Hydraulic Shear Stress Research Articles

Pressurised flow in cracks in embankment dam cores

A major hazard to embankment dams is internal erosion and piping arising from concentrated leaks through cracks in the core due to differential settlement. Previous work (Peirson et al., 2023) quantified the hydraulics of flow through near-surface transverse cracks subject to near-horizontal pressure gradients. This present short note extends the previous work to address pressurised flow through cracks that might occur deeper within the core. Water speeds, hydraulic shear stresses, flows are computed as a function of the applied hydraulic gradient. These results extend previous work addressing the hydraulics of very narrow cracks.

Effects of initial soil moisture on rill erodibility and critical shear stress factors in the WEPP model across diverse soil types

Rill erosion, a significant issue in agricultural regions, is intricately linked to initial soil moisture conditions, affecting the development of concentrated flow erosion processes. However, understanding its dynamics amidst varying soil moisture conditions remain challenging. This study aimed to assess the impact of different soil moisture levels on rill erodibility parameters in the Water Erosion Prediction Project (WEPP) model and to evaluate soil cohesion across a spectrum of soils. Through laboratory experiments employing a small V-shaped rill channel, we investigated rill erodibility (Kr) and critical hydraulic shear stress (τcr), under three soil moisture scenarios: initially dry, saturated, and drainage, with incremental surface inflow rates. Additionally, we examined the efficiency of soil cohesion obtained from an Automated Soil Cohesion Measurement Apparatus in predicting Kr and τcr across various soil textures. Our analysis encompassed twenty soils representing nine texture classes, revealing significant correlations between basic soil properties, cohesion parameters, and WEPP model rill erodibility. Notably, initial soil moisture conditions exerted substantial influence on erodibility potentials. Soils with higher silt contents demonstrated better fits in terms of Nash-Sutcliffe model efficiency, particularly under initially dry and saturated conditions. However, predictions for initially drained soils yielded poor fits, emphasizing the intricate interplay between soil properties and hydrological conditions. In conclusion, our findings emphasize the critical role of topsoil water dynamics in rill erodibility. We propose that soil cohesion serves as a valuable predictor, complementing friction forces within the soil and enhancing simulations of rill erodibility under shallow flow conditions in rills, particularly in next-generation process-based modeling approaches.

Computational fluid dynamics simulation of passive downstream fish passage over a weir with OpenFOAM®

Many fish species are dependent on migration through river systems. Weirs are an obstacle to downstream migration, which can lead to obstruction as well as injury and mortality. The current level of knowledge about downstream migration over weirs is limited, and the current assessment of this is uncertain. This study uses a computational fluid dynamics (CFD) method for assessing the damage potential of the downstream migration over the weir, evaluating the effectiveness of the current recommendations. Two test cases were simulated using OpenFOAM® and an interFoam-based solver, extended with Lagrangian particles to represent passively transported fish. The results of the simulations show that adherence to the recommendation for a necessary tailwater level has no significant impact on the relevant hydraulic stressors, shear stress, pressure changes and collisions in certain situations. A thick nappe, however, leads to a significant reduction in collisions, especially of particles initialized near the surface. The CFD method used in this study proves to be suitable for evaluating downstream fish passage with certain limitations. This means that qualitative comparisons of different situations are possible, but not the determination of the damage potential of a specific situation. Further investigations are necessary to identify factors for safe downstream fish passage.

A comprehensive and molecular level evaluation of treated wastewater reusing via drip systems: Interactions of dissolved ions and hydraulic shear stresses on calcium carbonate scaling

