, 11.1 min and a liquid–solid ratio of 9.6. The predicted glucose yield was 92.78 wt.% at the optimum conditions. Experimental verification of the optimum conditions gave a glucose yield in good agreement with the estimated value of the model.

Pretreatment of Rice Straw by a Hot-Compressed Water Process for Enzymatic Hydrolysis

Hot-compressed water (HCW) is among several cost-effective pretreatment processes of lignocellulosic biomass for enzymatic hydrolysis. The present work investigated the characteristics of HCW pretreatment of rice straw including sugar production and inhibitor formation in the liquid fraction and enzymatic hydrolysis of pretreated material. Pretreatment was carried out at a temperature ranging from 140 to 240 degrees C for 10 or 30 min. Soluble oligosaccharides were found to constitute almost all the components of total sugars in the liquid fraction. The maximal production of total glucose at 180 degrees C and below accounted for 4.4-4.9% of glucan in raw material. Total xylose production peaked at 180 degrees C, accounting for 43.3% of xylan in raw material for 10-min pretreatment and 29.8% for 30-min pretreatment. The production of acetic acid increased at higher temperatures and longer treatment time, indicating more significant disruption of lignocellulosic structure, and furfural production achieved the maximum (2.8 mg/ml) at 200 degrees C for both 10-min and 30-min processes. The glucose yield by enzymatic hydrolysis of pretreated rice straw was no less than 85% at 180 degrees C and above for 30-min pretreatment and at 200 degrees C and above for 10-min pretreatment. Considering sugar recovery, inhibitor formation, and process severity, it is recommended that a temperature of 180 degrees C for a time of 30 min can be the most efficient process for HCW pretreatment of rice straw.