CHAPTER 1 INTRODUCTION - Shodhgangashodhganga.inflibnet.ac.in/bitstream/10603/9622/16/9-chapter-1.pdf · CHAPTER 1 INTRODUCTION ... India stood to gain a bigger share of the global

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CHAPTER 1

INTRODUCTION

1.1 GENERAL

Leather industry has gained high socio-economic relevance in

India. Leather sector has contributed significant economic growth by

providing job opportunities. Leather industry in India is spread over more in

the unorganized sector. The small scale, cottage and artisan sectors account

for over 90% of the total production. Today, the industry ranks 8th

in the

export trade in terms of foreign exchange earnings of the country. Leather

industry occupies a place of prominence in the Indian economy, by

contributing 2 billion US dollars in terms of export, and its share in world

trade is 2%. Leather industry is providing employment to nearly 2.5 million

people and the majority of tanneries fall under small and medium scale

enterprises (Taylor 2005).

The main reason for the development and growth of the leather

industry in the country is its large animal population. India enjoys nearly 10%

of the total global availability of raw hides and skins which are the basic raw

material for the leather industry. The raw material availability in Indian as per

the 2003 raw material survey report is presented in Table 1.1 (Chandramouli

2005).

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Table 1.1 Availability of Hides and Skins in India in 2003

Category No. of Pieces (in millions)

Cattle hides 22.770

Buffalo hides 27.875

Goat skins 81.900

Sheep skins 29.660

The tannery operation consists of converting the raw skin, a highly

putrescible material, into leather, a stable material, which can be used in the

manufacture of a wide range of products. The whole process involves a

sequence of complex chemical reactions and mechanical processes (UNEP

1991). Amongst these, tanning is the fundamental stage which gives leather

its stability and essential characters. Raw hides/ skins after various steps of

pre and post treatments are converted into a final product with specific

properties: stability, appearance, water resistance, temperature resistance,

elasticity and permeability for perspiration.

In India as per 2008 statistics around 2 billion sq. ft. of finished

leather per annum was produced and the industry has set a target to double

this figure by the year 2011-12 (Raghavan 2008). On the other hand, the

industry has been facing serious challenges on account of pollution related

problems (Langerwerf and Chandra Babu 1999). The presence of eco-

sensitive chemicals in leathers is an area of concern (Chandrababu et al 2003).

Due to high wage levels in developed countries, manufacturing of

leather products such as shoes, apparels and personal consumer leather goods

was shifted to developing countries. Hence developing countries became their

main sources of supply. The post liberalization era had opened up a plethora

of opportunities for the Indian leather industry. With global players looking

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for new sourcing options, India stood to gain a bigger share of the global

market. Leading brands from the USA and Europe are now outsourcing

mostly leather and leather products from India.

The malodorous atmosphere around traditional tannery clusters

creates the impression of a highly polluting industry. Tanneries fall under the

‘red’ category of industries in India based on the pollution potential. The

impact of tanning and associated activities on air, on surface and ground

water and soil pollution arises from the chemicals applied, the raw materials

used and the effluents, waste and off-gas releases generated in the process.

Many leading importers of branded products in industrialized

countries have started insisting on their suppliers that they must conform to

their respective national environmental and labour standards. The exporters of

developing countries, doing business with importers from developed

countries, have no option other than to comply with environmental standards.

Since early 80’s, tanning industry began to tackle environmental pollution

problems of liquid and solid wastes generated during tanning processes.

1.2 CLASSIFICATION OF TANNERIES IN INDIA

The leather industry in India has grown in clusters for historical

reasons. Tanneries are classified based on processing capacity and type of

process adopted, as below:

(i) Raw to semi-finish (wet-blue or vegetable tanning) stage

(ii) Semi-finish (wet-blue or vegetable tanning) to finish stage

and

(iii) Raw to finish stage.

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1.3 ENUMERATION OF TANNERIES IN INDIA

Primarily tanning operations are concentrated in the regions where

availability of good quality water and raw materials are abundant. In India,

tanning clusters are located in the states of Tamil Nadu, Andhra Pradesh,

Punjab, West Bengal and Uttar Pradesh and few isolated tanneries are in

Bihar, Madhya Pradesh and Kerala. The locations of tanneries in various

tanning clusters in India are presented in Figure 1.1. The state-wise

distribution of tanneries in India is given in Table 1.2.

