Dilute Slurries Research Articles

High-titer lactic acid production from pilot-scale pretreated non-detoxified rice straw hydrolysate at high-solid loading

Lignocellulosic biomasses are promising feedstocks for the production of high-value chemicals because they are abundant, inexpensive, renewable, sustainable, environmentally friendly, and can potentially reduce pollution. Furthermore, lignocellulose biomass is non-edible and a source of fermentable sugars, which makes it ideal for the fermentation of various biochemicals, such as bio-based lactic acid (LA). Furthermore, it contributes to the economic sustainability of biorefineries. LA is an industrially significant product with a large and rapidly growing market due to its attractive features and benefits. The current study demonstrates high-titer lactic acid (LA) fermentation from pretreated rice straw using co-fermenting (C5 & C6 sugars) Lactobacillus lactis 2369. Rice straw (RS) was chemically pretreated with mild acid additive in a pilot-scale (250 Kg day–1) steam-explosion unit. At first, the crude dilute acid pretreated slurry was enzymatically hydrolyzed using commercial cellulases (1.5–10 FPUg−1 residue) at 50 °C for 48 h followed by LA production for 96–140 h. In the current study high titer, LA production (82.2 gL−1) as well as higher conversion yield (87.2%) with the productivity of 0.61 gL−1h−1 were obtained with high substrate solid loading (20% wv−1) and low enzyme dose (5 FPU g−1) at 42 °C.

Biocrust Amendments to Topsoils Facilitate Biocrust Restoration in a Post-mining Arid Environment.

Soil cryptogamic biocrusts provide many ecological functions in arid zone ecosystems, though their natural reestablishment in disturbed areas is slow. Accelerating reestablishment of biocrusts may facilitate the establishment of vascular plant communities within the timeframes of restoration targets (typically 5–15 years). One technique is to inoculate the soil surface using slurries of biocrust material harvested from another site. However, this is destructive to donor sites, and hence the potential to dilute slurries will govern the feasibility of this practice at large spatial scales. We conducted a replicated experiment on a disturbed mine site to test the individual and combined effects of two strategies for accelerating soil cryptogamic biocrust reestablishment: (1) slurry inoculation using biocrust material harvested from native vegetation; and (2) the use of psyllium husk powder as a source of mucilage to bind the soil surface, and to potentially provide a more cohesive substrate for biocrust development. The experiment comprised 90 experimental plots across six treatments, including different dilutions of the biocrust slurries and treatments with and without psyllium. Over 20 months, the reestablishing crust was dominated by cyanobacteria (including Tolypothrix distorta and Oculatella atacamensis), and these established more rapidly in the inoculated treatments than in the control treatments. The inoculated treatments also maintained this cover of cyanobacteria better through prolonged adverse conditions. The dilute biocrust slurry, at 1:100 of the biocrust in the remnant vegetation, performed as well as the 1:10 slurry, suggesting that strong dilution of biocrust slurry may improve the feasibility of using this technique at larger spatial scales. Psyllium husk powder did not improve biocrust development but helped to maintain a soil physical crust through hot, dry, and windy conditions, and so the potential longer-term advantages of psyllium need to be tested.

Enzymatic depolymerization of highly crystalline polyethylene terephthalate enabled in moist-solid reaction mixtures.

Less than 9% of the plastic produced is recycled after use, contributing to the global plastic pollution problem. While polyethylene terephthalate (PET) is one of the most common plastics, its thermomechanical recycling generates a material of lesser quality. Enzymes are highly selective, renewable catalysts active at mild temperatures; however, they lack activity toward the more crystalline forms of PET commonly found in consumer plastics, requiring the energy-expensive melt-amorphization step of PET before enzymatic depolymerization. We report here that, when used in moist-solid reaction mixtures instead of the typical dilute aqueous solutions or slurries, the cutinase from Humicola insolens can directly depolymerize amorphous and crystalline regions of PET equally, without any pretreatment, with a 13-fold higher space-time yield and a 15-fold higher enzyme efficiency than reported in prior studies with high-crystallinity material. Further, this process shows a 26-fold selectivity for terephthalic acid over other hydrolysis products.

