CHARACTERS OF SEDIMENTATION OF SUSPENSION FLOCCULATED OR COAGULATED

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Vertical Diffusion Coefficient with Stratification Effect for Silty Sediment Suspension Under Waves

To analyze previous experimental data of suspended sediment concentration for silty sediment with different sediment particle sizes due to waves, a new stratification correction coefficient is presented. The suspended sediment concentration gradient and sediment particle diameter are selected as parameters. Furthermore, a diffusion coefficient model with a stratification effect over the whole water depth for silty sediment suspension under waves is developed. The comparison between the suspended sediment concentration calculated by the presented model and several groups of experimental data shows that the model can reasonably reflect the vertical distribution of silty sediment suspension.The stratification effect calculated by the present model decreases with an increase in the sediment particle diameter,which indicates that the model can be extended to describe the suspended sediment concentration of fine to medium sand when the near-bottom sediment concentration is not very high. Although the original model needs to be iteratively solved, the approximate method without iteration is recommended for applications when the near bottom sediment concentration is between 10 and 20 kg/m~3 due to the small difference between the non-iterative and iterative solution for near bed layer suspended sediment concentration, which plays a major role in sediment transport.

Numerical Simulation of Breaking Wave Generated Sediment Suspension and Transport Process Based on CLSVOF Algorithm

The sediment suspension and transport process under complex breaking wave situation is investigated using large eddy simulation (abbreviated as LES hereafter) method. The coupled level set (LS) and volume of fluid (VOF) method is used to accurately capture the evolution of air-water interface. The wall effect at the bottom is modeled based on the wave friction term while the complicate bottom boundary condition for sediment is tackled using Chou and Fringer's sediment erosion and deposition flux method. A simulation is carried out to study the sediment suspension and transport process under periodic plunging breaking waves. The comparison between the results by CLSVOF method and those obtained by the LS method is given. It shows that the latter performs as well as the CLSVOF method in the pre-breaking weak-surface deformation situation. However, a serious mass conservation problem in the later stages of wave breaking makes it inappropriate for this study by use of the LS method and thus the CLSVOF method is suggested. The flow field and the distribution of suspended sediment concentration are then analyzed in detail. At the early stage of breaking, the sediment is mainly concentrated near the bottom area. During the wave breaking process, when the entrapped large-scale air bubble travels downward to approach the bottom, strong shear is induced and the sediment is highly entrained.

Flow Behavior of Clay-Silt to Sand-Silt Water-Rich Suspensions at Low to High Shear Rates: Implications for Slurries, Transitional Flows, and Submarine Debris-Flows

Water-rich clay to sand suspensions show a shear rate dependent flow behavior and knowledge of the appropriate rheological model is relevant for sedimentological, industrial and hydraulic studies. We present experimental rheological measurements of water-rich(40 to 60 wt%) clay to silt(population A) and silt to sand(population B) suspensions mixed in different proportions. The data evidence a shear rate dependent shear thinning-shear thickening transition. At lower shear rates, the suspensions organize in chains of particles, whereas at higher shear rates, these chains disrupt so increasing the viscosity. The viscosity, consistency and yield stress decrease as the A+B fraction decreases as the content of B particles increases. This behavior reflects the competing effects of the lubrication and frictional processes as a function of particle size and water content. Transitional flows form by the incorporation of small amounts of the finer fraction while ‘oceanic floods’ form at the estuary of rivers and the submarine debris-flows increase their velocity by incorporating water. The critical Reynolds number of the studied suspensions is ～2000±100 suggesting that the grainsize plays a major role in the laminar to turbulent transition. Our results have implications for the modeling of sediment flows and the hazard related to floods.

