384
I. Licsko et al.
250%
225%
200%
+ Prelloc
175%
DAI2(004)3
'"
~
0
150%
=
• •
-;
1250/0
=
:5!
100°/.
'"
..
~
·0
~
1 •
•
•
10
75°/.
50-V.
2S'V"
00/0
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.
Metal dose [mmol Me 3 + II)
Fig. 7. Residual BODs concentrations at BI WWTP
Fig. 7, where the organic matter is expressed in BODs, demonstrates that the
chemical pretreatment has not provided significant dissolved organics removal.
The remaining BODs decreased to the concentration of dissolved organics in raw
sewage only in the case of aluminum compound feeding. Increasing the aluminum
dose above 0.25 mmolr 1 did not cause any positive effect concerning removal of
the organics. Although there is no significant difference in organics removal
expressed in CODer. there is a difference if we use BODs in the same samples. On
the other hand, chemical pretreatment is able to remove dissolved organics as
CODer. but not as BODs.
Phosphorus removal was efficient during the lab experiments (see Fig. 8).
Considering the special situation of B 1 WWTP, the required effluent
concentration is 1.0 mgr 1 as TP. The results demonstrated that meeting the limit
value in the effluent of chemical pretreatment had not required more coagulants
than the comparable reduction of organic content.