Sewage Treatment PowerPoint


22 Φεβ 2014 (πριν από 3 χρόνια και 3 μήνες)

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Sewage Treatment


Wastewater treatment is vital to the purification of our water and the health of the
population. At present, two basic stages exist in the treatment of wastes: primary and

In the

stage of treatmen
t, solids are allowed to settle and are removed from the
water. Here's how it works: as sewage enters a plant for treatment, it flows through a
screen. The screen removes large floating objects such as rags and sticks that may clog
pumps and small pipes. A
fter the sewage has been screened it passes into what is called a
grit chamber where sand, grit, cinders and small stones are allowed to settle to the

The unwanted grit or gravel from this process is usually disposed of by filling land near a
reatment plant. With screening completed and the grit removed, the sewage still contains
dissolved organic matter along with suspended solids. In a sedimentation tank the
suspended solids will gradually sink to the bottom, forming sludge. Then, the sludge
mechanically removed from sedimentation tanks.


stage of treatment removes up to 90% of the organic matter by making
use of the bacteria in it. Two techniques are used in this stage: trickling filters and the
activated sludge process.

A trickling filter is a bed of stones from 3
6 feet deep through which sewage passes.
Bacteria gather and multiply on these stones until they can consume most of the organic
matter in the sewage. The cleaner water trickles out through pipes in the botto
m of the
filter, then flows to another sedimentation tank to remove the bacteria. To complete the
process, the water gets chlorinated for disinfection purposes.

The other technique which is being used more today is the activated sludge process. After
he sewage leaves the settling tank in the primary stage, it is pumped to an aeration tank
where it is mixed with air and sludge loaded with bacteria. It is allowed to remain here
for several hours. During this time, the bacteria break down the organic matt
er. The
sludge can be reused by returning it to the aeration tank and mixing it with new sewage
and an ample amount of air.

Meanwhile, the sewage flows from the aeration tank to another sedimentation tank to
remove the bacteria. The final step, as with

the first technique, is the addition of chlorine.

In some cases, tertiary treatment also is used. In this final step, chemical treatment is used
to remove specific compounds such as phosphates. This allows the water to be in better
condition before it

is put back into the water cycle system.

As our water supply demands are increasing, tertiary treatment allows us to use
wastewater to recharge the groundwater supply. However, most wastewater plants do not
employ this procedure due to cost and feasib


Construct a

presentation illustrating with photos and diagrams the stages of
primary, secondary, and tertiary sewage treatment, and
briefly describing each step

description should be a brief statement…something YOU can

Try to include the following steps:

Primary Treatment


may help


(material coming in…be creative!)

Filter Screening

Grit chambers

ing tanks

Sludge Digester

Secondary Treatment

Aeration Tank

Settling Tank

Chlorine Disinfection

Sludge Drying Beds

Advanced (tertiary treatment)

Alum, flocculation





Nitrate and “special compounds” removal

(sometimes this one is
tough to find..)