Fully resolved simulations of viscoelastic suspensions by an efficient immersed boundary-lattice Boltzmann method

An efficient immersed boundary-lattice Boltzmann method(IB-LBM)is proposed for fully resolved simulations of suspended solid particles in viscoelastic flows.Stress LBM based on Giesekus and Oldroyd-B constitutive equation are used to model the viscoelastic stress tensor.A boundary thickening-based direct forcing IB method is adopted to solve the particle-fluid interactions with high accuracy for non-slip boundary conditions.A universal law is proposed to determine the diffusivity constant in a viscoelastic LBM model to balance the numerical accuracy and stability over a wide range of computa-tional parameters.An asynchronous calculation strategy is adopted to further improve the computing efficiency.The method was firstly applicated to the simulation of sedimentation of a single particle and a pair of particles after good validations in cases of the flow past a fixed cylinder and particle migration in a Couette flow against FEM and FVM methods.The determination of the asynchronous calculation strategy and the effect of viscoelastic stress distribution on the settling behaviors of one and two particles are revealed.Subsequently,504 particles settling in a closed cavity was simulated and the phenomenon that the viscoelastic stress stabilizing the Rayleigh-Taylor instabilities was observed.At last,simulations of a dense flow involving 11001 particles,the largest number of particles to date,were performed to investigate the instability behavior induced by elastic effect under hydrodynamic interactions in a viscoelastic fluid.The elasticity-induced ordering of the particle structures and fluid bubble structures in this dense flow is revealed for the first time.These simulations demonstrate the capability and prospects of the present method for aid in understanding the complex behaviors of viscoelastic particle suspensions.

EFFECTS OF SUBMERGED MACROPHYTES ON SEDIMENT SUSPENSION AND NH_4-N RELEASE UNDER HYDRODYNAMIC CONDITIONS

Aquatic vegetation affects sediment suspension and nutrient release by changing the flow structure. Experiments on the influence of submerged vegetation on flow structure, sediment suspension, and NH4-N release were carried in a flume with natural submerged vegetation. Turbulence characteristics in the vegetation section were measured using a three-dimensional acoustic Doppler velocimeter. The effects of submerged vegetation on bed shear stress （ τb ）, sediment suspension, and NH4-N release were analyzed. Results show that with vegetation, bed shear stress is reduced by about 20% - 80%, which, in turn, reduces sediment suspension. The impact of submerged vegetation on sediment suspension and NH4-N release should be considered along with flow intensity. When the flow Reynolds number is relatively small, the submerged vegetation is quite capable of inhibiting sediment suspension and reducing NH4-N release, but when the Reynolds number reaches a certain value, the presence of aquatic plants exacerbates sediment suspension and promotes NH4-N release. Results also reveal that a highly significant positive correlation exists between NH4-N concentration and water turbidity in both vegetated and non-vegetated channels.

In-situ observations of internal dissolved heavy metal release in relation to sediment suspension in lake Taihu, China

Despite laboratory experiments that have been performed to study internal heavy metal release,our understanding of how heavy metals release in shallow eutrophic lakes remains limited for lacking in-situ evidence.This study used automatic environmental sensors and a water sampling system to conduct high-frequency in-situ observations(1-hr intervals)of water environmental variables and to collect water samples(3-hr intervals),with which to examine the release of internal heavy metals in Lake Taihu,China.Under conditions of disturbance by strong northerly winds,sediment resuspension in both the estuary area and the lake center caused particulate heavy metal resuspension.However,the patterns of concentrations of dissolved heavy metals in these two areas were complex.The concentrations of dissolved Se and Mo increased in both areas,indicating that release of internal dissolved Se and Mo is triggered by sediment resuspension.The concentrations of dissolved Ni,Zn,As,Mn,Cu,V,and Co tended to increase in the estuary area but decrease in the lake center.The different trends between these two areas were controlled by pH and cyanobacteria,which are related to eutrophication.During the strong northerly winds,the decrease in concentrations of dissolved heavy metals in the lake center was attributable primarily to absorption by the increased suspended solids,and to growth-related assimilation or surface adsorption by the increased cyanobacteria.The findings of this study suggest that,short-term changes of environmental conditions are very important in relation to reliable monitoring and risk assessment of heavy metals in shallow eutrophic lakes.

