of research on N2O emission control in waste water treatment field. Keywords : Nitrous oxide emission, nitrous oxide producing microorganism, waste water treat.
151
[Japanese Journal of Water Treatment Biology Vol.31 No.3. 151-160
Nitrous
Oxide
Emission
XIAO-LEI
From
WU1, HAI-NAN
YUHEI
1995]
KONG2,
INAMORI2,
Microorganisms
MOTOYUKI
HUANG
XIA1, and
MIZUOCHI2,
QIAN YI1
1 Environmental Engineering Department, Tsinghua University / Haidan District Beijing 100084, China 2International Water Environment Renovation Research Team , Regional Environment Division, National Institute for Environmental Studies/16-2 Onogawa, Tsukuba, Ibaraki 305, Japan
Abstract N2O has activity
been
caused
in biosphere
modify the activity microorganisms, -tigation,
factors
affecting
treatment
on N2O emission
: Nitrous
oxide
control
in waste
emission,
Then,
current
was described
nitrous
water
oxide
to control In the
under
in the paper
producing
paper,
based were
and
accompanying
with
of research
on inves
There
conditions.
for making
from
emphasized
different
situation
Microbial clear
N2O emission
and denitrifiers.
and analyzed
treatment
effect. to make
microorganisms
nitrifiers
organisms
detailed
N2O emission.
from wastewater
of research
were
reducing
traditional
for different
Therefore,
importance situations.
and nitrate
N2O, besides
of its green-house
N2O source.
treatment
respiring
of N2O yielding
tion of various
Keywords
in Wasetwater
nitrate
because
is of fundamental
of N2O emission
sible mechanisms
attention
as an important
able to produce
pathways
N2O emission
more
of microorganisms
especially,
being
and
is regarded
heterotrophic,
as those ferent
more
are difThe
the
pos-
descrip-
on control clear
of
the trend
field.
microorganism,
waste
water
treat
- ment
volved in all activities of biosphere,
INTRODUCTION Nitrous more
oxide
attention
increase
of
phere
its
could
layer1)、2) sphere,
the its
be
farmer,
control
our
of ozone in
ruminant3),
N2O
strato-
due
to or
sources aquatic
of
system
nitrous like
on.
In
treat-
fact, is
the live-
wastewater so
the both.
exhaust,
emission
an
atmos-
N2O3)、4),
automobile
plants3)、7)、8), and
cessfully
in
destruction
various
and that
reactions
of
industry4),
stock
more
increase
effect
soil 1)、5),natural
ocean6),
ment
in
temperature
may
caused
of recognition
concentration
result
or
oxide:
been
through
' greenhouse' There
has because
to
almost
sucin-
and is a
big ecological problem, scientifically and socially. We can use soil as an example, to reduce N2O emission from soil, soil conditions like its structure, moisture, permeability, acidity or alkality and soil aeration are of major importance; secondly we should know exactly the situation of vegetation, including its composition, farming cultivation, fertilizing, etc.,which sometimes are determined by climate, economic status interests of local people, the country's tilizer industry,
and fer-
etc.. In short, control of N2O
emission from soil may involve in agricultural science and technology, soil science,
152
Japanese
meteorology,
official
chemical Since
industry,
will
it is such focus
review
microorganisms
Studies
microorganisms).
on
N2O
emission
on
were
can
be
in
which
often
used.
microbes
ecosystem, the
pure While
treatment
marine
of
have
soil5)、9)-15) and
3)、17)in wastewater
tewater
N2O
by
microorganisms,
soil and
N2O
(hereafter
concentrated
microbes
system,
on
same
the
etc.. here
means
N2O
been
be
1
based
situations,
in wastewater
the
Biol. Vol.31
on the review
the current treatment
and
ing factors
of soil and
research
processes
mechanisms
will be introduced
and
No.3
work will be
influenc-
for trying
to
provide some ideas to control N2O emission from wastewater treatment processes.
mainly
marine6)、16) cultures
found
of
N2O PRODUCING
MICROORGANISMS
later
More and more
most in was-
conclusions
Classification
of
studies
show
many
kinds
of microorganisms
other
than
conventional
trifying
suitability.
