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: Using the data obtained in the first week of water filtration lab, present, analyze, and discuss the data. Your data should be presented in graphical form. Remember that Ms. Ashman is not an engineer—explain the concepts in terms that will help her understand the data and make an informed choice about the filter.

Part 2: Consider the filters in the lab using only sand as the filter medium. The flowrate through the filter is 1,300 ml/min, the diameter of the filter is 3.5 inches, the depth of the filter bed is 9 in., the sand has a particle diameter of 0.5 mm or 0.02 inches 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 hydraulic loading rate, classify the filter as either a slow sand filter or a rapid sand filter.
   
            For a hydraulic loading rate of 7,401 gpd/ft.² -  rapid sand filter
    
3. Determine the required backwash velocity to expand the sand filters in lab to a porosity of 0.80.
   
      
         
   
    
4. Determine the depth of the expanded filter bed.
   
    
   
         

Part 3: 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 the 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 4: Read Chapter 12 in the Strategies for Creative Problem Solving by Fogler and LeBlanc.

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