Sludge treatment and disposal: most of the suspended solids and some of the dissolved organic solids, in a converted form, are separated from the main flow of the, in the form of sludge. The quantity and the characteristics of sludge depend upon its origin. In general, the sludge contains 92-98% of moisture. The higher organic content of the sludge demands further treatment prior to its final disposal either on land or into the sea.          

Sludge treatment process:  sludge treatment may include all or a combination of the following unit operation and process-

        (1) Thickening (2) digestion (3) conditioning (4) dewatering (5) incineration

• Thickening is meant for the reduction of moisture content of the sludge.
• Digestion is a biological method of treatment and is meant of the reduction of organic content of the sludge. The digestion may be accomplished under either aerobic or anaerobic conditions.
• Condition improves the drainability of the digested sludge, and may be accomplished by any of the following process like elutriation, chemical conditioning, heat treatment; freezing etc. chemical conditioning consists of addition of some coagulants like ferric chloride, lime, alum etc.
• Dewatering is accomplished either by air drying in sand, drying beds, or by mechanical means using vacuum filtration, heat drying, centrifugation etc.
• Dewatered sludge may sometimes require further treatment such as incineration.
• The ultimate disposal of dewatered sludge after incineration may be on to the land or into the sea.