Figs. 12.2, 12.3, 12.4 and 12.5 show concentrations of P, COD, BOD, and SS
from various samples during the given test running period as well as the relevant
percentage removals. For the above-stated low dose (0.16 mg Fe
(VI)
/L), ferrate
(VI) achieved, in average removals, 64% of SS, 44% of phosphate, 46% of COD,
and 40% of BOD when the pH was above 9. The comparative performance of ferrate
(VI) and ferric sulfate shows that the ferrate(VI) dose of 0.16 mg Fe
(VI) /L can
achieve similar results to those of ferric sulfate at a relatively high dose (25 mg
Fe
(III) /L). Much smaller dose demand of ferrate(VI) can significantly reduce the
chemical requirement and sludge production, so it could result in cutting the
operating cost in the treatment of sewage.
Table 12.4 Comparative performance
a of crude sewage treatment with ferric sulfate and ferrate
(VI)
Chemical and dose
Average percentage removal for the given doses of given chemical
(%)
SS
P
COD
BOD
Ferrate(VI) (0.03 mg Fe/L) 79
56
50
30
Ferric sulfate (37 mg Fe/L) 78
59
54
43
aCrude sewage properties: [SS] ¼ 730 mg/L; [P] ¼ 18.5 mg/L; [COD] ¼ 1125 mg/L;
[BOD] ¼ 388 mg/L
Average R% = 44.1
0.00
5.00
10.00
15.00
20.00
25.00
30.00
35.00
40.00
1
2
3
4
5
6
7
8
9
10 11 12 13
Day
[T-P] (mg/L)
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
% Removal
Crude
PST Effluent
% removal
Fig. 12.2 Total phosphorus concentration in crude sewage and the effluent after pre-sedimentation
tank (PST) and percentage removals of P. (Reproduced from Jiang et al. 2018)
294
J.-Q. Jiang