Bioenergy conversion lecture notes

B Y
JEAN DE DIEU IYAKAREMYE
UR/CAVM
iyakjdd@gmail.com
BIOENERGY
CONVERSION

Chap.1 : BIOMASS AS A SOURCE OF
ENERGY
Introduction:
Bioenergyis anyrenewableenergyproducedfromlivingorganism
Biomass is a vital source of energy for the poor and
underdeveloped countries for cooking and heating of
food. There are three types of energy crops.

Types of energy crops
Annual Energy crops (Grains and Grasses) :
 The crop residues of cotton, maize etc can be used as bio
fuel.
 Grains like sorghum, wheat and maize contain high
amount of starch which can be converted in to fuel
alcohol to run the petrol and diesel engine.
 If we have surplus land and surplus food production
then we can divert a part of our land into fuel crops.
 To day the prices of essential food commodities are
increased this because USA has diverted much of its food
production land into the production of jatropha which is
a fuel crop to produce bio diesel.

Silviculture Energy farms (Trees)
 Energy farming in Rwanda can be practiced in the
areas where food crops cannot be cultivated like: the
bordering areas of swamps, slopes of rocky
mountains and other unproductive lands having lot
of gravels and stones.
 Even in the cultivated lands, a small part of the land
can be allocated for native species of trees like Alnus
and eucalyptus.

Aquatic Energy Farms (both land based and open
Kivu lake)
 Sewage water from cities forms the source of biomass
production like algae and water hyacinth. Water hyacinth
can be harvested and anaerobically digested to produce
methane gas.
 Addition of CO2 to the system is required for higher
biomass production. Attempts should be made to grow
water born plants in the stagnant waters of ponds and
lakes.
 Open banks of Kivu lake can be considered for the
development of certain giant tree species.

There are 3 factors that influence the amount of energy
in Rwanda can derive from energy farms. They are:
 Land and water availability for energy farms
 Productivity of biomass species
 Economics of bio fuel produced in the farms

ENERGY PLANTATIONS
 When land plants are grown purposefully for their fuel
value by capturing the solar radiation. It is called energy
plantation.
 Plants are considered as solar energy storage devices.
 Energy plantation by design are managed and operated
to provide substantial amount of usable fuel continuously
through out the year at competitive costs with other
fuels.
 This energy plantation can be converted and released in
to heat with high temperature like fossil fuels like coal
and petroleum.
 The suitable calorie plants should be grown in agro
forestry plantations to fill the gap of energy problem.

Energy plantations
 Factors influence energy plantations are: Soil
conditions, and species of vegetation, land
availability, Design and management of
energy plantation

Energy plantations
Soil conditions and species of vegetations.
 Agricultural land cannot be fully diverted for calorie crops.
 Hence, identify suitable land and climate for calorie crops
which needs a few cm of top soil to retain soil moisture and a
moderate growing season.
 Lands are available in Rwanda which needs a survey. The next
requirement is choosing the species of calorie crop for a
particular zone.
 The species must capture maximum solar energy in small area
of its exposure. More number of trees should be planted per
unit area. There should be little space between tree to tree.
 The geometry of the leaves bearing branch should be such that
maximum surface area faces the sun.

Energy plantations
Design and management of energy plantation
 Rwanda has to develop its energy plantation based on its
demand of fuel.
 Energy plantation has to be developed such that the new
planting and harvesting should exactly coincide with the
fuel requirement of the country.
 It is found that a typical calorie crop gives 12000 to
24000 trees/hectare. It yields the biomass of 17 to 25 dry
tons/ha/year.
 The harvesting period of the crop vary from one to three
years. Planting of tree should be made in such a way that
harvesting must give the annual demand of the country.

Advantages of Energy plantations
 Storage
 Economics
 Air pollution
 Ash content
 Ecological condition
 CO2 balance of the earth

Storage
 Solar energy as such cannot be stored.
 If we want to store in the form of photovoltaic based
electricity we need costly battery cells.
 If we want to store solar thermal in hot boxes, it also cost
considerable amount.
 Even then there is problem of energy loss. Energy
plantation store solar energy in the form of wood. There
is no problem of energy loss.
 It is not a costly solution. There is flexibility for the user
in the form of harvesting period and storage of woods.

Economics
 The cost involved in the energy plantation is less than the cost
involved in purchasing the fossil fuels like petrol and diesel.
 The cost of processing wood into charcoal (amakara) is less
compared to the refining of crude mineral oil in to kerosene or
petrol.
 The cost of bio fuel depends only upon the cost of land and the
period of maturity of calorie crop. If the period of maturity of fuel
plant is less then the cost of production of fuel is comparatively less.
 The cost of production of bio fuel can be reduced by adopting
multiple crops and increasing the population density of the energy
plantation.
Under optimized conditions, the cost of bio fuel is less than
the cost of fossil fuels.

Air pollution
Wood and other plant residues contain less than
0.1% sulphur content. Therefore, it produces very
less SO2 production during combustion of bio fuel in
cooking and other operations.
Fossil fuels like petrol and diesel produce more SO2
during its combustion.

Ash content
 Wood and other plant residue produce more ash
during their combustion.
 The ash contains more plant nutrients. It can be
directly used as fertilizer for the crop growth.

Ecological condition
 Energy plantation can be raised in arid, semi arid
and in unproductive rocky mountain slopes having
mostly gravel stones and very little soil.
 These unproductive land tracks are turned into green
belts.
 This causes more evapotranspiration and soil
conservation.
 This leads to more conducive ecological balance.

CO2 balance of the earth
Combustion of biomass produce large amount of CO2
to the atmosphere. However, it will not affect the
CO2 balance in the atmosphere because plant
consumes more CO2 during its growth stage than the
CO2 it releases during its combustion.
Combustion of fossil fuels releases more CO2 in to
the atmosphere and takes more O2 from atmosphere
for burning than the biomass.
Hence compared to fossil fuels, biomass does not
affect CO2 balance of the atmosphere.

