Environmental Engineering Reference
In-Depth Information
2.2 Biogeochemical Functions of HO
•
in Natural Waters
•
The HO
is responsible for the occurrence of many important biogeochemi-
cal functions in natural waters: (i) photoinduced decomposition of DOM, which
causes the production of a number of low molecular weight (LMW) photoprod-
ucts. The latter are microbiologically labile and constitute a significant source of
carbon and energy to the microbial food chains, as well as an important pathway
for DOM turnover in natural waters (Zhou and Mopper
1990
; Blough and Zepp
1995
; Tranvik
1992
; Moran and Zepp
1997
; Bertilsson and Tranvik
1998
; Mopper
and Kieber
2000
; Mostofa et al.
2009a
,
b
). However, despite the major role played
by HO
•
in the mineralization processes of organic pollutants in the framework of
the AOPs, the HO
•
is expected to contribute to a minor extent to the photomin-
eralization of natural DOM in surface waters (Vione et al.
2009
); (ii) photoin-
duced production of low-molecular weight chemical species such as H
2
O
2
and
CO
2
(both dissolved and gaseous forms). These processes play some role in the
occurrence of photosynthesis, which produces algal biomass that is involved into
the generation of autochthonous DOM in natural waters (Mostofa et al.
2009a
,
b
;
Komissarov
2003
; Fu et al.
2010
). However, the importance of such reactions is
limited by the relatively low generation rate of HO
•
in surface waters (Brezonik
and Fulkerson-Brekken
1998
); (iii) photo-bleaching of DOM induced by solar
radiation in waters (Moran et al.
2000
; del Vecchio and Blough
2002
; Mostofa
et al.
2005
,
2007
); (iv) photodegradation of persistent organic pollutants, which are
usually recalcitrant to biological, chemical, and direct photodegradation in water
(Brezonik and Fulkerson-Brekken
1998
; Haag and Yao
1992
; Grannas et al.
2006
;
Vione et al.
2009
); (v) cycling of transition metal ions that can be oxidized by HO
•
(Jeong and Yoon
2004
; Faust and Zepp
1993
; Kwan and Voelker
2002
); (vi) use
of HO
•
in water treatment processes such as the Advanced Oxidation Technology
(AOT), to purify sewerage or industrial wastewater effluents, with the purpose of
controlling the organic pollution for sustainable development (Safazadeh-Amiri
et al.
1996
,
1997
; Kang et al.
2000
); (vii) damage to macromolecules such as
DNA, proteins and lipids, membrane leakage, breakdown of the cellular metabo-
lism, and finally of tissues in biological systems. These processes can be induced
by the HO
•
•
•
) radicals, which may be produced
by the autooxidation of biomolecules such as ascorbate, catecholamines or thiols
in organisms (Paradies et al.
2000
; Blokhina et al.
2003
; Berlett and Stadtman
1997
; von Sonntag
2006
).
, alkoxyl (RO
) and peroxyl (ROO
2.3 Steady-State Concentration and Life-Time of HO
•
in Natural Waters
•
The steady state concentration of HO
can be determined on the basis of its major
sources, which control the total photoinduced formation rate constants, and on sinks
or scavengers of HO
•
that control the total consumption rate constants in natural
