STUDY OF WASTE WATER, DISCHARGED FROM

TANNERY INDUSTRIES.

Prepared by:-ABHISHEK RAJPUT

PROCESS OF TANNERY INDUSTRY. WASTE GENERATION POINTS. CHARACTERSTICS OF WASTE WATER,

DISCHARGED FROM TANNERY INDUSTRY. TREATMENT SCHEMES FOR WASTE WATER. INNOVATIVE TECHNOLOGY.

CONTENTS:

1.LEATHER MANUFACTURING PROCESS IN TANNERY INDUSTRIES.

Preparatory stages

Tanning and Crusting

Surface coating

PROCESS INCLUDES:-

The preparatory stages are when hide/skin is prepared for tanning.Many options for pretreatment of skin exist.Not all of the options may be performed.Preparatory stages may include:-

Preservation-the hide/skin is treated with a method which renders it temporarily. unputrescible.

Soaking-water for purpose of washing or rehydration is reintroduced.

Liming-unwanted proteins and “opening up” is achieved.

Preparatory stages :

Unhairing-the majority of hair is removed. Fleshing-subcutaneous material is removed. Splitting-the hide/skin is cut into two or more

horizontal layer. Reliming-the hide/skin is further treated to

achieve more “opening up” or more protein removal.

Deliming-liming & unhairing chemicals are removed this step.

Bating-proteolytic proteins are introduced to the skin to remove further proteins and to

assist with softening of the pelt.

Degreasing-natural fats/oils are stripped or as much as is possible from the hide skin.

Frizing-physical removal of fat layer inside the skin.

Bleaching-chemical modification of dark pigments to yield a lighter coloured pelt.

Pickling-lowering of pH value to the acidic region. Must be done in presence of salt.

Depickling-raising of the pH out of the acidic region.

SOAKING HIDES.

TRIMMING.

Tanning is the process that converts the protein of the raw hide or skin into a stable material which will not putrefy and is suitable for a wide variety of end applications. Tanned material dries out to a flexible form. That does not become putrid when wetted back.

TANNING:

Crusting is when the hide/skin is thinned, retanned and lubricating often a coloring operation is included in the crusting sub process. The chemicals added during crusting have to be fixed in place. The culmination of the crusting sub process is the drying and softening operation.

CRUSTING:

For some leathers a surface coating is applied. Tanners refer to this as finishing. Finishing may include:-

Oiling Brushing Padding Spraying Roller coating Curtain coating Polishing Plating Embossing Ironing Combing Glazing

SURFACE COATING:

WASTE GENERATION POINTS:

Maximum waste generation points in tannery industry are processes such as:

Soaking:-generation of waste water. Unhairing:-waste generation. fleshing:-subcutaneous material waste

generation. Splitting. Trimming. Bleaching. Bating. Deliming.

CHARACTERSTICS OF WASTE WATER,DISCHARGED FROM TANNERY INDUSTRY:

pH 8.2-8.9

Alkalinity(mg/l) 2000-2700

Total BOD(mg/l) 2000-3100

Soluble BOD(mg/l) 1670-2600

Total COD(mg/l) 4500-7500

Soluble COD(mg/l) 25000-37000

Chlorine(mg/l) 10000-15000

Sulphates(mg/l) 1540-3300

Chromium(mg/l) 160-300

Typical characteristics of tannery waste water:

SOLIDS:-Solids to be found in tannery effluent fall into several distinct categories:-

SUSPENDED SOLIDS:-Quality of insoluble matter contained in waste water.

SETTELEABLE SOLIDS:-Quantity of solids, having tandency of settle down.

GROSS SOLIDS:-They are larger than a sampling machine can handle.

ex-leather pieces,fleshing residue.

TANNERY EFFLUENT CONTAINS:-

BOD:-Tanning waste have a long break down period,this longer digestion periods can apply to a variety of chemicals used in manufacturing leather.

NITROGEN:-Nitrogen is contained in several different compounds:-

Total kjeldahl nitrogen:-Nitrogen contained in proteinaceous material(liming and unhairing)

SULPHIDES:-Sulphide content is tannery effluent result from the use of sodium sulphide & sodium hydrosulphide.and the breakdown of hair in unhairing process.

