References

References:

1. Rao M.N. and Dutta, Waste Water Treatment, Oxford and IBM Publications Ltd.
2. Eckenfelder, WW., Industrial waste Pollution control. Me Graw Hill Book Co.
3. C.S Rao, Environmental Pollution Control Engineering, Wiley Eastern Ltd., New Delhi.
4. M.N. Rao, H. V.N. Rao, Air Pollution Control, Tata McGraw Hill
5. Sincero and Sincere, Environmental Engineering, Prentice hall of India.
6. Kelley,Environmental Engineering, McGraw Hill Publication.
7. NPTEL video lecture by Dr. Ligy Philip
8. Industrial waste management web notes by I W M Srinivas (GITAM university
9. Handbook of water and wastewater treatment technologies - Nicholas P. Cheremisinoff, Butterworth-Heinemann publications
10. Waste treatment in the process industries - edited by Lawrence K. Wang, Yung-Se Hung, Howard H. Lo, Constantine Yapijakis, CRC press
11. Waste to resources: A waste management handbook, The Energy Resources Institute, 2014
12. Lectures and presentations by Dr. Shrikant Jahagirdar, Head of Department (Civil Engineering) at NKOCET, Solapur, Maharashtra
13. An introduction to stack sampling - Wallace, Saskechewan Research Council 2013
14. Treatment of waste generated from waste generated from cement industry - Kuldeep Sharma, Ujjwal Jain, Anupam Singhal, BITS Pilani
15. Guidelines for abatement of waste from textile industry, Rajasthan State Pollution Control Board
16. Textile dyeing wastewater treatment - Zongping Wang, Miaomiao Xue, Kai Huang and Zizheng Liu, Huazhong University of Science and Technology, China published by InTechOpen
17. Industrial wastewater treatment - Rein Munter
18. "Parivesh" A newsletter from ENVIS center, CPCB
19. Physico-chemical analysis of wastewater from cement units - D. Freeda Gnana Rani, K. Arunkumar, & S.R. Sivakumar, Jr. of Industrial Pollution Control - Enviromedia
20. Hazardous Material (Management, Handling and Transboundary movement) Rules published by Government of India, MoEF
21. Industrial Waste Treatment Handbook - Frank Woodard
22. Industrial Wastewater Treatment - NG Wun Jern, Imperial College Press
23. Industrial wastewater - UNESCO - Encyclopedia Of Life Support Systems
24. Industrial wastewater - Abdulrzzak Alturkmani
25. Liquid waste from industry - theories, practice and treatment - Numersorn N.L
26. Handbook of water and wastewater treatment plant operations - Frank R. Spellman, Lewis publishers

Generalised EIA process flowchart

Manufacturing processes & Wastewater characteristics for Cement industry

Manufacturing processes & Wastewater characteristics for Cement industry
The major contaminant from cement industry is SPM and RSPM in the form of dust due to mining and grinding operations involved in the process. Hence, cement industries contribute to air pollution and virtually zero water pollution.
Cement is a compound madeup of

• calcium oxide and 
• silicon dioxide along with 
• aluminium oxide, 
• ferric oxide and 
• magnesium oxide. 

 Raw materials required for the manufacture of cement are

• lime
• sand
• clay
• shale
• iron ore and
• blast furnace slag

In order to manufacture cement, the raw materials are passed through the following six phases:

• Raw material extraction / Quarrying
• Grinding, Proportioning and blending
• Pre-heater phase
• Kiln phase
• Cooling and final grinding
• Packing and shipping

Several cement plants have made a sustained effort in controlling and regulating emissions by using air pollution control devices like electrostatic precipitators and bag filters. Fugitive emissions in cement plants is still a problem

