Methods of dewatering:-

• Sludge should never be applied to a bed until the preceding dose has been removed.
• Several drying beds will be generally required with their number increasing with an increase in the number of days for which the sludge is kept on beds.
• Normally sludge is removed from the beds after a period of about 7-10 days as within this period, about 30% of the moisture goes away and the surface of the sludge gets cracked.
• The sludge cakes are removed by spades and they are dumped into the pit for further drying. The dried sludge is generally used as manure in our country as it contains 1.7% nitrogen, 1.5% phosphoric acid and 0.5% potash.
• It may also be used for filling up-low lying areas. It may sometimes be disposed of by burning.

The selection of the method of treatment of the sludge:-

The process involved in the sludge treatment vary from gravity thickening to incineration.

The following factors are adapted for dewatering:-

1. The character of the sludge i.e. raw digested.
2. The availability of land
3. The suitability of sludge for disposal by dilution.
4. The local conditions for making use of sludge as a soil conditioner or fertilizer.
5. The type of weather condition i.ie. hot, humid, dry, cool.
6. The availability of capital and the expected operational costs.
7. The size and type of waste water treatment plant .
8. The local air pollution control regulation

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