Figure 1.1 Location of Tanneries in India

Source: Comprehensive Industry Document on Tanneries (COINDS), CPCB, 2010

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Table 1.2 State-wise Distribution of Tanneries in India

State No. of

Tanneries

Percentage

Tamil Nadu 712 35.60

West Bengal 218 10.90

Punjab 45 2.25

Uttar Pradesh 431 21.55

Andhra Pradesh 15 0.75

Bihar 6 0.30

Haryana 13 0.65

National Capital Region (NCR) 20 1.00

Other States 540 27.00

Total 2000 100.00


1.4 WATER USAGE AND POLLUTION POTENTIAL

The quantity of chemicals used in tanning processes is almost in the

same range in all the regions in India. Depending on the availability of water,

the wash water volume usage varies and wash water contains chemicals in

various concentrations in the sectional and composite wastewater. The

concentration of the pollutants present in the wastewater also depends on the

cleaner technology adopted in the tanneries like dusting of salt, recovery and

reuse of chromium and quality of the chemicals used. In Tamil Nadu, it is

mandatory for the tanneries processing raw to semi-finish (chrome tanning

process), to have chrome recovery system. Due to scarcity of water, the

quantity of water used for washing is less in Tamil Nadu State, when

compared with other parts of the country. Due to this, the concentrations of

the chemical oxygen demand (COD) and biochemical oxygen demand (BOD)

are comparatively high in wastewater. But in the case of tanneries in Uttar

Pradesh, Punjab and West Bengal, the volume of water used for washing are

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high and this results in dilution of the pollutants. In Andhra Pradesh and

Tamil Nadu, soak and pickle liquor are segregated and conveyed to solar

evaporation pans. But in other parts of the country, no segregation of soak and

pickle is done and they are combined with the remaining sectional streams.

The volume of water usage for the tanning process in Tamil Nadu and other

states are given in Table 1.3.

Table 1.3 Water usages for Processing Raw to Semi-Finish and Semi-

Finish to Finished Leather

Sl.

No.Name of the Stream

Water Usage*

Tamil

Nadu

Other States

in India

1 Water usage for raw to semi-finish

process12-14 12-14

2 Water usage for Washing 8-10 14-18

Total water usage for Raw to Semi-Finish

Operations20-24 26-32

3 Water usage for semi-finish to finish

process4-6 4-6


Total water usage for Semi-Finish to

Finished Leather10-14 14-18

5 Water usage for raw to finish process 16-20 16-20


Total water usage for Raw to Finished

Leather Operations30-38 40-50

* Water consumption in m3 for processing one tonne of raw hides/ skins


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SOLAR EVAPORATION PAN

CHROME RECOVERY SYSTEM

SOLAR EVAPORATION PAN

WETBLUE LEATHER

CHROME TANNING(Drums)

WASTEWATER, SULPHATE,

CHLORIDE, CHROMIUM,TDS

WASTEWATER,TDS

Low pH, CHLORIDES,

SULPHATE

WASTEWATER with TDS

NITROGEN, BOD, COD

FLESHING (WASTEWATER in

the case of mechanical

operation)

WASTEWATER, High pH, BOD,

COD, SS, SULPHIDES

WASTEWATER, TDS, SS

CHLORIDES, BOD, COD

WATER, SALT

SULFURIC ACID

WATER, AMMONIUM SALTS

BATING ENZYMES

WATER, LIME

SODIUM SULPHIDES

WATER, BIOCIDESENZYMES

LIMING/

(Pits, Paddles, Drums)

SALTED SKINS / HIDES

(Drums)PICKLING

(Drums)DELIMING

WATER(Manual/Mechanical)

FLESHING

RELIMING/UNHAIRING

(Pits, Paddles, Drums)SOAKING

WATER

BASIC CHROMIUM SULPHATE

SODIUM SALTS

1.5 WASTEWATER GENERATION

The leather tanning is a raw materials and labour intensive industry.

