Introduction to Water pollution

Water Quality Two of the biggest measures for water quality are: – Dissolved Oxygen  Amount of Oxygen ready to use in the water – Biochemical Oxygen Demand  Amount of Oxygen needed f

 Water pollution occurs when harmful

substances are released into the water in

large quantities which cause damage to

people, wildlife, or habitat or indirectly into water bodies without proper treatment to

remove harmful compounds.

 Water pollution is a major problem in the

global context It has been suggested that it

is the leading worldwide cause of deaths and diseases, and that it accounts for the deaths

of more than 14,000 people daily.

– Biology.

 Bacteria, virus, protozoa, helminthes.

WATER POLLUTION

 Will also cause

– Breeding of diseases vector.

– Spreading of water borne diseases.– Food poisoning.

– Skin problem.

Pollution Defined

Any chemical , biological, or

physical change in water quality that has a harmful effect on

living organisms or makes water unsuitable for desired uses.

Types and Sources of Water

Water Pollution

Two major classifications

Source

Sources of Pollution

Point Sources

-Discharge from a specific

location (pipe, ditch or sewer) -Easier to identify and regulate

Ex: Factories, Sewage Treatment

Plants, Mines, Thermal Outlets and Oil Tankers.

Point Sources

– Industrial Plants

- Sewage pipes

Point Source - Example

Non-point Sources

Diffuse source or many smaller point sources

 Automobiles

 Fertilizer on fields

Sources of Water Pollution

Examples of

Polluted Waters

Water Quality Indicators

TOTAL DISSOLVED SOLIDS (TDS)

TDS is the measure of the material

dissolved in water.

This measure is related to hardness,

salinity and conductivity.

Hard water has more TDS than soft

water.

Salinity refers to the salt

concentration in water, mostly sodium chloride.

Salinity is historically measured

in parts per thousand (ppt) or grams per liter.

TOTAL SUSPENDED SOLIDS (TSS)

TSS is the measure of the sediment

suspended in the water.

TSS is related to turbidity.

Water with high TSS usually has high

Total Dissolved Solids (TDS) as well.

Erosion causes loose soil

to enter the waterways

Suspended sediment blocks sunlight to plants and

reduces dissolved oxygen.

As sediments settle, they can smother bottom (benthic)

organisms.

A secchi disk is one type of instrument used to measure turbidity

 Water hardness often originates from

limestone.

 Hardness is used as an indicator of

alkalinity but hardness is not a measure of alkalinity

– magnesium or calcium sulfate increases

hardness but has no affect on alkalinit

Conductivity measures the water’s ability

to conduct an electrical current.

Pure water is a poor conductor.

Thermal Pollution

 Thermal pollution is the rise or fall in the

temperature of a natural body of water

caused by human influence.

 A common cause of thermal pollution is the

use of water as a coolant by power plants and industrial manufacturers.

 Elevated water temperatures decreases

oxygen levels (which can kill fish) and affects ecosystem composition.

 Thermal pollution can also be caused by the release of very cold water from the base of

reservoirs into warmer rivers.

Most aquatic organisms live within a

temperature range of +0º C (+32º F) to +32º C (+90º F ).

Temperature can be measured using

field thermometers but digital probes

are much more accurate.

Temperature is measured in Fahrenheit and Celsius degrees.

Temperature affects the oxygen-carrying

 Effects

– metabolic rate doubles

for every 18 o F increase

We can also have cold water

pollution

In many areas fish and Other river organisms are Adapted to relatively

warm water

Building a dam results in very cold water released Downstream killing

organisms and changing species

 Measure of the hydrogen

ion concentration

 1-14 scale

– less than 7 acidic

– greater than 7 basic

 Safe range

– 6.5-9

pH = – log [H+]

Log scale means 10X

change per unit!

[H+]= 10 -1 M

[H+]= 10 -9 M

pH tolerance

Most aquatic organisms exist within a pH range of 5.5 to 9.5

Water Quality

 Two of the biggest measures for water

quality are:

– Dissolved Oxygen

 Amount of Oxygen ready to use in the water

– Biochemical Oxygen Demand

 Amount of Oxygen needed for organic growth.

– When both measurements are graphed we

get a oxygen sag curve

Dissolved Oxygen

 For most solutes (sugar, salt, etc):

solubility increases as temperature increases

 For DO:

solubility decreases as temperature increases

DO: Reduced by Degradeable Wastes, Heat, and Algae Growth from Excess Inorganic Nutrients

 Water quality and dissolved oxygen (DO) content

in parts per million (ppm) at 20°C.

