Demonstration of the sedimentation tank removal efficiency evaluation (coursework 1) Sonila Vito ______________________________________________________________________________________________________ This project has been funded with support from the European Commission. This publication reflects the views only of the authors, and the Commission cannot be held responsible for any use which may be made of the information contained therein.

NETCHEM Remote Access Laboratory Guide Demonstration of the sedimentation tank removal efficiency evaluation (coursework 1) In this exercise, you will: Learn how to evaluate the removal efficiency of a sedimentation tank based on the experimental data. ______________________________________________________________________________________________________ This project has been funded with support from the European Commission. This publication reflects the views only of the authors, and the Commission cannot be held responsible for any use which may be made of the information contained therein.

Rectangular (rectangular in plans and cross sections) Background Sedimentation principles Sedimentation is the process in which the solids, present at the water body, fall down the water column in response to gravity. Types of the sedimentation basins: Rectangular (rectangular in plans and cross sections) Circular (in plan) At the rectangular basins the length may vary from two to four times the width. The length may also vary from ten to 20 times the depth. The depth of the basin may vary from 2 to 6 m. The influent is introduced at one end and allowed to flow through the length of the clarifier toward the other end. The solids that settle at the bottom are continuously scraped by a sludge scraper and removed. The clarified effluent flows out of the unit through a suitably designed effluent weir and launder. Unlike the rectangular basin, circular basins are easily upset by wind cross currents. For this reason, circular basins are typically designed for diameters not to exceed 30 m in diameter. ______________________________________________________________________________________________________ This project has been funded with support from the European Commission. This publication reflects the views only of the authors, and the Commission cannot be held responsible for any use which may be made of the information contained therein.

Background Sedimentation principles Particle will settle if: vh < vo or vp In industrial practices for light flocculent suspensions, vh < 9.0 m/h; for heavier, discrete-particle suspensions, vh > 36 m/h. The figure above shows the basic principles of removal of solids in the settling zone. A settling column (to be discussed later) is shown moving with the horizontal flow of the water at velocity vh from the entrance of the settling zone to the exit. As the column moves, visualize the solids inside it as settling; when the column reaches the end of the zone, these solids will have already been deposited at the bottom of the settling column. The behaviour of the solids outside the column will be similar to that inside. Thus, a time in the settling column is the same time in the settling zone. A particle possesses both downward terminal velocity vo or vp, and a horizontal velocity vh (also called flow-through velocity). Because of the downward movement, the particles will ultimately be deposited at the bottom sludge zone to form the sludge. For the particle to remain deposited at the sludge zone, vh should be such as not to scour it. The schematic view of a settling zone. vh is the water velocity (flow-through velocity); vo or vp is the particle downward terminal velocity; Zo is the water column depth; and Zp is the particle depth at a certain time. (A. Sincero and G. Sincero, 2003) ______________________________________________________________________________________________________ This project has been funded with support from the European Commission. This publication reflects the views only of the authors, and the Commission cannot be held responsible for any use which may be made of the information contained therein.

Background Sedimentation principles If A is the vertical cross-sectional area, Q the flow, Zo the depth, W the width, L the length, and t0 the detention time (or retention time or removal time) than: For a rectangular reservoir: Where As is the surface area of the tank; V is the reservoir volume and Q/As is called the overflow rate, qo. The detention time is the average time that particles of water have stayed inside the tank. For discrete particles, the detention time to normally ranges from 1 to 4 h, while for flocculent suspensions, it normally ranges from 4 to 6 h. For a circular reservoir: Thus: ______________________________________________________________________________________________________ This project has been funded with support from the European Commission. This publication reflects the views only of the authors, and the Commission cannot be held responsible for any use which may be made of the information contained therein.

Background Sedimentation principles Sedimentation types: Type 1 (discrete sedimentation)- refers to the removal of discrete particles Type 2 (flocculant sedimentation)- (refers to the removal of flocculent particles) Type 3 -(refers to the removal of particles that settle in a contiguous zone) Type 4 -(is a type 3 settling where compression or compaction of the particle mass is occurring at the same time.) ______________________________________________________________________________________________________ This project has been funded with support from the European Commission. This publication reflects the views only of the authors, and the Commission cannot be held responsible for any use which may be made of the information contained therein.

Background Discrete sedimentation The terminal settling velocity of the particle, v, could be evaluated: Where ρp is the mass density of the particle; ρw is the mass density of water; CD is the drag coefficient; d is the particle diameter; and g is the acceleration due to gravity The value of CD is a function of the flow regime Values of Re less than 1 indicate laminar flow, while values greater than 104 indicate turbulent flow. Intermediate values indicate transitional flow. For laminar flow Where Re is the Reynolds number (vρwd/) and  is the dynamic viscosity of water. For transitional flow For turbulent flow ______________________________________________________________________________________________________ This project has been funded with support from the European Commission. This publication reflects the views only of the authors, and the Commission cannot be held responsible for any use which may be made of the information contained therein.

