Civil Engineering Reference
In-Depth Information
18
16
14
12
10
8
6
4
2
0
0
0.1
0.2
0.3
0.4
0.5
0.6
Ratio of Nitrate as CaCO
3
Ratio of Total Anions as CaCO
3
Nitrate as CaCO
3
Total Anions as CaCO
3
Fig. 18-3.
Typical plot showing nitrate removal capacity as a function of the nitrate / total anion
ratio (From Culp, Gordon, and Williams, Robert,
Handbook of Public Water Systems.
Copyright
1986 by John Wiley & Sons, Inc. Reprinted by permission of John Wiley & Sons, Inc.)
A check of the service flow rate per cubic foot of resin shows that it is 173.6 gpm /
153 cu ft, or 1.13 gpm / cu ft. This is less than the maximum rate recommended by
the manufacturer and is therefore acceptable. At a 3-foot bed depth, the required con-
tactor area is:
153 cu ft
51 sq ft
3 ft bed depth
This is equivalent to a loading rate of 3.4 gpm / sq ft. Consideration should be given
to a deeper resin depth, which would give a higher loading. Loading rates up to 20
gpm / sq ft are reported to provide satisfactory nitrate removal.
Bed Expansion During Backwash.
Contactor design must include allowance for bed
expansion during backwash. As with cation-exchange resins, the percentage bed ex-
pansion is a function of water temperature and backwash flow rate. Figure 18-5 pres-
ents backwash expansion curves for Amberlite IRA-900 operating in the chloride form.
Resin Regeneration.
Resin regeneration can be either complete of partial. If resin is
completely regenerated, the salt requirement is high, but there is little leakage of nitrate
ions during operation. Conversely, if a low amount of salt is used, regeneration is
incomplete, and nitrate leakage occurs during normal operation. Run time between
