Initial Solid Loading Research Articles

Characterization of sugarcane bagasse solubilization and utilization by thermophilic cellulolytic and saccharolytic bacteria at increasing solid loadings

In Brazil the main feedstock used for ethanol production is sugarcane juice, resulting in large amounts of bagasse. Bagasse has high potential for cellulosic ethanol production, and consolidated bioprocessing (CBP) has potential for lowering costs. However, economic feasibility requires bioprocessing at high solids loadings, entailing engineering and biological challenges. This study aims to document and characterize carbohydrate solubilization and utilization by defined cocultures of Clostridium thermocellum and Thermoanaerobacterium thermosaccharolyticum at increasing loadings of sugarcane bagasse. Results show that fractional carbohydrate solubilization decreases as solids loading increases from 10 g/L to 80 g/L. Cocultures enhance solubilization and carbohydrate utilization compared to monocultures, irrespective of initial solids loading. Rinsing bagasse before fermentation slightly decreases solubilization. Experiments studying inhibitory effects using spent media and dilution of broth show that negative effects are temporary or reversible. These findings highlight the potential of converting sugarcane bagasse via CBP, pointing out performance limitations that must be addressed.

Strong and tough 3D-(SiC–Si3N4)/Al co-continuous composite with enhanced interfaces

Materials with high specific strength and toughness are urgently needed in the fields of electronic packaging, armor, and aerospace. SiC/Al composites show good potential for these applications but the problem of mutual exclusion of strength and toughness still needs to be solved. Herein, we propose a new strategy to simultaneously enhance its strength and toughness from the perspective of structural optimization and interface enhancement. Inspired by the nacre structure, a 3D-(SiC–Si3N4)/Al co-continuous composite was prepared by freeze-casting combined with the pressure infiltration method. During the process, elongated Si3N4 grains were introduced into the ceramic framework to design the internal lamella wall structure and increase the contact area with the aluminum substrate. Moreover, a favorable interfacial bonding was designed between Si3N4 and Al to improve interface wettability. The reliable microstructure of porous 3D-(SiC–Si3N4) preform was tailored through the adjustment of initial solid loading and the α-Si3N4 component. The effects of initial solid loading and the α-Si3N4 component on the microstructure, interfacial wettability, and mechanical properties of the final composites were investigated. The results showed that the SiC–Si3N4/Al composites possess high flexural strength (769 MPa) and fracture toughness (15.1 MPa m1/2), which is superior to data reported in general literature. Numerous elongated β-Si3N4 grains are produced on the ceramic skeleton, forming an interlocking structure with the aluminum matrix, which increases the contact area with the aluminum substrate. A chemical reaction layer was formed at the interface of the composite, greatly improving the interfacial bonding strength. This work provides a promising design guideline for developing and optimizing high-strength and tough composite.

Modeling and design of fed-batch strategies for achieving 255 g/L sugar concentration from high-solid enzymatic hydrolysis of pretreated corn stover

Achieving high sugar concentrations through enzymatic hydrolysis of pretreated lignocellulose with low enzyme loadings is crucial for reducing the costs of lignocellulosic biorefineries. However, the adverse effects of the “solid effect” pose essential challenges in this regard. In this study, the objective is to improve the sugar concentrations through enzymatic hydrolysis of Densifying Lignocellulose with Ca(OH)2 or H2SO4 followed by Autoclave pretreated corn stover (DLCA(ch)-CS or DLCA (sa)-CS) at 40 % w/w solid loading through kinetic analysis and a statistically designed fed-batch feeding strategy. Initially, the hydrolysis kinetics of different pretreated biomass were analyzed using fractal kinetic modeling, aiming to elucidate the reasons for the observed differences in hydrolysis. Furthermore, leveraging the kinetic differences, the optimal initial solid loading was determined, and statistical models were employed to optimize feeding modes for enzymatic hydrolysis. The result revealed that compared with H2SO4, Ca(OH)2 serves as an better catalyst for improving the hydrolysability of biomass, enhancing cellulose accessibility to cellulases and reduce the mass transfer rate during enzymatic hydrolysis. Interestingly, the optimal feeding mode for less digestible substrate (DLCA(sa)-CS) is different from the more digestible substrate (DLCA(ch)-CS). Notably, by using the optimized fed-batch feeding mode, the sugar concentration can reach a maximum of 255 g/L, with glucan conversion of 89.8 %, at low enzyme loading (10 mg protein/g glucan). This is the highest total sugar concentration achieved through 72 h enzymatic hydrolysis with low enzyme loadings using a fed-batch strategy. This approach proves highly effective in designing fed-batch strategies for pretreated biomass and has great potential to serve as a universal tool for designing suitable feeding schemes for various bionconversion process.