The raw materials account for 50 to 70 % of production costs, labour 7 to 15

%, chemicals about 10% and energy 3%. It involves a series of batch

processes during which each hide must be processed separately and

sometimes manually. The processes of tanning of raw hides/ skins into semi-

finish leather and semi-finish to finished leather are presented in Figures 1.2,

1.3a and 1.3b. The schemes of generation of wastewater and their

characteristics are also presented in the figures.

Figure 1.2 Wastewater Generated in Tanning of Raw Hides/ Skins into

Semi-Finish Leather (Source: Comprehensive Industry Document on

Tanneries (COINDS), CPCB, 2010)

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(a) For Processing Vegetable Tanned EI Leather (b) For Processing Chrome Tanned Leather

DYEING & FAT

LIQUORING(Pits/Drums)

FINISHED LEATHER

DRY FINISHING

WASTEWATER, BOD,

COD, TDS, TANNIN

WASTEWATER,

CHROMIUMTDS, SULPHATE

WASTEWATER,TDS

WASTEWATER,BOD, COD,

TDS, SULPHATE

WETTING BACK

and BLEACHING(Drums)

NEUTRALISATION(Drums)

SEMI- CHROME

TANNING(Drums)

VEGETABLE

TANNED EI LEATHER

WATER, DYES

FAT LIQUORS

WATERSODIUM BICARBONATE/

SODIUM FORMATE

WATER, CHROMIUM

SYNTAN

WATERSODIUM SALTS

SAMMYING

and SHAVING

CHROME TANNED

WETBLUE LEATHER

WATER,CHROMIUM,

SYNTANS

WATER, DYES, FAT LIQUOR

FINISHED LEATHER

(Drums)

RETANNING

(Drums)

FAT LIQUORING

(Machinery operations)

DRY FINISHING

WASTEWATER,TDS

CHROMIUM,WETBLUE SHAVING

WASTEWATER,TDS

CHROMIUM,SULPHATE

WASTEWATER,TDSCOD,BOD

SULPHATE

DRYING &

RECHROMING/

Figure 1.3 Wastewater Generated in Processing Semi-Finish to Finished Leather (Source:

Comprehensive Industry Document on Tanneries (COINDS), CPCB, 2010)

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Water and material used for processing 1000 kg of raw hides/skins into

finished leather are presented in Table 1.4.

Table 1.4 Water and Material Used for Processing of Raw Hides/skins into

Finished Leather

Process

Description

Water

including

Washing

(cubic

meter)

Chemical Quantity (kg)

Before soakRaw material 1000

soaking 6-9

Wetting agent - 1-3

Preservative 0.1 - 1

Surfactant 2-4

liming 6-11Calcium Hydroxide 35-40

Sodium Sulphide 20-25

Re-Liming 2-3

Calcium Hydroxide

5-10

Deliming and

bating3-4

Ammonium salts 25-27

Acids 8-10

Enzyme 3-5

Pickling and

Chrome tanning3-5

NaCl 50-55

H2SO4/HCOOH 10-12

Chrome extract

(25% Cr2O3)

80-90

MgO/NaHCO3 6-8

Reaction salts

Post tanning 8-14

NaHCO3/ HCOONa 6-8

Chrome extract

(25% Cr2O3)

10-13

Organic tannins 15-20

Fat liquors 12-15

Dyestuffs 3-4

Acids 3-4

finishing 2-4Grain leather crust 170-190

Solvent 25Source: Comprehensive Industry Document on Tanneries (COINDS), CPCB, 2010

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During the beam–house operations, a huge quantity of water is used in

proportion to the weight of the pelts and this contributes immensely to the

pollution load from the tannery. Comparatively, the BOD and COD loads are 50–

70% of the total load from a tannery wastewater while total solids (TS) (lime

sludge, fleshings and hair) load accounts for 15–20% (Ramasami and Prasad

1991). Post tanning activities are mechanical operations (e.g. sammying,

splitting, shaving and trimming), wet work, drying and finishing. These

operations will yield a combination of solid wastes, squeezed-out water and

unfixed tanning chemicals with the finishing process producing mostly air

emission of solvents (UNEP 1994).

