Bio Gas From Distillery Spent Wash
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Transcript of Bio Gas From Distillery Spent Wash
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INTRODUCTION
In present scenario the cost of conventional energy is increasing day by day
and demand for such energy sources is also rising so it has become necessary to
utilizing bio-gas as a fuel for domestic and industrial purpose is the most
economical reliable and time tested method for conserving energy.
Bio gas is also known as swamp gas sewer gas fuel gas, marsh gas, wet gas
and in India more commonly as gobar gas. Bio-gas consists of 60-65% methane
(CH4), 35-40%. Carbon dioxide (CO2) and traces of hydrogen sulfide (H2S)
ammonia (NH3).
1.1 HISTORICAL BACKGROUND OF BIOMETHANATION
The first person to observe the phenomenon of Biomethanation was
ALESSONDRO VOLTA of Italy was back to 1776 he wrote to a friend to that
consumables air was being produced continuously in lakes and ponds in the
variety of Como in northern Italy. Volta observed that when he distributed the
bottom sediment of the lake, bubbles of gas would rise to surface. He also noticed
that more bubbles come of when sediment contains more plant material.
In 1806 William Henry showed that Volta’s gas was identical with methane
gas was identical with methane gas. Humphrey Davy in the early 1800’s observed
that methane was present in farmyard manure pieces. In 1808 Davy conducted the
first laboratory experiment to produce methane by anaerobic fermentation was
wasted. In the initial periods anaerobic fermentation was carried out mainly as a
municipal waste treatment process and energy recovery has not of primary
concern. In 1895 biogas from a waste treatment plant in extra. In England was
collected and use to light nearly streets.
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The interest in biogas reserve further fill up during second world war.
French scientists to particular interest in advocating gas technology in French
colonies in Africa. During this period fuel Starred French and Germans used
biogas as a fuel for vehicles and farm tractors. Followed the war several nation
such as UK, USA, CANADA, RUSSIA, China, Kenya, Uganda, S.A. and India
showed interest in Biomethanation.
Broker 1956 postulated that anaerobic digestion is two step of multistep
biological process. Kirsch and Sakes 1971 elaborated Barkers postulate and
suggested involvement of two stage conversion of organic matter to methane. The
concept of two stage anaerobic digestions was modified by meinorney and Bryant
(1981) suggested three steps anaerobic digestion is now considered as balanced
three stage process in which three group of micro organisms work.
However series of energy crisis which rocked the world from 1973 onwards
coupled with concern for environment. Protection interest in Biomethanation.
1.2 BIOENERGY
India predominantly has on agricultural population with about 70% people
living in village the development of village depends to a great extent on the
availability of the energy. The potentiality of use of biogas as a suitable energy
alternative requires vital importance.
The importance and utility of biogas in our country can be extracted from
the fact that the cattle population in India is nearly 287 million assuming the avg.
wet drug obtained per day to be 10 Kg. and the collection rate of 66% the total
availability of cow drug would be 575 million tones per annum. This it self would
enable production of 22, 425 million m2 of biogas which can replace oil to an
extent of 13,900 million liters apart from which manure which is also obtained and
as per rough estimate 200 million tones of organic manure per annum will be
obtained.
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1.2.1 Bio energy from Solid Wastes
If all solid wastes are collected and used as a fuel it can supply about more
than 10% of the total requirements. Urban wastes include household, sewage, and
commercial, institutional.
Manufacturing plants and demolition wastes. Agricultural wastes include
animal manure, crop waste and forest and hogging residues. The only available
wastes in this sector are those animal waste generated on large feed lots and
diaries and the portion of those crop wastes i.e. biogases and fruit tree pruaings not
readily required back to the soil
The various sources to obtain biomass for production of bio energy are
numerous. However, they can broadly be categorized in following main heads.
1. Agricultural Wastes
2. Community Wastes
3. Animal Wastes
4. Industrial Wastes
1.3 FEW STORIES FROM WASTE TO ENERGY
1. Bio gas from wastewater at starch and Glucose mfg. unit
Versa Biotek ltd, samalokot in A.P. produces starch and liquid glucose
from about 40,000 metric tones of maize and about 25,000 metric tones of
tapioca tuber, per annum. The process also generates about 1600 cum per day
liquid waste. A Biomethanation plat based on up flow Anaerobic sludge
Blanket secondary treatment has been installed for treating the waste water.
The Biomethanation plant has been generating about 8000 cum. Biogas
everyday for the last one year. The biogas is not only leading to substantial
saving in cost of fuel in the boiler but also results in large saving on cost of
chemicals, which were required for wastewater treatment prior to installation
of this project the payback period of this project works out to about four years.
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2. Power from Biogas at Distillery
About 12000cum biogas per day being produced from Bio methanation
plants installed for treating distillery Wastewater (Spent wash) at K.M. sugar
mills (Distillery) Faziabad, U.P. is being utilized for generating power through
the steam turbine route for meeting the total electricity requirement of their
distillery as well as that of their residential colony. The project has been
performing satisfactorily for last four years and has been generating an avg. of
about 4 lakh units of electricity every month. The payback period for such a
project works out to be about 3 - 4 years.
3. Power from Biogas
About 21000 cum. Biogas per day being produced from Biomethanation
plants treating distillery wastewater (spent wash) at kanoria chemicals and
industries Ltd. Ankelshwar, Gujarat is being utilized from generation of power
required for their captive use. The project is based on two internal combustion
energies fuelled of own biogas, each of 1.003 cum capacity. The waste heat of
the flue gases of the engines, which is at a temp of more the 5000C, is also
being utilized for generation of about 1.5 tones per hour steam at about 1300C.
