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‘’ What is a sludge digestion tank ?’

Today, let's try to answer this question in detail!

A sludge digestion tank is a R.C.C. tank of cylindrical shape with
a hopper bottom and is covered with a fixed or floating type of
roof. The latter makes the operation much more effective. The
weight of the cover is supported by sludge, and the liquid forced
between the tank wall and the side of the cover provides a good
seal. The raw sludge is pumped into the tank where it is seeded
with digested sludge.

On undergoing anaerobic digestion, gases of decomposition (chiefly
methane and carbon dioxide) are given out. The gas rises out of the
digesting sludge, moves along the ceiling of the cover and collects
in the gas dome. The cover can float on the surface of the sludge
between the landing brackets and the overflow pipe. Rollers around
the circumference of the cover keep it from binding against the
tank wall.

The digested sludge, which settles down to the bottom of the tank
is removed under hydrostatic pressure periodically, say, once a
week. To maintain optimum temperature, the tank is generally
provided with heating coils through which hot water is circulated.

The supernatant liquor i.e., the part of the tank content lying
between the scum and the sludge is withdrawn at the optimum level
through a number of withdrawal points located at different
elevations of the tank. As it is high in BOD and suspended matter
contents, it is sent back to the incoming raw sewage for undergoing
re-treatment. The scum formed at the surface gets broken up by the
recirculating flow or through mechanical rackers called
scum-breakers.

The amount of sludge gas produced varies from 0.014 to 0.028 cubic
m per capita with 0.017 cubic m being quite common. The gas
produced contains 65 per cent of methane with a calorific value
5400 - 5850 kcal. cubic m , 30 per cent of carbon dioxide and
balance 5 per cent of nitrogen and other inert gases. It resembles
natural gas and may be used as a fuel for cooking. Principal uses
however, are for driving gas engines, and for heating sludge to
promote quick digestion.

With this background on sludge digestion tanks, you will be able to
manage any sludge digestion tanks with ease. In the next
newsletter, we will see the different methods of sludge disposal.

For more:...
http://www.all-about-wastewater-treatment.com/inst1.html

"Everything you really need to know about
Wastewater treatment, in one place!"

From the Desk of Richard Runion and Team

Richard Runion
The Water Patriot
6423, Woodbine Court,
St. Louis, Missouri,
63109, USA
http://www.all-about-wastewater-treatment.com/inst1.html

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