Design Of Sedimentation Tanks Research Articles

Sedimentation Tanks for Treating Rainwater: CFD Simulations and PIV Experiments

The removal of solids is the most important step when treating rainwater. The article evaluates two designs of sedimentation tanks that can be used for the continuous separation of fine particles from water: OS—standard sedimentation tanks, and OW—swirl sedimentation tanks. The tanks were studied by conducting computational fluid dynamics (CFD) modeling and particle image velocimetry (PIV) experiments. The settling process in sedimentation tank was carried out at varying operating flow rates. A tank with a modified structure was used for the tests, where water was supplied by a nozzle placed at an angle. This solution made it possible to obtain a rotational flow that transported the suspended particles towards its wall, where downward axial velocity resulted in the settling of particles. Based on the research, it was observed that the flow patterns showed inward flow at the bottom of the tank and an upward flow and the lifting of the settled particles near the hatch at the bottom. The presented experimental measurements provided detailed insight into flow patterns, and valuable calibration and verification data for further CFD modeling. Traditional PIV techniques are useful in the case of standard design, whereas CFD is invaluable for supporting this work and for investigating the design of novel sedimentation tanks.

Optimal design of sedimentation tanks for effluent of marble works and use of settled solids in concrete

The aims of this study are to determine the settling characteristics of wastewater from the marble works in Elazig-City province experimentally and to optimise the dimensions of the sedimentation basins. The results can be directly used in small plants. Quiescent settling experiments were carried out at constant temperature for retention times of 0.5 to 2 hours by taking composite samples of two hours. The results obtained from through frequency distribution curves have shown that the settling was of a discrete type. The relationship between the hydraulic loading and the efficiency curves was obtained and thus the efficiency value of basins at different surface areas was determined. The dimensions of the basins for minimum turbulence, stable flow without bottom drift and maximum settling efficiency were investigated. The Froud Number that expresses the flow stability, the Reynolds Number that indicates the turbulence effect, and the horizontal velocities at basins were considered as limiting factors, while the surface areas of basins were held constant. The basin 9, with surface area of 80 v m 2 (4 v m 2 20 v m), is the most suitable one with efficiency of 99.5%. Basin 7, with surface area of 45 v m 2 (3 v m 2 15 v m), where the efficiency could be increased by building an entry region, is the most economic one according to construction. The use of settled solids at the bottom of basin within concrete classes C14 and C20 was experimentally investigated through compression tests. The compression strength of cube samples adulterated with the settled solids for both concrete classes of C14 and C20 were 3-4% better than the cube samples with normal aggregate.

An empirical model for primary sedimentation of sewage

Theoretical mathematical models of primary sedimentation and column settling tests have failed until now to predict the behaviour of sedimentation tanks under actual operating conditions due to the difficulties in simulating the effect of the density currents and the complex phenomenon of flocculation. Therefore, empirical models can be helpful in the design of sedimentation tanks. Using performance data from three different pilot-scale sedimentation tanks, empirical mathematical models were developed in this paper relating suspended solids (SS) removal efficiency to surface overflow rate, influent SS concentration, and sewage temperature. The model coefficients were derived from the combined analysis of three well correlated sets of data, thus giving a good indication for their possible general applicability. The analysis of experimental data also gave a relationship between SS and chemical oxygen demand (COD) removal efficiencies.

Optimum design of sedimentation tanks based on setting characteristics of Karachi tannery wastes

A study was carried out in a specially designed settling column to investigate the settling characteristics of effluents arising from Karachi tanneries. The Jar-tests were conducted to determine the optimum dosage of coagulants such as potash alum and ferric chloride to maximize the removal of suspended solids (S.S) from the wastes. For alumn, the optimum dosage was found to be 150 mg L−1, whereas with ferric chloride it was 30 mg L−1. Experiments carried out in the settling column with the optimum coagulant dosages showed that the coagulation with ferric chloride was much better than with alumn, as it removes about 84% S.S from the wastes compared to 70% removal obtained in case of alumn. Design curves in terms of percent removal of S.S. vs loading rate and detention time were constructed using data obtained from settling column. These curves can be used in designing the settling tanks employed in the tannery wastes treatment plants.