Rare-Earth-Zirconate Porous High-Entropy Ceramics with Unique Pore Structures for Thermal Insulating Applications.

Porous high-entropy ceramics are a new alternative material for thermal insulation. Their better stability and low thermal conductivity are due to lattice distortion and unique pore structures. In this work, rare-earth-zirconate ((La0.25Eu0.25Gd0.25Yb0.25)2(Zr0.75Ce0.25)2O7) porous high-entropy ceramics were fabricated by a tert-butyl alcohol (TBA)-based gel-casting method. The regulation of pore structures was realized through changing different initial solid loadings. The XRD, HRTEM, and SAED results showed that the porous high-entropy ceramics had a single fluorite phase without impurity phases, exhibiting high porosity (67.1-81.5%), relatively high compressive strength (1.02-6.45 MPa) and low thermal conductivity (0.0642-0.1213 W/(m·K)) at room temperature. Porous high-entropy ceramics with 81.5% porosity demonstrated excellent thermal properties, showing a thermal conductivity of 0.0642 W/(m·K) at room temperature and 0.1467 W/(m·K) at 1200 °C. The unique pore structure with a micron size contributed to their excellent thermal insulating performance. The present work provides the prospect that rare-earth-zirconate porous high-entropy ceramics with tailored pore structures are expected to be thermal insulation materials.

Cascade utilization of rice straw for biogas production.

To improve the biogas yield of rice straw, an innovative cascade utilization process for biogas production was proposed using a method referred to as "the first digestion + NaOH treatment + the second digestion" (labeled FSD). Both the first digestion and the second digestion of all treatments were conducted at the initial total solid (TS) loading of straw of 6%. A series of lab-scale batch experiments were conducted to investigate the effect of first digestion time (5, 10, and 15days) on biogas production and lignocellulose structure destruction of rice straw. The results showed that the cumulative biogas yield of rice straw using the FSD process was increased by 13.63-36.14% compared with the control (CK), and the highest biogas yield of 233.57mLg-1 TSadded was obtained when the first digestion time was 15days (FSD-15). The removal rates of TS, volatile solids, and organic matter were increased by 12.21-18.09%, 10.62-14.38%, and 13.44-16.88%, respectively, compared with those of CK. The results of Fourier transform infrared spectroscopy analysis revealed that the skeletal structure of rice straw was not significantly destroyed after the FSD process, but the relative contents of functional groups in rice straw were changed. The FSD process accelerated the destruction of crystallinity of rice straw, and the lowest crystallinity index of 10.19% was obtained at FSD-15. The abovementioned results indicated that the FSD-15 process is recommended for cascade utilization of rice straw in biogas production.

Numerical investigation of erosion characteristics of coupling separators with different conical profiles

Solid particles exist widely in liquid–liquid systems. Although a separator coupled centrifugal and electric fields can achieve liquid–liquid separation efficiently, the solid particles are usually not considered, and the erosion characteristics are unclear. Thus, in this study, a numerical model was established to investigate the erosion characteristics of coupling devices. Two conical profiles, namely bi-cone and elliptical, were examined. The effect of structural parameters on erosion was investigated, and the relationships between the erosion rate and the inlet velocity, initial drop size and solid loading were explored. The results showed that maximum erosion occurred in the interaction regions of the two cones for the bi-cone, and that the cone with an elliptical profile had a lower erosion rate. The maximum erosion rate depended on the centrifugal force acting on the solid particles and the inertial effect of particles in the mixture. Furthermore, the precessing vortex core was the dominant factor influencing the position, including maximum erosion rate, which depended on the centrifugal force and the vortex core radial deviation. Moreover, the potential reason for the effect of geometric parameters on wall erosion is different. From the perspective of erosion resistance, the optimal values of straight and underflow pipe section diameters and conical structure length for the device with an elliptical profile cone were 35, 400, and 430 mm. Additionally, increasing inlet velocity, initial drop size and solid loading can increase average erosion rate on the walls, and strengthen of breakage effect can indirectly reflect that the increase in erosion rate.