The steam is used for meeting process heat requirement. A H2S removal plant
based on a bio-chemical terminology has also been installed to avoid the
corrosion of biogas engines. The project has been performing satisfactory for
the last three years and generating about 10 lakh units of electricity every
month. The payback period of this project works out is about 3 years.
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4. Biogas from Slaughterhouse Wastes:
Alkabeer exports Ltd. (AKEL) hare an integrated meat processing unit at
rudraram village in medak dist. Of A.P. solid and liquid and liquid waste being
generated during slaughtering and processing of meat is being treated through
Biomethanation plants. While about 2000cubm. Biogas is being generated
from liquid wastes thus reducing the COD content by 75-80% and BOD
content and 85-90%; about 2500 cum. Biogas is being generated from solid
wastes. Adoption of biomethanation technology has resulted in saving of
furnace oil as well as chemicals used for treatment of wastewater. The sludge
from the anaerobic digester is dried and is being marketed as a nutrient rich
soil conditioner.
5. Biogas from Tannery Wastes
In India have about 1600 tanneries with total processing capacity of 0.7
million tones of raw hide and skies. Fleshing and sludge are the two wastes
emanating from tannery and treatment of tannery wastewater. A project for
demonstration of application of Biomethanation technology for treatment of
tannery fishing and sludge from tannery effluent treatment plant has been set
up at Visharam tanner’s environmental system, Melvisharam, Tamilnadu. The
plant has been designed to handle about 3 tones of tannery fleshing and 2 tones
of primary tannery fleshing and 2 tones of primary sludge from. The generated
biogas is then used for generation of electricity in a dual fuel engine.
1.4 Pollution from Distilleries
Distillery wastewater posses a serious threat to water quality in several
regions of the country lowering of PH value of the stream, increase in organic load,
depletion of oxygen content, destruction of aquatic life and bad smell are some of
the major pollution problems due to distillery wastewater. The high BOD causes
depletion of dissolved oxygen and proves very harmful to aquatic life. In some
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cases, particularly in Maharashtra the colour problem in groundwater is so acute
that distilleries have to provide separately potable water to surrounding villages.
Indian standards for disposal of industrial effluent (4)
Sr.No Characteristics Tolerance limit for effluent discharge
In to land
surface
IS: 2490 1974
In to public
sewers
IS: 3306 1974
On land for
irrigation
IS: 3306 1965
1. BOD (mg/lit.) 30 500 500
2. COD (mg/lit.) 250 - 5.0-9.0
3. PH 5.5-9.0 5.5-9.0 5.5-9.0
4. Suspended solids/L. 100 600 -
5. Total dissolved solid
(mg/lit.) - 2100 2100
6. Oil and grease (mg/lit.) 10 100 30
7. Sulphide (mg/lit.) 2 - -
8. Chloride (mg/lit.) - 600 600
9. Sulphate (mg/lit.) - 1000 1000
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TREATMENT OF DISTILLERY EFFLUENT
2.1 COMPOSITION OF SPENT WASH (6)
The distillery wastewater known as spent wash is characterized in its color,
high temp, low PH, high ash content and contains high percentage of dissolved
organic and inorganic matter of which 50% may be present as reducing sugars.
It contains about 90-93% water and 7-10% solids, sugar being 2-20% and
protein 10-11% in the dry spent wash. The metals present in spent wash are Fe –
348mg/lit. Mn – 12.7 mg/lit, Zn – 4.61 mg/lit. With Cu – 3.65mg/lit., Cr – 0.64
mg/lit. , Cd – 0.48mg/lit., Co – 0.08 mg/lit. With electrical conductivity in the
range of 15-23ds m-1
.
Indian spent wash contains very high amounts of potassium calcium,
chloride, sulphate compared to spent wash in other countries. Organic compounds
extracted from spent wash using alkaline reagents are of humic in nature. Similar
to those found in the soil excepting that fulvic acid predominates over humic acid.
Indicative spent wash quality of typical sugarcane molecules based distillery
in India (6)
Sr. No. Parameter Units Concentration Range
1. Color - Dark brown
2. Odor - Sugar smell
3. Temperature 0C 80-90
4. P.H. 4 – 5
5. Total solid mg/lit 52000 - 86000
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6. Total suspended
solid mg/lit 3000-5000
7. Total volatile
solid mg/lit 40000-60000
8. BOD mg/lit 30000-70000
9. COD mg/lit 65000-130000
10. Chlorides (Cl) mg/lit 1000-1500
11. Sodium (Na) mg/lit 40000-60000
12. Calcium (Ca) mg/lit 2000-3500
13. Potassium (K) mg/lit 8000-11000
2.2 TREATMENT OF DISTILLERY EFFLUENT
The characteristics of spent wash do not allow in discharge into a water
body, hence it requires treatment physiochemical treatment such as sedimentation
with the addition of coagulant and other additives such as alum, lime, ferric
chloride, activated charcoal etc. have been found to be unsatisfactory, only the
biological treatments are most often found to be effective which are amply
demonstrated by adoption of these methods by all the distilleries. Despite
installing huge anaerobic lagoons, aeration tanks and solar drying pits, the
problems of pollution control in cane molasses distilleries in India have not been
solved yet therefore, severe water pollution problems in the nearly rivers and lakes
are frequently encountered as the partially treated effluents find access to water
bodies.