Table
marine evaluated
from
field . Since
can
we
emission
it began
research
In the paper,
policy,
consciousness,
a complicated
our
produced
agricultural
public
J. Wat. Treat.
N2O producing
bacteria,
including
microorganisms
that
there
producing
nitrifying
and
heterotrophic
are N2O denini-
Nitrous
triflers,
non-denitrifying
fungi,
etc..
They
bacteria,
can
be
Oxide
Emission
yeasts
divided
and
into
ases,
5
can
gaseous
reduce
reduction
nitrifiers,
paid
is that
can
reduce
behaviors
and nitrite-oxidizers emission. -oxidizing
toward
N2O
Goreau et al.18) found that ammonia bacteria like Nitrosomonas , Nit-
rosolobus,
Nitrosospira
and Nitrosococcus
products ly
can
tities
sp. do not produce
of N2O during
trite-oxidizing subgroup
detectable
growth.
bacteria
in Table
are
not
as
a
1.
be
mentioned
below.
may
be
ment7)、25), anoxic
Some tion
investigations
might
both
be
soil
ing
to
an
and
can
produce
For
autotrophic
be
and
a
the
phaera
which
special
complish
both
and
can
they
Ni-
of
N2O
NO2-
as kinds
of are
N2O
at
to Anderson
am-
and
P.
near
status
faecalis
but
to
is
yield
perfectomarina16)
most
of them
use
microorganisms
NO3-
Both
are
sp. and
are
included
and
condition.
Levine19)
and
in
Thios-
heterotrophic,
organisms, aerobic
and
deserved
Alcaligneces
pantotropha.
24) , they
environ-
anoxic
substrate.
attention
phaera
to
natural
at
like
as substrate,
denitrifiers
aerobic
them
mainminor
Pseudomonas
the
Alcaligneces
of
not
which in
nitrifying-denitrifying
under
was
referred and
generate
to
like
Alcaligneces
nitrification
which and
N2O
be as ni-
at
even
can
both
can
According
Robertson
et al.
denitrifiers.
Thios-
anions
with
roorganisms, and
accomplish
referred
NH4+ to
as
which
reduction as
nit-
product mic-
bacterium,
bacteria
and
can
consist
yeast
bacteria
N2O
mechanism
are
aerobic
and
when production
they
groups.
like
etc.15)、26)、27) generate
N2O
of nitrate-
nitrate-reducing
denitrification
tionsl9).
of
major
non-denitrifying
cover
Non-denitrifying respiring
faecalis,
condi-
the
fungus.
rate-respiring
ac-
microorganisms
which
be
denitrifier.
nitrifiers
organisms
Those rogen
Focht20) a
Non-denitrifying
20,
should
europaea
and
'
reference
situation
Poth
pantotropha
NO2-
or
produce
word'anaerobic',
heterotrophic
some
i.e. both
like
product
(in
the
denitrification.
use
Two
conditions.
reduction
the
Nitrosomonas
While
be
Some
extra
nitrifiers,
as
N2O
oxidation3),10)､15)、18),
used
called'anoxic'),
in
Accord-
bacteria
nitrite
nowadays
called
of
certain
can
in
Focht
N2O
nitrifiers,
condition19)、20)
however,
are
under
hydroxylamine
anaerobic'
trifier
sorts
nitrifying
resulted
Poth
two
sp., N20
and
nitrificaof
researchers5)、15)、
heterotrophic
N2O
trosomonas
or
other
are and
that source
system5)、6)、12).
and
16)、19)、27) ,there
monia
showed
important
aquatic
Anderson
autotrophic
N2O).
