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For corresponding treatment in the tanneries, decanters from GEA Westfalia Separator Group are used which optimally prepare a subsequent biological treatment.
Tanneries belong to industrial sectors with the highest levels of water consumption. To make good quality leather from one ton of raw material, experience has shown that up to 60 m 3 of water are required. The volume of waste water, which contains high levels of alkaline and organic substances is, of course, correspondingly high. Direct discharge or treatment in municipal waste water clarification plants is therefore not possible without appropriate treatment of the waste water.
Leather production is one of the oldest trades. Modern industrial-scale production still requires extremely high volumes of process water. The water is not only needed for transportation in the production process but also for various tasks such as unhairing or soaking the hides. The waste water problem is correspondingly acute – in European producer countries like Italy and Spain but also in China, India, Korea, Brazil and the USA, to name just the most important producers.
As a result of the specific production methods, the waste water not only has high alkaline levels (pH value 10), but is also contaminated with chemicals such as sulphite and chrome, and has a high level of organic substances. This means that waste water from tanneries cannot usually be discharged directly into public sewerage systems. To solve the problem, biochemical processing of the waste water is a standard operation in many installations. Decanters from GEA Westfalia Separator also play a significant role.
After the waste water has been collected from the tanning process and polymer has been added, the decanters continuously separate all organic solids such as hair from the thickened sludge. The separated solids can be composted and find application, for example, in horticulture or forestry. The liquid phase is then subjected to biological treatment. The resultant sludge is recycled into the dewatering process; the waste water can be sent safely to conventional municipal waste water treatment plants.
The advantages of decanters provide optimum dewatering capacity and use very little rinsing water. The closed system prevents aerosols from escaping; such aerosols would otherwise pose a hazard for humans and the environment.