Initial Solid Loading Research Articles

Aeration challenge in high BSG suspended fermentation: Impact of stirred-tank bioreactor scale

The high loading of lignocellulosic substrates could merge the advantages of solid-state and submerged fermentations. However, high solid loading in bioreactors could result in oxygen mass transfer complications and caused extra waste of inlet air. In this work, the effects of Brewer's Spent Grain (BSG) loading on enzyme production, oxygen transfer rate (OTR) and carbon dioxide evolution rate (CER) were investigated at 50, 75 and 100 g L−1 BSG in a 2.5-L stirred tank bioreactor. However, in small-scale bioreactor, the short contact time and inadequate mixing of bubbles in liquids affected the OTR and gas holdup negatively. Therefore, xylanase production in a 14-L vessel with 100 g L−1 BSG has been studied. In a larger bioreactor, a remarkable improvement in OTR and a significant reduction in total air consumption were recorded. Furthermore, the enzyme production per 1 L of consumed air was four times greater than 2.5-L vessels. As a result, the energy consumption for aeration was less in the larger bioreactor with high solid loading. Additionally, the residual xylan content monitoring during enzyme production has revealed that the BSG's xylan content decreased in the first 12 h of cultivation and then it remained approximately constant that probably means further xylanase induction is influenced by the concentration of BSG's hydrolysis products. Concisely, it seems that initial higher solid loading could be used as a practical alternative to solid substrate feeding during the fermentation. These findings would be useful for the fermentation of high loading lignocellulosic material in the industrial-scale bioreactor.

Improved Cellulosic Ethanol Titres from Highly Lignified Cotton Trash Residues Using Various Batch and Fed-Batch Process Configurations

This study investigates a fed-batch simultaneous saccharification fermentation (F-SSF) process to increase ethanol titres from highly lignified (41.6 wt.%) cotton gin trash residue. The optimal initial solid loading, enzyme dose, feed quantities and intervals to maximize substrate feed and subsequent ethanol titres were examined. Under batch SSF conditions, initial extracted cotton gin trash (ECGT) solid loadings were maximised at 19.35 wt.% and attained an ethanol titre of 23.3 g/l with a corresponding yield of 53.7%. Operating under optimised F-SSF mode, fermentations were initiated with 16.13 wt% EGCT solids followed by fresh ECGT feeds of 16.13 wt% and 12.9 wt.% at 12-h intervals. Cellulase levels were maintained at 44 FPU/g glucan throughout the fermentations. The final ethanol titre of 41 .4 g/l with a corresponding conversion rate of 70.1% was achieved after 72 h. Comparable ethanol yields of 40 g/l with 67.8% conversion were realized with lower cellulase dosing (25 FPU g/glucan) but only after extending the fermentation by 24 h.

Numerical simulation of solid-liquid mixing characteristics in a stirred tank with fractal impellers

The hydrodynamics of solid-liquid mixing process in a stirred tank with four pitched-blade impellers, fractal 1 impellers, and fractal 2 impellers were investigated using computational fluid dynamics (CFD) simulation. An Eulerian-Eulerian approach, standard k-ε turbulence model, and multiple reference frames (MRF) technique were employed to simulate the solid-liquid two-phase flow, turbulent flow, and impeller rotation, respectively. The effects of impeller speed, impeller type, impeller spacing, impeller blade tilt angle, impeller blade shape, solid particle size and initial solid particle loading on the solid particle suspension quality were investigated. Results showed that the homogenous degree of solid-liquid system increased with the increase of impeller speed. The impeller spacing of T5/6 and T and impeller blade tilt angle of 60° and 45° were appropriate for the solid-liquid suspension process. Fractal shape impeller was more efficient than jagged shape impeller in solid-liquid mixing process. Larger particle diameter and higher initial solid particle loading resulted in less homogenous distribution of solid particles. It was found that fractal impeller could improve the solid particle suspension quality compared with four pitched-blade impeller under the same power consumption, increasingly so with the fractal iteration number of fractal impeller. Moreover, fractal impeller reduced the size of impeller trailing vortex and consumed less power consumption compared with four pitched-blade impeller at the same impeller speed, and the more the number of fractal iteration, the higher the impeller energy utilization rate of fractal impeller.

