Environmental Chemistry PDF

ENVIRONMENTAL CHEMISTRY Hardness of water The property of water which prevents lather formation with soap solution is called hardness of water. It is due to the presence of dissolved salts of Ca, Mg and some other heavy metals. On the basis of hardness, water is of two types; 1. Soft water 2. Hard...

ENVIRONMENTAL CHEMISTRY Hardness of water The property of water which prevents lather formation with soap solution is called hardness of water. It is due to the presence of dissolved salts of Ca, Mg and some other heavy metals. On the basis of hardness, water is of two types; 1. Soft water 2. Hard water Soft water Water which can form ready and permanent lather with soap solution is called soft water. Hard water Water which cannot form ready and permanent lather with soap solution is called hard water. Soap is sodium or potassium salts of higher fatty acid which when treated with hard water produces insoluble Ca-Soap and Mg-Soap (white scum ). Hardness is of two types. 1. Temporary (Carbonate) hardness 2. Permanent (Non-carbonate) hardness Temporary (Carbonate) hardness Hardness which will remain for a shorter period and can be easily removed by boiling is called temporary (Carbonate) hardness. It is due to the presence of bicarbonates of Ca & Mg. On boiling, soluble bicarbonate changes to insoluble carbonates and hydroxides. Removal of temporary hardness 1. Boiling On boiling, soluble bicarbonate changes to insoluble carbonates and hydroxides. Ca(HCO3)2 → CaCO3 + H2O + CO2  Mg(HCO3)2 → Mg(OH)2 + 2CO2 2. Clark‘s process In this method, calculated quantity of lime is added to convert it as insoluble carbonate. Ca(HCO3)2 + Ca(OH)2 → 2CaCO3 + 2H2O Mg(HCO3)2 + Ca(OH)2 → MgCO3 +CaCO3 + H2O Permanent (Non-carbonate) hardness Hardness due to the presence of chlorides and sulphates of Ca, Mg, Fe, etc. are called permanent hardness. Removal of Permanent (Non-carbonate) hardness 1. Lime soda process 2. Zeolite process 3. Ion exchange process Disadvantages of Hard water 1. Scale and Sludge formation in boilers Boilers are used for the production of high temperature steam and are integral parts of most of the industries, thermal and nuclear power stations. During to the continuous evaporation of water in boilers, the concentrations of dissolved salts, if present, increase progressively. Finally , the concentrations attain saturation and at this point, the salts are driven out of water as precipitates, which stick on the inner walls of the boiler. If these precipitates are in the form of loose and slimy deposits, they are called sludge and if the precipitates are hard and adhering coating on the inner walls of the boiler, they are called scales. Scale and Sludge formation leads to decrease of heat transfer efficiency which results in wastage of fuel. It also affects the boiler safety and may lead to explosion of boiler. 2. Priming and Foaming in boilers When a boiler produces steam rapidly, some particles of liquid water will also be carried along with the steam. This wet steam formation is called priming. Foaming is the process of formation of small, but persistent foam or bubbles at the surface of water in boilers, which do not break easily. Foaming is caused by the presence of oils, alkalis etc.in boiler feed water. Priming and foaming leads to deposition of dissolved salts on the turbine blades and super heater which reduces their efficiency. 3. It causes boiler corrosion 4. Hard water is not good for dyeing cloth. 5. It tastes bitter, but it provides useful calcium ions for the healthy growth of bones and teeth. Hardness level between 60 to 100 ppm is recommended for drinking water. 6. It produces stains in bathroom fittings. 7. It causes the wastage of soap in laundry. Degree of hardness Hardness is expressed in terms of degree of hardness. Degree of hardness is expressed in terms of CaCO3 equivalent hardness. The concentration of hardness producing ions and non-hardness producing ions are expressed in terms of equivalent amount of CaCO3 and is called CaCO3 equivalent hardness. The choice of CaCO3 in particular due to, 1. Molecular weight is 100. 2. Equivalent weight is 50. 3. It is the most insoluble precipitate in most of the water treatment processes. Where HPS is hardness producing substance. The same formula can be modified by replacing the equivalent weight by molecular weight. Let X be the mass of HPS, then Units of hardness The important units of hardness are 1. Parts per million (ppm) 2. Milligram per litre (mg/L) 3. Degree French (°F) 4. Degree Clark (°Cl) 5. Equivalents per million (epm) Parts per million (ppm) It is the number of parts of CaCO3 equivalent hardness present per million parts of water. 𝟏 𝟏𝐩𝐩𝐦 = or 𝟏𝟎𝟔 𝐩𝐩𝐦 = 1 𝟏𝟎𝟔 Milligram per litre(mg/L) It is the number of milligrams of CaCO3 equivalent hardness present per litre of water. 𝟏 𝟏𝐦𝐠/𝐋 = = 𝟏 𝒑𝒑𝒎 or 𝟏𝟎𝟔 𝐦𝐠/𝐋 = 1 𝟏𝟎𝟔 Degree French (oF) It is the number of parts of CaCO3 equivalent hardness present per 105 parts of water. 