– Only a few fish species can survive in water less than

4ppm at 20°C.

chemical oxygen demand COD

 the chemical oxygen demand (COD) is

commonly used to indirectly measure the

amount of organic compounds in water Most

applications of COD determine the amount of

organic pollutants found in surface water (e.g lakes and rivers), making COD a useful measure

of water quality It is expressed in milligrams per liter (mg/L), which indicates the mass of oxygen consumed per liter of solution Older references may express the units as parts per million

(ppm)

Inorganic molecule Eliminated by Elimination forms

Chloride Mercuric sulfate Mercuric chloride complex

Nitrite Sulfamic acid N2 gas

Ferrous iron -

- Some samples of water contain high levels of

oxidizable inorganic materials which may interfere with the determination of COD Because of its high concentration in most wastewater, chloride is often the most serious source of interference Its reaction with potassium dichromate follows the equation:

6Cl - + Cr 2 O 72- +14H + = 3Cl 2 +2Cr 3+ + 7H 2 O

 a number of other inorganic substances that may cause interference and lists chemicals that may be used to eliminate such interference:

Biological Oxygen Demand (BOD)

 Biochemical oxygen demand or BOD is the amount of dissolved oxygen needed by aerobic biological

organisms in a body of water to break down organic material present in a given water sample at certain

temperature over a specific time period It is not a

precise quantitative test, although it is widely used as

an indication of the organic quality of water

 It is most commonly expressed in milligrams of

oxygen consumed per litre of sample during 5 days of incubation at 20 °C and is often used as a robust

surrogate of the degree of organic pollution of water (BOD 5 ).

 BOD can be calculated by:

– Undiluted: Initial DO - Final DO = BOD

– Diluted: [(Initial DO - Final DO)- BOD of Seed] x Dilution

Factor

 BOD is similar in function to chemical oxygen demand (COD), in that both measure the

amount of organic compounds in water

However, COD is less specific, since it

measures everything that can be chemically oxidised, rather than just levels of

biologically active organic matter.

-The breakdown of degradable

wastes by bacteria depletes

-Recovery from oxygen

depletion is based on the

volume of the pollutant and …

Clean Zone Decomposition

Zone

Septic Zone Recovery Zone Clean Zone

(Trout, perch, bass,

mayfly, stonefly) (carp, gar,Leeches)

Fish absent, fungi, Sludge worms, bacteria (anaerobic)

Normal clean water organisms

Under normal conditions, the

nitrogen cycle keeps the amount

of available nitrogen in balance

with the demands However,

excessive use of fertilizers and

nutrient rich sewage release have created a surplus of nitrate The

result is eutrophication from

excess algae and bacteria with

reduced dissolved oxygen.

TOXIC CHEMICALS

Toxic chemicals usually come from industry

and energy production.

The effects are often not known until years after they have entered the environment.

Toxic chemicals include heavy metals (lead,

mercury), organic compounds (DDT, PCB),

inorganic substances (arsenic) and others.

Nitrate is a primary plant nutrient.

Nitrate is water soluble and moves

easily from surface to groundwater.

Excess nitrate causes algal blooms that reduce water quality.

Phosphate

Phosphate’s concentrations in clean water is generally low; however, phosphorus is used extensively in fertilizer and

other chemicals.

The primary sources of

phosphates to surface water are fertilizers, and natural mineral

deposits.

High levels of phosphate can over

stimulate the growth of aquatic plants and algae.

This in turn, will cause high DO

consumption and death to fish and

many aquatic organisms.

These chemicals are very complex

Effects on aquatic organisms

Moderately to highly toxic to

mammals, molluscs, aquatic

insects, amphibians and fish.

Most bacteria are important in nutrient and other organic cycles.

Excess nutrients cause algal blooms

As algae die and decay, the high

bacterial load rapidly consumes

dissolved oxygen.

Certain types of bacteria indicate animal and human waste pollution.

Escherichia coli are coliform bacteria

found in the intestines of

warm-blooded organisms Most strains are

harmless but one E coli strain can

cause severe diarrhea and kidney

damage.

Biological Pollution: Pathogens in Water

Methods of Determining

Water Quality

A Coliform Bacteria

 0 colonies per 100ml for drinking water

 200 colonies per 100ml for swimming

Major Water Pollutants

and Their Effects

 A fecal coliform bacteria test is used

to indicate the likely presence of disease- causing bacteria in water.

 The standard for drinking water is zero fecal coliform colonies per culture!

Measurement of water pollution

 Water pollution may be analyzed through several broad categories of methods:

physical, chemical and biological Most

involve collection of samples, followed by specialized analytical tests Some methods may be conducted without sampling, such

as temperature

Water Pollution

Water Eutrophication

POLLUTION OF FRESHWATER LAKES

 Dilution of pollutants in lakes is less

effective than in most streams because

most lake water is not mixed well and has little flow.

