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MEV-015: Environmental Pollution, Control and Management

MEV-015: Environmental Pollution, Control and Management

IGNOU Solved Assignment Solution for 2021-22

If you are looking for MEV-015 IGNOU Solved Assignment solution for the subject Environmental Pollution, Control and Management, you have come to the right place. MEV-015 solution on this page applies to 2021-22 session students studying in MSCENV, MAEVS courses of IGNOU.

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Assignment Code: MEV-015/TMA-01/2021-2022

Course Code: MEV-015

Assignment Name: Environmental pollution, Control and Management

Year: 2021-2022

Verification Status: Verified by Professor

Q1. Describe in detail the properties of soil and the influence of soil pollutants on these properties.

Ans) The upper layer of earth in which plants grow is called soil. It is black or dark brown material typically consisting of a mixture of organic remains, clay, and rock particles. The soil has the following special properties:


The texture of the soil depends upon the relative amount of these particles. Clay has the smallest sized particles. Because of very small size, the clay is felt smooth. Silt particles are larger than the clay particles. Their size range from0.002 to 0.02mm in diameter. So silt does not feel smooth. Sand particles are largest sized particles of soil. Their diameter is more than0.02mm.

Absorption of Water

Water holding capacity in different types of soils is different. Soil absorbs water because it is porous. Sandy soil holds less water than clay soil and loamy soil. Clay soil holds more water than sandy soil. Sand absorbs less water than clay. Some plants require more water to grow; they grow well in clay soil and loam soil, since sand hold less water, so less vegetation is found in sandy soil.


Texture decides the water holding capacity of the soil. The soil has some amount of water inside it as a moisture. Water is usually present as a thin film around the soil particles. It is absorbed by the roots of the plants. The capacity of a soil to hold water is important for the growth of various crops. Even a dry soil has some water in it.


Soils are of different colours. They are red, white, and black. The red colour of the soil is due to the presence of iron oxide. The black colour soil is rich in minerals and humus. It is good for the growth of wheat and jowar

Soil pH

Soil can be acid, alkaline or neutral. Some plants grow in acidic soil (pH below 7) such as potatoes and kumara. Carrots and lettuces prefer soil with neutral pH (7.0). Soil become more acidic over time as minerals are leached away.

Percolation Rate

When we sprinkle water on the ground, it is soon absorbed by the soil. This is because water percolates through the soil. The process in which water passes down slowly through the sol is called percolation of water. But water does not percolate at the same rate in all types of soils. Sandy soil allows maximum percolation of water and clay soil allows minimum percolation of water. Rainwater percolates through the soil and collects above the bedrock. This level of groundwater is called water table. Sandy soil is quite loose, so the percolation rate of water is highest in sandy soil but lowest in the clay soil because it is very compact.

Paddy (rice crops)is planted in standing water in the fields. Hence, the soil with a low percolation rate of water would be the most suitable for growing paddy because it will allow the water to remain in the fields for a much longer time.

Soil contains Air

Air is present in the space between the soil particles. This air provides the oxygen required for respiration by roots of plants and other organisms. Sand particles are quite large. Sand particles cannot fit closely together, so there is large space between sand particles.

The large space between sand particles is filled with air. Due to this, sandy soil provides much more air to the plant root. But clay particles pack tightly together leaving little space for air. So, clayey soil provides much less air to the plant root which grows in it.

Q2. Distinguish between Noise and Sound. What do you understand by threshold limit of hearing?

Ans) The differences between noise and sound are as follows:

These are the important differences between sound and noise. Similarly, we can note the difference between the sound and music, music, and noise, etc.

Threshold Limit of Hearing

The hearing threshold is the sound level below which a person’s ear is unable to detect any sound. For adults, 0 dB is the reference level. A threshold shift is an increase in the hearing threshold for a particular sound frequency. It means that the hearing sensitivity decreases and that it becomes harder for the listener to detect soft sounds. Threshold shifts can be temporary or permanent.

The hearing threshold is known as the lowest auditory pressure sensation threshold an organism can perceive. It is a subjective attribute that can vary by itself. The hearing threshold is the lowest limit of listening. Sound pressure (P) refers to differences in pressure in a compressible transmission medium (e.g. air), resulting from sound propagation. In our eardrums, the sound pressure generated by vibrations is translated into ossicle movements and, after transmission, developed into audible sensations in the inner ear. Pascal is its unit. The higher the threshold, the more sensitive the ear responds to the corresponding frequency range, the lower the sound intensity. The acoustic response is best seen in the shown graph at a frequency of 3 kHz. That is clearly seen in the graph created by the lowering of the hearing threshold in the valley. In this region, it takes only a very low level of noise to induce a sensation of hearing.

