Unit-4

Environmental Pollution and Water Chemistry

1.List the common pollutants present in the Air, elaborate any two?

Primary air pollutants are those pollutants that are directly emitted into the air from sources like natural gas power plants, coal fired power plants, volcanoes, burning of biomass, burning of natural forest fires and many more.

These pollutants effect the environment both directly and also form a precursor of secondary pollutants, examples of primary pollutants include- Sulphur dioxide, nitrogen oxides of dioxide, nitrogen organic matter, particulate matter etc.

• Sulphur dioxide (SO2)

During processes like fossil fuel combustion, metal smelting or oil refining, Sulphur is exposed to very high temperatures leading to the formation of Sulphur dioxide, Sulphur dioxide is toxic at very high concentrations, the most adverse effect to the environment is the formation of Acid rain, where the Sulphur dioxide dissolves in the cloud droplets and oxidizes to form sulphuric acid, that falls to the earth as acid rain, or they may also form sulphate aerosol particles in the atmosphere.

• Nitrogen oxides (includes NO NOx and NO2)

When oxygen and nitrogen react at very high temperatures, either during combustion or lightning very highly reactive gas NOx is formed. This reactive gas is also emitted during fossil fuel combustion and biomass burning.

Through a complicated chain reaction NOx reacts with volatile compounds and carbon monoxide in the atmosphere to form ground level ozone through a complicated chain mechanism, and oxidises to form Nitric acid, that also contributes to acid deposition and aerosol formation.

2. What do you understand by Ozone Depletion?

The gradual thinning of the earth’s ozone layer in the upper atmosphere due to the presence of chemical compounds containing gaseous bromine or chloride from human activities and industries.

The thinning of the ozone layer, present in the upper atmosphere occurs when a chlorine and bromine atoms present in the atmosphere come in contact with the ozone and destroy the ozone molecules, a chlorine molecule can destroy up to 100,000 molecules of ozone these molecules are more quickly destroyed than created. Few compounds are released when chlorine and bromine are exposed to UV light that cause a depletion in 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 Bromo fluorocarbons.

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.          

3. Explain the Solid waste management?

Solid waste

Solid wate management is the collection, treatment and disposal of the solid material that is discarded as they are no longer useful, improper disposal of the municipal waste can create unsanitary conditions, resulting in pollution of the environment and outbreaks of vector borne disease spread by mice and insects.

Solid waste included commercial, industrial, residential and also institutional waste, waste can become hazardous as certain types of waste can cause immediate danger to the individuals or the environment when they are exposed to it. Municipal solid waste or Refuse is the non-hazardous solid waste from a community that needs collection of the waste and transporting them to a disposal site. Refuse includes both garbage and rubbish, rubbish is mostly the dry material like rubbish, rubbish or wood, garbage is the decomposable food waste. This waste is decomposable and highly putrescible. Trash is rubbish that includes couches, tree stumps and old refrigerators, they require special collection and handling.

Construction and demolition waste is a significant component of the total solid waste quantities; however, they are inert and non-hazardous and is usually dispose in municipal landfills.

4. Define Scientific Landfills?

Scientific landfill

Is a kind of landfill that is a scientifically designed construction. The most important problem in ordinary landfill, is that the solid waste seeps into the underlying soil and water thus contaminating them. In scientific landfills a base layer of 90 metres of clay is constructed, thus the risk of waste seeping into the underground water and soil is eliminated. On top of the base layer a drainage layer made of soil, measuring 15 metres in length and a vegetative layer of 45 centimetres to minimise soil erosion. The presence of these layers ensures the safety of underground water and soil.

This method also helps as a degassing system, and also helps in the production of methane, as the layers soak most of the impurities in the disposed waste, methane is produces slowly compared to the ordinary landfills where methane is generated very fast. Vertical walls are also installed in scientific landfills, to help in extraction of methane regularly and the gas can then be used for electricity and heat generation purposes.

5. Explain the impurities present in water?

There are several impurities in water

BIOLOGICAL IMPURITIES IN WATER

Biological impurities are caused due to the presence of microorganisms, they reproduce in water rapidly and contaminate the water, the organisms present in water include protozoans, algae, viruses, bacteria, microbes, pathogens and also parasites along with their eggs, contaminated water are one of the main causes of gastroenteritis in humans.

COLLOIDAL IMPURITIES IN WATER

Colloidal impurities present in water include the organic waste products, which occurs when suspended particles and elements like sand, organic matter and rocks that flow into rivers lakes streams and make the water impure and unable to drink it.

Sources of chemical impurities in water include:

• Atmospheric Gases that get mixed with rain water and torrential downpours.
• Impurities are added near streams, rivers and lakes, when animals and plants are decomposing near them.
• Waste water and sewage from industries.
• River water that contains higher levels of iron, calcium, magnesium, chloride and sodium.
• Anthrogenic contaminants, that are found in natural and drinking water, arise from organic compounds produced from industrial, domestic and agricultural waste.
• Other inorganic compounds that are formed from medical wastewater and other equipment systems.

