Evaluación y dimensionamiento de unidades de sedimentación convencional para cinco diferentes aguas superficiales utilizando el tamaño de Flocs como parámetro.

Abstract

A drinking water treatment plant (WTP) design is based on the flowrate to be treated. A conventional WTP has coagulation, flocculation, sedimentation and filtration units. Conventional sedimentation, also known as clarification process, is a physical separation of flocs particles generated in the coagulation and flocculation steps. To be dimensioned the clarification units required design parameters such as the velocity sedimentation of floc particles (Vm), which include the water density, the density of the particles, a drag coefficient, the acceleration of the gravity and the mean particle diameter of flocs (dp). The main objective of this research was to assess and design conventional sedimentation units for five different surface waters using two different methods: Method I (taking a hydraulic surface charge) and method II (using a mean flocs size for calculating the hydraulic surface charge). The mean floc size of five different waters used in this research was taken from the results reported by (González-Galvis et al. 2022) in which a flocs size imagen analysis technique and a cell phone camera was used. With this technique a mean floc sizes between (68-277μm) was found. The results obtained in this research showed that the waters that should be treated with sedimentation were: 1) Soracá (initial turbidity of 5.95 NTU); 2) Ventaquemada (initial turbidity of 2.27 NTU); and 3) Tunja (initial turbidity of 3.61 NTU). For the other two waters tested in this research it is recommended to be treated using direct filtration, or in other words (coagulation, flocculation, and filtration) due to their very low raw water turbidity (1.67 and 0.53 NTU, respectively). In addition, the results showed that the method I trend to undersize the sedimentation tank area in comparison with the method II. In the same way, the method I reduces the hydraulic retention time for some waters, but for all the waters treated the Reynold number was lower than 20.000, regardless of the design method used. However, the Froude number was not acceptable for any of the two methods used and for all the waters assessed in this research because the values obtained were higher than 10-5.