– Lakes and reservoirs are often stratified and undergo

little mixing (Low DO in lower layers)

– Low flow makes them susceptible to runoff.

 Various human activities can overload

lakes with plant nutrients, which decrease

DO and kill some aquatic species.

Cultural Eutrophication

 Eutrophication : the natural nutrient

enrichment of a shallow lake, estuary or slow moving stream, mostly from runoff of plant nutrients from the surrounding land.

 Cultural eutrophication : human activities

accelerate the input of plant nutrients

(mostly nitrate- and phosphate-containing

effluents) to a lake.

– 85% of large lakes near major population centers in the

U.S have some degree of cultural eutrophication.

Oligotrophic vs Eutrophic

 Oligotrophic lakes are lakes with low

nutrient, clear water, BIG fish, and Cold, High DO, low BOD

 Eutrophic Lakes high nutrient,

murky/brackish water, small fish and

bugs, warm, Low DO, High BOD

 Oligotrophic lakes -> Eutrophic Lakes

– Cultural Eutrophism

Cultural Eutrophication

 Cultural Eutrophication of lakes causes

sudden fish kills when DO drops due to

1. Overpopulated algae respiring at night

without producing any O 2 via photosynthesis and/or

2. Bacteria respiring as they decompose dead

overpopulated algae

Eutrophication

Eutrophication

Ground Water

Ground Water Pollution

Ground Water

surface, filling the pore space between grains in

bodies of sediment and clastic sedimentary rock, and filling cracks and crevices in all types of rock

particularly in the dry western areas of the US and

Canada

the ground a portion of which percolates down into the ground to become ground water

Porosity and Permeability

• porosity: the percentage of rock or sediment that consists of voids or openings

• permeability: the capacity of a rock to transmit a fluid such as water or petroleum through pores and fractures

• porous: a rock that holds much water

• permeable: a rock that allows water to flow easily through it

• impermeable: a rock that does not allow water to flow through it easily

The Water Table

• saturated zone: the subsurface zone in

which all rock openings are filled with water

• water table: the upper surface of the zone of saturation

• vadose zone: a subsurface zone in which

rock openings are generally unsaturated and filled partly with air and partly with water; above the saturated zone

• capillary fringe: a transition zone with

higher moisture content at the base of the

The Water Table (cont.)

The Water Table (cont.)

• perched water table: the top of a body of ground water separated from the main

water table beneath it by a zone that is not saturated

The Movement of Ground Water

• most ground water moves relatively slowly through rock underground

• because it moves in response to differences

in water pressure and elevation, water

within the upper part of the saturated zone tends to move downward following the

slope of the water table

Movement of ground water beneath a

sloping water table in uniformly

permeable

rock Near the surface the ground

water tends to flow parallel to the

sloping water table

Movement of Ground Water

• factors affecting the flow of ground water:

• the slope of the water table - the steeper the

water table, the faster ground water moves

• permeability - if rock pores are small and

poorly connected, water moves slowly; when openings are large and well connected, the flow of water is more rapid

• aquifer: a body of saturated rock or sediment through which water can move easily

• good aquifers include sandstone,

conglomerate, well-joined limestone, bodies of sand and gravel, and some fragmental or

fractured volcanic rocks such as columnar

basalt

• aquitards: when the porosity of a rock is 1%

or less and therefore retards the flow of

ground water

Aquifers (cont.)

• unconfined aquifer: a partially filed aquifer exposed

to the land surface and marked by a rising and falling water table

• confined aquifer (artesian aquifer): an aquifer

completely filled with pressurized water and

separated from the land surface by a relatively

impermeable confining bed, such as shale

• well: a deep hole, generally cylindrical, that is dug of drilled into the ground to penetrate an aquifer within the saturated zone

• recharge: the addition of new water to the saturated zone

• the water table in an unconfined aquifer rises in wet seasons and falls in dry seasons as water drains out of the saturated zone into rivers

Wet season: water table and rivers are high;

springs and wells flow readily

Dry season: water table and rivers are low;

some springs and wells dry up

Wells (cont.)

• artesian well: a well in which water rises

above the aquifer

Artesian well spouts water above land surface in

Wells (cont.)

• cone of depression: a depression of the water table formed around a well when water is pumped out; it is shaped like an inverted cone

• drawdown: the lowering of the water

table near a pumped well

Pumping well lowers the water table into a cone of depression

POLLUTION OF GROUNDWATER

 Groundwater can become contaminated with a variety of chemicals because it

cannot effectively cleanse itself and dilute and disperse pollutants.

Groundwater Pollution

 Sources

 Slow flow, dilution, dispersion

 Low dissolved oxygen

 Fewer bacteria

 Cooler temperatures