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Unit 3 b: Water Pollution and control
______________________________________________
Lecture Objectives
i. Describe the main sources and composition of water contaminants
ii. Discuss the treatment options available for liquid contaminants
iii. Give an overview of the present methods available for the disposal of liquid hazardous waste
iv. Outline local and Global statutory framework available to reduce contamination of water sources
_______________________________________________________________________
Water Resources
The various sources of water, which can be harnessed economically, can be divided into the following
two categories:-
(A) Surface sources such as
(i) Ponds and lakes
(ii) Streams and rivers
(iii) Storage resources (dams)
(B) Subsurface or underground sources such as
(i) Springs
(ii) Wells (open and tube-wells)
All of the above water resources are replenished by precipitation in various forms like rain, snow, hail,
dew etc. Rainfall is the main source and forms the major constituent of the hydrological cycle.
Hydrologic Cycle
When the sun heats the oceans, the cycle starts. Water evaporates and then falls as precipitation in the
form of snow, hail, rain, or fog. While it’s falling, some of the water evaporates or is sucked up by thirsty
plants before soaking into the ground. The sun’s heat also keeps the cycle going. Water is constantly
circulating between the atmosphere and the Earth and back to the atmosphere through a cycle involving
condensation, precipitation, evaporation, and transpiration. This is called the hydrologic cycle.
Water vapor is carried by wind and air currents throughout the atmosphere. When an air mass cools
down, its vapor condenses into clouds and eventuallyfalls to the ground as precipitation in the form of
snow, rain, sleet, or hail.Water takes one route from the atmosphere to the ground, but can take a
variety
of paths and time periods to get back up into the atmosphere. These paths
include the following:
• Absorption by plants;
• Evaporation from the sun’s heating;
• Storage in the upper levels of soil;
• Storage as groundwater deep in the earth;
• Storage in glaciers and polar regions;
• Storage or transport in springs, streams, rivers, lakes; and
• Storage in the oceans.
When water is stored somewhere for any length of time, it is called a water reservoir. A reservoir is a
holding area. Nature’s reservoirs are oceans, glaciers, ice, underground storage (aquifers), lakes, rivers,
streams, the atmosphere, and the biosphere (within living organisms). Surface water in streams and
lakes returns to the atmosphere as a gas (vapor) through the process of evaporation. Water held inside
plants returns to the atmosphere as a vapor through a biological process called transpiration. When
plants pull water up through their roots from the soil, use some of the dissolved minerals to grow, and
then release the water back through the leaves, the entire cycle is known as evapotranspiration.
This happens the most during times of high temperatures, wind, dry air, and sunshine.In temperate
climates, this occurs during the summertime. When air currents rise into the colder atmospheric layers,
water vapor condenses and sticks to tiny particles in the air. This is called condensation. When a lot of
water vapor coats enough particles (dust, pollen, or pollutant), it forms a cloud.
Water Pollution and Treatment
Water pollution comes from the loss of any real or potential water uses caused by a change in its
composition due to human activity.
Water pollution is caused by the sudden or ongoing, accidental or deliberate, discharge of a polluting
material. Increasing human populations put pressure on the oceans and marine environment. More and
more people on the planet lead to more of the following:
• Sewage produced;
• Fertilizers, herbicides, and pesticides used for crops, lawns, golf courses, and parks;
• Fossil fuels extracted and burned;
• Oil leaked and spilled;
• Land deforested and developed; and
• Various byproducts of manufacturing and shipping generated.
Cultural, political, and economic forces affect the types, amounts, and management of waste produced.
Increasing population is just one contributor to increasing pollution. As with everything in the
environment, the causes and effects are complex.
Groundwater has been contaminated by leaking underground storage tanks, fertilizers and pesticides,
unregulated hazardous waste sites, septic tanks, drainage wells, and other sources.
The three major sources of water pollution are municipal, industrial, andagricultural. Municipal water
pollution comes from residential and commercial waste water. In the past, the main way to treat
municipal wastewater was to reduce suspended solids, oxygen-demanding materials, dissolved
inorganic compounds, and harmful bacteria. Today, the focus is on the improvement of solid residue
disposal from municipal treatment processes.
pH
The measurement of pH is important into wastewater treatment before its release into natural water
ecosystems.
The measurement of the number of hydrogen ions in water, on a scale from 0 to 14, is called the water’s
pH.
The pH of natural waters becomes acidic or basic as a result of human activities, such as acid mine
drainage, emissions from coal-burning power plants, and heavy automobile traffic.
DISSOLVED OXYGEN
Oxygen enters the water by direct atmospheric absorption or by aquatic plant and algal photosynthesis.
Oxygen is removed from water by respiration and the decomposition of organic material.
Dissolved oxygen is the amount of oxygen measured in a stream, river, or lake.
