Treatment Plants for Phosphorus Removal from Wastewater
Dissolved phosphate
(gP/m3)
10
2\ 5
Alkalinity meq/1
A
8
1 1\ \
1\ \ \
\ 1\ 1\
6
0.5 1\ 1\ \
r'\.
\
1\.
r-...
~
4
0.25 t\.
"
'\ ~
r-... I' ""' " r-...
-2
;;;,;: ~""""
0
4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5
Dissolved phosphate
pH
(gP/m3)
2.0
8
Alkalinity meq/1
MF(AI/P)=2
1.5
51\
··- 1--1-1.0
2
\
v
1
\
'\
[/
v /
1\.
r-....
1--1--- 0.5
t:
,.....;
.... v
0.~5
r-... t' -.. 1' --~ I--'
1--1--..... ;..;: f': ..... ......
~ 1---: r;.....
0.5
0.0
4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5
pH
Fig 10.25 Post precipitation with Al(III). Dissolved phosphate as a function of pH and alkalinity.
Calcium activity = 40 g/m 3 .
344
A: Al!P molar ratio 1. B: Al/P molar ratio 2.
Notice the difference between the scale of the ordinate axis of curves A and B. /4/.
From Fig 10.23 we find that in order to obtain Sp = 1.05, the molar ratio must be 0. 71.2 mol Fe+++/mol P.
Here a molar ratio of 1.1 mol Fe+++/mol P, is chosen, that is,
mol Fe+++/mol P = 1.1
mol Fe+++ = 1.1 · mol P
= 1.1 . (13 g P/m 3 )/(31 g P/mol)
= 0.46 mol Fe+++/m 3
The dosing of ferric chloride must be 0.46 mol = 0.46 mol · 162.5 g/mol
= 75 g FeCI3 (100% pure)/m 3 .1f the technical substance contains for example 32%
FeCI3, the dosing is 75 g/m 3 /0.32 = 234 g/m 3 .