Rectangular Sedimentation Tank Research Articles

Numerical Investigation of the Effect Dimensions of Rectangular Sedimentation Tanks on Its Hydraulic Efficiency Using Flow-3D Software

Settling basins are among the essential units built to separate sediment suspended and within the inlet flow particles in water and wastewater treatment plants and irrigation canals. These basins' high efficiency requires proper design, creating a smooth and uniform flow along the basin, and reducing circulation zone as a factor in disrupting the sedimentation process. The present study investigates basin dimensions' effect on its flow pattern. Hence In the current study, the primary rectangular sedimentation basin was modelled three-dimensionally using Flow-3D software. This software takes advantage of two new advanced technique of VOF and FAVOR to model the free surface of the flow and the geometry, respectively. The dimensions of the basin were examined in two scenarios. In the first set-up, the length-to-width ratio was evaluated by increasing length and decreasing width simultaneously and the second part examined the length to depth ratio by decreasing depth and increasing width. In both situations, the volume and location of the inlet and outlet of the basin were constant and unchanged. The outcomes indicate that increasing the ratio of length-to-width and length to depth reduces the volume of the circulation zone significantly. The volume of these zones decreased from 53% for the L/W ratio of one (square basin) to 22% associated with the L/W ratio of eight. Likewise, the volume of these zones decreased by 38% as a result of increasing the L/d ratio from five to ten.

A new combination approach for optimal design of sedimentation tanks based on hydrodynamic simulation model and machine learning algorithms

The current study aims to propose a novel approach to design rectangular primary sedimentation tanks using computational fluid dynamics (CFD) and artificial intelligence. Hybrid adaptive neuro-fuzzy inference system and particle swarm optimization algorithm (ANFIS-PSO) is trained using CFD model's results. ANFIS-PSO is coupled with two multi-objective algorithms to optimize two objectives: Mean velocity and baffles' configurations. For the single-baffle tank, the optimal baffle position regarding flow velocity was approximately at 0.13 of the basin length, with the height ratio (ratio of baffle height to weir height) of 0.21, but the most cost-effective design was obtained when the single baffle was placed at about 0.06 of total length, with the height ratio of 0.17. Using two baffles could enhance the tank's hydraulic performance, especially when the first and second baffles were at 0.11 and 0.25 of the tank's length, respectively, with the height ratio of 0.33 and 0.22, respectively.

An experimental sedimentation tank for enhancing the settling of solid particles

Sedimentation tanks have a vital role in the overall efficiency of solid particles removal in treatment units. Therefore, an in-depth study these tanks is necessary to ensure high quality of water and increasing the system efficiency. In this work, an experimental rectangular sedimentation tank has been operated with and without a baffle to investigate the system behaviour and effectiveness for the reduction of solid particles. Turbid water was prepared using clay, which was collected from the water treatment plant of Al Maqal Port (Iraq), mixed with clear water in a plastic supply tank. Raw and outflow samples were tested against turbidity after plotting a calibration curve between inflow suspended solids versus their corresponding turbidity values. The key objective was to assess the impact of different flow rates, particle concentrations, heights and positions of the baffle on the system efficiency. Findings showed that the tank performance was enhanced significantly (p < 0.05) with the use of a baffle placed at a distance of 0.15 of tank length with height equal to 0.2 of tank depth. Higher removal efficiency (91%) was recorded at a lower flow rate (0.015 dm3∙s–1) and higher concentration (1250 mg∙dm–3), as the treatment efficiency enhanced by 34% compared with the operation without a baffle. Placing the baffle in the middle of the sedimentation tank produced the worst results. System efficiency for solids removal reduced with increasing baffle height. Further research is required to evaluate the efficiency of an inclined baffle.

The influence of wind in secondary settling tanks for wastewater treatment - A computational fluid dynamics study. Part II: Rectangular secondary settling tanks.

