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Design
Criteria
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1. Design Parameters
Average flow = 9.45 MCD
Peak flow = 17.0 MCD
Influent BOD = 200 mg/l
Effluent BOD = 10 mg/l
Influent NH3(N) = 30 mg/l
Effluent NH3(N) = 1.5 mg/l
Influent SS = 220 mg/l
Effluent SS = 30 mg/l
2. Headworks
a. Influent force main = 36"
b. Parshall flume = 30" throat
27.1 MGD capacity
c. Fine Screens
2 - ¼" hydraulicly driven fine screens with
a capacity of 20 MGD each. Solids are moved by hydraulic
auger to the truck bay. Hydraulic drive units are 2 hp each,
with interconnect piping so either drive unit can drive
either screen.
d. Grit Removal
1 - circular swirl-type unit, 2 hp drive, 16' diameter,
20 MGD flow capacity with 2 Wemco type horizontal grit slurry
pumps, 15 hp variable speed drive, 220 - 350 gpm.
e. Bypass to Detention Basin
Flow controlled gate and 24" throat parshall flume
with a capacity of 20 MGD. 30" pipe to detention basin.
f. Flow Measurement to Plant
30" throat, 27.1 MGD capacity.
g. Flow Distribution
Weir box for distribution of flow to the clarifiers, 3'
weir & 25% of flow to Clarifiers #1 and 2 each; 6' weir
and 50% of flow to Clarifier #3.
3. Primary Clarifiers
a. Existing: 2 - 75' diameter,
10 SWD Lakeside scrapper clarifiers.
New: 1 - 100' diameter, 13 SWD
Lakeside scrapper clarifier.
50% of flow to existing units
Area = 4,418 sq. ft. each
Vol = 330,500 gal each
SOR = 535 gpd/sq. ft. at Peak SOR-- 962 gpd/sq. ft.
HDT = 3.36 hrs.
50% of flow to new unit
Area =7,854 sq. ft.
Vol = 763,723 gal.
SOR = 601 gpd/sq. ft. at Peak SOR --1,082 gpd/sq. ft.
HDT = 3.88 hrs.
b. Primary Sludge Pumping
Existing return is by gravity in a 4" line or by pumping
with 2 - 100 gpm Wemco Model EV pumps.
A new pump station is provided
for the new 100' ø primary. It has 2
- 100 gpm Wemco Model EV pumps. An 8" gravity force
main replaces
the existing 4" as a common gravity pumping line
for both pump
stations.
4. Aeration Tanks
a. Design Factors
3 aeration tanks --2 existing, 1 new
125 x 30 x 15SWD
Total Volume = 168,750 ft.3
Assume 30% BOD reduction in primary
clarifiers
BOD loading = 140 mg/l
Assume 50 mg/l BOD from aeration
tanks
BOD loading = 90 mg/l x 8.34 x 9.45 = 7,093 lb/day
7,093/169 = 42 lb. BOD/l,000 cu. Ft.
HDT = 168,750 x 7.48 - 0.1336 day = 3.21 hr.
9.45
Air required = 7,093 x 1.2 lb. O2/lb. BOD
= 8,512 lb. O2 = 4,600 cfm for fine bubble aeration
Air provided 2,000 - 10,000 cfm
Sufficient return sludge capability
exists to maintain the MLSS and
F/M ratio in the desired ranges for the aeration tanks.
b. Fine bubble aeration will be
used, final decisions have not yet been made on the exact
system.
c. Return sludge system
Existing pumps are for 800, 1,500 and 2,400 gpm.
A 5,000 gpm pump will be provided in place of the existing
800 gpm pump.
Parallel force mains and flow meters
will allow aeration return sludge rates of 1,500 gpm, 23%
to 7,500 gpm, 114%
5. Intermediate Clarifiers
The intermediate clarifiers
are identical to the primaries in all the design criteria.
The sludge system is a suction system piped directly to
the return pumping system discussed above.
6. Nitrification Tanks
a. Design factors
3 tanks- -2 existing, 1 new
121 x 30 x 15 SWD
Total Vol. = 163,350 ft.3
BOD loading @ 50 mg/l = 3,941 lb. BOD
3,941/163.35 = 24.1 lb. BOD/1,000 cu. ft.
HDT = 163,350 x 7.48 = 0.129 day = 3.1 hrs.
9.45
Air required = (3,941 x 1.2) + (2,246
x 4.6)
=15,061 lb. O2 = 8,120 cfm
Air provided = 2,000 - 10,000 cfm with a 10,000 cfm blower
in
reserve.
Sufficient return sludge capability exists to maintain the
MLSS and F/M ratio in the desired ranges in the aeration
tanks.
NOTE: It should be pointed out that preliminary aeration
system designs by Sanitaire and FMC show air requirements
of approximately 6,000 scfm in the aeration tanks and 2,000
to 6,000 scfm in the nitrification tanks. The difference
is dependent upon the removals projected for the aeration
tanks. In order to provide maximum operator flexibility,
the aeration system in both the aeration and nitrification
tanks will be essentially the same. This is good engineering
judgement and will allow the operator the widest range of
treatment schemes to meet the effluent requirements.
b. Fine bubble aeration will
be used, final decisions have not been made on the exact
system.
c. The calculations and plans are the same as for the aeration
return
sludge system.
7. Final Clarifiers
Existing: 2 - 75' diameter, 10 SWD
Lakeside suction return clarifiers.
New: 1 - 120' diameter, 14 SWD Lakeside suction return clarifier.
40% of flow to existing units
Area = 4,418 sq. ft. each
Vol = 330,500 gal each
SOR = 428 gpd/sq. ft. at Peak SOR =770 gpd/sq. ft.
HDT = 4.17 hrs.
Solids Loading Rate = *287.13
x .2 = 13 lb./day/sq. ft.
????4,418
* From the 201 Amendment
60% of flow to new unit
Area = 11,310 sq. ft.
Vol = 1,184,383 gal.
SOR = 501 gpd/sq. ft. at Peak SOR = 902 gpd/sq. ft.
HDT = 5.01 hrs.
Solids Loading Rate *287.130 x .6 = 15 lb./day/sq. ft.
???11,310
8. Chlorination
Install 1 - 5 hp jet mixer
in each chlorine contact tank. Capacity is 4-7 mgd each
with a peak of 12.5 mgd. This takes approximately 10% of
each basin.
Detention time remaining at design flow =15.94 minutes
Detention time at peak flow = 9.6 minutes
9. Cascade Aeration
Raise DO to 6 mg/l
Assume 2 mg/l influent DO
Drop required (by EPA formula)
= 10'
Design is 10' drop, 16' wide with 15 8" drop x 2' run
steps.
Depth of flow at 9.5 MGD is approximately 3-4 inches.
Depth of flow at 17.0 MGD is approximately 6 inches.
10. Digesters
3 - 160 x 33.5 x 15 SWD tanks
Volume = 1,804,176 gallons
Solids Production = 9.5 x (200-10) x .85 x 8.34
= 12,795 lb/day
??12.795 lb/day = 51,142 gpd
??.03 x 8.34 lb/gal.
Detention time = 1,804,176 gal/51,142 gpd = 35 days
Air required = 241.2 cf at 30 cfm
= 7,236 cfm
or at peak air demands
Air required = 241.2 cf at 60 cfm = 14,472 cfm
Use the existing blowers
??5,250 scfm @ 8.2 psi each
Air from 2,500 - 15,000 cfm is available
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