Module II: Environmental Issues and Systems

Module II: Environmental Issues and Systems: Local, regional,

continental and global environmental issues including
greenhouse gases and global warming, acid rain, ozone layer
depletion, climate change - Extent of impact, scientific
responses and regulatory actions; Environmental systems

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Explosion of Environmental Issues
Spatial Scales
 Micro-scale (10 to 100 m) and Middle-scale (100 to 500 m)
 Local scale/Neighborhood scale (500 m to 5 km)
 Urban scale (5 to 100 km)
 Regional scale (100 to 500 km to 1000 km)
 Continental scale (1,000 to 10,000 km)
 Global scale (> 10,000 km) (Extends worldwide)

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Local Environmental Issues Regional and Global Environmental
Issues
 Waste Disposal  Global Warming
 Water Scarcity  Ocean Acidification
 Desertification Ocean acidification refers to a reduction in the pH of the
ocean over an extended period of time, caused primarily by
Desertification is the degradation process by uptake of carbon dioxide (CO2) from the atmosphere.
which a fertile land changes itself into a
desert by losing its flora and fauna, this can be  Pollution: Air, water, land, etc.
caused by drought, deforestation, climate change,
human activities or improper agriculture. The release of radioactivity from the accident at
Desertification is a process of degradation of the Chernobyl would be considered primarily a regional or
land. continental problem. However, higher than usual levels of
radioactivity were detected in the Pacific Northwest part of
the United States soon after the accident.
 Pollution: Air, water, land, etc. Likewise, persistent organic pollutants, such as
polychlorinated biphenyls (PCBs) have been observed in
 Endangered Species Arctic mammals, thousands of miles from their sources.
Bihar is planning to launch a conservation drive for
endangered blackbucks in Buxar district  Acid Rain
 Ozone Layer Depletion
 Polar Melting

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 Assignment
 Chipko movement
 Save Silent Valley movement
 Narmada Bachao Andolan
 Namami Gange Programme
 Taj Trapezium
 Jungle Bachao Andholan
 Desertification
 Endangered Species
 Ocean Acidification
 Polar Melting
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 What is the Ozone Layer?

• It is a layer in the earth’s

stratosphere that contains high
levels of ozone.
• This layer protects the earth from
the Sun’s harmful UV radiation. It
absorbs 97 – 99% of the UV
radiation from the Sun.
• In the absence of the ozone layer, millions of people would be affected
by skin diseases including cancer and weakened immune systems.
• UV radiation would also affect the environment adversely leading to
decreased productivity.
• Fauna on earth is also adversely affected by ozone layer depletion

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 Ozone Layer Depletion
• This refers to the thinning of the protective
ozone layer in the atmosphere.
• This happens when certain chemicals (chlorine
and bromine atoms) come into contact with
ozone and destroy it.
• One chlorine atom can destroy over 100,000 ozone molecules
before it is removed from the stratosphere.
• Chemical compounds that cause ozone layer depletion are called Ozone
Depleting Substances (ODSs).
• Examples of ODSs are chlorofluorocarbons (CFCs),
hydrochlorofluorocarbons (HCFCs), carbon tetrachloride, methyl
chloroform, hydrobromofluorocarbons, halons, etc.

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 Ozone Layer Depletion

• Chlorofluorocarbons are the most abundant ODSs.

• The indiscriminate use of these chemicals causes
ozone layer depletion.
• These ODSs are also powerful greenhouse gases
(GHGs) and have a long life as well.
• There are a few natural causes also which cause ozone
depletion such as volcanic eruptions, sunspots, and
stratospheric winds. However, these do not cause
more than 1 – 2 % of the ozone depletion.