Multiphase redistribution differences of polycyclic aromatic hydrocarbons （PAHs） between two successive sediment suspensions

Successive sediment suspensions often happen in estuary, yet little research has probed into the difference in the release behaviors of organic compounds among different suspensions. This study took polycyclic aromatic hydrocarbons （PAHs） as typical organic contaminants and investigated the release behaviors between two successive suspensions with a particle entrainment simulator （PES）. Results showed that successive sediment suspensions lowered the concentration of dissolved PAHs in the overlying water via facilitating the re-adsorption of dissolved PAHs onto the suspended particles. Fast-release and slow-release periods of PAHs were successively observed in the both suspensions. The concentration changes of dissolved PAHs in the second suspension were generally similar with but hysteretic to those in the first suspension. More vigorous desorption and re-absorp- tion of PAHs were induced in the second suspension. Successive sediment suspensions obviously decreased the concentrations of mineral composition and organic matters in the overlying water, which significantly affects multi- phase distribution of PAHs.

低压浑水管道输沙规律研究及水流挟沙力计算

【目的】确定输水工程适宜运行的水力条件。【方法】以巴音沟河流域输水工程为研究对象,通过数值模拟的方法研究不同泥沙质量浓度、压力条件下浑水管道输沙规律及水流挟沙力特性。【结果】(1)管道断面垂向泥沙质量浓度分布受压力、体积含沙量及管径等因素的影响;当压力及管径较小时,泥沙淤积厚度为6.3~8.0 mm,压力及管径较大时,在Y=-0.07区域以下淤积较多,淤积厚度达到8.6~9.4 mm;(2)同一管径及流速下,随着体积含沙量的增大,该区域流速梯度增大,最大增幅为14%;(3)随着水流速度增大,水流挟沙力增大,悬移质质量浓度也越大,但是悬浮指标逐渐变小。【结论】在低压浑水管道中,管径越大、泥沙质量浓度越大、压力越小,水流挟沙力越小,泥沙越容易淤积。

好氧-缺氧序批式反应器去除布洛芬和非诺洛芬的效能研究

布洛芬和非诺洛芬由于其难降解及生物富集性,对水生生态系统和人类健康具有潜在的生态毒性和生物累积风险。探究好氧/缺氧悬浮序批式反应器(O/ASSBR)去除制药废水中化学需氧量(COD)、总氮(TN)及新型污染物布洛芬(IBU)和非诺洛芬(FENO)的效能。结果表明,在O/ASSBR水力停留时间(HRT)为24 h、好氧阶段和缺氧阶段溶解氧分别为2.0和0.4 mg/L,COD有机负荷为1.2~10 kg/m^(3)·d、氨氮(NH_(4)^(+)-N)负荷为4.3~6.3 g/m^(3)·d、IBU负荷为1.71~5.1 mg/m^(3)·d、FENO负荷为0.39~2.1 mg/m^(3)·d的运行条件下,废水中COD、NH_(4)^(+)-N、TN、IBU、FENO的去除率分别为87.74%~89.36%、76.52%~96.75%、69.92%~93.94%、90.01%和91.57%。对反应器中活性污泥生物群落分析表明:系统中主要是革兰氏阳性菌,其中假蕈状芽孢杆菌(Bacillus pseudomycoides)、赤红球菌(Rhodococcus rubber)和地中海弧菌(Vibrio mediterranei)3株菌株对IBU和FENO具有较高的抗性。上述研究表明,O/ASSBR生物系统中存在的功能微生物可以有效降解IBU和FENO等新兴有机污染物,因此O/ASSBR工艺在处理制药废水方面有很好的应用潜力。

Effects of sediment and its re-suspension on the growth of Vallisneria asiatica Miki