6. Explain Boiler corrosion?

Corrosion in boilers occur in three ways, namely oxidation, electrolytic dissolution and by acid attack. The process of corrosion that occurs in boilers mainly an oxidational reduction reaction. When a metal dissoles in water , irrespective of water being acidic or alkaline, the metal is oxidized by hydrogen ion as the oxidising agent.therefore Iron  will more readily dissolve in acid solutions that have high ion concentration. Boiler corrosion is an electrochemical process and is represented as

Fe----> Fe+ + 2 electrons

The reaction continues in the presence of oxygen as

4 electrons + O2+2H2O---------> 4OH

This indicates that iron corrodes in pure water,there is liberation of hydrogen ions and pH increases at the site of attack , until the water, metal and corrosion produts reach equlibrium.

The main cause for boiler corrosion occurs from dissolved gases, carbondioxide and oxygen found in feed water, the presence of oxygen and carbondioxide can cause corrosion of the feed water,boilers or even the condensate systems.Therefore the concentration of oxygen carbondioxide and dissolved gases in the feed water should be very low. This can be achieved by mechanical meanns followed by chemical treatmentto remove traces of these gases

Sea water is a potential source of acid as its salt contents especially magnesium chloride hydrolysis to yield acid, magnesium chloride reacts with water in the following manner

MgCl2 + 2H2O------> Mg(OH2) + 2HCl

As magnesium is insoluble it separates as sludge, leaving HCl in solution causing corrosion in boilers.

7. What are the sources of water pollution?

Some of the important sources of water pollution are: (i) Domestic effluents and sewage, (ii) Industrial effluents, (iii) Agricultural effluents, (iv) Radioactive wastes, (v) Thermal pollution, and (vi) Oil pollution. 

Man is the major consumer of water and uses water for a lot of domestic purposes such as cooking, bathing, cleaning etc, on an average per day 135 litres of water is used. Around 70% to 80% of this water is discharged and drained out, into municipal drains and in many cases flows into rivers, lakes etc.

This water is known as domestic waste water and, when other waste material such as paper, plastic, deter­gents, cloth, etc., is mixed in it; it becomes municipal waste or sewage.

The sewage and domestic waste water form the main sources of water pollution, this organic waste forms depletion of oxygen in water and upsets the natural balance of the aquatic ecosystem.

Municipal sewage is the main pollutant in water, before discharge of the water it is not treated, with the growing population, the waste water is also increasing in addition to large quantities of sewage, sewage consists of mainly decomposed organic matter and exert an oxygen demand on the receiving waters.

Industry forms the major range of waste products that are discharged into the water sources. Major contri­butors are the pulp and paper, chemicals, petrochemicals and refining, metal working, food processing, textile, distillery, etc. The wastes are usually heavy metals or organic synthetic compounds, these reach the water bodies either by direct discharge or by leaching from dumps

Agricultural water pollution is caused by fertilisers, insecticides and pesticides, farm animal wastes and sediments. In recent times, use of chemical fertilisers has shown a sharp increase. The green revolution in India is a reflection of the increased use of fertilisers. The chemicals used in fertilisers enter the groundwater by leaching and the surface waters by run-off.

Radioactive elements like radium and uranium have a highly unstable atomic nuclei, the disintegration of these atoms in radiation emission is highly injurious. Many of the thermal and electric plants discharge hot effluents into the water bodies that causes thermal pollution in the water sources, warm water is undesirable as they do not have the same oxygen holding capacity as cold water.

As a result of this fishes like black bass, trout and walleyes etc that require a minimal amount of oxygen would rather move from the polluted waters or die in large numbers.

The spread of oil in the sea has become a common feature nowadays. Oil is transported across oceans through tankers and either due to some accident or leakage oil spills onto the water and causes the degradation of aquatic and marine environment.

8. Explain the terms BOD and COD?

Biochemical Oxygen Demand:

The determination of the Biochemical Oxygen Demand or Biological Oxygen Demand (BOD) evaluates the amount of biodegradable organic material present in wastewater, effluent and polluted waters. The BOD test reflects the amount of dissolved oxygen (DO) consumed by bacteria while oxidizing these materials. Dissolved oxygen is essential for the life of aquatic fauna and flora, and the BOD test is a measure of the ecological impact that effluent water may have on the receiving body of water (river, lake, etc.). This test is often required in discharge permits, as it is a means of assessing the degree of water pollution.

Chemical Oxygen Demand:  The chemical oxygen demand (COD) is a measure of water and wastewater quality. The COD test is often used to monitor water treatment plant efficiency. This test is based on the fact that a strong oxidizing agent, under acidic conditions, can fully oxidize almost any organic compound to carbon dioxide. The COD is the amount of oxygen consumed to chemically oxidize organic water contaminants to inorganic end products.

The COD is often measured using a strong oxidant (e.g., potassium dichromate, potassium iodate, potassium permanganate) under acidic conditions. A known excess amount of the oxidant is added to the sample. Once oxidation is complete, the concentration of organics in the sample is calculated by measuring the amount of oxidant remaining in the solution. This is usually done by titration, using an indicator solution. COD is expressed in mg/L, which indicates the mass of oxygen consumed per litter of solution.