• In cement industries, water is used only for cooling operation of manufacturing operation. Process wastewater with high pH and suspended solids may be generated in some operations. Water used for cooling is recycled and reused. Screening along with settling basin and clarifier is used for reduction of suspended solids. Treated water from wastewater treatment plant is used for development of green belt which helps in reducing noise pollution. Storm water flowing through pet-coke, coal and waste material stock piles exposed to the open air may become contaminated with high amount of sulphates, toxic metals like zinc, lead and chromium present in dust. Contaminated water from cement manufacturing industry may leach into the ground and contaminate groundwater with excessive TDS.
• The major sources of contaminants in water due to cement industry are:

1. Cooling water and
2. Wet scrubbing of kiln dust that yields an effluent with a high 
1. pH value
2. Alkalinity
3. Suspended and dissolved solids like sulphates and potassium

The flowchart for manufacturing process in the cement industry is shown below:

Manufacturing processes & Wastewater characteristics for Distilleries

Manufacturing processes & Wastewater characteristics for Distilleries

Manufacturing processes & Wastewater characteristics for Sugar industries

Manufacturing processes & Wastewater characteristics for Sugar industries
The process of manufacturing sugar involves the following processes:

1. Growing and harvesting cane
2. Cane preparation for milling
3. Milling
4. Clarification
5. Evaporation
6. Crystallization
7. Centrifugation
8. Drying
9. Refining

Beet sugar processing is similar except that it is done in one continuous process. Sugar beets are washed, sliced and soaked in hot water to separate the sugar containing juice from the beet fiber. The sugar laden juice is then purified, filtered, concentrated and dried in a series of steps similar to cane sugar processing. The process flowcharts are shown below:

Manufacturing processes & Wastewater characteristics for Fertilizer industry

Manufacturing processes & Wastewater characteristics for Fertilizer industry

Manufacturing processes & Wastewater characteristics for Thermal power plants

Manufacturing processes & Wastewater characteristics for Thermal power plants

Manufacturing processes & Wastewater characteristics for Steel plants

Manufacturing processes & Wastewater characteristics for Steel plants

Manufacturing processes & Wastewater characteristics for Textile industry

Manufacturing processes & Wastewater characteristics for Textile industry
Two types of wastes are generated in textile industries.
1. Process chemicals and
2. Process wastes
The nature of the waste generated depends on:
1. Type of textile facility
2. Processes and technologies and
3. Types of fibers and chemicals

Little or no wastewater is generated during the process of fiber preparation and yarn spinning
During slashing and sizing operations, the wastewater generated contains BOD, COD, metals, cleaning waste and size.
During weaving, knitting and tufting processes little or no wastewater is generated
Wastewater from desizing operations contains BOD from water soluble sizes, synthetic size, lubricants, biocides and anti-static compounds.
Wastewater from scouring operations contains disinfectants and insecticide residues, NaOH, detergents, fats, oils, pectin, wax, knitting lubricants, spin finishes and spent solvents
Bleaching process wastewater mainly contains hydrogen peroxide, sodium silicate and organic stabilizer and has a high pH
Singeing process yields little or no wastewater.
Mercerizing process in textile mills yields wastewater containing high pH and NaOH.
Little or no wastewater is generated during heatsetting processes
The dyeing process generates wastewater containing metals, salts, surfactants, toxics, organic processing assistants, cationic materials, colour, BOD, COD, sulphide, acidity, alkalinity and spent solvents
Printing process in textile industry produces wastewater containing suspended solids, urea, solvents, colour, metals, BOD, heat and foam
Finishing process in textile industry contains BOD, COD, suspended solids, toxics and spent solvents.
Finally, product fabrication produces little or no wastewater

Wastewater from the textile industry is classified into:
1. Dispersible wastes
Such wastes are highly dispersed and mixed with other wastes
2. Hard to treat wastes
Such wastes resist treatment and contain non biodegradable or inorganic substances that cannot be removed by conventional biological treatment methods
3. High volume wastes
Such wastes mainly contain wash water, alkaline waste and warp sizes
4. Hazardous or toxic wastes
Such wastes are a sub-group of hard-to-treat wastes. They contain metals, chlorinated solvents and non-degradable surfactants.