Application of response surface methodology to absorptive separation of SO2 from its mixture with air using marble waste

Absorptive separation of SO2 from its mixture with air was studied in a semi-batch bubble column reactor using marble waste (MARWAS) slurry as the absorbent. Scanning electron microscopy with energy-dispersive spectroscopy (SEM/EDS), thermogravimetric analyzer (TGA), and Fourier transform infrared spectroscopy (FTIR) were used to characterize the MARWAS sample. The effects of concentration of SO2 in the feed gas (500–1500 ppm), batch-volume of the slurry (250–450 mL), flow rate of gaseous mixture (20–40 L/min), and initial solids loading (1–3 g) on the percent SO2 removal efficiency (PRE) and slurry saturation time (SST) were studied. Response surface methodology was used to optimize the process parameters. The optimal conditions for absorption of SO2 were 750 ppm, 400 mL, 25 L/min, and 2.5 g. The corresponding experimental values of PRE and SST were 99.49% and 29.56 min, respectively. Experimental data collected under optimal conditions could be adequately fitted to quadratic models for the responses PRE and SST with the respective R2 values of 0.9562 and 0.9959. The developed models, therefore, predicted a reasonably accurate (<5% error) assessment of optimal conditions for separation of SO2 using MARWAS slurry. The results of the present study can be usefully employed for desulfurization of flue gases.

A novel approach to the fabrication of lamellar Al2O3/6061Al composites with high-volume fractions of hard phases

Freeze casting has been widely used in the preparation of nacre-inspired composites because of its prominent advantages in controlling the fine structure of ceramic scaffolds. However, the ceramic-phase content in composites prepared by this method is much lower than that in nacre due to the limitations of the dispersion and viscosity of the ceramic slurry. In this work, we combined the ideas of freeze casting and in-situ reaction to prepare nacre-inspired lamellar composites with high hard-phase contents. We first prepared the TiO2-−SiO2 porous scaffold with an initial solid loading of 20 vol% via unidirectional freeze casting and then infiltrated it with a 6061Al alloy. During the reaction process, the TiO2-SiO2 layers were progressively transformed into Al2O3 layers, and the Al layers were transformed into Al3Ti. Composites with different hard-phase volume fractions (approx. 29%, 38%, 52% and 65%) and different interfacial bonding strengths could be obtained by altering the infiltration temperature. Increases in the hard-phase content and the interfacial bonding strength substantially enhanced the bending and compressive strengths of the composites, with maximum values of 350 MPa and 854 MPa, respectively, achieved in the composites with approx. 65 vol% hard phases. However, the highest fracture toughness of 42.9 MPa m1/2 and maximum fracture work of 3.6 kJ/m2 appeared when the hard-phase content in the composite was approx. 38 vol%, sharing an appropriate interfacial bonding strength. A robust interface favors stress transfer but impedes crack deflection, while a weak interface fails to bear loads, even though it is conducive to crack deflection. A moderately-strong interface together with a considerable amount of layered soft phase contributes to the generation of multiple-cracking, and thereby greatly toughens the metal−ceramic composite.

Superabsorbent-mediated dewaterability of fine hydrophobic sulphide mineral slurries

ABSTRACTThis work investigates superabsorbent (SAB) polymer application to dewatering of fine pyrite (P) and chalcopyrite (CP) mineral slurries. The results showed that significant pulp water absorption, reflecting dramatic dewatering and hence, compact sediment consolidation (up to 80 wt%), may be achieved within 15 min of contact time. The rate of slurry water absorption increased with both decreasing SAB particle size and initial slurry solid loading. The SAB dewatering performance was higher for the CP than the P slurry. SAB regeneration and re-use investigations showed that multiple recycle and greater water recovery can be achieved with a given sample.

