Microbiology
of
Biogas Production
Biogas Production
Anaerobic digestion
of Biodegradable materials.
Biodegradation of Biomass,
manure , food waste etc., in
absence of Oxygen.
Biogas
Methane (CH
4
):
40
-
70%
Carbon dioxide
(CO
2
): 25
-
55%
Other gases: 2
-
7%
N
2
: 0
-
5%
H
2
: 0
-
1%,
H
2
S: 0
-
3%
Composition of Biogas
MICROBIOLOGY???
Bacteria “do the job”
Microorganisms
Invisible with naked eyes (size in
µm
)
Multiply at (very) high rate (doubling time : minutes to hrs)
control their local environment by:
utilizing biodegradables/waste as food and energy
releasing metabolites
Generating metabolic heat
Life styles
Aerobes
Anaerobes
Facultative
Obligate
Biogas process
–
Last choice
Produces lesser energy &
cells
Diverse Bacteria: No Eukaryotes!!
Schluter
et al., J Biotechnology; 136 (2008) 77
–
90
BAR:
10 µm
Biochemical Reactions
-
AD
Facultative
or obligate
anaerobes
Acetogenic
bacteria
((anaerobic))
Facultative or
obligate anaerobes
Methanogenic
bacteria
(anaerobic)
Low pH
Hydrogenotrophic e.g.
Methanobacterium
sp.
Aceticlastic e.g.
Methanosarcina
sp.
The Cell Wall of Methanogenic
bacteria do not contain
Muramic acid. The unique
chemical composition of the
cell wall makes the bacteria
“sensitive” to toxicity from
several fatty acids.
Also, many methane
-
forming
bacteria lack a protective
envelope around their cell wall
Methanogenic bacteria
Other bacteria
Some
Methanogenic
bacteria
Common form of
Methanogenic
bacteria
Factors Affecting Biogas Production
microbes
plant
design
construction
materials
climate
chemical
and
microbial
characteristics
of
inputs
the
inter
-
relationships
among
these
factors
Physical / Chemical Parameters
C/N Ratio
: 20 to 30
Dilution and Consistency of Inputs : TS
-
7 to 10 %,
pH value
:
6
.5
–
8
Temperature
: 35
º to
45
°
C
Loading Rate
:
6 kg of dung per m3 volume of
d
igester
*
Retention Time
: 45 to 55 days (for cattle dung)
* volume of digester including gas storage space.
C/N Ratio
Relationship
between
the
amount
of
carbon
and
nitrogen
present
in
organic
materials
O
ptimum
C/N
ratio
-
20
to
30
Very
high,
C/N
ratio
-
rapid
consumption
of
N
2
by
methanogens
for
protein
requirements
-
no
longer
react
on
the
left
over
carbon
content
of
the
material
-
results
very
low
gas
production
.
Very
low
C/N
ratio
is
-
ammonia
(NH
4
)
-
the
pH
value
increase
in
the
digester
.
pH
>
8
.
5
will
start
showing
toxic
effect
on
methanogen
population
.
Imbalanced C/N ratio
N
-
Sources
Animal Urine
(Rich in urea)
Mix
with
dung
and
water
every
day
Azolla
(N: 4
-
5 % of dry wt.)
After 2
-
3days
High methanogens
growth
High CH4
Production
Nitrogen rich
manure
Azolla
an aquatic fern (
pteridophyte
)
With size: 1
-
5 cm
Biomass doubles in 1
-
2 days
Color: bright green (changes to deep red when exposed to the
sun, thus the name Red Azolla)
Commonly called mosquito fern
lives in symbiosis with BGA (anabaena
azollae
)
floating on water surface of
◦
flooded rice fields,
◦
small ponds, and
◦
canals
Azolla Cultivation
The lined pit method
0.05
-
0.1%
inorganic P
Azolla : Fates
Azolla
BG
Production
Compos
-
ting
Bioremediation
Animal
Feed
Cold Climate
Winter seasons:
◦
Hilly areas: 5
–
20
°
C (4
-
5 months )
◦
Others: 10
-
25
°
C (2
-
3 months )
Azolla
-
200gm /kg of dung
Feed
After every 2
-
3 days
High Exothermic Heat
of Azolla degradation
Temp: 35
-
40
°
C
Animal
Urine
Water
heated
under sun
light
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