Acute toxicity of textile dyes leads to skin irritation, vomiting and diarrhea. Reactive dyes cause respiratory and skin problems.
The BOD/COD ratio of composite wastewater is around 0.25 implying that the wastewater contains a large amount of non-biodegradable organic matter.


In the primary treatment, the following sequence of operations is carried-out:
1. Screening
2. Sedimentation
3. Equalization
4. Neutralization
5. Chemical coagulation and
6. Mechanical flocculation
Screening and sedimentation helps remove organic color, suspended solids along with primary reduction of BOD and COD.
The conventional treatment is a physico-chemical treatment followed by a biological treatment system.
Sedimentation is sometimes combined with the equalization process.
Textile effluents are highly variable in terms of pH and extent of impurities
Individual process effluents affect the secondary treatment process due to the extreme variation in chemical characteristics from effluents from other processes. Hence, they are collected in a big tank and stirred continuously by rotating agitators or blowing compressed air from below. The tank has a conical bottom for enhancing the settling procces. Dilute sulphuric acid and boiler flue gas which is rich in carbondioxide is commonly used for neutralisation of alkaline effluents from neutralization. Chemical coagulation and mechanical flocculation are used to remove finely divided suspended solids and colloidal particles that cannot be removed by simple sedimentation by gravity.
Secondary treatment consists of aerated lagoon, trickling filter, activated sludge process and an oxidation pond. In this process, the dissolved and residual organic matter is removed in the aerobic or anaerobic mode. This is achieved by the digestive action of bacteria under suitable conditions. This helps to reduce the COD, BOD and toxicity.
Sometimes, an activated adsorption system along with an ozonation unit is used instead of biological treatment process.
The tertiary treatment process involves the following techniques:
Oxidation
Electrolytic precipitation and foam fractionation
Membrane technologies
Electrochemical processes
Ion exchange
Photocatalytic degradation
Adsorption and
Thermal evaporation

Adsorption is the most commonly used method for dye removal. It can also be used to remove toxic chemicals such as pesticides, phenols, cyanides and organic dyes.
It is an expensive process and the adsorbent should be re-activated resulting in 10 – 15 % loss of sorbent.
Other techniques used are:
1. Ion exchange
2. Membrane filtration
1. Activated carbon filter
2. Micron filter
3. Reverse osmosis
4. Post carbon filter
5. Ultraviolet light
Electrodialysis
Distillation
Advanced oxidation processes
Ozonation / UV radiation
Hydrogen peroxide / UV radiation

Hydrogen peroxide and ozone

Environmental legislation related to industrial effluents and hazardous wastes

Environmental legislation related to industrial effluents and hazardous wastes
The Hazardous Wastes (Management and Handling) Rules, 1989 came into effect on 28th July, 1989. These rules shall apply to hazardous wastes as specified in schedule and exclude waste water and exhaust gases as covered under the provisions of the Water act of 1974 and Air act of 1981. It also excludes wastes arising out of the operation from ships beyond five kilometres and  radio-active wastes. The following are the salient features under this act:

1. The occupier generating hazardous wastes specified in the Schedule in quantities equal to or exceeding the limits mentioned, shall take all practical steps to ensure that such wastes are properly handled and disposed of without any adverse effects which may result from such wastes and the occupier shall also be responsible for proper collection, reception, treatment, storage and disposal of these wastes either himself or through the operator of a facility.
2.  The occupier or any other person acting on his behalf who intends to get his hazardous waste treated shall give to the operator of a facility, such information as may be specified by the State Pollution Control Board.
3. The State Pollution Control Board may cancel an authorisation issued under these rules or suspend it if the authorised person has failed to comply with any of the conditions after giving the authorised person an opportunity to show cause and after recording reasons thereof.
4. Packaging, labelling and transport of hazardous wastes shall be in accordance with the provisions of the rules issued by the Central Government from time to time.
5.  The State Government shall undertake a continuing programme to identify the sites and compile and publish periodically an inventory of disposal sites within the State for the disposal of hazardous wastes.
6. The State Government shall undertake a continuing programme to compile and publish an inventory of sites within the State at which hazardous wastes have at any time been stored or disposed of and such inventory
7. The occupier generating hazardous waste and operator of a facility for collection, reception, treatment, transport, storage and disposal of hazardous waste shall maintain records of such operations in forms specified
8. The occupier and operator of a facility shall send annual returns to the State Pollution Control Board in forms specified
9. Where an accident occurs at the facility or on a hazardous waste site or during transportation of hazardous wastes, the occupier or operator of a facility shall report immediately to the State Pollution Control Board about the accident in forms specified.
10. The CPCB also sets guidelines regarding import of hazardous wastes.

