pretreatment methods for manufacture of biogas from agricutural wastes

50 %
50 %
Information about pretreatment methods for manufacture of biogas from agricutural wastes

Published on July 10, 2016

Author: sudiptaghosh75685



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

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


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.

Add a comment