Hydrothermal Pretreatment Process Research Articles

Synergistic treatment of sewage sludge and food waste digestate residues for efficient energy recovery and biochar preparation by hydrothermal pretreatment, anaerobic digestion, and pyrolysis

The safe disposal of sewage sludge (SS) and food waste digestate residues (DR) is a tough issue considering the difficulty of dewatering and the environmental risks from heavy metals and pathogens. This study combined hydrothermal pretreatment (HP), anaerobic digestion (AD), and pyrolysis to synergistically dispose of SS and DR to enhance dewaterability, recover energy, and prepare biochar with heavy metal immobilization. The results showed that the solid contents of centrifuged cakes increased after HP at 180 °C of SS with the addition of 25% and 50% mass fractions of DR. The centrate from co-HP had a high chemical oxygen demand (COD) and was further treated by AD at 37 °C, producing 193.75 and 210.39 mL/g CODinput (25 °C and 1 atm) of cumulative CH4 under the addition of 50% and 75% mass fractions of DR, respectively. The methanogenic types in AD converted from hydrogen utilization to acetic acid utilization with increasing DR ratio. Zn, Cu, Ni, and Pb were primarily left in the biochar after 50% mass fraction of DR was mixed in the HP combined with pyrolysis at 700 °C; the chemical fractionation of Zn, Cu, Cr, and Pb in the biochar increased to over 85% of the residual fractions, resulting in the lowest potential ecological risk index (15.22, low risk). The CH4 produced from the AD of the co-HP centrate (50: 50, w/w) can supply heat for the HP process, reducing the energy input by 89%. This co-disposal strategy can effectively recover carbon resources from solid wastes to reduce carbon emissions.

Nanoarchitectonics of self-supporting porous carbon electrode with heteroatoms co-doped: For high-performance supercapacitors

Wood possesses a uniform hierarchical porous structure and high mechanical strength, rendering it an excellent precursor for the preparation of self-supporting carbon electrodes without binders and conductive agents. This paper presents an efficient method for synthesizing a self-supporting carbon electrode (HCW-0.7) with high specific surface area, hierarchical pore structure and abundant surface functional groups, utilizing simple hydrothermal pre-treatment and one-step thermochemical conversion process. The HCW-0.7 electrode demonstrates remarkable electrochemical performance, achieving an excellent specific capacitance of 298.52 F g−1 under a current density of 0.5 A g−1. The wood-based symmetrical supercapacitor (HSC) constructed with HCW-0.7 as the electrode has excellent energy density, power density and rate performance. At the power density of 287.5 W kg−1, HSC demonstrates an energy density of 9.43 Wh kg−1, exhibits its excellent electrochemical performance. Notably, even when subject to a higher power density of 5750 W kg−1, the energy density remains at 5.16 Wh kg−1. Furthermore, even after 20,000 charge and discharge cycles, HSC demonstrates a remarkable capacity retention rate of 96.24 %.

Improvement of hydrochar/biochar pellets prepared from cotton stalk by hydrothermal pretreatment process

Hydrothermal (HT) pretreatment can change the internal components of biomass to efficiently improve the comprehensive utilization value of the resource. In this paper, cotton stalk (CS) was hydrothermally pretreated firstly at 180–280 °C and densified into hydrochar pellet and then pyrolyzed at 400 °C to prepare biochar pellet. A variety of the characterization analyses (SEM, XRD, etc.) were conducted to investigate the effect of the evolution behavior of the main components (cellulose, hemicellulose and lignin) in CS during HT process on the physicochemical property of the resulted biofuel pellets. The results show that HT process improves significantly the quality of the resulted biomass. As HT temperature increasing from 180 °C to 280 °C, the carbon content of the hydrochar increases from 46.91% to 67.26%, while the oxygen content decreases from 46.61% to 26.0%. Meanwhile, the alkali metal content of CS decreases significantly during HT process. HT process promotes the significant decompositions of the hemicellulose below the process temperature of 230 °C and cellulose below 280 °C and the aromatization growth of the resulted CS. Crystalline cellulose is the major contributor to the mechanical properties of the hydrochar and biochar pellets. Compared with the hydrochar pellet, the biochar pellet has the much lower properties due to the decomposition of the crystalline cellulose during the pyrolysis process. The combustion characteristic of the hydrochar decreases significantly due to the decreasing cellulose content with HT intensity, while the correlation between them is severely weakened by the pyrolysis process. HT process significantly improves HHV of the resulted hydrochar pellet and the lignin is responsible for the increasing HHV. However, HHV of the resulted biochar pellet shows a slowly downward trend with the increasing HT temperature. The hydrochar and biochar pellets with the maximum energy density both were prepared from CS pretreated at 230 °C and HT process improves the energy density of the resulted hydrochar pellet and biochar pellet to different certain. The apparent density has a crucial effect on the quality of the biofuel pellet. Thus, the quality of the biochar pellet can be improved greatly by HT process.