To overcome the global water shortage, the treated wastewater is increasingly utilized in agricultural irrigation, and thus reducing freshwater consumption and increasing the water sustainability. Drip irrigation technology is the most appropriate irrigation method to utilize these water sources. However, its operating performance is negatively affected by calcium carbonate (CaCO3) scaling, which is one of the most dominant precipitations and also closely related to dissolved ions and the hydraulic characteristics inside irrigation systems. Thus, the effects of eight common dissolved ions (K+, Mg2+, Mn2+, Zn2+, Fe3+, NO3−, SO42−, and PO43−) in these water sources and four hydraulic shear stresses (0, 0.2, 0.4, and 0.6 Pa) on CaCO3 scaling formation were assessed in this study. Results showed that CaCO3 scaling was primarily formed of calcite and aragonite. Fe3+ would significantly accelerate the CaCO3 scaling accumulation, as it reduced the unit cell volume and chemical bonds of calcite, enhancing calcite adhesion and stability. On the other hand, Mg2+, Mn2+, NO3−, SO42−, and PO43− significantly inhibited CaCO3 scaling. Among them, Mg2+, Mn2+, and PO43− followed the typical water chemical precipitation rule, while NO3− increased water molecule diffusion rate and thus decreased the possibility that Ca2+ and CO32− to precipitate. SO42− grabbed the binding point belonging to CO32− and was adsorbed on the calcite crystal, which inhibited crystal growth. However, those treatments under K+ and Zn2+ did not reach a significant level due to their solubleness. During the precipitation of CaCO3, there were significant (p < 0.01) interactions between dissolved ions and hydraulic shear stresses. When hydraulic shear stresses varied, the effects of Fe3+ and SO42− on the CaCO3 scaling were relatively weakened, while that of Mg2+ was relatively strengthened. In return, dissolved ions affected the effect of hydraulic shear stresses on CaCO3 scaling. Overall, the results obtained could provide theoretical reference for high-efficiency utilization of treated wastewater for agricultural irrigation through the management of CaCO3 scaling.

Enhancement of sewer sediment control and disruption of adhesive gelatinous sediment structure using low-dose calcium peroxide

Large quantities of sediments in urban sewer systems pose significant risk of pipe clogging and corrosion. Owing to their gel-like structure, sewer sediments have strong resistance to hydraulic shear stress. This study proposed a novel approach to weaken the erosion resistance of sewer sediments by destroying viscous gel-like biopolymers in sediments with low doses of calcium peroxide (CaO2). After treatment with 10–50 mg g−1 TS of CaO2, the critical erosion shear stress was significantly reduced by 25.7%–59.9%. The sediment aggregates gradually disintegrated into small diameter particles with increasing CaO2 dosage. Further analysis showed that the strong oxidizing and alkaline environment induced by CaO2 treatment led to cell lysis and changes in the composition and property of extracellular polymeric substances (EPS). After CaO2 treatment, aromatic proteins and humic acid-like substances associated with adhesion translocated from the inner EPS layers to outer layers while being disintegrated into small organic molecules. Concomitantly, CaO2 treatment disrupted the main functional groups (–OH, COO−, C–N, CO, and CN) in inner EPS layers, thus weakening EPS adhesion. Analysis of protein secondary structure and zeta potential reflected the reduced aggregation capacity of sediment microorganisms and loosening of sediment structure after CaO2 treatment. Thus, CaO2 treatment facilitated fragmentation and disaggregation of the gelatinous structure of sewer sediments. Such green strategy decreased the cost of sewer sediment disposal by 42.10–68.95% when compared to water flushing, and it would improve the self-cleaning capacity of sewer system and efficiency of dredging equipment.

The design and evaluation of the outflow structures of an interventional microaxial blood pump.

Blood pump design efforts are focused on enhancing hydraulic effectiveness and minimizing shear stress. Unlike conventional blood pumps, interventional microaxial blood pumps have a unique outflow structure due to minimally invasive technology. The outflow structure, composed of the diffuser and cage bridges, is crucial in minimizing the pump size to provide adequate hemodynamic support. This study proposed four outflow structures of an interventional microaxial blood pump depending on whether the diffuser with or without blades and cage bridges were straight or curved. The outflow flow structure's effect on the blood pump's hydraulic performance and shear stress distribution was evaluated by computational fluid dynamics and hydraulic experiments. The results showed that all four outflow structures could achieve the pressure and flow requirements specified at the design point but with significant differences in shear stress distribution. Among them, the outflow structure with curved bridges would make the blood dispersed more evenly when flowing out of the pump, which could effectively reduce the shear stress at the cage bridges. The outflow structure with blades would aggravate the secondary flow at the leading edge of the impeller, increasing the risk of flow stagnation. The combination of curved bridges and the bladeless diffuser had a relatively better shear stress distribution, with the proportion of fluid exposed to low scalar shear stress (<50Pa) and high scalar shear stress (>150Pa) in the blood pump being 97.92% and 0.26%, respectively. It could be concluded that the outflow structure with curved bridges and bladeless diffuser exhibited relatively better shear stress distribution and a lower hemolysis index of 0.00648%, which could support continued research on optimizing the microaxial blood pumps.