Land disposal of effluent could also be thought as on alternate for reducing
pollution, as its application in agricultural fields improves almost all factors
involved in soil fertility and provides condition for nitrogen assimilatory into the
soil. This is the most important effect leading to increases in yield and quality of
crops. These observations bear significance from the point of view of status of
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distilleries in India and their impact on the Agri-environment, many distilleries in
India are following their effluent for application on land as direct irrigation water,
spent wash cake and spent-wash press mud compost.
2.3 ALTERNATIVE TREATMENT METHODS FOR WASTE WATER (3)
Distillery waste treatment can be Classified into four groups
1. Biogas generation of about 25 lit of biogas can be produced per lit of Spent
wash.
2. Potash recovery – About 44 tones of K2SO4 per day can be produced from
2,30,000 Gallons of spent wash.
3. Production of Yeast as an animal feed from spent wash.
4. Treatment for removal of organics for water pollution control.
The alternatives for treatment of distillery spent wash may be identified as
solar drying, Ammonification and nitrification process, incineration, potash
recovery, anaerobic lagoon, anaerobic filter, up flow anaerobic sludge blanket
reactor, up flow blanket filter, anaerobic fluidized bed, acid-methane segregation
process.
2.3.1 Solar Drying
Spent wash is dried in open shallow pits and needs large surface area
sediment can be recovered and used for fertilizer, these is no scope for energy
recovery and causes water pollution problem.
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2.3.2 Ammonification and Nitrification Process
This process is dependent on Ammonification and nitrifying bacteria which
are sensitive, slow growing, Temperature and PH dependent.
2.3.3 Incineration
This is direct wet catalytic combustion process and causes air pollution
problem.
2.3.4 Potash Recovery
It uses multiple effect evaporators with incinerator. But it is
cost intensive and consume lot of energy.
2.3.5 Anaerobic Lagoon
The treatment from the anaerobic lagoon is not very effective and
requires large area of land as the residence time is very high the reduction in BOD,
COD level of waste water is not more than 80% even with residence time of more
than 3 months.
2.3.6 Anaerobic Filter
Anaerobic filter is the first innovative reactor developed in 1969 Lat Young
and Mc carty. It contains insert packing material to support bio-film development.
The process found potential application for treatment of dilute soluble waste
water. Waste water in an anaerobic filter was carried out at 4-8 days HRT and 5-
16Kg. COD per m3 organic loading the COD removal of more than 80% was
found at an avg. loading 12.5Kg. COD per m3 at 5 days HRT.
Few full scale anaerobic filter plants installed in sugar industries in India
for the treatment at combined sugar mill waste water.
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2.3.7 Up flow Anaerobic Sludge Blanket Reactor (USAB) (5)
Up flow anaerobic sludge blanket reader was developed in the Netherlands
with unique features of biomass Immobilization, without supporting media. The
reactor was extensively evaluated in laboratory, pilot and full scale plant mainly
with sugar industry waste water in these studies both single and two phase mode
of digestion.
Bio methanation of cane-sugar waste water has been examined in
laboratory scale USAB reactor. The process was how to satisfactorily handle
organic loading up to 13 Kg. corresponding to 4 HRT. The COD removal of above
90% was achieved. The biogas production as high as 0.5m3/kg. COD applied was
achieved with methane content of 70-75% . The reactor was maintained at 30oC
temp.
2.3.8 Up-flow Blanket Filter(5)
The up-flow blanket filter which is a hybrid reactor mode by combining on
up-flow anaerobic sludge blanket and anaerobic filter has recently been evolved.
Plastic ring floating in the top third of the reactor 2/3rd
volume occupied and
USAB system. The reactor was operated as 27oC for treatment of sugar waste
water at loading rates varying from 5-51kg COD/m3d were obtained the filter at
the top of reactor was found very efficient in retaining biomass.
2.3.9 Acid – Methane Segregation Process
This is modified version of anaerobic activated sludge process in which
acid and methane formed are separated. It is more efficient than anaerobic
activated sludge process because of low HRT.
If is more efficient for energy recovery provided, the symbolic relationship
between two organisms (acid and methane forms) is clearly understood.
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2.3.10 Anaerobic fluidized Bed
In this treatment waste water is mixed with an approximate amount of
recycled effluent and introduced at the bottom of a column with sand particle (0.3-
0.4mm) at a rate sufficient to fluidize the medium.
It is more suitable treatment of soluble waste. Sufficient power input may
be require maintaining fluidization.
2.4 COMPARISON OF AEROBIC AND ANAEROBIC AND PROCESS (1)
Aerobic Process Anaerobic Process
• Short detention time
• Compact Plant
• Costly
• High power requirement
• Nearly complete treatment
• CO2 and biomass produced
• Large amount of sludge
produced
• More nutrient required
• Very long detention time
• Very large area required
• Usually cheap
• Low power requirement
• Particle treatment
• Usually CH4 produced in
addition to CO2
• Less sludge production
• Less nutrient required
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3
PROCESS SELECTION
3.1 METHODS FOR OBTAINING ENERGY FROM INDSUTRIAL
WASTE
1) Anaerobic digestion / Biomethanation
2) Landfill Gas Recovery
3) Incineration
4) Densification / Pelletization
5) Other Techniques
3.1.1 ANAEROBIC DIGESTION / BIOMETHANATION (9)
In this process, organic fraction of the wastes is segregated and fed to a
closed container (Biogas digester) where, in the presence of Methanogenic
bacteria and under anaerobic conditions, it undergoes bio-degradation producing
methane rich biogas and effluent biogas consists of methane, CO2, small quantities
of NH3 and H2S and has a C.V. of above 5000 Kcal/m3. Depending upon waste
composition, the biogas production ranges from 50-150 m3/tonne of wastes.