Though the Indian leather industry has been able to surmount many of

the challenges with huge investment on pollution control, there are still three

lingering problems viz., compliance to total dissolved solids (TDS) norm of 2100

mg/L in treated wastewaters, compliance with zero liquid discharge (ZLD)

requirement of regulatory authorities and securitization of solid waste generated

(Rajamani 2007). The tannery sector in India is being compelled to comply with

rigorous norms for TDS (Ramasami et al 1999). The threat of salt burden in land

locked areas can lead to the leather sector being phased out of such areas. The

tannery clusters may need to consider various options to reduce salt burden. It

has been estimated that the salt burden on soil and water on account of tanning

activity is about 0.5 million tonnes in terms of neutral salts (Ramanujam and

Mariappan 1999). Hence, the leather industry is under close scrutiny of the

environmentalists.

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1.5.1 Characteristics of Composite Wastewater

For (i) raw to semi-finish, (ii) semi-finish to finished leather and (iii)

raw to finished leather, the characteristics of composite wastewater are presented

Table 1.5.

Table 1.5 Characteristics of Composite Tannery Wastewater

DescriptionRaw to

Semi-Finish

Semi-Finish

to Finish

Raw to

Finish

Wastewater generation (m3/ tonne

of raw hides/ skins processed) 30 20 50

Composite Wastewater Characteristics

Biochemical Oxygen Demand

(BOD, mg/L) 1500 - 1800 800- 1000 1300-1500

Chemical Oxygen Demand

(COD, mg/L) 4000 - 5000 3000 - 4000 3000- 4000

Suspended Solids

(SS, mg/L) 2500-3500 1000-2000 3200-4200


1.6 SOLID WASTE GENERATION

1.6.1 Sources of Solid Waste Generation

With the help of process flow diagrams, sources of solid waste

generated during the processing of raw hides/skins into finished leather using

chrome tanning process and vegetable tanning process are presented in

Figures 1.4 and 1.5.

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Raw hides Raw hide trimmings

Dusting Dusted sa lt

Soaking

Liming

(Pits or Paddle)Lime sludge and hair pulp

Reliming

(Paddle or Drums)

FleshingFLESHINGS (used as substrate

in the present study)

Trimming Pelt trimmings

Deliming

Retanning, Dyeing and

Fat liquoring

Pickling

Chrome tanning

(wet blue)

SplitsSplitting

Shaving Chrome shavings

FinishingFinished lea ther trimmings

Figure 1.4 Solid Wastes Generated during Processing of Raw Hides /

Skins into Finished Leather (Chrome Tanning)

(Source: Comprehensive Industry Document on Tanneries (COINDS),

CPCB, 2010)

Hide, Water

Hide, Water, ammonium

salts, Bating Enzymes

Hide, Water, BCS

sodium salts

Hide, Water, Sulfuric acid

Hide(wet blue),Water, Dyes, Fat

Hide, Water,

Lime, Sodium

Hide, Water

Hide, salt, water

Hide, salt, water,

biocides,

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Raw hide trimmings

Dusted salt

Lime sludge & hair pulp

FLESHINGS (used as

substrate in the present study

Finished leather Trimmings

Raw hides

Dusting

Soaking

Liming

Fleshing

Deliming

Vegetable tanning (pits)

Finishing

Tanning sludge, bark, nuts

Figure 1.5 Solid Wastes Generated during Processing of Raw Hides/ Skins

into Finished Leather (Vegetable Tanning)

(Source: Comprehensive Industry Document on Tanneries (COINDS),

CPCB, 2010)

Solid waste generated during vegetable tanning process is about 15 to

20 % less than that for the chrome tanning process since no splitting operation

will be carried out and also the processed leather is mostly used as soles for

shoes in case of vegetable tanning process.