Development of a Novel Laboratory Rotating Surface Erosion Apparatus for Cohesive or Stabilized Soils

Abstract Soil surface erosion has been recognized as a major threat to the sustainability of infrastructure, particularly in the context of climate change that can accelerate changes in physicochemical properties of eroding fluids. This study proposes a rotating surface erosion apparatus (RSEA) for soil erosion tests on cohesive/stabilized soils. Compared to other erosion test apparatuses, RSEA possesses some unique features: (1) it enables testing both disturbed and undisturbed in-situ soil specimens while imposing uniform hydraulic shear stress on the specimens, (2) it produces negligible temperature changes in the eroding fluid during the erosion testing, and (3) it accommodates fluids with different physicochemical properties. The computational fluid dynamics analysis was conducted to guide the design of the apparatus. The details of the design and fabrication of this apparatus are presented, followed by the discussions of the calibration and test procedure. In the end, effect of suspension on erosion testing using the proposed RSEA was discussed. Preliminary tests on cemented sands considering different temperature and acidity in eroding fluids were also performed and the results are discussed.

Hemodynamic investigation of a novel rotary displacement blood pump for extracorporeal membrane oxygenation.

Extracorporeal membrane oxygenation (ECMO) is a life support system used in the treatment of severe respiratory and circulatory failure. High shear stress caused by the high rotational speed of centrifugal blood pumps can cause hemolysis and platelet activation, which are among the major factors leading to the complications of the ECMO system. In this study, a novel blood pump named rotary displacement blood pump (RDBP), which can considerably reduce rotational speed and shear stress while ensuring the normal pressure flow relationship, was proposed. We employed computational fluid dynamics (CFD) analysis to investigate the performance of RDBP under adult ECMO support operating conditions (5 L/min with 350 mmHg). The efficiency and H-Q curves of the RDBP were calculated to evaluate its hydraulic performance, and pressure, flow patterns, and shear stress distribution were analyzed to estimate the hemodynamic characteristics in the pump. In addition, the modified index of hemolysis (MIH) was calculated for the RDBP based on a Eulerian approach. The hydraulic efficiency of the RDBP was 47.28%. The velocity distribution of flow field in the pump was relatively uniform. Most of the liquid (more than 75%) in the pump was exposed to low scale shear stress (<1 Pa), which was close to normal physiological conditions. The gap area was the main distribution location of high scale shear stress. The high wall shear stress (>9 Pa) volume fraction of the RDBP was small and located in the boundary areas between the rotor's edge and the housing. The MIH value of the RDBP was 9.87 ± 0.93 (mean ± SD). The RDBP can achieve better hydraulic efficiency and hemodynamic performance at lower rotational speed. The design of this novel pump is expected to provide a new direction for developing a blood pump for ECMO.

Enzymatic-Induced Calcite Precipitation (EICP) Method for Improving Hydraulic Erosion Resistance of Surface Sand Layer: A Laboratory Investigation

