2. Biomass
• Biomass is renewable organic material that comes from plants and
animals.
• Biomass continues to be an important fuel in many countries, especially
for cooking and heating in developing countries. The use of biomass fuels
for transportation and for electricity generation is increasing in many
developed countries as a means of avoiding carbon dioxide emissions from
fossil fuel use.
• Biomass contains stored chemical energy from the sun. Plants produce
biomass through photosynthesis. Biomass can be burned directly for heat
or converted to renewable liquid and gaseous fuels through various
processes.
3. Biomass sources
Biomass sources for energy include:
• Wood and wood processing wastes—firewood, wood pellets, and wood chips, lumber and furniture mill sawdust and waste, and black
liquor from pulp and paper mills
• Agricultural crops and waste materials—corn, soybeans, sugarcane, switchgrass, woody plants, and algae, and crop and food processing
residues, mostly to produce biofuels
• Biogenic materials in municipal solid waste—paper, cotton, and wool products, and food, yard, and wood wastes
• Animal manure and human sewage for producing biogas/renewable natural gas
4. Biomass Conversion Process
Biomass is converted to energy through various processes, including:
1. Direct combustion (burning) to produce heat
2. Thermochemical conversion to produce solid, gaseous, and liquid
fuels
3. Chemical conversion to produce liquid fuels
4. Biological conversion to produce liquid and gaseous fuels
5. Direct combustion (burning)
• Direct combustion is the most common method for converting
biomass to useful energy. All biomass can be burned directly for
heating buildings and water, for industrial process heat, and for
generating electricity in steam turbines.
6. Thermochemical conversion
Thermochemical conversion of biomass includes pyrolysis and gasification. Both are thermal decomposition
processes in which biomass feedstock materials are heated in closed, pressurized vessels called gasifiers at high
temperatures. They mainly differ in the process temperatures and amount of oxygen present during the
conversion process.
• Pyrolysis entails heating organic materials to 800–900oF (400–500 oC) in the near complete absence of free
oxygen. Biomass pyrolysis produces fuels such as charcoal, bio-oil, renewable diesel, methane, and
hydrogen.
• Hydrotreating is used to process bio-oil (produced by fast pyrolysis) with hydrogen under elevated
temperatures and pressures in the presence of a catalyst to produce renewable diesel, renewable gasoline,
and renewable jet fuel.
• Gasification entails heating organic materials to 1,400–1700oF (800–900oC) with injections of controlled
amounts of free oxygen and/or steam into the vessel to produce a carbon monoxide and hydrogen rich gas
called synthesis gas or syngas. Syngas can be used as a fuel for diesel engines, for heating, and for
generating electricity in gas turbines. It can also be treated to separate the hydrogen from the gas, and the
hydrogen can be burned or used in fuel cells. The syngas can be further processed to produce liquid fuels
using the Fischer–Tropsch process.
7. Chemical conversion
A chemical conversion process known as trans-esterification is used for converting vegetable
oils, animal fats, and greases into fatty acid methyl esters (FAME), which are used to
produce biodiesel.
8. Biological conversion
• Biological conversion includes fermentation to convert biomass
into ethanol and anaerobic digestion to produce renewable natural gas.
• Ethanol is used as a vehicle fuel.
• Renewable natural gas—also called biogas or bio-methane, is produced in
anaerobic digesters at sewage treatment plants and at dairy and livestock
operations.
• It also forms in and may be captured from solid waste landfills.
• Properly treated renewable natural gas has the same uses as fossil fuel
natural gas.
9. Biogas from plant wastes
• Biogas is a mixture of different gases produced by the biological
decomposition of organic matter in the absence of oxygen, called an
anaerobic digestion process.
• It mainly consist of methane (CH4), carbon dioxide (CO2) and a trace
amount of other gases such as hydrogen sulfide (H2S), ammonia (NH3),
hydrogen (H2), nitrogen (N2) and carbon monoxide (CO).
• Biogas can be produced by anaerobically digesting several organic matters
such as agricultural wastes, municipal wastes and industrial wastes.
• Utilization
1. Cooking
2. Lighting
3. Power generation
4. Transport fuel
10. Types of biogas feed stocks
(a) Agriculture waste:
Include various organic materials originating from agriculture, such as crop residues like
stalks, leaves, husks, cobs, and industrial and municipal residues and wastes.
(b) Municipal waste:
Municipal wastes refer to the source-separated household waste, sewage sludge,
municipal solid waste (MSW), food residues, garden waste, and other similar organic
wastes. The organic fraction of MSW is biodegradable and defines as organic waste or
biowaste.
