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Raw water
Biologically treated water
Ozonated water
Ozonated-biologically treated water
(a)
0
0.01
0.02
0.03
0.04
2
3
4
5
6
7
8
9
10
pH
Norit 1240
Row supra
HD 4000
CAgran
(b)
0.3
0.2
0.1
0
2
3
4
5
6
7
8
9
10
0.1
0.2
0.3
0.4
pH
Figure 8.9 Surface charges on (a) NOM in raw and treated waters, (b) various GAC grades
(redrawn after Ref. [61]).
Norit 1240 was 51%, 38%, 24%, and 4%, respectively. Compared to raw water, in
ozonated waters, desorption slightly increased for all carbon grades. In the case of
'biologically treated water' and 'ozonated-biologically treated' waters, mainly con-
taining nonbiodegradable organics, desorption from GAC was similar. In any
case, the chemically activated carbon CAgran had the lowest surface loading (q),
and thus it exhibited the highest desorption. Also, HD 4000 desorbed to some
extent, whereas Norit 1240 and Row Supra exhibited relatively irreversible
adsorption (Figure 8.10). In particular, in the case of 'biologically treated' and
'ozonated-biologically treated' waters it is important that desorption from activated
carbon should be low, since these waters contain mainly nonbiodegradable matter
that can only be removed by adsorption.
In general, adsorption results indicated that the surface chemistry of NOM and
GAC grades was more influential on adsorption than the pore structure of GAC.
Although the GAC grade Cagran has the highest total pore volume (especially high
meso- and macropore volumes), it had a poorer adsorption capacity than others.
Moreover, the type of GAC outweighed the importance of ozonation with respect
to both adsorption and desorption of DOC [61]. The significance of adsorbability,
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