2003-Waste Water Treatment in Leather Industry

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WASTE WATER

TREATMENT IN LEATHER INDUSTRY

PRESENTATION

BY:



INTRODUCTION

Tannery wastes rank among the heaviest and most

polluting of all industrial wastes.

Characteristics-- disagreeable appearance, a bad smell,

and a high degree of intractability.

Animal skins consist of three layers:

The epidermis (cuticle or outer layer)

Layer of fatty tissue &

The inner layer, corium.

Tanning process objective: strip off the two outer layers

-- subject the corium to the action of agents -- from a

semi-solid protein to the tough insoluble mass --

LEATHER .



action of tanning agents

Corium undergoes atransformation (corium becomes insoluble in water,

tough, flexible and highly durable)

Main tanning process:

vegetable tanning process : sole, harness etcchrome tanning process: glove & garment leather.

miscellaneous tanning process ( Alum, oil etc):

furs, chamois etc.



TANNING-PROCESS



WASTEWATER CONTAINS:

Salts (Cl), fat, protein, preservatives (soaking);

Lime and ammonium salts, ammonia, protein

(hair), and sulphides (fleshing, trimming, bating);

Chromium(salts) and polyphenolic compounds

(tanning);

Dye and solvent chemicals (wet-finishing).



CHARACTERSTICS OF TANNERY

WASTES Heavy-- Large amount of suspended matter (hairs,

particles of flesh, suspended particles of lime and calciumcarbonate).

Ability to form a lime mortar inside receiving sewer (

lime calcium carbonate).

CO2

decomposition of organic matter

Vegetable tanneries high colour -- spent tan liquors.

Chrome tanneries color absent

Chrome tannery -- intermittent discharges --highly

insoluble, inorganic solids, low in pH value, and contain

considerable chromium (moderately toxic).



WASTEWATER TREATMENT

Physical treatment (mechanical treatment) screening,

filtering, grease removal, settling, sedimentation etc.

Physico-chemical treatment coagulation with

chemicals, followed by sedimentation.

Biological treatment sand filters and trickling filters.

Sludge handling.



STORAGE AND SEDIMENTATION

Beam house

scrub house

BY PASS

Dry weather operation Tan yard

waste

RIVER

FIG: FLOW DIAGRAM OF TANNERY WASTE TREATMENT PLANT

Settling basin

Settling basin

Pump Sump

Sludge

lagoon

Tan

liquor

storage

lagoon

Man hoi

Man hoi



Tannery waste treatment processes -- storage, sedimentation,

and regulated discharge.

The plant, designed for 200,000 gallons of waste per day-- 2

earthen settling basins, each of 500,000 gallons capacity--operated -- fill and draw units --24hour period.

The weaker waste -- discharged directly & stronger wastes

(intermittent wastes) are settled and subjected to regulated

discharge.

To eliminate a larger portion of BOD & to reduce the amount

of colour -- effluent vegetable tan liquors--separate lagoons

&discharged --periods of high water in the stream.

A separate lagoon for the spent tan liquors --storage for 200

days of normal tannery output. During low stream flow, the scrub house or bleaching wastes

will also be put in the spent tan lagoon to ensure a minimum of

colour in the waste discharge.



CHEMICAL PRECIPITATION

Degree of treatment -- plain sedimentation is insufficient --

coagulation by the addition of chemicals. Coagulants --sulphuric acid, carbon dioxide from flue gas, alum,

and iron salts.

Mechanical flocculation -- part of the treatment.

Alum probably --longest history of use-- tried by several tanneries --

auxiliary to sedimentation during period of low stream flow.

Flue gas -- elimination of caustic lime in tannery waste

Iron salts -- either alone or conjugation with lime.



TRICKLING FILTER PROCESS

A schematic cross-section of thecontact face of the bed media in a trickling filter

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A typical complete

trickling filter system



SLUDGE DISPOSAL

All methods -- tannery waste treatment -- sedimentation,

with or without the addition of chemicals -- formidablequantities of sludge (5-10%).

Disposal --sludge in an acceptable --difficult problem.

Common practice -- discharge sludge -- low lying areas

of waste land / to specially prepared sludge lagoons(feasible only if sufficient land area can be provided).

A thick sludge -- a smaller area-- thick tannery sludge ---

difficult to pump.

More satisfactory method of sludge disposal -- provisionof drying beds of sand and cinders, with or without under

drains.

Vacuum filters -- dewatering tannery sludge¶s.



PREVENTION OF WASTE

PRODUCTION Water conservation:

A reduction of water

Re-use of wastewater

Curing hides and skins:

Reduction of the use of salt for preservation

Chilling without salt

Radiation by electron beam or gamma rays.

Biodegradable preservatives (insecticides) should be

used instead of derivatives of chlorinated aromatic

hydrocarbons

Beamhouse processes:

Hair saving methods -- degraded keratin



Tanning: Aluminium, zirconium, titanium and iron are might

be used as substitutes for chromium salts

Finishing:Reduction of volatile organic compounds (VOC) --

aqueous finishes for base and middle finishing coatings.



REFERENCES

Rudolfs W., (2006). Industrial Wastes, Their Disposal

and Treatment. Agrobios (India). pp:148-171.

Mahopathra P.K., (2006). Environmental Biotechnology.,

I.K.International Publishing House Pvt. Ltd. pp:101-147. http://www.fao.org/wairdocs



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2003-Waste Water Treatment in Leather Industry