• Pakistan
     - BackGround
     - Leather Industry

 • Enviornmental Act of Pakistan

 • Kasoor City
     - Geographical BackGround
     - Tanning Industry

 • Project Introduction

 • Project Detail
     - Effluent Treatment Plant
     - Chromium Recovery Plant
     - Social Sector Of KTPC
     - Cleaner Technology

 • Project Brief
     - Cost Sharing and Funding
     - Financial Viability
     - Objective
     - Project Beneficieries

  • Tanning
     - Process
     - Chrome Tanning

 • Tannery Waste Treatment
     - Water Pollution Equipment
KASUR TANNERIES POLLUTION CONTROL PROJECT (KTPC)
  - A DOCUMENTARY		    
The treatment of the tannery waste for disposal into watercourses usually involves one or combination of following techniques:

1. Collection and storage of waste:
With the regulated discharge adapted to the conditions of the watercourses. This technique may be applied to the whole waste or it may be restricted to the one or more of the concentrated waste fractions.

2. Plain sedimentation:
In basins ranging from the simple earth lagoons to tanks with the mechanical sludge removal. Obviously, sedimentation is also involved first step but it is not, it's primary purpose. The accumulated sludge is discharged in the water course along with the waste.

3.Coagulation with the chemicals:
The coagulation is done by the chemicals known as the coagulants, which may be alum, iron salt, carbon dioxide with or without the addition of lime.

4.Biological treatment methods:
Including sand filter and trickling filters. Biological treatment methods are largely confined to the pilot plant studies, mainly because of the difficulty and expense involved in treating straight tannery waste by such methods.

Present practice is to adapt one or more of the three methods cited above. Usually the process comprises of the four stages, which are as follows:

A. MECHANICAL CLEANING

The coarse suspended particles are removed using grids and screens with the mesh size of about 0.5 to 5 mm. At least 40-60% of pieces of hides, flesh, fat, and felted hair can be removed.

B. STORAGE AND SEDIMENTATION

The majority of tanneries, which practice the waste treatment of any kind have resorted to processes which are made up of various combination of storage, sedimentation, and regulated discharge. In many instances, holding tanks are used which serve only to regulate the discharge into the stream and to extend it over a longer period of the day, making no attempt at the removal of the suspended and dissolved materials. Little attention is given to sludge removal until it is necessary to remove them because the capacity of the basin is no longer adequate. At this stage the BOD of the waste is largest and thus the storage tank must have the enough capacity to store the waste for the 24 hrs.

In the others, weaker wastes are discharged directly and only stronger wastes, usually so called intermittent wastes, are settled and subjected to the regulated discharge. Further refinements may be introduced, including the selective mixing of the components of the waste to produce mutual precipitation.

C. CHEMICAL PRECIPITATION

Where the degree of the treatment obtainable by plain sedimentation is insufficient , some tanneries have considered the coagulation by the addition of the chemicals. The coagulants tried are sulfuric acid, aluminum sulfate, iron sulfate, lime, carbon dioxide as the flue gas. Mechanical flocculation has sometimes been used as a part of treatment. The improvements observed are better removal of suspended solids and possibly of color. The additional BOD removal secured, are rather disappointing.
Among the coagulants the aluminum sulfate is the most widely used. After coagulation the carbon dioxide is used to adjust the pH of the effluent. The concentration of the chemicals commonly employed are :
400-1300 mg/l for calcium oxide
200-500 mg/l for iron salts and alum.
Other recommended coagulants are:
Hydrogen carbonate and ferrous sulfate
Ferric sulfate and hydrogen sulfate
Stack gas from boiler for neutralization.
Stack gas for neutralization of calcium containing waste materials.
In all four cases further treatment is required.

D. BIOLOGICAL TREATMENT

The last stage of the treatment is the biological treatment of the effluent. it is basically the oxidation process whose purpose is to reduce the BOD of the effluent. The treatment can be done by the sand filters, trickling filters or the activated sludge method. The chemical oxidation processes can also be used instead of the biological treatment. The tanning liquor can be re-used if following processes are used:
a. adsorption on activated carbon.
b. extraction with the acetone.
c. oxidation with the sodium hypochlorite.
d. Flocculation with aluminum or calcium hydroxide.
e. Coagulation with organic polyelectrolyte.
f. Ion exchange.

