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Sludge dewatering: filter press

Purpose

A major operating cost for water purification is the sludge disposal cost. The lower the dry matter content of this sludge, the more one is paying for the disposal of water. Sludge dewatering is often recommended in order to significantly reduce the costs for sludge disposal. Sludge dewatering implies free water between the solid materials is removed so that a semi-solid mass is obtained.

  • Concentration of solids, sludge dewatering
  • Separation of manure and digestate into a thick fraction and fine fraction
  • Dewatering biological or physicochemical sludge
  • Dewatering mineral slurries

Principle

A chamber filter press consists of a number of square plates over which filter cloths are stretched. The space formed between two plates becomes a chamber. The plates are pressed against each other and then filled under pressure with sludge The filter cloths provide a separation of water and solids. The sludge remains behind in the form of a press cake fraction, while the water exits the press as a filtrate. Once the press cakes are formed the plates are moved apart, the press cakes are removed and the press cycle starts again.

A variation on the classic chamber filter press is the membrane filter press, which enables significantly shorter cycle times

Scheme

Applications

A decanter centrifuge and a belt press require little supervision which is an advantage with respect to a chamber filter press. A decanter centrifuge is easily adjusted for various types of sludge though this is more difficult with a sieve belt press as well as the chamber filter press (other screen cloths). A chamber filter press has generally a higher dry matter content than a decanter centrifuge which, in turn, performs better than a sieve belt press.

Example of realisation

Approach Trevi

Trevi aims to initially minimize sludge production through process-oriented interventions. Next we investigate in function of the amount and type of sludge if there is an economic advantage to achieve by means of sludge dewatering and which technique is most appropriate. With the degree of sludge dewatering the dewatering cost also increases. The balance between intensity of dewatering and sludge disposal costs has to be found.