𝟏 𝟏°𝐅 = or 𝟏𝟎𝟓 °𝐅 = 1 𝟏𝟎𝟓 Degree Clark (oCl) It is the number of parts of CaCO3 equivalent hardness present per 70000 parts of water. 𝟏 𝟏°𝐂𝐥 = or 𝟕𝟎𝟎𝟎𝟎 °𝐂𝐥 = 1 𝟕𝟎𝟎𝟎𝟎 Equivalents per million (epm) It is the number of equivalents of CaCO3 equivalent hardness present per million parts of water.  𝟓𝟎 𝟏𝐞𝐩𝐦 = or𝟔 𝐞𝐩𝐦 = 1 𝟏𝟎 𝟏𝟎𝟔 𝟓𝟎 Inter conversion of various units of hardness: Water softening methods The process by which hard water can be converted as soft water is called water softening process. One of the very important types of water softening process is called ion exchange process. Ion exchange process Ion exchange process is a chemical process where an ion from a solution is exchanged for a similarly charged ion attached to an immobile solid particle (naturally occurring inorganic zeolites or synthetically produced organic resins). In the case of water softening by ion exchange method, it can be said that the process in which the dissolved ions present in water are completely removed by the help of some complex organic compounds (ion exchange resins) is known as ion exchange method. Principle In this method ion exchange resins are used for the removal ions from the water. Ion exchange resins are long chain, cross linked, insoluble organic polymers with a microporous structure. The functional groups attached to the chains are responsible for the ion exchanging properties. These resins act as ion exchangers and remove all minerals from the hard water. Since they remove all the cations and anions from hard water and make it completely free from ions, it is also called deionization/demineralization.  Ion exchange resins are of two types; Cation exchange resins and anion exchange resins. 1) Cation Exchange Resins: The cation exchange resins are mainly carboxylated or sulphonated styrene-divinylbenzene co-polymers. These resins possess acidic groups such as –COOH or –SO3H groups and may be represented as R-H+. The structure of cation exchange resin containing –SO3H groups can be represented as shown in figure. These types of resins exchange only the cations present in hard water with H+ ions. 2) Anion Exchange Resins: The anion exchange resins are mainly styrene- divinyl benzene or amine formaldehyde copolymers containing amino or quaternary ammonium groups. They possess basic groups such as OH - or NH2 group and may be represented as R-OH. The structure of an anion exchange resin may be represented as shown in figure. They after treatment with dilute NaOH solutions become capable of exchanging their OH- ions with anions present in hard water. OR  Procedure The arrangement of the apparatus is in such a manner than it consists of two chambers. One containing cation exchange resin and the other anion exchange resin. Hard water is first allowed to pass through the column containing cation exchange resin. The cations present in hard water (Ca2+, Mg2+, etc.) get exchanged with H+ ions of the resin as shown by the following reactions; The water coming out of the first chamber thus contains free H + ions and is acidic in nature. It is now passed through the column containing anion exchange resin. Anion exchange resin exchanges the anions (Cl-, SO 42-, etc.) with OH– ions of the resin as follows; The H+ ions and OH− ions liberated from cation and anion exchange resin columns respectively, combine to form water. Thus, the water coming out of the exchanger will be free from all cations and anions that were present in hard water. Hence, it is generally known as deionised or demineralised water. Regeneration of Resins As the continuous use of the process of demineralization makes the resins exhausted (exchange sites are block), therefore for further use, resins must be regenerated. The exhausted cation exchange resin can be regenerated by passing a dilute HCl or sulphuric acid solution through the column. It again makes the site of ion exchange active. This column is washed with de ionized water to remove the Cl- and SO42- etc. The exhausted anion exchange resin can be regenerated by passing a dilute NaOH solution through it. The regenerated resins are ready for reuse. The chamber is also washed with de-ionized water to remove Na+ ions. Thus, regenerated ion exchanger can be used again. Advantages  By this process it is possible to soften highly acidic or alkaline water.  The water obtained by this process will have very low hardness (nearly 2 ppm)  The resins can be regenerated and reused.  There is no scale or sludge is formation.  There will not be priming and forming. Disadvantages  The resins used in the process are quite costly, Hence, the process becomes expensive.  The resins need to be regenerated again and again, thus making the process inconvenient and complex.  