Impact of Hydrothermal Pretreatment Parameters on Mesophilic and Thermophilic Fermentation and Anaerobic Digestion of Municipal Sludge

Four parameters affecting hydrothermal pretreatment (HTP) of municipal sludge prior to anaerobic digestion and fermentation were investigated. Partial factorial design including several key HTP parameters at two distinct levels, including temperature (170 and 190 °C), retention time (RT) (10 and 30 min), pH (4 and 10), and solid content (SC) (4% and 16%), were studied. Further, the impact of HTP parameters on mesophilic and thermophilic fermentation was explored and compared. Results revealed a significant effect of all HTP parameters on COD solubilization, VFA, and methane yield. There were correlations between HTP parameters and process responses such as VFA yield and methane yield. HTP was found to increase COD solubilization and VFA production between 15 and 20% during thermophilic fermentation in relation to mesophilic treatment. All parameters, including SC, temperature, pH, and RT, were important contributing factors affecting methane production during anaerobic digestion. The highest methane production yield of 269 mL CH4/g TCOD added was observed at the highest SC (16%) and pH (10) and at the lower temperature (170 °C) and RT (10). HTP is expected to be combined with other intensification routes to treat waste with high solid contents improving the fermentation and anaerobic digestion processes.

Hydrothermal and Chemical Pretreatment Process for Bioethanol Production from Agricultural and Forest Lignocellulosic Wastes: Design and Modeling

Hydrothermal and Chemical Pretreatment Process for Bioethanol Production from Agricultural and Forest Lignocellulosic Wastes: Design and Modeling

Hydrothermal pretreatment optimization of hemicellulose dissolution of sugar palm starch industrial waste

Lignocellulosic biomass is a renewable source containing three main components: cellulose, hemicellulose, and lignin. The three main components can be processed into products that have high added value. Sources of lignocellulosic biomass includes wood, grass, industrial waste, and agricultural residu. Compared to other source, industrial wastes have a higher potential to be utilized without competition for other needs and assist industry in waste treatment. The production of sugar palm starch generate biomass waste which is disposed into the environment which disturbs the surrounding community and is not utilized. To utilize lignocellulosic biomass, pretreatment is a very important step. Hydrothermal is an environmentally friendly pretreatment, without using harmful chemicals in the process. The purpose of this study was to determine the level of solubility of hemicellulose in the hydrothermal pretreatment process of sugar palm starch industrial waste. The hydrothermal method used is liquid hot water with temperature and time parameters, optimization analysis using response surface methodology (RSM). The result obtained is that the liquid hot water pretreatment method is effective in dissolving the hemicellulose from the sugar palm starch industrial waste. The relationship between variables on hemiselulosa response is modeled Y = 7.7-3.04 X1 – 5.67X2 + 0.4250 X1X2 + 1.06 X1 2 + 3.61 X2 2. The optimization results showed the optimum temperature at 195.91°C for 36.725 minutes, with a hemicellulose dissolution of 81.59% and the level of desirability is 0.852.

An integrated acetic acid-catalyzed hydrothermal-pretreatment (AAP) and rapid ball-milling for producing high-yield of xylo-oligosaccharides, fermentable glucose and lignin from poplar wood

An integrated pretreatment that realizing effective fractionation and targeted valorization can guarantee the implementability to future biorefinery scenario. In the present study, a stepwise approach using acetic acid-catalyzed hydrothermal pretreatment (AAP) and rapid ball-milling process was successfully developed for producing high-yield of xylo-oligosaccharides (XOS), fermentable glucose and native lignin from poplar wood. It was found that the AAP removed the most hemicelluloses, releasing the highest yield (36.16%) of XOS at 160 °C for 1 h. Subsequent rapid ball-milling pretreatment for 10 min led to a remarkable increase in the saccharification efficiency from 40.68% to 91.35%. Meanwhile, the residual lignin fractions exhibited abundant β-O-4 linkages, which are beneficial to catalytic hydrogenolysis of these lignin fractions into the aromatic chemicals. Considering the integrated process could effectively produce XOS, fermentable glucose, and the residual lignin with well-preserved structures, the proposed process is a promising and efficient deconstruction strategy in current biorefinery scenario.

