AnaerobicTreatment_to_post_2010

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Unformatted text preview: ANAEROBIC
WASTEWATER
TREATMENT
MICROBIOLOGY
 ANAEROBIC
WASTEWATER
TREATMENT
MICROBIOLOGY
 Anaerobic
Wastewater
Treatment
Microbiology

 A.

Anaerobic
treatment
of
organic
maBer
‐
Anaerobic
digesEon

 
1.

In
the
absence
of
O2,
organic
maBer
is
fermented
to
carbon
dioxide
and
 methane: 
2CH2O


‐‐‐‐‐‐‐‐>


CH4

+

CO2


 
2.

More
than
75%
of
treatment
plants
in
the
US
use
anaerobic
digesEon
to
 reduce
the
sludge
yields,
also
energy
produced.

Sludge
[though
less
of
it]
is
sEll
 produced.

Some
faciliEes
burn
the
sludge
(costly),
while
other
haul
it
away,
e.g.
 landfill
cover,
off‐shore
dump
site,
land
applicaEon
of
'biosolids'.
 
3.

Also
used
directly
for
treatment
of
municipal
wastewater,
mostly
in
 Europe,
and
for
agriculture/farm
wastes.

In
addiEon,
in
Europe,
used
for
high
 organic
industrial
wastes
(e.g.
canning/food
wastes).
 
4.

GeneraEng
energy
from
refuse,
20
yrs
ago
energy
crisis
‐
from
fast
 growing
plants,
e.g.
kelp;
again
being
considered
by
USDA,
DOE.
 
5.

Municipal
solid
waste
is
60‐70%
organic
or
carbon
based.

If
all
the
refuse
 in
the
US
were
put
into
methane
digesters
11‐15%
of
the
enEre
US
energy
 consumpEon
could
be
saEsfied.
 B.

A
number
of
anaerobic
process
designs
are
described
in
the
literature.

VariaEons
are
 designed
to
largely
to
improve
the
operaEon
of
the
process.
 1.

ConvenEonal
flow
through
process
 
 
θ
=
θc
=
6
to
30
days
 2.

Anaerobic
contact
process
 
 
θ
=
0.5
several
days
 3.

Anaerobic
filter
 
 
θ
=
few
hours,
θc
=
~100
days
 4.

Upflow
anaerobic
sludge
blanket
(UASB)
 
 
Anaerobic
fluidized
bed
(low
strength
wastewater)
 
 
 
All
of
these
can
separate
the
hydraulic
reten.on
.me
from
the
cell
reten.on
 .me.

This
is
more
important
when
the
process
is
being
used
for
waste
treatment
rather
 than
when
it
is
used
for
solids
or
sludge
reducEon.
 θ 

=

1/D

=

V/F
 θ  =

hydraulic
detenEon
Eme
 θ c

=

cell
detenEon
Eme
 
1.

ConvenEonal
flow
through
process
 
 
θ
=
θc
=
6
to
30
days
 or
ACTIVATED
SLUDGE
 2.

Anaerobic
contact
process
 
 
θ
=
0.5
several
days
 3.

Anaerobic
filter
 
θ
=
few
hours,
θc
=
~100
days
 
 
‐

simplest
 
 
‐

very
stable
 
 
‐

relaEvely
low
efficiency
 
 



of
COD
removal
 
 
‐

clogging,
channeling
 All
these
treatment
 designs
separate
θ from
θc
 4.

Upflow
anaerobic
sludge
blanket
(UASB)
 
Anaerobic
fluidized
bed
(low
strength
wastewater)
 
 
 

 5.  Thin
film
bioreactor
 
(preferred
for

 ‐ 
biofilm
on
sand
 
industrial
wastes)
 ‐ 
good
contact
 with
waste
 ‐ 
no
clogging
 ‐ 
hi
biomass
 ‐ 
short
θ ‐ 
high
energy
 req.
 C.