If the water contains turbidity, it will decrease the efficiency of the process. Desalination Water containing high concentration of dissolved salt with a brackish taste is called brackish water. For example, sea water. The process of removal of dissolved salts such as NaCl, KCl, MgCl 2, etc. from water is known as desalination. The common method used for desalination of brackish water is reverse osmosis. Reverse osmosis Principle The spontaneous process, which involves the flow of the solvent from a dilute solution to a more concentrated solution through a semi-permeable membrane is called osmosis. In this process, only solvent can flow and not the solute, which develops pressure, known as osmotic pressure. But, when applying a greater pressure than the osmotic pressure on side of more concentrated solution reverses this process, which is called reverse osmosis. The flow of solvent under pressure from more concentrated solution to solvent or less concentrated solution through semi-permeable membrane is called the reverse osmosis. Procedure The desalination of saline water is carried-out in a reverse osmosis cell, which is shown diagrammatically in figure. Saline water is added to the cell through the water inlets. The chamber is separated from other chamber having some fresh water by a semi-permeable membrane made of very thin films of cellulose acetate. More recently, superior membrane made of poly methacrylate and polyamide polymers have been introduced. A pressure of 15- 40 kg/cm2 is applied to the sea water gently. The solvent or water starts flowing from saline water to side of fresh water through semi-permeable membrane. Hence, the reverse osmosis takes place. Fresh water obtained is taken out through an outlet. Advantages  This process is economical and convenient.  It can be used at room temperature.  The process can remove ionic as well as non-ionic dissolved salts easily.  It is also effective in removing colloidal impurities present in the water.  It is suitable for converting sea water into drinking water. Disadvantages  High usage of electricity Removal of microorganisms (Disinfection methods) The process of removing disease causing (pathogenic) microorganisms from water are called disinfection. The chemicals used for this purpose is called disinfectants. Common methods of disinfection include use of ozone, chlorine, or UV light. Types of disinfection methods a) Chlorination Chlorine is added to water either in the gaseous form or concentrated solution. When chlorine is added to water, it dissolves to form hydrochloric acid (HCl) and hypochlorous acid (HOCl). It reduces the alkalinity of water. HOCl being highly unstable readily decomposes into HCl and nascent oxygen [O]. The nascent oxygen oxidizes the microorganisms present in water by destroying their enzymes.  Factors affecting efficiency of chlorine  Time of contact: - The rate of killing of microorganism is maximum at the beginnings.  Temperature: - As temperature increase death rate also increase.  pH of water:- At lower pH, only a small contact period is required to kill a major percentage of organisms. Advantages  It is economical and effective  Storage is easy  Can be used at low and high temperature  Salty impurities are not introduced to water. Disadvantages  Chlorine, when added in excess, produces an unpleasant taste and odour.  Less effective at higher pH values (more effective below pH = 6.5). Break point chlorination Break point of chlorination is defined as the addition of sufficient amount of chlorine to kill all the microorganisms and to destroy them completely by the oxidation of reducing matter, organic matter, and free ammonia and leave behind free residual chlorine to continue the further disinfection. If we plot residual chlorine against applied chlorine, we get a curve. The dip in the curve shows the break point. Stage I: - Oxidation of reducing compounds Stage II: - Formation of chloro-organic compounds and chloramines Stage III: - Destruction of chloro-organic and chloramines Stage IV: - Free residual chlorine Break point of chlorination indicates that the point at which residual chlorine begin to appear. Advantages b) It completely oxidizes the organic compounds, ammonia and other reducing compounds. c) It removes colour, odour and taste from water. d) It destroys all the disease- producing bacteria and other microorganisms. e) It prevents the growth of any weeds in water. Dechlorination The amount of free chlorine required for continuing further disinfection is 0.1- 0.2 ppm. If over chlorination occurs, it‘ll produce unpleasant taste and odour in water. This excess chlorine can be removed by passing the water through molecular sieve or by stirring it with activated carbon followed by filtration. Excess chlorine can also be removed by adding dechlorinating agents like SO2, Na2SO3, sodium thiosulphate, etc. The process of removal of excess chlorine from water is called dechlorination. b) Using Ozone Ozone is a powerful disinfectant agent which is used in gaseous form and readily absorbed by water. Ozone is produced by passing silent electric discharge through cold and dry oxygen. Ozone thus produced is highly unstable and breakdown liberating nascent oxygen. O3 → O2 + [O] It is a powerful oxidizing agent and kills the bacteria and oxidize the organic matter present in water. Advantages  Simultaneous removal of colour, odour, taste without leaving any residual in water.   