Q4. Differentiate between the following:

a) Primary and secondary air pollutants

Ans) The differences between primary and secondary air pollutants are as follows:

  1. Primary pollutants are emitted directly into the atmosphere by a source. But secondary pollutants are formed as a result of a chemical reaction between primary pollutants or with any other atmospheric particle.

  2. Primary pollutants are generally found in the form of particulate matter, aerosol, reduced or oxidised. But secondary pollutants are generally in an oxidised form.

  3. While primary pollutants affect the ecosystem in a direct and indirect manner, secondary pollutants have a limited and inert effect. However, ozone is an exception case of secondary pollutant. It undergoes the process of photoactivation, making the chemical reaction highly reactive and dangerous.

  4. Controlling the emission of primary pollutants can be done by reducing the anthropogenic emissions such as vehicle emissions and industrial emissions. However, it is quite a herculean task to control the emission of secondary pollutants because it is formed through a reaction between primary pollutants and with atmospheric particles. Thus, reducing its emissions involves thoroughly understanding the process of its creation and the elements involved.

  5. Sulphur dioxide, nitrogen oxides and particulate matter (PM) are few examples of primary pollutants. But ozone, secondary particulate matter and nitrogen dioxide are few examples of secondary pollutants.

Q4. b) Biological Oxygen Demand (BOD) and Chemical Oxygen Demand (COD)

Ans) The differences between Biological Oxygen Demand (BOD) and Chemical Oxygen Demand (COD) are as follows:

Q 4. c) Pyrolysis and Composting

Ans) The differences between Pyrolysis and Composting are as follows:

Pyrolysis is the chemical decomposition of organic (carbon-based) materials through the application of heat. It is a thermochemical treatment, which can be applied to any organic product. In this treatment process, materials are exposed to a very high temperature, and in the absence of oxygen, it goes through a chemical and physical separation into different molecules. The rate of pyrolysis increases with an increase in temperature.

The process is commonly used to convert organic materials into a solid residue containing ash and carbon, small quantities of liquid, and gases. On the other hand, extreme pyrolysis yields carbon as the residue, and the process is termed carbonization. Other high-temperature processes including hydrolysis and combustion, pyrolysis process does not involve reacting with water, oxygen, or any other reagents.

E.g.: The charring of wood (or the incomplete combustion of wood) resulting in the formation of charcoal involves the process of pyrolysis. The well-known products created with the help of pyrolysis are a form of charcoal also called biochar, which is created by heating wood, and coke (which can be used as an industrial fuel and a heat shield), created by heating of coal. The pyrolysis process produces condensable liquids (called tar) and non-condensable gases.

Composting is a process of decomposing organic solid wastes. It is an aerobic method i.e. it requires the presence of air.

Composting is a method of waste disposal in which organic waste matter gets decomposed naturally under aerobic conditions. By this method, organic material can be recycled.

Thus, natural decomposition becomes an important process for waste disposal. It involves the conversion of organic substances into a humus-like material. This hummus-like substance is known as compost. It is a good fertilizer for plants and hence, used widely in gardening and organic farming.

E.g.: As the waste items are gathered, the composting process starts. Organic matters are broken down naturally by earthworms, bacteria, and soil living organisms. After some months, when all the organic material is broken down, the final product obtained is called humus –a good natural fertilizer for farming and gardening. Kitchen wastes e.g. banana peels, vegetable peels, used tea leaves, coffee grinds and eggshells are great items to compost. Yard wastes like grass clippings, dried weeds can also be added to compost containers.

Q5. Mention the importance of solid waste management. What are the effects of improper disposal of solid waste on Human Health?

Ans) In today's culture, solid waste management is a necessary service. Solid waste management is significant because it is critical to manage and handle solid waste in accordance with the law in order to avoid littering and polluting the environment, which may be extremely hazardous not only to the ecosystem as a whole, but also to the people who live in it. The most important reasons for today's need for solid management are environmental cleanliness and public health. Other goals include waste material reduction and elimination for a higher quality of life and economic progress in society.

Solid waste management is vital to the health and well-being of city dwellers. Several tonnes of garbage are left uncollected on the streets of most developing cities each day, acting as a breeding ground for pests that spread disease, obstructing sewers, and causing a slew of other health and infrastructure issues. The urban poor are particularly vulnerable, as they generally live in informal settlements with little or no access to solid waste collection and in locations near open landfills.