Plants proposed for energy plantation
S.No Name of the
species
Yield, m3/ha/year Calorific value,
Kcal/kg
1 Eucalyptus 7 to 10 4800
2 Sesbania Species 20 ------
3 Casuarina 7 to 10 4950
4 Prosopis Juliflora 5 to 6 High
5 Leucaena
Leucocephala
30 to 40 4200 to 4800

Plants proposed for energy plantation
 Sweet potato
 Irish potato
 Water hyacinth
 Jatropha

Simplified Biomass Conversion Process

Detailed biomass conversion process

Process and its definitions
S
N
Process Description
1 Drying Decreasing the moisture content by mechanical or
thermal means
2 Briquetting Densification by compression under heat and
pressure
3 Pelletization Densification and cutting into standards pellet size
under pressure
4 Combustion Burning with the liberation of heat
5 Pyrolysis Thermal decomposition of organic matter in the
absence of air
6 Carbonization Formation of charcoal by heating in an oxygen free
atmosphere

Process and its definitions
SN Process Description
7 Liquefaction Conversion to an oil by reaction with synthesis gas and an
alkaline catalyst under high temperature and pressure
8 Hydrolysis Chemical decomposition through addition of water
9 Aerobic fermentation Decomposition of organic matter in an enzymatically
controlled air
10 Anaerobic fermentation Biochemical decomposition in an enzymatically controlled
and oxygen-free atmosphere
11 Biophotolysis Production of hydrogen in a chemical form through solar
energy
12 Hydrogeneration Extraction of oxygen from cellulose in the presence of
steam and carbon monoxide at high pressure with
moderate temperature
13 Hydro-gasification Conversion to a gaseous state in the presence of hydrogen
14 Catalytic gasification Conversion to a gaseous state by using a catalyst in an
inert gas atmosphere
15 Chemical reduction Change in chemical composition through heat and
pressure

Chap 2. Biogas generation technology
 Biogas, a mixture containing 55-65 percent methane, 30-40
percent carbon dioxide and the rest being the impurities (H2,
H2S, and some N2), can be produced from the decomposition
of animal, plant and human waste.
 It is a clean but slow burning gas and usually has a colorific
value-between 5000 to 5500 kcal/kg. It can be used directly
in cooking, reducing the demand for firewood.
 Moreover, the material from which the biogas is produced
retains its value as a fertilizer and can be returned to the soil.
 It is not only the excreta of the cattle, but also the piggery
Waste as well as poultry droppings are very effectively used
for biogas generation

Biogas generation technology
A few other materials through which biogas can be
generated are algae, crop residues (agro-wastes),
garbage kitchen wastes, paper wastes,. sea wood,
human waste, waste from sugarcane refinery, water
hyacinth etc., apart from the above mentioned
animal wastes.
Any cellulosic organic material of animal or plant
origin which is easily biodegradable is a potential
raw material suitable for biogas production.

Biogas generation technology
Biogas is produced by digestion. Digestion is the
biological process that occurs in the absence of
oxygen and in the presence of anaerobic organisms
at ambient pressures and temperatures of 35-70°C.
The container in which this digestion takes place is
known as the digester.

Anaerobic digestion
 Biogas technology is concerned to microorganisms.
These are living creatures which are microscopic in size
and are invisible to unaided eyes.
 These are different types of microorganisms. They are
called bacteria.
 Fungi, virus etc. Bacteria again can be classified into two
types:beneficial bacteria and harmful bacteria.
 Compost making production of biogas, vinegar, etc., are
examples of beneficial bacteria.
 Bacteria causing cholera, typhoid, diphtheria are
examples of harmful bacteria. This type of bacteria which
causes disease both in animals and human beings is
called pathogen.

Anaerobic digestion
 Bacteria can be divided into two major groups based on their
oxygen requirement.
 Those which grow in presence of oxygen are called aerobic
bacteria
 while the others grow in absence of gaseous oxygen are called
anaerobic bacteria.
 When organic matter undergoes fermentation (process of
chemical change in organic matter brought about by living
organisms) through anaerobic digestion, gas is generated.
 This gas is known as biogas. Biogas is generated through
fermentation or bio-digestion of various wastes by a variety of
anaerobic and facultative-organisms.
 Facultative bacteria are capable of growing both in presence
and absence of air or oxygen.

Aerobic digestion
 Aerobic and anaerobic fermentation can be used to decompose
organic matter.
 Normally aerobic fermentation produces CO2, NH3 and small
amounts of other gases along with a decomposed mass and
evolution of heat.
 Anaerobic fermentation produces CO2, CH4, H2 and traces of other
gases along with a decomposed mass.
 Aerobic fermentation is used when the main aim is to render the
material hygienic and to recover the plant nutrients for reuse in the
fields. The residue is C, N2, P, K and other nutrients.
 In a biogas plant the main aim is to generate methane and hence
anaerobic digestion is used. Here the complex organic molecule is
broken down to sugar, alcohols, amino acids by acid producing
bacteria. These products are then used to produce methane by
another category of bacteria.

Uses of biogas
 The biogas technology offers an appropriate
technique to convert non-conventional energy into
conventional energy.
 The gas thus produced is a neat, combustible and
pollution-free fuel.
 The technology is simple and appropriate for both
rural and urban areas .
 The plant can be maintained and operated by the
housewife with little training education.

Uses of biogas
 Cooking fuel
 Fuel for lighting
 Fuel for motive power to replace diesel oil
 Enriched organic manure of agriculture and aquaculture
 Manure for mushroom growing
 Manure for seed coating
 Use of light to trap insects at the farm
 To treat human excreta and for pollution control
 The slurry which is the byproduct is used to improve the
soil retention capacity and as organic manure

Development of Fixed dome Biogas plant
 This digester was originally developed and is used in
China.
 It runs on a continuous batch basis. It can digest plant,
human and animal wastes.
 It is usually built below ground level, hence it is easy to
insulate in a cold climate.
 The digester can be built from bricks, cement and sand.
The variable pressure inside the digester was found to
cause no problems in China in the use of the gas.
 The bottom of the gas plant is flat concrete, the digester
has cylindrical wall and the dome is a semi sphere with
the brick masonry.

Designing of Fixed dome type Biogas Plant
The fixed dome plant has four important components:
 Digester (fermentation chamber)
 Gas storage chamber;
 Plant dome; and
 Displacement chambers (Inlet & outlet).

Theoretical equations for designing a biogas
plant
1. D : H : : 1.75 : 1
2. D /H = 1.75
3. D = 1.75 Hd
4. D for the smallest size plant should not be less than 2 mt.
5. Pmax = 90 cm of water column (approx. 900 Kg/m2)
6. Vg = 33% of the daily gas production (corresponds to 8 hours gas
production)
7. Vi = Vo
8. Hm is fixed at 60 cm (600 mm) of waste column (assuming density of
slurry equal to the density of water for Janata plant design) for Janata
plant of 2 to 6 cum capacity.
9. Average gas production per day for 50-60 HRT= 0.04 cum/Kg of fresh
cattle dung.
10. The minimum Hp should be 7cm (7,0 mm) for the smaller size
Janata plant.

