Characteristics of wastes from Tannery industries.
The tannery industry belongs to one of the most polluting industrial sectors. Almost every tannery industry uses significant amounts of chemicals in the process of transforming animal hides into leather.
Stages of Tanning
- Liming and unhairing
- De-liming and bating
- Chrome-tanning (Chrome splitting)
- Re-tanning and dying
- Post-tanning and finishing process
Wastes from Tannery industries (Generated stagewise)
- In the soaking stage, the most polluting stage of the tanning process contributes around 50–55% of the total pollution load of the tanning industry.
- In the liming stage, protein, hair, skin and emulsified fats are removed from the hides, they are released in the effluent and increase its total solids contents.
- The effluents from the tan-yard processes, de-liming and bating contain sulfides, ammonium salts, and calcium salts, and the effluent is slightly alkaline.
- The pickling and chrome tanning effluents contain sulphuric acid, chrome, chlorides, sodium bicarbonate and sulfates.
- The major pollutants of the post-tanning process are chrome salts, dyestuff residues, fatliquoring agents, syntans and other organic matter.
Nature of wastes
Characteristics of wastes
TDS and TSS values
BOD and COD values
Pollution and health concerns
Human health can also be affected by toxic hazards generated through the unskilled and unprotected handling of pesticides, tanning chemicals, and treated hides and skins. The lack of effective implementation of legislative control, poor processing practices and use of unrefined conventional leather processing methods have further aggravated the pollution problems.