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Carbon Cycle
• Carbon is found as graphite and diamond in nature, it also occurs
as carbon dioxide (0.03% V/V) in the atmosphere.
• An atom of carbon can form covalent bonds with H, O, N, P and
other carbon atoms. It can form four such bonds at any one time
and because of this versatility, the carbon atom is the principal
building block of many kinds of molecules which make up living
organisms.
• Hence the carbon cycle is essential for the existence and survival
of life.
• Carbon is a basic constituent of all organic compounds and is
involved in the fixation of energy by photosynthesis.
• The source of all carbon in both living organisms and fossil
deposits is CO2 in the atmosphere and the waters of Earth.
• Carbon may be present as gaseous atmospheric CO2, dissolve in
surface water and ground water as HCO3-, present in minerals
(CaCO3, MgCO3), petroleum and natural gas.
• The atmosphere is the source of CO2, which is utilized by plants in
photosynthesis reduced to form carbon compounds/living
component. Just as energy flows through the grazing food chain,
carbon passes to herbivores and then to carnivores. Some of these
carbon compounds are oxidized during respiration and in the
process energy and CO2 are released. CO2 also released when
some carbon compounds are decomposed by microorganisms.
• Photosynthesis:
H2O + CO2 + Solar Energy
• Respiration:
• (CH2O)n + O2
• 2(CH2O)n
Chlorophyll
of plants
(CH2O)n + O2
CO2 + H2O (aerobic respiration)
CO2 + CH4
(anaerobic respiration)
•Organic or biological carbon {CH2O} is contained in energy-rich
molecules that can react biochemically with molecule O2, to
regenerate CO2 and produce energy through aerobic respiration.
•Organic carbon fixed by microorganisms is transformed by
biogeochemical processes to fossil petroleum, coal and etc.
Microorganisms degrade organic carbon from biomass, petroleum,
and xenobiotic sources, ultimately returning it to the atmosphere as
CO2.
•The fossils (coal and petroleum) are the important energy source for
modern man and produce CO2 when burnt. Thus, the C cycle is
maintained by the processes of photosynthesis, respiration,
decomposition and fossil fuel burning.
•Manufacturing processes are used to convert hydrocarbons to
xenobiotic compounds with functional groups containing halogens,
oxygen, nitrogen, phosphorus or sulfur. These compounds are
particularly significant because of their toxicological chemical
effects.
•Oceans regulate the CO2 content in the atmosphere and thus play a
very important role. Sea water contains 50 times more CO2 than air,
in the form of carbonates and bicarbonates.
•Photosynthesis algae are the predominant carbon-fixing agents in
water; as they consume CO2 to produce biomass, the pH of the water
is raised, enabling precipitation of CaCO3 and CaCO3.MgCO3.
• In
aquatic ecosystem, CO2 dissolve in water before being used by
aquatic primary producers. The CO2 dissolves in sea water to form
carbonic acid.
H2O + CO2
H2CO3
•Carbonic acid further dissociates in to a hydrogen ion and a
bicarbonate ion:
H2CO3
H+ + HCO3-
•Bicarbonate may further dissociate into another hydrogen ion and a
carbonate ion:
HCO3H+ + CO32•The carbon dioxide-carbonic acid-bicarbonate system is a complex
chemical system that tends to stay in equilibrium. Therefore, if CO2
is removed from water, the equilibrium is disturbed and the
equation will shift to the left, with carbonic acid and bicarbonate
producing more CO2 until a new equilibrium is produced.
Theoretical percentage of CO2 in each of its three forms in water in relation to pH
• Phytoplankton uses the CO2 that diffuses into the upper layers of
water or is present as carbonates and converts it into plant tissues.
The carbon then passes through the aquatic food chain. CO2
produced through respiration process is either reutilized or
reintroduced to the atmosphere.
• Sea water is alkaline and rich in Ca and accelerates carbonate
deposition in the bodies of mollusks and foraminifers and
incorporated into their exoskeletons. Some of the carbonates
dissolved back into solution, while some become buried in the
bottom mud at very depths when the organisms die. In warm
climates, greater salinity and alkalinity coupled with high
temperatures favor the formation of coral reefs and thicker shells
of mollusks.
CO2 in the atmosphere
Biodegradation
Photosynthesis
Solubilization and chemical processes
Fixed organic carbon,
{CH2O} and xenobiotic carbon
Xenobiotics manufacture
with petroleum feedstock
Soluble inorganic carbon,
Predominantly HCO3-
Biogeochemical
processes
Fixed organic
Hydrocarbon, CxH2x
And kerosen
Dissolution with
dissolved CO2
Chemical precipitation
And incorporation of
Mineral carbon into
Microbial shells
Insoluble inorganic carbon,
Predominantly CaCo3 and
CaCO3.MgCO3
The Carbon Cycle. Mineral carbon is held in a reservoir of limestone, CaCO3,
from which leached into a mineral solution as dissolved hydrogen carbonate ion,
HCO3-, In the atmosphere carbon is present as CO2. Atmospheric CO2 is fixed
as organic matter by photosynthesis, and organic carbon is released as CO2 by
microbial decay of organic matter.
