Resumo de Pollution (brief)

CAUSES OF POLLUTION
Many causes of pollution including sewage and fertilizers contain
nutrients such as nitrates and phosphates. In excess levels,
nutrients over stimulate the growth of aquatic plants and algae.
Excessive growth of these types of organisms consequently clogs our
waterways, use up dissolved oxygen as they decompose, and block light
to deeper waters. This, in turn, proves very harmful to aquatic
organisms as it affects the respiration ability or fish and other
invertebrates that reside in water. Pollution
is also caused when silt and other suspended solids, such as soil,
washoff plowed fields, construction and logging sites, urban areas, and
eroded river banks when it rains. Under natural conditions,
lakes, rivers, and other water bodies undergo Eutrophication, an aging
process that slowly fills in the water body with sediment and organic
matter. When these sediments enter various bodies of water, fish
respirationbecomes impaired, plant productivity and water depth become
reduced, and aquatic organisms and their environments become
suffocated. Pollution in the form of organic material enters
waterways in many different forms as sewage, as leaves and grass
clippings, or as runoff from livestock feedlots and pastures.
When natural bacteria and protozoan in the water break down this
organic material, they begin to use up the oxygen dissolved in the
water. Many types of fish and bottom-dwelling animals cannot
survive when levels of dissolved oxygen drop below two to five parts
per million. When this occurs, it kills aquatic organisms in
large numbers which leads to disruptions in the food chain. CLASSIFYING WATER POLLUTION
The major sources of water pollution can be classified as municipal,
industrial, and agricultural. Municipal water pollution consists
of waste water from homes and commercial establishments. For many
years, the main goal of treating municipal wastewater was simply to
reduce its content of suspended solids, oxygen-demanding materials,
dissolved inorganic compounds, and harmful bacteria. In recent
years, however, more stress has been placed on improving means of
disposal of the solid residues from the municipal treatment
processes. The basic methods of treating municipal wastewater
fall into three stages: primary treatment, including grit removal,
screening, grinding, and sedimentation; secondary treatment, which
entails oxidation of dissolved organic matter by means of using
biologically active sludge, which is then filtered off; and tertiary
treatment, in which advanced biological methods of nitrogen removal and
chemical and physical methods such as granular filtration and activated
carbon absorption are employed. The handling and disposal of
solid residues can account for 25 to 50 percent of the capital and
operational costs of a treatment plant. The characteristics of
industrial waste waters can differ considerably both within and among
industries. The impact of industrial discharges depends not only
on their collective characteristics, such as biochemical oxygen demand
and the amount of suspended solids, but also on their content of
specific inorganic and organic substances. Three options are available
in controlling industrial wastewater. Control can take place at
the point of generation in the plant; wastewater can be pretreated for
discharge to municipal treatment sources; or wastewater can be treated
completely at the plant and either reused or discharged directly into
receiving waters.

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