pretreatment methods for manufacture of biogas from agricutural wastes
1. MANUFACTURE OF BIOGAS FROM
AGRICULTURAL WASTES
PRESENTED BY-
SUDIPTA GHOSH
&
PALLAVI JHA
NIT DURGAPUR
PAPER NO.- AISEC/16/T-1/16
2. WHY WE NEED RENEWABLE
ENERGY SOURCES?
Do not lead to emission of greenhouse gases.
Environment friendly
Available in abundant quantity and are free to use
3. BIOGAS
Biogas typically refers to a mixture of different gases produced by the
breakdown of organic matter in the absence of oxygen.
Biogas is primarily methane (CH4): 50-75% and carbon dioxide(CO2): 25-
50% and may have small amounts of hydrogen sulphide (H2S), H2, O2,
N2.
BIOGAS
UTILIZATION
Domestic &
Industrial
Fuel
Automobile
Fuel
Fuel Cells for
Electricity
Generation
Production
of various
chemicals
like
methanol
5. ANAEROBIC DIGESTION
Anaerobic digestion is a series of biological processes in which
microorganisms breakdown biodegradable materials in the absence of
oxygen to produce biogas.
OPTIMUM CONDITIONS FOR AD
Absence of Oxygen
Temperature: Mesophilic Range- 20 to 45°C
pH: 6.4 to 7.2
Carbon to Nitrogen Ratio(C:N) : 20-30
RetentionTime: 15 to 30 days
Slow Mixing
7. SINGLE BATCH AD REACTOR
SYSTEM
The concrete reactor with integrated heating system is loaded with
biowaste and closed, starting the anaerobic degradation.
High organic content leachate is produced
The leachate is stored, heated and continuously redistributed in the
reactor to increase the biogas yield.
The waste is kept in the reactor from 20 to 40 days, until the biogas
production stops or drops
8. BIOGAS YIELD FROM DIFFERENT
SUBSTRATES
REFERENCE: J ranjhita et al. Production of biogas from flowers and vegetable
wastes using anaerobic digestion, International Journal of Research in
Engineering &Technology
10. PRETREATMENT
THE MAIN PURPOSE OF PRETREATMENT:
Increase porosity
Destroy lignin shell protecting cellulose and hemicellulose
Decrease crystallinity of cellulose
Must break the shell for enzyme to access substrate(sugar)
PRETREATMENT METHODS:
Chemical
Physical
Biological
11. CHEMICAL PRETREATMENT
ALKALINE PRETREATMENT:
Alkali used are mainly lime and NaOH
Causes swelling of lignocelluloses & partial lignin solubilization
Process Conditions- relatively mild, long reaction time
High Cost of Chemicals
REFERENCE: MohsenTaherdanak & Hamid Zilouei, Improving biogas production from
wheat plant using alkaline pretreatment, Elsevier
12. CHEMICAL PRETREATMENT
DILUTE ACID PRETREATMENT:
Breaks down hemicellulose, disrupts ether bonds between lignin and
hemicellulose & increases p0rosity of cell wall
Typical conditions:
Acid used: Dilute H2SO4
Concentration: low(<2%, w/w)
Temp: 160-200°C
Demerits: i) Removal of lignin is insignificant(<70%)
ii) Corrosive to the metal of the reactor
iii) Forms furfural & HMF which is inhibitory to fermentation
13. CHEMICAL PRETREATMENT
OXIDATIVE PRETREATMENT:
Oxidizing agents used are H2O2, O3, O2 & air
Effectively removes lignin & does not produce toxic residues
Ozonolysis occurs at room temperature & pressure
Expensive
ORGANOSOLV PROCESS:
Uses organic solvents like ethanol, acetone, carboxylic acid etc.
Temp: 200°C, high pressure
Removes lignin, hydrolyses hemicellulose
Increased risk of combustion & explosion in case of use of flammable
organic solvent
Solvent recovery is difficult
14. PHYSICAL PRETREATMENT
MECHANICAL PRETREATMENT:
Carried out by mills which breaks open the cellulose structure & increases the
specific surface area of the biomass
Mills divided into hammer or knife mills
Greater possibility for enzyme attack
Particle size- 1 to 2 mm(effective hydrolysis)
Repair cost of mills is large
The figure above shows that knife milling slices the fibers &
hammer milling grinds the fibers
15. PHYSICAL PRETREATMENT
THERMAL PRETREATMENT:
Temperature- 125 to 190°C under pressure, time-1 hr
Carried out in pressure cooker, autoclave or microwave heater
Water is added to the dry substrate. Presence of heat & H2O disrupts H2 bonds that
holds together the cellulose & lignocellulose complex
Effective for crops upto 190°C
Large scale application –TDH developed at ATZ Entwicklungszentrum in Germany,
increase in biogas yield by 20-30%
16. COMBINED PRETREATMENT
STEAM EXPLOSION:
Most applied process, low use of chemicals & limited energy
consumption
Demerit: Long retention time & high temperature can decrease CH4
yield
REACTOR
FILLEDWITH
BIOMASS
T=160-260°C
High
Pressure
Sat.
Steam
Sudden pressure
reduction Hemicellulose
degradation
& lignin
matrix
disruption
17. BIOLOGICAL PRETREATMENT
Wood degrading microbes like white, brown & soft rot fungi & bacteria
are used
Modifies the chemical composition & structure of the lignocellulosic
biomass.
The modified biomass is more amenable to enzyme digestion
ADVANTAGES:
•No chemical requirement
•Low energy input
•Mild environmental Conditions
•Environment friendly working
manner
DISADVANTAGES:
•Slow
•Requires careful control of growth
conditions
•Large space requirements
18. CONCLUSION
Biogas is being watched with keenest interest as environment-friendly,
alternative energy source instead of petroleum.
The major shortcoming is the presence of H2S in biogas which can be
overcome by biogas cleanup process like biological desulphurization and
biofiltration.
It is not possible to define the best pretreatment method as it depends
on many factors such as type of lignocellulosic biomass and desired
products.
Research has shown that it is possible to increase the methane yield by
over 1,000 % and therefore, cost effective commercial application is
possible if the correct techniques are applied.