Environmental Engineering Reference
In-Depth Information
equal during the incubation of reduced sediments (Fig.
8
c,d) (Roden and Wetzel
1996
). Therefore, the occurrence and the nature of organic matter and its fermen-
tation or disintegration products are key factors for the production of CO
2
, CH
4
and other end products in the aquatic environments.
4.3 Temperature
The growth of homoacetogenic bacteria and methanogenic archaea signifi-
cantly depends on the ambient temperature (Table
2
) (Kotsyurbenko et al.
2001
;
Kotsyurbenko et al.
2007
; Thebrath et al.
1993
; Westermann
1994
; Kotsyurbenko
et al.
1995
; Simankova et al.
2000
; Zinder
1990
). It is shown that the micro-
bial function is typically much higher at low temperature (5.0-7.0 °C), showing
maximum bacterial abundance (3.9-7.9
×
10
5
cells ml
−
1
, mean
=
6.4) and bio-
mass (4.0-6.7
μ
g C L
−
1
, mean
=
5.2). Lower values (1.3-2.5
×
10
5
cells ml
−
1
,
mean
=
1.8; and 1.3-2.4
μ
g C L
−
1
, mean
=
1.7, respectively) have been found
at higher temperature (7.5-11.1 °C) in open water in Lake La Caldera (Carrillo
et al.
2002
). Homoacetogenic bacteria and methanogenic archaea can consume H
2
over a temperature range of 1-35 °C, but their optimum temperature is often high
(~20-30 °C, Table
2
). Homoacetogenic
A. bakii, A. tundrae
and the methanogenic
strain MSB have shown the largest temperature range for optimal H
2
consumption,
which is extending at least from 4 to 30 °C (Kotsyurbenko et al.
2001
). However,
A. fimetarium,
,
A. paludosum
and strain MSP become less efficient toward H
2
consumption when the temperature decreases below 10 °C (Kotsyurbenko et al.
2001
). Low temperatures are often favorable for acetogenesis, which becomes a
quantitatively important process in anaerobic environments (Nozhevnikova et al.
1994
; Kotsyurbenko et al.
1993
).
At low temperature, homoacetogenic bacteria outcompetes methanogens for
H
2
in laboratory experiments (Conrad et al.
1989
; Kotsyurbenko et al.
1993
).
According to kinetic estimations, homoacetogens have a much higher growth
rate at low temperature than methanogens (Kotsyurbenko et al.
1996
). It is also
shown that the contribution of methanogenic bacterial associations (MBA) to
H
2
-dependent methanogenesis is enhanced (it reaches 99 %) when the tempera-
ture is shifted from 30 to 17 °C, or when the soil is planted with rice (Conrad
et al.
1989a
,
b
). This enhancement is partially due to an increased utilization of
dissolved H
2
by chloroform-insensitive non-methanogenic bacteria, most prob-
ably homoacetogens, so that CH
4
production is almost completely restricted to
H
2
-syntrophic MBA. Acetate is the precursor of approximately two-thirds of the
methane produced in mesophilic (30-40 °C) and thermophilic (45-65 °C) anaer-
obic bioreactors (Zinder
1990
). Increasing the incubation temperature of two
swamp slurries from 2 to 37 °C resulted in a 8- to 18-fold increase in the H
2
par-
tial pressure (Westermann
1994
). The study also shows that the concentration of
volatile fatty acids remained fairly constant except for butyrate, which decreased
with increasing temperature.