Complete sterilization.  Its excess does not cause any harm to water as nascent oxygen is unstable and can be easily converted as molecular oxygen. Disadvantages  Expensive.  Applicable only for small quantity of water.  Microbial growth may again start in the treated water as it contains no residuals. c) Using UV radiation When electric current is passed through a mercury vapour lamp enclosed in quartz container, it produces ultraviolet radiations (200- 400 nm). These radiations are absorbed by the microorganisms present in water which initiates photochemical reactions at their DNA bases. Thus, the microorganisms are destroyed by UV radiation. The effectiveness of this method depends on the intensity of radiation and extend of irradiation. Advantages  There will not be any unpleasant taste or smell in water as no chemicals are used.  Quick process  All the pathogenic organisms are killed.  Complete sterilization.  It is mainly employed in swimming pools as disinfection using chemicals may cause harmful effects to the skin of the people swimming. Disadvantages  Equipment is costly.  Technical skill is required for this method.  Applicable only for small quantity of water Dissolved oxygen It is the amount of free, dissolved oxygen present in a sample of water. Oxygen enters in to water through air or aeration of water by wind. It can also be due to photosynthesis of aquatic plants. DO levels fluctuate seasonally and over a 24 hour period. They vary with water temperature and altitude. Pure water at 30oC can hold only 7.8 ppm dissolved oxygen at saturated condition. At 20oC, it can hold up to 9.2 ppm. This is according to Henry‘s law which states that dissolution of a gas in a liquid is directly proportional to pressure and inversely proportional to absolute temperature. That is solubility of oxygen decreases with rise in temperature and increases with pressure. Cold water holds more dissolved oxygen than warm water. Water holds less dissolved oxygen at higher altitude due to lowering of atmospheric pressure. DO can be measured using titration or by dissolved oxygen meter. Biological Oxygen Demand (BOD) BOD can be defined as the amount of oxygen required by aerobic bacteria for oxidation of all biologically oxidisable matter present in 1L of sewage water for a period of five days at 20 oC. BOD is proportional to the amount of organic waste in water. As BOD increases, DO decreases. So, BOD is an indication of the extent of pollution. Significance of BOD 1. Larger the concentration of organic matter, greater will be the BOD. 2. BOD helps for finding the degree of pollution. 3. To check the quality of water. 4. Larger the BOD, greater will be the pollution. Thus, it also helps for pollution study. 5. The demand for oxygen is proportional to the amount of organic waste to be degraded aerobically. 6. When BOD is high, CO become low.  Disadvantages  The results are obtained only after 5 days.  BOD gives only the case of biodegradable organic matter.  The process depends only on the activity of microbes, which can‘treliable completely. Chemical Oxygen Demand (COD) COD is defined as the amount of oxygen present in ppm, needed for the chemical oxidation of all oxidisable impurities present in the sewage water using an oxidising agent like K2Cr2O7. Dichromate is strong oxidizing agent than oxygen. Hence oxidations of all biologically oxidisable and biologically inert matters in the sample take place. So, COD value will be higher than BOD value. COD test needs only three hours, while BOD needs five days. Significance of COD 1. COD values are greater than BOD values. 2. Pollution measuring factor. 3. Time period – 3 hrs 4. COD values not effected by toxins 5. Proposing standards for discharging domestic or Industrial effluents. Advantages  Analysis in lesser time  Oxidation of both biodegradable and non-biodegradable matter occurs. Disadvantages  The quantity of biodegradable and non-biodegradable matter can‘t be distinguished. Sewage water treatment Sewage water has to be properly treated before sending it into running streams. Presence of biologically oxidisable matter (carbohydrates, proteins, etc.) in water increases the BOD of the water. The sewage treatment is carried out to reduce BOD of water. If high BOD water is sent to running streams, due to lack of dissolved oxygen aquatic life get extinct. Sewage treatment is carried out using an artificial process. The various steps involved are, 1. Primary treatment 2. Secondary treatment 3. Tertiary treatment 