Granular Bed Research Articles

Behaviour of circular footings resting on a reinforced granular bed underlain by a single floating stone column

Behaviour of circular footings resting on a reinforced granular bed underlain by a single floating stone column

Discrete element model of low-velocity projectile penetration and impact crater on granular bed

The present study investigates the low-velocity impacts of a spherical projectile into a bed of spherical particles using Discrete Element Method (DEM) simulations and laboratory experiments. The findings reveal intricate forces and energy transformations, indicating the phenomena leading to projectile impact, penetration, cessation, and crater formation. The DEM result indicates that the penetration stopping time of the projectile is not influenced by impact velocity. Further, simulations show that projectile penetration depth correlates with 1/2.7 power of total impact height, while crater diameter and depth scale with 1/4.32 power of nondimensional impact energy. The shape of the resulting crater appears independent of impact velocity and the maximum diameter of the fluidized region varies with the 1/2.68 power of impact velocity. Experimental validation confirms the accuracy of predicted penetration depths and crater diameters, enhancing confidence in DEM simulations. These findings extend scaling laws and reveal the influence of larger particles on low-velocity impact dynamics, addressing unexplored aspects of granular cratering.

Biogas production from piloted wood-based bioethanol process using high-rate anaerobic treatment – Focusing for inhibition and improving biodegradability

To promote the bioeconomy, biorefineries with novel processes are developed. Biogas technology is commonly applied in biorefineries, and in this study, its feasibility for biogas production from wastewaters generated in a novel piloted wood-based bioethanol process was examined in expanded granular sludge bed reactors (EGSB). The novel wastewater was found to have high organic matter content and contained potentially inhibitory compounds. Wastewater was diluted with reactor effluent or tap water (control), and the proportion of wastewater in the feed was increased gradually to increase the organic loading rate. The wastewater was acidic (pH 4.2–4.6) and contained high concentrations of soluble chemical oxygen demand (sCOD 21–51 g/L) and sulfate (1–2.5 g/L). EGSB reactors had high sCODww (sCOD in the wastewater) removal of 74–77 % with OLRs up to 22 kg-sCODww/m3d and no inhibition either by the sulfide resulting from the high influent sulfate concentration or by the re-use of reactor effluent was seen. Integration of anodic oxidation (AO) to the EGSB reactor was studied in batch experiments increasing the biodegradability and total sCOD removal to 80–83 % and enhancing the methane production by 3 %. The results provide valuable information to support the implementation of anaerobic treatment plants as part of new industrial scale bioproduct production processes and encourages further studies on AO.

Continuous self-circulating up-flow granular sludge fluidized bed process treating low-strength real municipal wastewater at high hydraulic loads

Conditions conducive to aerobic granular sludge (AGS) growth and maintenance are very difficult to realize in continuous-flow biological treatment processes. This study conducted a continuous-flow self-circulating up-flow granular sludge fluidized bed (Zier process) treating real urban wastewater approximately one year. The substantial self-circulating multiple times (RSCMT, 8–15 times) and up-flow velocity (8–15 m/h) generated by aeration, the only power equipment in Zier process, facilitated pollutant removal, particle granulation and stabilization. With hydraulic retention time of 5 h, RSCMT of 9.3–14.4 times and chemical oxygen demand (COD)/total nitrogen (TN) ratio of 5.9 ± 1.0, the effluent COD, ammonia nitrogen and TN were 28.6 ± 7.7, 1.1 ± 1.2, and 13.3 ± 1.7 mg/L, respectively. The median particle size was 150–250 μm and effluent suspended solids concentration was 33.4 ± 14.5 mg/L. It is unnecessary to set up sludge reflux which simplifies the subsequent mud-water separation facilities. The Zier process provides a new process structure for implementation of continuous-flow AGS process.

On the Relation between the Viscoelastic Properties of Granular Hydrogels and Their Performance as Support Materials in Embedded Bioprinting.

Granular hydrogels, formed by jamming microgels suspension, are promising materials for three-dimensional bioprinting applications. Despite their extensive use as support materials for embedded bioprinting, the influence of the particle's physical properties on the macroscale viscoelasticity on one hand and on the printing performance on the other hand remains unclear. Herein, we investigate the linear and nonlinear rheology of κ-carrageenan granular hydrogel through small- and large-amplitude oscillatory shear measurements. We tuned the granular hydrogel's properties by changing the stiffness (soft, medium, stiff) and the packing density of the individual microgels. Characterizations in the linear viscoelasticity regime revealed that the storage modulus of granular hydrogels is not a simple function of microgel stiffness and depends on the microgel packing density. At larger strains, increasing the microgel stiffness reduced the energy dissipation of the granular beds and increased the solid-fluid transition point. To understand how the different rheological properties of granular support materials influence embedded bioprinting, we examined the printing fidelity and cellular filament shrinkage within the granular beds. We found that microgels with low packing density diminished the printing quality, while stiff microgels promoted filament roughness. In addition, we found that highly packed stiff microgels significantly reduced the postprinting contraction of cellular filaments. Overall, this work provides a comprehensive knowledge of the rheology of granular hydrogels that can be used to rationally design support beds for bioprinting applications with specific characteristics.