A Review of On-farm Roadway Runoff Characterisation and Potential Management Options for Ireland

Runoff from farm roadways within farm boundaries are acknowledged as a year-round source of pollutants discharging to surface water, particularly during the main grazing season (Feb-Nov) when their usage is high. These losses are considered to be a significant catchment scale pressure and have led to recent legislation in Ireland to prohibit direct runoff from farm roadways to waters with similar guidance in the UK and New Zealand. However, roadway runoff (RR) remains an undocumented and understudied part of the transfer continuum where knowledge gaps remain in relation to its quantity and composition and in relation to the impacts of RR management options on adjacent surface waters. Indeed some information on mitigation measure design and efficacy is only available from non-agriculture land uses e.g. forestry and needs to be presented in a farm specific context. The present review brings together knowledge on RR in terms of content on- or off-roadway management options and proposes alternative mitigation measures that may require pilot scale testing. Studies show that RR contains a mix of legacy (surface materials) and incidental (fresh urine and faeces) constituents such as phosphorus (P), Escherichia coli (E. Coli) and sediment which become temporarily mobilised during rainfall events. Once mobilised, the roadway network can quickly transport pollutants providing connectivity between farmyards, hard standings, underpasses where attached to a watercourse, fields and even public roadways to watercourses. Its contents are not dissimilar to dilute slurry or dairy soiled water with loads being highest where animals congregate (within 100 m of the farmyard or where roadway configuration or quality impedes stock movement along the network). On-roadway management options include regularly spaced diversion structures that divert runoff for passive treatment in a field or drainage ditch or the application of chemical amendments to roadway surfaces. Off-roadway options can include natural or enhanced features, which attenuate flow leading to settlement of suspended sediment and in some cases treatment of a percentage of the load before delivery to a watercourse. It should be noted that the options presented in this review need to be retrofitted to site specific conditions. Therefore, a number of factors, including their effectiveness, cost and management needs on a particular farm, as well as local regulation requirements will need to be considered prior to implementation. Therefore, only the measures that divert RR away from waters are applicable to Ireland. Future research should develop and validate a farm roadway risk assessment tool to identify vulnerable roadway sections that need management and/or re-design, and identify means of incorporating RR into catchment scale risk assessment models. In addition, design of on- and off-RR management options should consider the wide variations in farm configuration and management with regard to size, topography, soil type/drainage class, enterprise, intensity, scale, stage of development and the potential impacts of climate change.

Erosion under turbulent slurry flow: Effect of particle size in determining impact velocity and wear correlation by inverse analysis

Surface topography after slurry erosion contains meaningful information concerning the process of erosive wear. This paper describes a procedure of inverse analysis to determine particle impact velocity from collective erosive features through image processing and further modeling. Slurry pot is used to produce wear damage on copper in exposure to a highly turbulent flow of dilute slurry of glass beads. Topography data for image processing is acquired by non-contact 3D profilometry. The analysis is carried out using two empirical models (Oka and Huang) and one analytical model (Cheng). The results reveal that the back-calculated velocity depends significantly on the model used. Whereas Huang's and Cheng's models produce values representative of the nominal flow conditions, the Oka's model results in unrealistic values. Finally, monotonic correlations between experimental variables associated with individual erosive features are discussed in the context of collective erosion models.