1. Primary treatment Primary treatment of sewage water is done by mainly two processes. They are: a) Screening In this process, large solids and inorganic matter which are suspended in the sewage are removed. Sewage is passed in upward direction through bar and mesh screens to remove suspended and coarse solids. b) Sedimentation Continuous flow type sedimentation tanks are employed for this purpose. Most of the suspended solids are removed by this process. Sometimes, chemical coagulant is added to sewage before sedimentation. Coagulant forms gelatinous precipitate, which can entrap small sized organic matter making them settle down easily. Aluminium sulphate, alum, etc. are the commonly used coagulants. Al2(SO4)3 + 6 H2O → 2 Al(OH)3(Gelatinous precipitate) + 3 H2SO4 2. Secondary treatment (Biological process) Secondary treatment involves the biological decomposition of organic matters percent in sewage water. It can be done by two methods; Trickling filter method and UASB process. a) Trickling filter method (Aerobic oxidation method) It is a type of biological treatment carried out using a special type of filter called trickling filter. Trickling filter is rectangular in shape with 2m depth. It is filled with crushed rocks, broken bricks, etc. on that microbial growth  occurs and fitted with rotating distributor. The microorganisms react with the inert packing material, and a gelatinous film is formed (contains microorganisms) on the surface of filtering medium. Sewage trickles through the filter with the help of rotating distributor. Then it moves down through the filtering medium. During this movement, microorganisms start consuming organic matter in the sewage. A more or less clear effluent is collected through the under-drainage system. During aerobic oxidation, the carbon is converted into carbon dioxide while nitrogen is converted into nitrates and nitrites. Advantages  Highly effective  BOD is reduced by 60-80%  Low maintenance cost Disadvantages  The equipments are costly and thus capital investment is high  Efficiency decreases when load increases. b) Upflow Anaerobic Sludge Blanket (UASB) process This is an anaerobic methane producing process. A blanket of granular sludge is suspended in the UASB reactor. It is a rectangular tank made of concrete. In this process, the effluent is fed from the bottom of the reactor so that it moves upward through a sludge blanket. Sludge blanket is composed of biological granules containing large number of bacteria. The suspended sludge filters and treats the waste water. The anaerobic microorganism living in the sludge breakdown the organic matter producing gases like methane. The rising gas bubbles mix the sludge and waste water. The gases with biological granules move towards the upper region of the reactor, where the gases only set free and the granules come back to the sludge blanket. Gases are collected at the gas collector dome at the top of the reactor. The upflow velocities are 0.6-0.9 m/hour. Advantages  High BOD reduction  Low sludge production  No need of aeration system  Little CO2 emission. Disadvantages  Needs skilled operations  Long startup time  Constant power supply  Difficult to set up 3. Tertiary treatment This is the advanced phase of sewage treatment. By this process, nitrogen and phosphorous content in the effluent get reduced. Three important processes employed for this purpose are: a) Precipitation In this process, effluent from the secondary process is treated with CaO so that calcium phosphate (Ca3(PO4)2) will be precipitated.  b) Nitrogen stripping In this process, ammonia gas is removed by passing the effluent through a series of baffle plates. c) Chlorination Disinfection of effluent is done by treating it with chlorine. Chlorine is added to water either in the gaseous form or concentrated solution. When chlorine is added to water, it dissolves to form hydrochloric acid (HCl) and hypochlorous acid (HOCl). HOCl being highly unstable readily decomposes into HCl and nascent oxygen [O]. The nascent oxygen oxidizes the microorganisms present in water by destroying their enzymes. Flow diagram of sewage (waste water) treatment E-Waste Electronic waste (or e-waste) describes discarded electrical or electronic devices. It is also commonly known as waste electrical and electronic equipment (WEEE) or end-of-life (EOL) electronics. Used electronics which are destined for refurbishment, reuse, resale, salvage recycling through material recovery, or disposal are also considered e-waste. Informal processing of e-waste in developing countries can lead to adverse human health effects and environmental pollution. The growing consumption of electronic goods due to the Digital Revolution and innovations in science and technology, such as bitcoin, has led to a global e-waste problem and hazard. The rapid exponential increase of e-waste is due to frequent new model releases and unnecessary