Environmental Engineering Reference
In-Depth Information
Fig. 10
Relationship
between DOC concentration
and production rates
of H
2
O
2
generated
from photoexperiments
conducted on upstream
river, groundwater, lake and
seawaters (
a
); as well as on
the waters of the downstream
river (
b
)
5000
(a)
y = 3.4x - 147 (Groundwater)
R
2
= 0.898 (linear)
4000
y = 2.32x - 169 (lake)
R
2
= 0.666 (Linear)
3000
2000
Upstream River
Groundwater
Lake
Seawaters
1000
0
8000
(b)
Downstream River
Linear (Downstream River)
Poly. (Downstream River)
6000
4000
2000
R
2
= 0.948 (non-linear)
0
0
500
1000
1500
2000
DOC (µMC)
stagnant lake or seawaters or during the transportation of water from the source
to the lake or ocean (Moran et al.
2000
; Mostofa et al.
2005a
,
2007a
,
b
; Wu et al.
2005
). Indeed, previous photoprocessing is a likely reason for the photostability of
DOM sampled in surface lake environments (Vione et al.
2009
). H
2
O
2
production
is less efficient in the presence of DOM from lake or seawater, which suggests that
the generation of hydrogen peroxide depends also on the nature and not only on the
total amount of DOM in natural waters. Therefore, H
2
O
2
production follows the
order: upstreams > groundwater > rivers > lake > coastal sea > open ocean.
Fluorescent DOM (FDOM) or chromophoric DOM (CDOM) plays an active
role in the generation of H
2
O
2
and ROOH in natural waters (Table
1
) (Mostofa and
Sakugawa
2009
; Obernosterer et al.
2001
; Fujiwara et al.
1993
; Moore et al.
1993
;
O'Sullivan et al.
2005
). It can be noted that CDOM or FDOM moieties undergo
rather efficient photoionization under sunlight (Wu et al.
2005
; Senesi
1990
). For
example, a significant correlation has been observed between fluorescence inten-
sity (FI) of fulvic acid and the photoproduction of hydrated electrons (Fujiwara
et al.
1993
). Similarly, the production rates of H
2
O
2
are highly correlated with
the fluorescence of fulvic acid present in river (Mostofa
2005
) and lake waters,
rather than with DOC concentrations (Scully et al.
1996
). Moreover, the produc-
tion of H
2
O
2
by a variety of river waters is highly different due to a variation in
their DOM components such as fulvic acid, fluorescent whitening agents and
