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Concentración y deshidratación de lodos: prensa de banda

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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. To significantly lower the costs for sludge disposal dewatering is often recommended. Sludge dewatering means that the 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 belt press is an advanced version of a dewatering table, in which the sludge ends up between two sieve belts, and is compressed by pressure rollers, whereby water is pressed through the pores of the filter belt and is so separated from the sludge. There is also a difference in speed between the two belts so that in addition to pressure shear forces also assist in the drainage; thereby obtaining a higher dry matter content. Like a decanter centrifuge a belt press is a non-stop device.

Typically, a belt press is preceded by a gravity drying step, whereby already a large amount of free water can be separated from the sludge-water mixture. The sludge is then conditioned with polymer in order to increase the dewatering efficiency through the sieve belt press. The sludge water is then compressed under low pressure through the belt press in the first instance, possibly followed by compression under high pressure.

The performance of the filter belt press is determined by, i.a. sludge quality, chemical conditioning, speed of and pressure exerted by the mud on the sieve belt press and porosity of the sieve. For safety reasons the moving parts of the sieve belt press are to be screened from the environment.

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 and 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.

Approach Trevi

Trevi aims to initially minimize the sludge production by means of process oriented interventions. For this we look both to a reduction of the pollution load from the production as well as optimization of the water treatment plant (load, chemical use). We then investigate in function of the amount and type of sludge if there's an economic advantage to be gained by sludge dewatering and if so by what technique.With the degree of sludge dewatering the cost of dewatering increases. The balance between intensity of dewatering and sludge disposal costs have to be found.