A DEM study on the criteria for particle movement over a granular bed

The collision of a spherical particle onto a granular bed, generating a splash of ejected grains, is a crucial process in the study of wind-blown sand. Previous research has faced challenges in clearly distinguishing between particles in saltation, reptation, and creep motion. This study employs the Discrete Element Method (DEM) to simulate particle trajectories during sand-bed collisions, providing a systematic analysis of the vertical mass concentration profiles and the probability density functions (PDFs) for splash velocity, splash angle, and the number of splashed particles associated with saltation, reptation, and creep particles. Our results reveal that reptation motion predominantly occurs within a vertical height range of 0.064 mm to 8 mm above the surface, creep motion occurs below 0.032 mm, and saltation occurs at heights greater than 8 mm.

Long-term and multiscale assessment of methanogenesis enhancement mechanisms in magnetite nanoparticle-mediated anaerobic digestion reactor

Magnetite nanoparticles (Fe3O4-NPs) have been demonstrated to be involved in direct interspecies electron transfer between syntrophic bacteria, yet a comprehensive assessment of the ability of Fe3O4-NPs to cope with process instability and volatile fatty acids (VFAs) accumulation in scaled-up anaerobic reactors is still lacking. Here, we investigated the start-up characteristics of an expanded granular sludge bed (EGSB) with Fe3O4-NPs as an adjuvant at high organic loading rate (OLR). The results showed that the methane production rate of R1 (with Fe3O4-NPs) was approximately 1.65 folds of R0 (control), and effluent COD removal efficiency was maintained at approximately 98.32% upon 20 kg COD/(m3·d) OLR. The components of volatile fatty acids are acetate and propionate, and the rapid scavenging of propionate accumulation was the difference between R1 and the control. The INT-ETS activity of R1 was consistently higher than that of R0 and R2, and the electron transfer efficiencies increased by 68.78% and 131.44%, respectively. Meanwhile, the CV curve analysis showed that the current of R1 was 40% higher than R3 (temporary addition of Fe3O4-NPs), indicating that multiple electron transfer modes might coexist. High-throughput analysis further revealed that it was difficult to reverse the progressive deterioration of system performance with increasing OLR by simply reconfiguring bacterial community structure and abundance, demonstrating that the Fe3O4-NPs-mediated DIET pathway is a prerequisite for establishing multiple electron transfer systems. This study provides a long-term and multi-scale assessment of the gaining effect of Fe3O4-NPs in anaerobic digestion scale-up devices, and provides technical support for their practical engineering applications.

Long-term performance and activity study of a two-stage anaerobic EGSB reactors system treating complex and toxic industrial wastewater.

Anaerobic treatment of industrial wastewater using upflow anaerobic reactors is an extended trend due to its high efficiency and biogas production potential, but its implementation in some sectors is limited due to the complexity and toxicity of the wastewaters. In this study, a two-stage expanded granular sludge bed (EGSB) reactors system has been investigated at both bench and pilot scale for the treatment of complex and toxic real wastewater from a petrochemical industry. The effect of different operational parameters including organic loading rate (OLR), hydraulic retention time (HRT) and influent characteristics over COD removal and biogas production and composition have been studied. Additionally, biomass specific methanogenic activity (SMA) and wastewater toxicity have been evaluated after long-term operation. Optimum total HRT of 24 h has been determined resulting in total COD and SO4 2- removal of 56.30 ± 5.25% and 31.68 ± 14.71%, respectively, at pilot scale, and average biogas production of 93.47 ± 34.92 NL/day with 67.01 ± 10.23 %CH4 content and 5210.11 ± 6802.27 ppmv of H2S. SMA and toxicity tests have confirmed inhibitory and toxic effects of wastewater over anaerobic biomass with average maximum inhibition of 65.34% in the unacclimated anaerobic inoculum while chronic toxicity produced a decrease of an order of magnitude in SMA after 600 days of operation. This study demonstrates the feasibility of applying an anaerobic treatment to this wastewater using EGSB reactors between a 0.97-1.74 gCOD/L/day OLR range. Nonetheless, periodic reinoculation would be necessary for long-term operation due to chronic toxicity of the wastewater exerted on the anaerobic biomass. PRACTITIONER POINTS: A two-stage EGSB reactors system has been operated at bench and pilot scale to treat complex and toxic petrochemical wastewater. Optimal total HRT of 24 h resulted in average COD removal ranging from 40% to 60%. SMA and toxicity tests have been performed to study long-term acclimation, detecting an activity depletion of an order of magnitude.