bacteria
but
of
conditions(however for
the
microorganisms
active
produce
be
which
nitrogen
are
among
most
beneficial
Ammonia-oxidizing
They
non-denitrifying
to
however,
amount
called
Denitrifiers,
ni-
listed
gaseous
small
the phos-
organisms
NO2-,
but
quan-
Therefore,
not
with
productl5)、19)、25)、27).
yield N2O at atmospheric oxygen levels, however nitrite-oxidizing bacteria, like Nitrobacter
and
couple
deserved
some
NO3-
to
transport
Attention are
oxides and
electron
there
are
NH4+,
nitrogen
N2O,etc.)
with
phorylation18)、25).
of ammonia-oxidizers
are different
the
products(N2,
groups as shown in Table 1. Each group has different N2O producing conditions. Among the
153
From Microorganisms
E.coli, by
Nit-
B.subtilis,
dissimilatory
at stationary
is in competition
with
phase NH4+
f ormmg. Among
nitrate-reducing
bacteria
Azotobac-
ter vinelandii, A. macrocytogenes, Acinetobac-
Denitrifiers Denitrifiers
here
which have
distinctive
are
referred dissimilatory
to as
those
reduct-
ter
sp.
Tiedje26)
and
Clostridiam only
KDHS2,
found Azotobacter
Bleakly
and
vinelandii
154
Japanese
yielded N2O with lower mechanism. Different which
from
produce
yeasts
Rhodotorula
can
No.3
bacteria
more
N2O under
like
Hansenulla
generate
Biol. Vol.31
by assimilatory
nitrate-respiring
much
conditions, aerobic
yield
J. Wat. Treat.
anoxic and
N2O only
under
microbes,
fungi
Fig. 1
Possible N2O producing ways (NH4+as the utmost N2O source).
Fig. 2
Possible N2O producing ways (NO2- as the utmost source).
conditions26).
Among have
all non-denitrifying
the
weakest
However,
N2O generating
when
Fusarium
Bollag
and
oxysporum,
amount
Tung
they
of N2O formed
ability26). 11) tested
found
when
higher
nitrite
was the
sole substrate. Above
all, many
besides fiers
kinds
conventional yield
N2O
knowledge
nitrifiers
at
is of treatment
known
in wastewater
ventional enough tewater ling ment
as
con-
denitrifiers.
Cont-
denitrification
is not
thesize
and
decay
was-
ressed,
how
the
treatment
process.
emission
been include
well
N2O emission
for us to extend
was-
has
there
as
and and
The
to
As
system,
to control
N2O
denitri-
importance
organisms
nitrification
and
conditions.
process.
nitrifiers
rolling
useful
certain
great
tewater
non-denitrifying
of microorganisms
from
Knowing
our
from
view
this
is
in control-
wastewater
inhibited
treat-
plants.
MECHANISMS
most
OF
is very
exactly
important
sion. However, cated
and
The
to make
involves
biochemistry,
and
perhaps
ecology.
the
enzymes
concerned
they
are, how
zymes transport,
and
what
when
kinds
substrate
active the
in
microbial
where
locate,
N2O emis-
it is a interdis-
which
logy,
tive sites
N2O yield
it clear is very compli-
because
question
zymology,
and how
for controlling
difficult,
ciplinary
when
sites,
For
their
of active
how
enzymes
example,
and
transport
ac-
centers
to the the
en-
psycho-
en-
electrons
concerned
syn-
repressed of
activated, be
the
etc.
researched
have
into origins
source
To know
are
Each
29) as
situation often shown
In Figure
of
occurs in
Figure
1, N2O
question
can
according NH4+ NH4+ in
are
many N2O-produc-
types
of N2O:
derep-
deeply.
proposed
two
and enzymes
waysl6)、20)、22)、24)、25), which
sifted
N2O PRODUCING
to
People ing
POSSIBLE
and
deserves
or
activities
or as
be to
NO3-(or the
clas-
the
ut-
NO2-).
utmost N2O
nitrification3)、18)、20)、28)、 1
.
can be oxidized
from
NH2OH by Alcaligences sp.28) and Nitrosomonas sp.l8) (scheme 1). N2O can also be resulted in N02-reduction by Nitrosomonas europaea at aerobic30) or at anoxic conditions 20) , Thiosphaera pantotropha at aerobic condition24) and nitrifying sludge at aerobic and anoxic conditions14) (scheme 2). The situation of N2O from the utmost origin NO3 or NO2- mainly takes place in denitrifiers, nitrate-respiring and reducing mic-
Nitrous
robes.