As a bio-inspired calcite precipitation method, bio-grouting via enzymatic-induced calcite precipitation (EICP) uses free urease enzyme to catalyze the urea hydrolysis reaction. This soil stabilization approach is relatively new and insufficiently investigated, especially for applications involving surface layer stabilization of sandy soil deposits for increasing hydraulic erosion resistance. This paper presents a laboratory investigation on the surface erosion resistance improvements for compacted medium-gradation quartz sand specimens mediated using 10 different EICP treatment protocols. They involved single- and two-cycle injections of the urease enzyme (activity of 2400 U/L) and 0.5, 0.75, or 1.0-M urea–CaCl2 cementation solution reagents. The urease enzyme was extracted from watermelon seeds. Erosion rates were determined for various hydraulic shear stresses applied using the erosion function apparatus. The spatial distribution and morphology of precipitated calcite within the pore-void spaces of the crustal sand layer were investigated with a scanning electron microscope. Compared to untreated sand, all 10 investigated EICP treatment protocols produced substantially improved erosion resistance, especially for the higher cementation solution concentration (1.0 M). Of these 10 EICP protocols, a single cycle of enzyme–1.0-M-cementation solutions injections was identified as the more pragmatic option for achieving near-optimum erosion resistance improvements. Highest and lowest amounts (18.8 and 5.0 wt%) of precipitated calcite corresponded to the best and worst performing EICP-treated specimens, although the calcite’s spatial distribution in treated specimens is another important factor.

Reducing the Erodibility of Sandy Soils Engineered by Cyanobacteria Inoculation: A Laboratory Investigation

Windblown and water-induced erosion cause substantial soil losses worldwide, especially for drylands. Any sustainable management program that increases soil organic matter and improves the stability of the crustal layer could considerably enhance soil productivity and the preservation of erosion-prone land. This paper presents a laboratory investigation of cyanobacteria-inoculated medium sand and fine sand soils studied for severe runoff conditions that were simulated using an erosion function apparatus (EFA). Loosely deposited sand specimens prepared by air-pluviation were inoculated with a single native filamentous-cyanobacterium strain (investigating both Nostoc sp. and Calothrix sp.) and then incubated under high exposure to white light for 32- or 48-day periods. Well-developed bio-crusts were produced on the specimens’ top surface that achieved substantial improvements in erosion resistance, as was demonstrated for a wide range of hydraulic shear stress investigated using EFA experiments. Relative improvements in hydraulic erosion resistance were explained in terms of the nature of the cyanobacteria-developed microstructures (cyanobacteria filament infiltration of pore-void spaces and exopolysaccharide excretion), as were observed by scanning electron microscope examinations. The developed microstructure depended on the cyanobacterium strain employed and the nominal pore-void sizes that are related to the sand gradation and density state. The encouraging findings of this experimental investigation suggest a tailored approach (i.e., employing a suitable native cyanobacterium strain chosen for its compatibility with the soil’s physical properties) could lay the basis for developing a novel technology for soil protection.

Hydrological and erosion responses of steep spoil heaps to taproot and fibrous root grasses under simulated rainfalls

Spoil heaps, resulting from excavation and backfilling activities at construction sites, are one of the most important risk sources of soil erosion, threatening local ecosystems and even leading to geological disasters. However, after revegetation, spoil heaps can be transformed into available land resources such as cultivated land and forest land. Previous studies have reported the runoff and sediment reduction benefits of different vegetation measures on spoil heaps, while little information has been documented about what differences in the taproot and fibrous root grasses were transferred into the differences in hydrological and erosion processes. This study compared the effects of taproot (Artemisia gmelinii (A. gmelinii)) and fibrous root (Cynodon dactylon (C. dactylon)) grasses on soil erosion and runoff production processes and the reduction benefits of spoil heaps with silt loam soil. A series of rainfall events at three intensities (0.8, 1.2, and 1.8 mm min−1) were simulated on runoff plots (length of 3.0 m and width of 1.0 m) under treatments of A. gmelinii, C. dactylon, and bare soil (BS, as control) (each treatment was replicated), and the initial runoff time (IRT), saturated hydraulic conductivity, runoff rate (RR), flow velocity, and soil loss rate (SLR) were measured. The results showed that grasses delayed the IRTs on spoil heaps by 0.69–12.96 min compared BS, and the delay effects were more significant for fibrous root grass than for taproot grass. The soil loss reduction benefits (91.1 %) of the two kinds of grass were approximately 2.2 times greater than those of runoff volume reduction (42.1 %), and shear stress could be used to predict the soil loss rate following power functions (R2 = 0.72–0.85) for the grass-covered plots. The taproot grass exhibited a higher erosion reduction than fibrous root grass and is thus preferred to control the soil erosion of spoil heaps. Taproot grass has a greater stem diameter and can insert deeper into spoil heaps to consolidate the soil particles, which can improve roughness and hydraulic resistance, thereby producing a lower effective hydraulic shear stress that is directly exerted on soil particles. This study enhances the understanding of different grasses on the water erosion process and mechanism of spoil heaps and provides scientific guidance for selecting erosion control practices.

