Civil Engineering Reference
In-Depth Information
storage, and later diluted for feeding. Table 24-4 illustrates the operation and main-
tenance labor for several chemicals commonly used as coagulants and coagulant aids.
These labor requirements include unloading, storing, and feeding operations. Unslaked
lime requires relatively high labor for slaking and feeding equipment. As Table 24-4
illustrates, there are differences in labor requirements, and these differences should be
considered in selecting chemicals. Water plant treatment costs, discussed in Chapter
32, include chemical feeding systems.
DESIGN CONSIDERATIONS
General Considerations
The design of chemical handling systems must take into account the type of chemical
to be fed and the form of the chemical. It must also consider the methods of chemical
delivery, storage, handling, mixing and feeding, and the conveyance of the chemicals
to the final feed points. The design must result in efficient handling of the chemicals
from delivery and storage to the application point. The operation should be convenient
and easy without placing an excess burden on operating personnel.
The chemical feeding and handling design should be versatile and allow maximum
operator flexibility. A sufficient number of feed points should be included in the treat-
ment plant, as well as control features, to allow the operator to vary the chemical
dosages to these points. The chemical feed equipment must have enough capacity to
provide for an adequate range of chemical addition. There must be enough feeders
TABLE 24-4. Typical Chemical Treatment Labor Requirements
Operation and
Maintenance*
Labor, hr / yr
Capacity
Chemical
lb/hr
(kg/h)
Alum
10
50
100
500
4.54
22.7
45.4
227
150
210
300
800
Lime (slaked)
100
500
1,000
45.4
227
454
1,800
1,850
2,100
Lime (unshaked)
100
500
1,000
45.4
227
454
2,400
2,400
2,900
Polymer (dry)
0.5
1.0
5.0
10.0
0.23
0.45
2.27
4.54
500
580
750
850
Polymer (liquid)
0.5
1.0
5.0
10.0
0.23
0.45
2.27
4.54
390
400
420
440
* Labor for operation and maintenance of unloading, storing, and feeding facilities.
