Civil Engineering Reference
In-Depth Information
TABLE 17-7. Design Criteria for Cincinnati Water Works GAC
Treatment Facilities
Item
Value
Facilities
Maximum hydraulic capacity
220 mgd (830 ML / d)
Maximum day flow
175 mgd (660 ML / d)
Average flow
124 mgd (470 ML / d)
GAC contactor
Number
12
Size
30 ft
65 ft (9.2 m
19.8 m)
Bed depth
11.4 ft (3.5 m)
Area per contactor
1,950 ft
2
(181 m
2
)
GAC volume per contactor
22,230 ft
3
(639 m
3
)
Backwash rate
11 gpm / ft
2
(27 m / h)
Bed expansion during backwash
30%
EBCT
Maximum hydraulic capacity
12.0 minutes
Maximum day flow
15.0 minutes
Average flow
21.2 minutes
Surface loading rate
Maximum hydraulic capacity
6.9 gpm / ft
2
(17 m / h)
Maximum day flow
5.5 gpm / ft
2
(13 m / h)
Average flow
3.9 gpm / ft
2
(4.5 m / h)
Carbon Regeneration and
Handling
Annual usage
40,000 lb / d (18,000 kg / d)
Peak carbon usage
80,000 lb / d (36,000 kg / d)
Carbon storage vessels*
Virgin carbon
34,000 ft
3
(960 m
3
)
Spent carbon
34,000 ft
3
(960 m
3
)
Regenerated carbon
34,000 ft
3
(960 m
3
)
Regeneration facilities
Number of systems
2
Type of regeneration system
Multiple-hearth furnace
Capacity of each system
40,000 lb / d (36,000 kg / d)
* Some storage vessels have duplicate functions.
monitors activities on the watershed to protect the water quality. It operates a 40-mgd
(150-ML / d) water treatment plant serving approximately 118,000 customers. Figure
17-16 shows the process schematic of the plant, which was completed in 1974. The
water treatment plant includes coagulation, sedimentation, and filtration before GAC
contacting.
GAC is used at this plant to provide taste and odor control as well as organics
(TOC) and THM control. Taste and odor problems are amplified only during the spring
snowmelt, but the agency runs the GAC system year-round to provide high-quality
water to its customers. In winter, fewer units are operated. A thermal fluidized bed is
used for carbon regeneration. Table 17-9 shows the design criteria for the plant's GAC
facilities.
Since the plant went on-line in 1974, performance has been excellent (see Table
17-10). The operational strategy is to target an effluent TOC of 2 mg / L or a THM