1.6.2 Quantity of Solid Waste Generation

Nearly 2000 tanneries are located throughout India with a total

processing capacity of 700,000 tonnes of hides/skins per annum. Out of 2000

tanneries, only 5 % of tanneries adopt vegetable tanning process and remaining

Hide, Water, ammonium salts,

Bating Enzymes

Hide, Water, Lime, Sodium

Sulphide

Hide, Water

Hide, salt, water

Hide, salt, water,

biocides, Enzymes

Veg. tanned hide, Water,

Bark, nuts

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95% of tanneries adopt chrome tanning. Therefore, the problem of solid wastes

generation in reality refers to the chrome tanning operations and this research

work also addresses only this problem. In chrome tanning’s, in the processing of

one tonne of raw hides/skins into finished leather, around 500- 600 kg of process

solid waste will be generated. In the waste so generated, 70-230 kg will be

fleshings (Sundar et al 2010). These fleshings were used in industries for glue

manufacturing until recently but now they are used in a very limited scale since

other types of glues are available. Thus the disposal of fleshings has become a

major environmental concern. Also, fleshings by themselves are not amenable

for digestion as a stand-alone substrate. The details of solid waste generation

during processing one tonne of raw hides/skins into finished leather in chrome

tanning are presented in Table 1. 6.

Table 1.6 Quantity of Solid Waste Generation

Sl.

No.

Process Average Solid Waste

generation (kg) per

tonne of raw hides/

skins processed

Total Solid Waste

Generation (tonnes

per annum) in

India

Chrome Tanning Process

a Raw trimming 120 84000

b Fleshings 150 105000

c Tanned splits 115 80500

d Trimming + Shavings

(after chrome tanning)

100 70000

e Buffing dust 2 1400

f Finished Trimmings 32 22400

Total 519 363300

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The explanations for the types of solid wastes generation are presented

below:

Raw Trimmings are the collagenous wastes generated before pre-tanning

operations when the hides and skins are sized for the convenience of machinery

operations.

Fleshings and non-tanned split are putrescible material consisting of protein and

fat.

Tanned Splits can be generated after liming or after tanning operations. The

flesh side of the splitting also referred to as the split, can be used to make leather

without a grain.

Trimmings are the collagenous wastes generated during finishing operations of

leathering processing to cut into leather a required size.

Shavings which are generated in leveling the surface of the leather are smaller

pieces than splits. Splits from tanned leather, shavings and dust from milling

buffing contain the tanning chemicals. Any further re-use and treatment depends

on the particular chemical composition.

Buffing Dust can be generated during finishing operations of leathering

processing.

1.7 REUSE AND DISPOSAL OF THE SOLID WASTES

The present modes of reuse and disposal of solid wastes are given in

Table 1. 7.

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Table 1.7 Reuse and Disposal Options for the Solid Wastes

Sl.No. Nature of the solid

waste

Reuse and Disposal Options

1 Fleshing process solid

waste

Very limited quantity is used for glue

manufacturing. Major portion is dumped in

low lying areas.

2 Dusted salt Mostly dumped in low lying areas

3 Raw trimmings Sold to small tanneries /dumped in low lying

areas

4 Shaving Limited quantity is used for leather board

manufacturing. Major portion is dumped in

low lying areas

5 Buffing dust Dumped in low lying areas

6 Finished leather

trimmings

Card board, carpet manufacturing, gift

articles etc.


1.7.1 Factors Affecting the Solid Wastes Generation

The quantity of solid waste generated in tanneries depends upon the

following factors:

a. Type of raw material used for processing (i.e. cow, buffalo

hides, sheep and goat skins etc).

b. Quality of raw material used (i.e. wet salted, dry salted, semi

finished etc).

c. Type of process adopted (i.e. vegetable tanning, chrome tanning

etc).

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d. Way of operation (pit tanning or drum tanning).

e. Quantity and quality of chemicals used (i.e. lime, barks and nuts

for vegetable tanning etc).

f. Utilization of solid wastes. (i.e. source buy back system of raw

hide trimmings by the supplier, supply of used barks and lime

to workers etc).

g. The level of implementation of waste minimization measures

1.7.2 Sludge Generation from Effluent Treatment Plants

Wastewater treatment and management is an important and increasing

concern in India. The total wastewater discharge from tanneries is about 175,000

m3/day in India. In India there are nearly 200 individual Effluent Treatment

Plants (ETPs) and 17 Common Effluent Treatment Plants (CETPs) exclusively

used for treatment of tannery wastewater. The treatment options considered for

treatment of tannery effluents are:

Option I: Primary treatment (Equalization and settling) followed by two

stage aerobic treatment (Activated Sludge Process)

Option II: Primary treatment (Equalization and Settling) followed by anoxic/

anaerobic treatment followed by aerobic treatment

A typical process flow diagram for treatment of tannery wastewater is

presented in Figure 1.6.

