Water Pollution and Water Treatment

What is the primary cause of water pollution?
In ancient times, people settled near water (river, spring etc.)

People used the same water from the river in which they disposed their wastes and washed themselves.

This action contaminated the water with disease causing organisms.

As cities grew, different types of wastes ended up on the streets, polluting rivers. Toxic chemicals also entered the water system.

How can pollutants enter the water system?
Pollutants can enter water system from both point and nonpoint sources.
What is a Point Source?
Point sources- sewage treatment plants, factories, electric power plant, mines. Are sources that discharge pollutants at specific location usually through pipes
What is a Non Point Source?
Nonpoint sources- discharge pollutants over wide area through runoff. Includes- feedlots, cultivated lands, forests, cities, construction sites. Discharges are more dilute, but difficult to identify and regulate.
What are the types of Water Pollutants
1. Disease causing agents
2. Oxygen Consuming waste
3. Plant Nutrients
4. Suspended Solids
5. Dissolved Solids
6. Toxic Substances
7. Thermal Pollution
How do disease causing agents affect the water system?
There are several types of water pollutants:
1) Disease causing agents
a) If feces or urine from individuals infected with pathogenic organisms get into water supply, an epidemic can result.
b) Common diseases
1) cholera – bacterial
2) typhoid fever – bacterial
3) bacterial dysentery – bacterial
4) amoebic dysentery – protozoan
5) infectious hepatitis – viral
6) polio – viral
c) In developing countries where no clean water, about 10 million die a year.
d) Coliform bacteria test is used to test for these
1) Millions of coliform live in human intestine.
2) Coliform are harmless, cause no disease.
3) If there is fecal contamination, then coliform will be present.
4) If no coliform, then probably no other pathogenic microorganisms.
e) Sewage treatment and chlorination have eliminated these as problems in the US.
How so oxygen consuming waste affect the water system
Oxygen is not very soluble in water and its solubility depends on T and P. At sea level, 20 oC there is 9 ppm O2 dissolved in water.
b) Organic waste from animal, human, meat packing and paper mills deplete dissolved O2.
1) Aerobic bacterial unable to multiply
2) Organic waste is decomposed and O2 is consumed.
c) If DO (dissolved oxygen) falls below 5 ppm desirable game fish die.
d) If DO falls to zero
1) Anaerobic bacteria take over.
2) H2S, CH4, NH3 produced
e) The biochemical oxygen demand (BOD) is a measurement that assesses this problem.
1) The amount of O2 required to decompose all organic material in a water sample is measured.
2) The higher the BOD, the higher the pollution.
3) Pure water has a BOD of 1ppm. 5ppm is considered a problem.
What is Henry’s Law for Dissolved Oxygen?
[O2] = KHPO2

Where [O2] is the equilibrium concentration of oxygen in water (mol/L)
KH is O2’s Henry’s law constant = 1.28 x 10-3 mol/L-atm (25oC)

How does Plant nutrients affect our water system?
a) Plants require N, P and K.
b) Commercial fertilizers
1) The natural ability of the soil to produce N is decreased by application of fertilizer.
2) Repeated yearly application causes crop yields to decrease unless larger amounts of fertilizer are added every year.
3) Commercial fertilizers reduce O2 content of soil by altering soil porosity.
4) Commercial fertilizers enter rivers and lakes through runoff.
c)Eutrophication
1) Excessive plant growth in marine systems accompanied by an explosion in the algae population.
a) P > 0.1 ppm
b) N > 0.3 ppm

2) Human waste:
NH2CONH2 ? CO + 2 NH3

3) phosphate detergents, sodium tripolyphosphate (STPP)

This can be controlled by reducing phosphate discharge from point sources.

How do suspended solids affect our water system?
a) Undissolved organic and inorganic Particulates
b) caused by erosion, amount of rainfall
c) Human activities increase the formation of sediments.
1) bulldozing for housing development
2) clear cutting of timber
3) strip-mining
4) overgrazing
d) sediments in water system cause many problems
Water turbidity
Sediment can bury bottom-dwelling organisms (fish)
Close irrigation ditches and clogging harbors and lakes
Toxics absorbed in sediments and concentrate
How do dissolved solids affect our water system?
Dissolved Solids – found in most freshwater.
Saline water- if dissolved solid is very high.
Causes are:
Irrigation is the main cause of salinity of natural water. Salinity is common if arid land is irrigated. 25-30% of irrigated crop land in USA have high level of salinity.

Natural water becomes saline also due to discharge from industries.

