Continuing the design of preliminary treatment facilities for the town of Pigeonroost’s...

Continuing the design of preliminary treatment facilities for the town of Pigeonroost’s WWTP ( Problem 13-1 ), estimate the headlosses for a bar rack using an inlet channel width of 0.68 m and the assumptions used in Example 13-4 .

Example 13-4

Estimate the headlosses for a bar rack for Waterloo ( Examples 13-1 , 13-2, and 13-3 ) with a clean bar rack and with partial blockage of the screen. Use the following assumptions:

1. Mechanically cleaned bar rack.

2. Bar width = 15 mm.

3. Bar spacing = 20 mm.

4. Angle from vertical = 30^o.

5. Differential headloss for activation of the cleaning rakes is 150 mm.

6. Maximum flow area blockage to initiate continuous operation of rakes is 50%.

Problem 13-1

Using the pumps given in Table 13-1, design a screw pump system for the town of Pigeonroost using the following assumptions:

Complete the design by providing the following: pump specifications (diameter, number of flights), number of pumps, and a sketch of the plan view with dimensions (assume the width of each pump equals the diameter of the screw plus 0.6 m).

Table 13-1

Example 13-3.

Design the channel for the bar rack for Waterloo ( Examples 13-1 and 13-2 ).

Assume the following:

1. Approach velocity at average flow rate ≥ 0.4 m/s.

2. Approach velocity at peak hour flow rate at design capacity ≤ 0.9 m/s.

3. Slope of channel is 0.0001 m/m.

4. Width of channel is equal to Parshall flume inlet.

5. Two channels will be provided for redundancy, but one channel must handle the flow for the peak hydraulic flow rate.

6. Freeboard = 0.6 m.

Example 13-2.

Continuing with the head works design for Waterloo ( Example 13-1 ), design a Parshall flume by specifying the throat width and estimating the maximum depth of the flume. Assume free flow conditions and 0.6 m freeboard above the maximum depth.

Example 13-1.

Design a screw pumping system for Waterloo’s WWTP that has the following characteristics:

Interceptor sewer

Minimum sewage elevation = 514.75 m

Maximum sewage elevation = 515.00 m

Discharge elevation to stilling well = 519.17 m

Average flow rate at design capacity = 37,000 m³/d