Treatment of Sludge: Conditioning, Dewatering, Drying

1. by
Prof . V. V. Sasane (Assistant Professor)
Department of Civil Engineering
Sanjivani College of Engineering, Kopargaon, 423603
Subject: - Environmental Engineering-II
B.E. Civil
Sanjivani Rural Education Society’s
Sanjivani College of Engineering, Kopargaon, 423603.
An Autonomous Institute Affiliated to Savitribai Phule Pune University, Pune
ISO 9001-2015 Certified, Accredited by NAAC (A Grade)
UNIT-V: Onsite Sanitation Treatment System
5.4: Treatment and Disposal of Sludge

2. Content
• Method to Treat and Dispose of Sludge
• Thickening or concentration
• Digestion or stabilization
 Conditioning
 Dewatering
 Drying
• Incineration or thermal reduction
• Ultimate disposal

3. Sludge Conditioning
• Sledge conditioning is mainly to improve its dewatering characteristics. The two methods
most commonly used for sludge conditioning are
• Chemical conditioning
• Heat treatment
• Chemical conditioning:
It is the process of adding certain chemicals to the sludge which result in coagulation of solid
and release of absorb water;
• Heat treatment:
In this process sludge heated for a short period of time under pressure. As a result sludge
sterilized, deodorized, and is dewatered readily on vacuum filter.

4. Sludge Dewatering
• Sludge dewatering is a physical unit operation used to reduce the moisture content of the sludge. It is
carried out for one or more of the following reason:
• 1. The cost of the trucking sludge becomes substantially lower when volume is reduced by the
dewatering.
• 2. Dewatered sludge is generally is here to handle then thickened or liquid sludge.
• 3. Dewatered sludge have more calorific value due to removal of excess moisture.
• 4. Dewatering provide odourless and non perishable sludge.
• 5. Landfilling of the water reduces leachate production.
• The dewatering of digested sludge is a complete by either by one year drawing to open sludge drying
bed three mechanical method: 1. Air drying 2. Open sludge drying bed 3. Mechanical method

5. Open Sludge Drying Beds
• This method of dewatering and drying the sludge is
especially suitable for those location where temperature
are higher similar to the one prevailing in our country.
• The method consists of applying the sludge on specially
prepared open beds of land.
• A typical cross section of sludge drying bed is shown in
figure. %he sludge drying bed are usually consists of
bottom layer of gravel of uniform size over which is laid
clean sand
• Open jointed tiled underdrain are laid in the gravel layer
to provide positive drainage as the liquid pass through
the sand and gravel.
• Underdrains are made of vitrified clay pipes of at least
10 cm diameter laid with open joint.

6. • Underdrains are placed not more than 6 metre apart
around underdrain graded gravel is placed in layer upto 30
cm with a minimum of 15cm about the top of the under
trains.
• Atleast 3 cm of the top layer should consist of gravel of 3 to
6 mm size clean sand of effective size 0.5 to 0.75 mm and
uniformity coefficient not greater than 4 is placed over the
gravel depth of the sand may vary from 20 to 30 cm.
• The finished sand surface should be level.
• The drying beds are commonly 6 to 8 m wide and 30 to 45
m long.
• Multiple discharge points should be used with large sludge
bed to reduce the length of the wet sludge travel

7. • In order to have a feasibility in operations beds should be at
least 2 in number.
• The sludge inlet to the drying bed have minimum diameter 20 cm
terminating at least 30 cm above the sand surface.
• When digested sludge is deposited on well drained bed of sand and
gravel, the dissolved gases tends to buoy up and float the solid leaving
a clear liquid at the bottom which drains through the sand rapidly.
• The major portion of the liquid drains off in few hour after which
drying commences by evaporation.
• The sludge cakes shrinks producing cracks which accelerate
evaporation from the sludge surface. The dried sludge cakes can be
removed by the showel or fork when the moisture content is less than
70%.
• Some send cling to the bottom of the sludge cake result in reduction of
sand death, when this depth reduces to 10 cm; clean course sand used
to replenished the original death of the bed