This document summarizes water treatment and sewage treatment processes. It describes how surface water is treated through steps like sedimentation, flocculation, filtration, chlorination and fluoridation to remove contaminants. Sewage treatment involves primary, secondary and sometimes tertiary levels to remove solids, break down organic waste biologically, and remove nutrients like nitrates and phosphates. The document also discusses how excess nutrients can cause eutrophication of waterways and pollution from heavy metals and legislation limits their levels.

1. Water Treatment

2. Surface Water Quality
Contaminants:
– Suspended solids, soil (turbidity)
– Pathogens (coliform indicator)
– Color (decaying vegetation, algae)
– Taste & odor
– Other SDWA contaminants

3. Water Treatment
Water
Sedimentation
Flocculation
Filtration
Chlorination
Fluoridation
pH Adjustment

4. Sedimentation
The water is
pumped into the
bottom of the
sedimentation
tanks, so as not to
disturb the clearer
water at the top.
The suspended
particles settle to
the bottom.

5. Filtration
 Remaining
suspended
particles are removed by
filtration. The water is
allowed to pass through
beds of graded sand and
gravel. The sand in the
filter bed acts as a filter
and removes the tiny
particles from the water

6. Chlorination
This is the addition of
chlorine or chlorine
compounds to kill
microorganisms in the
water and to prevent
reinfection. Both
chlorine and sodium
hypochlorite are added
to the water to form an
active disinfecting
agent in the water

7. Fluoridation
This is the addition of
fluoride compounds to
drinking water to
prevent tooth decay.
Sodium fluorosilicate is
the usually fluoridating
agent.

8. pH adjustment
It may be necessary to adjust
the pH of the water before
it leaves the treatment
plant. Tap water should
have a pH in the range of 6
– 8. If the water is too
acidic, lime is added to raise
the pH and if the pH is too
high, sulfuric acid is added.

9. Sewage Treatment
Primary
 Physical
Treatment
Process
Secondary
 Biological
Tertiary
Treatment
Process
Treatment
 Chemical
Process

10. Primary Treatment
Solids and large floating debris are
screened from the waste water
Remaining solids are removed by allowing
the waste to settle in sedimentation tanks

11. Secondary Treatment
 Activated
Sludge Method
 The
activated sludge method operates
aerobically. The sewage is fed continuously into
aerated tanks that is kept oxygenated by
mechanical agitators.
Aerobic Microorganisms break down
organic waste in the sewage by oxidation in
air to carbon dioxide and water

12. Tertiary Treatment
Removal of nitrates and phosphates
Phosphates are removed by precipitation
with Aluminium Phosphate
Nitrates are removed by biological
nitrification.
Tertiary treatment is a costly process

13. Eutrophication of Water
 Eutrophication
is caused
by the overenrichment of
water by nutrients such as
phosphates and nitrates.

14. Eutrophication of Water
 In
effect, the nutrients
behave as fertilisers that
increase the growth of
plants such as algae in
lakes and rivers
 The
algae are short lived.
As they decay, much of
the dissolved oxygen in
the water is used up,
leading to the death of
many forms of animal life.

15. Nitrate Fertilisers
Waterways
can also be polluted by
the run-off of excess fertiliser from
farmland. Excess nitrate in the
fertiliser may be washed into rivers
or lakes by rainwater.
Eutrophication will result.

16. Pollution of Heavy Metals
Metals
with high relative atomic masses
such as mercury, cadmium and lead are
known as heavy metals.
When recycling is inadequate, quantities
of these elements are dumped e.g. Car
batteries containing lead
or dry batteries containing
cadmium.

17. Pollution of Heavy Metals
 Dipositive
ions of these metals
 e.g. Hg2+ , Cd2+ , and Pb2+ sometimes get into
waterways from industrial effluent and
consequently into drinking water.
 These elements are cumulative poisons in
that frequent exposure causes build up in the
body, resulting in serious health damage.
Lead
ions can be removed from the
effluent by precipitation

18. EU Legislation on Water Quality
There
are limits to the quantities of
Hg2+ , Cd2+ , and Pb2+ ions that can be
tolerated in waterways because of their
toxic effects.
Limits on phosphates and nitrates help
to reduce the occurrence of
eutrophication in waterways.
Limits are also set for chemical species
dissolve in drinking water.