Environmental Engineering Reference
In-Depth Information
otherwise recalcitrant to biological and chemical degradation in natural waters
(Zepp et al.
1987
; Miller and Chin
2002
; Haag and Yao
1992
; Vione et al.
2009
; Grannas et al.
2006
; Pullin et al.
2004
; Draper and Crosby
1984
; Ollis
et al.
1991
; Sun and Pignatello
1993
; Zimbron and Reardon
2005
).
(ii) Degradation of organic pollutants or DOM in natural waters (Brezonik and
Fulkerson-Brekken
1998
; Southworth and Voelker
2003
; White et al.
2003
;
Westerhoff et al.
1999
; Goldstone et al.
2002
; Kang et al.
2000
; Gao and
Zepp
1998
; Arslan et al.
1999
; Katsumata et al.
2006
; Muñoz et al.
2006
;
Farias et al.
2010
). Suwannee River Fulvic Acid (SRFA) can produce H
2
O
2
,
which can give HO
•
by direct photolysis or through the Fenton reactions
(Fig.
9
) (Southworth and Voelker
2003
). The Fenton process can also be
exploited from a technological point of view. Recently, a new pilot-plant
solar reactor for the photo-Fenton treatment of waters containing toxic
organic substances has been developed. In this reactor, the combined pho-
toinduced and thermal effects of sunlight can degrade 98.2 % of the initial
pollutant, for a reaction time of 180 min and a relatively low iron concentra-
tion (Farias et al.
2010
).
(iii) A great interest is presently devoted to the utilization of HO
•
in the Advanced
Oxidation Technology (AOT) for treatment of sewerage or industrial effluents,
as a help to achieve sustainable development (Safazadeh-Amiri et al.
1996
,
1997
; Arslan et al.
2000
; Venkatadri and Peters
1993
).
(iv) The cycling of metals occurs through various redox chemical reactions in
natural waters, to which HO
•
gives a contribution (Faust
1994
; Voelker et al.
1997
; Jeong and Yoon
2005
; Faust and Zepp
1993
; Kwan and Voelker
2002
;
Emmenegger et al.
2001
).
(v) Photoinduced generation of HO
•
upon nitrite and nitrate photolysis in natural
waters can cause hydroxylation, nitration and nitrosation reactions of many
aromatic compounds or organic contaminants (Matykiewiczová et al.
2007
;
Torrents et al.
1997
; Vione et al.
2003a
,
b
,
2004
). Some of the reaction inter-
mediates are mutagenic or carcinogenic and are, therefore, of immense envi-
ronmental concern in the water bodies.
(vi) The HO
•
radical is for instance involved in the ultrasonically induced oxida-
tion of arsenite, which plays a key role in the conversion of As(III) in aqueous
media and may be applicable as a pretreatment step for the removal of arsenic
from water (Xu et al.
2005
).
6 Impact of Free Radicals on Biota (Proteins and Living
Cells) and Plants
Free radicals are an unavoidable by-product in biological systems and can
arise from foods containing unnecessary fat, smoking, alcohol, H
2
O
2
, ozone,
toxins including the carcinogenic ones, ionization, environmental pollutants