Theoretical equations for designing a biogas
plant
Where
Pmax = Maximum allowable gas pressure inside the plant
C = Rated gas production in Cumor the plant
Yg = Daily gas yield / unit from-manure for a given H
D = Diameter of the Digester = Diameter of the “Gas
storage chamber”
H = Total height of the digester including gas storage chamber
Hd = Height of the effective digester (fermentation chamber)
Vd = Volume of digester (fermentation' chamber)
Hg = Height of the "Gas storage chamber"
Vg = Volume of “Gas storage chamber”
Hf = Height of the plant dome
Fd = Daily feed (slurry) to the plant in Lts
HRT = Hydraulic Retention Time
Vi = Volume of inlet displacement chamber
Vo = Volume of outlet displacement chamber
Hm = Height of the displacement chamber
l =Length of the displacement chamber (Inlet or Outlet)
b = Breadth of the displacement chamber (Inlet or outlet)
Hp = Vertical distance (gap) between the ceiling of the Janata plant
dome where the gas outlet pipe is fixed and the lower end of
the discharge opening

Digester Design
The D and H of the Janata plant has to be designed by trial and error in
accordance with the assumption 3 & 4. The total digester of the fixed
dome plant consists of :-
a. Fermentation chamber or the effective digester of the plant and
b. Gas storage chamber.
Both (a) and (b) above are integrated part of each other as explained
in the section of special plant components of a fixed dome plant.

Digester Design
a. Design of the fermentation chamber
Vd = Fd X HRT__________________i
D2
Vd = ---- X Hd ___________________ii
4
4Vd
Hd = ----- ___________________iii
D2
b. Design of the gas storage chamber
Vg = 33% of C
Vg = 0.33 C __________________iv
D2Hg
Vg = -------- __________________v
4
4 Vg
Hg = ------- __________________vi
D2
Total Height of the digester
H = Hd + Hg _______________________vii

Digester Design
If the D/H is not correct as per assumption, take a new
value of D (not less than 2 mts.) for fresh calculation.
This procedure for calculation should be followed till
the D/H is close to 1.75 (or D = 1.75H)

Displacement chamber design
There are two displacement chambers in the fixed dome plant – Inlet
displacement chamber (IPC) and Outlet displacement chamber (ODC)
The IDC is the integral part of the Inlet tank and the ODC is the integral
part of the Outlet tank. The combined volume of both the displacement
chambers (IDC & ODC) is equal to the total volume of the "gas storage
chamber" (GSC) so that the slurry displacement due to biogas
accumulation in the latter is GSC may be accommodated equally in the
former i.e. IDC and ODC.

Displacement chamber design
Therefore Mg = Vi + Vo ______________________ viii
Vg = 2 Vi = 2 Va ___________________ ix
HM = 90 – Hg _____________________ x
Note : For family size fixed dome plants of 2,3,4 & 6 cum capacity, the
value of Hm is fixed as 61 cm (610 mm) for the sake of standardization
in the design; therefore the equation (X) does not hold good for these
four sizes of fixed dome plants
Vi = Vo = Hm x l x b ____________________ xi
By fixing appropriate value of either L or b, the value of other parameter
or the displacement chambers can be calculated from equation (xi)

Plant Dome Design
Hp = 70 mm (minimum as per assumption) __________ xii
Ht = D/45 _______________ xiii
Ht = (Hp + Hm) __________ xiv
Select value of Ht as the greater of the two calculated from equations
(xiii) and (xiv).
Note:
a. From the structural point of view, the minimum height of the dome
(without reinforcement) should be kept as D/4. 5.
b. Ht should always be kept more than Hm to avoid any dogging of gas
outlet pipe due to slurry getting in to it, when there is no gas stored
in the “Gas storage chamber,".
c. For the smallest family size fixed dome plant, the minimum practical
value of Hp would be 70 mm (or 7 cm)

Parameters Affecting Biogas Production

CHAPTER 3:
THERMAL GASIFICATION OF BIOMASS
GASIFIERS
Gasification means converting the solid biomass into
gaseous fuel without leaving any solid carbonaceous
residue. Gasification is carried out by the following two
processes:
 Heating the biomass with limited air or oxygen.
 Heating at high temperature and high pressure in
presence of steam and oxygen.

Gasifier
 It is an equipment to convert various types of biomasses like
wood, agricultural wastes and maize cobs into gases.
 It is a chemical reactor in which various physical and chemical
reactions takes place.
 Gasifier is a air tight closed container.
 There is partial supply of air into the system.
 Biomass kept in the container is ignited. It burns under
partial supply of air.
 Biomass gets dried, heated, pyrolysed, partially oxidized and
reduced as it flows through the gasifier.
 The gas produced in the gasifier is a clean burning fuel. It is
called producer gas

Gasifier
The calorific value of the gas is 950 to 1200 Kcal/m3.
The composition of the producer gas is as follows:
S.no Composition of producer gas Percent by volume base
1 Carbon mono oxide gas 18 to 22%.
2 Hydrogen 13 to 19%.
3 Methane 1 to 5%.
4 Heavier Hydrocarbons 0.2 to 0.4%.
5 Carbon di oxide gas 9 to 12%.
6 Nitrogen 4.5 to 5.5%.
7 Water vapour 4%

Gasifier
Uses of producer gas :
 Petrol engines can be run completely with producer gas.
 Diesel engine can be run with both diesel and producer
gas as dual fuel engine. The producer gas can save the
diesel consumption of the engine by 0 to 80%.
 Producer can be burnt directly in the industrial burners.
Advantages of gasifiers:
 It is easy to operate the gasifier.
 Its maintenance is easy
 It is sturdy in construction.
 It is reliable in operation.

Gasifier
Types of gasifiers according to the air inlet and
gas outlet are as follows:
 Up draught gasifier
 Down draught gasifier
 Cross draught gasifier

Up draught gasifier
 Air enters below the combustion zone.
 Producer gas leaves near the top of the gasifier.
 This type of gasifier is easy to build and operate.
 The gas produced has no ash content but it contains
tar and water vapour because of the fact that the gas
is passing through the unburnt fuel wood.
 Up draught gasifier are suitable for tar free fuels like
charcoal.

Down draught gasifier or concurrent
moving bed gasifer

Down draught gasifier or concurrent
moving bed gasifer
 Air enters at the combustion zone through the air tuyers.
 Combustion of wood takes place in front of the air tuyers.
 Heat produced during combustion pyrolysis the wood fuel and the hot
producer gas is passed downwards.
 Producer gas leaves near the bottom of the gasifier through the grate.
 The volatile material and the tar produced during the combustion moves
down to the reduction zone where they are further heated to become
hydrocarbons and produce ash. The gas produced is nearly clean gas.
 The ash is collected at the bottom. The gas produced is passed through the
ash pit.
 Hence it contains less tar and more ash. These gasifiers are most suitable to
wood and agricultural residues.
 This gasifiers are used to generate electricity up to 10 KW and beyond
which there is geometrical limitation of the gasifier and gas quality.

