Industries are often considered to be one of the potential sources that release toxic gases, fumes, vapours and particulate matter into the immediate work environment and the general living environment, which causes deterioration in the quality of air that we breathe and ultimately affects our health. The combustion of fossil fuels, viz. coal, oil and natural gas, ets. in various industries lead to emission of huge quantities of air pollutants in the atmosphere.

Air pollutants, which are found in the atmosphere, can be classified into two broad groups on the basis of their mode of origin.

• Primary Air Pollutant: These are directly emitted into the atmosphere from the source in the same form in which they exist in the atmosphere, The major primary air pollutants are particulate matter, sulphur dioxide, oxides of nitrogen, carbon monoxide and hydrocarbons, etc.
• Secondary Air Pollutant: These are generated in the atmosphere by the interactions between two or more primary pollutants or by reaction natural atmospheric constituents with or without photo-activation. The major secondary air pollutants are ozone, peroxyacetyl nitrate(PAN), aldehydes/ketones, sulphuric acid and nitric acid.

Given below is a table that describes the major industrial processes and their characteristics emissions.

Air Pollution Control

Air Pollution Control of fixed sources can be accomplished by two fundamental approaches, which are control by dilution in the atmosphere by dispersion, and control at the source designed to reduce the air pollution emitted to the bare minimum.

The techniques and devices used to control a gaseous pollutant depend on the properties of the specific gas to be controlled.
The technique used to control gaseous pollutants are:

• Gas Absorption
• Combustion
• Closed collection and recovery system
• Condensation

The devices used to control Particulate Matters are:

• Gravitational Settings Chambers
• Centrifugal Collector/Cyclone Separators
• Fabric Filter-
• Wet Collectors/Scrubbers
• Electrostatic Precipitators

An important problem of air pollution is the control of objectionable odours, which are discharged into the atmosphere from industrial, commercial and municipal operations. Source control is the most effective way of abating odour. He methods can be employed alone or in various combinations to eliminate or diminish odours.

1.Modification of the process: In some cases, a change in the process, either by way of changing the composition of process materials or removal of impurities may help in odour control.

2.Dilution by ventilation or dispersal: Proper well-designed ventilation is the most common method of removal of odours from enclosed place. Odours gas can also be released from tall stacks, which results in normal dispersal in the atmosphere and a consequent decrease in the ground-level concentrations below the threshold value.

3.Absorption: It is applicable when the odorous gases are soluble or emulsified in a liquid or react chemically in a solution. Liquid scrubbing of the gases in a suitable absorption unit is an important method of odour control.

4.Absorption: Since activated carbon is highly porous and has great absorptive power, it is widely used in odour control. The highly porous structure permits the carbon to remove and hold the organic vapours, hydrogen sulphide and other odour-producing substances.

5.Combustion of oxidation:

(a) Direct Incineration- The odour generating gases are made to pass through a combustion chamber at a temperature in the order of 650-815 degree C, in the presence of excess oxygen
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(b) Catalytic Incineration- When the cost of heating the gas stream to 650 degree C becomes very high, catalytic combustion may be the choice. In a catalytic unit, oxidation takes place at a much lower temperature than what is necessary for direct incineration.

6.Odour masking: It is based on the principle that, when two odours are mixed the stronger one will predominate. Thus, strong odours tend to mask the weaker ones.

7.Injection of a reactive substance: Odours can be controlled by injecting controlled quantities of Chlorine or ozone into the process gas-stream.

8.Irradiation: UV radiation can be used for control of odours.

Noise Control at Source

1. Reducing of impact/impulse force- Impact noise is created by hammers, crushers, hoppers, resulting from impacts of rock and steel. It can be reduced by optimizing the impact-distance and covering either or both the impact surfaces by rubber or materials of such type.
   
   
2. Balancing of moving mass- Some noises are created by sudden inrush or discharge of air, e.g. leakage of compressed air through pipelines, ventilation fans, air compressors. This type of noise is created due to discharge of high volume of air through restricted path. So this noise can be reduced by using "mufflers" which are simple expansion chambers to slow down the velocity of exhausting air. Mufflers can attenuate the noise level by 5-10 dB(A).
   
