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Lecture -15:
Water pollution and Treatment
ENV 107: Introduction to Environmental Science
Dr. A.K.M. Saiful Islam
ENV 107:Introduction to Environmental Science © Dr. Akm Saiful Islam
20.1 Water Pollution
† Water pollution refers to degradation of water quality.
„
We generally look at the intended use of the water, how far it departs
from the norm, it effects on public health or ecological view, a
pollutant is any biological, physical or chemical substance that in
identifiable excess is known to be harmful to other desirable living
organisms.
† Water pollutants include
„ excessive amounts of heavy metals,
„ certain radioactive isotopes,
„ fecal coliform bacteria, pathogenic bacteria and virus,
„ phosphorus, nitrogen, sodium.
† Water in domestic uses must be free from constituents
harmful to health. It should taste and smell good. It should
not damage plumping or household appliances.
† Water quality for industrial processes varies widely
depending on the process. Some requires distilled water etc.
ENV 107:Introduction to Environmental Science © Dr. Akm Saiful Islam
Some sources of water pollution
Surface water
1. Urban runoff
2. Agricultural
runoff
3. Accidental spills
of chemicals
4. Radioactive
material
5. Sediments
6. Air fallouts
Groundwater
1. Leaks from waste disposal site
2. Saltwater intrusion into
coastal aquifers.
3. Seepage from mines and
septic systems.
4. Seepage from pesticides.
5. Seepage from accidental
spills.
6. Seepage of solvents and
chemicals.
ENV 107:Introduction to Environmental Science © Dr. Akm Saiful Islam
20.2.Water pollutants
1. Biochemical Oxygen demand (BOD)
† The amount of oxygen required for bio-chemical
decomposition is called the BOD.
2. Water born diseases
† Fecal coliform bacteria as a standard measure
and indicator of diseases potential.
3. Nutrients
† Two important nutrients: phosphorous and
nitrogen.
4. Oils
† Discharged in usually in the ocean from spills.
5. Sediments
† Results from erosion and reduces the quality of
the water
ENV 107:Introduction to Environmental Science © Dr. Akm Saiful Islam
ENV 107:Introduction to Environmental Science © Dr. Akm Saiful Islam
The Eutrophication of a lake
†
The increase in the concentration of chemical elements
required for living things such as phosphorus is called the
eutrophication of the ecosystem.Eutrophication can be a
natural process or artificial (known as cultural eutrophication).
„
„
†
A lake that has a high concentration of chemical elements
required for life is called eutrophic lake. Eutrophic lakes have an
abundance of life, often mats of algae and bacteria that are
unplasant.
One that has a relatively low concentration of these elements is
called an oligotrophic lake. Oligotrophic lakes are relatively
sterile and therefore have clear waters that are pleasant for
swimmers and boaters.
The solution to eutrophication of a lake is fairly straightforward
and involves ensuring that high concentrations of nutrients
from human sources do not enter lakes and other water
bodies.
ENV 107:Introduction
ENV 107:Environemental
to Environmental
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© Dr. Akm
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Saiful Islam
ENV 107:Introduction to Environmental Science © Dr. Akm Saiful Islam
20.4 Surface-water pollution
† Water pollutants, like pollutants in general, are
categorized as emitted from point or non-point
sources.
† Point-sources are distinct and confined, such as
pipes from industrial or municipal sites that empty
into streams or rivers.
„
In general, point-source pollutants from industries are controlled
through on-site treatment or disposal and are regulated by
permit. Municipal point sources are also regulated by permit.
† Nonpoint sources, such as runoff, are diffused
and intermittent and are influenced by factors such
as land use, climate , hydrogen, topography, native
vegetation , and geology.
„
Common urban nonpoint source sources include urban runoff from
streets or fields; such runoff contains all sorts of pollutants, from
heavy metals to chemicals and sediments. Rural sources of
nonpoint pollution are generally associated with agriculture,
mining, or forestry.