purchases of electrical and electronic equipment (EEE), short innovation cycles and low recycling rates, and a drop in the average life span of computers. Electronic scrap components, such as CPUs, contain potentially harmful materials such as lead, cadmium, beryllium, or brominated flame retardants. Recycling and disposal of e-waste may involve significant risk to the health of workers and their communities. Methods of disposal There are a few different ways to dispose of e-waste that have historically been employed; each come with their own set of environmental issues. Landfilling This refers to the practice of essentially digging a massive hole in the ground, filling it with waste and then covering it back up with soil. While the pits are lined with clay or plastic with a leachate basin to prevent toxic waste from leeching into the surrounding environment, some substances such as cadmium, lead, and mercury inevitably finds their way into the soil and groundwater, causing contamination. Acid Bath Soaking electronic circuits in powerful sulphuric, hydrochloric, or nitric acid solutions separates metals from the electronic pathways. The metals can then be recycled and used in the manufacture of new products. However, the highly hazardous acid waste needs to be very carefully disposed of to prevent it from finding its way into local water sources – essentially trading one waste disposal problem for another. Incineration A very crude e-waste disposal method that involves burning the waste in an extremely high temperature incinerator. This has the twin benefit of significantly reducing the waste volume and generating energy that can be repurposed for other applications. Unfortunately, the process of burning the components which make up electronic waste also produces vast quantities of toxic gasses – including cadmium and mercury – which are released into the atmosphere. Recycling Many items of e-waste can be dismantled and their component parts repurposed into new products. E-waste recycling techniques can recover precious metals from circuit boards and be melted down to make new devices or used for other products such as jewellery. Reuse By far, the most environmentally friendly e-waste disposal technique is for, where possible, devices to be reused. Many charities will gladly accept old electronic devices that can then be refurbished and redistributed to people in more disadvantaged communities. Recovery Resource recovery is the activity of separating materials from waste that can be recycled into new products or used as an energy alternative to fossil fuels and is actioned with the goal of diverting as much waste from landfill as possible. It‘s a part of an important goal being adopted worldwide which is to secure a waste-free and more sustainable future. When complete avoidance and reduction of waste are not possible, resource recovery is most important. This not only involves the effective recovery of materials for recycling (processing waste materials to make the same or different products) but also, their re-use (without further processing). During the recovery process, the waste is processed by machine and hand sorting to extract all recoverable materials for re-use and recycling. Materials are separated and processed for re-use – soil is screened, masonry is crushed, timbers and vegetation are mulched, while metals, glass, plastics, and cardboard are sent for recycling. Whether it‘s gravel for a rural road, mulch for landscaping in a city park, or a new glass bottle for soft drink, the bulk of the waste stream is re-purposed while the remaining residue of non- recyclable material is taken to certified landfill sites. Chemistry of climate change Climate change refers to long-term shifts in temperatures and weather patterns. Such shifts can be natural, due to changes in the sun‘s activity or large volcanic eruptions. But since the 1800s, human activities have been the main driver of climate change, primarily due to the burning of fossil fuels like coal, oil and gas.Burning fossil fuels generates greenhouse gas emissions that act like a blanket wrapped around the Earth, trapping the sun‘s heat and raising temperatures. The main greenhouse gases that are causing climate change include carbon dioxide and methane. These come from using gasoline for driving a car or coal for heating a building, for example. Clearing land and cutting down forests can also release carbon dioxide. Agriculture, oil and gas operations are major sources of methane emissions. Energy, industry, transport, buildings, agriculture and land use are among the main sectors causing greenhouse gases. Many people think climate change mainly means warmer temperatures. But temperature rise is only the beginning of the story. Because the Earth is a system, where everything is connected, changes in one area can influence changes in all others. The consequences of climate change