The total global input of bovine hides, sheep, goat and pigskins is nearly eight million tonnes as wet salted weight a year. On this basis, it could be estimated that tanning operations world-wide use some four million tonnes of various chemicals, produce over 300 million m~3 of waste water, and about eight million tonnes of solid waste and dewatered sludge. However, these figures do not include the amount of salt used for preservation. Since possibly a half of the worlds production of bovine hides and a great deal of skins are preserved by applying about 40% of salt on green weight, it is evident that hundreds of thousands tonnes of preserving-salt end up in waste water. Despite frequent deficiencies in design and size of effluent treatment plants (ETPs), when properly designed, constructed and operated, the usual discharge limits for the main pollution load parameters such as BOD, Suspended Solids, Nitrogen, and the major part of COD can be met. However, in virtually no case are tanneries able to meet the typical limits applicable for chlorides and sulphates, the two main components of the Total Dissolved Solids.
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