While low-income cities create less solid waste per capita than high-income cities, their cities' ability to collect, process, dispose of, or re-use solid trash in a cost-effective and safe manner is severely constrained. Although many of the 'best practises' for SWM improvement are far more accessible and cost-effective opportunities involving waste reduction programmes and recycling strategies, municipal SWM efforts frequently focus on expensive 'end-of-pipe' measures, such as those involving the collection and disposal of solid waste.

Effects of Solid Waste on Human Health

Improper solid waste management is a threat to the environment and human health. Direct health risks are primarily a problem for workers in this industry, who must be kept as far away from garbage as possible. Handling garbage from hospitals and clinics carries its own set of risks. The greatest health dangers for the general people are indirect and stem from the breeding of disease vectors, especially flies and rodents.

Hazardous trash from industries that mixes with municipal waste poses a health danger to humans. Toxic discharged wastes have the potential to cause traffic accidents. There is a specific risk of heavy metal concentration in the food chain, a problem that illustrates the relationship between municipal solid wastes and liquid industrial effluents containing heavy metals discharged to a drainage/sewerage system and/or open dumping sites of municipal solid wastes, and the wastes discharged as a result, maintaining a vicious cycle that includes these wastes.

The following are some examples of other types of issues:

  1. Inhalation of toxic chemicals causes poisoning.

  2. Uncollected trash can hinder storm water runoff, causing flooding.

  3. Birth weight that is too low

  4. Cancer

  5. Malformations that occur at birth

  6. Diseases of the nervous system

  7. Vomiting and nausea

  8. Mercury poisoning can be caused by consuming high-mercury fish.

  9. Birds eat plastic discovered in the ocean.

  10. As a result, there is a large algal population in rivers and the sea.

  11. Degrades the quality of water and soil.

Q8. Describe the physical and chemical processes involved in the treatment of waste water.


Physical Wastewater Treatment Processes

Physical methods of wastewater treatment accomplish removal of substances by use of naturally occurring forces, such as gravity, electrical attraction, and van der Waal forces, as well as by use of physical barriers. In general, the mechanisms involved in physical treatment do not result in changes in chemical structure of the target substances. In some cases, physical state is changed, as in vaporization, and often dispersed substances are caused to agglomerate, as happens during filtration.

Physical methods of wastewater treatment include sedimentation, flotation, and adsorption, as well as barriers such as bar racks, screens, deep bed filters, and membranes. In this stage, physical methods are used for cleaning the wastewater. Processes like screening, sedimentation and skimming are used to remove the solids. No chemicals are involved in this process. One of the main techniques of physical wastewater treatment includes sedimentation, which is a process of suspending the insoluble/heavy particles from the wastewater. Once the insoluble material settles down at the bottom, you can separate the pure water.

Another effective physical water treatment technique includes aeration. This process consists of circulating air through the water to provide oxygen to it. Filtration, the third method, is used for filtering out all the contaminants. You can use special kind of filters to pass the wastewater and separate the contaminants and insoluble particles present in it. The sand filter is the most commonly used filter. The grease found on the surface of some wastewater can also be removed easily through this method.

Separation Using Physical Barriers:

There are many separation processes that make use of a physical barrier through which the target pollutants cannot pass, simply because of their size. These physical barriers are classified according to the size of the passageways through which all but the target pollutants (and larger) can pass, and they range from bar racks to reverse osmosis. Bar racks, screens, and sieves are considered to be either part of the headworks or part of primary treatment, while filters, microscreens, dialysis processes, and reverse osmosis are normally considered either secondary or tertiary treatment, depending on specific use.

Chemical Wastewater Treatment Processes

Chemicals are used during wastewater treatment in an array of processes to expedite disinfection. These chemical processes, which induce chemical reactions, are called chemical unit processes, and are used alongside biological and physical cleaning processes to achieve various water standards. Specialized chemicals such as chlorine, hydrogen peroxide, sodium chlorite, and sodium hypochlorite (bleach) act as agents that disinfect, sanitize, and assist in the purification of wastewater at treatment facilities. There are several distinct chemical unit processes, including chemical coagulation, chemical precipitation, chemical oxidation, and advanced oxidation, ion exchange, and chemical neutralization and stabilization, which can be applied to wastewater during cleaning.