Entropy-based Model for Gully Erosion - A combination of probabilistic and deterministic components.

Gullies are a major threat to ecosystems, potentially leading to land degradation, groundwater depletion, crop loss, debris flow, and desertification. Gullies are also characterized by having a fast development and turning into primary sediment sources. Despite their impact, we have but scarce understanding of how gully erosion evolves and how to model it. In this paper, we propose a new gully erosion model that is based on the classical premise of net shear stress, i.e., hydraulic shear stress minus critical (resistant) shear stress, to calculate detachment rates. In order to calculate hydraulic shear stress, we developed a new equation derived from the principle of minimum cross-entropy; it was validated with laboratory measures from the literature with a Nash-Sutcliffe Efficiency of 0.95. Soil samples were analysed in the laboratory to assess critical shear stress and other soil properties. The novel gully erosion model was implemented in three gully impacted locations with catchment areas ranging from 10-2 to 10+1 ha. To assess channel geometry and eroded volumes, we used Unmanned Aerial Vehicle and Structure-from-Motion technique. The model successfully estimated long-term erosion rates, its efficiency was 0.77, and it is recommended for catchments up to 8 ha. Therefore, the new model provides planners and stakeholders with a tool to assess gully erosion, sediment yield and geometry in most areas.

Reducing hydraulic erosion of surficial sand layer by inoculation of cyanobacteria

Biological approaches have captured the attention of researchers regarding the beneficial effects of cyanobacteria inoculation in improving surficial soil stability. However, a gap exists in the literature regarding the impact of inoculation by individual cyanobacteria on stability of sand under intense surface-water erosion. This study assesses the improvements achieved in erosion resistance for biological soil crust (BC) formed on medium–coarse silica sand. Specimen groups were inoculated with Nostoc sp. and Calothrix sp., incubated for 32- or 48 day periods and then tested using an erosion function apparatus (EFA), investigating a wide range of flow velocities (hydraulic shear stresses). The significance of BC attachment to (or detachment from) the specimen container sidewall was also investigated in the EFA testing. Compared with untreated sand, inoculated specimens had a significantly greater erosion resistance that increased with the incubation period, with Nostoc inoculum producing greater reductions in erodibility coefficients (45–75%) compared with Calothrix (16–67%). Contrasting bond structures introduced by Nostoc and Calothrix are highlighted by scanning electron microscopy images that showed long Nostoc filaments were entangled more strongly in sand pore voids compared with short Calothrix filaments. In conclusion, this study supports the idea of using cyanobacteria inoculation as an eco-friendly, cost-benefit and effective technique for mitigating land degradation.

Controlling the hydraulic resistance of membrane biofilms by engineering biofilm physical structure

The application of membrane technology for water treatment and reuse is hampered by the development of a microbial biofilm. Biofilm growth in micro-and ultrafiltration (MF/UF) membrane modules, on both the membrane surface and feed spacer, can form a secondary membrane and exert resistance to permeation and crossflow, increasing energy demand and decreasing permeate quantity and quality. In recent years, exhaustive efforts were made to understand the chemical, structural and hydraulic characteristics of membrane biofilms. In this review, we critically assess which specific structural features of membrane biofilms exert resistance to forced water passage in MF/UF membranes systems applied to water and wastewater treatment, and how biofilm physical structure can be engineered by process operation to impose less hydraulic resistance (“below-the-pain threshold”). Counter-intuitively, biofilms with greater thickness do not always cause a higher hydraulic resistance than thinner biofilms. Dense biofilms, however, had consistently higher hydraulic resistances compared to less dense biofilms. The mechanism by which density exerts hydraulic resistance is reported in the literature to be dependant on the biofilms’ internal packing structure and EPS chemical composition (e.g., porosity, polymer concentration). Current reports of internal porosity in membrane biofilms are not supported by adequate experimental evidence or by a reliable methodology, limiting a unified understanding of biofilm internal structure. Identifying the dependency of hydraulic resistance on biofilm density invites efforts to control the hydraulic resistance of membrane biofilms by engineering internal biofilm structure. Regulation of biofilm internal structure is possible by alteration of key determinants such as feed water nutrient composition/concentration, hydraulic shear stress and resistance and can engineer biofilm structural development to decrease density and therein hydraulic resistance. Future efforts should seek to determine the extent to which the concept of “biofilm engineering” can be extended to other biofilm parameters such as mechanical stability and the implication for biofilm control/removal in engineered water systems (e.g., pipelines and/or, cooling towers) susceptible to biofouling.