Dissolved oxygen is also an important marker of a river or lake’s ability to support aquatic life. Fish need
oxygen to survive and absorb dissolved oxygen through their gills. The actual level of dissolved oxygen
present in even the cleanest water is extremely small. The amount of dissolved oxygen in water depends
on several factors, including temperature (the colder the water, the more oxygen that can be dissolved),
volume and velocity of water flow, and number of organisms using oxygen for respiration.
TURBIDITY
Turbidity is a measure of water’s cloudiness. The cloudier the water, the higher the turbidity. Water
turbidity is caused by suspended matter such as clay, silt, and organic matter. It can also result from
increases in plankton and other microscopic organisms that interfere with the passage of light through
the water.
Turbidity itself is not a major health concern, but high turbidity can interfere with disinfection and
provide a suspended medium for microbial growth. High turbidity also points to the presence of
microorganisms. High turbidity can be caused by soil erosion, urban runoff, and high flow rates.
Water Treatment
Whenever water is used for humans, it must be treated from two different angles. First, any surface
water from rivers that is used in cities is treated for drinking, usually by chlorination. After water is used
for drinking, washing, lawns, toilets, and so on, it has to be treated at a wastewater treatment plant
before it can be released back into the environment.
CONTAMINANTS
Water pollution is bad news. It poisons drinking water, poisons food animals (through buildup of
environmental toxins in animal tissues), upsets the biological diversity of river and lake ecosystems,
causes acid rain deforestation, and lots of other problems. Most of these problems are contaminant
specific.
In general, four main contaminants types exist: organic, inorganic, radioactive, and acid/base. These are
released into the environment in a variety of different ways, most pollutants enter the hydrologic cycle
two ways, as direct (point source) and indirect (non–point source) contamination.
Point sources include effluents of various qualities from factories, refineries,
and waste treatment plants that are released directly into urban water supplies.
Non–point sources include contaminants that come into the water supply from soil/groundwater
systems runoff and from the atmosphere through rainfall. Soils and groundwater contain fertilizer and
pesticide residues and industrial wastes. Atmospheric contaminants also come from gaseous emissions
from automobiles, factories, and even restaurants.
CHEMICALS
Many pollution sources come from sewage and fertilizers containing nutrients like nitrates and
phosphates. In high levels, nutrients overstimulate the growth of water plants and algae. Uncontrolled
growth of these organisms clogs waterways that use up dissolved oxygen and as they decompose, keeps
sunlight from penetrating into deeper water. When this happens, the photosynthetic cycle of good
water plants and organisms is affected. This hurts fish and shellfish that live in the affected water.
Nitrogen
Nitrogen is needed by all organisms to form proteins, grow, and reproduce. Nitrogen is very common
and found in many forms in the environment. Inorganic forms include nitrate (NO3), nitrite (NO2),
ammonia (NH3), and nitrogen gas (N2). Organic nitrogen is found in the cells of all living things and is a
part of proteins, peptides, and amino acids. High levels of nitrate, along with phosphate, can
overstimulate the growth of aquatic plants and algae, causing high dissolved oxygen consumption, killing
fish and other aquatic organisms. This process is called eutrophication. Nitrate, nitrite, and ammonia
enter waterways from lawn fertilizer runoff, leaking septic tanks, animal wastes, industrial wastewaters,
sanitary landfills, and discharges from car exhausts.
Phosphorus
Phosphorus is also a nutrient needed by all organisms for basic biological processes. Phosphorus is an
element found in rocks, soils, and organic material. Its concentration in fresh water is usually very low.
However, phosphorus is used widely in fertilizer and other chemicals, so it is often found in higher
concentrations in populated areas. Phosphorus is commonly found as phosphate (PO4 –3). High levels of
phosphate and nitrate cause eutrophication. The main sources of phosphates in surface waters are
detergents, fertilizers, and natural mineral deposits.
ORGANIC MATTER
Pollution also takes place when silt and other suspended solids like soil run off from plowed fields,
construction and logging sites, urban areas, and eroded river banks after a rain. This can also happen
with snow melt. Lakes, slowly moving rivers, and other areas of water go through eutrophication
(in the presence of excess nitrogen and phosphorus), which gradually fills a lake with sediment and
organic matter. When these sediments dump into a lake, for example, fish respiration is impacted, plant
growth and water depth are limited, and aquatic organisms asphyxiate. Removal of nitrogen and
phosphorus help to prevent eutrophication.
Organic pollution enters waterways as sewage, leaves, and grass clippings, or as runoff from livestock
feedlots and pastures. When bacteria break down this organic material (measured as biochemical
oxygen demand, BOD), they use the oxygen dissolved in the water.