Interaction between gas channels in water-saturated sands.

This work investigates the interaction between gas channels in a vertical Hele-Shaw cell when air is injected simultaneously from two points at a constant flow rate. Unlike single-injection experiments, this dual-point system induces the formation of numerous bubbles, thereby intensifying the interactions between air channels. We use an image analysis technique for tracking motion in the granular bed to define a flow density parameter throughout the cell. The vertical accumulation of this parameter (n_{z}) reveals two specific heights, one marking a finger-to-fracture transition and another indicating the average interaction height of the air channels. Conversely, its horizontal accumulation (n_{x}) assesses the extent of overlap in the fluidized zones created by each airflow. Notably, the analysis indicates that the optimum distribution of the three phases in the system is more closely related to the interaction's variability than its intensity. This finding is significant for industrial applications such as air sparging and catalytic reactors.

Start-up strategy of single-stage partial nitrification-anammox process for anaerobic digestion effluent

The objective of this study was to improve the nitrogen removal efficiency and reduce the start-up period of a single-stage partial nitritation-anammox (SPNA) system using iron particle-integrated anammox granules (IP-IAGs). Anammox granules were enriched in sequencing batch and expanded granular sludge bed (EGSB) reactors. The EGSB reactor produced larger and more uniform granules with higher specific anammox activity. IP-IAGs were then inoculated into a two-stage partial nitritation-anammox reactor treating anaerobic digestion (AD) effluent, followed by an internal recirculation strategy to acclimate the granules to oxygen exposure for SPNA. Finally, the SPNA process operated to treat real AD effluent under optimal conditions of 0.05 L/min aeration intensity (0.01 vvm) and 24 h of hydraulic retention time, achieving TNRE of 86.01 ± 2.64 % and nitrogen removal rate of 0.74 ± 0.04 kg-N/m3·d for 101 d.

An experimental and numerical study of the influence of the additive manufacturing process in packing properties of particles: the printed shape matters

Investigations into the various properties of granular matter composed of particles with defined shapes have gained increasing attention. Additive manufacturing, with its freedom of shape and rapid prototyping capabilities, has significantly contributed to these studies. However, this technique may introduce defects in the manufactured particles, which can significantly affect the properties of granular materials. The extent of these defects on particles of different shapes is investigated here. Particles of various shapes (cube, octahedron, quatropod, stellated octahedron, tetrahedron, and tetrapod) were manufactured and subsequently imaged using micro-Computed Tomography. The surface roughness, solidity, and convexity of the particles were quantified. Discrete element simulations of granular bed porosity, utilizing both idealized and real particle shapes, were conducted with different surface mesh resolutions and frictional parameters. A clear influence of the manufacturing process on the packing properties of 3D printed particles was identified. This influence is not uniform across all shapes and is directly correlated with the particle convexity. For numerical simulations, a shape-dependent correction of particle density and surface characteristics are imperative for each shape under consideration, despite the fact that the particles were manufactured using the same technique and material.Graphic abstract

A Coupled CFD-DEM Approach to Model Reactive Granular Beds

Packed and moving bed reactors are widely used in process industry to process granular material. Shaft furnaces are one example of this. Due to their counterflow layout, a high thermal efficiency can be achieved. Shaft furnaces have a wide range of length and time scales that makes them challenging to model. Geometric details, like injection nozzles, are smaller than the particle size, which need a computationally highly expensive resolved Discrete Element Method (DEM) approach. To overcome this problem, a computing technique called Volume Fraction Smoother (VFS) was developed. Since the time scales in those systems reach from milliseconds for the particle collisions to hours of process time, the process time scale must be separated to model a quasi-steady state with reasonable computing time. For this, the Time Scale Splitting Method (TSSM) was introduced. This method was also adapted to model the self-heating behaviour of direct reduced iron (DRI).