Acid Hydrolysis of Pretreated Sugarcane Bagasse, Macroalgae Sargassum sp. and Its Mixture in Bioethanol Production

Sustainable biofuel feedstock could become a critical issue in the light of the recent fuel crisis. The use of mixed biomass could reinforce to overcome this issue. The present work examined the parallel use of agricultural residue sugarcane bagasse (SCB) and natural invasive marine seaweed Sargassum sp. (SSP) as a single feedstock and its mixture in two-step concentrated acid hydrolysis followed by yeast fermentation in order to produce reducing sugar with minimal formation of furfural, and bioethanol. In this work, alkali pretreated SCB and SSP were used as feedstock in acid hydrolysis. To investigate the influenced parameters of acid hydrolysis, biomass type (SCB, mixed biomass MB (SCB and SSP in 1:1 ratio by weight) and SSP), initial acid concentration (64–80 wt%), reaction time (30–90 min) and solid loading (10–20%w/w) were optimized by using Taguchi method. The optimized conditions were obtained with mixed biomass type, the initial acid concentration of 64 wt%, reaction time of 60 min and solid loading of 10%w/v. Under these conditions, 0.51 g/g of reducing sugar was achieved without furfural formation although ethanol yield was relatively low compared to that of Taguchi experimental runs. The result indicated that biomass type highly influenced the acid hydrolysis on sugar yield and furfural formation. This study provides the potential route for converting pretreated cellulosic biomass to value-added products, such as sugar and ethanol via the biorefinery process.

Study on the solid–liquid suspension behavior in a tank stirred by the long-short blades impeller

We investigated the solid–liquid suspension characteristics in the tank with a liquid height/tank diameter ratio of 1.5 stirred by a novel long-short blades (LSB) impeller by the Euler granular flow model coupled with the standard k–ε turbulence model. After validation of the local solid holdup by experiments, numerical predictions have been successfully used to explain the influences of impeller rotating speed, particle density, particle size, liquid viscosity and initial solid loading on the solid suspension behavior, i.e. smaller particles with lower density are more likely to be suspended evenly in the liquid with higher liquid viscosity. At a low impeller rotating speed (N), increase in N leads to an obvious improvement in the solid distribution homogeneity. Moreover, the proposed LSB impeller has obvious advantages in the uniform distribution of the solid particles compared with single Rushton turbine (RT), dual RT impellers or CBY hydrofoil impeller under the same power consumption.

EFFECT OF UREA ADDITION ON BIOGAS PRODUCTION FROM THE CO-DIGESTION OF RICE STRAW AND PIGGERY DUNG

The anaerobic co-digestion of Rice straw (RS) and Piggery dung (PD) at initial Total Solid (TS) loading of 10% was studied. This paper has investigated the effect of supplementing this co-digestion of RS and CD at with urea with an objective of reducing pH as well as improving biogas yield. These experiments were also carried out at different substrate mixing ratios of RS-CD 1:1 and RS-CD 1:2. The anaerobic digestion was carried out in a digester designed and fabricated locally with retention time of between 40 days and 60 days. Results show that addition of 1g of urea improved the maximum Biogas Yield of RS-PD 1:1 by 17.7% and RS-PD 1:2 by 23.4%. Further experiments with 0.5g, 1.5g and 2g of urea added to a co-digestion of RS-CD 1:1 produced a Cumulative Gas Yield of 75 L/Kg, 85.2 L/Kg and 76 L/Kg respectively. Experiments also showed that increasing urea concentration also leads to an increased methane content of the biogas produced.