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Figure 1.6 A Typical Process Flow Diagram for Treatment of Tannery Wastewater (Source: Comprehensive Industry Document on Tanneries (COINDS), CPCB, 2010)

COMPOSITETANNERY

WASTEWATER

MECHANICALDEWATERING

SYSTEM

FLASH

MIXER

PRIMARY

CLARIFIER

POLY ELECTROLITEEQUALISATIONTANK

FLOCCULATOR

ANOXIC TANK

AERATION TANKSLUDGE DRYING BEDS

(for emergency)

SLUDGEHOLDING

TANK

TREATEDTANNERY

WASTEWATER

SECONDARY

CLARIFIER

COARSE

SCREENALUM LIME

FILTRATE

BLOWER

HOUSE

SL

UD

GE

RETURN SLUDGE

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During the treatment of tannery wastewater, primary sludge will be

generated from primary clarifiers and secondary sludge will be generated

from biological treatment units. The quantity of primary and secondary

sludges generated during treatment of tannery wastewater generated from

various stages of leather processing i.e. raw to semi-finish, semi-finish to

finished leather and raw to finished leather are presented in Table 1.8

Table 1.8 Quantity of Primary and Secondary Sludge Generation for

Processing One Tonne of Raw Hides/Skins into Finished

Leather

Description

Raw to

Semi-

finish

Semi-finish to

Finished

Raw to

Finished

Primary sludge generation

(range in kg)

60 - 90 10 - 30 140-190

Secondary sludge generation

(range in kg)

28-33 16-19 39-46

Total sludge production ( kg) 88-123 26-49 179-236

Overall sludge generation during the treatment of tannery

wastewater will be in the range of 18200 to 165200 tonnes per annum in

India. At present, the sludge is stored within the premises of the common

effluent treatment plants (CETPs) except in Tamil Nadu. In Tamil Nadu, as

per directions of Honorable Supreme Court, secured landfill facilities have

been created for disposal of primary sludge generated from the treatment of

tannery wastewater. The disposal of fleshings and the secondary sludge into

the landfill is not encouraged due to their unstable conditions. Hence, the

management of the fleshings and the secondary sludge is a challenge for

Indian tanning industry. A comparison of conventional and modern

tanning process, treatment of tannery wastewater and tannery wastes are

given in Table 1.9.

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Table 1.9 A comparison of Conventional and Modern Tanning

Process, Treatment of Tannery Wastewater and Tannery

Wastes


Sl.No. Description ConventionalProcess

Modern Process

1. Tanning Processa Soaking Pits, Drums Drumsb Liming Pits, Drums Pits, Drumsc Fleshing Manual or

MechanicalMechanical

d Deliming Pits, Drums Drumse Pickling Pits, Drums Drumsf Chrome Tanning Drums Drumsg Rechroming Drums Drumsh Dyeing and Fat

LiquoringDrums Drums

i Finishing Manual or Machines Manual or Machines2. Tannery

WastewaterTreatment

Screen cumCollection Tank,Equalization Tank,Flash Mixer, PrimaryClarifier, ActivatedSludge Process,Secondary Clarifier,Pressure Sand Filters,Activated CarbonFilters

Screen cum CollectionTank, Equalization Tank,Flash Mixer, PrimaryClarifier, MembraneBioreactor, Cartridge Filter,Nano Filtration, ReverseOsmosis

3 Tannery SolidWaste Management

a Fleshing processsolid waste

Very limited quantityis used for gluemanufacturing. Majorportion is dumped inlow lying areas.

Composting, AnaerobicDigestion

b Dusted salt Mostly dumped inlow lying areas

Salt less curing

c Raw trimmings Sold to smalltanneries /dumped inlow lying areas

d Shaving Limited quantity isused for leather boardmanufacturing. Majorportion is dumped inlow lying areas

Leather BoardManufacturing

e Buffing dust Dumped in low lyingareas

f Finished leathertrimmings

Card board, carpetmanufacturing, giftarticles etc.

Card board, carpetmanufacturing, gift articlesetc.