now include, among others, intense droughts, water scarcity, severe fires, rising sea levels, flooding, melting polar ice, catastrophic storms and declining biodiversity. Greenhouse Gases Greenhouse gases, such as carbon dioxide, methane, nitrous oxide, and certain synthetic chemicals, trap some of the Earth's outgoing energy, thus retaining heat in the atmosphere. This heat trapping causes changes in the radiative balance of the Earth—the balance between energy received from the sun and emitted from Earth—that alter climate and weather patterns at global and regional scales. Multiple lines of evidence confirm that human activities are the primary cause of the global warming since the start of the 20 th century.Natural factors, such as variations in the sun's output, volcanic activity, the Earth's orbit, the carbon cycle, and others, also affect Earth's radiative balance. However, beginning in the late 1700s, the net global effect of human activities has been a continual increase in greenhouse gas concentrations. This change in concentrations causes warming and is affecting various aspects of climate, including surface air and ocean temperatures, precipitation, and sea levels. Human health, agriculture, water resources, forests, wildlife, and coastal areas are all vulnerable to climate change. Many greenhouse gases are extremely long-lived in the atmosphere, with some remaining airborne for tens to hundreds of years after being released. These long-lived greenhouse gases become globally mixed in the atmosphere and their concentrations reflect past and recent contributions from emissions sources worldwide. Others, like tropospheric ozone, have a r Some greenhouse gases are emitted exclusively from human activities (e.g., synthetic halocarbons). Others occur naturally but are found at elevated levels due to human inputs (e.g., carbon dioxide). Anthropogenic sources result from energy-related activities (e.g., combustion of fossil fuels in the electric utility and transportation sectors), agriculture, land-use change, waste management and treatment activities, and various industrial  processes. Major greenhouse gases include carbon dioxide, methane, nitrous oxide, and various synthetic chemicals.  Carbon dioxide is widely reported as the most important anthropogenic greenhouse gas because it currently accounts for the greatest portion of the warming associated with human activities. Carbon dioxide occurs naturally as part of the global carbon cycle, but human activities have increased atmospheric loadings through combustion of fossil fuels and other emissions sources. Natural sinks that remove carbon dioxide from the atmosphere (e.g., oceans, plants) help regulate carbon dioxide concentrations, but human activities can disturb these processes (e.g., deforestation) or enhance them.  Methane comes from many sources, including human activities such as coal mining, natural gas production and distribution, waste decomposition in landfills, and digestive processes in livestock and agriculture. Natural sources of methane include wetlands and termite mounds.  Nitrous oxide is emitted during agricultural and industrial activities, as well as during combustion of solid waste and fossil fuels.  Various synthetic chemicals, such as hydrofluorocarbons, perfluorocarbons, sulfur hexafluoride, and other synthetic gases, are released as a result of commercial, industrial, or household uses.  Many other gases are known to trap heat in the atmosphere. Examples include water vapor, which occurs naturally as part of the global water cycle, and ozone, which occurs naturally in the stratosphere and is found in the troposphere largely due to human activities. Each greenhouse gas has a different ability to absorb heat in the atmosphere, due to differences in the amount and type of energy that it absorbs, and a different ―lifetime,‖ or time that it remains in the atmosphere. Ozone layer Depletion Ozone Layer Depletion refers to the thinning the Ozone layer in the Earth‘s Stratosphere.The ozone layer is the layer present in the Stratosphere. It absorbs the harmful ultraviolet rays that come from the sun. Moreover, it causes harmful radiation that has a high concentration of ozone (O3) which is harmful to living beings on the earth. The ozone layer is basically present in the lower stratosphere that is near about 20 to 35 kilometers above the earth. Moreover, the thickness of the ozone layer may differ depending upon the seasonal and geographical changes. The ozone layer is important for the earth because it protects the earth from the harmful ultraviolet radiation. This radiation comes from the sun and is harmful to the earth‘s surface. According to the studies done by the scientists the cause of the ozone layer depletion is human activity. All the activities are done by human beings. Through which the chemicals are made that contain chlorine or bromine. These are basically