Sedimentation Tank Design Program

The design of the sedimentation tank is a critical piece of the design of the entire plant. Its properties, such as depth and critical velocity, are important in determining the dimensions and lamella spacing. This program requires inputs from the user and from our basis of design in order to determine the design and dimensions necessary to generate the AutoCAD drawing and design report.

Sedimentation Tank Design Program Algorithm

Sedimentation Tank Inputs
Sedimentation Tank Outputs
Sedimentation Tank AutoCAD Drawing Program

Algorithm

The sedimentation program calculates the dimensions of one sedimentation tank and the break down of what portion of the tank is allotted for the inlet slopes versus the lamella. The details of the inlet slopes, drain pipe, launders and lamella to be in the tank are calculated in separate programs. All sedimentation tanks in the plant are designed to be identical.
The number of tanks is specified by the user. Based on the number of tanks given by the user the flow rate through one tank must be calculated first.

This flow rate will then determine the cross sectional area of the tank given the desired upflow velocity. The upflow velocity is set to allow for possible sludge blanket formation (70m/day). The width of the tank is a user input determined by the width of the material used for the plate settlers (42in = 1.07m). The specified width allows for the tank length to be calculated.

The height or depth of the tank is simply the water height in the tank plus the plant freeboard of 10cm. This plant freeboard is a design assumption used through out the design algorithms to give a buffer to allow for possible variation in water levels without resulting in tank overflow. The water height is set in the basis of design. It should be noted that this value will have to be higher if larger plants are designed.

Within the given waterdepth the tank is divided into sections. The user is asks to give a ratio (Pi.SedBottomHWSed)of how the sedimentation tank should be divided, this fraction represents the portion of the tank devoted to the inlet slopes below the lamella, this includes the drain pipe at the bottom of the tank. The rest of the tank is aportioned to lamella and effluent launders. The user given fraction is multiplied by the design water depth to give a vertical height of the tank occupied by the inlet slopes and the drain pipe.

In this current design the top of the slopes are designed to meet the bottom of the lamella. The bottom of the slopes are designed to slope down to the top of the drain pipe. If the depth of the water is increased to the point where the angle of the slopes is greater than 60deg the angle of the slopes will be set to 60 deg and the rest of the height to the bottom of the lamella will be straight vertical wall.

For deeper plants the height of the platform is calculated based on the bottom of the platform being even with the bottom of the inlet channel.