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Ozone hole is not really a hole through the ozone layer, but rather a
large area of the stratosphere with extremely low amounts of ozone
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 Ozone altitude UV graph

 UV-c (red) is entirely

screened out by ozone
around 35 km altitude

 Most UV-a (blue) reaches

the surface, but it is not
as genetically damaging

 UV-b (green) radiation that can cause sunburn and that can also cause
genetic damage, resulting in things like skin cancer, if exposure to it is
prolonged
 Ozone screens out most UV-b, but some reaches the surface. Were
the ozone layer thin, more UV-b radiation would reach the
surface, causing increased genetic damage to living things.
Dobson unit (DU) is a unit of measurement of the amount of a trace gas Source: NASA, 2011
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 Maximum ozone hole extent over the southern hemisphere, from 1979 to 2022
The blue colours indicate lowest ozone columns, while yellow and red indicate higher ozone columns.
Ozone columns are commonly measured in Dobson Units. One Dobson Unit is the number of molecules
of ozone that would be required to create a layer of pure ozone 0.01 millimetres thick at a temperature of
0 degrees Celsius and a pressure of 1 atmosphere. 300 DU corresponds to 3 millimetres of ozone.
Source: Copernicus Atmosphere Monitoring Service 12
 Vienna Convention for the Protection of the Ozone Layer
 The Vienna Convention came into force in 1988 and was universally ratified by
2009
 It is called the Convention for the protection of the Ozone layer
 International Day for the Preservation of the Ozone Layer?

 The purpose of the Vienna Convention is to protect the ozone layer from
depletion
 8 countries originally signed the convention on 22nd March 1985
 On 16th September 2009, Vienna Convention along with Montreal Protocol
was universally ratified and thus became the first treaties in the history of the
United Nations to achieve universal ratification
 There are 198 members under the Vienna Convention

Convention provided the framework necessary to create

regulatory measures in the form of the Montreal Protocol

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 Vienna Convention & India
 India is a member of the Vienna Convention. It acceded to the
convention in 1991 and became a party to the Montreal Protocol
in 1992.

India’s Actions in protecting the Ozone Layer

 The Ministry of Environment, Forest & Climate Change is entrusted
with the work related to the Montreal Protocol protection and
implementation.
 Ozone Cell is set up for effective and timely implementation of the
Montreal Protocol.
 Carbon tetrachloride (CTC) has been completely phased out by
India as of 1st January 2010.

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 Montreal Protocol
• The Montreal Protocol on Substances that Deplete the
Ozone Layer is an important Multilateral Agreement
regulating the production, consumption, and emissions of
ozone-depleting substances (ODSs)
• By the late 1970s, scientists were able to prove that chemical
substances that were used in air conditioners, refrigerators,
and aerosol cans were causing damage to the ozone layer.
• In 1985, a huge hole was discovered in the ozone layer over
Antarctica. This hole allowed hazardous levels of
ultraviolet (UV) radiation to reach the earth’s surface.

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 Montreal Protocol
• The Vienna Convention for the Protection of the Ozone Layer
was signed in 1985 under which UN member countries
recognized the importance of curbing damage to the ozone
layer.
• As per the Convention’s provisions, countries agreed to adopt
the Montreal Protocol to further the goals of the Vienna
Convention.
• Adopted on 15 September 1987, the Protocol is to date the
only UN treaty ever that has been ratified every country on
Earth - all 198 UN Member States.

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 Montreal Protocol – Important Points
The Protocol was signed in 1987 and entered into force in January 1989. The
protocol gives provisions to reduce the production and consumption of ODSs to
protect the ozone layer.

 It phases down the use of ODSs in a stepwise, time-bound manner.

 It gives different timetables for developing and developed countries.
 All member parties have specific responsibilities related to the phasing out of
various groups of ozone-depleting substances, controlling ODS trade,
reporting of data annually, controlling export and import of ODs, etc.
 Developing and developed countries have common but differentiated
responsibilities.
 However, both groups of nations have time-bound, binding, and measurable
commitments under the protocol, making it effective.

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 Montreal Protocol – Important Points
 Under the protocol, there is a provision for it to be amended and adjusted
according to the new scientific, economic, and technological advancements
made.
 Multilateral Fund: The Multilateral Fund for the Implementation of the
Montreal Protocol was set up in 1991 to help developing countries to
comply with the provision of the Protocol. This is under Article 10.
 It provides financial and technical assistance to developing member
countries whose yearly per capita consumption and production of
ODSs is less than 0.3 kg.