New Erodibility Parameterization for Applying WEPP on Rangelands Using ERMiT

HighlightsA practical parameterization approach to estimate erodibility was developed for WEPP applications on rangelands.Soil texture had a greater effect on rill erodibility than vegetation cover.Vegetation cover had a greater effect on interrill erodibility than soil texture.A new set of erodibility input parameters was defined for ERMiT applications on rangelands.Abstract. The USDA Water Erosion Prediction Project (WEPP) is a process-based soil erosion prediction model. WEPP uses three soil erodibility parameters: rill erodibility (Kr), interrill erodibility (Ki), and critical hydraulic shear stress (tc). In this study, a new parameterization approach for estimating erodibility was developed for WEPP applications on rangelands. Data from overland flow experiments on disturbed and undisturbed rangelands were used to develop empirical equations to predict rill erodibility variation as a function of vegetation cover and soil texture. Data from rainfall simulation experiments were analyzed by piecewise regression to develop empirical equations for predicting the variability of interrill erodibility before and after disturbance and across a wide range of soil textures as a function of vegetation cover and soil texture. Critical shear values corresponding to the developed rill and interrill erodibility parameters were proposed. Our results show that the new erodibility approach predicts erosion at the plot scale with a satisfactory range of error (PBIAS =35.6 and Nash-Sutcliffe efficiency = 0.49). The new approach was used to provide soil erodibility values for the Erosion Risk Management Tool (ERMiT), which uses WEPP as the runoff and erosion calculation engine. Keywords: ERMiT, Erosion, Interrill, Rangeland management, Rill, Shrub, Soil burn severity, WEPP.

Artificial bifurcation effect on downstream channel dynamics of a large lowland river, the Atchafalaya

AbstractArtificial river bifurcations have been widely created for different purposes. Yet, long‐term dynamics in the bifurcated channels and natural channels downstream of the artificial bifurcation nodes are not well investigated. Herein, we employed an approach combining three decades (1977–2006) of bathymetric survey records, geographic information system (GIS) application, and bed material transport modeling to investigate riverbed dynamics in an artificially bifurcated channel and the downstream natural channel of the Atchafalaya River, the largest distributary of the Mississippi River. Decadal changes in the riverbed volume were determined, and erosion/deposition patterns in these channels were assessed. Hydraulic properties under low, medium, and high flow conditions were quantified to analyze main factors affecting the long‐term trend of channel dynamics. Our study found that flow from the Atchafalaya River into the artificially bifurcated Wax Lake outlet channel (WLOC) steadily increased. Hydraulic gradient, stream power, and shear stress under all flow conditions of the WLOC were greater than those of the Atchafalaya River natural mainstem channel (ARMC) downstream of the artificial bifurcation. On average, 52% of the total bed material loads (BMLs) from the Atchafalaya entered the steeper and straight WLOC with 41% of the river's flow from 1977 to 2006. Despite the higher sediment inflow, the WLOC degraded with an average rate of −0.12 × 105 m3 km−1 yr−1, while the ARMC downstream of the bifurcation aggraded substantially with an average rate of 0.38 × 105 m3 km−1 yr−1 over the three decades. The disproportional flow–sediment ratio and channel erosion‐aggradation patterns below the artificial bifurcation were apparently a reflection of the difference in the river hydraulic properties. These findings imply that lowland alluvial river diversions for introducing sediment to build new land in world's sinking deltas need to develop sustainable solutions in order to avoid causing severe bed scouring in one but excessive deposition in the other channel downstream of the bifurcation.

