Write a note on disposal of sludges. Explain floatation and centrifugation.
1 Answer

Disposal of sludge:-

  • Final or ultimate disposal of sludge, which cannot be reused, is by landfilling or incineration.

  • Since sludge for landfilling usually contains heavy metals or toxic chemicals, lining of the landfill with clay or plastic liner may be required to prevent contamination of ground water.

  • Incineration of sludge is by a multiple hearth furnace or fluidized bed furnace.

  • Energy input is required to dry the sludge before combustion is self-sustaining.

  • Combustion flue gases usually need treatment to meet air pollution control standards. Investment and operating costs are high.


  • It may also refer to as froth floatation which is a process for selectively separating hydrophobic materials from hydrophilic. This is used in several processing industries.

  • Historically this was first used in the mining industry, where it was one of the great enabling technologies of the 20th century.

  • It has been described as the single most important operation used for the recovery and upgrading of sulphide ores.

  • The development of froth floatation has improved the recovery of valuable minerals, such as copper and lead bearing minerals.

  • Along the mechanized mining, it has allowed the economic recovery of valuable metals from much lower grade ore than previously.


  • Centrifugation is a process which involves the application of the centripetal force for the sedimentation of heterogeneous mixtures with a centrifuge and is used in industrial and laboratory settings.

  • This process is used to separate two immiscible substances. More dense components of the mixture migrate away from the axis of the centrifuge, while less dense components of the mixture migrate towards the axis.

  • Chemists and biologists may increase the effective gravitational force on a test tube so as to more rapidly and completely cause the precipitate to gather on the bottom of the tube. The remaining solution may be discarded with a pipette.

  • The rate of centrifugation is specified by the angular velocity usually expressed as revolutions per minute (RPM) or acceleration expressed as g.

  • The most common application is the separation of solid from highly concentrated suspensions, which is used in the treatment of sewage sludges for dewatering where less consistent sediment is produced.

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