Characteristics of waste water of tannery industry:

• Average flow: 1310 $m^3/day$

• pH: 8-9

• Alkalinity: 260 mg/l

• Cl content: 4280 mg/l

• Total solids: 10505 mg/l

• Suspended solids: 1080 mg/l

• BOD: 1725 mg/l

• COD: 3700 mg/l

Origin of waste generated from tannery industry:

• Soaking effluent: Soak liquors contain soluble proteins like albumin and are a major source of proteolytic and other bacteria. Suspended matter likes dirt, dung and blood adhering to the hides and skins are discharged intermittently with the soak liquor.

• Liming effluent: Lime liquors contain suspended and dissolved lime and sodium sulphide. It is highly alkaline and is one of the heaviest of the fractions in terms of BOD.

• Unhairing and fleshing effluent: The effluent from the unhairing operation is more or less continuous and contains mostly hair and sulphides. Fleshing operation gives rise to an effluent which is also more or less continuous and contains fatty and fleshy matter in suspension.

• Deliming effluent: Spent deliming liquors which are discharged as waste also carry a significant pollution load in terms of BOD.

• Spent bate liquor: It has high amount of organic matter and ammonical nitrogen due to the presence of soluble skin proteins and ammonium salts in bating. BOD is usually low.

• Vegetable tanning effluent: The spent vegetable tan liquor is probably the strongest fraction in a composite tannery effluent. Although its discharge is intermittent and constitutes about 10% of the total volume of the effluent.

• Chrome tanning effluent: The spent chrome tan liquor is greenish in colour and highly acidic. The waste contains a high concentration of trivalent chromium. Hexavalent chromium is not generally present in the waste chrome liquor because of the reducing agent used and one-bath process utilized.