COD is a second method of estimating how much oxygen would be depleted from a body of receiving water as a result of bacterial action. The COD test uses a strong chemical oxidizing agent (potassium dichromate or potassium permanganate) to chemically oxidize the organic material in the sample of wastewater under conditions of heat and strong acid. The COD test has the advantage of not being subject to interference from toxic materials, as well as requiring only two or three hours for test completion, as opposed to five days for the BOD test. It has the disadvantage of being completely artificial, but is nevertheless considered to yield a result that may be used as the basis upon which to calculate a reasonably accurate and reproducible estimate of the oxygen-demanding properties of a wastewater. The COD test is often used in conjunction with the BOD test to estimate the amount of non-biodegradable organic material in a wastewater. In the case of biodegradable organics, the COD is normally in the range of 1.3 to 1.5 times the BOD. When the result of a COD test is more than twice that of the BOD test, there is good reason to suspect that a significant portion of the organic material in the sample is not biodegradable by ordinary microorganisms. As a side note, it is important to be aware that the sample vial resulting from a COD test can contain leachable mercury above regulatory limits. If such is the case, the sample must be managed as a toxic hazardous waste.

8. Write a note on sewage treatment?

 Sewage treatment

Primary method

In this method, the sewage flows through large tanks called as pre settling basins, or primary clarifiers, or primary sedimentation tanks, the tank are used to settle the sludge, while the oils and grease rise to the surface of the tank and are skimmed off. The primary tanks are provided with scrapers that are mechanically driven, that help to continually drive the sludge that is collected to a hopper that is present at the base of the tank, where it is later pumps to sludge treatment methods, the oil and grease is however recovered by saponification

Secondary treatment

In this method, the waste is substantially degraded, on the basis of the biological content of sewage present in human waste, food waste, soaps and detergents. Aerobic biological process is implemented by majority of the municipal plants. Microorganism like the bacteria and protozoa consume the biodegradable organic contaminants like fats organic carbon molecules.

Suspended-growth systems include activated sludge, in the activated sludge the biomass is mixed with the sewage and require smaller space than trickling filters, both require the same amount of water.

Tertiary treatment

Before the water is discharged to the environment (sea, river, ground, wet lands), the water is treated finally in the tertiary treatment, it is carried out mainly to improve the effluent quality of the water. Therefore, at the treatment plant more than one treatment process is carried out, the final process is always is disinfection.

10.Explain the ion exchange process for softening of water?

Ion exchange technology is a proven method of producing high purity softened and demineralized water. It is used in most industries that require high purity water and to reclaim water from processes. The Ion exchange process involves the exchanging of contaminant ions for Na+ ions in a softening application and H+ and OH- ions in pure water application. Cations and anions can be removed by the cation and anion exchange resins. Resins containing –COOH, SO3H are capable for exchanging their H+ ions to cationic portion of minerals then it is called as cation exchanger while the resins containing –NH2, NHCH3 are capable for exchanging the anionic portion of the minerals then it is termed as anionic exchanger.

On supplying the hard water in first chamber which consists of Ca2+ or Mg2+ then the cation exchanger exchanges it with H+ hence the cation exchanger absorbs the Ca2+ ions the left water is free from cations are passed to another chamber by the help of pump this water consists of anions such as Cl or SO4 on sprinkle up of these water at anion exchanger bed then it exchanged the anions and hence release the demineralise water. The absorbed cation and anion are sinked out through the outlet present in chamber.

Unit-4

Environmental Pollution and Water Chemistry

1.List the common pollutants present in the Air, elaborate any two?

Primary air pollutants are those pollutants that are directly emitted into the air from sources like natural gas power plants, coal fired power plants, volcanoes, burning of biomass, burning of natural forest fires and many more.

These pollutants effect the environment both directly and also form a precursor of secondary pollutants, examples of primary pollutants include- Sulphur dioxide, nitrogen oxides of dioxide, nitrogen organic matter, particulate matter etc.

• Sulphur dioxide (SO2)

During processes like fossil fuel combustion, metal smelting or oil refining, Sulphur is exposed to very high temperatures leading to the formation of Sulphur dioxide, Sulphur dioxide is toxic at very high concentrations, the most adverse effect to the environment is the formation of Acid rain, where the Sulphur dioxide dissolves in the cloud droplets and oxidizes to form sulphuric acid, that falls to the earth as acid rain, or they may also form sulphate aerosol particles in the atmosphere.

• Nitrogen oxides (includes NO NOx and NO2)

When oxygen and nitrogen react at very high temperatures, either during combustion or lightning very highly reactive gas NOx is formed. This reactive gas is also emitted during fossil fuel combustion and biomass burning.

Through a complicated chain reaction NOx reacts with volatile compounds and carbon monoxide in the atmosphere to form ground level ozone through a complicated chain mechanism, and oxidises to form Nitric acid, that also contributes to acid deposition and aerosol formation.

2. What do you understand by Ozone Depletion?

The gradual thinning of the earth’s ozone layer in the upper atmosphere due to the presence of chemical compounds containing gaseous bromine or chloride from human activities and industries.

