Homework 4

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Due: February 29th

Discreet & Flocculant Sedimentation

Work as a team of two for this assignment.

Deliverables: Spreadsheet with calculations.

Size grit removal and primary settling facilities for the City of Spunkindale, Illinois' wastewater treatment plant. Spunkindale has an average flow of 12 MGD and a peak flow of 25 MGD.

Grit Removal

Size square grit tanks. Use a minimum of two tanks, each capable of accepting the entire plant flow. 65 Mesh grit should be removed 100% at a water temperature of 15C. Provide tank sizes, estimated grit removal. For comparison, size aerated grit tanks for the same system. Provide air requirements.

Established Design Criteria for Aerated Grit Removal

Parameter Value
Unit Length

25 to 65 ft.

Unit Depth

7 to 16 ft.

Unit Width

8 to 23 ft.

Width to Depth Ratio

1:1 to 2:1

Length to Width Ratio

3:1 to 5:1

Detention Time

2 to 5 min. (at peak)

Air Supply

2 to 5 ft.3/min-ft.

 

Primary Sedimentation

Use a minimum of two tanks. Provide the diameter and depth of the tanks. Also, provide the detention time at average flow, and the overflow rate at both peak and average flow. Show all calculations on the attached spreadsheet. The tanks should remove 65 to 70% of the suspended solids at average flow. Provide the following information: detention time at average and peak flows, overflow rate at average and peak flows, weir loading at average and peak flows, removal at average and peak flows with all tanks operable, and removal at average and peak flows with one tank out of service.

Please submit this assignment electronically to ray@engr.siu.edu

Download the discreet and flocculant settling data as an Excel spreadsheet  (right click to save file).

The following are accepted design standards for primary sedimentation tanks used in wastewater treatment.

Parameter Minimum Maximum
Detention time, hrs 1.5 2.5
Overflow rate, peak flow, Gal/ft2-day 2000 3000
Overflow rate, average flow, Gal/ft2-day 800 1200
Weir loading, Gal/ft-day 10,000 40,000

Weir loading is based on length of the weir. Thus, if the weir is placed at the outside of a circular tank, it is equal to the circumference of the tank.

Typical physical dimensions are as follows.

Parameter Minimum Maximum
Circular Tanks    
     Depth, ft. 10 15
     Diameter, ft. 10 200
     Slope of bottom, in./ft. 0.75 2
     Flight speed, rev./hr. 1.2 3
Rectangular Tanks    
     Depth, ft. 10 15
     Length, ft. 50 300
     Width, ft. 10 80
     Flight speed, ft./min. 2 4

Note: Spunkindale, Illinois is a sister city to Spunkindale, Arkansas. Spunkindale, Arkansas was a mythical city created for wastewater design projects by the late Professor Dee T. Mitchell of the University of Arkansas.