Hydrothermal pretreatment reduced microplastics in sewage sludge as revealed by the combined micro-Fourier transform infrared (FTIR) and Raman imaging analysis

The massive amount of sludge was considered one of the significant sinks of microplastics (MPs). Low-temperature hydrothermal treatment applied as a pretreatment process (e.g., 170 °C & 30 min) of sludge received growing attention since it could improve the dewaterability and increase the methane yield of sludge. However, the changes of sludge-based MPs during the hydrothermal pretreatment (HTP) were not studied. The present study combined micro-Fourier transform infrared and Raman imaging to explore the removal effect of sludge-based MPs (minimum test-limitation is 1 μm) via the HTP process. When the conditions of HTP changed from 170 °C & 30 min to 220 °C & 30 min, the removal rate of prominent MPs (with size >50 μm) increased from 11.5 ± 6.1% to 85.01 ± 5.2% and the removal rate of tiny MPs (with size <50 μm) increased from 50.21 ± 5.6% to 87.35 ± 1.11%, indicating that MPs’ degradation was strongly associated with the treatment temperature and particle size. Physiochemical property changes (morphology, functional groups, surface elements) and dissolved organic carbon (DOC) releasing of three HTP-treated typical MPs were further characterized. The results proved that sludge-based MPs were degraded in two stages via HTP, including particle cracking by harsher conditions and polymer backbone scissions by the dihydroxylation and carbonylation effects.

Effect of hydrothermal pretreatment on deashing and pyrolysis characteristics of bamboo shoot shells

Bamboo shoot shells (BSS) were treated at hydrothermal temperatures of 160 °C, 180 °C, and 200 °C with residence times of 6 h, 8 h, and 10 h. The variation of ash-forming elements and the influence of deashing behavior on fuel and pyrolysis characteristics of BSS hydrochars were originally investigated during hydrothermal pretreatment (HTP) process. The results showed that HTP decreased 53.82–64.00% of BSS ash because 95.2–96.5% of K, 61.3–82.1% of Mg, 22.0–39.2% of Al, 23.7–51.8% of Fe, and 28.8–43.6% of Ca were removed. This improved fusion characteristics of BSS ash and reduced the risk of deposition, slagging and scaling. With increase in hydrothermal temperatures and residence times, the contents of fixed carbon, C, and high heating value of BSS hydrochars increased, while the contents of volatiles and O decreased. HTP shifted pyrolysis process of BSS to high temperature zone, and increased their activation energy and the amount of all gaseous products, including CO groups, C–O–C groups, alkyls, H2O, and CO. In conclusion, HTP is helpful for BSS to be used as feedstocks of bioenergy and biomaterials due to decrease of ash contents and improvement of thermal stability.

Sludge slurry treating using hydrothermal pre-treatment process and its property evaluation

Sludge slurry treating using hydrothermal pre-treatment process and its property evaluation

Hydrothermal Pretreatment of Rice Straw with Alkaline Addition for Enhancing Biogas Production in Semicontinuous Anaerobic Digester

This study presents the results of hydrothermal pretreatment of rice straw on its ability to improve the biogas production process in anaerobic digesters. Hydrothermal treatment on rice straw biomass was carried out with the addition of 0%, 3% and 5% NaOH (w/w rice straw) for one hour at a temperature of 140 °C. This study showed that hydrothermal and alkaline hydrothermal pretreatments were able to increase organic degradation of rice straw as indicated by an increase in the dissolution of lignin and hemicellulose from rice straw. Temperature and NaOH worked synergistically to dissolve lignocellulose in the hydrothermal pretreatment process. In the semicontinuous digester fed with pretreated rice straw, NaOH content in the pretreatment stage was found to give significant effect in enhancing biogas production. Average daily biogas production by the untreated rice straw, hydrothermal pretreated without NaOH addition, hydrothermally treated rice straw with 3% NaOH and 5% NaOH was 23.9, 57.1, 95.8 and 108.8 L/kg rice straw, respectively.

The effects of hydrothermal carbonization operating parameters on high-value hydrochar derived from beet pulp

Beet pulp is an extremely very wet organic waste derived from sugar production. It can be utilized for energy purposes, e.g. biogas production or as very valuable fodder for animals, mainly horses. The high moisture content (80%) in beet pulp makes it an adequate feedstock for the hydrothermal carbonization process. Therefore, this study is focussed on the hydrothermal carbonization of beet pulp. The following parameters were studied: temperatures of 180, 200, and 220 °C through 1, 2, 3, and 4 h of residence time. The optimal conditions of the process were determined (220 °C and 1 h), based on the physical and chemical properties of solid product hydrochar. The ultimate and proximate analyses, high heating value, energy and mass yields, and energy densification ratio were investigated. The obtained hydrochars were of a coal-like solid biofuel, with high heating values much higher than raw feedstock (c.a. 150% higher). The combustion performance and kinetics of hydrochar based on TGA were determined, indicating better combustion. Moreover, the fibre analysis of hydrochar, supported by infrared spectra and scanning microscope analysis confirmed the changes in its structure. Concluding, organic waste, beet pulp, is of great potential as an energy source using the hydrothermal pretreatment process.