The sludge from anaerobic digestion, after stabilization can be used as a
soil conditioner or as manure depending upon its composition.
a) Biomethanation
Methanogenous is a microbiological phenomenon associated in the
breakdown of the complex organic matters to methane, CO2 and water in the
absence of oxygen. This microbiological phenomenon how lead to an industrial
process called Biomethanation by which a large part of energy from waste organic
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materials are converted to energy rich biogas. The formation of methane has key
role in Methanogenesis because it is related directly to the COD reduction of the
waste.
The Biomethanation of industrial waste water is more attractive because it
provides a compact and economical treatment process requiring no creation
producing only minimum quantities of excess sludge and generating a gaseous
fuel of significant commercial value.
b) Biological Process of Methanogenesis (7)
The biological process of Methanogenesis is currently recognized as 3 stage
degradation of complex organic materials. The organic compound present in sugar
mill waste water is sucrose which is readily amenable to Methanogenesis. The
sucrose is first hydrolyzed in to their monomers, glucose and fructose by extra
cellular enzymes produced by fermentative bacteria. The monomers molecules are
the basic substrate of fermentative organisms for energy assimilation required for
cell growth and maintenance. The major route of fermentative or sugar is via
pyruvic acid formation in the reaction, hydrogen is also produced from
dehydrogenation of pyruvate. A number of bacterial species, called obligate proton
reducing on acetogenic bacterial oxidize the higher fatty acids to acetic acid and
hydrogen.
Methane is formed from acetic acid by Acetoclastic Mathenogenis and
from CO2, H2 , by Hydrogenoclastic Methanogenation in Methanogensis 70% of
the methane come from Decarboxylation of acetate which 30% derived from
hydrogen and Carbondioxide.
Methane can also be formed from methanol and formic acid in small
quantity which have little practical significance. The formation of methane from
acetate and CO2/H2 proceeds according to the following reaction.
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CH3COO + H2O � CH4 + HCO3
CO2 + 4H2 � CH4 + 2H2O
The Methanogensis under normal conditions, proceeds mainly via the
acetate and hydrogen route to methane. But whenever unstable condition arises
due to accumulation of Hydrogen, the bacteria will adopt an alternative strategy by
the formation of higher fatty acids. The accumulation of these higher Fatty acids in
mixed liquor leads to the final Methanogensis more and more inhabited.
Also when the PH of mixed liquor drops below the acid forming bacterial
may supplant the Methanogenic bacteria and acetate buildup will occur.
c) Features of Process
The process developed is based on concepts of phase separation having the
methane reactor configuration as hybrid i.e. up-flow blanket filter (UBF) the phase
separation was chosen because of the obvious advantages in controlling the
operational parameters by providing a selective environment for Acidogens and
Methanogens separately. The USAB design of reactor normally employed for
anaerobic digestion of other effluents is not suitable for distillery effluents, owing
to the poor granulation of biomass and subsequently its wash out from the bed
reactor particularly having the matrix of high voltage and above becomes
extremely expansion, this is particularly not feasible for very high effluent
generations unit like distillery.
d) Advantages of Anaerobic Digestion / Biomethanation
1. Generation of gaseous fuel.
2. Can be done on a small scale.
3. No external power requirement like aerobic treatment.
4. Enclosed system enables all the gas produced to be collected for use. Green
house gases emission to the atmosphere is avoided.
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5. Free from bad order, rodent and fly menace, visible pollution and social
resistance.
6. Modular construction of plant and closed treatment needs less land area.
7. Production of biogas and high grade soil conditioner.
e) Disadvantages
1. In case of digesters operated under Mesophilic temperatures, Destruction
of pathogenic organisms may be less than that in Aerobic composing.
However several digester systems operated. At high Thermophlic
temperatures are also available.
2. It is more capital intensive compared to compositions and
3. Land fills.
4. Not suitable for wastes containing less biodegradable matter.
3.1.2 LANDFILL GAS RECOVERY (9)
The waste deposited in a landfill gets subjected, over a period of time, to
anaerobic conditions and its organic fraction gets slowly volatilized and
decomposed, leading to production of landfill gas which contains a high
percentage of methane (50%).
Typically, production of landfill gas starts within a few months after
disposal of wastes and generally last for 10 years of even more depending upon
mainly the composition of wastes and availability of moisture. As the gas has a
calorific value of around 4500 K cal/m3 , it can be used as source of energy either
for direct heating/cooking applications or to generate power through IC engines of
turbines.
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Advantages of landfill Gas Recovery
1. Low cost means for waste disposal.
2. The gas can be utilized for power generation or as domestic fuel.
Disadvantages
1. Insufficient gas recovery process yielding only 30-40% of the total amount
of gas actually generated. Balance gas escapes to the atmosphere.
(Significant source of two major green house gases, carbon dioxide and
methane).
2. Utilization of methane may not be feasible for remote sites.
3. Cost of pre-treatment to upgrade the gas may be high.
4. Explosion may occur due to possible buildup of methane concentrations in
atmosphere.
3.1.3 INCINERATION (9)
It is the process of direct burning of wastes in the presence of excess air
(oxygen) at high temperature (about 8000C) liberating heat energy, inert gases and
ash. Net energy yield depends upon the density and composition of waste,
percentage of moisture and inset materials which add to the heat loss, ignition
temperature, size and shape for the constituents, etc. combustion results in transfer
of 65-80% of the heat content of the organic matter into hot air, steam and hot
water.