Early Detection of the Wear of Coriolis Flowmeters Through In Situ Stiffness Diagnosis

Coriolis flowmeters have been widely employed in a variety of industrial applications. There is a potential that the measuring tube of a Coriolis flowmeter may be eroded when it is used to measure abrasive fluid such as slurry flow. However, it is challenging to verify the structural health of the flowmeter without process interruptions or using on-site calibration devices such as meter provers. This article presents an in situ structural health-monitoring technique through stiffness diagnosis to identify the potential wear occurring on the measuring tube. To measure the frequency response of a Coriolis flowmeter, which strongly depends on the structural characteristics of the tube, the tube is not only excited at a resonant frequency but also at two additional off-resonant frequencies. Through digital processing of the drive and sensor signals, the frequency response is obtained and a stiffness-related diagnostic parameter (SRDP) is extracted from a Coriolis flowmeter. The proposed stiffness diagnosis technique was experimentally evaluated on a commercial bent-tube Coriolis flowmeter with dilute sand-water slurry flow. The results illustrate that the slight tube erosion is successfully identified when a relative change in SRDP reaches -1%, showing a good capability for an early detection of tube wear. In addition, the outcomes from recalibration with water suggest that, after the erosion occurs, the flowmeter overestimates the mass flowrate and underestimates the flow density.

Thermophysical properties of dilute acid slurries of cassava bagasse as a function of biomass loading, acid concentration, and temperature

AbstractFor suitable design of equipment and process optimization, the determination of thermophysical properties of the raw materials is necessary. Therefore, this work was aimed at determining and modeling the density, specific heat, thermal diffusivity, and thermal conductivity of acid slurries of cassava bagasse used during its conversion into bioethanol. Experimental measurements were carried out in slurries with different mass fractions of cassava bagasse (0.00 to 0.10) and phosphoric acid (0.00 to 0.10) at temperatures from 278.13 to 318.13 K. Results obtained show that density varied from 986.5 to 1,029.3 kg∙m−3, specific heat from 3,830.0 to 4,142.6 J∙kg−1∙K−1, thermal diffusivity from 0.9624 × 10−7 to 1.5249 × 10−7 m2∙s−1 and thermal conductivity from 0.3825 to 0.6212 W∙m−1∙K−1. While density increased with increasing solids and acid content at decreasing temperature, the thermal properties decreased at higher solids and acid content and increased when heating the slurries. The values were well‐fitted to polynomial models with good accuracy (R2 > 0.921 and MRE < 1.75%), allowing the application of the models to obtain reliable and ready‐to‐use data for cassava bagasse processing. Thus, the data reported in this study can be used for designing and managing momentum, heat and mass transfer processes for enhancing bioethanol production from cassava bagasse.

Use of frothers to improve the absorption efficiency of dilute sodium carbonate slurry for post combustion CO2 capture

With current environmental regulations, CO2 capture is very crucial for the survival of coal-fired power plants in the near future. In this work, the CO2 absorption performances of Na2CO3, NaOH, Monoethanolamine (MEA) and frother-enhanced Na2CO3 were investigated experimentally in a pilot scale gas−liquid countercurrent column. A surfactant was added to the sodium carbonate solution in order to increase the surface area available for CO2 transport within the packed bed. This increased the CO2 capture efficiency of dilute sodium carbonate slurry from 55.6% to 99.9%, before reaching saturation. The main intent of this study is to compare the efficiency of frothers and conventional reagents for chemical absorption CO2 capture. We analyzed the advantages and disadvantages of each of these reagents along with frother-enhanced sodium carbonate slurry.

Superabsorbent dewatering of refractory gold concentrate slurries

In this paper, superabsorbent polymer (SAB) dewatering behaviour of selected mineral pulps comprising low-grade, refractory gold flotation concentrate, bio-oxidation product and cyanide leach residue was investigated as an alternative to conventional, gravity thickening. The shear rheology of the resulting sediments was also investigated for pulp handleability. All slurries displayed better SAB-mediated dewatering performance, in terms of reduced processing time, volume minimization and greater water recovery for recycle, in comparison with gravity thickening. Specifically, SAB absorbed >94 wt.% water from the dilute slurries within 30 min of contact time. 45–76 wt.% more water was recovered after 60 min at high supernatant clarity using the SAB dewatering approach compared with gravity settling. The observed non-Newtonian, shear thinning rheological behaviour of SAB-dewatered consolidated slurries, reflecting low to moderate yield stresses in the range 1–40 Pa and shear thinning viscosities (<10 mPa⋅s), indicate their “handleability” in hydro-transport. The cost effectiveness of the SAB dewatering process engendered by its significantly greater water recovery and SAB polymer recovery, regeneration and multiple reuse capacity.