(c) Industrial waste:
Massive amounts of organic wastes, by-products, and residues are produced in agro-
industries, food industries, fodder, and brewery industries, including organic byproducts
and organic-loaded wastewaters sludges from biorefineries that need to be treated or
disposed off.
11. Characteristics and Analysis of biogas feedstocks
• The digestion type and size selections are based on the substrate's
characterization to be treated, the investment capital required, the target
outcome power, etc.
• Besides, feedstock selection should also consider optimizing other aspects of
performance, such as digestate quality and biogas production.
• It is essential to know that some feedstocks are difficult or unsuitable for
producing biogas because of their unfavorable C/N ratios or high lipid content.
12. Characteristics and Analysis of biogas feedstocks
1. Preparation of sampling:
– Details on biogas feedstocks' sampling are generally described in standard
VDI 4630, and the selection of sludges and wastewater is defined in ISO
5667-13.
2. Laboratory analysis of feedstocks :
– A laboratory analysis is done to determine the biophysical characteristics,
and a Biochemical methane potential (BMP) assay is used to measure
anaerobic biogas production. The biophysical characteristics involve
analysis of TS or DM, VS, organic dry mass (ODM), chemical oxygen
demand (COD), nitrogen content, and carbon/nitrogen ratios.
13. Characteristics and Analysis of biogas feedstocks
(a) Total solids (TS) and volatile solid (VS)
• TS and VS tests are conducted to determine the percentages of dried solids
content and organic dried solids content in the substrates.
• TS is the amount of solid remaining after heating the feedstock sample so that
water is allowed to evaporate.
14. Characteristics and Analysis of biogas feedstocks
(b) Chemical oxygen demand: A chemically oxidizable material is determined by
measuring the COD of a feedstock. COD represents the maximum chemical energy
present in the feedstock. Since microbes convert chemical energy to methane, this
is also the maximum energy recovered as biogas.
(c) Nitrogen content: Nitrogen is essential for protein synthesis and is primarily
required as a nutrient by the microorganisms in anaerobic digestion.
(d) Biochemical methane potential : Biochemical methane potential tests are
mainly used to determine the possible methane yield of a feedstock. These tests
also provide information on the anaerobic degradability of a feedstock, including
the degradation rate.
16. Process Description
• The waste is sorted from the different station and the organic
matter classified.
• The organic waste is then crushed for size reduction and effective
anaerobic digestion.
• Digestion is allowed to take place under mesophilic conditions.
Two digesters of 60m3 and 420m3 are required for optimal biogas
production from the waste.
• The generated biogas is then sent for upgrading. Mesophilic
conditions of 35°C are maintained using heat from combined
heat and power generation (CHP).
• Bio solids (digestate) are removed for further processing as bio
fertilizers.
17. Component affecting biogas production
1. Temperature and pH:
• Temperature has a significant effect on the microbial community, process kinetics and stability, and
methane yield. Lower temperature decreases microbial growth, substrate utilization rates, and biogas
production during the process, resulting in cell energy exhaustion, leakage of intracellular substances,
or complete lysis. On the contrary, high-temperature results in lower biogas yield due to ammonia's
volatile gases, suppressing methanogenic activities.
• A temperature range between 35–37 °C is considered suitable for methane production under
mesophilic conditions.
• The pH value determines the acidity or basicity of an aqueous solution. The pH value can be
measured in a liquid feedstock with a standard potentiometric electrode.
• The optimal pH ranges of the hydrolysis and acidogenesis stages are 5.0–6.0 and 5.5–6.5,
respectively, whereas the ideal pH range for methanogenic bacteria is 6.8–7.2
18. Component affecting biogas production
2. Moisture:
• High moisture contents usually facilitate the AD process and likely affect the
process performance by dissolving readily degradable organic matter. The high
yield of methane production occurs at 60–80% of humidity.
3. Raw material composition:
• Methane yield varies for different chemical constituents or the same biomass
feedstock.
• Fats and proteins produce more methane than carbohydrates and lignin.
4. Total solids and volatile solids:
• Three main types of AD technologies that work according to the TS content of
feedstocks are ≤10%, 10–20%, and ≥20% TS for conventional wet, semi-dry, and
modern dry processes, respectively.
• Total methane yield decreases typically with an increase of TS contents from 10%
to 25% in batch AD under mesophilic conditions.
19. Component affecting biogas production
5. Chemical and biological demand:
• Chemical oxygen demand (COD) quantifies the amount of organic matter (OM) in
feedstocks.
• COD is a parameter that indicates the total chemically oxidizable material in the
sample and represents the maximum chemical energy present in the feedstock.
• Theoretical CH4 production is 0.35–0.5 Nm3 /kg COD removal; thus, biogas
production will be higher as CH4 is only part of the biogas.