Effect of integrated treatment on enhancing the enzymatic hydrolysis of cocksfoot grass and the structural characteristics of co-produced hemicelluloses

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

Synergistic effects on co-pyrolysis of low-temperature hydrothermally pretreated high-protein microalgae and polypropylene

Protein-rich (58.50%) Chlorella sp. was hydrothermally pretreated at 175 °C to remove part of N, and the obtained solid residue (ChSR) was then co-pyrolyzed with polypropylene (PP) to reduce O content and improve bio-oil quality. About 48.25% of N was enriched into the aqueous phase during hydrothermal pretreatment (HTP) process, and about 15.70% of bio-oil with low N content (3.45%) was obtained. Compared with that of raw sample, the structure of ChSR was further aromatized as revealed by 13C NMR analysis. The interaction between ChSR and PP was deeply investigated with the help of online TG-FTIR-MS and Py-GC/MS. The co-pyrolysis process of ChSR-PP blends was generally divided into two thermal decomposition stages. The first stage (150–400 °C) was mainly associated with decomposition of ChSR, while the second stage (400–550 °C) was the results of combination of thermal degradations of ChSR and PP, with the primary contribution from the degradation of PP. The addition of PP accelerated pyrolysis of ChSR and inhibited the release of C2H5O+/COOH+ and NH3 but promoted CO2 releasing at the first stage. However, ChSR delayed the pyrolysis of PP and prohibited release of H2 and light hydrocarbons (i.e., CH4, C2H2, C2H6, C3H7, and so on) from PP at the second stage. Kinetic analysis based on the Flynn-Wall-Ozawa (FWO) method revealed that the average activation energy (E) of the blends at the two decomposition stages were 159.10–164.12 kJ/kg and 194.20–219.86 kJ/kg, respectively. Results of Py-GC/MS indicated that, the synergistic effect between ChSR and PP significantly enhanced the formation of hydrocarbons (i.e., cyclohexane derivatives and 2,4-Dimethyl-1-heptene), and the interaction achieved maximum when the ratio of ChSR:PP was 80:20. The yields of O-containing compounds (alcohols, and phenols) and BTEXs (Benzene series) were decreased. It should be noted that both the amounts and kinds of N-heterocyclic compounds were decreased. Finally, the possible mechanism on interaction between ChSR and PP was also proposed. This work will provide useful information on better utilization of high-protein microalgae.

Biogas Production and Microbial Communities in the Anaerobic Digestion of Sewage Sludge Under Hydrothermal Pretreatment with Air and a Catalyst

Hydrothermal pretreatment (HTP) of sewage sludge (SS) has been shown to improve the subsequent biogas production by anaerobic digestion (AD), but the effect of catalysts on HTP performance was less explored. This study intended to investigate the SS pretreatment by wet air oxidation (WAO) with the addition of K2CO3 as a catalyst on the performance of methane production by AD. WAO was found to improve the solubilization of SS, the soluble chemical oxygen demand, dissolved organic carbon, and total dissolved nitrogen. The methane yield from WAO increased from 202 mL/gVSin with no catalyst added to 277 mL/gVSin with 10 wt% of K2CO3 added at 180 °C with 30 min of residence time. Under this pretreatment condition, the highest methane production rate could achieve 15.8 mL/gVSin day, and the percentage of methane reached 73%. The structure of the microbial community involved in the AD was affected by the residence time, working gas, and catalyst of the HTP process. The results showed that Bacteroidetes, Bacteroidia, and SC103 were the dominant phylum, class, and genus of bacteria, respectively, of almost all of the samples. In addition, the most abundant archaeal order was Methanosarcinales, while Methanosaeta was the dominant archaeal genus of most of the samples. However, Methanosarcina largely increased the relative abundance, corresponding to the amount of K2CO3 catalyst used. The findings in this study demonstrated the potential use of K2CO3 during WAO of SS and implied the link between shift of methanogen community and the enhanced methane yield in AD.