Advantages of Incineration
1. Suitable for high calorific value waste (paper), plastics, hospital wastes etc.
2. Units with continuous feed and high throughput can set up.
3. Thermal energy recovery for direct heating / power generation.
4. Relatively noiseless and odorless.
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5. Low land area requirement.
6. Can be located within city limits, reducing cost of waste transportation.
7. Hygienic.
Disadvantages
1. Least suitable for high moisture contently low C.V. wastes and chlorinated
wastes.
2. Excessive moisture and inert content in waste affects net energy recovery.
Auxiliary fuel support may be necessary to sustain combustion.
3. Toxic metals may concentrate in ash.
4. In addition to particulates, chlorinated compounds ranging from HCL to
Organic compounds such as dioxins, and heavy metals are a cause of
concern, which requires elaborate pollution control equipment.
5. High capital and organization and management cost.
3.1.4 DENSIFICATION (9)
Densification involves the process of segregating, crushing, and mixing
high and low heat value organic waste material and solidifying the same to
produce fuel pallets or briquettes, also referred to as Refuse Derived Fuel (RDF).
This can be conveniently stored and transported and used as s Supplementary fuel
for combustion process and utility boilers. The calorific value of RDF is about
4000 Kcal/kg. And it depends upon the content of combustion organic materials in
the waste, additive and binder materialist acid, used in process.
Densification is a waste processing method, which densifies the waste or
changes its physical form and enriches its organic content through removal of
organic materials and moisture.
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Advantages of Densification
1. High calorific value of pellets 3500-4000 Kcal/kg. against that of
unprocessed garbage i.e. 800-900 Kcal/kg.
2. Pellets can be conveniently stored and transported and used as
supplementary fuel for combustion process and utility boilers.
Disadvantages of Densification
1. The processing unit can’t be operated during the rainy season, as the
garbage will be too wet.
2. High moisture content increases the cost of drying.
3. Consumes more energy than biological process.
4. Uncontrolled burning of the pellets derived from msw may lead to harmful
emissions.
3.1.5 OTHER TECHNIQUES
In addition to the above methods there are some other conversion
techniques such as
• Pyrolysis
• Gasification
• Alcohol Fermentation
• Slurry carb Process
• Plasma Arc Technology
Which could be used for energy recovery from waste.
From study of various methods given above and with all their
advantages and disadvantages it has been concluded that Anaerobic digestion /
Biomethanation process is economical and environmental friendly than any other
process discussed above.
Hence, Anaerobic Digestion process has been discussed in detail, in
further chapters.
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4
PROCESS DESCRIPTION
4.1 ANAEROBIC TREATMENT OF SPENT WASH – SMAT PROCESS (10)
Indian company offers “SMAT process” for anaerobic treatment of spent
wash.
Spent wash which is often termed as ‘distillers’ distress’ happens to be a
potential source of renewable energy when treated Anaerobically, this ‘liquid
gold’ releases millions of kilo calories in the form of methane rich biogas that can
be fed into boiler or biogas engines to generate electricity.
SMAT process:
The raw spent wash has very high BOD and COD concentration of 45,000
mg/l and 100,000 mg/l. respectively. This waste is digested Anaerobically in three
stages i.e.
1. Hydrolysis
2. Acid formation / Acidognenesis
3. Methane formation / Methanaogensis.
1. Enzymatic Hydrolysis
Where the fats, starches and proteins contained in cellulose biomass are
broken down into simple compounds.
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2. Acid Formation / Acideoenesis
Where the micro-organisms of facultative and anaerobic group collectively
called as acid formers, hydrolyze and ferment, are broken to simple compound
into acid and volatile solids. As a result complex organic compound are broken
down to short chemical simple organic acid. In some cases these acids may be
produced in such large quantities that the PH may be lowered to a level where
all biological activity is arrested. This initial acid phase of digestion may last
about two weeks and during this period a large amount of carbon dioxide is
given off.
3. Methane Formation / Methanogenesis
Where organic acids are formed above then converted into methane (CH4)
and CO2 by the bacteria anaerobes. These bacteria are called methane
fomenters. A PH value between 6.5 to 8 is the best for fermentation and normal
gas production.
In controlled waste digestion the environment must be maintained suitable
for the continued growth of both acid forming and methane forming bacteria.
These three stages i.e. hydrolysis, Acidogenesis and Methanaogenesis,
which are carried out in a single SMAT digester. The SMAT digester is filled
with specially designed rigid PVC media for bacterial to get immobilized on its
surface and hence very large population of bacteria is available inside the
digester.
The vertical straight flute media is geometrically structured and so designed
that is has optimum contact with raw spent wash which in turn ensures very
high biogas generation, round the year.
Biogas generation depends chiefly on two factors
1. Population of bacteria inside the digester.
2. Maximum assured contact between bacteria and food i.e. raw spent wash.
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Both these factors are taken care of by the structured media as explained
above.
The reactor content is kept completely mixed re-circulating the treated
spent wash 15-20 times which also helps in maintaining the reactor PH at around
7.2 without adding chemicals.
SMAT is a down flow reactor with distribution network provided at the top
through which the effluent is distributed uniformly over the entire area inside the
digester. The treated effluent is collected from bottom so as to avoid any short
circulating and is discharged at a suitable head. The biogas is collected at the top
gas dome which is fitted with state of the art safety devices. It is then transported
through a biogas blower for burning in boiler or biogas engine.