Cross draught gasifier
 In a cross-flow gasifier the feed moves downwards while the
air is introduced from the side, the gases being withdrawn
from the opposite side of the unit at the same level of air
entry.
 A hot combustion/gasification zone forms around the
entrance of the air, with the pyrolysis and drying zones being
formed higher up in the vessel.
 Ash is removed at the bottom and the temperature of the gas
leaving the unit is about 800-900˚C: as a consequence this
gives low overall energy efficiency for the process and a gas
with high tar content.
 In this type of gasifier, the path length of travel of air into
producer gas is very less. The gas contains more tar.
 This type of gasifiers is not commonly used.

Reactions taking place in a gasifier
C + O2  CO2 + 393800 kJ/kg mol (Combustion)
C + H2O  CO + H2 – 131400 kJ/kg mol (Water gas)
CO + H2O  CO2 + H2 + 41200 kJ/kg mol (water shift reaction)
C + CO2  2CO – 172600 kJ/kg mol (Boudouard reaction)
C + 2H2O  CO2 + 2H2 – 78700 kJ/kg mol
C + 2H2  CH4 + 75000 kJ/kg mol (Methane reaction)

Reactions in a downdraft gasifier

Gasifier
In a gasifier, the composition of the producer
has produced depend upon the following
aspects:
 Temperature distribution within the gasifier
 Average gas residence time in the gasifier
 Mode of air supply in to the gasifier
 Heat loss to the surrounding of the gasifier

Gasifier
Reasons for purifying and cooling the
producer gas before admitting into the engine
cylinder.
 The generated gas contains varying amount of
moisture, dust and char particles and tar
 The gases are also at high temperature

Gasifier
Various processes carried out in a producer
gas cooling and cleaning train are:
 Removal of larger char particles
 Scrubbing of gas to remove the tar
 Cooling the gas
 Removal of moisture
 Removal of fine dust particles

Fluidized Bed Gasifier
 Fluidized bed gasifier is most versatile and any biomass
(including sewage sludge; pulping effluents etc.) can be
gasified using this type of gasifier.
 It provides a means of burning any combustible
material from wet sewage sludge to refuse, with high
efficiency and with minimal pollution.
 At the heart of a fluidized bed combustor is a hot bed of
inert particles which are held in suspension'fluidised'-
by an upward current of air (refer Fig.).
 The calorific value of biomass is not a constraint.
Besides being highly efficient because of high heat
release rates as well as effective heat transfer resulting
from rapid mixing and turbulence within the fluidized
bed, fluidized bed gasifier can handle biomass with
high ash content (for example rice husk).

 Fluidized bed generally contain either inert
material (sand) or reactive material (limestone or
catalyst).
 These aid heat transfer and provide catalytic or gas
clearing action.
 The bed material is kept in fluid state by the rising
column of the gas.
 Normally the operating temperature of the bed is
maintained within the range of 750-950°C, so that
the ash zones do not get heated to its initial
deformation temperature and this prevents
clinkering or slagging.

Advantages of fluidized bed gasifier
 Fuel flexibility and type of fuel with calorific value ranging from 800 to
8000 kcal/kg can be used.
 Good heat storage capacity. The bed has a very high heat storage
capacity to always ensure combustion.
 Quick start up.
 High combustion efficiency.
 High output rate.
 Consistent rate of combustion.
 Usage of fuel with high moisture content.
 Rapid response to fuel input changes.
 Because of the low temperature combustion, corrosion caused by alkali
compounds in ash significantly reduced.
 Require much less boiler plan area than a stoker.
 Uniform temperature throughout the furnace volume.
 Reduced emission of harmful nitrous oxide.
 Sulphur dioxide emission can be reduced to acceptable level with less
expense.
 Operation is as simple as that of an oil fired boiler.

Fuel cleaning and cooling system of fluidized bed
gasifier

 The gasifier produces the producer gas.
 It is hot and contain lot of impurities like ashes.
 Hence there is a need to clean and cool the fuel.
Admission of hot fuel into the engine results in loss
of power produced by the engine.
 Hence; the gas has to be cooled. The impurities
present in the fuel gas will be detrimental to the
operation of engine. Hence, it has to be cleaned

The following has to be removed from the gas:
 Removal of larger char particles
 Scrabbing of gas to remove tar
 Cooling the gas
 Removal of moisture
 Removal of fine dust particles

Pyrolysis of biomass
Pyrolysis is a general term for all processes of
heating or partial combustion of biomass to produce
secondary fuels and chemical products. The input
may be wood, biomass residues, municipal waste or
coal. The products are gases, condensed vapours as
liquids, tars and oils and solids residue as char
(charcoal) and ash.

Traditional charcoal making is pyrolysis adapted
to produce charcoal in which the vapours and gases are
not collected.

 A charcoal kiln is a device which converts wood (cut
into sizes of 200 mm diameter and length in the
order of 500-1000 mm) into charcoal.
 There are three types of kilns to produce charcoal.
They are:
o Earth kiln
o Brick kiln
o Metallic Kiln

Earth kilns
 Earth kilns are heaps of wood covered with a layer of herbs,
grass, leafy biomass and toped with earth to act as
insulation and to control draft (air flow).
 While the kiln is operation, the mass of wood shrinks due to
devolatilization and this has to be made up by covering the
heap with fresh mud to isolate it from the ambient air
entering into the earth kiln.
 Earth kilns can be above ground or in a specially dug pit.
 As a safety measure, the surrounding area must be cleared
and several barrels of water placed in the vicinity.
 Inspection of kilns is needed every 2-3 hours and clear days.
More frequently inspection is needed in windy or rainy
days.
 Earth kilns have a efficiency of 25% and give charcoal yield
above 15% by weight of the biomass input used.
 The types of earth kilns built above the ground level are
horizontal earth kiln, vertical earth kiln and parabolic mud
walled kiln.

Brick kilns
 It give much higher yields (20%) and efficiencies
(35%) in comparison to earth kilns.
 This is because of much superior control of the air
to flue ratio to give the right extent of
devolatilization.

Metallic kilns
 These are internally fired batch type.
 The simplest of these is the drum kiln, which is nothing
but an oil barrel (200 liters capacity) converted into a
kiln by cutting out the bottom, making four holes at
top, two bug holes and two large holes of 150 mm,
Wood layers are packed vertically, leaving a small
space in the centre, which is filled with leaves and twigs
for lighting the fuel.
 The kiln needs continuous monitoring and shaking
every 15-20 minutes. After about 90 minutes, the
wood should be refilled. This should be done three
times.
 White smoke indicates charcoal formation, while black
smoke or clear exhaust indicates that excess
combustion is in progress.

