Lecture -15: Water pollution and...

Lecture Lecture --15:15:

WWater pollution and Treatment ater 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 PollutionWater 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, apollutant 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.


Some sources of water pollution

Surface water Groundwater1. Urban runoff2. Agricultural

runoff3. Accidental spills

of chemicals4. Radioactive

material 5. Sediments6. Air fallouts

1. Leaks from waste disposal site2. 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.


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 diseasesFecal coliform bacteria as a standard measure and indicator of diseases potential.

3. NutrientsTwo important nutrients: phosphorous and nitrogen.

4. OilsDischarged in usually in the ocean from spills.

5. SedimentsResults from erosion and reduces the quality of the water


The Eutrophication of a lakeThe 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 iscalled 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 to Environmental Science © Dr. Akm Saiful IslamENV 107:Environemental Science © Dr. Akm Saiful Islam


20.4 Surface-water pollutionWater 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.


20.5 Groundwater pollutionWe 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 millionTotal number of affected tube wells = 1.12 million Number of people suffering from arsenicosis = 7,600


20.6 Wastewater TreatmentThe 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-tankdisposal systems in rural areas and centralized water treatment plants that collect wastewater from sewer systems in cities.


Septic-Tank Disposal SystemsThe 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.


Wastewater Treatment plantsWastewater 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, secondarytreatment, 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.


Water reuseGenerally 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.


Environmental Lawis 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

Refuse Act-1899Federal Water and Pollution Control Act-1956Fish and Wildlife Coordination Act-1958National Environmental Policy Act -1969Federal Safe Drinking Water Act-1974Hazardous and Solid Waste amendments to the Resource conservation and recovery Act-1984Water Quality Act -1987

Unfortunately these is no such water and environmental law exists in Bangladesh.

Lecture -15: Water pollution and...

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