An insight into the various pretreatment methods applied to the raw wastes before the preparation of biogas

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

4. DIFFERENT SOURCES OF
BIOMASS

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

6. STAGES OF ANAEROBIC
DIGESTION
Carbohydrates
Fats
Proteins
Sugars
Fatty
Acids
Amino
Acids
Carbonic
Acids &
Alcohol
Hydrogen
Carbon dioxide
ammonia
Methane
Carbon
dioxide
Hydrogen
Acetic Acid
Carbon
dioxide
Hydrolysis Acidogenesis Acetogenesis Methanogenesis

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

9. LIGNOCELLULOSIC BIOMASS

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.