Disadvantages
of
the
anaerobic
process
‐
almost
all
are
related
to
the
slow
growth
 rate
of
anaerobic
digester
communiEes,
 
e.g.

Ks
for
aerobic
treatment
systems
=
1
to
20
mg/L
 
 

Ks
for
anaerobic
treatment
systems

=

200‐400
mg/L
 1.  Long
detenEon
Eme,
14‐30
days
‐
therefore,
need
a
larger
reactor
–
cost
factor.
 2. 
Long
start‐up
period,
up
to
several
months
 3. 
High
sensiEvity
to
varying
waste
loads,
toxic
inputs,
adjusts
very
slowly
 4.  Hence,
upsets
require
very
long
Eme
for
recovery.
 5. 
Process
is
very
sensiEve
to
pH,
cannot
drop
below
6.2
 6. 
OpEmum
at
85‐95°F,
may
need
heaEng.
 D.  Advantages
of
the
anaerobic
process
(go
to
next
slide)
 
1.

Lower
yield
of
biological
solids
(sludge
yield),
e.g.


Y

=

dx/‐dS
 
 
 
 
 
ae
=
equiv.
cells
formed/equiv.e‐
donor
consumed
 
 
 
 
 
 
 
aerobic 
 
anaerobic 
 
 
___
 
 
 
glucose 
 
 
0.79
 
 
0.27
 
 
 
acetate 
 
 
0.58
 
 
0.06
 
 
 
domesEc
waste 
0.5 
 
 
0.1 
 
 
 
 
 

 
 

 
e.g.
without
oxygen,
less
energy
available,
less
cells
synthesized,
but
it
also
means
less

 
sludge
to
dispose
of.
 
What
is
a
disadvantage
for
the
cell
is
an
advantage
for
the
designed
process.
 MICROBIALLY MEDIATED OXIDATION-REDUCTION REACTIONS Electron donor reactions glucose toluene xylenes C6H12O6 } } } } CO2 + H2O (+ cells) C 7H 8 C8H10 benzene C6H6 2.

Higher
degree
of
'waste
stabilizaEon',
e.g.
higher
mineralizaEon,
e.g.
higher
COD,
BOD
 removal,
e.g.
higher
transformaEon
from
the
organic
to
the
inorganic.
 
 
C10H19O3N

+

4.7
H2O

‐‐‐‐‐‐‐‐>

0.145
C5H7O2N

+

5.75
CH4

+

2.48
CO2

 
 
 
 
 
 
 
 
+

0.81
NH4+

+

0.81
HCO3‐
 
Compare
to
 
 
C10H19O3N

+

9O2


‐‐‐‐‐‐‐‐‐>


C5H7O2N

+

5CO2

+

H2O
 
e.g.

Most
of
the
carbon
has
been
transformed
to
CO2
and
CH4,
very
liBle
remains
in

 
 
 
the
organic
form.
 
 
Overall
with
anaerobic
processes
80‐90%
of
the
waste
is
converted
to
gas
or

 
 
 
inorganic
form
and
is
'stabilized'.


 
 
In
the
above
equaEon,
more
than
90%
is
converted
compared
to
50%
in
aerobic

 
 
 
process.
 
3.

lower
N
&
P
requirement
since
lower
cell
yield
 
4.

No
oxygen
requirement,
therefore,
no
need
to
aerate,
not
limited
by
oxygen

 
 
transfer,
important
reducEon
in
cost.
 
 
Note:

mixing
in
anaerobic
unit
is
to
keep
cells
mixed,
while
mixing
in
 
 
 
 
aerobic
units
is
much
more
vigorous
in
order
to
deliver
oxygen.
 
5.

ProducEon
of
a
useful
product,
fuel
‐
methane,
used
to
heat
and
run
digester.
 

