Environmental Engineering Reference
In-Depth Information
NO
2
-N
Partial Nitrification
(Oxygen Limited condition
Diffusion in
anoxic
/anaerobic zone
NH
4
-N
Anammox
NH
4
-N+NO
2
-N
N
2
+ NO
3
-N
Organic
Carbon
Denitrification
in anoxic Zone
Escaping further
denitrification
N
2
NO
2
-N
Denitrification
Fig. 1
Conceptual diagram of simultaneous nitrogen removal via Anammox process and denitrification in sub-surface
flow wetland (Saeed and Sun
2012
)
members of Basidiomycotina, Ascomycotina and
Deuteromycotina are important phosphate-
solubilising microbes.
Penicillium
sp.,
Aspergillus
niger
,
A. flavus,
,
A. fruticans
,
Fusarium
sp.,
Rhizopus nigricans
and
Alternaria
sp. are impor-
tant fungi used in bioremediation processes.
tion and denitrification metabolism (Jianlong and
Ning
2004
).
3.3
Removal of Organic Content
Organic matter is decomposed in constructed
wetlands by both aerobic and anaerobic micro-
bial processes as well as by sedimentation and
filtration of particulate organic matter. Organic
matter is broken down by microorganisms colo-
nising the wetland by fermentation and aerobic
or anaerobic respiration and mineralised as a
source of energy or assimilated into biomass.
Other removal mechanisms include sedimenta-
tion, sorption and volatilisation. Aerobic degra-
dation of soluble organic matter is governed by
the aerobic heterotrophic bacteria according to
the following reaction:
3.2
Removal of Nitrogen
Besides conventional nitrogen removal, newly
discovered nitrogen removal routes are solely
dependent on microbiological metabolism such
as partial nitrification, denitrification, Anammox
(anaerobic ammonium oxidation: anaerobic
oxidation of ammonium directly to nitrogen gas
by nitrite in the presence of planctomycete
bacteria group) and Canon processes (com-
pletely autotrophic nitrite removal over nitrate).
Nitrogen removal through partial nitrification
and denitrification process includes conversion
of NH
4
-N to NO
2
-N, followed by denitrification
of NO
2
-N to N
2
gas (Fig.
1
) (Saeed and Sun
2012
).
CHOO CO HO e nergy
+→ + + −+
In most types of wastewaters with the excep-
tion of some industrial wastewaters and run-off
waters, the supply of dissolved organic matter is
sufficient, and aerobic degradation is limited by
dissolved oxygen concentration (Vymazal
2001
).
Organic matter is composed of a complex mixture
of biopolymers (Megonigal et al.
2004
). Some of
these compounds, such as proteins, carbohydrates
and lipids, are easily degraded by microorgan-
isms (i.e. labile), while other compounds, such as
6
6
6
12
6 26 2
2
2
NH O OHOH
NO
415
+
+ →++
+
.
/
−
2
+
2
2
2
−
12
CH OH H
+ →+
+
12 12 15
/
N
/
CO
+
.
H
O
2
3
2
2
2
The advantages of partial nitrification and
denitrification include approximately 25 % lower
oxygen and 40 % lower organic concentration
requirements, compared with traditional nitrifica-
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