Materials needed
 200L of oil tank
 1m. 4in (Ø) of fiber stone tube
 5 pieces of brick
 Red brick
 Bambou tree
Those materials can be easily
found in many rural areas of
Rwanda

Horizontal drum
kiln
Vinegar
wood(byproduct)

Energetic of a traditional earth kiln
 The kiln is a wood stock in the ground firmly
converted by earth with holes for the escape of flue
gases.
 About 5 tones of wood give about 1.05 tonnes of
charcoal. The average charring temperature is
4000C.
 The kilning operation takes place in about 96 hours.
 When the volume of wood in the kiln shrinks
continuously, earth has to be added to prevent
exposure of the fuel to the atmosphere. The
theoretical heat output is taken as

Q = McCc
= 1050 x 7200
= 75.60 x105
kcal.
Mass of input biomass used in earth kiln is 5 tonnes, that is 5000 Kg.
Mc - Mass of charcoal = 1.05 tonnes 1050 Kg
Cc - Calorific value of charcoal = 7200 Kcal/Kg.
Q - Heat content charcoal produced = 75.60 x105
kcal.

The main losses in the kiln are unburnt volatiles and
thermal energy of the exhaust gas

The heat losses can be reduced in two
ways
 Using the gas as such after cooling and cleaning to
do mechanical work (IC engine or for heating
(burners).
 Condensing the gas: The flue gas from the earth kiln
lose its heat to the atmosphere without any use.

GASIFICATION
 Gasification is pyrolysis adapted to produce fuel
gases
 Gasifiers are designed to produce maximum amount
of producer gas rather than char, volatiles, and
ashes. Gasifiers are also special case of pyrolysis to
produce producer gases.
 Vertical-top loading pyrolysis devices are usually
considered the best. The fuel products are more
convenient clean or transportable than the original
biomass.

GASIFICATION
The efficiency of the pyrolysis unit:

Summary of operating conditions needed
for Pyrolysis plant
 Input biomass should be cleaned so as to remove soil and
metals which are non combustible in the pyrolysis unit.
 Biomass should be dried but complete dry material is
avoided with gasifiers.
 Biomass should be chopped to small size to be used in
pyrolysis plant.
 Air/Biomass fuel ratio during combustion is a critical
parameter affecting both the temperature and the type of
product.
 Pyrolysis units are most easily operated below 6000C.
Higher temperatures of 600 to 10000C, need more
sophistication, but more hydrogen will be produced in
the gas.

Summary of operating conditions needed
for Pyrolysis plant
 Below 6000C there are generally four stages in the
distillation process:
 100 to 1200C: Input biomass material get dried within the
pyrolysis plant.
 120 to 2750C: Output gases produced are N2, CO and CO2;
acetic acid and methanol.
 280 to 3500C: Exothermic reactions occur, driving off
complex mixtures of chemical (ketones, aldehydes, phenol,
esters), CO2, CO, CH4, C2H6 and H2. Certain catalysts, e.g.
ZnCl, enable these reactions to occur at power temperature.
 Above 3500C: All volatile materials s are driven off, a
higher proportion of H2 is formed with CO, and carbon
remains as charcoal with ash residues.

Pyrolysis by gasification products
S.No Type of output obtained
from pyrolysis
Yields per 1000 kg
dry wood
Percent of yield in
pyrolysis
1 Charcoal 300 Kg Mass yield 25 to
35%
2 Gas (Combustion 10465 kJ/m3) 140m3 (NTP) Mass yield 80% in
gasifiers
3 Methyl alcohol 141 Condensed vapours
mass yield is 30%
maximum.
4 Acetic acid 531
5 Esters 81
6 Acetone 31
7 Wood oil and light tar 761
8 Creosote oil (tar) 121
9 Pitch 30 Kg Mass yield 3%

Difference between Direct Combustion and Gasification
of Wood
S.No Particulars Combustion
by earth kiln
Gasification by pyrolysis
plant
1. Principal products H2O, CO2,
traces of CO
CO, H2, CO2, traces of
CH4, C2H2, etc.
2. Permissible moisture in wood Up to 30% Up to 15%
3. Wood feed surface area to volume
ratio,1/m
Up to 30%
150-1700
Up to 15%
500-1000
4. Grate heat release rate, MW/m2
0.10-0.20 0.25-1.0
5. Overall excess air factor for small
sized systems, kg air/kg fuel
2-5 0.2-0.5 kg/kg for
gasification
1.0-1.2 kg/kg of
combustion
6. Overall thermal efficiency,% 30-80 50-75
7. Overall mechanical efficiency, % 10-15 16-20
8. Mechanical power production
rate.
Steam
engines
Diesel and Petrol
engines
9. Processing steps Moisture
removal
Moisture removal, size
reduction, cleaning,
cooling and compression
of product gas.
10. Sensitivity of system to mixing of
wood with other biomass fuels
like basks
Not very
sensitive
Extremely sensitive to
types of woods at times
gasification may be
impossible
11. Particulate carbon in exhaust gas High Low

CHAPTER 5:ETHANOL (ALCOHOL) FROM
BIOMASS
Selection of Raw Material:
 Alcohol is one the renewable energy source. It is a
fuel to run petrol engines.
 It can be used for lighting.
 Any material which is capable of being fermented
by enzymes can serve as a source for alcohol
production

Ethanol from biomass
The three basic types of raw materials for ethanol production are:
 SACCHARINE (sugar containing) materials in which the carbohydrate
(the actual substance from which the alcohol is made) is present in the
form of simple, directly fermentable six and twelve carbon sugar
molecules such as glucose, fructose, and maltose. Such materials include
sugar cane, sugar beets, fruit (fresh or dried), citrus molasses, cane
sorghum, and skim milk.
 STARCHY MATERIALS that contain more complex carbohydrates such
as starch that can be broken down into the simpler six and twelve
carbon sugars by hydrolysis with acid or by the action of enzymes in a
process called malting. Such materials include corn, grain sorghum,
barley, wheat, potatoes, sweet potatoes and so on.
 CELLULOSE MATERIALS such as wood, wood waste, paper, straw, corn
stalks, corn cobs, cotton, etc., which contain material that can be
hydrolyzed with acid, enzymes or otherwise converted into fermentable
sugars called glucose.

Ethanol production from different sources

UNIT OPERATIONS FOR ETHANOL
(ETHYL ALCOHOL) CH3CH20H
 CLEANING
The raw material is cleaned with water to remove mud
and dirt sticking on the outer surface.
 PEELING
 Manual Peeling
The outer skin is removed manually by peeling.