PATHOGENS
It’s important to include pathogens as a type of pollution with wide-reaching health risks. Pathogens
(disease-causing microorganisms) cause everything from typhoid fever and dysentery to respiratory and
skin diseases. They include such organisms as bacteria, viruses, and protozoa. These living nemeses
enter waterways through untreated sewage, storm drains, septic tanks, farm runoff, and bilge water.
Although microscopic, biological pathogens have a monstrous effect in their ability to bring about
sickness.
Fecal coliform bacteria, present in the feces and intestinal tracts of humans and other warm-blooded
animals, can enter rivers and lakes from human and animal waste. If any fecal coliform bacteria are
present, it is an indication of the possible presence of pathogenic microorganisms.
Acid Rain
Acid precipitation describes wet acid pollution forms found in rain, sleet, snow, fog, and cloud vapor
Acid rain refers to all types of precipitation (rain, snow, sleet, hail, fog) that is acidic (pH lower than the
5.6 average of rainwater) in nature.
Acid rain is formed when chemicals in the atmosphere react with water and return to the earth in an
acidic form in raindrops. When acid rain falls on limestone statues, monuments, and gravestones, it can
dissolve, discolor, and/or disfigure the surface by reaction with the rock’s elements. The process is
known as dissolution. Historical treasures such as statutes and buildings, hundreds to thousands of years
old, suffer from this kind of weathering. Acid rain is a byproduct of the industrial revolution: Industry
releases the chemicals that form the acid in the atmosphere.
The sulfur and nitrogen oxides that form acid rain are released mostly from industrial smokestacks and
automobile, truck, and bus exhausts, but they can also come from burning wood. When they reach the
atmosphere, they mix with moisture in the clouds and change to sulfuric and nitric acid. Then, rain and
snow wash these acids from the air.
Acid rain has been measured in the United States, Germany, Czechoslovakia, Yugoslavia, the
Netherlands, Switzerland, Australia, and elsewhere. It is also becoming a big problem in Japan, China,
and Southeast Asia.
Acid rain affects lakes, streams, rivers, bays, ponds, and other bodies of water by increasing their acidity
until fish and other aquatic creatures can no longer live there.
Acid Deposition
Acid deposition forms in two ways. It is belched out as hydrochloric acid directly into the atmosphere or
from secondary pollutants that form during the oxidation of nitrogen oxides or sulphur dioxide gases
released into the atmosphere. These pollutants can travel hundreds of kilometers from their original
source.
Acid precipitation also takes place when nitrogen oxides and sulphur dioxide settle on the land and
interact with dew or frost. Roughly 95% of the elevated levels of nitrogen oxides and sulfur dioxides in
the atmosphere come from human actions. Only 5% comes from natural processes. The five main
nitrogen oxide sources include:
1) Burning of oil, coal, and gas;
2) Volcanic action;
3) Forest fires;
4) Decay of soil bacteria; and
5) Lightning.
Nitrogen oxide and sulfur dioxide concentrations are much lower than atmospheric carbon dioxide,
primarily responsible for the natural acidity of rainwater. These gases are much more soluble than
carbon dioxide, however, and have a greater impact on the pH of precipitation.
ACID RAIN EFFECTS
In the mountains, many acidified aquatic ecosystems go through acid shock. This happens when acidic
deposits buildup in the snow pack during the winter. With the spring melt, the stored snow melts and
acids are released suddenly at concentrations 5 to 10 times more acidic than precipitation. Although
most adult fish survive this acid shock, eggs and fry of many spring-spawning species are
hit hard by this acidification. Acid precipitation can also damage plant leaves, particularly in the form of
fog or clouds when their water content can be up to ten times more acidic than regular rainfall.
TREATMENT
There are a number of things that can be done in order to alleviate the problems of acid deposition. For
example, liming is done to normalize the pH of lakes that have been acidified. This involves adding large
amounts of hydrated lime, quick lime, or soda ash to lake waters to increase the alkalinity (make the
water more basic). This fix has some drawbacks, as some lakes are unreachable, too big and
therefore too costly to treat, or have a high flow rate and quickly become acidic again after liming.
The best way to slow or stop acid deposition is to limit the chemical emissions at their source. In several
environmentally conscious countries, regulations now limit the amount of sulfur and nitrogen oxide
emissions that can enter the atmosphere from industrial sources. Industrial sources limit acidic
pollutants three ways: 1) by switching to fuels that have no or a low sulfur content, 2) by using
smokestack scrubbers to reduce the amount of sulfur dioxide being released, and 3) by requiring the use
of specially designed catalytic converters on vehicles.
Oil, Radioactivity, and Thermal Problems
OIL SLICKS
Fossil fuels cause atmospheric pollution from combustion, but they affect water through spills.