The
pathways
trate-respiration shown in Figure Different trification
take
and 2.
the
way
have
deni-
Pseudomonas
scheme
by
are
different
perfec
Pseudomonas
of
represented
ni-
nitrate-reduction
pathways. and
Emission
of denitrification,
denitrifiers
-tomarina16)
Oxide
a; while
scheme
is
and
P seudomonas aeruginosa22);
scheme
c
by
Pseudomonas
scheme
d
by
denitrificans25);
Pseudomonas stutzeri22)、25).
Almost
all
reducing
nitrate-respiring
microbes
take
enzymes:
which
act
pathways,
reductases
differently conditions
robial status.
It can reduce
and
FACTORS
different
at
are
oxidases, en-
different
mic-
N2O emission
to in-
the enzyme
producing or to prevent transporting to contact
N2O.
there
or
under
vironmental
hibit or repress
nitrate-
way 2 to yield
In each step of different different
and
beneficial
for N2O
NO2 or NH2OH from with the enzymes.
AFFECTING
N2O
mentioned
influence
the
above,
above
factors
pathways
production. Factors affecting from the investigated papers trogen
compounds
and N2O; tors
organic
carbon;
like oxygen
inhibitors,
Of course
ties like microbe influence N2O
pressure,
species
and their
production.
tion is given
N02-, NO fac-
pH
microbial
value, proper-
status
Detailed
nitrate
Paracoccus
also
informa-
below.
Pseudomonas
perfectomarina25).
trification,
substrates
nitrate
pathways. Nitrate is an
are
products,
inter-
of nitrification,
deni-
respiration
and
all
reductases It can
above
in
result
in
reductase
in
Bleakley
and
Tiedje26) reported that in denitrification system which had not previously exposed to NO3, NO3- may promote derepression of the reductases and stimulate N2O reduction. There are relationship
different between
arguments about the concentration of N03
and N2O emission. Knowles25) reported that at high NO3- concentration, it might inhibit N2O reduction and thus caused a greater mole fraction of N2O in the product in denitrification system. Inamori et al.4) noted that in an intermittent aeration system less NO3- leads to less N2O emission. While Schulthess et al.7),31) and Poth and Focht20) suggested that there was not significant relation between NO3and N2O reducing
yield. For nitrate respiring and microbes, more nitrate may risk
production is most possibly through generating NO2, a direct precursor of N2O. Almost can
all researchers
lead
to
possible
NO2-has
high
tive
biological
teriostat
reduction
of denitrification
en-
affinity
more s. So
a
control to
and
NO
much
be
is
lower
a
pathwayl9)、34). than
that
product
how
to extra
NO2
incomplete respiration avoid
in-
attention.
intermediate Its
im-
Since in
nitrate
deserves
possible
bac-
is very
emission.
reduction,
reactions
lead is a
more
resulted
denitrification,
nitrate
complete
produce
N2O
ac-
molecule16)、19);(3)
NO2-concentration
may
in the
which
toxic
may
ions
(2) NO2-may
of NO,
more
reduce
NO2-
include:(1)
metal
reductase 34);
substrates to
may
to
formation
or
thatmore
emission7)、8)、19)、25)、31)-
reasons
site of N2O
to
approve
more N2O
33).The
trification
inducer
of
in
Pseudomonas
oxide
stutzeri19)、20)、25).
nitrification,
compounds or
nitrous
induction
reductases
and
and
portant
compounds
Nitrogen mediates
nitrite
denitrificans23)
- accumulation
Nitrogen
and
aeruginosa25),
N2O
N2O generating may include ni-
environmental
partial
etc..
which
influence
like NH4+, N03,
like
155
yielding more N2O. No matter what kind of organism it is, the action of NO3- affecting N2O
GENERATING As
zymes
the
b
denitrificans
Microorganisms
Pseudomonas
aurefaciens25)
Paracoccus
From
of
deni-
production
of N2O7)、19)、21).
is It
has
156
Japanese
higher
affinity
to metal
of reductases than
NO2-7).