The influence of different shapes and size distributions of coating pigments on packing and dewatering

Particle shape and particle-size distribution (PSD) are important factors for pigment packing and water retention in the pigment coating process, being closely associated with many runnability problems. Diverse experimental investigations on the packing and dewatering of pigment slurries have been made. However, theoretical approaches remain lacking. This paper presents a joint experimental and theoretical analysis of the influence of pigment shape and PSD on pigment packing and dewatering. The relative viscosities of very dilute pigment slurries were measured and used to determine the intrinsic viscosity, based on the Einstein equation. The deviation of pigment shape from spherical caused an increase in viscosity of the slurries. Acicular precipitated calcium carbonates gave lower shape factor values than platy clay particles, which indicated that the needle-like particles could rotate more easily around their long axes under shearing conditions. The packing of pigments, which determines porosity, permeability, light scattering, and mechanical properties, was examined. The packing volumes of nonspherical pigments were estimated based on their respective PSDs, using an algorithm developed for spherical particles, modified with a correction factor. This model is based on the close random-packing volume fraction ( $$\emptyset_{\text{p}}^{ 2}$$ ) of particles of uniform size being an independent variable, regardless of their shape. Therefore, it was valid as long as the particles always achieve the same close random-packing volume ( $$\emptyset_{\text{p}}^{ 1}$$ ) by sedimentation or tapping. Overall, the effect of the particle shape and PSD on the dewatering and filter-cake permeability (Kf) was analyzed. The dewatering rates were measured with a common pressure filtration method, and the permeability of the filter cakes was obtained by fitting the data to a filtration equation. The particle size and PSD were found to influence the permeability constant, but there was little correlation between the permeability and particle shape.

Erosion under turbulent slurry flow: An experimental determination of particle impact angle, impact direction, and distribution thereof by image processing

In turbulent flows, the extent of erosive wear is given by particle impacts caused deviated from nominal flow by turbulent fluctuations. This paper describes an experimental determination of particle impact angle and impact direction distributions from collective wear scar features by image analysis. A slurry pot is used to produce wear damage on copper in exposure to a dilute slurry of glass beads. Degradation is evaluated by weight loss, and topography data for the image analysis is acquired by non-contact 3D profilometry. The results reveal that most of the kinetic energy is transferred by the tangential component of the impact velocity at shallow impact angles, regardless the particle size. Particle impact conditions do not distribute Gaussian and a statistical cut-off angle is established.

Converting a Dilute Slurry of Hollow Tube-like Papermaking Fibers into Dynamic Hydrogels

Commercially, assembly-directed packing of hollow tube-like papermaking fibers with widths of roughly 10–50 μm) into sustainable microfibrous bioassemblies (i.e., paper-based products) starts with a dilute fiber slurry. In this process, a huge amount of water is required to disperse and transport fibers, which also facilitates colloidal interactions and formation of interfiber bonds. To form bioassemblies in their dry states, unit operations associated with dewatering and drying are routine practices, and treatment of the generated wastewater is a necessity. We herein present a facile, easily scalable concept of converting fiber slurry into dynamic hydrogels by using chemical additives (similar to papermaking wet-end additives), but without water removal. We used a typical group of additives as an example in an attempt to demonstrate the applicability of the concept. With boron-based dynamic chemistry as a key theoretical foundation, the combination of crosslinking and hydrogen bonding can lead to the formation of phase-reversible, self-healable, and stretchable hydrogels. Essentially, the characteristics of hydrogels are facilely tunable, and process parameters such as polymer dosage are rather critical. It is worth noting that fibers can act as a structural skeleton or mechanical support for tailorable design of hydrogels. The concept demonstrated in this study provides insights into value-added utilization of mass-producible biopolymeric fibers in accordance with existing industrial facilities. Fiber-based hydrogels would find use in diversified applications: toys, 3D/4D printing materials, soft robots, drug delivery systems, among others.