A study of properties and enzymatic hydrolysis of bacterial cellulose

This study evaluates how bacterial cellulose (BC) properties influence the efficiency of enzymatic hydrolysis. BC was produced by the Medusomyces gisevii Sa-12 symbiotic culture in an enzymatic hydrolyzate obtained from oat hulls and was characterized by Fourier-transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, and X-ray diffraction. The enzymatic hydrolysis was examined with dried BCs unwashed and washed of culture medium components and cell debris, as well as with wet BC washed of culture medium components, at initial solid loadings of 10 and 30 g/L. The enzymatic hydrolysis of the BC sample unwashed of culture medium components and cell debris exhibited a substrate conversion degree of 56.3–66.6%. The conversion degree of the BC samples washed of culture medium components and cell debris was 89.4–99.5%. The removal of culture medium components and cell debris increased the conversion degree by 1.5 times. The drying of wet BC was found to decrease the enzymatic hydrolysis rate but it did not affect the conversion degree: the maximum yield of reducing sugars of 99.5% was achieved in 56 h for dried BC and in 16 h for wet BC. The substrate’s impurity content (growth medium components and cells) and moisture had the greatest effect on the performance of enzymatic hydrolysis of BC. The high BC crystallinity index of 90% was found to be not a determinant for the enzymatic hydrolysis efficiency.

Biogas Production from the Co-Digestion of Cornstalks with Cow Dung and Poultry Droppings

The Anaerobic digestion of Corn Stalk (CS) with Cow Dung (CD) and Poultry Droppings (PD) was investigated. Batch mono-digestion and Co-digestion experiments were performed with initial total solid loading of 37.5%. The main objective of this work was to investigate the biogas yield at different CS to CD ratios and CS to PD ratios. Results show that the highest Cumulative Gas Yield (CGY) of 6833 mL/g of biomass was achieved in 21 days for CS-CD ratio of 2:1. Similarly high CGY of 6107 mL/g, 6100 mL/g and 5333 mL/g were obtained for CS-PD ratio of 2:1, CS-CD ratio of 1:1 and CS-PD ratio of 1:1 respectively. It is concluded that co-digestion of Cow dung or poultry droppings is beneficial for improving bio-digestibility and Biogas yield from corn stalk. The results of this work provide useful information to improve the efficiency of co-digestion of CS with CD and PD under anaerobic conditions.

Hydrogenation and hydrodeoxygenation of aromatic lignin monomers over Cu/C, Ni/C, Pd/C, Pt/C, Rh/C and Ru/C catalysts: Mechanisms, reaction micro-kinetic modelling and quantitative structure-activity relationships

In this integrated in silico and experimental study, the activity, selectivity and mechanisms of commercially-available noble and transition metal heterogeneous catalysts, on neutral (carbon) support were investigated for hydrodeoxygenation (HDO) of eugenol. The latter was selected as a model compound of lignin building blocks. An influence of the process operating conditions (temperature, pressure and initial solid loading) on the reaction pathway and product distribution was studied as well. The previously-proposed reaction network for phenols HDO over Ru/C was found valid also for other platinum-group- (Pd, Pt and Rh) and non-noble (Cu or Ni) metallic clusters supported on C. Ru/C system exhibited the best HDO turnover performance, followed by the Rh/C, which especially demonstrated an excellent hydrogenation activity. Pt and Pd showed low deoxygenation and moderate hydrogenation activity. Kinetic parameters for all reactions on the surface were determined for all tested metals with a micro-kinetic model, by regression analysis on the foundation of 5760 experimentally-determined concentration values. Computation took into account resistances caused by transport phenomena, adsorption/desorption kinetics, and especially surface and bulk reaction kinetics. Ratio between adsorption and desorption rate constants for dissolved saturated, aromatic and hydrogen species were predicted, indicating a notable coverage effect on the catalyst reactivity. The saturation of functionalised benzene ring was approximately 3-, 11-, 32-, 10-, and 6-times faster than the C–O hydrogenolysis over ruthenium, platinum, palladium, rhodium and nickel, respectively. Methoxy group removal is easier from aromatics, compared to aliphatic species and also compared to the hydroxyl group removal. The heteroatom bond breaking for 2-methoxy-4-propylcyclohexanol proceed mostly via catechol-type diol formation, and subsequently, de-hydroxylation, particularly observable on Pt.