There
are
two
effect
noted
contradictory
of N2O.
that N2O
and
might
thess
inhibit
of net N2O
et al.7)、31)suggested could
will
Zumft23)
NO2- reductase which
might
production.
Schul-
that
reduce N2O
means N2O
and
reductase,
decrease
o ut
stripping N2O
accumulation,
stimulate
may produce
more hydroxylamine
which may turn20).
cause
high N2O
and NO2-
production
only at stationary phase, thus organic carbon may influence N2O emission through influencing microbial living status. Bleakly and
in
medium inversely affected the amount of N2O produced. Smith and Zimmerman15) also noted that glucose added to TSB suppressed N2O production. On the other hand, improper COD/NO3value may lead to incomplete denitrification and
increase N2O
on
Oxygen Oxygen
is a
key
factor
affecting N2O
can
anoxic
emission4)、35).
govern
pH
value
culture
through
Organic
in the forming
emission from nitrifiers increases with decreasing availability of oxygen18)-20).However, Zheng et al. 8) argued that there was a criti-
pH value is one of the basic al factors for microbes. Optimal
cal low DO level (0.2 mg/l) corresponding
the
denitrifiers
may
nitrogen
4.0, N2O may
21)、32)、33) . Many change
of
investigations
that
aerobiosis
production.
It
is
oxygen
can
and
those
and
that
oxide
when
reductases
oxygen
oxygen sion
23) found
totally
stopped.
for
electrons
of Besides
that
a competition
during
between
removed
be
well
from
oxide
and
trophic
especially
N2O
inhibited,
the
rate
decreases,
of N2O produce be the
nitrification
main may
nitrification
Low
pH value
which
was
also reported
but the
increases.
At pH
product25).
Auto-
be
replaced
at low
favors
by
pH value24)
N2O production
by Zheng
et al.8).
Inhibitors
nit-
expressed
was
100%,
0%;
the
those,
and
at
expres-
ammonia,
there oxygen which
Inhibitors which
Anderson
nitrification nitrite
as-
reductases,
progressively
denitrification
mole fraction
heterotrophic
Korner
nitrite
pressure
pressure
et al.19) proposed was
could
are
low pH value,
activities
bacteria.
nitrate,
partial
partial
nitrogen their
in
the
might
generally
repress
inhibit
7)、25)、32) , especially
rous
that
to
reductases
Zumft
showed
anaerobiosis
cause N2O sumed
extent7)、
overall
environmentpH range for
be 7.0-8.0. At
oxide
sure
some
of
pH
reductase
to
and
yield.
the peak N2O production in nitrifying sludge. On the contrary, N2O emission from denitrifiers is proportional to oxygen partial presconcentration
and
VFA
fect N2O
to
carb-
anaerobic
producing and almost all papers involved in it. Many microbes emit N2O at anoxic and near anoxic conditions as shown in Table 1. N2O
DO
carbon and
energy source for heterotroph to live. As mentioned above, many microbes generate N2O
Tiedje26) found that increasing concentration of glucose added to TSB (trypic soy broth)
which
its producing.