The thinning of the ozone layer, present in the upper atmosphere occurs when a chlorine and bromine atoms present in the atmosphere come in contact with the ozone and destroy the ozone molecules, a chlorine molecule can destroy up to 100,000 molecules of ozone these molecules are more quickly destroyed than created. Few compounds are released when chlorine and bromine are exposed to UV light that cause a depletion in 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 Bromo fluorocarbons.

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.          

3. Explain the Solid waste management?

Solid waste

Solid wate management is the collection, treatment and disposal of the solid material that is discarded as they are no longer useful, improper disposal of the municipal waste can create unsanitary conditions, resulting in pollution of the environment and outbreaks of vector borne disease spread by mice and insects.

Solid waste included commercial, industrial, residential and also institutional waste, waste can become hazardous as certain types of waste can cause immediate danger to the individuals or the environment when they are exposed to it. Municipal solid waste or Refuse is the non-hazardous solid waste from a community that needs collection of the waste and transporting them to a disposal site. Refuse includes both garbage and rubbish, rubbish is mostly the dry material like rubbish, rubbish or wood, garbage is the decomposable food waste. This waste is decomposable and highly putrescible. Trash is rubbish that includes couches, tree stumps and old refrigerators, they require special collection and handling.

Construction and demolition waste is a significant component of the total solid waste quantities; however, they are inert and non-hazardous and is usually dispose in municipal landfills.

4. Define Scientific Landfills?

Scientific landfill

Is a kind of landfill that is a scientifically designed construction. The most important problem in ordinary landfill, is that the solid waste seeps into the underlying soil and water thus contaminating them. In scientific landfills a base layer of 90 metres of clay is constructed, thus the risk of waste seeping into the underground water and soil is eliminated. On top of the base layer a drainage layer made of soil, measuring 15 metres in length and a vegetative layer of 45 centimetres to minimise soil erosion. The presence of these layers ensures the safety of underground water and soil.

This method also helps as a degassing system, and also helps in the production of methane, as the layers soak most of the impurities in the disposed waste, methane is produces slowly compared to the ordinary landfills where methane is generated very fast. Vertical walls are also installed in scientific landfills, to help in extraction of methane regularly and the gas can then be used for electricity and heat generation purposes.

5. Explain the impurities present in water?

There are several impurities in water

BIOLOGICAL IMPURITIES IN WATER

Biological impurities are caused due to the presence of microorganisms, they reproduce in water rapidly and contaminate the water, the organisms present in water include protozoans, algae, viruses, bacteria, microbes, pathogens and also parasites along with their eggs, contaminated water are one of the main causes of gastroenteritis in humans.

COLLOIDAL IMPURITIES IN WATER

Colloidal impurities present in water include the organic waste products, which occurs when suspended particles and elements like sand, organic matter and rocks that flow into rivers lakes streams and make the water impure and unable to drink it.

Sources of chemical impurities in water include:

• Atmospheric Gases that get mixed with rain water and torrential downpours.
• Impurities are added near streams, rivers and lakes, when animals and plants are decomposing near them.
• Waste water and sewage from industries.
• River water that contains higher levels of iron, calcium, magnesium, chloride and sodium.
• Anthrogenic contaminants, that are found in natural and drinking water, arise from organic compounds produced from industrial, domestic and agricultural waste.
• Other inorganic compounds that are formed from medical wastewater and other equipment systems.

6. Explain Boiler corrosion?

Corrosion in boilers occur in three ways, namely oxidation, electrolytic dissolution and by acid attack. The process of corrosion that occurs in boilers mainly an oxidational reduction reaction. When a metal dissoles in water , irrespective of water being acidic or alkaline, the metal is oxidized by hydrogen ion as the oxidising agent.therefore Iron  will more readily dissolve in acid solutions that have high ion concentration. Boiler corrosion is an electrochemical process and is represented as

Fe----> Fe+ + 2 electrons

The reaction continues in the presence of oxygen as

4 electrons + O2+2H2O---------> 4OH

This indicates that iron corrodes in pure water,there is liberation of hydrogen ions and pH increases at the site of attack , until the water, metal and corrosion produts reach equlibrium.

The main cause for boiler corrosion occurs from dissolved gases, carbondioxide and oxygen found in feed water, the presence of oxygen and carbondioxide can cause corrosion of the feed water,boilers or even the condensate systems.Therefore the concentration of oxygen carbondioxide and dissolved gases in the feed water should be very low. This can be achieved by mechanical meanns followed by chemical treatmentto remove traces of these gases

Sea water is a potential source of acid as its salt contents especially magnesium chloride hydrolysis to yield acid, magnesium chloride reacts with water in the following manner

MgCl2 + 2H2O------> Mg(OH2) + 2HCl

As magnesium is insoluble it separates as sludge, leaving HCl in solution causing corrosion in boilers.

7. What are the sources of water pollution?

Some of the important sources of water pollution are: (i) Domestic effluents and sewage, (ii) Industrial effluents, (iii) Agricultural effluents, (iv) Radioactive wastes, (v) Thermal pollution, and (vi) Oil pollution. 

