Module 9. Pollutions and control

Lesson 15


15.1 Introduction

Pollution is the effect of undesirable changes in our surroundings that have harmful effects on plants, animals and human beings. This occurs when only short-term economic gains are made at the cost of the long-term ecological benefits for humanity. During the last few decades we have contaminated our air, water and land on which life itself depends with a variety of waste products.

Pollutants include solid, liquid or gaseous substances present in greater than natural abundance produced due to human activity, which have a detrimental effect on our environment.

15.2 Types of Pollutants

Pollutants can be classified as follows:

Degradable or Non-Persistent Pollutants: These can be rapidly broken down by natural processes. Eg: Domestic sewage, discarded vegetables, etc.

Slowly Degradable or Persistent Pollutants: Pollutants that remain in the environment for many years in an unchanged condition and take decades or longer to degrade. Eg: DDT and most plastics.

Non-Degradable Pollutants: These cannot be degraded by natural processes. Once they are released into the environment they are difficult to eradicate and continue to accumulate. Eg: Toxic elements like lead or mercury, heavy metals.

15.3 Air Pollution

Air pollution occurs due to the presence of undesirable solid or gaseous articles in the air in quantities that are harmful to human health and the environment.

Air may get polluted by natural causes such as volcanoes, which release ash, dust, sulphur and other gases, or by forest fires that are occasionally naturally caused by lightning.

15.3.1 Primary pollutants

Pollutants that are emitted directly from identifiable sources are produced both by natural events (for example, dust storms and volcanic eruptions) and human activities (emission from vehicles, industries, etc.).

There are five primary pollutants that together contribute about 90 percent of the global air pollution. These are:
  • Carbon oxides (CO and CO2),
  • Nitrogen oxides,
  • Sulfur oxides,
  • Volatile organic compounds (mostly hydrocarbons) and
  • Suspended particulate matter.
15.3.2 Secondary pollutants

Pollutants that are produced in the atmosphere when certain chemical reactions take place among the primary pollutants are called secondary pollutants. E.g: sulfuric acid, nitric acid, carbonic acid, etc.
  • Carbon monoxide is a colorless, odorless and toxic gas produced when organic materials such as natural gas, coal or wood are incompletely burnt. Vehicular exhausts are the single largest source of carbon monoxide. Vehicles are alsopoorly maintained and several have inadequate pollution control equipment resulting in release of greater amounts of carbon monoxide.
  • Sulfur Oxides are produced when sulfur containing fossil fuels are burnt.
  • Nitrogen Oxides are found in vehicular exhausts. Nitrogen oxides are significant, as they are involved in the production of secondary air pollutants such as ozone.
  • Hydrocarbons are a group of compounds consisting of carbon and hydrogen atoms. They either evaporate from fuel supplies or are remnants of fuel that did not burn completely. Hydrocarbons are washed out of the air when it rains and run into surface water. They cause an oily film on the surface and do not as such cause a serious issue until they react to form secondary pollutants. Using higher oxygen concentrations in the fuel-air mixture and using valves to prevent the escape of gases, fitting of catalytic converters in automobiles, are some of the modifications that can reduce the release of hydrocarbons into the atmosphere.
  • Particulates are small pieces of solid material dispersed into the atmosphere. The effects of particulates range from soot to the carcinogenic effects of asbestos, dust particles and ash from industrial plants that are dispersed into the atmosphere. Repeated exposure to particulates can cause them to accumulate in the lungs and interfere with the ability of the lungs to exchange gases.
  • Lead is a major air pollutant that remains largely unmonitored and is emitted by vehicles. High lead levels have been reported in the ambient air in metropolitan cities. Leaded petrol is the primary source of airborne lead emissions in Indian cities.
Pollutants are also found indoors from infiltration of polluted outside air and from various chemicals used or produced inside buildings. Both indoor and outdoor air pollution are equally harmful.

15.3.3 Effects of pollution On living organisms
  • Carbon monoxide: Prolonged smoking or exposure to air pollutants can breakdown the natural defenses causing diseases such as lung cancer, asthma, chronic bronchitis and emphysema. Exposure to air containing even 0.001 percent of carbon monoxide for several hours can cause collapse, coma and even death. As CO remains attached to hemoglobin in blood for a long time, it accumulates and reduces the oxygen carrying capacity of blood. This impairs perception and thinking, slows reflexes and causes headaches, drowsiness, dizziness and nausea. Carbon monoxide in heavy traffic causes headaches, drowsiness and blurred vision.
  • Sulfur dioxide: It irritates respiratory tissues. Chronic exposure causes a condition similar to bronchitis. It also reacts with water, oxygen and other material in the air to form sulfur-containing acids. The acids can become attached to particles which when inhaled are very corrosive to the lung.
  • Nitrogen oxides: It can irritate the lungs, aggravate asthma or chronic bronchitis and also increase susceptibility to respiratory infections such as influenza or common colds.
  • Suspended particles: They cause aggravate bronchitis and asthma. Exposure to these particles over a long period of time damages lung tissue and contributes to the development of chronic respiratory disease and cancer.
  • Toxic particulates: Toxic particulates such as lead, cadmium, benzene and formaldehyde can cause mutations, reproductive problems or cancer.
  • Ozone: It is a component of photochemical smog causes coughing, chest pain, breathlessness and irritation of the eye, nose and the throat when inhaled. On plants

Chronic exposure of the leaves to air pollutants will break down the waxy coating that helps to prevent excessive water loss and leads to damage from diseases, pests, drought and frost.