Optimization of alkaline hydrothermal pretreatment of biological sludge for enhanced methane generation under anaerobic conditions

This paper investigated the effect of alkaline hydrothermal pretreatment (HTP) on the hydrolysis, biodegradation and methane generation potential of waste activated sludge (WAS). A multi-variable experimental approach was designed, where initial solids content (1–5%), reaction temperature (130–190 °C), reaction time (10–30 min.) and caustic concentration (0–0.2 mgNaOH/mgVS) were varied in different combinations to assess the impact of alkaline HTP. This process significantly enhanced the hydrolysis of organic compounds in sludge into soluble fractions, whereby increasing the chemical oxygen demand (COD) leakage up to 200–900% with the 17–99% solubility. It boosted volatile solids (VS) biodegradation up to 40%, which resulted in a parallel increase in methane generation from 216 mLCH4/gVS to as high a 456 mLCH4/gVS methane generation basically relied on the conversion of solubilized COD. Alkaline HTP process was optimized for the maximum methane production. Optimum conditions were obtained at 190 °C reaction temperature, 10 min. reaction time, 0.2 mgNaOH/mgVS and 5% dry matter content. Under these conditions, 453.8 mLCH4/gVS was predicted. Biochemical methane potential (BMP) value was determined as 464 mLCH4/gVS supporting predictive power of the BMP model. The biodegradability compared to the untreated raw WAS was enhanced 78.2%.

Effect of hydrothermal pre-treatment on physical properties and co-digestion from food waste and sewage sludge mixture.

Anaerobic digestion (AD) is generally considered to be an economic and environmentally friendly technology for treating waste activated sludge, but has some limitations, such as the time it takes for the sludge to be digested and also the ineffectiveness of degrading the solids. Various pre-treatment technologies have been suggested to overcome these limitations and to improve the biogas production rate by enhancing the hydrolysis of organic matter. This paper studies the use of hydrothermal pre-treatment (HTP) for a food waste and sewage sludge mixture (FW-SS mixture) as pre-treatment of co-digestion. The results of the capillary suction time, time to filter, and particle size decreased with increasing HTP temperature. These results of the assessment that was conducted in this study confirm that the HTP process indeed modifies the physical properties of the FW-SS mixture to enhance the solubilization of organic solids. A maximum increase in biogas production of 50% is achieved with a HTP temperature of 140oC. These findings show that to achieve high conversion efficiency, an accurately designed pre-treatment step must be included in the overall AD process for wastewater treatment.

A Catalytic Hydrothermal Pretreatment process for sugar recovery from pearl millet biomass for Biofuels Production

A Catalytic Hydrothermal Pretreatment process for sugar recovery from pearl millet biomass for Biofuels Production

Syngas production at low temperature via the combination of hydrothermal pretreatment and activated carbon catalyst along with value-added utilization of tar and bio-char

Syngas was acquired at 500 °C by the combination of hydrothermal pretreatment (HP) and activated carbon catalyst (ACC) in this work. It's found that HP process removed AAEMs and hemicellulose from biomass, which significantly elevated volatiles release and made sugars and mono-phenols as main components in volatiles. Through the reforming via ACC, oxygen-containing groups in sugars and mono-phenols were deprived and contributed to syngas formation. Top-quality syngas was obtained at HRH150 with CO of 66.68% and syngas purity of 71.17%. More importantly, owing to low enough reforming temperature, phenol was the only dominant organic of tar in this study. In addition, HP process endowed bio-chars with elevated porosity. After NaOH activation, activated bio-char (AC) with highest meso-pore ratio was also obtained at AC-HRH150 (BET of 2366.8 m2/g). All in all, results above provided a brand-new angle for further poly-generation of biomass resources.

Effect of bifunctional acid on the porosity improvement of biomass-derived activated carbon for methylene blue adsorption

Activated carbon (AC) with high specific surface area was prepared by using bifunctional H3PO4 agent, which led to dehydrating and activation effects through hydrothermal pretreatment and subsequent pyrolysis process. N2 adsorption and desorption isotherms of AC showed a high BET surface area of 2434m2g-1 and a total volume of pores (VT) of 2.0447m3g-1 for AC. The morphology and the chemical components of hydrochar and AC were characterized by scanning electron microscopy and Fourier transform infrared spectroscopy, which indicated that H3PO4 was benefitting for the formation of porous structure of AC. Subsequently, the effect of H3PO4 in hydrothermal pretreatment and activation process was investigated by comparative experiments. The removal and adsorption of methylene blue (MB) dye with different concentrations onto the AC were studied. The monolayer equilibrium adsorption capacity was 644mgg-1, showing that AC has good adsorption qualities for methylene blue (MB). The adsorption balance data of MB on AC was best fitted to the Redlich-Peterson model. The adsorption kinetic data fit better to the pseudo-first-order model at low MB concentration, and the pseudo-second-order and Elovich models fit better when the MB concentration was rising.