EFFECT OF SOLID LOADINGS ON BIOGAS PRODUCTION FROM THE CO-DIGESTION OF CORN STALKS WITH COW DUNG

In an extension to our previous work where we investigated the anaerobic digestion of Corn stalk (CS) and Cow dung (CD) with co-digestion experiments at initial total solid loading of 37.5%. This paper has investigated the anaerobic co-digestion of CS and CD at lower solid loadings of 10%, 15 % and 20% TS. These experiments were also carried out at different substrate mixing ratios of CS-CD 1:1 and CS-CD 1:2. The anaerobic digestion was carried out in a digester designed and fabricated locally with retention time of 45 days. Results show a maximum Biogas Yield of 67.85L/Kg TS and 75.75L/Kg TS for 10%TS at CS-CD 1:1 and CS-CD 1:2 respectively. Experiments carried out at 20% TS showed the lowest Biogas Yield/Kg of 44.5L/Kg and 50.38L/Kg for CS-CD 1:1 and CS-CD 1:2 respectively. Results also showed that studies carried out at CS-CD 1:2 showed higher biogas yields for substrate concentrations of 10%, 15 % and 20% TS when compared to corresponding experiments carried out at a mixing ratio of CS-CD 1:1.

Properties and estimation of mullite thermal insulators prepared by gelation–freezing with alumina nanofibers

AbstractThermal insulators were fabricated by freezing gelatin gels containing calcined kaolinite with alumina nanofibers, followed by sintering. The resultant porosity could be varied from 81.0% to 89.8% by solid loadings in the initial slurry. The relationship among porosity, microstructure, compressive strength, and thermal conductivity was examined. The compressive strength and thermal conductivities of the insulators prepared with initial solid loadings from 3 to 6 vol% ranged from 11.6 to 56.7 MPa and from .25 to .46 W/mK, respectively. Those properties were also estimated by simulation using modeling of overall pore morphology, resulting in good agreement.

Fed-batch simultaneous saccharification and fermentation including in-situ recovery for enhanced butanol production from rice straw

This paper describes a study of fed-batch SSFR (simultaneous saccharification, fermentation and recovery) for butanol production from alkaline-pretreated rice straw (RS) in a 2-L stirred tank reactor. The initial solid (9.2% w/v) and enzyme (19.9 FPU g-dw-1) loadings were previously optimized by 50-mL batch SSF assays. Maximum butanol concentration of 24.80 g L-1 was obtained after three biomass feedings that doubled the RS load (18.4% w/v). Butanol productivity (0.344 g L-1h−1) also increased two-fold in comparison with batch SSF without recovery (0.170 g L-1h−1). Although fed-batch SSFR was able to operate with a single initial enzyme dosage, an extra dosage of nutrients was required with the biomass additions to achieve this high productivity. The study showed that SSFR can efficiently improve butanol production from a lignocellulosic biomass accompanied by the efficient use of the enzyme.

High-solid enzymatic hydrolysis of sugarcane bagasse and ethanol production in repeated batch process using column reactors

The online version contains supplementary material available at 10.1007/s13205-021-02932-3.

Fabrication and properties of 3-3 type PZT-ordinary Portland cement composites

In this study, porous lead zirconate titanate (PZT) ceramics with porosity ranging from 46.4% to 82.3% were produced by the gel casting technology of particle-stabilized ceramic foams with the solid loading of 5–25 vol%, then the Portland cement paste was cast in porous PZT ceramics with continuous vibration to fabricate 3-3 type cement-based piezoelectric composites. The microstructure, dielectric, piezoelectric, and electromechanical coupling properties of the composites were characterized. With the increase in initial solid loading of PZT slurry, both the porosity, open porosity and pore size of porous PZT ceramics decreased correspondingly, which have prevented the filling of cement paste into the porous ceramics and led to the increment of PZT content in the composites. Increase in the PZT content contributed to the relative permittivity (εr) and longitudinal piezoelectric strain coefficient (d33), and a resultant reduction in piezoelectric voltage coefficient (g33). The prepared composites possessed a maximal thickness electromechanical coupling coefficient (Kt) value of 41.22%, higher than that of planar electromechanical coupling coefficient (Kp), indicating enhanced thickness mode oscillations of the composite. With the increase in PZT volume fraction, the PZT-cement composites turned from typical 3-3 structure to appoximate sandwich structure gradually, leading to more energy loss during electromechanical process and obvious decrease of the mechanical quality factor (Qm). The acoustic impedance (Z) of specimens ranged from 6.69 to 8.27 MRayls, close to that of cement materials (∼10 MRayls), making them promising candidate for application in civil engineering.