Nacre-inspired lightweight and high-strength AZ91D/Mg2B2O5w composites prepared by ice templating and pressureless infiltration

We developed a facile and low-cost approach to prepare lightweight and high-strength magnesium–matrix composites with a nacre-inspired laminated structure. First, lamellar Mg2B2O5 whisker (Mg2B2O5w) scaffolds with initial solid loadings of 10, 15 and 20 vol% were prepared by ice templating. The wettability between a molten AZ91D alloy and the Mg2B2O5w scaffold was greatly improved by the incorporation of nano-SiO2 sol in the aqueous slurry, making the preparation of nacre-mimetic AZ91D/Mg2B2O5w composite by way of pressureless infiltration feasible. The SiO2 content in the Mg2B2O5w scaffold has a significant effect on the processing and the microstructure and properties of the composites. The optimum SiO2 content was about 6–8 wt% of the total ceramic loading. A lower SiO2 content resulted in incomplete infiltration, while a higher content led to the formation of a large quantity of Mg2Si in the composite. The flexural strength of the composites seemed independent of the initial ceramic loading (10–20 vol%), whereas the compressive strength and elastic modulus increased considerably and the crack-growth fracture toughness decreased with increasing ceramic content. The mechanism for such variations was addressed.

Comparison of fermentation strategies for ethanol production from olive tree pruning biomass

Olive tree pruning is a widely available and low cost lignocellulosic residue generated every year, being a potential source for bioproducts and renewable fuels production. In this context, this work has as main objective to propose an efficient scheme for the production of second generation ethanol from olive tree pruning biomass, focusing on the evaluation of different detoxification strategies (activated carbon, ammonium hydroxide and overliming) of the liquid fraction obtained after pretreatment, as well as different configurations of enzymatic hydrolysis and fermentation (including hydrolysis and sequential or simultaneous fermentation, pre-saccharification or co-fermentation) of the pretreated olive tree pruning solid. The best results of each fraction were tested in slurry, at varying initial solid loadings and aeration levels. The use of NH4OH 5N as a detoxification method and the pre-saccharification and co-fermentation configuration without aeration are proposed, resulting in 13.86 g ethanol/100 g raw material after 46 h of process.

Enzyme kinetics of cellulose hydrolysis of Miscanthus and oat hulls.

Experiments were done to model enzymatic hydrolysis of Miscanthus and oat hulls treated with dilute solutions of nitric acid and sodium hydroxide in direct and reverse sequences. The enzymatic hydrolysis kinetics of the substrates was studied at an initial solid loading from 30 to 120g/L. The effects of feedstock type and its pretreatment method on the initial hydrolysis rate and reducing sugar yield were evaluated. The fitting results by the developed models showed good agreement with the experimental data. These models designed for developing the production technology of concentrated glucose solutions can also be applied for glucose fermentation into ethanol. The initial solid loading of 60-90g/L provides the reducing sugar concentration of 40-80g/L necessary for ethanol synthesis. The kinetic model can also be applied to investigate enzymatic hydrolysis of other substrates (feedstock type, pretreatment method) under the similar conditions used herein, with adjusted empirical coefficient values.

Simultaneous saccharification and viscosity reduction of cassava pulp using a multi-component starch- and cell-wall degrading enzyme for bioethanol production.

In this study, an efficient ethanol production process using simultaneous saccharification and viscosity reduction of raw cassava pulp with no prior high temperature pre-gelatinization/liquefaction step was developed using a crude starch- and cell wall-degrading enzyme preparation from Aspergillus aculeatus BCC17849. Proteomic analysis revealed that the enzyme comprised a complex mixture of endo- and exo-acting amylases, cellulases, xylanases, and pectina ses belonging to various glycosyl hydrolase families. Enzymatic hydrolysis efficiency was dependent on the initial solid loading in the reaction. Reduction in mixture viscosity was observed with a rapid decrease in complex viscosity from 3785 to 0.45Pas with the enzyme dosage of 2.19mg/g on a dried weight basis within the first 2h, which resulted from partial destruction of the plant cell wall fiber and degradation of the released starch granules by the enzymes as shown by scanning electron microscopy. Saccharification of cassava pulp at an initial solid of 16% (w/v) in a bench-scale bioreactor resulted in 736.4mg glucose/g, which is equivalent to 82.92% glucose yield based on the total starch and glucan in the substrate, after 96h at 40°C. Simultaneous saccharification and fermentation of cassava pulp by Saccharomyces cerevisiae with the uncooked enzymatic process led to a final ethanol concentration of 6.98% w/v, equivalent to 96.7% theoretical yield based on the total starch and cellulose content. The results demonstrated potential of the enzyme for low-energy processing of cassava pulp in biofuel industry.

