L- 28L- 28Tannery Industry

Industrial Waste Treatment

Introduction

• Tannery industry is one of the oldest in

India.

• Usually tannery waste consists of

- Strong odour

- High BOD,- High BOD,

- High pH

- High dissolved salts

• Treatment of waste is essential before

treatment.

Manufacturing Process

•It consists of basic three stages

1. Preparation of hides for tanning

2. Tanning proper

3. Finishing3. Finishing

i] Preparation of hides

1) In first stage hides are washed to

remove dirt and preservative salts

used earlier and then soaked into

the fresh water containing NaCl and

preservative chemical.preservative chemical.

2) The hides are washed in running

water. Washed hides are pasted with

lime and sodium sulphide

3) Limed hides are then mechanically

cleaned of hairs and fleshing in

wooden vats with running fresh

waters.

4) Bating prepares the hides for tanning

by reducing pH, reducing swelling and

removing the protein degradation

products of it.

5) The deliming and bating is carried

out in verrrrtically rotating drums in

warm solution of ammonium salts

and enzymes

ii] Tanning proper

•Tanning makes hides

nonputrescible and soft.

•There are two types of tanning

1. Vegetable tanning1. Vegetable tanning

2. Chrome tanning

Vegetable tanning• Tannins bind to the collagen proteins in the

hide and coat them causing them to become

less water-soluble, and more resistant to

bacterial attack.

• The process also causes the hide to become • The process also causes the hide to become

more flexible.

• Hides are stretched on frames and immersed

for several weeks in vats of increasing

concentrations of tannin. Vegetable tanned

hide is flexible and is used for luggage and

furniture.

Chrome tanning

•Chromium salts such as chromium

sulphate is used.

•Chrome tanning is faster than vegetable

tanning (less than a day for this part of the tanning (less than a day for this part of the

process) and produces a stretchable

leather which is excellent for use in

handbags and garments.

iii] finishing

•Finishing consists of stuffing and fat

liquoring followed by dyeing

Treatment alternative -

Chrome recovery recovery

Objective Questions

1. Two types of tanning processes are

________ and ______ tanning

2. _________ tanning requires very less time.

3. Amount of Chromium present in spent 3. Amount of Chromium present in spent

chrome tan liquor is _______ mg/lit

Theory Questions

Q1. Discuss detailed process involved in the

tannery with the help of process flow

sheet.

Q2. Give general characteristics of Q2. Give general characteristics of

Combined waste from tannery industry.

Q3. Discuss treatment alternatives for

leather tanning industry.