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Water Pollution

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by

Shailly Pandey

on 2 April 2014

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Transcript of Water Pollution

Water Treatment
Primary Pollutants
Excessive nitrate levels in the water can interact with hemoglobin by oxidizing the Fe2+ to Fe3+ to form methaemoglobin which can't transport oxygen. This can cause a rare syndrome called blue baby syndrome.
Nitrates can also cause stomach cancer in adults -- NO3- molecules are converted to NO2- molecules (nitrites), which can combine with amines from proteins to form nitrosoamines -- these are carcinogenic.
The major sources of nitrates in drinking water are runoff from fertilizer use; leaking from septic tanks, sewage; and erosion of natural deposits.
Waste-Water Treatment
Chlorine - prevents waterborne diseases like typhoid fever. It remains in water longer than ozone and protects people against pathogenic bacteria for a long time. It isn't effective towards viruses, however, and can create carcinogenic compounds by chlorinating dissolved organic solvents.
Ozone - More expensive than chlorine, but since it is more effective, less of it is used. It does not provide residual protection against microorganisms, like chlorine, but does kill viruses.
I. Nitrates
III. Heavy Metals
Heavy metals are serious water pollutants that are very poisonous. Heavy metal ions of mercury, lead and cadmium interfere in the work of necessary Ca2+, Mg2+ and Zn2+ ions. Small traces can have very significant effects.
Mercury
Source: Paints, batteries and agriculture
Health hazard: Most dangerous of all metal pollutants because of the damage it can cause to the brain and nerves -- this damage is what causes the symptoms of mercury poisoning: depression, irritability, blindness and insanity.
Environmental hazard: Reproductive system failure in fish, inhibition of growth of and death of fish, biological magnification in the food chain.
Lead
Source: Paints, pipes, glazes on glasses/pottery, tetraethyl lead in petrol
Health hazard: Burning pains in mouth and digestive system followed by constipation or diarrhea. Severe cases include liver, kidney or heart failure which can lead to comas or death. It can cause brain damage as well.
Environmental hazard: Toxic to plants and animals, biological magnification in the food chain
Cadmium
Source: Metal plating, rechargeable batteries, pigments, by-product of zinc refinement
Health Hazard: It can replace zinc in the enzyme system, making it ineffective. It can cause Itai-Itai disease (makes bones brittle) and kidney and lung cancer.
Environmental Hazard: Toxic to fish, causes birth defects in mice.
The purpose of waste-water treatment is to remove hazardous materials, reduce BOD (biological oxygen demand) and kill harmful microorganisms prior to discharge
There are three levels of waste-water treatment: Primary, Secondary and Tertiary.
Primary: insoluble solid objects and floating objects are removed, resting sludge is removed from bottom (flocculation, which allows disparate particles in the water to clump, speeds this process). The process typically removes 30-40% of BOD waste
Secondary: the activated sludge process (a biological process) removes bacteria by aerating the water. The air bubbles allow aerobic bacteria to mix with sewage, oxidizing the organic matter and thus purifying the water. The process removes 90% of organic, oxygen-demanding waste
Tertiary: only tertiary treatments remove inorganic substances (nitrates, phosphates, heavy metal ions, etc.).
II. Pesticides, Dioxins and PCBS
Pesticides
Include insecticides (kill insects), fungicides (kill fungus) and herbicides (kill weeds). They are poisonous, causing pollution when they enter the water.
Ex: DDT -- dichloro-diphenyl trichloroethane -- imprecise name. The structure is 2 benzene rings with one chlorine each and a three chlorine molecule attached.
DDT are introduced in low, harmelss levels to birds and animals, but its use is dangerous. it is very stable and fat soluble, and so it remains in food chains, allowing toxic levels to build up over time in animals at the top of these food chains. This is biological magnification. DDT has been banned in many countries as it has had bad effects on birds.
Dioxins
General name for a range of compounds that have a structure with 2 benzene rings connected by one or two O atoms. Each benzene ring can have up to 4 Cl atoms. It is 10,000 times more poisonous than the cyanide ion.
They are added to the environment when waste containing organochloro compounds are burned. There are traces of dioxins in herbicides.
They remain in fat and liver cells. Symptoms include: cirrhosis of liver, damage to heart and memory, and concentration problems and depression.
Chloroacne is a skin disease caused by the body attempting to remove dioxins through the skin. It can cause fetal abnormalities.
Fun fact (or not so fun): It was present in Agent Orange during the Vietnam War.
PCBs -- Polychlorinated Biphenyls
These have a high electrical resistance; hence, they are used in electrical transformers and capacitators. They are made of a number of chlorine atoms attached to two connected benzene rings.
These persist in the environment and retain in fats. They reduce reproductive efficiency, can impair learning in children and are said to cause cancer.
Precipitation - used to remove mostly heavy metals as sulfide salts, as their solubility is very low. For example, to remove cadmium ions, hydrogen sulfide gas is bubbled through the solution, forming solid cadmium which can be filtered out. Excess hydrogen sulfide is then removed through a neutralization reaction. Phosphate ions can be removed by adding calcium or aluminum ions.
Ion Exchange - used to remove nitrates, which are soluble and mroe difficult to remove. It involves exchanging nitrate ions with hydroxide ions (OH-). Positive ions also may be used (H+) and the products combined to form water. Ion exchange resin may also be used to remove salt from water. However the method is expensive as regenerating resins is costly.
Biological Methods - used to remove nitrates. Anaerobic organisms turn nitrogen in nitrates to atmospheric nitrogen (N2). Algae ponds also use nitrate ions as nutrients, and can be used to remove them from water
Activated Carbon Bed Method - used to remove salt.
Three Stages
Tertiary Method of Water Treatment
Distillation - used to obtain fresh water from sea water. Sea water is heated, then boiled in a chamber so the compounds dissolve in solution. The steam is passed through a condenser. The water is cooled by pipes containing more sea water, which is then distilled in turn.
Reverse Osmosis - used to obtain fresh water from sea water. Reverse osmosis is a process by which salt water, under osmotic pressure, passes through a semi-permeable membrane to filter out into fresh water. The membrane allows the solvent but not the dissolved solutes to be passed through it. If a pressure of at least 70 atm is applied to the salt solution, the water passes through the membrane leaving the sissolved salts behind.
Chlorine and Ozone Treatment
Summary of Advantages and Disadvantages of Chlorine vs. Ozone
Chlorine
Ozone
Effective against bacteria but not viruses
Cheaper to produce
longer retention time
can easily be liquified and shipped
can form toxic chloro-organic compounds
leaves a chemical taste behind
functions as a strong oxidizing agent
effective against both bacteria and viruses
more expensive
shorter retention time
must be produced on the site because of high reactivity
oxidized products are not nearly as toxic
no chemical taste is left behind
functions as a strong oxidizing agent.
Structure for DDT
Structure for Dioxins
Structure for PCBs

percentage of population without access to safe drinking water
By: Nivu Jejurikar, Jane Wang, Shailly Pandey
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