There are not many papers about how NH4+ affects N2O generating, however, more NH4+
or
No.3
was not beneficial for NO2- to reduce to N2O. Organic carbon Organic carbon is the essential
arguments
Korner
activate N2O
cause
sites
Biol. Vol.31
and may give rise to higher N2O
emission about
ions in the active
J. Wat. Treat.
robes hibitors tigated include azide7) functions
here
inhibit and
are
the
may
oxygen
denitrification
H2S21)、28), and
are
to
those of
situations. and
the
micIn-
mainly
derivatives25).
inhibit
as
production. were
acetylene
toluidine
to
metabolism
increase N2O
besides in
referred
normal
inves-
They
can
nitrapyrin2O), Their
reaction
main of
N2O
Nitrous
reducing tion.
to N2 and
Acetylene
trification
to cause N2O
and
factors expression
tases
oxidases
or
pecially those NO2 oxidase, nitrification,
also
ni
and
nitrate
to control N2O
emission.
RESEARCHES
ON N2O
estimation
tewater
can
of
shows certain
emission
even
nitrogen
N2O
is
now
suspected
very
small. to
3)、8)、17) .Research
a
on
treatment Laboratory-scale
made
under
perto
wastewater
is source
control N2O
wastewater
been
the
potential N2O
recently3)、4)、17).
to
converting
Therefore, be
emission began
only
experiments
three
different
types
conditions. Schulthess
et
of Swiss Federal
al.7)、31) and
Institute
Wild
et
al.32)、33)
for Environment
Science and Technology and Swiss Federal Institute of Technology can be considered as the representatives
accumulation of N2O would be reduced. Based on these results, they established a mathematical model and estimated that the net N2O
production
rification, they examined tween N2O production
was-
contribution
compound
fect on denitrification pathway and led to increasing N2O production only when the denitrifiers were at their active state; NO and
of those who focused their
attention on behaviors of denitrifying activated sludge. In their sequencing batch reac-
at
the relationship beand oxygen con-
centration and solid retention time (SRT). Their main results were that: N2O emerged at all tested DO levels from 0.1 mg/l to 6.8 mg/l; at DO concentration of 0.2 mg/l, peak N2O production 22 mgN/l of influent emerged; N2O produced at all SRT levels (from 3-20 days); the difference between the influences of DO and SRT located at that N2O production decreased as SRT increased. They found that high amount of N2O production was accompanied by incomplete nitrification with residual NH4+ -N or accumulated NO2- -N. They
suggested
production centration.
that
SRT influenced N2O
more significantly
Inamori
et
sentatives
of
than DO con-
al.3)、4)can
be
researchers
trification-denitrification
system.
to exclude the possible nitrifiers. They tested the influence of oxygen concentration and NO3-, NO2- pulsing on N2O emission and the
35) have
work
inhibitory trification
the
effects of NO and N2O on denipathway. Their main results were:
also
emission
done
relationship
of
production,
they
situation
NO3
of
tivities; NO3- had not marked influence on N2O
from
Considering microbes,
1) and
the
operating found of
some
et al
a
their
. On
produced
at
aeration,
low
COD/NO3from
questions
.8) It
the
and N2O
more N2O
of
niet al.
testing
parameters
results
at-
combined Hanaki
continuous and
the
experiments
Zheng
from
some
concentration
oxygen could repress the synthesis of denitrification enzymes and inhibit their acinhibitory of
N2O
repre-
paid
tention
to
the
who
tor with 8-liter volume, pH was adjusted at 7.0. The sludge age was controlled below 3 days
production. NO2 had significant
emerged
trifying sludge. NH4+ was used as the sole nitrogen source to exclude the influence of denit-
from
though
157
1.5 mg/l oxygen and 10 gN/l of nitrite. The main work of Hanaki et a1.30)and Zheng et al. 8) was testing production of N2O by ni-
EMISSION
that N2O
Microorganisms
maximum
is necessary
TREATMENT
make
global N2O centage
es
respiration
them
WASTEWATER
Rough
reduc
activities,
From
N2O had inhibitory effects on denitrification reductases, and when they were stripped out,
whici
oxide
their
denitrification,
FROM
emission,
of nitrous oxide reductase anc and which lead to incompletE
So to avoid
of
are
of nitrogen
and reduction.
have
accumula
nitrapyrin
favor N2O
influence
from
Emission
inhibitors20).