• Biological oxygen demand (BOD) measures oxygen used by microorganisms to
decompose OM. Typical BOD values are: pig slurry 20,000–30,000, cattle slurry
10,000–20,000, and wastewater 1,000–5,000 mg L-1 .
20. Component affecting biogas production
6. Carbon/nitrogen ratio:
• The C/N ratio represents the relationship between nitrogen and carbon in a
feedstock.
• A low ratio means that the material is protein-rich. AD of such material results in
increased free ammonia content that causes high pH leading to methanogenic
inhibition.
• Therefore, a higher C/N ratio would be required to reduce the risk of ammonia
inhibition when the temperature is increased. However, a high ratio causes rapid
depletion of nitrogen needed for the reproduction of the bacteria, causing lower gas
production.
• Typical C/N ratios for some feed stocks: cattle manure 13:1, chicken manure 15:1,
grass silage 25:1, rice husks 47:1, while 25:1 is a broad practice value.
21. Strengths: -
1. Potential for converting waste
to biogas, electricity, and bio-
fertilizer
2. Applicable for a variety of feed
stocks: manure, slaughterhouse,
and wastewater from agro-
industry such as cassava starch,
ethanol production, rice flour
production
3. - Suitable climatic conditions for
biogas production
4. - Low production cost of
electricity
5. - Existing biogas plant
technology
6. - Available biogas equipment
suppliers
Weaknesses: -
1. High investment cost for biogas
construction
2. - High O&M cost
3. - Long payback period
4. - Biodigester technology is still
limited
5. - Limitation of technology
supplier
6. - Competition for biomass (use
for other purposes instead of
biogas)
7. - Lacking marketable RE
technologies/business models
8. - Lack of data from other biogas
resources such as municipal
waste, slaughterhouse, and
other biogas resources
22. Community biogas plant (CBP)
• Majority of the biogas plants in India are individual,
household level plants. However, since only
comparatively rich villagers have adequate number of
cattle, most small farmers and landless labour and
artisans in the villages cannot have biogas plants. The
common needs of the villagers such as organic
fertilizers in large quantities, lighting and water supply
cannot be met from individual plants as privately
owned individual biogas plants are used mostly for
cooking and the sludge for fertilizing the fields.
23. Advantages
1. Sanitation: with proper management of animal and other agriculture/organic wastes/ village will be clean
leading to better health and hygiene in rural areas.
2. Energy security: conversion of organic waste into methane and its use as fuel will lead to energy security
because the fossil fuel is not going to last forever.
3. Pollution control: normally aerobic decay of organic waste leads to emission of green house gases like
carbon dioxide or carbon monoxide. The process of methanation reduces green house gas emission and
helps in arresting depletion of the ozone layer. This is likely to earn carbon credits.
4. Employment generation: Such plants can be easily set up and operated at village level and can be
managed by women self help groups or local entrepreneurs with lower per capita investment. Since the
product has a captive market the plant is bound to be economically viable and generate employment
opportunity for a large number of people
• Despite the advantages mentioned above, there are very few successful community biogas plants (CBP)
in India, most of which are institutional biogas plants constructed by organizations such as the Khadi &
Village Industries Commission, other commercial entities (as part of their Corporate social responsibility
programs) etc. At present, the number of community biogas plants established in villages to cater to the
cooking fuel, organic fertilizer or electricity requirements of the village is very small.
24. Constraints
• 1. Economic:
– a. High capital and interest cost of CBP compared to the smaller family biogas plant.
– b. High repair and maintenance cost.
• 2. Social:
– a. Women gather fuel wood for cooking while the decision making for CBP is by the men folk.
Therefore, the need for construction of such plants in not dealt with urgency.
– b. Lack of awareness.
• 3. Technical:
– a. Inadequate dung availability.
– b. Initial gestation period of about two months of feeding.
– c. Scarcity of water.
– d. Non-availability of space.
– e. Maintenance problems.
– f. High rate of plant failures.
• 4. Institutional:
– a. Complex procedures to obtain loan, subsidy and repair charges.
– b. Inadequacy of funding.
– c. Lack of masons and skilled labour.
25. Important Components of the CBP:
1. Mixing tank: Water and cow dung is mixed mechanically using pressurized
air in the mixing tank. This process of mixing requires electricity supply.
2. Digester: There are 2 digesters each of size 85 m3 and floating dome type.
The digestion time is 40 days.
3. Pressure regulation tank: Gas generated in the floating domes gets
transferred to the pressure regulation tank which pressurizes the gas using
water column. Gas pressurization is essential for its distribution through
underground pipes.
4. Vermicompost sheds: Vermicompost sheds are constructed near the plant
to process the output slurry into vermicompost.