Direct O&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; control on the partitioning between denitrification and dissimilatory nitrate reduction to ammonium in lake sediments

Abstract. Lacustrine sediments are important sites of fixed-nitrogen (N) elimination through the reduction of nitrate to N2 by denitrifying bacteria, and they are thus critical for the mitigation of anthropogenic loading of fixed N in lakes. In contrast, dissimilatory nitrate reduction to ammonium (DNRA) retains bioavailable N within the system, promoting internal eutrophication. Both processes are thought to occur under oxygen-depleted conditions, but the exact O2 concentration thresholds particularly of DNRA inhibition are uncertain. In O2 manipulation laboratory experiments with dilute sediment slurries and 15NO3- additions at low- to sub-micromolar O2 levels, we investigated how, and to what extent, oxygen controls the balance between DNRA and denitrification in lake sediments. In all O2-amended treatments, oxygen significantly inhibited both denitrification and DNRA compared to anoxic controls, but even at relatively high O2 concentrations (≥70 µmol L−1), nitrate reduction by both denitrification and DNRA was observed, suggesting a relatively high O2 tolerance. Nevertheless, differential O2 control and inhibition effects were observed for denitrification versus DNRA in the sediment slurries. Below 1 µmol L−1 O2, denitrification was favoured over DNRA, while DNRA was systematically more important than denitrification at higher O2 levels. Our results thus demonstrate that O2 is an important regulator of the partitioning between N loss and N recycling in sediments. In natural environments, where O2 concentrations change in near-bottom waters on an annual scale (e.g., overturning lakes with seasonal anoxia), a marked seasonality with regards to internal N eutrophication versus efficient benthic fixed-N elimination can be expected.

Persistence of three bisphenols and other trace organics of concern in anaerobic sludge under methanogenic conditions

ABSTRACT The degradation and distribution of bisphenol A (BPA), bisphenol S (BPS) and bisphenol AF (BPAF) were evaluated in dilute anaerobic sludge slurries amended with a single bisphenol or a mixture of all three and maintained under methanogenic conditions over a 28-d period. No significant degradation of the bisphenols was observed in methane-generating microcosms. Rapid sorption to sludge particles was the primary removal process with sorption observed: BPAF > BPA > BPS. Several other trace organic chemicals of concern in the sludge were detected using quadrupole time of flight mass spectrometry. Of those detected, triclosan and triclocarban had sufficiently high intensities to quantify changes over the 28-d period in the bisphenol-amended microcosms. Similar to the bisphenols, triclosan and triclocarban concentrations also did not significantly change over the 28-d period with concentrations quantified at 2021 ± 627 and 1864 ± 769 μg/kg dry weight, respectively. Findings exemplify that methane-generating microcosms do not appear conducive to significant degradation of trace organics of concern in anaerobic sludge digesters.

Discovery of potential pathways for biological conversion of poplar wood into lipids by co-fermentation of Rhodococci strains