Computational fluid dynamics (CFD) model is used to study the effect of wind on the performance of a rectangular secondary sedimentation tank (SST) in a wastewater treatment plant (WWTP). Unlike most of the previous CFD modeling studies which evaluated the wind effect on the sedimentation tank in only water treatment plants, this study evaluates a rectangular SST in a WWTP at different wind speeds and directions, and under different inflow loading conditions. The wind is qualitatively and quantitatively analyzed for a range of wind speeds and directions as well as loading rates. The net effect is to change the three-dimensional hydrodynamics profiles, effluent suspended solids, and sludge blanket height. The simulation results show that the wind deteriorates overall clarification performance of the rectangular SST and has little effect on the sludge thickening under mild wind conditions until the speed increases an extreme windy condition. These CFD simulation results suggest that in strong windy climates, covering SSTs or protecting them from strong winds may be justified. PRACTITIONER POINTS: This is the first comparison of wind effects on a rectangular secondary sedimentation tank The effects of varied flow conditions, wind directions, and velocities are compared Wind-induced currents in the settling tank negatively affect removal efficiency Winds have strong negative impact on the performance of sedimentation tanks.

Poboljšanje efikasnosti sedimentacionih rezervoara u uklanjanju taloga korišćenjem različitog ulaznog i izlaznog položaja

Sedimentation by gravity is the oldest water treatment. Inlet and outlet of rectangular sedimentation tank are often located in the middle of the tank. The present investigation studies the effect of changing inlet and outlet position of rectangular sedimentation tank on removal efficiency using Computational Fluid Dynamics method. Two different configurations are proposed and they have been tested with varying particles diameters and concentration. Numerical model ability to describe flow field behaviour inside the tank is confirmed by an experimentation data. Results show that inlet and outlet position influence the flow field and removal efficiency of sedimentation tanks, especially for the case of fine particles (50 and 120µm).

The influence of lamellar settler in sedimentation tanks for potable water treatment — A computational fluid dynamic study

Lamella gravity settlers are often used in water treatment to make sedimentation tanks more cost-effective. Effective surface area for settlement is increased by the inclined plates giving such systems a smaller footprint than the conventional tanks. In this paper a numerical model was used to simulate the dynamics and flow structure of a rectangular sedimentation tank for potable water through a multiphase approach, using computational fluid dynamic (CFD) methods. Two configurations have been examined, one with a system of inclined parallel plates (lamellar settlers) and another with a conventional design, in order to evaluate the influence of lamellar settlers in the process efficiency. Unlike most of the previous numerical investigations which studied the lamellar settlers separately, the present numerical approach studies the whole sedimentation tank with a full scale system of inclined parallel plates. The momentum exchange between the primary and the secondary phase (particles) is taken into account, using a Lagrangian method (discrete phase model) with two-way coupled calculations. Contours of stream function, velocity and concentration are presented, as well as the velocity and concentration profiles for the inclined plates. The results show that the lamellar settlers influence the flow field and increase the sedimentation efficiency by 20% in comparison with the convectional design.

Eulerian–Eulerian solid–liquid two-phase flow of sandstone wastewater in a hydropower station rectangular sedimentation tank

The treatment of high-turbidity sandstone wastewater in hydropower projects is a major concern for environment assessment. In this paper, an Eulerian–Eulerian solid–liquid two-phase model for describing water flow and sedimentation in a two-stage rectangular tank was presented. Relative to the Eulerian–Lagrangian approach, the Eulerian–Eulerian two-phase model can investigate the concentration distribution behaviour of particles with specific characteristics in greater detail. The molecular kinetic theory of gases was used to determine the microcosmic flow characteristics, and the collision force between the particles during two-phase solid–liquid flow was obtained. The flow pattern and the distribution of solids in the rectangular clarifiers were investigated. The simulated results were in good agreement with the measured results obtained from the removal efficiency of the first and second tanks. Furthermore, the sensitivity of the suspended solids distribution for the collision force and the effect on particle settling of the baffle position in the rectangular sedimentation tank were evaluated.