Salt spread on road

How does thermal pollution affect our water system?
Thermal pollution- caused by Power plants and other industries use river water for cooling and return the heated water (10-20oC high) to the rivers.
Effects are:
Affect aquatic life by increasing body T, not good for some fish.
Decrease in solubility of oxygen.
Disrupt the normal growth of life in water.
How do toxic substances affect our water system?
Toxic substances
A substance that when ingested causes harm or death by interfering with normal metabolism.

b) Bioaccumulation is the increase in concentration as the toxin moves up the food chain.
1) More of a problem in aquatic systems where there are four to six trophic levels.
2) Fat soluble materials are a big problem.

Describe pollution of Ground Water and its sources.
Is of concern, because GW flows and is renewed slowly, contaminants are not diluted or washed away. Contaminants remain long in GW

Sources of pollution
Damp sites-industries disposed waste
Chemical wastes from paints, metals, textile, petroleum, etc. production.
Pesticides and fertilizers from farm
Sewage from septic tank and leaking sewer pipes.
Gasoline from service stations

How is sewage treated in the USA
By two processes: Primary and Secondary
Describe the primary treatment of sewage.
Primary treatment
sewage passed through screen
Grit Chamber remove suspended solids
Sedimentation Tank – Ca(OH)2 and Al2 (SO4)3 are added to speed up sedimentation process. The two chemicals react to produce gelatinous precipitate that carry suspended material and bacteria with it.
Describe the secondary treatment of sewage.
Secondary treatment is a biologic process that relies on aerobic bacteria to break down all oxygen consuming wastes.

Activated sludge is added to the sewage and air bubbled to enhance oxidation of organic matter.

Activated sludge is the name given to the active biological material produced by activated sludge plants and which affects all the purification processes.

Water is chlorinated and released into waterway.
Inorganic substances like phosphate are not removed.

aerobic bacteria
Waste + O2 ? CO2 + H2O

90 % of organic material removed by primary and Secondary treatment

Describe the chlorination process of sewage
Chlorination

1) Hypochlorous acid, HClO is formed when chlorine is added to water.

2) HClO kills disease causing bacteria.

3) Over chlorination can produce chlorinated electrophiles, disinfectant byproducts (DBPs) which are carcinogenic.

4) Many European countries use O3 rather than chlorine.

Chlorination
Cl2 + H2O ? HOCl + H+ + Cl-
HOCl<-> OCl- + H+ pKa = 7.6
Describe the tertiary treatment of sewage
1) most municipalities do not use tertiary

2) phosphates are removed by CaO or Al2(SO4)3

3) Activated carbon is used to remove organics

What is Henry’s Law for Dissolved Oxygen?
[O2] = KHPO2

Where [O2] is the equilibrium concentration of oxygen in water (mol/L)
KH is O2’s Henry’s law constant = 1.28 x 10-3 mol/L-atm (25oC)

How does Plant nutrients affect our water system?
a) Plants require N, P and K.
b) Commercial fertilizers
1) The natural ability of the soil to produce N is decreased by application of fertilizer.
2) Repeated yearly application causes crop yields to decrease unless larger amounts of fertilizer are added every year.
3) Commercial fertilizers reduce O2 content of soil by altering soil porosity.
4) Commercial fertilizers enter rivers and lakes through runoff.
c)Eutrophication
1) Excessive plant growth in marine systems accompanied by an explosion in the algae population.
a) P > 0.1 ppm
b) N > 0.3 ppm

2) Human waste:
NH2CONH2 ? CO + 2 NH3

3) phosphate detergents, sodium tripolyphosphate (STPP)

This can be controlled by reducing phosphate discharge from point sources.

How do suspended solids affect our water system?
a) Undissolved organic and inorganic Particulates
b) caused by erosion, amount of rainfall
c) Human activities increase the formation of sediments.
1) bulldozing for housing development
2) clear cutting of timber
3) strip-mining
4) overgrazing
d) sediments in water system cause many problems
Water turbidity
Sediment can bury bottom-dwelling organisms (fish)
Close irrigation ditches and clogging harbors and lakes
Toxics absorbed in sediments and concentrate
How do dissolved solids affect our water system?
Dissolved Solids – found in most freshwater.
Saline water- if dissolved solid is very high.
Causes are:
Irrigation is the main cause of salinity of natural water. Salinity is common if arid land is irrigated. 25-30% of irrigated crop land in USA have high level of salinity.

Natural water becomes saline also due to discharge from industries.

Salt spread on road

How does thermal pollution affect our water system?
Thermal pollution- caused by Power plants and other industries use river water for cooling and return the heated water (10-20oC high) to the rivers.
Effects are:
Affect aquatic life by increasing body T, not good for some fish.
Decrease in solubility of oxygen.
Disrupt the normal growth of life in water.
How doo toxic systems