Impact of benzalkonium chloride on anaerobic granules and its long-term effects on reactor performance

This study assessed the inhibitory and performance-degrading effects induced by the cationic surfactant benzalkonium chloride (BAC) on anaerobic granules during the long-term operation of a laboratory-scale expanded granular sludge bed (EGSB) reactor. To address the critical scientific problem of how BAC affects the efficiency of EGSB reactors, this research uniquely evaluated the long-term stress response to BAC by systematically comparing continuous and discontinuous inhibitor exposure scenarios. The novel comparison demonstrated that inhibitor concentration is of minor relevance compared to the biomass-specific cumulative inhibitor load in the reactor. After exceeding a critical biomass-specific cumulative inhibitor load of 6.1–6.5 mg BAC/g VS, continuous and discontinuous exposure to BAC caused comparable significant deterioration in reactor performance, including accumulation of volatile fatty acids (VFA), decreased removal efficiency, reduced methane production, as well as the wash-out, flotation, and disintegration of anaerobic granules. BAC exposures had a more detrimental effect on methanogenesis than on acidogenesis. Moreover, long-term stress by BAC led to an inhibition of protein production, resulting in a decreased protein-to-polysaccharide ratio of extracellular polymeric substances (EPS) that promoted destabilizing effects on the granules. Finally, hydrogenotrophic methanogenesis was triggered. Reactor performance could not be restored due to the severe loss of granular sludge.

Enhancing submicron dust capture in high-temperature flue gases: A computational study on gradient pore-buried tube granular bed filters

Granular bed filters (GBF) represent a highly effective technology for purifying high-temperature dusty flue gases, although their efficiency in capturing submicron particles remains limited. A novel gradient porosity GBF model with varying bed structures and heat exchange capabilities was proposed. In this research, we employed CFD software to elucidate the movement and heat transfer process of 1 μm dust particles within gradient porosity GBFs and heat exchanger tubes. By optimizing the model under the conditions of a 0.5 m/s inlet flue gas flow rate and 1 μm dust particle size, we achieved a 345.62% increase in filtration efficiency and a 76.61% reduction in pressure drop. The findings indicate that the proposed GBF outperforms other models across various flue gas flow rates in terms of filtration efficiency. The impact of the flue gas flow rate on the combined filtration efficiency for submicron dust on the proposed GBF model was notably significant.

Enhanced sludge granulation and stable performance of an anammox expanded granular sludge bed (EGSB) reactor through the utilization of hydroxyapatite (HAP) particles

The reuse of hydroxyapatite particles (HAPs) as a granulation activator for anammox sludge was explored to address the remaining issues of time-consuming and unstable granular structure in anammox granulation. During the granulation, nitrogen removal capacity from 2.8 to 13.7 gN/L/d was obtained within 193 days, accompanied by an enhancement in bio-activity from 0.23 to 0.52 gN/gVSS/d. HAPs and anammox microorganisms coupled well to aggregate into granules for denser biomass, higher settleability, and stronger mechanical properties, which effectively improved the biomass retention capacity and structural strength of the sludge system. A skeleton structure formed by the HAPs was characterized during the transformation of the granules, playing a crucial role in strengthening the stability of the sludge. The intermediate processes of granulation were thus clarified to propose an evolutionary pathway for anammox-HAP granules. The pre-addition of HAPs is conducive to achieving faster anammox granulation and rapid process start-up for high-strength wastewater treatment.

An Improved Porosity Calculation Algorithm for Particle Flow Code

The widely used discrete-element particle flow software PFC’s (PFC 7.0 and previous versions) algorithm for calculating porosity is not sufficiently accurate. Because of this, when the particles are densely packed, the solution to the equation produces an algorithm exception for odd calculations of porosity, which results in the inability to calculate the results. This paper, based on a Darcy seepage model of fluid flow through a granular bed, analyzed the shortcomings of the two porosity calculation methods of PFC and the function analysis method. Combining this analysis with the theory of computer graphics, a new and efficient porosity calculation algorithm was proposed. The result showed that the new proposed porosity calculation algorithm calculated a more accurate and reasonable porosity field and made the iterative solution of the CFD equation more stable. This method makes porosity-related models of PFC more accurate. The algorithm can be not only used to calculate porosity, but also applied to other fields.

Cylinders intruding wet granular beds – experiment and simulation

ABSTRACT Quantitative visualization experiments and numerical simulations on cylindrical “alien” particles penetrating a liquid-saturated granular bed have been performed. The bed consists of mono-sized spheres. In dimensionless terms the bed is characterized by an Archimedes number, an angle of repose that represents friction, and a solids volume fraction. The conditions are such that the fluid flow generated by alien and bed particle motion is laminar. The experiments are well reproducible. The most important experimental observation is deeper penetration of the alien particle for higher liquid viscosities. The spatial resolution of the three-dimensional, time-dependent simulations is such that they resolve the flow around, and the motion of the individual particles. The flow solver is based on the lattice-Boltzmann method. To a certain extent the simulations are able to reproduce the viscosity effect observed experimentally.