It interferes with photosynthesis and plant growth, reduces nutrient uptake and causes leaves to turn yellow, brown or drop off altogether.

At a higher concentration of sulphur dioxide majority of the flower buds become stiff and hard. They eventually fall from the plants, as they are unable to flower. On materials

Air pollutants break down exterior paint on cars and houses.

All around the world air pollutants have discolored irreplaceable monuments, historic buildings, and marble statues. On climate

Atmospheric changes induced by pollution contribute to global warming, green house effect and acid rain. Global warming

It is a phenomenon which is caused due to the increase in concentration of certain gases like carbon dioxide, nitrogen oxides, methane and to a lesser extent the CFCs. Greenhouse effect

The atmospheric constituents such as water vapor, carbon dioxide, methane, nitrogen oxides and Chloro Fluro Carbons trap heat in the form of infra-red radiation near the earth’s surface known as the ‘Greenhouse Effect’. Acid rain

When sulphur dioxide and nitrogen oxides are transported by prevailing winds they form secondary pollutants such as nitric acid vapour, droplets of sulfuric acid and particles of sulphate and nitrate salts.

15.3.4 Air quality in dairy plant

The main emissions from dairy manufacturing processes are odours and particles.

Odours in and around milk processing plants come from the biological decomposition of milk derived organic matter, generally found in wastewater. Often these odours are due to poor housekeeping, overloaded or improperly run wastewater treatment and disposal facilities, and prolonged storage of strong wastes such as whey. Particles Particle emissions are caused either by combustion of solid or liquid fuel or, more often, spray drying of milk and whey. Excessive emissions are often sporadic and happen during plant upsets, shutdowns or startups. The use of solid or liquid fuel such as briquettes and oil can result in fallout – carbonaceous ash particulate is usually emitted during boiler upsets or tube soot-blowing operations. Milk powder particles – while not toxic – accumulate on flat surfaces such as roofing, guttering and rainwater tanks, and may seriously compromise the quality of storm water discharged from the site or taint the drinking water. A further source of annoyance to residents and factory workers is powder settling on nearby motor vehicles. The drier emissions depend on the product being dried – for example, skim milk tends to result in the highest emissions. Measures to reduce emissions

The suggested measures to reduce emissions are
  • Maintain aerobic conditions for wastewater processing.
  • Use filters or scrubbers to eliminate or reduce particles. (Particles less than 20mg/Nm3represents best practice.)
  • Use automatic process control.
  • Carry out continuous routine monitoring of emission points using audible, visible alarms.
15.3.5 Control measures for air pollution

Air pollution can be controlled by two fundamental approaches:

1. Preventive techniques

2. Effluent control
  • The devices for removal of pollutants from the flue gases through scrubbers, closed collection recovery systems through which it is possible to collect the pollutants before they escape,
  • Use of dry and wet collectors, filters, electrostatic precipitators,
  • Providing a greater height to the stacks can help in facilitating the discharge of pollutants as far away from the ground as possible,
  • Industries should be located in places so as to minimize the effects of pollution after considering the topography and the wind directions,
    • Substitution of raw material that causes more pollution with those that cause less pollution can be done
15.4 Noise Pollution

Noise is undesirable and unwanted sound. Not all sound is noise. Sound is measured in a unit called the ‘Decibel’.

There are several sources of noise pollution that contribute to both indoor and outdoor noise pollution. Noise emanating from factories, vehicles, playing of loudspeakers during various festivals can contribute to outdoor noise pollution while loudly played radio or music systems, and other electronic gadgets can contribute to indoor noise pollution.

The permitted noise level is 125 decibels, as per the Environment (Protection) (second amendment) Rules, 1999. Location specific noise limits are mentioned below in the text.