   
3. Vibration Isolation-Machine vibration is the source of one of the highest volume of noise. Noise generated by the mechanical vibration of a machine or its part can be reduced by damping or isolation of the vibration. Damping can be achieved by applying damping materials (rubber) to the vibrating components. The Water Cooling Jacket of the internal combustion engine dampens noise. Vibration of the source can also be minimized by changing the mass or stiffness of the vibrating elements. Isolation of vibration can be achieved by introducing an elastic device such as metal spring. rubber or cork between the moving parts of the machine and the surrounding stationary structure.
   
   
4. Modified manufacturing design-Problem of noise emission can be tackled at the design and manufacturing stage by making suitable adjustments in the design itself, e.g. enclosing the engine parts within proper noise insulating material.

Noise Control at Path

If noise cannot be reduced to a desired level at the source, then it can be reduced in the path in between the source and the receiver by using the following techniques.

1. Orientation of Location- By moving the source away from the noise sensitive area, the noise can be attenuated.
   
   
2. Enclosure
   • Housing the noisy machines in isolated buildings can reduce the noise.
   • A glass cabin may be provided for the operator of a noisy machine.
   • Thick walls and heavy materials are more effective. A 25 cm. thick wall can attenuate noise level by 45 dB(A)
   • Double walls separated by an air space can act as the most effective barrier. Wider the air space, lesser will be the noise transmission.
   • An operator confirmed in a chamber lined with absorbent material will experience some 5-10 dB(A) less sound than in an ordinary chamber.
     
     
3. Silencers: These can be used to suppress the noise generated when air, gas or stream flow in pipes or ducts, or are emitted into the atmosphere.
   
   
4. Pipe lagging: On pipes carrying steam or hot fluids, lagging can be used as an alternative to enclosure and can achieve attenuations of 10-20 dB(A). Their effectiveness reduces with increase in the distance of noise source from the Screen.
   
   
5. Acoustic Screens and Barriers: A masonry wall can form a substantial barrier. Such acoustic screens can reduce direct noise transmission by up to 15 dB(A). Their effectiveness reduces the increase in the distance of noise source from the screen.
   
   
6. Absorption Treatment: Where there is a high degree of reflection of sound waves, introduction of an acoustically absorbent material, in the form of wall treatment (wall first covered with a thick layer of mineral wool and then with a polythene sheet), will reduce noise level by up to 10 dB(A) and will not reduce the noise radiated directly by the source.
   
   
7. Damping: When large panels are radiating noise, a significant reduction can be achieved by fitting damping pads.
   
   
8. Green Belt: Location of green belt around residential areas can act as noise barriers. They can reduce noise level by absorption by ground cover and tree foliage.

Noise Control at Receiver

When it is not practical or economical to reduce noise level, ear protectors are used. Ear protectors are capable of reducing the noise level at the ear by 10 dB. The most commonly used ear protected devices or HDP are ear plugs and ear muffs.

• Ear plugs fit directly into the ear canal and is made up of rubber, plastic or wax-impregnated cotton.
• Ear muffs are plastic domes lined with foam that cover the ears and are connected by a spring band. These offer the greatest amount of noise attenuation and are easy to fit.

Usually a small fraction of the water used by the industry is held back in its product or lost by evaporation. Most of the flow is eventually emptied into the natural water courses as spent water. Because of rapid industrialization, there is more and more stress on available water resources and as a result there is more and more attention on treatment of industrial waste waters. Characteristics of industrial waste waters vary widely from industry to industry, and even within the same industry depending on raw materials used, process employed, and various other factors.