The carbon cycle as it occurs in both terrestrial and aquatic
ecosystems
Carbon Cycle
• The carbon cycle is the biogeochemical cycle by which carbon is
exchanged between the biosphere, geosphere, hydrosphere, and
atmosphere of the Earth (other astronomical objects may have
similar carbon cycles, but nothing is yet known about them).
• The cycle is usually thought of as four major reservoirs of carbon
interconnected by pathways of exchange. The reservoirs are the
atmosphere, the terrestrial biosphere (which usually includes
freshwater systems and non-living organic material, such as soil
carbon), the oceans (which includes dissolved inorganic carbon and
living and non-living marine biota), and the sediments (which
includes fossil fuels). The annual movements of carbon, the carbon
exchanges between reservoirs, occur because of various chemical,
physical, geological, and biological processes. The ocean contains
the largest active pool of carbon near the surface of the Earth, but
the deep ocean part of this pool does not rapidly exchange with the
atmosphere.
Global Carbon Budget
• The global carbon budget is the balance
of the exchanges (incomes and losses) of
carbon between the carbon reservoirs or
between one specific loop (e.g.,
atmosphere - biosphere) of the carbon
cycle. An examination of the carbon
budget of a pool or reservoir can provide
information about whether the pool or
reservoir is functioning as a source or sink
for carbon dioxide.
Carbon cycle modeling
• Models of the carbon cycle can be incorporated into
global climate models, so that the interactive response of
the oceans and biosphere on future CO2 levels can be
modelled. There are considerable uncertainties in this,
both in the physical and biogeochemical submodels
(especially the latter). Such models typically show that
there is a positive feedback between temperature and
CO2. For example, Zeng et al. (GRL, 2004 [2]) find that
in their model, including a coupled carbon cycle
increases atmospheric CO2 by about 90 ppmv at 2100
(over that predicted in models with non-interactive
carbon cycles), leading to an extra 0.6°C of warming
(which, in turn, may lead to even greater atmospheric
CO2).
Carbon footprint
• Carbon footprint is a measure of the amount of
carbon dioxide or CO2 emitted through the
combustion of fossil fuels; in the case of an
organization, business or enterprise, as part of
their everyday operations; in the case of an
individual or household, as part of their daily
lives; or a product or commodity in reaching
market. In materials, is essentially a measure of
embodied energy, the result of life cycle
analysis.
A carbon footprint is often expressed as tons of carbon dioxide or tons of
carbon emitted, usually on a yearly basis. There are many versions of
calculators available for carbon footprinting
.
• This is directly related to the amount of natural resources consumed,
increasingly used or referred to as a measure of environmental
impact. Carbon dioxide is recognized as a greenhouse gas, of which
increasing levels in the atmosphere are linked to global warming
and climate change.
• The Clean Development Mechanism (CDM) under the Kyoto
Protocol sets forth a methodology by which voluntary emission
reduction can be monetized in the form of a carbon project. These
standards involve the use of an environmental proof called
additionality.
• A carbon label - which shows the carbon footprint embodied in a
product in bringing it to the shelf was introduced in the UK in March
2007 by the Carbon Trust. Examples of products featuring their
carbon footprint are Walkers Crisps, Innocent Smoothies and Boots
shampoos.
• CarbonCounted, which launched in early 2007, is a Canadian based
GHG carbon label system that allows companies to link with and
leverage their supply chain. By displaying the CarbonCounted
footprint on a product, a supplier is publishing their footprint and
committing to emissions reduction.
Kyoto Protocol
• The Kyoto Protocol to the United Nations Framework Convention
on Climate Change is an amendment to the international treaty on
climate change, assigning mandatory emission limitations for the
reduction of greenhouse gas emissions to the signatory nations.
• The objective of the protocol is the "stabilization of greenhouse gas
concentrations in the atmosphere at a level that would prevent
dangerous anthropogenic interference with the climate system."[1]
• As of December 2006, a total of 169 countries and other governmental
entities have ratified the agreement (representing over 61.6% of
emissions from Annex I countries).[2][3] Notable exceptions include the
United States and Australia. Other countries, like India and China, which
have ratified the protocol, are not required to reduce carbon emissions
under the present agreement.
• There is some debate about the usefulness of the protocol, and there
have been some cost-benefit studies performed.
Capture of CO2 from Industrial
Sources:
Absorption/Stripping Technology
• The main industrial sources of CO2: NG reformer gases, refinery gases,
power plant/incinerator flue gases
• The majority of CO2 emissions come from thermal power plants fired
with fossil fuels.
• In 2003, 32.4% of total CO2 produced in the US came from coal-fired
power plants.
• The predicted increase in CO2 emissions is ∼ 1.8% per year and by 2030
it will be 70% above 2000 levels – IEA World Energy Outlook (2002).
• There is an urgent need for research into the development of cost effective
and viable technologies for CO2 capture and sequestration.
• This presentation focuses on current technology options, technology
development and future opportunities.