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 Montreal Protocol – Successes
 With universal ratification and a time-bound binding framework, the Montreal
Protocol has been largely successful in setting out to achieving its mission of
reversing the damage done to the ozone layer.
 It has been considered the most successful international environmental action
taken by countries.
 The Protocol has been successful in levelling off or decreasing the atmospheric
concentrations of the most important chlorofluorocarbons and related
chlorinated hydrocarbons.
 Although halon concentrations have gone up, their rate of increase has come
down, and their concentration is expected to decline by 2020.
 The Protocol has successfully sent clear signals to the global market.

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 Montreal Protocol – Successes
 The full implementation of the Montreal Protocol is expected to help in the
avoidance of over 280 million skin cancer incidents, almost 1.6 million deaths
due to skin cancer, and millions of cases of cataracts.
 With the Protocol, the ozone layer is expected to recover by the year 2050.
 Parties to the Protocol have been able to phase out 98% of ODSs compared to
levels in 1990.
 The Protocol is also helping fight climate change because most of the ODSs are
also greenhouse gases.
 It is estimated that from 1990 to 2010, the protocol has helped reduce
greenhouse gas emissions by the equivalent of 135 gigatons of carbon dioxide,
the equivalent of 11 gigatons a year.
 The Kigali Amendment, an amendment to the Protocol, has helped reduce HFC
emission and decrease global temperature rise.

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 India and the Montreal Protocol
India became a signatory to the Montreal Protocol in 1992.

 India is an Article 5 country and is entitled to assistance from the Multilateral Fund in
its efforts to phase out ODSs and switch over to non-ODS technologies.
 India mainly manufactured and utilized 7 of the 20 substances controlled under the
Protocol. These are CFC-11, CFC113, CFC-12, Halon-1301, Halon-1211, Carbon
tetrachloride, Methyl Bromide and Methyl Chloroform.
 In India, the implementation of the Montreal Protocol comes within the ambit of the
Ministry of Environment, Forests, and Climate Change.
 The Ministry has established an Ozone Cell to implement the Protocol.
 As per the National Strategy for ODS Phase out, the Ministry has notified the Ozone
Depleting Substances (Regulation and Control) Rules 2000.
 Rules prohibit the use of CFCs in manufacturing various products.
 They provide for the mandatory registration of ODS producers, sellers, importers, and
stockists.

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 Taj Mahal

Agra, Uttar Pradesh, India

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 Statue of Liberty

Liberty Island, New York Harbor, New York City, USA

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 Acid Rain
Acid rain, or acid deposition, is a broad term that
includes any form of precipitation with acidic
components, such as sulfuric or nitric acid that
fall to the ground from the atmosphere in wet or dry
forms.

This can include rain, snow, fog, hail or even dust that is
acidic.

Source: US EPA 24
 Causes of Acid Rain
 Acid rain results when sulfur dioxide
(SO2) and nitrogen oxides (NOX) are
emitted into the atmosphere and
transported by wind and air currents.
 The SO2 and NOX react with water,
oxygen and other chemicals to form
sulfuric and nitric acids.
 These then mix with water and other
materials before falling to the ground.

2SO2 (g) + O2 (g) + 2H2O (l) → 2H2SO4 (aq)

4NO2 (g) + O2 (g) + 2H2O (l) → 4HNO3 (aq)

Source: US EPA 25
 Causes of Acid Rain
While a small portion of the SO2 and NOX that cause
acid rain is from natural sources such as
volcanoes, most of it comes from the burning of
fossil fuels.
The major sources of SO2 and NOX in the
atmosphere are:
 Burning of fossil fuels to generate electricity.
 Two thirds of SO2 and one fourth of NOX in the
atmosphere come from electric power
generators.
 Vehicles and heavy equipment.
 Manufacturing, oil refineries and other industries.

Winds can blow SO2 and NOX over long distances and across borders
making acid rain a problem for everyone and not just those who live close
to these sources.
Source: US EPA 26
 Acid Rain Pathway
1) Emissions of SO2 and
NOx are released into
the air, where

2) The pollutants are

transformed into acid
particles that may be
transported long
distances.