called ODS that stands for Ozone-Depleting Substance. The ozone layer depletion was observed by the researchers in the early 1970s. Furthermore, the ozone-depleting substances are said to be Eco- friendly and they are very popular for the last some decades and are still in use. These ozone depletion substances float and then reach the stratosphere. Therefore, the formation of chlorine and bromine takes place and these chemicals cause the depletion of the ozone layer at a very high speed. They are capable of breaking down the molecules of the ozone layer. One chlorine molecule has a capacity to breakdown thousands of molecules present in the ozone layer, therefore, it results in the depletion of the ozone layer. The ozone-depleting substances that contain chlorine include chlorofluorocarbon, carbon tetrachloride, hydrochlorofluorocarbons, and methyl chloroform. Whereas, the ozone-depleting substances that contain bromine are halons, methyl bromide, and hydro bromofluorocarbons. Chlorofluorocarbons are the most abundant ozone-depleting substance. It is only when the chlorine atom reacts with some other molecule, it does not react with ozone. Montreal Protocol was proposed in 1987 to stop the use, production and import of ozone-depleting substances and minimise their concentration in the atmosphere to protect the ozone layer of the earth. Sustainable Development The concept of sustainable development has received much recognition after the Stockholm declaration in the year 1972. Sustainable development is the development which meets the needs of the present without compromising the ability of future generations to meet their own needs. The three pillars of sustainable development are environment, society and economy as shown in Fig.3. Sustainable development should have the following features 1. Satisfying human needs 2. Favouring a good quality of life through decent standards of living 3. Sharing resources between rich and poor 4. Acting with concern for future generations 5. Looking at the ‗cradle-to-grave‘ impact when consuming 6. Minimizing resource use, waste and pollution Sustainable Development Goals The Sustainable Development Goals (SDGs) are a set of 17 global objectives established by the United Nations in 2015 to be achieved by 2030. The goals are intended to provide a blueprint for peace and prosperity for people and the planet. The 17 SDGs are integrated—they recognize that action in one area will affect outcomes in others, and that development must balance social, economic and environmental sustainability. Countries have committed to prioritize progress for those who're furthest behind. The SDGs are designed to end poverty, hunger, AIDS, and discrimination against women and girls. GOAL 1: No Poverty End poverty in all its forms everywhere (eradicate extreme poverty currently measured as people living on less than $1.25 a day.) GOAL 2: Zero Hunger End hunger, achieve food security and improved nutrition and promote sustainable agriculture GOAL 3: Good Health and Well-being Ensure healthy lives and promote well-being for all at all ages GOAL 4: Quality Education Ensure inclusive and equitable quality education and promote lifelong learning opportunities for all GOAL 5: Gender Equality Achieve gender equality and empower all women and girls GOAL 6: Clean Water and Sanitation Ensure availability and sustainable management of water and sanitation for all GOAL 7: Affordable and Clean Energy Ensure access to affordable, reliable, sustainable and modern energy for all GOAL 8: Decent Work and Economic Growth Promote sustained, inclusive and sustainable economic growth, full and productive employment and decent work for all GOAL 9: Industry, Innovation and Infrastructure Build resilient infrastructure, promote inclusive and sustainable industrialization and foster innovation GOAL 10: Reduced Inequality Reduce inequality within and among countries GOAL 11: Sustainable Cities and Communities Make cities and human settlements inclusive, safe, resilient and sustainable GOAL 12: Responsible Consumption and Production Ensure sustainable consumption and production patterns GOAL 13: Climate Action Take urgent action to combat climate change and its impacts GOAL 14: Life Below Water Conserve and sustainably use the oceans, seas and marine resources for sustainable development GOAL 15: Life on Land Protect, restore and promote sustainable use of terrestrial ecosystems, sustainably manage forests, combat desertification, and halt and reverse land degradation and halt biodiversity loss GOAL 16: Peace and Justice Strong Institutions Promote peaceful and inclusive societies for sustainable development, provide access to justice for all and build effective, accountable and inclusive institutions at all levels GOAL 17: Partnerships to achieve the Goal Strengthen the means of implementation and revitalize the global partnership for sustainable development.