Fabrication of porous silica ceramics by gelation-freezing of diatomite slurry

Diatomite-derived porous silica ceramics with high porosities of up to 90% were fabricated using a gelation-freezing method, which resulted in unidirectional cellular or random microstructure with micrometer-sized cells. The ice crystals that were formed during freezing of a diatomite powder dispersed gel were removed by sublimation during vacuum drying, and the green bodies were sintered at 1150–1350°C for 2h in air. The thermal conductivity of the porous ceramics prepared with initial solid loadings of 5 and 10vol% ranged from 0.09 to 0.16W/(mK) at room temperature. The proposed method is therefore promising for the preparation of ceramic thermal insulators with very low thermal conductivity.

Dilute nitric-acid pretreatment of oat hulls for ethanol production

Oat hulls are a promising feedstock annually renewable at an industrial scale for the production of second generation ethanol. Chemical pretreatment of oat hulls with a 4% (w/w) nitric acid solution at atmospheric pressure was performed in pilot production to give a pulp in which hydrolyzables account for 79.9%. Acid-insoluble lignin totaling 12.5% in the pulp does not deteriorate the efficiency of enzymatic hydrolysis using an enzyme cocktail of commercial BrewZyme BGX and CelloLux-A. At an initial solid loading of 33.3g/L, a hydrolyzate was obtained with a reducing sugar yield of 93.0% of the overall hydrolyzables. The high yield is assured only by removal of residual, water-soluble, nitrated lignin by water washing. Alcoholic fermentation was run using Saccharomyces сerevisiae Y-1693. Simultaneous saccharification and fermentation with delayed inoculation (dSSF) at an initial pulp loading of 90g/L was found to improve the ethanol yield by 1.2 times compared to separate hydrolysis and fermentation (SHF), i.e. 0.428 versus 0.343g/g cellulose, respectively. The ethanol samples obtained from oat hulls contain low percentages of esters and methanol.

Preparation of tubular hierarchically porous silicate cement compacts via a tert-butyl alcohol (TBA)-based freeze casting method

Tubular porous silicate cement compacts with hierarchical porosity were successfully fabricated via a tert-butyl alcohol (TBA)-based freeze-casting technique in one single step. These samples were characterized by unidirectional aligned pore channels and completely open porosity. Various experimental parameters affecting the macropore size, mesopore size, porosity, and compression strength were investigated, including the initial solids loading, freezing temperature and curing period. Both the research findings of microstructure observations and property tests show that the pore size decreased significantly with decreasing freezing temperature and increasing solids loading. The porosity increased significantly with decreasing solids loading, while the compressive strength decreased remarkably. In addition to their tunable physical characteristics, these brand-new inorganic porous materials with oriented aligned pore channels and dense layer surface showed high permeation performance and desirable separation ability. These results endow the silicate cement, a kind of low-cost and high-performance architecture material, with great potential as a novel ordered porous inorganic material for numerous applications, especially in separation process.

The role of CuO–TiO2 additives in the preparation of high-strength porous alumina scaffolds using directional freeze casting

Lamellar porous Al2O3 scaffolds with initial solid loading of 30 vol% were prepared by freeze casting using micron-sized Al2O3 powders as raw material and CuO–TiO2 additives as sintering aid. The effects of the composition of CuO–TiO2 on the microstructure, porosity and compressive property of the Al2O3 scaffolds were investigated and the mechanisms for sintering promotion addressed. The sintering aid effect was prominent when CuO:TiO2 was 1:2 in mass and their amount reached 3 wt% of the total ceramic powders. The corresponding compressive strength reached 176 ± 20 MPa with the porosity being 45 ± 1 % after sintering at 1450 °C for 2 h. Activation of the Al2O3 lattice due to partial substitution of Ti4+ for Al3+ and formation of a low-melting eutectic liquid were presumed to play a significant role in the sintering and strengthening of the Al2O3 scaffolds.

