Biogas Technology

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