Determination of the effect of wind velocity and direction changes on turbidity removal in rectangular sedimentation tanks

In the present study, a pilot-scale sedimentation tank was used to determine the effect of wind velocity and direction on the removal efficiency of particles. For this purpose, a 1:20 scale pilot simulated according to Frude law. First, the actual efficiency of total suspended solids (TSS) removal was calculated in no wind condition. Then, the wind was blown in the same and the opposite directions of water flow. At each direction TSS removal was calculated at three different velocities from 2.5 to 7 m/s. Results showed that when the wind was in the opposite direction of water flow, TSS removal efficiency initially increased with the increase of wind velocity from 0 to 2.5 m/s, then it decreased with the increase of velocity to 5 m/s. This mainly might happen because the opposite direction of wind can increase particles' retention time in the sedimentation tank. However, higher wind velocities (i.e. 3.5 and 5.5 m/s) could not increase TSS removal efficiency. Thus, if sedimentation tanks are appropriately exposed to the wind, TSS removal efficiency increases by approximately 6%. Therefore, energy consumption will be reduced by a proper site selection for sedimentation tank unit in water and waste water treatment plants.

Computational investigations of baffle configuration effects on the performance of primary sedimentation tanks

AbstractTo increase the performance of a primary sedimentation tank (clarifier), it is essential to have a uniform and calm flow field. The use of suitable baffle configurations may help forming favourable flow field and increase the efficiency of the primary sedimentation tank. To find the proper position and height of a baffle in a rectangular primary sedimentation tank, computational investigations are performed. Also, laboratory experiments are conducted to verify the numerical results, and the measured velocity fields that were by acoustic Doppler velocimeter (ADV) are used. The results of computational investigations performed in the present study indicate that the favourable flow field (uniform in the settling zone) would be enhanced for the case that the baffle position and height provide small circulation regions volume, or the recirculation region forms a small portion of the flow field and dissipate the kinetic energy in the tank.

Numerical modeling of baffle location effects on the flow pattern of primary sedimentation tanks

Computational fluid dynamics (CFD) is used extensively by engineers to model and analyze complex issues related to hydraulic design, planning studies for future generating stations, civil maintenance and supply efficiency. In order to find the optimal position of a baffle in a rectangular primary sedimentation tank, computational investigations are performed. Also laboratory experiments are conducted to verify the numerical results and the measured velocity fields which were by Acoustic Doppler Velocimeter (ADV) are used. The GMRES algorithm as a pressure solver was used in the computational modeling. The results of computational investigations performed in the present study indicate that the favorable flow field (uniform in the settling zone) would be enhanced for the case that the baffle position provide small circulation regions volume and dissipate the kinetic energy in the tank. Also results show that the GMRES algorithm can obtain the good agreement between the results of numerical models and experimental tests.

Inverse Calculation Model for Optimal Design of Rectangular Sedimentation Tanks

Because of the difficulty of specifying optimal design parameters of rectangular sedimentation tanks using a forward numerical model, an inverse calculation model based on an optimization algorithm and a forward model were developed in this paper. Using this model, a numerical simulation of the sedimentation tank involving determination of the velocity field and the concentration distribution of the particles by the forward model was conducted. The eddy viscosity was obtained with the aid of k−ε turbulence model equations. The inverse model was applied to the optimal design of the horizontal baffle location in a given sedimentation tank. As a one-dimensional nonlinear optimization method, Brent’s method was used. Moreover, the effect of the horizontal baffle location on flow and solids removal ratio was also discussed. Compared with the traditional forward model for specifying optimal design parameters for rectangular sedimentation tanks, the inverse calculation model can search directly for the optimum design parameters and can obtain good results.