 Chemical Peeling
Peeling can also be done by chemical treatment. The
material is put in hotwater with sodium hydroxide and
then it is washed off by water under pressure to remove the
outer skin.
 CUTTING
After peeling the material is manually cut into chips using
knife.
 CRUSHING
The cut material is ground by mea ns of a hammer mill.

COOKING
The crushed starchy material is cooked for one hour at 2-
3 atmospheric pressure to gelatinize the starch present.
In its native state, starch consists of microscopic partly
crystalline granules in which the amylose and
amylopectin molecules are arranged in complex folded
and ;stratified manner. At ambient temperature these
granules are practically insoluble in water and not very
susceptible in enzymatic hydrolysis. However, when
treated with water the starch granules swell and
gradually ruptured. The amylose and amylopectin
molecules unfolding and dispersing into solution. This
process is referred as gelatinization of starch.

HYDROLYSIS
Hydrolysis is the enzymatic reaction that converts
starch to sugars Hydrolysis is the chemical reaction
involving water and another substance in which the
water molecule is ionized, and the compound
hydrolyzed to split.
It may be done by acid or enzymatic hydrolysis. Acid
hydrolysis is the one step process, in which the
feedstock is mixed with a mild solution of sulphuric
acid. Enzymatic hydrolysis is the process in which the
material is mixed with an enzyme solution.

FERMENTATION
To the hydrolysed material, yeast is added and
aeration is given for yeast multiplication.
Fermentation is the process of conversion of sugars to
enthanol and carbon di oxide.
The Ethyl alcohol is produced in plenty from biomass

Fermentation
 The chemical equations of conversion of starch to
Ethyl alcohol by fermentation are as follows:
Enzyme
C6H10O5 + nH2O  nC6H12O6
Starch Dextrose
Enzyme
(C12H22O11)n + H2O  2C6H12O6
Maltose Dextrose
Yeast
(C6H12O6)n  2C2H5OH + 2CO2
Dextrose Ethyl alcohol Carbon dioxide

Fermentation
Fermentation temperature varies from 20 to 30°C.
Fermentation process is completed in 50 hours.
Alcohol content of the fermented beer is 10 to 20%
depending upon the source of biomass and alcohol
tolerance of yeast.

DISTILLATION
Distillation is a separation process of two or more
liquids in solution that is based on the relative
volatilities and takes advantages of the different
boiling temperature. The fermented liquid mass is
subject to distillation.

CONDENSATION
The distillate is condensed with cold water in a
condensation unit obtain ethanol. Again redistillation
is carried out to obtain ethanol with high
concentration.

Uses of ethanol
 Engine fuel: Ethyl alcohol can be used as an additive to the
petrol in the automobile engines. There should be no traces
of water in alcohol. Absolute alcohol is used for this purpose
is called power alcohol. It is not sufficiently volatile to give
proper starting in cold weather. It is therefore mixed with
petrol. A mixture of 20% of power alcohol and 80% petrol
has been used as engine fuel in many countries as a
substitute of petrol. This mixture is called Gasohol.
 Organic chemicals
 Solvent
 Drugs plastic, lacquers, polishes plasticizers, perfumes
 Liquid detergents, sprays

Flow chart for preparation of alcohol from sweet potato

CHAPTER 6: METHANOL PRODUCTION
Raw Materials
Methanol production from wood involves two stages of
thermo chemical transformation.
The first stage involves gasification of the wood to
produce synthesis gas.
The second stage is the actual synthesis step which
converts synthesis gas to methanol. This step is proven
commercially available process. Gasification has been
the bottleneck to commercialization. Considerable
research and development is required to make the use
of wood more economic than the use of natural gas.
About 2.25 kg of natural gas is required to produce 4
litre of methanol. Similarly 9 kg of dry wood is required
to produce 4 liter of methanol

METHANOL PRODUCTION
Physical properties of Methanol
 Methanol is a clear, colorless liquid that freezes at -
73°C and boils at 65°C.
 It is excellent antifreeze, as it is completely miscible
with water.
 Its octane rating is high and it burns cleaner than
petrol in an internal combustion engine.

METHANOL PRODUCTION
Methanol production from natural gas:
Natural gas is used to produce synthesis gas which is a
mixture of CO and H2. This mixture is reacted under pressure
of 100-200 Kg/cm2 at high temperatures of 250-330°C to
yield methanol in the presence of a suitable catalyst:
CO + 2H2  CH3OH
The methanol-containing gases leaving the converter after the
reaction are cooled to condense the methanol, and the
unreacted gases are recycled. The methanol is then purified by
distillation. Only a small amount of by product is obtained,
including dimethyl ether and higher alcohols. Natural gas has
been used because of cost, convenience and efficiency.

METHANOL PRODUCTION
Methanol production from Biomass:
Any carbon source can be used to make synthesis
gas, It is possible to generate mixture of CO and H2
from coal, wood (including wood wastes) peat or
urban solid wastes.
A drawback to any biomass-to-methanol scheme is
the size of the plant required and the amount of raw
materials needed. The minimum practical plant size
(about 200 tones/day of methanol) required about
500 tones/day of oven-dry wood or equivalent
biomass. Such volumes of biomass are not usually
available at a given site without extensive gathering
and transportation costs

METHANOL PRODUCTION
Gasification of wood
S.N
o
Action Reactions
1 Drying
(1000–
2000C)
Moist wood and heat  Dry wood
and water vapour
2 Pyrolysis
(200 –
5000C)
Dry wood and heat  char + CO +
CO2 + H2 + CH4 +tar and
pyroligneous acids
3 Gasificati
on
>(5000C
Char + O2 + H2O  CO + H2 + CO2

METHANOL PRODUCTION
Composition of final raw gas:
S.No Elements Composition of raw
gas,%
1 H2 18.0
2 CO 22.8
3 CO2 9.2
4 C H4 2.5
5 Hydrocarobons 0.9
6 O2 0.5
7 N2 45.8

METHANOL PRODUCTION
Gas purification and Shift Conversion
 The raw gas is purified to remove all gases except H2
and CO.
 This mixture is reacted with water so that the final gas
mixture contains 2 : 1 ratio of H2 and CO. During the
reaction with water, additional CO2 is formed.
 It should be removed before synthesis. The raw gas is
allowed to cool at 32˚C and it is compressed at a
pressure of 7 Kg/cm2.
 Still some CO2 is formed in the raw gas. It has to be
removed. In the first stage, hot potassium carbonate
solution reduces the CO2 concentration to 300 ppm

METHANOL PRODUCTION
Gas purification and Shift Conversion
 In the second stage, Mono Ethanoloamine (MEA)
reduces the CO2 content to 50 ppm.
 The gas is allowed to pass through a cryogenic system
so as to remove the residual CO2, water vapour,
methane, hydro carbons and nitrogen.
 Thus we get a purified gas of 44% H2 and 56% CO.
Further processing is required to make 2 : 1 ratio of H2
and CO.
 Then the gas is compressed to 28 Kg/cm2 m apart of
CO2 react with water vapor in the presence of iron
catalyst and produces hydrogen.
 The final gas contains 2: 1 ratio of H2 and CO.