Aquatic macrophytic growth and its distribution in eutrophic lakes are described in relation to its sediment type and irradiance. Hence, it is necessary to characterize the response of macrophytic growth to lake sediment and its re-suspension. We conducted two independent experiments to measure the effects of sediment and its re-suspension on the growth of Vallisneria asiatica Miki. Based on our study, we conclude that the amount of total biomass of V. asiatica is related, in important ways, to the type of sediment and its re-suspension. According to our comparison, plants and biomass cultured on lake sediments are 2.1 times and 1.5 times greater than that on brown clay from nearby places beside Lake Taihu. The number of plants and the amount of biomass in a turbid water column are smaller than those in a clear water column. The results indicate that the nutrient-rich lake sediments have promoted the growth of V. asiatica, while the re-suspension of the sediment leads to a high turbid level and low light penetration which has a negative impact on the growth of V. asiatica.

布洛芬混悬液抑菌效力的研究与质量分析

目的:通过分析2021年国家评价性抽验工作,考察市售布洛芬混悬液的抑菌效力,了解产品的质量情况同时查找风险点。方法:采用《中国药典》2020年版四部通则<1121>抑菌效力检查法对市售的7个企业的产品进行抑菌效力测定。结果:只有1家企业的布洛芬混悬液抑菌效力不符合规定。对影响抑菌效力的因素进行分析探讨,发现pH设定可影响抑菌效力。结论:建议结合处方,对现行产品标准中的pH值进行重新考察,修订一个合理的pH范围,提高产品用药安全。

基于国家药品抽检的布洛芬混悬液中抑菌剂含量测定及评价

目的 对国家药品抽检品种布洛芬混悬液中苯甲酸钠、山梨酸、羟苯甲酯、羟苯乙酯、羟苯丙酯和羟苯丁酯6种抑菌剂进行监测、分析和评估,以期为国家药品监管提供参考,确保公众用药安全。方法 采用ZORBAX SB C_(18)(250 mm×4.6 mm, 5μm)色谱柱,以浓度为0.01 mol·L^(-1)乙酸铵溶液(用氨试液调pH值至8.0)为流动相A,甲醇为流动相B,梯度洗脱,检测波长分别为230 nm和254 nm,流速为1.0 mL·min^(-1)。结果 苯甲酸钠、山梨酸、羟苯甲酯、羟苯乙酯、羟苯丙酯和羟苯丁酯等6种抑菌剂分别在0.644 8~161.2、0.237 1~47.43、0.314 9~52.48、0.203 4~50.85、0.218 0~54.49μg·mL^(-1)和0.208 3~52.07μg·mL^(-1)浓度范围内与峰面积呈良好的线性关系;平均回收率在99.4%~100.8%之间,RSD在0.2%~1.7%之间(n=9);对市售8个企业共61批样品进行抑菌剂的含量测定。结论 本实验建立的分析方法专属性强、灵敏度高、适用性好,首次应用于国家药品抽检品种61批布洛芬混悬液抑菌剂的质量控制和评价分析。

波浪条件下悬移质泥沙分布特性的数值模拟研究

在近海区域,波浪是引起掀沙的常见动力因素,而泥沙的运动又对海岸工程具有较强的参考价值,所以对波浪条件下悬移质泥沙分布特性开展数值模拟具有重要的现实意义。引入三维水动力学代码求解Navier-Stokes(NS)方程,采用流体体积法(VOF)捕捉自由水面运动,在悬沙运动模拟中,求解浓度扩散方程,并利用Van Rijn实验分析得出的经验泥沙扩散系数,较好地解决了泥沙扩散系数的难确定性问题,充分考虑非恒定流条件下对流与扩散的混合模式,实现波浪条件下悬移质泥沙分布特性的数值模拟。