NEUTRAL SALTS:-Two common types of salts are to be found in tannery effluent:-

Sulphates Chlorides OIL & GREASE:-During leather

manufacture,natural oils and grease are released from within the skin.

pH value:-acceptable limit ranges from 5.5 to 10.0.

CHROMIUM COMPOUNDS:-Two forms of chrome are associated with the tanning industry :-

Chrome 3+(trivalent chrome) Chrome 6+(hexavalent chrome)

TREATMENT SCHEMES FOR WASTE WATER .

Most solids can be removed using simple sedimentation techniques with the solids recovered as slurry or sludge. Very fine solids and solids with densities close to the density of water pose special problems. In such case filtration may be required. Although flocculation may be used, using alum salts or the addition of polyelectrolysis.

SOLIDS REMOVAL:

Biodegradable organics material of plant or animal origin is usually possible to treat using extended conventional wastewater treatment processes such as activated sludge or trickling filters.

REMOVAL OF BIODEGRADABLE ORGANICS

Activated sludge is a biochemical process for treating sewage and industrial waste that uses air(or oxygen) and micro-organisms to biological oxidize organic pollutants,producing a waste sludge(or floc) containing the oxidizing material.

ACTIVATED SLUDGE PROCESS

A trickling filter process consists of bed of rocks,gravel,slag,peat moss or plastic media over which wastewater flows downwards and a contacts a layer of microbial slims covering the bed media.Aerobic conditions are maintained by forced air flowing through the bed or by natural convection air.The process involves adsorption of organic compounds in wastewater by the microbial slime layer, diffusion of air into the slime to provide the oxygen required for the biochemical oxidation of organic compounds .The end projects include carbon dioxide gas,water and other products of oxidation.As the slime layer thickness,it becomes the air to penetrate the layer and an inner anaerobic layer is formed.

TRICKLING FILTER PROCESS

TREATMENT OF OTHER ORGANICS:- Synthetic organics material including

solvents,paint,pharmaceuticals,pestricides,cooking products and so forth can be very difficult to treat.Treatment methods are often specific to the material being treated.Methods include advanced oxidation processing,distillation,adsorbtion,vitrification,incineration,chemical immobilisation or landfill disposal.

TREATMENT OF ACIDS & ALKALIS: Acids & alkalis can usually be neutralised under

controlled conditions.neutralisation frequently produces a precipitate that will require treatment as a solid residue that may also be toxic.In some cases,gases may be evolved requiring treatment for the gas stream.Some other forms of treatment are usually required following neutralisation.

OIL AND GREASE REMOVAL: Oil and grease can be recovered from open

water surfaces by skimming devices.

Chromium, present in tannery effluent is removed by using chromium salts(chromium chloride as adsorbate) and cement kiln dust (a waste from white cement industry) as adsorbent.

Treatment of chromium:

DEMONSTRATION OF EFFECTIVE AND EFFICIENT TANNERY EFFLUENT TREATMENT

USING AN INNOVATIVE INTEGRATED AND COMPACT BIOLOGICAL AND PHYSICAL TREATMENT PLANT

INNOVATIVE TECHNIQUES

A significant number of operations within a tannery are wet operations consuming large

amounts of water, chemicals and energy and leading to large amounts of polluted water.

Through “process integrated” measures a significant reduction of water consumption

and pollution load can be achieved, however tanneries keep producing wastewater

requiring special treatment. In cases where the potential for “process integrated”

measures has worn out, further pollution reduction has to be found in the improvement

of end-of-pipe measures.

Compared to Best Available Technology1 the following effluent quality performance is demonstrated:

- better COD-removal efficiency (+ 5 to 10 %); - better Chromium removal efficiency (+ 5 to 10 %); - better Sulphur removal efficiency (+ 30 %); - equal Nitrogen removal.

This all is being realised against lower total annual cost than in the BAT situation as a result of:

- lower costs for sludge discharge (reduction sludge volume 50 % compared to BAT);

- lower costs for discharging waste water to municipal treatment plant;

- significantly lower chemical consumption.

QUERIES???????