Neutralization involves the addition of chemicals for the purpose of adjusting the pH of the wastewater. This involves the addition of acids (to lower pH) or alkalis (to raise pH) depending on the initial pH of the influent.

Chemical Precipitation:

Chemical precipitation is the most common method for removing dissolved metals from wastewater solution containing toxic metals. To convert the dissolved metals into solid particle form, a precipitation reagent is added to the mixture. A chemical reaction, triggered by the reagent, causes the dissolved metals to form solid particles. Filtration can then be used to remove the particles from the mixture. How well the process works is dependent upon the kind of metal present, the concentration of the metal, and the kind of reagent used. In hydroxide precipitation, a commonly used chemical precipitation process, calcium or sodium hydroxide is used as the reagent to create solid metal hydroxides. However, it can be difficult to create hydroxides from dissolved metal particles in wastewater because many wastewater solutions contain mixed metals.

Chemical Coagulation:

This chemical process involves destabilizing wastewater particles so that they aggregate during chemical flocculation. Fine solid particles dispersed in wastewater carry negative electric surface charges (in their normal stable state), which prevent them from forming larger groups and settling. Chemical coagulation destabilizes these particles by introducing positively charged coagulants that then reduce the negative particles’ charge. Once the charge is reduced, the particles freely form larger groups. Next, an anionic flocculant is introduced to the mixture. Because the flocculant reacts against the positively charged mixture, it either neutralizes the particle groups or creates bridges between them to bind the particles into larger groups. After larger particle groups are formed, sedimentation can be used to remove the particles from the mixture.

Chemical Oxidation/Reduction and Advanced Oxidation:

With the introduction of an oxidizing agent during chemical oxidation, electrons move from the oxidant to the pollutants in wastewater. The pollutants then undergo structural modification, becoming less destructive compounds. Alkaline chlorination uses chlorine as an oxidant against cyanide. However, alkaline chlorination as a chemical oxidation process can lead to the creation of toxic chlorinated compounds, and additional steps may be required. Advanced oxidation can help remove any organic compounds that are produced as a byproduct of chemical oxidation, through processes such as steam stripping, air stripping, or activated carbon adsorption.

Redox reactions are used for the treatment of potable water. Chlorinated hydrocarbons and pesticides can be effectively removed from wastewater by the use of ozone and hydrogen peroxide treatments. Advanced oxidation processes are also used for the degradation of drug substances like antibiotics or cytostatic drugs that might be found in the water. Reduction processes can also be used for the transformation of heavy metal ions into sulphides.

Ion Exchange:

When water is too hard, it is difficult to use to clean and often leaves a grey residue. (This is why clothing washed in hard water often retains a dingy tint.) An ion exchange process, similar to the reverse osmosis process, can be used to soften the water. Calcium and magnesium are common ions that lead to water hardness. To soften the water, positively charged sodium ions are introduced in the form of dissolved sodium chloride salt or brine. Hard calcium and magnesium ions exchange places with sodium ions, and free sodium ions are simply released in the water. However, after softening a large amount of water, the softening solution may fill with excess calcium and magnesium ions, requiring the solution to be recharged with sodium ions.

Adsorption and Chemisorption:

Adsorption is a process whereby substances accumulate on the surfaces of a solid body due to the van der Waal force. This process is a physical one – when the same thing happens as a result of a chemical bond, the process is known as chemisorption. In wastewater treatment, activated carbons are often used to bind to soluble elements in the water which were unable to be removed in earlier stages of the treatment process such as mechanical or biological. Colorants from textile dying, pharmaceutical residues, arsenic, and heavy metals are examples of substances that can be effectively removed through this process.


The chemical process of precipitation involves the addition of suitable agents to the wastewater which can transform dissolved substances to ones that are not easily soluble. With this transformation, the material precipitates and lowers the concentration of the material. Heavy metals can precipitate as metal hydroxides, and anions can precipitate as calcium, iron, or aluminium salts, for example.


Flocculation uses flocculants to help remove very fine particles from wastewater that would not normally accumulate as larger agglomerates as a result of their electrical repulsion from having an identical charge. By adding specialty chemicals, larger formulations of particles will occur which will then settle out in a sedimentation process.

Chemical Stabilization:

This chemical wastewater treatment process works in a similar fashion as chemical oxidation. Sludge is treated with a large amount of a given oxidant, such as chlorine. The introduction of the oxidant slows down the rate of biological growth within the sludge and also helps deodorize the mixture. The water is then removed from the sludge. Hydrogen peroxide can also be used as an oxidant and may be a more cost-effective choice.

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