The intruder motion in a cubic granular container

The Brazil nut effect is a key issue impeding the uniform distribution of particles in a mixed granular system. Extensive research was conducted on this segregation phenomenon in the 1990s and 2000s to identify the mechanisms and influencing factors involved. However, due to limitations in experimental techniques, the scope and effectiveness of research have been restricted. In this study, the Hall-effect magnetic sensing technique was utilized to track the motion of a single magnetic sphere (referred to as the intruder) within a cubic granular bed. This tracking method allowed for the measurement of the intruder's equilibrium positions as well as its trajectories. In a vibration-fluidized cubic granular container, an interesting phenomenon was observed: the intruder displayed a unique periodic helical oscillatory motion near the corner of the cubic container, with the oscillation amplitude gradually attenuating until stabilizing at its equilibrium position. A discrete element method simulation was carried out, revealing that the granular convection flow ascends from the center and descends near the container walls, with a faster flow rate at the four corners. An equation of motion was established accordingly for an intruder in such a convective granular flow, providing a comprehensive explanation for the observed intruder behavior. As a result of this comprehensive approach, we have uncovered the unique phenomenon of different mechanisms collectively driving the periodic spiral oscillation of the intruder before it eventually rested in its equilibrium position, a phenomenon whose mechanism has not previously been investigated in the literature.

Basal Force Fluctuations and Granular Rheology: Linking Macroscopic Descriptions of Granular Flows to Bed Forces With Implications for Monitoring Signals

AbstractGranular flows are ubiquitous in nature with single flows traversing a wide range of dynamic conditions from initiation to deposition. Many of these flows are responsible for significant hazards and can generate remotely detectable seismic signals. These signals provide a potential for real‐time flow measurements from a safe distance. To fully realize the benefit of seismic measurements, basal‐granular forces must be linked to macroscopic internal flow dynamics across a wide range of flow conditions. We utilize discrete element simulations to observe dry and submerged granular flows under plane‐shear and inclined‐flow configurations, relating bulk kinematics to basal‐force distributions. We find that the power and frequency of force fluctuations scale with non‐dimensional shear rate (I). This scaling tracks three pre‐established regimes that are described by μ(I) rheology: (a) an intermittent particle rearrangement regime, where basal forces are dominated by low frequencies; (b) an intermediate regime where basal forces start to increase in frequency while showing correlations in space and (c) a fully collisional regime where the signal is nearly flat up to a cutoff frequency. We further identify a newly defined fourth regime that marks a “phase change” from the intermediate to collisional regime where increases in basal force fluctuations with increasing shear rates stalls as the granular bed dilates, partially destroying the contact network. This effort suggests that basal forces can be used to interpret complex granular processes in geophysical flows.

Anaerobic treatment of fruit and vegetable wastewater using EGSB: From strategies for regulating over-acidification to microbial community

Fruit and vegetable waste (FVW) are characterized by high-water content. Solid-liquid separation of FVW by crushing-extrusion physical pre-treatment provides fruit and vegetable wastewater (FVWW), and then for anaerobic biological treatment to recover methane, which is considered a cost-effective approach. However, anaerobic treatment of FVWW faces difficulties with low methane productivity and over-accumulation of volatile fatty acids (VFAs). In this study, the expanded granular sludge bed (EGSB) reactor was used for the anaerobic treatment of FVWW and the regulatory strategy to alleviate over-acidification was proposed. When the influent chemical oxygen demand (COD) concentration was 10000 mg/L, the hydraulic retention time (HRT) was 2 days, the organic loading rate (OLR) reached 5 g COD/L/d, the maximum methane productivity reached 301.14 ± 2.32 mL/g COD with a COD removal rate of 96 % ± 2 %. Lower VFAs accumulation was observed when decreasing the influent COD concentration to the same OLR compared with extending HRT, resulting in 38.5 % higher methane productivity. Decreasing the influent COD concentration not only benefited the enrichment of acetogens and hydrogenotrophic methanogens but also specifically enriched syntrophic bacteria. The enhanced syntrophic acetogenesis and hydrogenotrophic methanogens maybe the main reasons for promoting the degradation of propionate and butyrate and improving the methane productivity.