Petroleum pollutes rivers, lakes, seas, and oceans in the form of oil spills. Oil pollution is increasing and
devastating to coastal wildlife. Since oil and water don’t mix, even small oil amounts spread quickly
across long distances to form deadly oil slicks. Oil tanker spills are a growing environmental problem
because once oil has spilled, it is almost impossible to remove or contain completely. Oil floats on the
water for long periods of time and then washes up along miles of shoreline. When efforts to chemically
treat or sink the oil are made, area marine and beach ecosystems are often disrupted even more.
RADIOACTIVITY
Nuclear medicine is the specific focus of radiology that uses minute amounts of radioactive materials, or
radiopharmaceuticals, to study organ function and structure. Nuclear medicine imaging is a combination
of many different sciences, including chemistry, physics, mathematics, computer technology, and
medicine
Radioactive waste materials are also created by nuclear power plants, industry, and mining of
radioactive minerals. Dust and waste rock from uranium and thorium mining and refining processes
contain minute levels of nuclear contaminants. When rainfall washes these away from the mining sites,
they eventually make their way to waterways. Over time, levels increase and there is a problem.
THERMAL POLLUTION
The final form of water pollution we will study is thermal pollution. At first glance, it seems like a fairly
harmless form of water pollution, but it can have far-reaching and damaging effects on an ecosystem.
Heat pollutes water through its impact on aquatic organisms and animal populations.
The release of a substance, liquid or air, which increases heat in the surrounding area is known as
thermal pollution.
Industries are the main culprit of thermal pollution. Not thinking of thermal pollution as a problem,
industries release high-temperature wastewater directly into rivers and lakes without a second thought.
The immediate and long-term effects are felt by complex ecosystems at the discharge site and
downstream. Although the aquatic environment is less impacted when heated wastewater cools,
upstream species near the release location take a thermal hit that affects their population numbers in
ecosystems further downstream.
TREATMENT OF WATER
The available raw water has to be treated to make it fit, i.e. potable, means safe for human
consumption. It should satisfy the physical, chemical and bacteriological standards as specified above.
The various methods of purification of water are
(i) Screening
Screens are provided before the intake works so as to prevent the entry of big objects
like debris, branches of trees, part of animals etc. Screens may be of two types, coarse
screen and fine screens.
(ii) Plain sedimentation
Sedimentation is done to remove the impurities which have specific gravity more than
that of water and are settleable.
(iii) Sedimentation aided with coagulation
The sedimentation is aided with coagulation. Coagulation is a process in which some
chemical like alum or ferrous sulphate is mixed in water resulting in particle destabilization.
(iv) Filtration
Filtration is a physical and chemical process for separating suspended and colloidal
impurities from water by passage through a porous bed made up of gravel and sand
etc.
(v) Disinfection
The process of killing these bacteria is known as disinfection.
(vi) Aeration
Aeration is done to remove taste and odour.
(vii) Softening
The reduction or removal of hardness from water is called as water softening
(viii) Miscellaneous treatments like demineralization etc.
the demineralization is done mainly to make the brackish water (as sea water) useful for
drinking.
WATER POLLUTION MANAGEMENT PROGRAMME OF TRINIDAD &
TOBAGO
The Programme overall objective is to control, reduce and prevent water pollution from point and non-
point sources discharges into the waters of Trinidad and Tobago. The benefit to be derived for meeting
this long-term objective would be the preservation and maintenance of good quality water that would
support present and future generations.
In order to achieve the overall objective of the Programme the following sub-programmes will be
developed and implemented simultaneously/sequentially:
1 Water Pollutant Registration
2 Water Pollution Permitting
3 Best Management Practices
4 National Water Quality Standards
5 Monitor and Control Environmental Incidents
6 Watershed Management Programme
7 Non-Point Source Pollution Control Programme
8 Inter-Governmental Approach to Remedy Abandoned and Malfunctioning Sewage Treatment Plants
9 Laboratory Registration and Certification Programme
REVIEW QUESTIONS
1. Explain what is meant by thermal liquid pollution and one possible source.
2. Discuss briefly the present methods for disposal of hazardous liquid waste.
3. Outline the requirements for disposal of hazardous liquid wastes in Trinidad.
4. Define the term “liquid”?
5. Identify the potential sources of liquid pollutants
6. State the types of hazardous liquids. Give the effects of each of these liquids.
7. State the ways in which hazardous liquids can be disposed
8. How do you determine the amount of suspended material carried in water?
9. Which is a common test used to determine the level of contamination of a river?
10. What is the rate at which a chemical spill spreads is dependent on?
11. What does Effluent refer to?
12. Explain Turbidity testing.
13. What does the abbreviated term - BOD mean?
14. What is the best form of treatment for hazardous waste?
15. What is a liquid?
16. Why is water described as the universal liquid pollution „carrier‟?
17. State the types of hazardous liquids. Give the source and effect of each of liquids.