3) These acid particles then fall to the earth as wet and dry
deposition (dust, rain, snow, etc.) and

4) May cause harmful effects on soil, forests, streams, and lakes.

Source: US EPA 27
 Effects of Acid Rain
Acid rain is very harmful to agriculture,
plants, and animals. It washes away all
nutrients which are required for the
growth and survival of plant.

When acid rain falls down and flows into

the rivers and ponds it affects the
aquatic ecosystem.

It causes respiratory issues in

animals and humans.

Source: US EPA 28
 Effects of Acid Rain

Acid rain also causes the corrosion

of water pipes, which further
results in leaching of heavy metals
such as iron, lead and copper into
drinking water.

It damages the buildings and

monuments made up of
stones and metals.

Source: US EPA 29
 Taj Mahal

One of the worst hit monument by acid rain is Taj Mahal

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 High levels of sulfur and
nitrogen oxides are present in
the air around the city of Agra,
where the Taj Mahal is situated.

This is primarily because of

presence of numerous
industries and power plants in
nearby area that generate
significant amounts of sulfur and
nitrogen oxides.

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Acidic gases like SO2, SO3, and NO2
react with atmospheric water vapor or
rainwater to produce sulfuric and
nitric acids. The Taj Mahal's marble
reacts with these acids to produce
calcium sulfate and calcium nitrate.

As a result, the marble of the monument progressively becomes

dull and discolored. 32
 Action plan by Govt. of India (1995)
The air in the Taj Trapezium – the
area including the towns of Agra,
Firozabad, Mathura and
Bharatpur should be pollution free.

About 2000 industries located in this area

should stop using coal or kerosene/furnace oil
and switch over to either natural gas or LPG.

The people living in this area should be encouraged to use LPG in

place of coal/wood or kerosene.

The vehicles running through this

area including the highways should be
encouraged to use low–sulfur diesel.
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Climate Change: A Primer

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Science of Climate Change
The Greenhouse Effect

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Science of Climate Change
The Greenhouse Effect

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Science of Climate Change
The Greenhouse Effect

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The Earth’s Climate in the Past

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39
 Impacts of Climate Change

Extreme Weather Events

 The 2009 State of the Climate report served as a basis for the poster
 More than 300 scientists from 160 research groups in 48 countries
contributed to the report, which confirms that the past decade was the
warmest on record and that the Earth has been growing warmer over the
last 50 years
 In a warming world, based upon simple physical principles we would
expect some indicators to increase land surface air temperature, sea-
surface temperature, marine air temperature, sea level, tropospheric
temperature, ocean heat content and specific humidity
 Conversely, we would expect the following indicators to decline: snow
cover, sea-ice extent, glacier mass, and stratospheric temperatures.
Stratospheric temperature decline is also influenced by ozone depletion.
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CO2 is the Major Cause of Global Warming

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Emission of Green House Gases (GHGs)

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 Global Warming Potential

Global warming potential (GWP) and CO2 equivalence are used to

compare the potential warming influence of emissions of the same mass of
different GHGs

GWP compares the warming effect of a given mass of GHG to the same mass of
CO2 over a specified time. As GHGs do not have the same life time in the
atmosphere, the GWP depends on the time horizon chosen. 43
 Impacts of Climate Change
Melting of More Ice and Snow

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 Impacts of Climate Change
Sea Level Rise

Many low lying coastal land areas are expected to be gradually submerged by
rising sea levels

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 Impacts of Climate Change

Sea Level Rise

For a low lying island nation like the Maldives in the Indian Ocean, even a small
rise in sea level could spell disaster for most of its people. About 80% of the 1192
small islands making up this country lie less than 1 meter above sea level.

