Objective

The purpose of this assignment is to estimate the hydraulic loading rate on a filter and to determine the required backwash velocity and the depth of the expanded medium bed in a sand filter.

Part 1: Consider the filters in the lab using only sand as the filter medium. The flowrate through the filter is 900 ml/min, the diameter of the filter is 3.5 in., the depth of the filter bed is 8 in., the sand has a particle diameter of 0.5 mm or 0.02 in. with a settling velocity of 0.27 ft./s, and the porosity of the sand is 0.30.

1. Determine the hydraulic loading rate in gpd/ft².
      
                           
                           
   
    
2. Based on the hydraulic loading rate, classify the filter as either a slow sand filter or a rapid sand filter.
   
            For a hydraulic loading rate of 5,126 gpd/ft.² -  rapid sand filter
    
3. Determine the required backwash velocity to expand the sand filters in the lab to a porosity of 0.80.
   
      
         
   
    
4. Determine the depth of the expanded filter bed.
   
    
   
         

Part 2: Develop the equations to describe how to compute filter efficiency (see the project description for more details). Write this section as if it would be cut-and-pasted into your Project #3 report.

The Total Volume treated is the sum of the all Incremental Volume collected during the 90-minute filter run.

(1)

where

(2)

where FLowrate_i-1 is the flowrate (ml/min) at time interval i-1 and Time_i is the time increment (minutes).

The Average Turbidity is calculated using the following equations:

(3)

where

(4)

where Turbidity_i is the recorded turbidity at time i.

The Filter Efficiency of the filter is measured as:

(5)

where

(6)

Part 3: Read Chapter 12 in the Strategies for Creative Problem Solving by Fogler and LeBlanc.

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