All those
Y
Oxide
value.
pure
may
high
be
culture arising
Schulthess
et al.7)、3
is
that
certain
ac-
158
Japanese
Fig.
3
Possible
nitrogen
flow
tivated sludge (or biofilm) contains heterotrophic nitrifiers, non-denitrifying microbes as well as conventional nitrifiers and denitrifiers, so it is doubted whether N2O emission from their sludge was caused only by nitrification or denitrification. Generally speaking, research on control of N2O emission in wastewater treatment field is just at its beginning, there is much work waiting to be done. QUESTIONS TO BE ANSWERED IN WASTEWATER TREATMENT FIELD As mentioned above, since many kinds of microorganisms emerge in both wastewater and
soil or marine
environment,
the
N2O
producing mechanisms and the influencing factors concluded from soil and marine microbes can be adapted to the situation of was-
in an actual
nitrogen
J . Wat. Treat.
removal
Biol. Vol .31
No. 3
system
tures of various kinds of microbes. Do we need to modify the results from pure culture to let them adaptable to wastewater treatment situations, or are there any special mechanisms in wastewater treatment processes? 2. In actual nitrogen removal systems containing A/O, or A/A/O or SBR process, anoxic (A stage) and aerobic/oxic (O stage) conditions or nitrification and denitrification, nitrate-respiration, nitrate-reduction may occur simultaneously or alternatively. The diagram of nitrogen change in the system may be like that shown in Figure 3. From Fig. 3, following questions may be put forth: 1) Since
in an actual
include
conventional
system, autotrophic
there
may
nitrifiers
tewater treatment. However, since some microbial properties depend upon the ecosys-
and denitrifiers as well as heterotrophic nitrifiers and non-denitrifying organisms, which of them produce dominant N2O,
tem,perhaps the results from pure culture should be modified before they are used in
how about the relationship between them or how about the roles of non-denitrifying
wastewater treatment system. Because of these, some questions are put forth here as following. To make them clear is of funda-
microorganisms. In other words, between A and O stages, which one makes more
mental importance to control N2O emission from wastewater treatment processes. 1. Activated
sludge
and
biomass
are
mix-
contribution to N2O emission; and under what kinds of conditions, it is the dominant N2O source. 2) Products
of O stage are substrates
of A
stage. So it is certain that A and O
stage
Nitrous
Oxide
Emission
may influence each other. For example, complete nitrification requires more dissolved oxygen, unfortunately, it may lead to more residual dissolved oxygen to A stage, which will increase N2O emission. How do these influences accomplish and how to optimize their relationship to minimize N2O emission? 3) Whether in O stage or in A stage, NO2 is an intermediate, is there any possibility to connect A and O stage by omitting NO3-? 3. Besides the above factors, there are some other things like temperature, HRT, etc. which may influence biological reaction and thus influence N2O emission. How about their effects? 4. What kind of process is better to effectively remove nitrogen and reduce N2O production. Is there any possibility to develop new processes like that containing immobilized specific microbes?