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 Impacts of Climate Change
Coastal Flooding
Sea level rise will magnify the adverse impact of storm surges and high waves on
the coast

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 Impacts of Climate Change

Ocean Acidification
Acidification of ocean water can harm marine life

Declining pH levels in the world's oceans interferes with many species ability to form shells 48
 Impacts of Climate Change

Extreme Weather Events

As the climate has warmed, some types of extreme weather have become more
frequent and severe in recent decades

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Impact on Food Production

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 Threat to Human Health

Climate crisis can have serious consequences for human health and well being

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Climate solutions

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 Carbon capture, utilization and storage
Carbon capture, utilization and storage (CCUS) is a combination of technologies for
(1) Selectively removing CO2 from smokestacks of fossil-fuelled powerplants and
other large industrial sources,
(2) Compressing and transporting it as a supercritical fluid to a suitable site,
(3) Utilizing it as a feedstock in industrial process and/or
(4) Storing it by a natural or engineered trapping mechanism.

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Governments can play a critical role

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Governments can play a critical role

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Governments can play a critical role

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 Kyoto Protocol
 It is an international treaty to reduce greenhouse gas emissions.

 Kyoto Protocol applies to 6 greenhouse gases; carbon dioxide, methane, nitrous oxide,
hydrofluorocarbons, perfluorocarbons, sulfur hexafluoride.

 The Kyoto Protocol was adopted on 11 December 1997

 It entered into force on 16 February 2005.

 Currently, there are 192 Parties to the Kyoto Protocol.

 The Kyoto Protocol operationalizes the United Nations Framework Convention on Climate
Change by committing industrialized countries and economies in transition to limit and reduce
greenhouse gases (GHG) emissions in accordance with agreed individual targets.

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 Carbon credits
 An objective of the Kyoto Protocol was to enable developed nations, which
had profited from economic development based upon high-carbon GDPs, to
economically assist the growing economies of developing nations, impacted
by carbon emission constraints and heavily indebted to foreign
creditors.
 A carbon credit system was devised that imposed national caps on
greenhouse gas emissions of developed nations that ratified the Kyoto
Protocol.
 Each of these countries was given an allotment and corresponding number of
emission allowances known as Assigned Amount Units (AAUs).
 Participating countries were required to reduce their emissions to well below
1990 levels and more than 5% by 2012.
 They could also reduce their emissions by trading in emission allowances with
countries that already had surplus allowances. They could meet their targets
by buying carbon credits.

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 Carbon credits
 A carbon credit (often called a carbon offset) is a credit for greenhouse
emissions reduced or removed from the atmosphere by an emission
reduction project, which can be used by governments, industry, or private
individuals to compensate for the emissions they generate elsewhere.

 The Kyoto Protocol provides for three mechanisms that enable countries, or
operators in developed countries, to acquire greenhouse gas reduction credits:

1. Under Joint Implementation (JI) a developed country with relatively high

costs of domestic greenhouse reduction would set up a project in another
developed country.

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 Carbon credits
2. Under the Clean Development Mechanism (CDM) a developed country
can “sponsor” a greenhouse gas reduction project in a developing country
where the cost of greenhouse gas reduction project activities is usually much
lower, but the atmospheric effect is globally equivalent. The developed country
would be given credits for meeting its emission reduction targets, while the
developing country would receive the capital investment and clean technology
or beneficial change in land use.

3. Under International Emissions Trading (IET) countries can trade in the

international carbon credit market to cover their shortfall in Assigned Amount
Units (AAUs). Countries with surplus units can sell them to countries that are
exceeding their emission targets under Annex B of the Kyoto Protocol.

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 Carbon credits
2. Under the Clean Development Mechanism (CDM) a developed country
can “sponsor” a greenhouse gas reduction project in a developing country
where the cost of greenhouse gas reduction project activities is usually much
lower, but the atmospheric effect is globally equivalent. The developed country
would be given credits for meeting its emission reduction targets, while the
developing country would receive the capital investment and clean technology
or beneficial change in land use.

3. Under International Emissions Trading (IET) countries can trade in the

international carbon credit market to cover their shortfall in Assigned Amount
Units (AAUs). Countries with surplus units can sell them to countries that are
exceeding their emission targets under Annex B of the Kyoto Protocol.