Geometric Optimization of an Extracorporeal Centrifugal Blood Pump with an Unshrouded Impeller Concerning Both Hydraulic Performance and Shear Stress

Centrifugal blood pumps have provided a powerful artificial support system for patients with vascular diseases. In the design process, geometrical optimization is usually needed to acquire a more biocompatible model for clinical uses. In the current paper, we propose a method for multi-objective optimization concerning both the hydraulic and the hemolytic performances of the pump based on the near-orthogonal array in which the traditional hemolysis index (HI) is replaced with the maximum scalar shear stress criteria to reduce the computation load. The method is demonstrated with the optimization of an extracorporeal centrifugal blood pump with an unshrouded impeller. CFD studies on the original and nine modified pump models are carried out. The calculated hydraulic performances of the optimized model are also compared against the experiments for validation of the numeric method, with an error of 3.6% at the original design point. The resulting blood pump with low maximum scalar shear stress (132.2 Pa) shows a low degree of calculated HI (1.69 × 10−3).

Enhancing stability of aerobic granules by microbial selection pressure using height-adjustable influent strategy

Optimizing granules size distribution is critical for both reactor performance and stability. In this research, an optimal size range of 1800 to 3000 μm was proposed regarding mass transfer and granules stability based on granules developed at DO around 8.0 mg L−1 with the feed COD:N:P at 100:5:1. A height-adjustable influent strategy was applied to facilitate the nutrient storage of granules at optimum size range via microbial selective pressure. Results suggested insufficient hydraulic shear stress led to overgrowth of granules size. High abundance of filamentous bacteria (Thiothrix sp.) was observed in oversized granules, which detached and affected the remaining granules, resulting in severe sludge bulking. Strong hydraulic shear stress suppressed uncontrolled growth of granules. However, fewer abundance of simultaneous nitrification and denitrification (SND) bacterium was acquired, which led to unfavored SND effect and total nitrogen (TN) removal efficiency. The height-adjustable influent strategy facilitated the poly-β-hydroxybutyrate (PHB) storage of granules at optimum size range, while limiting the overgrowth of granules size. Additionally, more than 87.51% of total granules situated in optimal sizes range, which led to higher abundance of SND bacterium and higher TN removal efficiency.

Heyde’s syndrome as a rare cause of gastrointestinal bleeding in aortic stenosis patients

Heyde’s syndrome is one of the causes of gastrointestinal bleeding in patients with heart disease. It is characterized by the acquired destruction of high molecular weight multimers of von Willebrand factor due to high hydraulic shear stress on the aortic valve in severe stenosis, followed by gastrointestinal bleeding due to angiodysplasias. Management of such patients is a complex and relevant problem. The central method of treatment for Heyde’s syndrome is aortic valve replacement, which reduces the risk of recurrent gastrointestinal bleeding in more than 90% of patients.

Experimental investigation on seepage erosion of the soil–rock interface

Internal erosion under seepage flow affects the hydraulic and mechanical behavior of the soil, which is one of the most important factors of geological disasters. Due to that the soil–rock interface can be the potential preferential seepage channels commonly, the characteristics of erosion are more significant and hazardous at the soil–rock interface. In this study, a series of laboratory experiments are performed to investigate the failure mechanism and evolution of interfacial seepage erosion. The influences of two essential influence factors (i.e., the confining pressure and the roughness of the interface) are investigated by comparing the seepage velocity, hydraulic conductivity, failure hydraulic gradient, and failure hydraulic shear stress in experiments. Furthermore, the failure pattern of interfacial seepage erosion is particular investigated by the CT scanning. The interfacial seepage erosion tests indicate that the interfacial seepage erosion shows a three-phase progressive failure as the hydraulic gradient increases and the hydraulic conductivity decrease with the progress of suffusion in the initiation phase. The increase of confining pressure leads to the increase of failure hydraulic gradient. The results of CT scanning show that the roughness of the soil–rock interface significantly affects the size and shape of resulting zone of erosion.