Experimental and Numerical Simulation of the Effect of Particles on Flow Structures in Secondary Sedimentation Tanks

Sedimentation tanks are designed for removal of floating solids in water flowing through the water treatment plants. These tanks are one of the most important parts of water treatment plants and their performance directly affects the functionality of these systems. Flow pattern has an important role in the design and performance improvement of sedimentation tanks. In this work, an experimental study of particle-laden flow in a rectangular sedimentation tank has been performed. Kaolin was used as solid particles in these experiments. Also, a numerical simulation was developed using the finite volume method with a k-e turbulent model. The results of the numerical model agree well with the experimental data. Hydrodynamic parameters and flow patterns of the fresh water flow and particle-laden flow are also compared in this study. The results show that the existence of particles completely changes the flow structures. It seems that the main reason for this phenomenon is the particles settling. Our experimental observations and numerical results show that parameters such as the maximum streamwise velocity, fully developed location, shear stress coefficient at the bottom of the tank and so on are different in water-containing particles compared to pure water and the inlet concentration strongly intensifies the differences.

Experimental Investigation of the Influence of Baffle Position on the Flow Field, Sediment Concentration, and Efficiency of Rectangular Primary Sedimentation Tanks

AbstractSedimentation due to gravitation is applied extensively in water and wastewater treatment to remove suspended solids. Suitable baffle configurations may help form favorable flow fields and increase the efficiency of a primary sedimentation tank. Experimental tests were performed to determine the best position for a baffle in a rectangular primary sedimentation tank. The experimental measurements consisted of three parts. First, the velocity fields were measured using an acoustic Doppler velocimeter. The concentration at different vertical and horizontal points was then evaluated. Finally, the removal efficiency of the sedimentation tank was measured. The results of the present study indicate that a uniform flow field in the settling zone is enhanced when the baffle position provides a small volume of circulation regions. In this case, the maximum concentration of the suspended sediments inside the settling zone and the highest removal efficiency are achieved.

The effect of number of baffles on the improvement efficiency of primary sedimentation tanks

In this study, the effect of different numbers of baffles is investigated using computational simulation. Laboratory measurements using different numbers of constant height baffles in a rectangular primary sedimentation tank are conducted. The velocity fields measured by an Acoustic Doppler Velocimeter (ADV) are used to verify the results of the computational model. The effects of the number of baffles arrangement on the hydraulic performance of primary settling tanks are studied by using two different ways: the parameters of flow pattern and the Flow Through Curves (FTCs) method. The results of both the experimental and computational investigations indicate that increasing the number of baffles in suitable positions provides minimum volume of the recirculation region, dissipates the kinetic energy, creates a uniform flow field in the tank and finally the hydraulic efficiency of the sedimentation tank will be improved.

Experimental investigation of effects of baffle configurations on the performance of a secondary sedimentation tank

Sedimentation tanks are designed for the settling of floated solids in water. These tanks are one of the most important parts of water treatment plants and their performance directly affects the functionality of these plants. One challenging method for increasing the performance of sedimentation tanks is to use baffles. A useful baffle should be installed in a suitable place with a proper height. In this work, an experimental study of particle-laden flow in a rectangular sedimentation tank has been performed and kaolin is used as solid particles. The effects of baffle configurations on the velocity and concentration profiles along the tank were studied. Sedimentation tank performance was directly investigated by measurement of the mean concentration along the tank. In order to determine the best baffle configuration, two positions of single and double-baffle arrangements with various heights were investigated. Results show that the best baffle position and proper baffle height relates to the inlet concentration. In any case, the middle baffle, with suitable height, is efficient and increases sedimentation tank performance.

Numerical Analysis of Solid−Liquid Two-Phase Flow on Sandstone Wastewater of Hydropower Stations in a Rectangular Sedimentation Tank

The lack of knowledge on water flow and particle behavior of sandstone wastewater in sedimentation tanks of hydropower stations is a significant challenge for the design of these processes. In this study, the Euler-Lagrange two-phase model was applied to study the flow, sedimentation, and particle trajectories in a two-stage rectangular tank that is divided into two sections with different hydraulic retention times. The interfacial momentum transfer, buoyant force, and the collision force were considered, and the Lagrange approach was employed to determine the particle trajectories of the particles. The flow patterns, removal efficiency of the particles, and particle trajectories along the tank were investigated. The experimental and numerical results revealed that the two-stage rectangular tank is efficient in dealing with high turbidity sandstone wastewater. In addition, the simulated removal efficiencies were in good agreement with the experimental results. Last, the sensitivity of particle behavior to the collision force was studied, and the effect of the baffle length on particle settling in the rectangular sedimentation tank was evaluated.

