Unit 3 b: Water Pollution and control - wALHSE · Unit 3 b: Water Pollution and control _____ Lecture Objectives i. Describe the main sources and composition of water contaminants

Unit 3 b: Water Pollution and control

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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

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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.