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1.8 NEED FOR THE STUDY

Today the tanneries face the twin problem of managing process

solid waste and ETP/ CETP sludge. The majority of tanneries in India fall

under small and medium scale enterprises with a minimum processing

capacity in the range of 2 to 3 tonnes per day. Considering the mean

processing capacity as 2.5 tonnes per day, the process solid waste generated

will be around 1300 kg/day. In this, fleshings will account for 375 kg.

Similarly, the ETP/CETP sludge generated will be around 500 kg/day.

Considering the tannery will be in operation for a period of 200

days per annum based on availability of raw materials, the annual solid wastes

generation i.e. fleshings and ETP/CETP sludge will be 75 and 100 tonnes

respectively. It means every tannery faces this enormous problem of

managing the disposal of 75 tonnes of fleshings and 100 tonnes of sludge

annually. At present, each tannery is spending around Rs.700 to Rs.750 per

tonne for disposal of sludge into the secured landfill facility which includes

transportation of sludge from tannery to the secured landfill facility, loading

and unloading.

As already stated, fleshings pose serious environmental threat.

There is no reuse potential and disposal appears to be the only option

available. Therefore, any option available to reduce the quantum of fleshings

waste to be managed is a welcome message. Likewise, the treatment of

ETP/CETP sludge in a sludge digester demands huge investment cost. The

technical options to economize on the design and operation of sludge digester

will be of help to the tanners. Keeping these two specific needs, this research

work has been planned.

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1.9 SCOPE OF THE STUDY

The scope of the study is to scientifically investigate the process of

co-digestion of fleshings i.e. a process solid waste and the primary and the

secondary sludges generated from the treatment of tannery wastewater.

Specifically the study aimed to demonstrate the feasibility and also to

illustrate the environmental and economic benefits arising out of such a

process. At the time of investigation, this research work was first of its kind.

As a part of this investigation, certain selected pretreatment

technologies were applied to enhance the soluble chemical oxygen demand

(SCOD) in primary and secondary sludges separately.

Fleshings, as the lipid rich wastes, are attractive substrates for

anaerobic digestion due to the higher methane yield. They are difficult to

degrade when compared with carbohydrates and proteins. For the fat and

lipid containing wastes, the rate of hydrolysis is slower than the other organic

fractions present in the substrate. Enzyme application is an option to hasten

the digestion process. Hence the present study also covers the application of

lipase in co-digestion process.

1.10 OBJECTIVES OF THE STUDY

• To characterize (i) the substrates i.e. fleshings and the

primary and secondary sludges generated during treatment

of the tannery wastewater and (ii) the inoculum obtained

from an anaerobic digester operating for the digestion of

waste activated sludge generated in a sewage treatment

plant.

• To optimize the mix proportion of substrates, residence time,

inoculum to substrate ratio for the co-digestion of tannery

solid wastes.

23

• To conduct a detailed investigation on co-digestion process

and evaluate the performance.

• To characterize the digestate samples using instrumental

analysis.

• To study the effect of pretreatment of primary and secondary

sludges on biogas generation.

• To study the effect of application of lipase on the digestion

process.

1.11 ORGANIZATION OF THE THESIS

Chapter 1 deals with general introduction about tanning industry,

process wastes generation, sludge generation during treatment of tannery

wastewater, need for the study and the scope and objectives of the present

study.

Chapter 2 provides an overview of literature related to co-digestion

of solid waste, sources of lipid rich waste, lipid degradation and mechanism,

significance of inoculum to substrate ratio, digestate stability, various

pretreatment processes to increase SCOD and enzyme application in waste

treatment process.

Chapter 3 discusses the materials and methods adopted for

characterization of substrates such as fleshings, primary sludge, secondary

sludge, inoculum and digestate and the methodology adopted to conduct

studies.

Chapter 4 presents the results of experiments and detailed

discussion on co-digestion of tannery solid wastes.

Chapter 5 covers the summary and conclusion of the thesis by

highlighting the salient features of the studies carried out.

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CHAPTER 1 INTRODUCTION - Shodhgangashodhganga.inflibnet.ac.in/bitstream/10603/9622/16/9-chapter-1.pdf · CHAPTER 1 INTRODUCTION ... India stood to gain a bigger share of the global