A CFD methodology for the design of rectangular sedimentation tanks in potable water treatment plants

Several modifications with different construction costs were proposed to enhance the performance in large rectangular sedimentation tanks. A two-dimensional fully mass conservative sedimentation model, based on modern computational fluid dynamics theory, was applied to evaluate proposed tank modifications of the existing and modified sedimentation tanks. The usually unknown and difficult to be measured particle density is found by matching the theoretical to the easily measured experimental total settling efficiency. The proposed strategy is computationally much more efficient than the corresponding strategies used for the simulation of wastewater treatment. It is noteworthy that even small differences in the particle velocity can cause large changes in the percent of settled particles; in this work, the overall solids removal efficiency increased when using the modifications from 84.4 and 98.8%, leading to a reduction of the effluent solids concentration of approximately 85%. The comparison of model predicted results with the field data collected in tanks before and after modifications shows very good agreement.

Three-Dimensional Simulation on the Water Flow Field and Suspended Solids Concentration in the Rectangular Sedimentation Tank

A 3D computational fluid dynamics model for describing the water flow and suspended solids (SS) concentration distribution in a rectangular sedimentation tank is presented. The interfacial momentum transfer, buoyant forces, and the effect of sediment-induced density currents are considered. A convection-diffusion equation, which is extended to incorporate the sedimentation of activated sludge in the field of gravity, governed the mass transfer in the clarifier. The double-exponential law is used to describe the dependence of the settling velocity on the concentration. The results show that during the dynamic settling process of the sludge, the mud surface rose slowly, and a period of time later, the mud surface kept stability and reached dynamic equilibrium in the tank. The distribution of velocity along the z axis in the rectangular tank is not uniform, and the surface return flow is found. The turbulent kinetic energy is larger and dropped drastically in the inlet zone, while in the settling zone the tu...

Flow models for rectangular sedimentation tanks

The hydrodynamic behaviour of a pilot-scale sedimentation tank has been analyzed as a function of the flow and type of feed. As part of a qualitative approach, the main flow lines have been determined under different experimental conditions, including the purge ratio, which does not seem to significantly affect flow patterns. Quantitative analysis has been carried out by the study of the residence times distribution (RTD) in order to quantify the volumes of the different regions of the settler, including dead volumes, and in order to establish the model (dispersion model, tank in series model and a combined model) that better describes the hydrodynamic behaviour of the tank. Among all the configurations studied here, the most suitable are those fed through a distributor with a centre inlet section in medium flow conditions and fed through a distributor with a lower inlet section in low flow conditions. It can therefore be concluded that a change in the arrangement of feed inlet can allow a device to handle higher volumes by maintaining the flow conditions that improve sedimentation.

Design measures to increase the efficiency of secondary sedimentation tanks

Due to the fact that there is very little difference between the density of water and activated sludge, turbulences and energy inputs in secondary sedimentation tanks impair the sedimentation behaviour of the sludge particles. Consequently, all measures that reduce turbulence can be said to be positive and, thus, desirable. Bearing this in mind, a new type of secondary sedimentation tank has been developed. As hydraulic energy is predominantly introduced via the inflow, it is recommendable to feed the sludge/water mixture directly into the sludge layer on the bottom of the tank. In addition, sludge and water should, if possible, flow in the same direction. If these principles, which can be applied to both rectangular and circular secondary sedimentation tanks, are taken into account, the tanks can be designed more cost-effectively and efficiently.