Performance of Food Waste Feeding Pilot Plant Biodigester Operated with Identified Potential Substrate Properties

Anaerobic digestion has been proven as sustainable process technology for organic waste conversion into renewable bio-energy. This study was conducted to evaluate the performance of mono-digestion process for different types of food waste substrates using pilot scale anaerobic bio-digester (1200 L) in terms of biogas production and the chemical oxygen demand (COD) removal efficiency. The biochemical methane potential (BMP) test of rice waste (R), vegetable waste (VW) and coconut meat residue (CMR) were tested at initial volatile solid (VS) loading of 0.1631, 1.1690, 1.0059 g VS/L, respectively at fixed inoculum/substrate (I/S) ratio of 0.5. Further study conducted by using rice waste (R) in pilot plant anaerobic bio-digester (1200L) for 43 days to investigate the reactor performance in term of COD removal efficiency. Interestingly, inoculum used for this study performs very well and able to digest food waste. Results demonstrate that the maximum specific biogas yield (SBY) was observed from rice waste (R) at 0.0587 L/kg VS compared to other substrates. Specific biogas yield (SBY) of rice waste (R) was 16.01% and 11.92% higher than substrate vegetable waste (VW) and coconut meat residue (CMR) respectively. High COD removal efficiency of pilot plant bio-digester (up to 93 %) using rice waste (R) as sole substrate indicates a good performance of reactor in treating food waste. Conversion of food waste to biogas in pilot plant bio-digester is highly potential as one of the sustainable waste treatment technology.

Enhancing the thermal insulating properties of lanthanum zirconate porous ceramics via pore structure tailoring

The potentially useful role of lanthanum zirconate (La2Zr2O7, LZO) porous bulk ceramics has been rarely explored thus far, much less the optimisation of its pore structure. In this study, LZO porous ceramics were successfully fabricated using a tert-butyl alcohol (TBA)-based gelcasting method, and the pore structures were tailored by varying the initial solid loading of the slurry. The as-prepared ceramics exhibited an interconnected pore structure with high porosity (67.9 %–84.2 %), low thermal conductivity (0.083–0.207 W/(m·K)), and relatively high compressive strength (1.56–7.89 MPa). The LZO porous ceramics with porosity of 84.2 % showed thermal conductivity as low as 0.083 W/(m·K) at room temperature and 0.141 W/(m·K) at 1200 °C, which is much lower than the counterparts fabricated from particle-stabilized foams owing to its unique pore structure with a smaller size, exhibiting better thermal insulating performance.

High-solids enzymatic hydrolysis of biomass: Hydrodynamics and reaction kinetics integration via numerical modeling

This study presents a novel computational fluid dynamics (CFD) model to investigate important aspects of the complex high-solids enzymatic hydrolysis (HSEH) process. The uniqueness of this CFD model lies in integrating the biochemical reaction taking place in the secondary phase and the corresponding mass transfer of the products from the secondary phase to the non-Newtonian primary phase, while dual axial impellers blend the multiphase system. The distribution of the reactants and products in the non-Newtonian primary phase affects the overall conversion of glucan to glucose, which, in turn, affects the commercial deployment of these systems for the production of renewable sugars. We investigated the effect of slurry viscosity on insoluble and soluble solids distribution, the impact of initial insoluble solids loading on total solids distribution, and varying the initial chemical composition of the insoluble solids on the total solids distribution. The comprehensive CFD model results show that variations in the chemical composition of the insoluble solids and the solids loading can each have a pronounced effect on the distribution of solids. This behavior would then affect the rate and extent of conversion of insoluble solids to soluble solids. Thus, the comprehensive CFD model can account for the interactions between independent variables, facilitating the design of small and large-scale reactors, while improving the conversion of insoluble solids to soluble solids. This novel CFD model thus represents the combined effects of key factors that influence HSEH in a realistic process environment.