 Conceptual
Model
 (first
described
by
Perry
McCarty)
 CO2
,
H2
 1.  2.  3.  4.  facultaEve
microbes
 no
waste
stabilizaEon
 relaEvely
rapid
process
 co‐dependency
 1.  2.  3.  4.  anaerobes
 relaEvely
slow
process
 rate
limiEng
part
of
process
 co‐dependency
 This
is
a
conceptual
model,
and
not
an
actual
2
step
process.
 HCOOCH3OH CH3NH2 CH3COO- Tracing
the
source
of
methane
in
an
anaerobic
digester
 CO2
,
H2
 formate
 X
 methanol,
formate
 methylamine,
CO2
,
H2
 DescripEon
of
overall
process
of
anoxic
decomposiEon
 • 
First
described
in
anaerobic
digesters
30
 yrs
earlier
by
an
environmental
engineer
 • 
This
is
the
same
conceptual
model
 • 
Methanogens
only
use
acetate
&
single
 C
compounds
 • 
Acetate
is
one
of
the
most
important
C‐
 sources
in
anoxic
habitats
 • 
Methane
cannot
come
from
propionate
 • 
Methane
can
account
for
30‐80%
of
C
 fixed
through
primary
producEvity
in
 freshwater
environments
 4.

Methane
bacteria
 
‐

alot
was
known
about
them
before
they
were
separated
into
their
own
domain
 
 
a)

very
sensiEve
to
O2,
ox‐red
potenEal
<‐300mV
 
 
b)

sensiEve
to
pH,
opEmum
=
6.6
‐7.6.

Below
6.2
digester
will
die.
 
 
 
Hence,
organic
acids
cannot
get
too
high.
 
 
c)

slow
growth
 
 
d)

limited
number
of
species
and
their
limited
number
of
substrates


 5.

Source
of
methane
 
 
a)

methyl
group
cleavage
 
 
 
*CH3COOH


‐‐‐‐‐>


*CH4

+

CO2
 
 
 
 
acetate
 
 
 
4CH3OH


‐‐‐‐‐>


3CH4

+

CO2

+

2H2O
 
b)

CO2

reducEon
 
 
 
4H2

+

CO2


‐‐‐‐‐>


2H2O

+

CH4
 
 
c)
from
propionate?
 
 
 
CH3CH2COOH

+

4H2O


‐‐‐‐‐>


2HCOOH

+

CO2

+

5H2
 
 
 
 
propionate 
 
 



formate
 
 
d)

from
formate
 
 
 
HCOOH

+

3H2


‐‐‐‐‐>


CH4

+

2H2O
 
 

 e)  “Methanobacterium
omelianskii”
illustrates
close
syntrophic
relaEonship
 
interspecies
hydrogen
transfer
 
 
 
2CH2H5OH

+

CO2


‐‐‐‐‐>


2CH3COOH

+

CH4
 
 
 
 
Actually
2
reacEons
mediated
by
2
different
organisms
 
 
2CH2H5OH

+

2H2O


‐‐‐‐‐>


2CH3COOH

+

4H2
 
 
4H2

+

CO2


‐‐‐‐‐>


2H2O

+

CH4
 6.

More
difficult
to
operate
 
Process
is
much
less
forgiving
than
aerobic
process
 
1.

Unbalance
caused
by
sudden
changes
in
temp.,
organic
loading,
waste
character.
 
2.

None
of
these
things
are
good
for
any
biological
process,
but
anaerobic
systems
is

 
 
much
less
forgiving
and
more
sensiEve
to
change
because
 
 
a)

if
one
group
is
knocked
out,
a
major
proporEon
of
the
organisms
are
affected

 
 
 
and

 
 
b)

their
slow
growth
rates
mean
that
it
is
more
difficult
and
slower
to
recover.
 
3.

The
3
parameters
to
monitor
are
 
 
a)
volaEle
acids
buildup
‐
formate,
acetate,
propionate,
butyrate,
etc
 
 
b)
pH
decrease
 
 
c)
hydrogen
levels
 ...
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