4.2 PROCESS OF THE ANAEROBIC TREATMENT WASTEWATER
TRANSPORT
Raw effluent i.e. raw spent wash from the distillery is carried to the
treatment site through suitably designed channel or a closed pipe depending upon
the topography of the site. Raw spent wash is then received in a sump. The sump
is constructed in RCC M 20 and lined with suitable protective lining to protect
sump from corrosive nature of raw spent wash. The raw spent wash which is at the
temp. 900C is passed through the heat exchanger before feeding it to the reactor
for bringing down the temperature to 36-400C. Pumps are installed to transfer raw
spent wash from sump to reactor through heat exchanger pump discharge is taken
to a feed tank located at centre of reactor.
4.3 SMAT REACTOR
The SMAT reactor is erected and fabricated at site using mild steel plates of
designed thickness conforming to IS 226. The SMAT reactor is used on floating
type foundation. The roof of the reactor is fixed type supported in grid of ISMB.
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The reactor is painted from inside using chlorinated rubber paint, whereas the
outside surface is painted by synthetic enamel or aluminum paint.
The SMAT reactor is partially packed with structured media out of PVC.
The structured media is provided in the form of modules. This specialty of the
media lies on offering very large surface area at a void ratio of 90%. The surface
area provided by media is around 95-105 sqm per cum. The entire media remains
submerged in the reactor content. The bacteria developed on media surface take
upon organic content of wastewater to metabolize it and produce biogas and
biomass.
The reactor content is kept under constant recirculation pumps. To achieve
optimized mixing the recirculation pump suction network is placed next to the
bottom of the reactor. This suction network is designed in such a way that it sucks
reactor content from entire bottom cross sectional area. All recirculation pumps
their discharge into roof feed tank.
4.4 TREATED EFFLUENT DISCHARGE
As SMAT reactor is down flow, the treated effluent is collected from the
bottom of reactor. To utilize head available, the overflow arrangement is so
designed that treated effluent is discharged at suitable head.
4.5 BIOGAS RECOVERY
The biogas produced by anaerobic digestion inside the reactor is collected
at the Gas Dome. The gas dome is placed at Reactor Roof and it’s fitted with all
essential safety equipment such as breather valve, flame arrestor etc. The biogas
is then conveyed to blower for further utilization is boiler or biogas engines.
25
4.6 Advantages of this Process
1. No dilution water required for treating COD up to 110,000 mg/l.
2. Higher organic loading rate in terms of COD per m3 of reactor volume and
thus requires smaller tank.
3. Special Media : SMAT reactor employs honeycomb type, specially
designed geometrically structured rigid PVC media to immobilize the
bacteria inside the reactor. This immobilization of the bacteria on the
specially designed performed media with the result that (I) the bacteria are
neither washed away not settled at the bottom of the reactor tank. (II)
There is an optimum (designed contact) between the bacteria and the
organic impurities contained in raw spent wash, ensuring continuous,
generation of biogas at the optimum.
4. Extremely quick restart within 48-72 hrs, even after long factory shut down
of 6 to 8 weeks as bacteria are always available in active condition attached
to very large surface area provided by the media. Also there is no loss of
biogas.
5. No biomass/ anaerobic sludge recycling required as bacteria are always
present in very large quantity in the form of bio-film or media.
6. Most Rugged System : Can withstand variation in flow, PH, COD,
concentration.
7. Very high bacterial population as bacteria are attached to media surface in
the from of bio-film. The film neither gets washed away not settles at the
bottom hence SMAT digester continuously generates higher amount of
Biogas.
8. Higher digestion : BOD reduction up to 90% and COD reduction up to
70% .
9. High resistance to toxicity and shock loading
10. No smell nuisance.
11. Aesthetically pleasing and extremely neat and clean system.
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12. Payback period of two years due to higher and continuous biogas
generation
13. Lower operation and maintenance cost power is required only for feed and
recirculation pumps.
14. Lowest life cycle cost as no loss of biogas in startup after shutdown.
27
28
5
FACTORS AFFECTING BIO DIGESTION
OR GENERATION
1. PH or the hydrogen ion concentration
2. Temperature
3. Total solid content of the Feed material
4. Loading rate
5. Seeding
6. Uniform feeding
7. Diameter to depth ratio
8. Carbon to Nitrogen ratio
9. Nutrients
10. Mixing or stirring or agitation.
11. Retention time or rate of feeding.
12. Type of Feed stocks.
13. Toxicity due to end products.
14. Pressure.
15. Acid accumulation inside the digester.
1) PH
or Hydrogen ion Concentration
PH of the slurry changes as various stages of the digestion in the initial acid
formation stage in the fermentation process. PH is around six or less and more
of carbon dioxide is given off. In the latter two three weeks time, the PH
increases as the volatile acid and nitrogen dioxide components are digested and
CH4 is produced.
29
The ideal values of PH
for digestion of sewage solid are reported to be in the
range 7 to 7.5. But slightly higher value of 8.2 has been reported to be
optimum for digestion of raw material.
2) Temperature
Methane bacteria work best at a temp between 35 to 38 .The fall in
production starts at 20 and stops at 10 .The temp is very important factor since
it affects the bacterial activity directly.
3) Total solid content
The total solid content in raw material should be 8 to 10%. The adjustment
of total solid content helps in bio-digesting the material at faster rate.
4) Loading Rate
Loading is defines as the amt of raw material fed to digester per day per
unit volume most plant operate loading rate at 0.5 to 1.0 kg. Of volatile solid
per m3 per day 2f loading rate is so high that add will accumulate and
fermentation will stop.