Man is the major consumer of water and uses water for a lot of domestic purposes such as cooking, bathing, cleaning etc, on an average per day 135 litres of water is used. Around 70% to 80% of this water is discharged and drained out, into municipal drains and in many cases flows into rivers, lakes etc.

This water is known as domestic waste water and, when other waste material such as paper, plastic, deter­gents, cloth, etc., is mixed in it; it becomes municipal waste or sewage.

The sewage and domestic waste water form the main sources of water pollution, this organic waste forms depletion of oxygen in water and upsets the natural balance of the aquatic ecosystem.

Municipal sewage is the main pollutant in water, before discharge of the water it is not treated, with the growing population, the waste water is also increasing in addition to large quantities of sewage, sewage consists of mainly decomposed organic matter and exert an oxygen demand on the receiving waters.

Industry forms the major range of waste products that are discharged into the water sources. Major contri­butors are the pulp and paper, chemicals, petrochemicals and refining, metal working, food processing, textile, distillery, etc. The wastes are usually heavy metals or organic synthetic compounds, these reach the water bodies either by direct discharge or by leaching from dumps

Agricultural water pollution is caused by fertilisers, insecticides and pesticides, farm animal wastes and sediments. In recent times, use of chemical fertilisers has shown a sharp increase. The green revolution in India is a reflection of the increased use of fertilisers. The chemicals used in fertilisers enter the groundwater by leaching and the surface waters by run-off.

Radioactive elements like radium and uranium have a highly unstable atomic nuclei, the disintegration of these atoms in radiation emission is highly injurious. Many of the thermal and electric plants discharge hot effluents into the water bodies that causes thermal pollution in the water sources, warm water is undesirable as they do not have the same oxygen holding capacity as cold water.

As a result of this fishes like black bass, trout and walleyes etc that require a minimal amount of oxygen would rather move from the polluted waters or die in large numbers.

The spread of oil in the sea has become a common feature nowadays. Oil is transported across oceans through tankers and either due to some accident or leakage oil spills onto the water and causes the degradation of aquatic and marine environment.

8. Explain the terms BOD and COD?

Biochemical Oxygen Demand:

The determination of the Biochemical Oxygen Demand or Biological Oxygen Demand (BOD) evaluates the amount of biodegradable organic material present in wastewater, effluent and polluted waters. The BOD test reflects the amount of dissolved oxygen (DO) consumed by bacteria while oxidizing these materials. Dissolved oxygen is essential for the life of aquatic fauna and flora, and the BOD test is a measure of the ecological impact that effluent water may have on the receiving body of water (river, lake, etc.). This test is often required in discharge permits, as it is a means of assessing the degree of water pollution.

Chemical Oxygen Demand:  The chemical oxygen demand (COD) is a measure of water and wastewater quality. The COD test is often used to monitor water treatment plant efficiency. This test is based on the fact that a strong oxidizing agent, under acidic conditions, can fully oxidize almost any organic compound to carbon dioxide. The COD is the amount of oxygen consumed to chemically oxidize organic water contaminants to inorganic end products.

The COD is often measured using a strong oxidant (e.g., potassium dichromate, potassium iodate, potassium permanganate) under acidic conditions. A known excess amount of the oxidant is added to the sample. Once oxidation is complete, the concentration of organics in the sample is calculated by measuring the amount of oxidant remaining in the solution. This is usually done by titration, using an indicator solution. COD is expressed in mg/L, which indicates the mass of oxygen consumed per litter of solution.

COD is a second method of estimating how much oxygen would be depleted from a body of receiving water as a result of bacterial action. The COD test uses a strong chemical oxidizing agent (potassium dichromate or potassium permanganate) to chemically oxidize the organic material in the sample of wastewater under conditions of heat and strong acid. The COD test has the advantage of not being subject to interference from toxic materials, as well as requiring only two or three hours for test completion, as opposed to five days for the BOD test. It has the disadvantage of being completely artificial, but is nevertheless considered to yield a result that may be used as the basis upon which to calculate a reasonably accurate and reproducible estimate of the oxygen-demanding properties of a wastewater. The COD test is often used in conjunction with the BOD test to estimate the amount of non-biodegradable organic material in a wastewater. In the case of biodegradable organics, the COD is normally in the range of 1.3 to 1.5 times the BOD. When the result of a COD test is more than twice that of the BOD test, there is good reason to suspect that a significant portion of the organic material in the sample is not biodegradable by ordinary microorganisms. As a side note, it is important to be aware that the sample vial resulting from a COD test can contain leachable mercury above regulatory limits. If such is the case, the sample must be managed as a toxic hazardous waste.

8. Write a note on sewage treatment?

 Sewage treatment

Primary method

In this method, the sewage flows through large tanks called as pre settling basins, or primary clarifiers, or primary sedimentation tanks, the tank are used to settle the sludge, while the oils and grease rise to the surface of the tank and are skimmed off. The primary tanks are provided with scrapers that are mechanically driven, that help to continually drive the sludge that is collected to a hopper that is present at the base of the tank, where it is later pumps to sludge treatment methods, the oil and grease is however recovered by saponification

Secondary treatment

In this method, the waste is substantially degraded, on the basis of the biological content of sewage present in human waste, food waste, soaps and detergents. Aerobic biological process is implemented by majority of the municipal plants. Microorganism like the bacteria and protozoa consume the biodegradable organic contaminants like fats organic carbon molecules.

