The Pollution Control measures
a) sewage treatment
b) the control of agricultural wastes
c) industrial effluents
a) Sewage treatment
Domestic sewage is purfied in a sewage treatment plant before it is
discharged into rivers or sea to reduce water pollution and the hazard
on health.
Sewage treatment processes
There area variety of processes used in treating sewage. The
processes consist of three steps: (1) primary treatment, which removes
the suspended solids; (2) secondary treatment, which removes the
organic components by biological actions; and (3) tertiary treatment,
which involves chlorination (sterilization).
(1) Primary treatment
During this treatment the solid matter and suspended particles are
removed away.
a) Screening – Bulky solid matters are screened out by a grid.
b) Removing grit- The “filtered” sewage flows along a grit
chamber to allow heavy inorganic particles settle out at the
bottom as grit which is then removed away by a conveyor.
c) Sedimentation ( setting chamber)- The suspension flows from
the grit chamber itno the sedimentation tank where the large
particles of organic matter settle down at the bottom as primary
slukge within 10 hours. Some fats and wood will float on the
surface. These scums are skimmed off nad may be treated
further with sludge in a sludge digestion chamber
(fermentation tank). The supernatant liquid is called effluent.
(2) Secondary treatment
During the secondary treatment the organic matter in effluent is
oxidized to harmless forms
The effluent introduced into the aeration tank is aerated by either
violent mechanical stirring or by the bubbling of compressed air
through the fluid. This treatment greatly encourages the growth of
bacteria and protozoa in a thin layer of sludge which consume much
of the organic matter of sewage.
The sewage is passed into a settlement tank where micro organisms
and large particles settle down as sludge. The effluent is chlorinated
before discharged into river or sea.
Sludge digestion tank (fermentation tank)
-The sludge in this chamber undergoes anaerobic decomposition that
produces carbon dioxide and methane. Methane can be used as fuel
for power generation or for heat.
-The remains of sludge can be dried and used as fertilizers. But it may
contain pathogens or some toxic industrial wastes.
(3) Tertiary treatment
During this treatment the fertilizing elements, mainly phosphates and
nitrates are removed to reduce the danger of eutrophication.
Benefits of sewage treatment to the environment
a) Reduction of organic pollution by decomposint the organic wastes
under the action of micro organisms
b) Reduction of disease by killing the pathogenic micro organisms
c) Increased speed of recycling nutrients by increasing the speed of
decomposition of organic wastes into organic nutrients.
(b) Agricultural wastes
Farmers can help in the control of agricultural wastes in various ways:
1) Using moderate amount of fertilizers to reduce runoff into aquatic
bodies.
2) Using the method of alternate planting between row crops and soya
bean or other plants containing nitrogen-fixing bacteria, so as to
reduce the demand for fertilizers/
3) Applying pesticides only if necessary to reduce runoff and
leaching.
4) Managing the density of livestock and locating feedlots away from
surface waters, so as to reduce runoff of manure;
5) Diverting runoff into well-designed detention basins. So that the
nutrient- rich water can be reused for agricultural practices and
pollution can be reduced.
(c) Industrial effluents
1) Using chemicals effectively.
2) Using less toxic chemicals o replace more toxic ones in
manufacturing processes.
3) Controlling pollution at the point of pollutant generation by pretreating the waste water before discharging to the environment.
4) Reusing the treated chemicals if possible.