Biogas Technology

beefzoologistBiotechnology

Feb 21, 2013 (4 years and 5 months ago)

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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