Environmental Engineering Reference
In-Depth Information
(O
2
•
−
), H
2
O
2
and HO
•
, respectively. Indeed, photogeneration of H
2
O
2
from ultra-
filtered river DOM is substantially increased with salinity, from 15 to 368 nM h
−
1
at circumneutral pH (Osburn et al.
2009
). Salinity or NaCl salts are responsible for
generating high production of aqueous electrons (e
aq
−
) photolytically in aqueous
media (Gopinathan et al.
1972
; Assel et al.
1998
) that may subsequently enhance
the H
2
O
2
production in waters (Mostofa and Sakugawa
2009
; Moore et al.
1993
;
Richard et al.
2007
; Fujiwara et al.
1993
).
Recent studies observe that the sea-salt particulate matter extracted from
coastal seawaters show substantially high HO
•
production (rate: ~2778-
27778 M s
−
1
), approximately 3-4 orders of magnitude greater than HO
•
photo-
formation rates in surface seawater (Anastasio and Newberg
2007
). Note that
comparison of river and salinity of sea waters shows that Na
+
, Ca
2
+
, Mg
2
+
,
K
+
, HCO
3
, Cl
−
and SO
4
2
−
are typically 1,670 times, 27 times, 330 times,
170 times, 2.4 times, 2,400 times and 245 times, respectively, higher than
those in rivers (Livingstone
1963
; Hem
1985
). The order of the other cations is
Mg
2
+
> Ca
2
+
> K
+
> Sr
2
+
and the anion Cl
−
is approximately equal to the sum
of the cations and the other anions are SO
4
2
−
, HCO
3
−
, Br
−
, and F
−
(Livingstone
1963
; Hem
1985
; Carpenter and Manella
1973
). Second, the reaction of HO
−
•
with
halide ions (X
-
) can form reactive halogen radicals (X
2
•
−
) that can react with
electron-rich functional groups within DOM more selectively than HO
•
(Zafiriou
et al.
1987
; Song et al.
1996
; Von Gunten and Oliveras
1997
; Goldstone et al.
2002
; Grebel et al.
2009
). The absorption of radiation by CDOM is usually
increased in ionic solutions of NaCl, which might suggest an increase of CDOM
absorption in coastal waters. However, such an effect is more than compensate for
by the efficient photodegradation of CDOM chromophores in saline waters.
5 All Colored DOM is Chromophoric DOM, But
Not All Chromophoric DOM is Colored
The main chromophores in colored or chromophoric DOM are Schiff-base deriva-
tives (-N
=
C-C
=
C-N-) and groups such as -COOH, -COOCH
3
, -OH, -OCH
3
,
-CH
=
CH-, -CH
=
O, -C
=
O, -NH
2
, -NH-, -CH
=
CH-COOH, -OCH
3
, -CH
2
-
(NH
2
)CH-COOH, and S-, O- or N-containing aromatic compounds or func-
tional groups (Mostofa et al.
2009
; Malcolm
1985
; Corin et al.
1996
; Senesi
1990
; Leenheer and Croue
2003
; Peña-Méndez et al.
2005
; Zhang et al.
2005
;
Steelink
2002
; Seitzinger et al.
2005
). The allochthonous fulvic and humic acids
(humic substances) of vascular plant origin and the autochthonous fulvic acids of
algal (or phytoplankton) origin show absorbance in a wide wavelength interval,
200-800 nm (Figs.
2
,
3
,
4
) (Zhang et al.
2009
; Ishiwatari
1973
; Lawrence
1980
;
Zepp and Schlotzhauer
1981
; Hayase and Tsubota
1985
; Dubach et al.
1964
),
and contain the above mentioned chromophores (or functional groups) in their
molecular structure. These macromolecular substances are both colored DOM
(they absorb in the visible) and chromophoric DOM. On the other hand, there are