Suspended-growth systems include activated sludge, in the activated sludge the biomass is mixed with the sewage and require smaller space than trickling filters, both require the same amount of water.

Tertiary treatment

Before the water is discharged to the environment (sea, river, ground, wet lands), the water is treated finally in the tertiary treatment, it is carried out mainly to improve the effluent quality of the water. Therefore, at the treatment plant more than one treatment process is carried out, the final process is always is disinfection.

10.Explain the ion exchange process for softening of water?

Ion exchange technology is a proven method of producing high purity softened and demineralized water. It is used in most industries that require high purity water and to reclaim water from processes. The Ion exchange process involves the exchanging of contaminant ions for Na+ ions in a softening application and H+ and OH- ions in pure water application. Cations and anions can be removed by the cation and anion exchange resins. Resins containing –COOH, SO3H are capable for exchanging their H+ ions to cationic portion of minerals then it is called as cation exchanger while the resins containing –NH2, NHCH3 are capable for exchanging the anionic portion of the minerals then it is termed as anionic exchanger.

On supplying the hard water in first chamber which consists of Ca2+ or Mg2+ then the cation exchanger exchanges it with H+ hence the cation exchanger absorbs the Ca2+ ions the left water is free from cations are passed to another chamber by the help of pump this water consists of anions such as Cl or SO4 on sprinkle up of these water at anion exchanger bed then it exchanged the anions and hence release the demineralise water. The absorbed cation and anion are sinked out through the outlet present in chamber.

Unit-4

Environmental Pollution and Water Chemistry

1.List the common pollutants present in the Air, elaborate any two?

Primary air pollutants are those pollutants that are directly emitted into the air from sources like natural gas power plants, coal fired power plants, volcanoes, burning of biomass, burning of natural forest fires and many more.

These pollutants effect the environment both directly and also form a precursor of secondary pollutants, examples of primary pollutants include- Sulphur dioxide, nitrogen oxides of dioxide, nitrogen organic matter, particulate matter etc.

• Sulphur dioxide (SO2)

During processes like fossil fuel combustion, metal smelting or oil refining, Sulphur is exposed to very high temperatures leading to the formation of Sulphur dioxide, Sulphur dioxide is toxic at very high concentrations, the most adverse effect to the environment is the formation of Acid rain, where the Sulphur dioxide dissolves in the cloud droplets and oxidizes to form sulphuric acid, that falls to the earth as acid rain, or they may also form sulphate aerosol particles in the atmosphere.

• Nitrogen oxides (includes NO NOx and NO2)

When oxygen and nitrogen react at very high temperatures, either during combustion or lightning very highly reactive gas NOx is formed. This reactive gas is also emitted during fossil fuel combustion and biomass burning.

Through a complicated chain reaction NOx reacts with volatile compounds and carbon monoxide in the atmosphere to form ground level ozone through a complicated chain mechanism, and oxidises to form Nitric acid, that also contributes to acid deposition and aerosol formation.

2. What do you understand by Ozone Depletion?

The gradual thinning of the earth’s ozone layer in the upper atmosphere due to the presence of chemical compounds containing gaseous bromine or chloride from human activities and industries.

The thinning of the ozone layer, present in the upper atmosphere occurs when a chlorine and bromine atoms present in the atmosphere come in contact with the ozone and destroy the ozone molecules, a chlorine molecule can destroy up to 100,000 molecules of ozone these molecules are more quickly destroyed than created. Few compounds are released when chlorine and bromine are exposed to UV light that cause a depletion in 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 Bromo fluorocarbons.

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.          

3. Explain the Solid waste management?

Solid waste

Solid wate management is the collection, treatment and disposal of the solid material that is discarded as they are no longer useful, improper disposal of the municipal waste can create unsanitary conditions, resulting in pollution of the environment and outbreaks of vector borne disease spread by mice and insects.

Solid waste included commercial, industrial, residential and also institutional waste, waste can become hazardous as certain types of waste can cause immediate danger to the individuals or the environment when they are exposed to it. Municipal solid waste or Refuse is the non-hazardous solid waste from a community that needs collection of the waste and transporting them to a disposal site. Refuse includes both garbage and rubbish, rubbish is mostly the dry material like rubbish, rubbish or wood, garbage is the decomposable food waste. This waste is decomposable and highly putrescible. Trash is rubbish that includes couches, tree stumps and old refrigerators, they require special collection and handling.

Construction and demolition waste is a significant component of the total solid waste quantities; however, they are inert and non-hazardous and is usually dispose in municipal landfills.

4. Define Scientific Landfills?

Scientific landfill

Is a kind of landfill that is a scientifically designed construction. The most important problem in ordinary landfill, is that the solid waste seeps into the underlying soil and water thus contaminating them. In scientific landfills a base layer of 90 metres of clay is constructed, thus the risk of waste seeping into the underground water and soil is eliminated. On top of the base layer a drainage layer made of soil, measuring 15 metres in length and a vegetative layer of 45 centimetres to minimise soil erosion. The presence of these layers ensures the safety of underground water and soil.