激光散射法测定布洛芬混悬液粒度的研究

目的 建立激光散射法测定布洛芬混悬液中布洛芬的粒度及粒度分布的方法。方法 使用Malvern Mastersizer 2000激光粒度分析仪,Hydro 2000SM进样器;背景及样品的扫描时间为15 s,搅拌速率为850 r/min;分散剂为水,以辅料溶液为背景测试样品溶液;颗粒折射率为1.400~1.500;颗粒的吸收率为0.001;遮光度为5%~20%。结果 激光散射法可以测定布洛芬混悬液的粒度及其分布,由体积平均粒径D(4,3)可以直观地表征不同批号的布洛芬混悬液中布洛芬颗粒的大小差异,由d(0.1)、d(0.5)、d(0.9)数值表示其粒度分布的特征。方法学考察结果和样品测定结果的d(0.1)、d(0.5)和d(0.9)的RSD均小于8%。结论 本方法适合布洛芬混悬液中布洛芬药物的粒度及粒度分布的测定。

引黄灌区干渠水沙运移与防淤研究

为处理山西尊村引黄灌区干渠淤积严重的问题,对一干渠做实地水沙试验,运用垂线悬浮指标、规划求解方法探究渠道中悬移质泥沙分布规律、渠道流量与泥沙淤积关系以及渠道水流挟沙能力,使其能够在一定范围内表达出水流的挟沙状况。并提出了渠道粒径所对应的临界悬浮流量,根据工况与粒径大小调整流量益于防淤;优化了水流挟沙力公式。结果表明,引水流量在4.46~24.52 m^(3)/s时,渠道泥沙含量在0.9~4.0kg/m^(3)之间,泥沙含量与流速大小呈正相关;渠道流量调整至39.6 m^(3)/s以上可使渠道内大粒径泥沙有效悬浮;优化后的挟沙力公式针对干渠泥沙计算值与实测值相关性达0.828,说明此公式能够较高程度地反映当前含沙量,为后期渠道冲淤平衡设计与分析提供支撑。

混凝沉淀工艺去除碳钢鳞皮悬浮液颗粒物实验研究

本研究针对碳钢鳞皮悬浮液中悬浮物含量高、颗粒物粒径小不易沉降,水质排放不达标等问题,采用混凝工艺进行处理。探究了氯化铁(FeCl_(3))和硫酸铁(Fe_(2)(SO_(4))_(3))这两种混凝剂的处理效果以及絮凝剂聚丙烯酰胺(PAM)用量对出水水质的影响。实验结果显示仅使用混凝剂进行处理时FeCl_(3)效果优于Fe_(2)(SO_(4))_(3),FeCl_(3)投加量为20 mg/L时,出水水质就可达到10 NTU以下。絮凝剂PAM最佳投加量为0.5 mg/L,进一步提高絮凝剂投加量会导致处理效果较低,实际工程中推荐采用FeCl_(3)+PAM组合处理,投加量为5 mg/L+0.5 mg/L或10 mg/L+0.5 mg/L,出水水质可以保证符合宝钢一类串接水的回用指标。

基于泥沙悬浮高度假设的恢复饱和系数研究

针对大坝下游单向冲刷条件下次饱和挟沙水流的恢复饱和系数取值问题,基于泥沙悬浮高度假设,采用理论推导与对比验证的方法对恢复饱和系数公式进行了分析研究。分析了泥沙颗粒在挟沙水流中的动力机理和能量转换过程,推导了泥沙颗粒的单步悬浮高度和步长公式,改进了恢复饱和系数公式。采用经典的恢复饱和系数公式和黄河非均匀沙恢复饱和系数率定值,与改进的恢复饱和系数公式进行了对比分析。结果表明:改进的公式可以较好的预测恢复饱和系数,粒径0.025 mm~1.5 mm泥沙的恢复饱和系数在1.9 cm/s~100.0 cm/s的摩阻流速范围内取值在0.01~3.00之间,恢复饱和系数随摩阻流速的变化规律也随泥沙粒径的不同而不同。