Hazardous substances pervade today’s industrial society. Industry generates, uses and discards hazardous substances. The Hazardous Waste, because of its quantity, concentration, physical, chemical or infectious characteristics may cause potential health hazard to human health or environment when improperly treated, stored, transported or disposed of. Specifically, a waste is hazardous if it contains one or more of the following characteristics-

• Ignitability
• Corrosivity
• Reactivity
• Radioactivity
• Toxicity

Industries that are major producers of hazardous waste include petrochemicals, pharmaceuticals, pesticides, paints and dyes, petroleum, fertilizers, asbestos, caustic soda, inorganic chemicals and general engineering. Over the years, the sources of hazardous waste generation have increased manifold and their impact on the environment have grown more severe. There has been a significant increase in the number of tanneries and units manufacturing pesticides, drugs and pharmaceuticals, textiles, dyes, fertilizers, paint, chlor-alkali, etc. which have a major potential for generating hazardous waste such as heavy metals, cyanides, pesticides, complex aromatic compounds (such as PCBs), and other chemicals, which are toxic, flammable, reactive, corrosive or have explosive properties. These wastes require proper treatment and disposal; these are found to remain scattered on the seashore and contaminate the marine environment.

Hazardous Waste Management

Waste minimization efforts should be made prior to considering the hazardous waste for treatment and disposal. Waste minimization is an important hazardous waste management strategy, which includes source reduction, recycling and treatment. Many different hazardous waste treatment technologies can be used prior to ultimate disposal. The aim is to modify the physical or the chemical properties of the waste. The choice of the best practicable way of treating the waste depends on the availability and suitability of treatment or disposal facilities, discharge standards and cost considerations. Generally, the following types of treatments are provided to the wastes:

• Physical Treatment
• Chemical Treatment
• Biological Treatment

Physical Treatment Process

The physical treatment processes include various methods of phase separation and solidification. The phase separation includes lagooning, sludge drying in beds and prolonged storage in tanks. All these processes depend on the gravitational settlement. Lagooning and tank storage are widely used to separate oil and water from mixed wastes. Solidification or fixation processes convert the waste into an insoluble, rock-hard material and they are generally used as pre-treatment prior to land-fill disposal. The conversion is achieved by blending the waste with various reactants to produce a cement-like product.

Chemical Treatment Process

The chemical treatment methods are used to both facilitate the complete breakdown of hazardous waste into non-toxic gases and more usually, to modify the chemical properties of the waste e.g. to reduce water solubility or to neutralize acidity or alkalinity.

Biological Treatment Process

Many industrial wastes are treated by biological methods similar to those used for sewage treatment. Hazardous waste is occasionally amenable to such treatment, even though the concentrations of toxic materials present are often lethal to micro-organisms. Major industrial users of land treatment have included petroleum refining, industrial organic chemicals, petroleum production, plastic materials, residues and paints and allied products.

Hazardous Waste Treatment Facility

The choice of appropriate technology for treatment of hazardous waste should be based on the concept of “best practicable means”. The owner or operator of a hazardous waste management facility should have a sufficient knowledge of waste characteristics expected and treatment technologies required, so as to decide the best practicable technology for the waste. The detailed design of the treatment facility including the technologies should be submitted to the regulatory authorities for their approval.

The treatment and disposal of hazardous waste in a centralized facility depends upon the types of wastes received. However, any centralized facilities need to have certain minimum facilities for storage, treatment and disposal. Extensive planning is required to enable a venture providing centralized hazardous waste treatment to be profitable and environmentally sound. The planning process for such a facility is complex and is a project in itself. The process is not straightforward because many of the issues are dependent on each other. The process is also costly and time consuming. The planning process identifies the three main issues that affect profitability—commercial, technical, and financial issues. All of these issues are regulatory driven and affect profitability. One of the most important elements of a hazardous waste treatment facility is a revenue stream, meaning sufficient hazardous waste to sustain a profitable operation.

Affordability of treating hazardous waste is a major concern to the generator. The proper treatment and disposal of hazardous waste will increase the generator’s product cost, and this increase should be treated as an operating cost. The cost of treatment/disposal can be minimized by the generator’s operating procedures, including waste minimization and recycling.