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The Paris Agreement

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The Paris Agreement

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64
Environmental Systems
 Natural
 We are concerned with understanding and describing
changes

 Engineered
 We are concerned with the selection of conditions
required to effectively accomplish specific changes

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Environmental Systems

Natural wetland Constructed wetland 67

 Transport
(mass)
Input Output
(mass) (mass)
A+B C+D
Transport
(mass)
Natural Engineered
systems systems

CIN
COUT COUT
CIN

DESCRIBE DESIGN
Measure given conditions and Determine desired changes in
describe (model) anticipated constituent(s) and prescribe (model)
changes in constituents required conditions
Environmental System Characterization - System Dynamics

• Matter and energy flow: Studying systems allows engineers to think

about how energy and matter flow in the environment.
• Open system: A system in which exchanges of matter or energy occur
across system boundaries.
• Closed system: A system in which matter and energy exchanges do not
occur across boundaries.
• Input: An addition to a system.
• Output: A loss from a system.
• Systems analysis: An analysis to determine inputs, outputs, and changes
in a system under various conditions.
• Steady state: A state in which inputs equal outputs, so that the system is
not changing over time.

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 Environmental System Characterization - System
Dynamics

Open and closed systems. (a) Earth is an open system with respect to energy.
Solar radiation enters the Earth system, and energy leaves it in the form of heat and
reflected light. (b) Earth is essentially a closed system with respect to matter because
very little matter enters or leaves Earth’s system. The white arrows indicate the
cycling of energy and matter.
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Example :
The slurry inlet composition has been measured by sampling the inlet and has a
composition (by mass) of 50% solid and 50% water, with a mass flow of 100 Kg per
minute, the tank is assumed to be operating at steady state. The removal efficiency
for the slurry is 60%, then calculate solid content in the water outlet. If the
measured flow rate of combined solids and water from the outlet is equal to 60 Kg
per minute then calculate the amount of water exiting via slurry outlet.

Wastewater
Settling tank Water outlet
inlet

Slurry outlet

Answer:

Solid content in the water outlet = 20 Kg/min

amount of water exiting via slurry outlet = 10 Kg/min

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Example:
Measuring dilution in streams: A treated wastewater enters a stream as
shown in the figure. The concentration of sodium in the stream at point A is
10 mg/ L and the flow rate is 20 m 3/s. The concentration of sodium in the waste
stream is 250 mg/L, and the flow rate is 1.5 m3/s. Determine the concentration of
sodium at point B assuming the complete mixing has occurred.

Answer:

Concentration of sodium at point B = 26.7 mg/L

Example :
A river with a flow rate of 1000 cumecs (m3/sec) has a BOD of 10 mg/L and
receives multiple discharges of wastewater from both sides. One wastewater
discharge has a flow rate of 10 cumecs and a BOD of 300 mg/L (it is untreated
sewage) while the other discharge from the opposite bank is 50 cumecs and 200
mg/L of BOD (wastewater after primary settling). Calculate the BOD downstream
of the two discharges. The DO levels in the river upstream of the wastewater
discharges is 5 mg/L and wastewaters have zero DO. Calculate the DO levels
downstream of the two discharges.

Answer:

BOD of the river downstream of the discharges, BOD =21.70 mg/L

DO of the river downstream of the discharges, DO = 4.72 mg/L

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Example :
Effluent from a wastewater-treatment plant is discharged to a surface stream. The
characteristics of the effluent and stream are as follows:

Effluent Stream
Flow = 8640 m3/d Flow = 1.2 m3/s
BOD5 = 25 mg/L BOD5 = 2.1 mg/L
Ammonia = 7 mg/L Ammonia = 0 mg/L
Nitrate = 10 mg/L Nitrate = 3.0 mg/L
Chloride = 15 mg/L Chloride = 5.0 mg/L

Determine the stream characteristics after mixing with the waste has occurred.

