Environmental Engineering Reference
In-Depth Information
Phosphate regeneration cycles
140
#5041 media
120
100
80
60
40
20
0
1
2
3
4
5
6
No. of cycles
FIGURE 31.13
Capacity after regeneration.
saturation, phosphorus is chemically removed and media regenerated for reuse. Figure 31.13
shows that it is feasible to retain >90% of the original media capacity after six regenera-
tions and >10 uses of media is expected to commonly occur; however, more veriication is
needed through ield testing. Competing ions can reduce capacity and mechanical degrada-
tion of this very porous material with repeated uses; therefore, the lifetime is still unknown.
Regeneration can be done on site or in modules removed and regenerated off site.
Economically, on-site regeneration makes the most sense when higher concentrations of
phosphorus and/or larger volumes of water are treated. It is anticipated that regeneration
will be done in the same module used for phosphorus capture.
The data shown in Figure 31.13 was prepared by circulating water with high concentra-
tions of phosphorus through a bed of media for saturation, followed by removal using a
mild base. Media is regenerated with a mild acid. Phosphorus saturation and extraction is
considered to be one cycle. The increases in capacity shown are believed to be due to the
activation of some of the iron powder used in the porous media composition, adding some
additional capacity. The base iron media itself has a capacity of 15-20 mg/g.
The cost for regeneration can be 20% or less of the initial cost, which signiicantly
reduces life-cycle costs of media. With regeneration and reuse at phosphorus concentrations
>10 mg/L, it is feasible for 1 kg of media to remove in its lifetime >1 kg of phosphorus,
considerably higher than other sorptive media.
In practice, the operating conditions in the ield will determine the number of regen-
eration cycles for the media. In a two-stage operating system, the point at which the irst
module is regenerated will occur when the efluent reaches its desired limit. The media
will not be fully saturated.
31.5 Phosphorus Recovery
Phosphorous is a valuable resource, and its recovery as a usable product is a goal that can
be accomplished with use of Meta-PO4 media. Since phosphorus can be removed in a