15.4.1 Effects of noise pollution on physical health

The excessive noise causes physical damage to the ear and the temporary or permanent hearing loss often called a temporary threshold shift (TTS).
  • It can cause harmful effects on the circulatory system by raising blood pressure and altering pulse rates.
  • It causes emotional or psychological effects such as irritability, anxiety and stress.
  • It also causes lack of concentration and mental fatigue.
  • It can also lead to lowered worker efficiency and productivity and higher accident rates on the job.
15.4.2 Ambient noise levels (db)

Table 15.1 Noise levels at different times: According to Environment Protection act


15.4.3 Noise in dairy plant

The principal causes of continuous noise include:
  • Air discharges from drier stacks.
  • Heater fans.
  • Air supply fans.
  • Ventilation.
  • Boilers.
  • Pumps.
  • Cooling towers.
  • Refrigeration units.
  • Aerators on aerated lagoons.
Truck movements to and from the site or in streets are a source of noise, as are refrigeration compressors on trucks. This is a particular problem when fresh milk delivery means late night trucking.
Noisy operations at dairy plants include milk drying – which requires high air flows – and the movements of transport vehicles to and from the site. Depending on the distance to sensitive receptors such as residential areas, suitable noise suppression or abatement measures – such as noise silencers on equipment, enclosure of outdoor equipment, concrete housing for mechanical plant, mufflers on transport vehicles – may be required.

15.4.4 Noise control techniques

There are four fundamental ways in which noise can be controlled: i) Reduce noise at the source. ii) Block the path of noise. iii) Increase the path length.iv) Protect the recipient.

One of the best methods of noise source reduction is regular and thorough maintenance of operating machinery.

Source reduction can be done by effectively muffling vehicles and machinery to reduce the noise.

In industries noise reduction can be done by using rigid sealed enclosures around machinery lined with acoustic absorbing material.

Isolating machines and their enclosures from the floor using special spring mounts or absorbent mounts and pads and using flexible couplings for interior pipelines also contribute to reducing noise pollution at the source.

Noise levels at construction sites can be controlled using proper construction planning and scheduling techniques.

A smooth flow of traffic also causes less noise than does a stop-and-go traffic pattern.

Proper highway planning and design are essential for controlling traffic noise.

Establishing lower speed limits for highways that pass through residential areas, limiting traffic volume and providing alternative routes for truck traffic, construction of vertical barriers alongside the highway are effective noise control measures.

Planting of trees around houses can also act as effective noise barriers.

In industries different types of absorptive material can be used to control interior noise.

Increasing the path length between the source and the recipient offers a passive means of control.

Municipal land-use ordinances pertaining to the location of airports make use of the attenuating effect of distance on sound levels.

Use of earplugs and earmuffs can protect individuals effectively from excessive noise levels.

15.5 Soil Pollution

Soil is a thin covering over the land consisting of a mixture of minerals, organic material, living organisms, air and water that together support the growth of plant life.

15.5.1 Causes of soil pollution

Runoff from pollutants like paint, chemicals, rotting organic material leaching out of landfill

Polluted water discharged from factories

Oil and petroleum leaks from vehicles washed off the road by the rain into the surrounding habitat

Chemical fertilizer runoff from farms and crops

Acid rain i.e. fumes from factories mixing with rain

Sewage discharged into rivers instead of being treated properly

Over application of pesticides and fertilizers

Purposeful injection into groundwater as a disposal method

Interconnections between aquifers during drilling

Septic tank seepage, Lagoon seepage

Sanitary/hazardous landfill seepage

Cemeteries , Scrap yards (waste oil and chemical drainage)

Leaks from sanitary sewer

15.5.2 Some effects of soil pollution
  • Pollution runs off into rivers and kills the fish, plants and other aquatic life,
  • Crops and fodder grown on polluted soil may pass the pollutants on to the consumers,
  • Polluted soil may no longer grow crops and fodder,
  • Soil structure is damaged (clay ionic structure impaired).
  • Corrosion of foundations and pipelines.
  • Impairs soil stability.
  • May release vapors and hydrocarbon into buildings and cellars.
  • May create toxic dusts.
  • May poison children playing in the area.
15.5.3 Causes of soil degradation

Soil erosion can be defined as the movement of surface litter and topsoil from one place to another. While erosion is a natural process often caused by wind and flowing water it is greatly accelerated by human activities such as farming, construction, overgrazing by livestock, burning of grass cover and deforestation.

Loss of the topsoil makes a soil less fertile and reduces its water holding capacity. The topsoil, which is washed away, also contributes to water pollution clogging lakes, increasing turbidity of the water and also leads to loss of aquatic life.

There are several techniques that can protect soil from erosion.
  • Area treatment which involves treating the land,
  • Drainage line treatment which involves treating the natural water courses.
  • Continuous contour trenches can be used to enhance infiltration of water reduce the runoff and check soil erosion.
  • These are actually shallow trenches dug across the slope of the land and along the contour lines basically for the purpose of soil and water conservation.
  • These bunds are stabilized by fast growing tree species and grasses.
  • In areas of steep slopes where the bunds are not possible, continuous contour benches (CCBs) made of stones are used for the same purpose.
  • Gardenias can also be used to convert wastelands into agricultural lands.
  • In this narrow trenches with bunds on the downstream side are built along contours in the upper reaches of the catchments to collect run-off and to conserve moisture from the trees or tree crops.
  • Live check dams which barriers created by planting grass, shrubs and trees across the gullies can be used for this purpose.
  • A bund constructed out of stones across the stream can also be used for conserving soil and water.
Last modified: Friday, 5 October 2012, 7:15 AM