Characterisation of mechanical and surface properties of novel biomimetic interpenetrating alumina-polycarbonate composite materials

ObjectiveTo determine the mechanical and surface characteristics of two novel biomimetic interpenetrating phase alumina-polycarbonate (Al2O3-PC) composite materials, comprising aligned honeycomb-like porous ceramic preforms infiltrated with polycarbonate polymer. MethodTwo composite materials were produced and characterised. Each comprised a porous structure with a ceramic-rich (polymer-poor) top layer, graduated through to a more porous ceramic-poor (polymer-rich) bottom layer. In addition, pure polycarbonate and dense alumina specimens were subjected to the same characterisation namely: density, compression, three-point bend, hardness, surface loss and surface roughness testing. Scanning electron microscopy and micro computerised tomography were employed for structural examination. ResultsThree-dimensional aligned honeycomb-like ceramic structures were produced and full interpenetration of the polymer phase was observed using MicroCT. Depending on the ceramic volume in the initial aqueous ceramic suspension, the density of the final interpenetrating composites ranged from 2.64 to 3.01g/cm3, compressive strength ranged from 192.43 to 274.91MPa, flexural strength from 105.54 to 148.47MPa, fracture toughness from 2.17 to 3.11MPa.m½, hardness from 0.82 to 1.52GPa, surface loss from 0.71 to 1.40μm and surface roughness, following tooth brushing, from 0.70 to 0.99μm. Composite specimens showed characteristic properties part way between enamel and polycarbonate. SignificanceThere was a correlation between the initial solid ceramic loading in the aqueous suspension, used to produce the porous ceramic scaffolds, and the subsequent characteristic properties of the composite materials. These novel composites show potential as aesthetic orthodontic bracket materials, as their properties fit part way between those of ceramic, enamel and polycarbonate.

CFD Modeling of the Catalyst Oil Slurry Hydrodynamics in a High Pressure and Temperature as Potential for Biomass Liquefaction

The paper presents the simulation of a catalyst-paraffin oil slurry hydrodynamics under high pressure and temperature in a convex bottom reactor with a Rushton turbine which was conducted with an application of computational fluid dynamics (CFD) modeling. An analysis to obtain a uniform distribution of solid catalyst particles suspended in paraffin oil was carried out as a potential for biomass liquefaction. The effects of the particle diameter, bed density, liquid viscosity, and the initial solid loading on slurry hydrodynamics in high pressure and temperature behavior were investigated using the Eulerian–Eulerian two-fluid model and the standard k-ε turbulence model. The main objective was to assess the performance in agitating highly concentrated slurries to obtain slurry velocity, concentration, the degree of homogeneity, and to examine their effect on the mixing quality. The results of the analysis are applied to predicting the impact of the most efficient conditions on slurry suspension qualities as potential for biomass liquefaction.

A technology for pilot production of bacterial cellulose from oat hulls

The complete production cycle of bacterial cellulose (BC) was studied on a pilot scale. Oat hulls, a globally abundant agricultural residue, was utilized as the feedstock. A technology for producing BC from oat hulls has been developed herein and involves four process operations: exclusive chemical pretreatment with HNO3, enzymatic saccharification, mixed-culture fermentation, and purification. The HNO3 pretreatment was studied under atmospheric pressure at concentrations of 2–6 wt%. The optimum HNO3 concentration for pretreatment of oat hulls was found to be 4 wt%. The pretreatment was run in a 250-L vessel to furnish a pulp in 37.5% yield with 71.5% Kürschner cellulose content. The resultant pulp was well hydrolyzable: enzymatic saccharification with commercial enzymes at an initial solid loading of 30.0 g/L resulted in 79.5% reducing sugar (RS) yield. However, the test synthesis of BC using Medusomyces gisevii showed a very low yield of only 3.5%. It was therefore decided to improve the pulp with the aid of 4 wt% NaOH, whereupon oat-hull cellulose was obtained in 24% yield comprising 93.2% α-cellulose. The enzymatic saccharification of oat-hull cellulose ended with 73.5% RS yield. The test synthesis of BC exhibited 11% yield. Then, the biotechnological stages were scaled up: enzymatic saccharification of oat-hull cellulose was performed in a 100-L fermentor, and BC synthesis in the resultant hydrolyzate was run in a Binder KB-400 incubator. After purification, the BC yield was 10% of the RS concentration. BC was composed of 100% cellulose Iα-allomorph and had 93% crystallinity index. The BC production from oat hulls was thus scaled up successfully with an optimistic BC yield: 80.5 tons of 98%-wet hydrogel per 100 tons of oat hulls.