Under the Air (prevention and control of air pollution) Act, 1981, 

1. State boards may lay down standards for emissions of air pollutants from industrial units
2. State boards should examine manufacturing process and pollution control equipment to verify if they meet standards prescribed
3. State board can advise the state government to declare heavily polluted areas as pollution control areas
4. Operation of Industrial unit is prohibited in heavily polluted areas without the consent of the central board.
5. Violation of this law is punishable with imprisonment a term which may extend to three months or fine upto Rs. 10,000 or both.

Water act came into effect in 1974 to prevent pollution of water by industrial, agricultural and household water.

Under the Water (prevention and control of air pollution) Act, 1984,

1. The water act is designed to assess pollution levels and punish polluter
2. The central government and state governments have set-up pollution control boards to monitor water pollution.
3. Central and state boards have been created under this act for preventing water pollution The act empowers the board to take:           -  water samples for analysis, govern discharge of sewage, trade effluents, study or inspect appeals, revision of policies, set minimum and maximum penalties, publication of names of offenders, offences by companies or government departments, establish or recognize water testing laboratories and standard testing procedures. Prevention and control of water pollution is achieved through a 'permit' or a 'consent administration' procedure

In addition to the above, the government has also enacted the water pollution cess act in 1977 requiring industrial consumers to pay cess depending on the type of use as listed below:

1. Industries using water for industrial cooling, spraying in mine pits or as boiler feed
2. Domestic purposes
3. Processing (pollutants are biodegradable. Eg: water from slaughter houses)
4. Processing (pollutants are not biodegradable and are toxic. Eg: water from tannery waste, industrial wastewater from electroplating industries)

Industries that have a treatment plant installed for treating their effluents can get a rebate of 70% on the cess payable.

Issues related to rehabilitation and resettlement of displaced communities

Issues related to rehabilitation and resettlement of displaced communities

Preparation of EIAs of road project, industry and dam

Preparation of EIAs of road project, industry and dam

EIA for road project
As per the EIA notification of 14th September 2006 and its amendment dated 1st December 2009,

highway projects are divided into two categories as mentioned below :

1. Highways New National Highways & Expansion of National Highways greater than 30 km,involving additional right of way greater than 20m involving land acquisition and passing through more than one State come under category A.
2. All state highway projects State highway expansion projects in hilly terrain (above 1,000 m AMSL) and or ecologically sensitive areas come under category B.

Any project or activity specified in category B will be treated as category A, if located in whole or in part within 10 km from the boundary of:

• Protected area identified by wildlife act
• Critically polluted areas as identified by CPCB
• Eco-sensitive areas identified by Environment (Protection) Act

The environmental clearance process for all projects will comprise a maximum of four stages. These four stages in sequential order are:

1. Screening that entails the scrutiny of an application seeking prior environmental clearance to determine whether or not the project or activity requires further environmental studies for preparation of an Environmental Impact Assessment (EIA) for its appraisal prior to the grant of environmental clearance depending upon the nature and location specificity of the project.
2. Scoping’ refers to detailed and comprehensive TOR addressing all relevant  environmental concerns for the preparation of an EIA report.
3. “Public consultation” refers to the process by which the concerns of local affected persons and others. After completion of the public consultation, the applicant shall address all the material environmental concerns expressed during this process, and make appropriate changes in the draft EIA and EMP.
4. Appraisal involves detailed scrutiny of the application and other document like the Final EIA report, outcome of the public consultations including public hearing proceedings, submitted by the applicant to the regulatory authority concerned for grant of Environmental Clearance (EC).

