TECHNOLOGY AND THE GLOBAL ENVIRONMENT

sixcageyMécanique

22 févr. 2014 (il y a 3 années et 7 mois)

78 vue(s)

Water Treatment

Surface Water Quality


Contaminants:


Suspended solids, soil (turbidity)


Pathogens (
coliform

indicator)


Color (decaying vegetation, algae)


Taste & odor


Other SDWA contaminants

Water
Treatment

Flocculation

Sedimentation

Filtration

Chlorination

Water

Fluoridation

pH Adjustment

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.

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

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

Fluoridation

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

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
.

Sewage Treatment


Primary Treatment


Physical Process


Secondary Treatment


Biological Process


Tertiary Treatment


Chemical Process

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

Secondary Treatment

Aerobic Microorganisms break down
organic waste in the sewage by oxidation in
air to carbon dioxide and water


Activated Sludge Method


The activated sludge method operates
aerobically. The sewage is fed continuously into
aerated tanks that is kept oxygenated by
mechanical agitators
.

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

Eutrophication

of Water


Eutrophication

is

caused

by

the

overenrichment

of

water

by

nutrients

such

as

phosphates

and

nitrates
.


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
.

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.

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.

Pollution of Heavy Metals


Dipositive

ions of these metals


e.g. Hg
2+
, Cd
2+
, and Pb
2+

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



EU Legislation on Water Quality


There are limits to the quantities of
Hg
2+
, Cd
2+
, and Pb
2+

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.