METHANOL PRODUCTION
Synthesis gas:
 The synthesis gas is compressed to 140 to 280
Kg/cm2 and then passed methanol synthesis
reactor.
 In the reactor, 95% of the gas is converted to
methanol by using a zinc chromium catalyst. The
unreacted gases are separated for recycling to
produce methanol.

METHANOL PRODUCTION
Uses of methanol
 Methanol can be used as a fuel in engines. It is better
than petrol because of high octane number of the
fuel.
 Methanol is converted in to formaldehyde.
 It is also used as a solvent.
 It is also used as a intermediate chemical in many
processes.

CHAPTER 8: VERMICULTURE
 As the name indicates, vermiculture means artificial raring or
cultivation of worms (earth worms) and the technology is the
scientific process of using them for the betterment of human
beings.
 Vermi-compost is the excreta of earth worms, which is rich in
humus.
 Farm waste, house waste and non toxic solid and liquid industrial
waste etc can be converted in compost by earth worms. Earth
worms eat them and pass it through their body and in the process
convert it into vermi compost.
 Thus, it is understandable that earth worms not only convert
garbage into gold but keep the environment health.
 Earth worms are natural bio reactors that do not require fossil
fuel to be operated.
 Conversion of garbage by earth worms into compost and the
multiplication of earth worm are simple processes and can be
easily handled by any layman in the village.

Earth worms
 Earth worms are tiny creature which like dark moist environment.
It breaths through skin.It cnot tolerate solar light and if exposed,
may die in few minutes. It may live for 4 to 5 years. The optimum
temperature for breeding is 14ºC to 27º C. The grown up weighs
about one gram and produce one gram excreta daily.
 Under ideal circumstances, the worm’s population can double his
size in a month.
 Californian red worms get coupled regularly every 7 days depositing
one cocoon each one.
 Under ideal circumstances, can produce 20 new worms from each
cocoon.
 The new worms will get their sexual maturation at the age of two
months, and they'll get coupled every 7 days for the rest of their
life.

Earth worms
Earth worms Vermiculture unit in ISAE

Earth worms
Preparation of Bed
 First of all 1.5 m wide and 6.6 m long shed made of
bamboo/ wood and straw is erected.
 It should be high enough to human entrance for
watering.
 Under this shed dried grass of 10 cm thickness are
spread on the ground, there after a layer of 6 inches
of well rotten FYM is placed over it.
 This layer needs thorough watering then it is kept as
such for 48 hours.

Earth worms
 Now some earth worms (1000 worms/m²) are put
into it, about 20 cm thick layer of garbage, cow dung,
farm waste or city waste except pieces of glasses,
metal and plastics are placed and watering is done
above it.
 It needs watering every day to remain sufficiently
moist (50-60%). During dry season 2 watering, per
day are required. After 30 days garbage is turned up
and down and again kept on watering for next 30
days.

Earth worms
Precautions for Compost making
 Moisture level in the bed should not exceed 50 – 60 % water
logged in the bed leads to anaerobic condition and change in pH
of medium hampers normal activities of worms leading to weight
loss and worm biomass and population,
 Temperature of bed should be within the range of 20 – 30 degree
centigrade;
 Worms should not be injured during handling,
 Bed should be protected from predators like red ants, white ants,
centipedes and others like toads, rats, cats, poultry birds etc.
 Frequent observation of culture bed is essential as accumulated
casts retards growth of worms.
 Space is the criteria for growth and establishment of culture;
space required is 2 square metes per 2000 worms with 30 – 45
cm of bed.
 Earth worms find it difficult to adapt themselves in new
environment hence addition of inocular as a bait from earlier
habitat helps in adaptation to new site of raring.

Vermicomposting
Compost Harvesting
 After two months of composting a sheet of plastic is spread on
open ground and the decomposed garbage is transferred on it. It
is kept open on sunny day for about 5 -6 hours without watering.
 The earth worms are sensitive to heat, light and dry condition,
hence they will settle down inside for protection. Now the upper
layer is removed. This is vermin-compost.
 One may use a sieve to separate earth worm from the compost. It
is observed that 40% of the garbage that are fed to earth worm
converted into compost and the population of earth worm is
doubled. One can erect another shed and thus repeat the process
further for more production of compost.
 The species that is used for conversion of garbage is called Eisenia
foetede, essentially a surface feeds.

Vermicomposting
Use of Vermicompost
 The final product (vermicompost) can be used directly on
farms and in the pots. The vermi-compost is 5 times
richer in N , 7 times richer in P, 11 times richer in K, 2
times in Mg, 2 times richer in Ca and 7 times richer in
actionomy-cites than the ordinary soil; Besides it
contains valuable vitamins, enzymes and hormones like
gibberellins. It can be used in following doses:
 For horticulture crops 100 – 200 gm per tree
 For forest tree 100 – 200 gm per tree
 For raising crop 2 tones per ha
 For kitchen garden and pots 50 gm per pot

Vermicomposting
Earth worm can directly be placed near the stem /
trunk of horticultural trees @ 100 -200 worms per tree
and 10 – 15 litres of water per hectares in the field that
has sufficient moisture all year.

CHAPTER 9
AEROBIC AND ANAEROBIC BIOCONVERSION
SYSTEMS
Composting Methods
 From time immemorial it has been known that decaying organic
wastes improve the fertility of the soil.
 The accumulation of raw sewage is increasing in every city in
addition to city refuses like garbages.
 In the farm, animal wastes and crop residues are accumulating.
 However, as raw material these agricultural and city refuses cannot
be used as organic manures because of high C/N ratio and having
highly resistant. lignin like materials, other cellulose and
hemicelluloses.
 Varying factors influence the maturity of the composts and also the
rapidity and nutrient status of the composts.
 Different methods of biodegradation and composting are available
for adoption depending on the source of material available and
other facilities present in the farm.

FACTORS INFLUENCING COMPOSTING
In nature there are many internal and external factors
affecting the rapidity of compost making. The nature
of material to be composted influences greatly than the
other factors.

AEROBIC AND ANAEROBIC
BIOCONVERSION SYSTEMS
Composition of waste materials:
The important factor in the type of waste material to be
converted into compost is its nutrient composition.
Generally the microorganisms act on these nutrients for
biodegradation. The carbon nitrogen ratio of the waste
material influences significantly. The rate of
decomposition of organic matter of the waste depends on
the amounts of carbon and nitrogen present. The C:N ratio
of the biomass is in the order of 30:1 and it is an ideal ratio
for the organic wastes to undergo biodegradation.
However, in nature many of the organic wastes available
are having a wider C:N ratio than this. The microbes
utilizes the carbon of wastes as energy source and nitrogen
for their body cell build up.