In terms of the EIA notification of the MOEF dated 14th September 2006, the structure of the EIA document shall be as listed below:

• Introduction
• Project Description
• Analysis of Alternatives (Technology and Site)
• Description of the Environment
• Anticipated Environmental Impact & Mitigation Measures
• Environmental Monitoring Program
• Additional Studies
• Project Benefits
• Environmental Cost Benefit Analysis
• Environmental Management Plan
• Summary & Conclusion
• Disclosure of Consultants engaged

EIA for building industry

The EIA Notification, 2006 is to set procedures of environmental clearance before establishment of identified nature and size. The suitability of site for a proposed development is one of the main concerns in awarding an environmental clearance to a project.

A project is considered B category if the built-up area is between 20,000 and 150,000 sq. m. or a township area greater than 50 ha or built-up area greater than 150,000 sq. m.

Any project or activity specified in category B will be treated as category A, if located in whole or in part within 10 km from the boundary of:

Protected area identified by wildlife act

Critically polluted areas as identified by CPCB

Eco-sensitive areas identified by Environment (Protection) Act

The prior environmental clearance granted is valid for a period of five years. The regulatory

authority concerned may extend this validity period by a maximum period of five years provided

an application is made to the regulatory authority by the applicant within the validity period

The structure of the EIA document listed below:

1. Introduction
2. Project Description
3. Description of the Environment
4. Anticipated Environmental Impacts & Mitigation Measures
5. Analysis of Alternatives (Technology and site)
6. Environmental Monitoring Programme
7. Additional Studies
8. Project Benefits
9. Environmental Management Plan
10. Summary & Conclusion
11. Disclosure of Consultants engaged

EIA for dam
An EIA for a dam project should discuss the following:

1. Location of the project, characteristics of the dam, total land area required, catchment area above the dam site,storage capacity and total cost of the project
2. It should clearly state  the need for the project
3. Based on facts and the guidance manual provided by the MoEF, the project should be classified as category A or category B enabling the decision makers to opt for a Rapid EIA (REIA) or a Comprehensive EIA (CEIA)
4. The study comprises of the following five stages
1. Determination of baseline conditions
2. Identification of differ

Preparation of EMP

Evaluation of Impacts

Evaluation of Impacts

Baseline data collection required for EIA

Baseline data collection required for EIA
Baseline data collection refers to collection collection of baseline information information on biophysical biophysical, social and economic aspects of a project area.
Project area is defined as the area where environmental environmental effects effects and impacts impacts are felt during construction or operational stages of a project.

Collection of baseline information serves two purposes: 

• It provides a description of the status and trends of environmental factors (e.g., air pollutant concentrations) against which predicted changes can be compared and evaluated in terms of importance.
• It provides a means of detecting actual change by monitoring once a project has been initiated.

Major environmental environmental parameters parameters to be considered in field are:

• Physical: topography, geology, soil types, surface and ground water condition, watershed condition, pollution levels etc.
• Biological: terrestrial and aquatic ecosystems, types flora and fauna, environmentally environmentally sensitive sensitive wetlands wetlands, prime agricultural land etc
• Socio‐economic: demography, development needs and potential, infrastructure facilities, economic activities etc.
• Cultural: location and state of archeological, historical, religious sites

DATA SOURCES AND METHODS OF COLLECTION
Primary Sources: Result of the field and laboratory data collected and analyzed directly
Secondary sources: Data collected indirectly from published records or documents such as project documents, village proFlie, maps,photos, internet sources etc

Methods of data collection:

1. General methods: Literature review, map interpretation, checklists (e.g. scaling and questionnaire checklists, matrices etc)
2. Resource‐based methods: methods: Scientific Scientific instruments instruments and techniques techniques(inventory, species area curve, sampling techniques, PRA, RRA)

Data Processing
Raw data is converted into knowledge and information that is more easily comprehensible. Tools such as tables, graphs, maps can be used for presentation.