This method also helps as a degassing system, and also helps in the production of methane, as the layers soak most of the impurities in the disposed waste, methane is produces slowly compared to the ordinary landfills where methane is generated very fast. Vertical walls are also installed in scientific landfills, to help in extraction of methane regularly and the gas can then be used for electricity and heat generation purposes.

5. Explain the impurities present in water?

There are several impurities in water

BIOLOGICAL IMPURITIES IN WATER

Biological impurities are caused due to the presence of microorganisms, they reproduce in water rapidly and contaminate the water, the organisms present in water include protozoans, algae, viruses, bacteria, microbes, pathogens and also parasites along with their eggs, contaminated water are one of the main causes of gastroenteritis in humans.

COLLOIDAL IMPURITIES IN WATER

Colloidal impurities present in water include the organic waste products, which occurs when suspended particles and elements like sand, organic matter and rocks that flow into rivers lakes streams and make the water impure and unable to drink it.

Sources of chemical impurities in water include:

• Atmospheric Gases that get mixed with rain water and torrential downpours.
• Impurities are added near streams, rivers and lakes, when animals and plants are decomposing near them.
• Waste water and sewage from industries.
• River water that contains higher levels of iron, calcium, magnesium, chloride and sodium.
• Anthrogenic contaminants, that are found in natural and drinking water, arise from organic compounds produced from industrial, domestic and agricultural waste.
• Other inorganic compounds that are formed from medical wastewater and other equipment systems.

6. Explain Boiler corrosion?

Corrosion in boilers occur in three ways, namely oxidation, electrolytic dissolution and by acid attack. The process of corrosion that occurs in boilers mainly an oxidational reduction reaction. When a metal dissoles in water , irrespective of water being acidic or alkaline, the metal is oxidized by hydrogen ion as the oxidising agent.therefore Iron  will more readily dissolve in acid solutions that have high ion concentration. Boiler corrosion is an electrochemical process and is represented as

Fe----> Fe+ + 2 electrons

The reaction continues in the presence of oxygen as

4 electrons + O2+2H2O---------> 4OH

This indicates that iron corrodes in pure water,there is liberation of hydrogen ions and pH increases at the site of attack , until the water, metal and corrosion produts reach equlibrium.

The main cause for boiler corrosion occurs from dissolved gases, carbondioxide and oxygen found in feed water, the presence of oxygen and carbondioxide can cause corrosion of the feed water,boilers or even the condensate systems.Therefore the concentration of oxygen carbondioxide and dissolved gases in the feed water should be very low. This can be achieved by mechanical meanns followed by chemical treatmentto remove traces of these gases

Sea water is a potential source of acid as its salt contents especially magnesium chloride hydrolysis to yield acid, magnesium chloride reacts with water in the following manner

MgCl2 + 2H2O------> Mg(OH2) + 2HCl

As magnesium is insoluble it separates as sludge, leaving HCl in solution causing corrosion in boilers.

7. What are the sources of water pollution?

Some of the important sources of water pollution are: (i) Domestic effluents and sewage, (ii) Industrial effluents, (iii) Agricultural effluents, (iv) Radioactive wastes, (v) Thermal pollution, and (vi) Oil pollution. 

Man is the major consumer of water and uses water for a lot of domestic purposes such as cooking, bathing, cleaning etc, on an average per day 135 litres of water is used. Around 70% to 80% of this water is discharged and drained out, into municipal drains and in many cases flows into rivers, lakes etc.

This water is known as domestic waste water and, when other waste material such as paper, plastic, deter­gents, cloth, etc., is mixed in it; it becomes municipal waste or sewage.

The sewage and domestic waste water form the main sources of water pollution, this organic waste forms depletion of oxygen in water and upsets the natural balance of the aquatic ecosystem.

Municipal sewage is the main pollutant in water, before discharge of the water it is not treated, with the growing population, the waste water is also increasing in addition to large quantities of sewage, sewage consists of mainly decomposed organic matter and exert an oxygen demand on the receiving waters.

Industry forms the major range of waste products that are discharged into the water sources. Major contri­butors are the pulp and paper, chemicals, petrochemicals and refining, metal working, food processing, textile, distillery, etc. The wastes are usually heavy metals or organic synthetic compounds, these reach the water bodies either by direct discharge or by leaching from dumps

Agricultural water pollution is caused by fertilisers, insecticides and pesticides, farm animal wastes and sediments. In recent times, use of chemical fertilisers has shown a sharp increase. The green revolution in India is a reflection of the increased use of fertilisers. The chemicals used in fertilisers enter the groundwater by leaching and the surface waters by run-off.

Radioactive elements like radium and uranium have a highly unstable atomic nuclei, the disintegration of these atoms in radiation emission is highly injurious. Many of the thermal and electric plants discharge hot effluents into the water bodies that causes thermal pollution in the water sources, warm water is undesirable as they do not have the same oxygen holding capacity as cold water.