ENV 107:Introduction to Environmental Science © Dr. Akm Saiful Islam
20.5 Groundwater pollution
† We have long believed that groundwater is
in general pure and safe to drink.
† In Bangladesh, groundwater of 59 districts
(126,134 km2) are effected by Arsenic
contamination. A total of 75 million people
are at risk.
„ Total number of tube wells in Bangladesh = 4
million
„ Total number of affected tube wells = 1.12
million
„ Number of people suffering from arsenicosis =
7,600
ENV 107:Introduction to Environmental Science © Dr. Akm Saiful Islam
ENV 107:Introduction to Environmental Science © Dr. Akm Saiful Islam
20.6 Wastewater Treatment
† The water used for industrial and municipal purposes
is often degraded during use by the addition of
suspended solids, salts, nutrients, bacteria, and
oxygen-demanding material.
† By law, these wastewaters must be treated before
being released back into the environment.
† Conventional methods include disposal and treatment
of household wastewater by way of septic-tank
disposal systems in rural areas and centralized water
treatment plants that collect wastewater from sewer
systems in cities.
ENV 107:Introduction to Environmental Science © Dr. Akm Saiful Islam
Septic-Tank Disposal Systems
†
The sewer line from the house leads to an underground
septic tank in the yard.
†
The tank is designed to separate solids from liquid, digest
(biologically change) and store organic matter through a
period of detention, and allow the clarified liquid to
discharge into the drain field (absorption field) , a system of
piping through which treated sewage may seep into the
surrounding soil.
†
As the wastewater moves through the soil, it is further
treated by the natural processes of oxidation and filtering.
†
By the time the water reaches any freshwater supply, it
should be safe for other users.
ENV 107:Introduction to Environmental Science © Dr. Akm Saiful Islam
ENV 107:Introduction to Environmental Science © Dr. Akm Saiful Islam
Wastewater Treatment plants
† Wastewater treatment, or sewage treatment, occurs
at specially designed plants that accept municipal
sewage from homes, businesses, and industrial sites.
† Wastewater treatment methods are usually divided
into three categories: primary treatment, secondary
treatment, and advanced waste treatment.
„ Primary treatment removes 30% to 40% of the
pollutants volume from wastewater.
„ Secondary removes about 90%
„ Advanced treatment plan is used when it is
particularly important to maintain good water
quality.
ENV 107:Introduction to Environmental Science © Dr. Akm Saiful Islam
ENV 107:Introduction to Environmental Science © Dr. Akm Saiful Islam
Water reuse
†
Generally refers to the use of waste water following some sort of
treatment. It may be a long term solution to local water shortage, or
a fringe benefit to a reduction in water pollution.
Water reuse can be inadvertent, indirect or direct.
†
Inadvertent reuse refers to returned to the environment without
specific plans for further withdrawals and use. Several risks are
associated with inadvertent reuse such as diseases due to poor
quality water with virus, bacteria and harmful chemical.
†
Indirect reuse is planned endeavor. An example is the waste water
renovation and conservation.
†
Direct reuse refers to treated waste water that piped directly to the
next user. In most cases user is industry, agriculture or irrigation of
golf courses, or park. Very little direct use due to risk and cultural
attitude towards using treated wastewater.
ENV 107:Introduction to Environmental Science © Dr. Akm Saiful Islam
ENV 107:Introduction to Environmental Science © Dr. Akm Saiful Islam
Environmental Law
†
†
†
is a growing branch of law that becoming more and more
important as we debate environmental issues and make
decision about how best to protect our environment.
In the US Refuse Act of 1899, the purpose of which was of
the to protect navigable streams , rivers, and lakes from
being polluted.
Some examples of US environmental laws are
„
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„
†
Refuse Act-1899
Federal Water and Pollution Control Act-1956
Fish and Wildlife Coordination Act-1958
National Environmental Policy Act -1969
Federal Safe Drinking Water Act-1974
Hazardous and Solid Waste amendments to the Resource
conservation and recovery Act-1984
Water Quality Act -1987
Unfortunately these is no such water and environmental law
exists in Bangladesh.