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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.

26

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.

30

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.

31

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.

32

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