From Microorganisms
5)
6)
7)
8)
9)
10)
REFERENCES 1) Freney, J. R., Denmead, O. T. and Simpson, J. R.: Soil as a source or sink for atmospheric nitrous oxide, Nature (London), 273, 530-532 (1978). 2) Wang, W. C.: Greenhouse effects due to man-made perturbation of trace gases, Science, 194, 685-689 (1976). 3) Inamori, Y., Hasomi, M., and Sudo, R. Greenhouse effect gas control producing from astewater treatment process, Wat. Wast., 33(1), 28-34 (1991).(in Japanese) 4) Inamori, Y., Mizuochi, M., Terunuma,H., Yamamoto,M., Makuta, T., Utida, T., and Kimochi, Y.: Effects of anaerobic condition on biological nitrogen, phosphorus removal and inhibition of green house effect gas by intermittently aerated activated sludge process, Proceedings of the 28th Annual Symposium of Japan
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oxides production and cycling during dissimilatory reduction by Pseudomonas perfectomarina,J.Biol.Chem., 264, 56945699 (1989). Matsuo, T: Consideration on sewage works based on global warming, Journal of Japan Sewage Work, Association, 29, 18-22 (1992).(in Japanese) Goreau, T. J., Kaplan, W.A., Wosfy, S.C., Mcelroy, M. B., Valois, F. W. and Watso n, S. W.:Production of NO2- and N2O by nitrifying bacteria at reduced concentrations of oxygen,Appl. Environ. Microbio l., 40, 526-532 (1980). Anderson, I. C. and Levine, J.S.: Relative rates of nitric oxide and nitrous oxide production by nitrifiers, denitrifiers and nitrate respirers, Appl. Environ. Microbiol., 51, 938-945 (1986). Poth, M. andFocht, D.D. : 15N kinetic analysis of N2O production by Nitrosomonas Europaea: an examination of nitrifier denitrification, Appl. Environ. Microbiol., 49, 1134-1141(1985). Sorensen, J., Tiedje, J. M. and Firestone, R. B.: Inhibition by sulfide of nitric and nitrous oxide reduction by denitrifying Pseudomonas flourescens, Appl. Environ. Microbiol., 39, 105-108 (1980). Garber,E.A.E. and Hollocher, T.C.: 15N tracer study on the role of NO in denitrification, J. Bio. Chem., 256, 5459-5465 (1981). Korner, H. and Zumft, W. G.: Expression of denitrification enzymes in response to the dissolved oxygen level and respiratory substrate in continuous culture of pseudomonas stutzeri, Appl. Environ. Microbiol., 55, 1670-1676 (1989). Robertson,L.A., Niel, E.W.J.,Torremans, R. A.M. and Kuenen,J.G. Simultaneously nitrification and denitrification in aerobic chemostat cultures of Thiosphaera pantotropha, Appl. Environ. Microbiol., 54, 2812-2818 (1988). Knowles, R.: Denitrification, Micro. Rev.,
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46, 43-70 (1982). 26) Bleakley, B.H, and Tiedje,J. M.: Nitrous oxide production by organisms other than nitrifiers and denitrifier, Appl. Environ MicrobioL, 44, 1342-1348(1982). 27) Stewart, V.: Nitrate respiration in relation to facultative metabolism in Enterobacteria, Micro. Rev., 52, 190-232 (1988). 28) Castignetti,D. and Holocher, T. C.: Nitrogen redox metabolism of a heterotrophic nitrifying-denitrifying Alcaligenes sp. from soil, Appl. Environ. Microbiol., 44, 923-928 (1982). 29) Rittmann,B.E. and Langeland, W. E. Simultaneous denitrification with nitrification in a single-channel oxidation ditch, J. WPCF., 57, 300-308 (1985). 30) Hanaki, K., Wantawin, C. and Ohgaki, S. Effects of the activity of heterotrophs on nitrification in a suspended-growth react -or, Wat. Res., 24, 289-296 (1990). 31) Schulthess,R.V.,Wild, D. and Gujer, W.: Nitric and nitrous oxides from denitrifying activated sludge at low oxygen concentration, Wat. Sci.Tech., 30, 123-132 (1994) 32) Wild, D., Schulthess,R.V. and Gujer, W. Structure modeling of denitrification intermediates, Wat. Sci. Tech., 31, 4554 (1995) 33) Wild, D., Schulthess,R.V, and Gujer, W.: Synthesis of denitrification enzymes in activated sludge: modeling with structure biomass, Wat. Sci. Tech., 30,113-122 (1994) 34) Averill, B.A. and Tiedje, J. M.:The chemical mechanism of microbial denitrification, FEBS. Lett., 138,8-12 (1982) 35) Hanaki, K, Zheng, H, and Matsuo, T.: Nitrous oxide-green house effect gas-emission from denitrification process, Proceedings of 21th Symposium on Sewage Works (1990).(in Japanese)