BackgroundBiological routes for utilizing both carbohydrates and lignin are important to reach the ultimate goal of bioconversion of full carbon in biomass into biofuels and biochemicals. Recent biotechnology advances have shown promises toward facilitating biological transformation of lignin into lipids. Natural and engineered Rhodococcus strains (e.g., R. opacus PD630, R. jostii RHA1, and R. jostii RHA1 VanA−) have been demonstrated to utilize lignin for lipid production, and co-culture of them can promote lipid production from lignin.ResultsIn this study, a co-fermentation module of natural and engineered Rhodococcus strains with significant improved lignin degradation and/or lipid biosynthesis capacities was established, which enabled simultaneous conversion of glucose, lignin, and its derivatives into lipids. Although Rhodococci sp. showed preference to glucose over lignin, nearly half of the lignin was quickly depolymerized to monomers by these strains for cell growth and lipid synthesis after glucose was nearly consumed up. Profiles of metabolites produced by Rhodococcus strains growing on different carbon sources (e.g., glucose, alkali lignin, and dilute acid flowthrough-pretreated poplar wood slurry) confirmed lignin conversion during co-fermentation, and indicated novel metabolic capacities and unexplored metabolic pathways in these organisms. Proteome profiles suggested that lignin depolymerization by Rhodococci sp. involved multiple peroxidases with accessory oxidases. Besides the β-ketoadipate pathway, the phenylacetic acid (PAA) pathway was another potential route for the in vivo ring cleavage activity. In addition, deficiency of reducing power and cellular oxidative stress probably led to lower lipid production using lignin as the sole carbon source than that using glucose.ConclusionsThis work demonstrated a potential strategy for efficient bioconversion of both lignin and glucose into lipids by co-culture of multiple natural and engineered Rhodococcus strains. In addition, the involvement of PAA pathway in lignin degradation can help to further improve lignin utilization, and the combinatory proteomics and bioinformatics strategies used in this study can also be applied into other systems to reveal the metabolic and regulatory pathways for balanced cellular metabolism and to select genetic targets for efficient conversion of both lignin and carbohydrates into biofuels.

Porous Alumina Ceramics Obtained by Particles Self-Assembly Combing Freeze Drying Method.

An innovative approach for fabricating porous alumina ceramics is demonstrated in this paper. The distinguished feature is that the construction of the porous structure stems from the interaction between ceramic particles, which is a poorly explored area. By tailoring the Derjaguin-Landau-Verwey-Overbeek (DLVO) interaction energy to the second minimum, the dilute ceramic slurry would be gelled by the weakly assembled particle network, and the assembled structure is conserved via a freeze drying strategy. The DLVO theoretical analyses revealed that the second minimum of interaction energy could be obtained when the counter-ion concentration in colloidal suspension is 1.5 × 10−2 mol/L. The properties of the as-assembled samples were compared with one produced by the conventional freeze drying method. Results showed that the self-assembly of alumina particles has a positive influence on micro structures. Unlike the laminar pores generated by the traditional freeze drying procedure, the assembled samples show homogeneously interconnected and hierarchical open pores which were stable even after a 24 h dwell time at 950 °C (open porosity is 79.19% for the slurry of vol 20% solid loading). Particularly, after sintering at 1550 °C for 2 h, open porosity (67.01%) of the assembled samples was significantly greater than that of their un-assembled counterparts (39.97%). Besides, the assembled sample shows a narrower pore size distribution and a relatively higher cumulative pore volume.

A Theoretical Model for the Rake Blockage Mitigation in Deep Cone Thickener: A Case Study of Lead-Zinc Mine in China

Deep cone thickener (DCT) is key equipment in cemented paste backfill (CPB) technology. However, rake blockage occurs frequently in DCT during the dewatering process of the unclassified tailings being thickened from dilute slurry to thickened tailings or paste. Rake blockage has disastrous effects on the CPB operation. In order to investigate the influencing factors of rake blockage in DCT, a mathematical model of rake power in DCT was developed. In addition, stacking mud bed (made of thickened tailings) from the DCT in Huize lead-zinc mine (HLZM) in different rake blockage accidents was sampled and tested to investigate the effect of tailings characters on rake blockage. Results indicated that the concentration of the mud bed and the friction between the mud bed and the cone wall contributed to the rake blockage. The concentration and friction were influenced by the high content of coarse particles in the mud bed. Moreover, activating devices for bed mud, as the corrective and preventive action, were developed to prevent the rake blockage, which was valid in HLZM.