1. For physical data: graphs, tables, enumeration
2. For biological data: species numbers, volume, density, biomass can be calculated.
3. Species diversity (No. of species/Area sampled) can also be used for processing processing biological biological data calculated calculated through through species richness of an area.
4. Socioeconomic data: Data such as male/female male/female, skilled/semi skilled/semi skilled skilled labor force for construction and operational activities can be presented through, graphs, tables, population pyramids etc. which can be collected through sampling (random, stratified or mixed).

Baseline studies in EIA may take a long time, hence EIA is blamed for higher costs and delays in project implementation.
Therefore, the studies should be focused on those aspects that are likely to be affected.
Four critical points exist project implementation

1. Decision on Project Project Approval Approval
2. Decision on the Location of Project
3. Decision on the Project Design
4. Decision on the Operation of Project

Methods of EIA

Methods of EIA

Listed below are the important methodologies for assessing the impacts of any developmental activity on the environment:

1. Adhoc method
2. Checklist method
3. Matrix method
4. Network method
5. Overlay method
6. Environmental index using factor analysis
7. Cost/Benefit analysis
8. Predictive or Simulation methods

These methods might vary from:
Simple to Complex
Static piece-meal approach to Dynamic nature of the environment

The change in EIA is moving away from a simple listing of potential impacts to complex modes involving identification of feedback paths leading to higher order impacts as compared to the easily visible first order impacts involving uncertainities. This approach can be considered as an overall management technique requiring different

kinds of data in different formats along with varying levels of expertise and technological inputs to accurately forecast the results of any planned development.

1. Ad hoc methods

Ad hoc methods indicate broad areas of possible impacts by listing composite environmental parameters (Ex: flora and fauna) likely to be affected by the proposed activity.
These methods involve assembling a team of specialists who identify impacts in their area of expertise. Here, each parameter is considered separately and the nature of impacts (long term or short term, reversible or irreversible) are considered.
These methods give a rough assessment of total impact while giving the broad areas and the general nature of possible impacts. In this method, the assessor relies on an intuitive approach and makes a broad-based qualitative assessment. This method serves as a preliminary assessment and helps in identification of important areas like:

• Wildlife
• Endangered species
• Natural vegetation
• Exotic vegetation
• Grazing
• Social characteristics
• Natural drainage
• Groundwater
• Noise
• Air quality
• Visual description and services
• Open space
• Recreation
• Health and safety
• Economic values and
• Public facilities

Types of Ad hoc method are:

• Opinion poll
• Expert opinion and
• Delphi methods

This method is very simple and can be performed without any training. It does not involve any relative weighting  or any cause-effect relationship.
It provides minimal guidance for impact analysis while suggesting broad areas for possible impacts. Moreover, it does not even state the actual impacts on specific parameters that will be affected.
The drawbacks of this method are listed below:

1. It gives no assurance that a comprehensive set of all relevant impacts have been studied
2. Analysis using this method lacks consistency as it different criteria are selectively evaluated by different groups
3. It is blatantly inefficient as it requires a considerable effort to identify and assemble a panel for each assessment.

2. Checklist method
In this method, environmental factors are listed in a structured format by giving importance weightings for factors and application of scaling techniques for impacts of each alternative.
Checklists are strong indicators of impact identification. They effectively garner the attention and awareness of their audience. Impact identification is a fundamental function of an EIA. Checklists may be:

1. Simple
2. Descriptive
3. Scaling or
4. weighting type

Simple checklists are a list of parameters without guidelines regarding either interpretation or measurement of environmental parameters or specific data needs or impact prediction and assessment.