5) Seeding
The bacteria required for acid fermentation and methane fermentation are
artificially seed with digested sludge which is rich in methane formers. But
seeding should be up to a certain limit because beyond a certain seed
concentration, the gas production will decreases.
6) Uniform Feeding
One of the factors of good digestion is the uniform feeding of the digester
so that the micro organism is kept in a relatively constant organic solid
concentration at all times.
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7) Carbon Nitrogen Ratio of Input Material
All living organisms require digester is a culture a bacterial nitrogen oxide
to form their cell proteins from biological point of view, the element, carbon
and Nitrogen are the main food of anaerobic bacteria the optimum carbon
Nitrogen ratio that best suits for maximum microbiological activity is 30:1.
8) Diameter to Depth Ratio
Research investigation reveals that gas production per unit volume of
digester capacity was maximum when the diameter to depth ratio was in the
ranges 0.66 to 1.00. But reports from the field, digester of 16ft. depth and 4 ft.
to 5ft. Diameter to be working satisfactory.
9) Nutrients
The major nutrient required by the bacteria in digester are C, N2,02, H2, P &
S of these nutrients N2 and P are always in the short supply.
10) Mixing or Stirring
Since bacteria in the digester have very limited reach to their foods, it is
necessary that the slurry is properly mixed and bacteria get their food supply. It
is found that slight mixing improves the fermentation, however a violet slurry
agitation retards the digestion.
11) Retention Time
The period of retention of the materials for biogas generation inside the
digester is known as the retention period. It depends upon feed stock and
temperature normal value of retention period is between 40 to 45 days and in
some case 60 days.
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12) Type of Feed Stocks
When feed stock is woody or contains more lignin than bio digestion of
these feed stocks are combined in proportions.
13) Toxicity
The digested slurry if allowed to remain in the digester beyond a certain
name becomes toxic to the micro organisms and might cause fall in
fermentation rate.
14) Pressure
The pressure on the surface of slurry also affects the Fermentation. The rate
of gas production is higher at low pressure.
15) Acid Accumulation inside the Digester
Intermediate products such as acetic propionic acid, butyric acid are
produced during the process of bio digestion. This cause in decrease of PH,
especially when fresh feed material is added in large amount. This acid may be
converted into methane by addition of neem cake. Acid accumulation is
usually occurred in batch digestion Systems.
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6
AREAS OF APPLICATION
1) As a fuel for Domestic and Industrial Purpose (1)
As the biogas is a non poisonous, non toxic gas which when mixed with air
burns with blue flame, without soot or arch offensive small. The biogas has high
octane rating and calorific value ranges between 4700-6000 Kcal. Per cum. For
this above reasons biogas is used in domestic purposes like cooking etc.
2) The gas produced can be used directly for heating or for use in on engine
driven generator (7)
Depending upon its physical properties like; its boiling temperature is
161.50C, critical temperature is 82
0C and critical pressure 42 atoms it can be
directly used for heating.
• Biogas Fired Water Heater
One of the ways of heating water is placing it in a vessel over a gas burner.
This is not on efficient practice because bath water, unlike cooking items, is
needed in the order of 25 to 100 liter. The surface area of the vessel in contact
with hot gases is too small (0.13m2
for a 0.4m diameter vessel) besides being
open to the environment. Usually in such a system, for convenient handling ,
about 20 lit of water are heated at a time this is respected several times.
Water heating can be performed more efficiently by the use of water jacket
type heater because the heat transfer area is about 0.35m2 for a capacity of 140
liters. The gas burner is placed below at the base.
33
Figure shows a typical, Biogas heater in use in India.
Design of Gas-fired Bath Water Heater of 140 liters capacity (dimensions in mm)
Typical Results are given below.
• Energy output = 136 liters heated from 31 to 700C
• Fuel burning rate = 1.135m3/h
• Operating time = 0.75h
• Overall efficiency = 73%
34
3) Use of Biogas in Gas Turbines (7)
The main advantages of the use of gas turbines is that the capital cost is
considerably lower compared to reciprocating engines - particularly when used
aircraft engines whose normal flying duty is over are utilized. There are additional
advantages of easy installation, modular maintenance, quick starting and reliable
operation. National Aerospace laboratory has studied the application of Rolls
Royce ‘Dart’ Engines used by IAF and Indian Airlines to provide mechanical
energy for 1.0 to 2.5 MW electrical generators. These can be operates on duel
fuels [biogas diesel or kerosene] this approach seems to be promising.
The production of electrical energy only by biogas fuel is not economical.
However, cogeneration with IC engine connected with a generator and with waste
heat recovery would be economical. The waste heat recovered can be cycled for
digester heating.
4) Biogas Provides reasonably good fuel for both spark Ignition (Petrol) and
Compression Ignition (Diesel) Engine (1)
Biogas is combustion gas containing high percentage of methane, which is
an excellent gaseous fuel for running internal combustion engine. It has ignition
temp. Of 640 – 8400C, with acetone value of 130. The mixture containing
methane, carbon dioxide and air has wide combustible range and favorable
conditions for forming a mixed gas for running the engine, providing same power
for equal volume.
Modification required to be done in Existing Petrol Engine to switch it on to
Biogas
The spark ignition engine can be switched over to biogas (100%) offer it’s
starting on petrol and after initial heating. Therefore, a biogas supply pipe is
provided on air manifold between air cleaner and carburetor. After the engine has
35
run on petrol for 5-10 minutes the biogas supply value is opened slowly and petrol
supply valve closed simultaneously.