CFD simulation of viscosity modifier effect on cutting transport by oil based drilling fluid in wellbore

In this study particle transportation has been predicted in a wellbore for an oil based drilling fluid containing viscosity modifier using CFD simulation. The effects of fluid viscosity on particle transport capacity of fluid were studied by considering various particle parameters such as density, diameter, shape, and initial particle concentration and wellbore inclination through using the Algebraic Slip Mixture (ASM) model. Rheology of the drilling fluid was expressed by Herschel–Bulkley non-Newtonian fluid model. The influence of viscosifier concentration on fluid rheology show that it improves carrying capacity of particles but its effect attenuates in higher concentration. For 2 ppb of viscosifier in drilling fluid, the cutting transport capacity has been increased almost 12% whereas adding 4 ppb of viscosifier, only created about 14% escalation on the transportation of cuttings. Against this positive effect viscosity modifier make more pressure drop that was a costly effect for operation and this effect had constant rate (for each ppb viscosifier, pressure drop growth is equal to 200 kPa/m approximately). Also, the results indicate higher particle density or larger particle size results in less particles transportation in the wellbore. Increasing initial solid loading has an adverse impact on the transmission of solid particles in wellbore.

Techno-economic analysis of the deacetylation and disk refining process: characterizing the effect of refining energy and enzyme usage on minimum sugar selling price and minimum ethanol selling price.

BackgroundA novel, highly efficient deacetylation and disk refining (DDR) process to liberate fermentable sugars from biomass was recently developed at the National Renewable Energy Laboratory (NREL). The DDR process consists of a mild, dilute alkaline deacetylation step followed by low-energy-consumption disk refining. The DDR corn stover substrates achieved high process sugar conversion yields, at low to modest enzyme loadings, and also produced high sugar concentration syrups at high initial insoluble solid loadings. The sugar syrups derived from corn stover are highly fermentable due to low concentrations of fermentation inhibitors. The objective of this work is to evaluate the economic feasibility of the DDR process through a techno-economic analysis (TEA).ResultsA large array of experiments designed using a response surface methodology was carried out to investigate the two major cost-driven operational parameters of the novel DDR process: refining energy and enzyme loadings. The boundary conditions for refining energy (128–468 kWh/ODMT), cellulase (Novozyme’s CTec3) loading (11.6–28.4 mg total protein/g of cellulose), and hemicellulase (Novozyme’s HTec3) loading (0–5 mg total protein/g of cellulose) were chosen to cover the most commercially practical operating conditions. The sugar and ethanol yields were modeled with good adequacy, showing a positive linear correlation between those yields and refining energy and enzyme loadings. The ethanol yields ranged from 77 to 89 gallons/ODMT of corn stover. The minimum sugar selling price (MSSP) ranged from $0.191 to $0.212 per lb of 50 % concentrated monomeric sugars, while the minimum ethanol selling price (MESP) ranged from $2.24 to $2.54 per gallon of ethanol.ConclusionsThe DDR process concept is evaluated for economic feasibility through TEA. The MSSP and MESP of the DDR process falls within a range similar to that found with the deacetylation/dilute acid pretreatment process modeled in NREL’s 2011 design report. The DDR process is a much simpler process that requires less capital and maintenance costs when compared to conventional chemical pretreatments with pressure vessels. As a result, we feel the DDR process should be considered as an option for future biorefineries with great potential to be more cost-effective.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-015-0358-0) contains supplementary material, which is available to authorized users.

Comparison of anaerobic digestion characteristics and kinetics of four livestock manures with different substrate concentrations

Anaerobic digestions of pig manure (PM), dairy manure (DM), chicken manure (CM) and rabbit manure (RM) at initial volatile solid loading (VSL) of 8gVS/L, 16gVS/L, 32g VS/L, 64g VS/L were investigated under mesophilic conditions. The maximum methane yields of 410, 270, 377 and 323mL CH4/gVSadded for PM, DM, CM and RM were all obtained at initial VSL of 8gVS/L, respectively. The improvement of substrate concentration to 64gVS/L not only decreased the methane yield and biodegradability both by 22.4%, 37.3%, 49.1% and 34.6% for PM, DM, CM and RM respectively, but also reduced the methane content in final biogas production. The Cone model (R2: 0.9910–0.9974) showed a better fit to the experiment data and the calculated parameters indicated that anaerobic digestion of manures at higher loading has longer lag phase and lower hydrolysis rate.