Background Discrete sedimentation For a non spherical particle, the particle diameter is calculated through: Where β is the shape factor and dg the equivalent diameter Design of a pre sedimentation basin (Column experiments) The following values of sand volumetric shape factors β have been reported: angular = 0.64, sharp = 0.77, worn = 0.86, and spherical = 0.52 The figure shows a schematic of columns and the result of an analysis of a settling test. At time equals zero, let a particle of diameter do be at the water surface of the column in a. After time to, let the particle be at the sampling port. Any particle that arrives at the sampling port at to will be considered removed. In the prototype, this removal corresponds to the particle being deposited at the bottom of the tank. to is the detention time. The corresponding settling velocity of the particle is vo = Zo/to, where Zo is the depth. This Zo corresponds to the depth of the settling zone of the prototype tank. Particles with velocities equal to vo are removed, so particles of velocities equal or greater than vo will all be removed. If xo is the fraction of all particles having velocities less than vo, 1 − xo is the fraction of all particles having velocities equal to or greater than vo. Therefore, the fraction of particles that are removed with certainty is 1 − xo. ______________________________________________________________________________________________________ This project has been funded with support from the European Commission. This publication reflects the views only of the authors, and the Commission cannot be held responsible for any use which may be made of the information contained therein.

Background Discrete sedimentation Design of a pre sedimentation basin (continue) Evaluation of the removal efficiency, R The evaluation of the integral could be done using the plot of vp versus x. Note that the equation of R does not state that the velocity vp must be terminal. For discrete settling, this velocity is the terminal settling velocity. For flocculent settling, this velocity would be the average settling velocity of all particles at any particular instant of time. Where [co] is the original concentration in the column, and [c] is the remaining concentration measured after the settling time, t, at the sampling port. Where Zp is the depth to the sample port at time interval t from the initial location of the particles ______________________________________________________________________________________________________ This project has been funded with support from the European Commission. This publication reflects the views only of the authors, and the Commission cannot be held responsible for any use which may be made of the information contained therein.

Background Flocculent sedimentation When particles have affinity toward each other and coalesce to form flocs or aggregates. Design of the flocculent sedimentation process Column experiments are still performed but with more than one sampling port through the column high to consider the changing velocity of the particles during sedimentation as forming flocks. To evaluate the removal efficiency the same formulas are used but for each port. ______________________________________________________________________________________________________ This project has been funded with support from the European Commission. This publication reflects the views only of the authors, and the Commission cannot be held responsible for any use which may be made of the information contained therein.

Material For this exercise, you will need the following material: Computer Office program ______________________________________________________________________________________________________ This project has been funded with support from the European Commission. This publication reflects the views only of the authors, and the Commission cannot be held responsible for any use which may be made of the information contained therein.

Procedure: Fill the red cells with the assigned data. Note that the problem and the input parameters are presented at the red cells. After that the program automatically calculates for each sampling port the: effluent concentration (C, mg/l) X(C/C0) Vp(Zp/2t) at different sampling times given from the problem (sky blue cells). Sort the Vp data of all the sampling ports in descending order (yellow cells). Be careful to fill the corresponding value of X for each Vp. After that the program automatically calculates ΔX, Vp (in ΔX), and ΔX·Vp (in ΔX). Finally, considering the overflow rate value given from the problem, specify the input values at the formula that evaluates the removal efficiency (green cell). ______________________________________________________________________________________________________ This project has been funded with support from the European Commission. This publication reflects the views only of the authors, and the Commission cannot be held responsible for any use which may be made of the information contained therein.

Author, Editor and Referee References This remote access laboratory was created thanks to work done primarily at University of Niš. Contributors to this material were: Sonila Vito Refereeing of this material was done by: _____________________ Editing into NETCHEM Format and onto NETCHEM platform was completed by: ______________ ______________________________________________________________________________________________________ This project has been funded with support from the European Commission. This publication reflects the views only of the authors, and the Commission cannot be held responsible for any use which may be made of the information contained therein.

References and Supplemental Material The NETCHEM platform was established at the University of Nis in 2016-2019 through the Erasmus Programme. Please contact a NETCHEM representatives at your institution or visit our website for an expanded contact list. The work included had been led by the NETCHEM staff at your institution. ______________________________________________________________________________________________________ This project has been funded with support from the European Commission. This publication reflects the views only of the authors, and the Commission cannot be held responsible for any use which may be made of the information contained therein.