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Example :
A city has a population of 2.9 lakhs (2011 Census) while a residential academic
campus in this city has an additional resident population of 25,000.
a. If the average water consumption in the city is 300 Lpcd while that in the
campus is 500 Lpcd, determine the amount of wastewater being discharged by
the campus into the city’s municipal sewers. Also, determine the total amount
of wastewater that needs to be treated at a proposed wastewater treatment
plant. Assume 90% percent of the water consumed is discharged as wastewater.
b. An industry is proposing to discharge its wastewater to the city’s sewers also.
The amount of wastewater is likely to be 1 MLD with a BOD of 6000 mg/L.
The municipal wastewater has an average BOD concentration of 300 mg/L.
Determine the total flow to be treated and BOD loading to the proposed
wastewater treatment plant.
Answer:
a. Wastewater generated in academic campus = 11.25 MLD; Total wastewater
generated = (11.25 + 78.3) MLD = 89.55 MLD
b. Total wastewater discharge = 90.55 MLD; BOD concentration in combined
industrial and municipal flows = 363 mg/L
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Example :
A village pond is being used for long-term storage of water. The source of water is
a neighboring stream and the pond has no outlets. The pond volume is 1000 m3
with an average water depth of 5 m.
a. If the mean annual evaporation rate is 1 cm/d, and the infiltration rate is 0.5
cm/d, what is the mean annual flow rate into the pond, assuming that the pond
volume remains constant (volume of water in the pond) throughout the year?
b. The influent water contains nutrients like carbon, nitrogen and phosphorus.
Total Kjeldahl Nitrogen (TKN) concentration in the influent is 50 mg/L. Assume
that all TKN will be converted to nitrate, and nitrate does not evaporate but
can infiltrate into the subsurface. Can you predict the concentration of nitrate-
N over time in the pond? Assume that there are no reactions with nitrate.

Answer:
a. Volumetric flow rate of water into the pond = 3 m3/d
b. Rate of mass of nitrate accumulation in pond = 100 g/d

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 System Boundary
QA = 30,000 m3/min
I + II
River A
River B
QB = Unknown
LAKE I
AI = 2.6 X 107 m2
VI= 2.6 X 108 m3
Sub-System
Sub-System Boundary I
Boundary II
River C ; QC = 20,000 m3/min
River E
QE = Unknown

LAKE II
AII = 1.19 X 108m2
VII = 8.3 X 108 m3

QD = 95,000 m3/min
River F
River D
QF = 40,000 m3/min
Objective:
Find QB and QE
• Volumes of lakes are constant
i) Define boundary :  system boundary Lake I + Lake II
ii) Mass balance of water
QA + QD = QB + QE + QF ---- 1
steady state condition  temporarily stable condition
Otherwise
(QA + QD) – (QB + QE + QF) = d/dt (VI + VII) ---- 2
iii) Redefine boundaries:
Lake I – subsystem  QB = QA – QC = 10,000 m3/min ---- 3
Lake II – subsystem  QE = QC + QD – QF = 75,000 m3/min ---- 4
What allows us to write above equation is that mass concentration of
water in water is constant and equal to its density ρω
QA ρω – QB ρω – Qc ρω = 0 ---- 5
Assumption  System involved incurred no change in its properties

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Let us complicate by acknowledging that evaporation may
be important/significant (r = 0.5 cm/d  cm3/cm2/d)

• New sink term

 QA ρω – QB ρω – Qc ρω – EV,I ρω = 0 ---- 6
(EV,I ρω = 0.5 / 100 X 1440 m/min X 2.6 X 107 m2 = 90 m3/min)

 QC ρω + QD ρω – QE ρω – QF ρω - EV,II ρω = 0
(EV,II ρω = 0.5 / 100 X 1440 X 1.19 X 108 = 413 m3/min)

QB = 9910 m3/min
QE = 74,600 m3/min

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• Constituent mass balance
• Boundary same as before
• Chloride  no transformation  conservative
• Cl- is not evaporated
• CA (Cl-) = 40 mg/L; CD (Cl-) = 60 mg/L
Assumption CB (Cl-) = CC (Cl-) (complete mixing)

30,000 X 40
C B (Cl )  CC (Cl )   40.1 mg / L
9,910  20,000

(20,000 X 40.1)  (95,000 X 60)

CE (Cl )  C F (Cl )   56.7 mg / L
74,587  40,000

80