Environmental Engineering Reference
In-Depth Information
2000
; Lønborg and Søndergaard
2009
; Lovley and Chapelle
1995
; Coble
2007
;
Hopkinson et al.
2002
; Koschorreck et al.
2008
; Lønborg et al.
2009a
,
b
). An
increase in fulvic acid-like (or humic-like) fluorescence either in deeper waters of
lakes and oceans or in dark incubated water samples are considered to be the effect
of microbial degradation of organic matter and of the related transformation of the
functional groups of DOM (Ma and Green
2004
; Mostofa et al.
2007a
;
b
; Moran
et al.
2000
; Hayase and Shinozuka
1995
; Coble
2007
; Coble
1996
). Microbial
degradation of DOM depends on several key factors that can be distinguished as:
(1) Occurrence and nature of microbes in waters; (2) Sources of DOM and the
quantity of its fermentation products; (3) Temperature; (4) pH; and (5) Sediment
depths.
4.1 Occurrence and Nature of Microorganisms
Microbial degradation of organic matter and of functional groups of macro-
molecules depends on the occurrence and nature of microorganisms in waters
(Lovley
2006
; Uchida et al.
1998
; Lovley et al.
1996
; Kotsyurbenko et al.
2001
; Coleman et al.
1993
; Conrad et al.
1989
; Conrad et al.
1989
; Morvan
et al.
1994
). Recent studies demonstrated the presence of methanogens belong-
ing to the
Methanomicrobiaceae
,
Methanobacteriaceae
,
Methanococcaceae
,
Methanosarcinaceae
, and
Methanosaetaceae
, as well as new archaeal lineages
within the
Euryarchaeota
(Kotsyurbenko et al.
2007
; Basiliko et al.
2003
; Cadillo-
Quiroz et al.
2006
; Casper et al.
2003
; Galand et al.
2002
; Horn et al.
2003
; Sizova
et al.
2003
; Upton et al.
2000
; Utsumi et al.
2003
). It is shown that methanogenic
archaea and homoacetogenic bacteria are the main H
2
consumers in the absence of
inorganic electron acceptors such as nitrate, ferric iron and sulfate, which compete
for available H
2
in anoxic environments (Kotsyurbenko et al.
2001
). Degradation
of alcohols and fatty acids is usually enabled by syntrophy between H
2
-producing
syntrophic bacteria and H
2
-consuming methanogenic archaea (Conrad
1999
;
Schink
1997
). The most important reactions for hydrogenotrophic (Eq.
4.1
) and
acetotrophic methanogenesis (Eq.
4.1
) for degradation of glucose can be expressed
below (Eqs.
4.1
,
4.2
) (Conrad
1999
; Thauer et al.
1977
):
(4.1)
C
6
H
12
O
6
→
CH
3
COOH
+
CO
2
+
CH
4
∆
G
o
′
=−
346. 8
(4.2)
C
6
H
12
O
6
→
3CO
2
+
3CH
4
∆
G
o
′
=−
418. 1
An experimental study shows that
D. desulfuricans
can reduce the Fe(III) and
sulphate simultaneously at rates comparable to Fe(III) and sulphate reduction
under non-limiting H
2
concentration, when only one of the electron acceptors
is provided (Coleman et al.
1993
). On the other hand, H
2
is metabolized by
D.
desulfuricans
at lower concentrations with Fe(III) than with sulphate (Coleman
et al.
1993
). Interestingly, these bacteria do not metabolize H
2
below ~10
−
5
atm
partial pressure (Cord-Ruwisch et al.
1988
).
