MANUFACTURE OF BIOGAS FROM AGRICULTURAL WASTES

PRESENTED BY-SUDIPTA GHOSH

& PALLAVI JHA

NIT DURGAPURPAPER NO.- AISEC/16/T-1/16

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

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 Generatio

n

Production of

various chemicals

like methanol

DIFFERENT SOURCES OF BIOMASS

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 ADAbsence of OxygenTemperature: Mesophilic Range- 20 to 45°C pH: 6.4 to 7.2Carbon to Nitrogen Ratio(C:N) : 20-30Retention Time: 15 to 30 daysSlow Mixing

STAGES OF ANAEROBIC DIGESTION

Carbohydrates

Fats

Proteins

Sugars

Fatty Acids

Amino Acids

Carbonic Acids & Alcohol

Hydrogen Carbon dioxide

ammonia

Methane

Carbon dioxide

HydrogenAcetic Acid

Carbon dioxide

Hydrolysis

AcidogenesisAcetogenesisMethanogenesis

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 producedThe 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

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

LIGNOCELLULOSIC BIOMASS

PRETREATMENT

THE MAIN PURPOSE OF PRETREATMENT:Increase porosityDestroy lignin shell protecting cellulose and hemicelluloseDecrease crystallinity of celluloseMust break the shell for enzyme to access substrate(sugar)

PRETREATMENT METHODS:ChemicalPhysicalBiological

CHEMICAL PRETREATMENTALKALINE PRETREATMENT:Alkali used are mainly lime and NaOHCauses swelling of lignocelluloses & partial lignin solubilizationProcess Conditions- relatively mild, long reaction timeHigh Cost of Chemicals

REFERENCE: Mohsen Taherdanak & Hamid Zilouei, Improving biogas production from wheat plant using alkaline pretreatment, Elsevier

CHEMICAL PRETREATMENTDILUTE ACID PRETREATMENT:Breaks down hemicellulose, disrupts ether bonds between lignin and hemicellulose & increases p0rosity of cell wallTypical conditions: Acid used: Dilute H2SO4 Concentration: low(<2%, w/w) Temp: 160-200°CDemerits: i) Removal of lignin is insignificant(<70%) ii) Corrosive to the metal of the reactor iii) Forms furfural & HMF which is inhibitory to fermentation

CHEMICAL PRETREATMENTOXIDATIVE PRETREATMENT:Oxidizing agents used are H2O2, O3, O2 & airEffectively removes lignin & does not produce toxic residuesOzonolysis occurs at room temperature & pressureExpensive

ORGANOSOLV PROCESS:Uses organic solvents like ethanol, acetone, carboxylic acid etc.Temp: 200°C, high pressureRemoves lignin, hydrolyses hemicelluloseIncreased risk of combustion & explosion in case of use of flammable organic solventSolvent recovery is difficult

PHYSICAL PRETREATMENT

MECHANICAL PRETREATMENT:Carried out by mills which breaks open the cellulose structure & increases the specific surface area of the biomassMills divided into hammer or knife millsGreater 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

PHYSICAL PRETREATMENTTHERMAL PRETREATMENT:Temperature- 125 to 190°C under pressure, time-1 hrCarried out in pressure cooker, autoclave or microwave heaterWater is added to the dry substrate. Presence of heat & H2O disrupts H2 bonds that holds together the cellulose & lignocellulose complexEffective for crops upto 190°CLarge scale application – TDH developed at ATZ Entwicklungszentrum in Germany, increase in biogas yield by 20-30%

COMBINED PRETREATMENTSTEAM EXPLOSION:Most applied process, low use of chemicals & limited energy consumptionDemerit: Long retention time & high temperature can decrease CH4 yield REACTOR

FILLED WITH BIOMASST=160-260°C

High Pressure Sat. Steam

Sudden pressure reduction

Hemicellulose

degradation & lignin

matrix disruption

BIOLOGICAL PRETREATMENT

Wood degrading microbes like white, brown & soft rot fungi & bacteria are usedModifies 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

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.