                                        CHROMIUM TREATMENT

The chromium hydroxide can be precipitated from the waste water if lime or caustic soda is added to the water. It is believed that there is a considerable effect of the pH on the solubility of the chromium hydroxide. The precipitation is believed to be best at the pH of 7.5-8.5. soda ash is also used for the precipitation but still commonly used is the lime. The coagulant aid has also improved the efficiency of the recovery. Filtration of the effluent after post precipitation has been employed to remove the small, non-settable chromic hydroxide not readily removable by the sedimentation.
The recovery of the chromium hydroxide is also possible by the ion exchange method. As the chromium is positively charged thus a cationic type of resin is employed. The ion exchange may be employed for the removal of the chromium in two modes:

1. A concentration mechanism to recover the trivalent chromium value.
2. Other mode is as a polishing treatment by the precipitation.

There is following two reasons for the Ion exchange method for the recovery of trivalent chromium.

1. To pass chromium acid baths through the cation resin for the removal of Iron, aluminium, and trivalent chromium. But the chromic acid if above the concentration of 250g/l will destroy the resin and it must be diluted before ion exchange.
2. The second reason for ion exchange is for complete purification of plating rinse water.
In this method diluted waste water through both an Ionic and cationic resin to remove chromium species of both positive and negative charge. The treated rinse water can then be recycled.

Assuming a 16 hr / day operating costs are estimated at 0.40 $ / gal ( 1000 ) according to an estimation.

The waste of tannery is characterized by high contents of the organic matter , but which also contains the high level of inorganic contents and thus it is ranked among the heaviest and most polluting industry. The waste contains neolithic characteristics, notably disagreeable appearance, bad smell, and high degree of tractibility.
The tannery wastes of the Kasur exihibit following properties;


The primary pollutants that leather industry in Pakistan create are heavy metals ( chromium, cadmium, etc.) various organic chemicals and acids. Different pollutants at different stages of tanning are shown below;

SOURCE: pollutants from hides, decomposed chemicals and various spent solution for preparation of hides.

PROCESS: preliminary soaking.
POLLUTANTS: fats, blood, hair, salts, solid particles, pieces of flesh.
COLOUR: dull grey colour
ODOUR: perceptible odour of hydrogen sulphide.

PROCESS: liming
POLLUTANTS: mainly calcium compounds, sodium and potassium sulphide, albuminous substance, residual hair, pieces of flesh and fat. Suspended matter as high as 2-4%.
COLOUR: dirty green.
ODOUR: putrid odour.
pH: as high as 11.6

PROCESS: pickling and chrome tanning.
POLLUTANTS: traces of protenious material, sodium chloride, mineral acids, trivalent chromium. Low contents of suspended matters.
pH: below 4.0 i.e highly acidic.

PROCESS: other tanning processes
POLLUTANTS: tanning compounds and organic impurities.
COLOUR: dirty brown
pH: below 5.0

PROCESS: dyeing and oiling.
COLOUR: black to dark brown.
POLLUTANTS: fat, mineral oils, dyes, and high contents of suspended matters.

 

                                
 
The chromium is most dangerous element in the effluent discharged from the tanneries. If chromium gets into the human body by any means like drinking water etc. then it can cause gastric cancer, liver cancer, kidney failure, ulcer, acidity. The most dangerous part is that the metal can enter the blood and can cause any kind of blood problems. It can cause serious complications in pregnancy and can subject to birth of handicapped child.

Smell is produced when the vapours of that effluent are present in air. If the vapours contain metal or acid fumes they again cause blood and kidney problems. Also in extreme smell man can suffer from "Anosmia", which is the loss of the sense of smell. Apart from that it can cause allergy reactions, lung infections and in excessive dosage can be fatal.


There are number of ways to re-use the waste or recovery of the useful by-products from the wastes can contribute towards the reduction of the strength of tannery discharge. Waste pickle liquor are brought upto the strength by the addition of the necessary chemicals and can be re-used over considerable period.
Spent chrome liquor may be partially recovered by combining them with fresh liquor for re-use. Direct recovery of chromium from these liquor has been resorted to when the chromate have been in short supply. The process consists of precipitation of chromium hydroxide by the addition of the alkali, filtration of the precipitate and treatment of the precipitate with sulfuric acid to produce chromic sulfate solution.