Modification done is SI Engine for Biogas fuel.
The necessary modification to be done on engine for running it on biogas is
shown in frg. The biogas contain 30 – 40 percent carbon dioxide, therefore the air
regulation valve is used to control air / biogas mixture.
The biogas also contains moisture and sometimes traces of hydrogen
sulphide which effect the engine performance and life of Cylinder / Piston. The
presence of moisture will give pulsating power output or engine may close after
some time. The Hydrogen sulphide will attack valves, piston cylinder, etc. thus
reducing the life of engine. Therefore, it is necessary to remove moisture by
passing it through a hydrous material and for removing Hydrogen sulphide, it is
passed through iron chips.
36
Modification to be done in Diesel Engine to operate it on Duel – Fuel
The existing diesel engine can be modified without any difficulty to operate
it on biogas and diesel.
Modification in Diesel Engine for Biogas Fuel.
A biogas inlet manifold is provided such that the engine can run on diesel
alone when biogas is exhausted. This manifold is fitted to air inlet pipe between
the inlet port and air cleaner (Fig.). The biogas is required @ 2.12 cum per hr and
20-35 percent diesel for 5hp. Duel-fuel engine.
5) Diesel Engine (CI) runs on Biogas as Dual-Fuel Comprising both oil and
Gas which helps to achieve about 80% saving in Diesel: (used as Vehicle fuel)
petrol engine (SI) also work on Gas having petrol Replacement of the work of
100% (1)
The Biogas has been used successfully for short distance transportation of
vehicle. The Gas compressed up to 120-150 Kg/cm2 , pressure in standard eight
cylinders was used for operating a 95 bhp, six cylinder truck. In one go it can
travel a distance of 96 Km. The pressure reduction is achieved in two stages. I
(120 Kg/cm2 to 1.5 Kg/cm
2) and II (1.5 Kg/cm
2, to 0.02 Kg/cm
2).
37
Performance Characteristics of Vehicle Running on Biogas: (1)
Particulars Units Tractor Truck Bus
Fuel Consumption / hr M3/hr 12 54 54
Fuel For 100Km travel M3 48.5 107.4 107.4
Fuel Consumption/ tone km M3 0.32 0.15 0.26+
Vehicle speed [max] Km/hr 20 40 45
Volume of fuel tank M3 2x2x2 8x4x1 8x4x1
(+) 20 passengers = 1 tones km
6) Biogas can also used for Electricity Generation
As per studies 1KWH of electricity can be generated from 0.7m3 of gas
which can light about is electric bulbs of 60 watt. Rating for 1 hour.
Biogas Lamp:
The biogas lamps are similar to Kerosene mental lamps consuming 0.11 to 0.18
cum gas per 100 candle power and use silk mental for lighting.
38
The lamp has a simple with reflector ad gives 100 candle power (60w)
light. The lamp can be double mental type also. The hot gas vent holes are
provided to open toward side to avoid entry of rain water. The biogas on-off lock
leaves is provided to supply gas for lighting.
7) It can be used effectively for operating small engine, utilizing power for
pumping water, and grinding flour by using known technology
8) In sewage treatment plants biogas is used as fuel for boiler.
9) Use of Biogas in Refrigerators (7)
Biogas can be used in absorption refrigeration system without only
problems as long as assured gas supply for burner is available for a Refrigerator of
230 liters capacity, the biogas consumption will be approximately 0.044 m2/l.
Particular problems also arise with biogas operated refrigerators. The
compositon of biogas varies substantially from day to day. The gas pressure
fluctuates excessively with the amount of gas stored even in a floating drum plant,
special, stable-burning jets are therefore needed – especially if the refrigerator is
thermostatically controlled and the flame burns only when required. On every
ignition there is a risk of the flame going cut. Gas will then discharge without
burning. The gas supply must therefore automatically be cut off it the flame goes
out.
39
7
CONCLUSION
The proper utilization of distillery wastes for production of biogas will not
only reduce the load on fossil fuel ,but will also help in environmental protection
due to reduction in organic dung .
The importance of distillery spent wash as a source of renewable energy
especially when the sources for the fossil fuel are depleting is obvious but the
contribution of distillery to organic load on receiving steam is also a matter of
serious concern because of limited assimilation capacity.
Biological treatment of distillery effluent results in production of ‘Biogas’.
Thus it is an advantage for sources of renewable non-conventional energy and
waste management.
40
8
BILBLIOGRAPHY
1. N. Mathur, N.S. Rathore “Biogas Production Management” and
utilization”P.P. – 2-5, 89 - 143.
2. D. S. Shah, D.P. Mishra and Shrivstav “Unconventional energy Sources”
(1982).
3. Soil J Acceivala, “ Wastewater treatment for pollution control” IInd
Edition PP – 33 - 39.
4. Mahajan S.P. ,” Pollution control in Process Industry”, Total McGrowlkill
PP – 103 - 105 (1988)
5. ‘ All India Seminar on Pollution control in Sugar Industry”, PP - 1- 31 ,
(1995)
6. Vipul Goyal, “ Chemical Engg. World”, Vol 32 No 7 PP - 43 - 47
(2002).
7. T. Nijaguna, “Biogas Technology”, Newage International Publisher PP
– 224 - 259.
8. WWW. Undp.org.in (United Nation’s Development Program).
9. WWW.mnes.nic.in
10. WWW.apctt.org, (Asian and Pacific center for Transfer of Technology).
11. WWW.terlin.org