Improved dewatering of clay rich mineral dispersions using recyclable superabsorbent polymers

Despite the achievement of fast sedimentation rates in gravity-driven thickeners using flocculants, characteristically low to mediocre sediment consolidation with undesirably high water content (e.g., >87vol.%) is observed for clay-rich suspensions. The present work investigates the application of unconventional, recyclable sodium polyacrylate superabsorbent (SAB) polymer to dewater fine, hydrophilic Na-montmorillonite swelling clay and saprolitic nickel (Ni) laterite slurries for dramatic improvement. The results indicated that SAB application to concentrated and dilute slurries led to remarkably high water recoveries, unattainable via flocculation and thickening. In most cases, >95% of the water absorption occurred within 3h. The extent of SAB water absorption was greater for saprolitic slurries than for Na-montmorillonite slurries, regardless of dispersion conditions. Consequently, 66–85wt.% of the water in the slurry was recovered for recycle, exemplifying the efficacy and beneficial use of the superabsorbent in hydrophilic mineral slurry dewatering applications.

Beneficiation of Low Grade Calcium Bentonite Claystone

The beneficiation of Ca-bentonite claystone has been studied with dispersion sedimentation technique using polyionic salts as dispersant.The claystone is located in the Western Desert of Iraq. It is of a low grade, associated with different amount of clay and non-clay mineral impurities. Calcite (CaCO3) constitutes the major proportion of these impurities. Various parameters; solid concentration, dispersant amount (e.g. sodium tripolyphosphate, and tetrasodium pyrophosphate), conditioning time, and centrifugal sedimentation speed and time on the efficiency of the beneficiation process were investigated and followed through the measurement of CaO% and cation exchange capacity (CEC) values of the upgraded claystone concentrate. Centrifugal sedimentation were tested to separate the impurities from the clay suspension. Design experiments by Taguchi method, orthogonal array L16, was used for optimizing the different process parameters of the beneficiation process. Experiments were conducted at different solid concentrations (1, 3, 5, 7) wt.%, dispersion agent amount (0.2, 0.4, 0.6, 0.8) wt.%, conditioning time (5, 10, 15, 20) min, centrifugal sedimentation speed (500, 600, 700, 800) rpm, and centrifugal time (5, 10, 15, 20) min. The optimum beneficiation conditions obtained from the experimental work are, 7 wt.% solid concentration, 0.8 wt.% of dispersant, 15 min conditioning time attachment of the dispersant agent with the bentonite slurry, 800 rpm centrifugal speed, for 10 min time. Under studied condition, tetrasodium pyrophosphate showed better output t for achieving good beneficiation of bentonite clay from dilute crude slurry.

Formulation and validation of a computational model for a dilute biomass slurry undergoing rotational mixing

In this paper we develop a computational model for the mixing and transport of a dilute biomass slurry. The objective was to create a sufficiently simple and efficient model for biomass transport that can be coupled with reaction models for the study of conversion of cellulosic biomass into fermentable sugars. Our target system is 5%-by-mass α-cellulose, which is our proxy for more complex lignocellulosic biomass. In the authors’ previous work, an experimental investigation with α-cellulose under two vane-mixer configurations showed a bifurcation between a settling regime, for which settling effects dominate, and a suspended regime, for which solids are mostly suspended. Here, a mixed-fluid model was chosen, for which the model for the mixture-velocity field is the incompressible Navier-Stokes equations under the Boussinesq approximation for buoyancy. Solids transport includes solids motion due to diffusion, settling, advection, and shear. Comparison of simulated and experimental results show good agreement in the suspended regime, and in capturing the bifurcation rate. While the model captured well the distribution of solids in the settling regime, the model was incapable of capturing the high torque values seen in experiments with vanishing mixer rotation rate.