Composition of waste materials
 During this process the C:N ratio is narrowed down. Because
the carbon is degraded to gaseous carbon dioxide whereas N
remains in the compost itself as part of microbial tissues. This
process proceeds slowly and depending on the C:N ratio the
time taken varied widely. Wider the C:N ratio greater the time
it takes for getting a finished compost.
 When we use wider C:N ratio materials like rice straw, wheat
straw, sugarcane trash, leaf litter coir pith etc., it is advisable
to mix these wastes with either FYM slurry or biogas slurry or
green manure or legume green leaf manure or even limited
application of nitrogenous fertilizers to narrow down the C:N
ratio, i.e. optimum for quicker degradation.

Composition of waste materials
 The time required for composting is reduced by the addition of the
above materials.
 Carbon: Phosphorus ratio optimum for better microbial activity is
100:1. Whenever waste materials having wider C:P ratio are to be
composted it is recommended to apply phosphate fertilizer to
narrow down the C:P ratio for quick degradation of the material and
for conservation of nutrients. Compositions of some of the waste
materials available in and around farm area are given in Table 8.1
 In addition to C, N and P other nutrients like K, Ca, Mg, Na, S, Fe,
Zn, Co etc are also needed for the microbial degradation. However,
these nutrients are present in the waste materials to the required
extent and have not created problem of external addition for
composting.

Size of the waste materials:
The size of waste materials must be reduced to small
pieces of about 5 cm to 10 cm length to provide higher
surface area when the microbes can easily attack on
these materials.

Moisture content:
 There must be optimum moisture for quick degradation of the
organic wastes.
 In general organics contain sufficient amount of moisture.
While mixing for composting wet and dry materials can be
mixed together to get a balanced moisture.
 Moisture to the level of field capacity is optimum. If the
materials contains higher moisture we can mix it with soil or
saw dust to reduce the moisture per cent. When the moisture
content is in excess adequate per cent.
 When the moisture content is in excess adequate turning can
be given at intervals to reduce the moisture content and to
increase aerobic decomposition.
 About 40 to 50 per cent moisture is ideal to be maintained.

Aeration:
 Adequate supply of gaseous oxygen is necessary
specially for aerobic decomposition.
 In the absence of oxygen anaerobic decomposition
will dominate with the survival of anaerobic
microorganisms.
 Aeration is an important factor for proper
decomposition.
 Turning of the compost/manure pits is carried out
for providing aerobic decomposition.

Type Source Nutrient content (%)
N P2O5 K2O
Animal
Oil cake
Crop
Weeds
Industrial wastes
Cattle dung
Cattle urine
Sheap and goat dung
Night soil
Human urine
Leather waste
Hair and wool waste
Horn and hoof wastes
Castor
Coconut
Cotton seed
Groundnut
Neem
Niger
Mahua
Rapeseed
Safflower
Sesame
Rice straw
Wheat straw
Sorghum
Pearl millet
Maize
Pulses
Sugarcane trash
Banana stem
Water hyacinth
Parthenium
Ipomoea
Legume weeds
Coir pith
Pressmud
Seaweed residue
Cotton mill waste
Bagasse
Saw dust
Sewage sludge
0.40
0.80
0.65
1.5
1.2
7.0
12.3
12.5
5.8
3.2
6.5
7.8
5.2
4.8
2.6
5.1
7.8
6.2
0.58
0.49
0.40
0.65
0.59
1.60
0.35
0.11
1.79
1.43
1.31
2.00
0.26
1.15
1.50
1.40
0.25
0.25
1.50
0.15
0.02
0.50
0.8
0.2
0.1
0.1
7.5
1.8
1.8
2.8
1.7
1.0
1.8
0.8
1.8
2.2
2.0
0.23
0.25
0.23
0.75
0.31
0.15
0,04
0.26
0.28
0.29
0.35
0.17
0.05
2,40
0.50
0.60
0.12
0.20
2.00
0.20
0.70
0.20
0.5
0.3
0.2
0.3
1.2
1.0
1.7
2.1
1.4
1.4
1.3
1.8
1.0
2.0
1.2
1.66
1.28
2.17
2.50
1.31
2.00
0.50
0.43
0.43
0.74
0.55
1.70
0.84
1.98
4.20
1.20
0.40
-
1.50

Temperature:
 During decomposition of organic waste considerable
amount of heat is developed. Initially mesophilic
microorganisms dominate in the decomposition with
temperature below 40˚C. As the temperature
increases subsequently above 40˚C the thermophilic
microorganisms dominate.
 If the moisture is maintained at optimum level the
temperature will not rise above 50˚C. At higher
temperatures the pathogenic organisms and weed
seeds are destroyed.

Reaction:
 In general, the reaction of the composting medium will
be near neutral.
 It may fall down to slight acetic range during
decomposition due to release of organic acids by
microbes.
 The pH may rise to slight alkaline range when the
maturity of the compost is attained. When the pH rises to
alkaline range there is the possibility of loss of nitrogen
in the form of ammonia volatilization.
 Therefore, the pH is to be maintained at slightly acidic to
near neutral level.

Micro Organisms:
 In the early stage of composting fungi and acid producing
bacteria dominate. It is the mesophilic stage.
 As the temperature increases above 40˚C thermophilic
bacteria, actinomycetes and fungi dominate.
 Mesophilic organisms act on readily degradable
carbohydrates and proteins. Actinomycetes degrade water
soluble fractions.
 Thermophilic bacteria attack on protein, lipids, and
hemicelluloses. Thermophilic fungi acts on cellulose and
lignin.
 Depending upon the type of organic waste materials to be
degraded the appropriate micro-organisms are inoculated.

Blending materials:
 When the organic waste to be composed has a wide C/N
ratio, then the material is to be supplemented with a
narrow C/N ratio materials like leguminous plants, water
hyacinth, biogas slurry etc.
 Depending upon the necessity urea or ammonium
sulphate or other nitrogenous materials can also be
added.
 When wet materials are to be composed, they are mixed
with dry materials like dry soil also to reduce moisture
and to absorb the released ammonia. Phosphate is also
added for hastening the composting process.

METHODS OF COMPOSTING
There are:
 Indore method of composting farm wastes
 Bangalore Methods of Composting
 Sugarcane trash composting
 Biodegradation of weeds
The students will be able to explain these different
methods of composting

Bioenergy conversion lecture notes

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