Page 203 - Fundamentals of Water Treatment Unit Processes : Physical, Chemical, and Biological

158 Fundamentals of Water Treatment Unit Processes: Physical, Chemical, and Biological

Solution 0.2 mm grit leaving the grit chamber). Assume the new
3
3
Flows: Q(avg) ¼ 0.22 m =s, Q(max) ¼ 0.66 m =s, grit chamber must handle flows of about 15 mgd.
3
3
3
Q(min) ¼ 0.066 m =s. Table CDprob7.3 and Table Flows: Q(avg) ¼ 0.22 m =s, Q(max) ¼ 0.66 m =s,
3
CD7.7 contains the algorithm for calculation of the Q(min) ¼ 0.066 m =s.
Q(max) and Q(min) depths, H a (max) and H a (min), in
Required
the ‘‘a’’ and ‘‘b’’ sections, respectively. The ‘‘c’’ section
Using the 1976 grit chamber performance and sizing
shows the calculations for the parabolic cross section
as a guide, determine a sizing for a new one, along
and the v H values for different depths, ‘‘y,’’ and flows
with determining airflow and compressor horsepower.
(columns ‘‘a’’ and ‘‘b’’; as seen, the v H values calculated
Using your spreadsheet, explore alternatives that
are all about 0.31 m=s (1.0 ft=s). The formulae are given
may be considered. Also determine Q(air) and
at the bottom of the table. The plot of the parabolic cross
P(compressor).
section at the bottom of the table is linked to the table
7.9 Grit Quantity
values of (x, y).
Given
7.4 Trapezoidal Grit Chamber with Parshall Flume 3
Flows: Q(avg) ¼ 0.22 m =s 5.0 mgd), Q(max) ¼ 0.66
Control 3 3
m =s (15 mgd), and Q(min) ¼ 0.066 m =s (1.5 mgd).
Given
3
3
Flows: Q(avg) ¼ 0.22 m =s, Q(max) ¼ 0.66 m =s, and Required
3 Estimate the volume rate of grit to be expected at a
Q(min) ¼ 0.066 m =s.
WWTP in your locale for
Required
1. Daily dry weather flow.
Design a trapezoidal section grit chamber with a Parshall
2. Wet weather flow.
flume as control, approximating this from the parabolic
3. What size (volume) of container would you set
section in Problem 7.3.
below your grit conveyor belt and how frequently
7.5 Aerated Grit Chamber—Rational
would you expect to transport the grit to a disposal
Given site?
3 3
4. Determine the disposal site for the plant. What regu-
Q(avg) ¼ 0.22 m =s, Q(max) ¼ 0.66 m =s, and Q(min) ¼
3
0.066 m =s. lations pertain?
Required 7.10 Pressure, p 3 , at Compressor Outlet—For Aerated
Design an aerated grit chamber using guidelines from Grit Chamber
Londong (1989). This problem involves an extensive spreadsheet; in lieu
7.6 Aerated Grit Chamber—Empirical of setting up the spreadsheet, an alternative is to review
the problem in principle, referring to the spreadsheet
Given
3 3 already developed.
Q(avg) ¼ 0.22 m =s, Q(max) ¼ 0.66 m =s, Q(min) ¼
3
0.066 m =s. Given
3
Required 1. Flows: Q(avg) ¼ 0.22 m =s (5.0 mgd), Q(max) ¼
3
3
0.66 m =s (15 mgd), and Q(min) ¼ 0.066 m =s (1.5
Design an aerated grit chamber using empirical guide-
mgd).
lines.
2. Assumptions: Assume the distance equals 50 m
7.7 Model to Estimate Performance
(164 ft) between the compressor and the diffuser
Given header pipe in the grit chamber. The pipe size should
3 3
Flows: Q(avg)¼ 0.22 m =s, Q(max) ¼ 0.66 m =s, and be a part of the spreadsheet so that you can examine
3
Q(min)¼ 0.066 m =s.
pipe losses for different pipe sizes. For sizing
Required the grit chamber, let q ¼ 20 min, with V(grit cham-
Estimate by Equation 7.21 the difference in performance ber) based on Q(max). For the cross-section, let
of any grit chamber designed for the range of flow width ¼ depth ¼ 5.0 m. Also, let Equation 7.24 be
specified. the means to estimate the air flow for the aerated
7.8 Model to Estimate Aerated Grit Chamber grit chamber, that is, Q(air, coarse bubble) ¼
Performance [0.07 þ 0.76 ln(d)] 1.33 , where d is the depth of
Given the diffuser header pipe below the water surface of
The Fort Collins WWTP (1976 North Plant at Drake the grit chamber; let d ¼ 3.50 m.
Road and Cache La Poudre River) had (before a plant Required
expansion, c. 1991) an aerated grit chamber that was 1. Compressor outlet pressure: Set up a spreadsheet
about 5 m wide 5 m deep 10 m long in dimensions to determine pressure, p 3 , in outlet pipe from the
for a flow of about 6 mgd. Performance is hypothetical, compressor.
but assume that C o 1000 mg=L for grit particles 2. Compressor power: Determine the power required
about 0.2 mm in size and that C 100 mg=L (for by the compressor for an adiabatic compression.