Environmental Engineering Reference
In-Depth Information
humic-like fluorophores) is 43 % in 20-40 cm and 88 % in 42-60 cm depth sam-
ples, compared to the average fluorescence intensity at 1-20 cm (Li W et al.,
unpublished data). Similarly, microbial processes can degrade the protein-like and
tryptophan-like components, which are labile to microbial degradation. Microbial
processing of these components can be monitored by a decrease in their fluorescence
intensity, experimentally under dark incubation and in field observations in deeper
layers of natural waters (Mostofa et al.
2005
,
2010
,
2011
; Baker and Inverarity
2004
).
(iv) Methanogenesis caused by microorganisms (methanogens and acetogens) is
an important anaerobic process that can produce CH
4
and CO
2
by converting
either acetate (and formate) or H
2
/CO
2
in anaerobic environments (Conrad
1999
; Zinder
1993
; Lovley et al.
1996
; Kotsyurbenko et al.
2001
).
(v) Microbial changes either in organic substances (e.g. glucose) or in the func-
tional groups of macromolecules such as fulvic and humic acids of vascular
plant origin, as well as autochthonous fulvic acids of algal or phytoplankton
origin, may occur with the release of a variety of byproducts such as CH
4
,
CO
2
, DIC (sum of dissolved CO
2
+
H
2
CO
3
+
HCO
3
−
+
CO
3
2
−
), PO
4
3
−
,
+
, H
2
O
2
and organic peroxides in waters (Conrad
1999
; Mostofa and
Sakugawa
2009
; Fu et al.
2010
; Ma and Green
2004
; Li et al.
2008
; Tranvik et
al.
2009
; Zhang et al.
2009
; Li W et al., unpublished data; Lovley et al.
1996
;
Palenik and Morel
1988
; Zhang et al.
2004
; Kim et al.
2006
).
(vi) The
Nitrospira
genus and
Nitrobacter
species are the key nitrite-oxidizing bacte-
ria (NOB) in nitrifying waste water treatment plants, which are likely to depend
mostly on nitrite concentration (Kim and Kim
2006
). In addition, extracellular pol-
ymeric substances (EPSs), biologically produced by most bacteria, are composed
of a mixture of polysaccharides, mucopolysacharides and proteins (Arundhati Pal
2008
). EPSs produced by anaerobic sludge under sulfate-reducing conditions are
capable of biosorption of heavy metals and can remove them from the waste water
treatment plant (Chen et al.
1995
; Zhang et al.
2010
).
(vii) A new metabolic class of microorganisms demonstrates that a wide diversity of
organic compounds can be effectively converted to electricity in self- sustain-
ing microbial fuel cells with long-term stability (Lovley
2006
; Chaudhuri and
Lovley
2003
; Logan and Regan
2006
; Cheng and Logan
2007
; Li and Fang
2007
;
Rozendal et al.
2007
; Call and Logan
2008
; Lee et al.
2008
; Lee and Rittmann
2009
,
2010
; Premier et al.
2012
). These organisms, known as electricigens, can
completely oxidize organic compounds to carbon dioxide, with direct quantitative
electron transfer to electrodes that serve as the sole electron acceptor (Lovley
2006
).
NH
4
2 Theoretical Model for DOM Degradation
in Natural Waters
Solar radiation causes the sequential degradation of functional groups in DOM,
which can be optically detected either as chromophoric dissolved organic matter
(CDOM, Fig.
1
a-c) or as fluorescent dissolved organic matter (FDOM, Fig.
1
d-f).