As a result of this fishes like black bass, trout and walleyes etc that require a minimal amount of oxygen would rather move from the polluted waters or die in large numbers.

The spread of oil in the sea has become a common feature nowadays. Oil is transported across oceans through tankers and either due to some accident or leakage oil spills onto the water and causes the degradation of aquatic and marine environment.

8. Explain the terms BOD and COD?

Biochemical Oxygen Demand:

The determination of the Biochemical Oxygen Demand or Biological Oxygen Demand (BOD) evaluates the amount of biodegradable organic material present in wastewater, effluent and polluted waters. The BOD test reflects the amount of dissolved oxygen (DO) consumed by bacteria while oxidizing these materials. Dissolved oxygen is essential for the life of aquatic fauna and flora, and the BOD test is a measure of the ecological impact that effluent water may have on the receiving body of water (river, lake, etc.). This test is often required in discharge permits, as it is a means of assessing the degree of water pollution.

Chemical Oxygen Demand:  The chemical oxygen demand (COD) is a measure of water and wastewater quality. The COD test is often used to monitor water treatment plant efficiency. This test is based on the fact that a strong oxidizing agent, under acidic conditions, can fully oxidize almost any organic compound to carbon dioxide. The COD is the amount of oxygen consumed to chemically oxidize organic water contaminants to inorganic end products.

The COD is often measured using a strong oxidant (e.g., potassium dichromate, potassium iodate, potassium permanganate) under acidic conditions. A known excess amount of the oxidant is added to the sample. Once oxidation is complete, the concentration of organics in the sample is calculated by measuring the amount of oxidant remaining in the solution. This is usually done by titration, using an indicator solution. COD is expressed in mg/L, which indicates the mass of oxygen consumed per litter of solution.

COD is a second method of estimating how much oxygen would be depleted from a body of receiving water as a result of bacterial action. The COD test uses a strong chemical oxidizing agent (potassium dichromate or potassium permanganate) to chemically oxidize the organic material in the sample of wastewater under conditions of heat and strong acid. The COD test has the advantage of not being subject to interference from toxic materials, as well as requiring only two or three hours for test completion, as opposed to five days for the BOD test. It has the disadvantage of being completely artificial, but is nevertheless considered to yield a result that may be used as the basis upon which to calculate a reasonably accurate and reproducible estimate of the oxygen-demanding properties of a wastewater. The COD test is often used in conjunction with the BOD test to estimate the amount of non-biodegradable organic material in a wastewater. In the case of biodegradable organics, the COD is normally in the range of 1.3 to 1.5 times the BOD. When the result of a COD test is more than twice that of the BOD test, there is good reason to suspect that a significant portion of the organic material in the sample is not biodegradable by ordinary microorganisms. As a side note, it is important to be aware that the sample vial resulting from a COD test can contain leachable mercury above regulatory limits. If such is the case, the sample must be managed as a toxic hazardous waste.

8. Write a note on sewage treatment?

 Sewage treatment

Primary method

In this method, the sewage flows through large tanks called as pre settling basins, or primary clarifiers, or primary sedimentation tanks, the tank are used to settle the sludge, while the oils and grease rise to the surface of the tank and are skimmed off. The primary tanks are provided with scrapers that are mechanically driven, that help to continually drive the sludge that is collected to a hopper that is present at the base of the tank, where it is later pumps to sludge treatment methods, the oil and grease is however recovered by saponification

Secondary treatment

In this method, the waste is substantially degraded, on the basis of the biological content of sewage present in human waste, food waste, soaps and detergents. Aerobic biological process is implemented by majority of the municipal plants. Microorganism like the bacteria and protozoa consume the biodegradable organic contaminants like fats organic carbon molecules.

Suspended-growth systems include activated sludge, in the activated sludge the biomass is mixed with the sewage and require smaller space than trickling filters, both require the same amount of water.

Tertiary treatment

Before the water is discharged to the environment (sea, river, ground, wet lands), the water is treated finally in the tertiary treatment, it is carried out mainly to improve the effluent quality of the water. Therefore, at the treatment plant more than one treatment process is carried out, the final process is always is disinfection.

10.Explain the ion exchange process for softening of water?

Ion exchange technology is a proven method of producing high purity softened and demineralized water. It is used in most industries that require high purity water and to reclaim water from processes. The Ion exchange process involves the exchanging of contaminant ions for Na+ ions in a softening application and H+ and OH- ions in pure water application. Cations and anions can be removed by the cation and anion exchange resins. Resins containing –COOH, SO3H are capable for exchanging their H+ ions to cationic portion of minerals then it is called as cation exchanger while the resins containing –NH2, NHCH3 are capable for exchanging the anionic portion of the minerals then it is termed as anionic exchanger.

On supplying the hard water in first chamber which consists of Ca2+ or Mg2+ then the cation exchanger exchanges it with H+ hence the cation exchanger absorbs the Ca2+ ions the left water is free from cations are passed to another chamber by the help of pump this water consists of anions such as Cl or SO4 on sprinkle up of these water at anion exchanger bed then it exchanged the anions and hence release the demineralise water. The absorbed cation and anion are sinked out through the outlet present in chamber.