Descriptive checklists  include list of environmental factors along with information on measurement, impact prediction and assessment.

Scaling and weighting checklists facilitate decision making. Such checklists are strong in impact identification. While including the function of impact identification, they include a certain degree of interpretation and evaluation. The aforementined factors make these methods attractive to decision-making analysis.
However, the scaling and weighting methods are subjective and hence pose the danger of imparting equal importance to every impact. Another defect observed by critics is that numerical values assigned to impacts can be derived on the basis of expert knowledge and judgement alone.
Scaling and weighting checklist techniques quantify impacts reasonably well although they use subjective extimates. However, they make no provision for assessing dynamic probabilistic trends or mitigation, enhancement and monitoring programmes. These methods cannot identify higher order effects, impacts and interactions.

Simple and descriptive checklists simply identify the possible potential impacts without any rating regarding their relative magnitudes.

Scaling and weighting checklists remove decision making from the hands of decision makers while they impart a single number to various inherently different impacts and this aspect prevents the decision maker to consider the possibility of trade-offs.

In checklist method, the impacts are tabulated in the form of cells with information either in the descriptive form that gives information regarding possibility or potential existence of an impact whereas in the scaling or weighing methods the magnitude or importance of impact is given. Sample checklists or weighing methods used in EIA are shown below:

The advantages of this method are:

1. It is simple to understand and use
2. It is good for site selection and priority setting

Disadvantages of this method are:

1. It does not distinguish between direct and indirect impacts
2. It does not link action and impact
3. It is cumbersome at times

3. Matrix Method
This methodology provides a framework of interaction of different activities of a project with potential environmental impacts caused by them. A simple interaction matrix is formed when project actions are listed on one axis (usually vertical) and environmental impacts are listed along the other axis. This technique was pioneered by Leopold et al in 1971. It lists about 100 project actions and about 88 environmental charateristics and conditions. An example of this matrix is shown below:

Similarly, a sectoral matrix is shown below:

• The advantage of the matrix method is that it links action to impact
• This is a very good method for displaying EIA results

The disadvantages of this method are listed below:

• It is difficult to distinguish between direct and indirect impacts using this method
• There is potential for double-counting of impacts
• It is qualitative in nature and does not refer to quantity of impact

4. Network method:

• This method uses the matrix approach and extends it to include both the primary as well as the secondary impacts
• It is shown in the form of a tree called impact tree. This diagram is also called as reference or sequence diagram
• Identification of direct, indirect along with short, long term impact is a crucial and basic step of making an impact tree
• The impact tree is used to identify cause-effect linkages
• The impact tree is a visual description of linkages
• The diagram below shows the example of a network analysis:

The advantages of the network method are:

• It links action to impact
• It is useful to check second order impacts in a simplified form
• It handles direct and indirect impacts

The disadvantages of this method are:

• It becomes overly complex if used beyond simplified version
• It is completely qualitative in nature

5. Overlays

• This method depends on a set of maps of a project area's environmental characteristics covering physical,  social, ecological and aesthetic aspects
• It enables separate mapping of critical environmental features at the same scale as project's site plan (Ex: wetlands, steep slopes, soils, floodplains, bedrock outcrops, wildlife habitats, vegetative communities, cultural resources, etc)
• In the old technique, environmental features were mappped on transparent plastic in different colours
• Modern technique of the same activity is done using computer software, hardware, data and skilled people. It is called GIS (Geographic Information Systems)

The advantages of this method are:

• It is easy to understand and use
• It has a good display and
• It is good for setting site selection

The disadvantages of this method are:

• It addresses only direct impacts
• It does not address impact duration or probability

Capabilities and limitations of EIA

Capabilities and limitations of EIA

CAPABILITIES OF EIA
The capabilities of an EIA are listed below:

• An EIA is capable of establishing baseline data (concerning social, physical and biological parameters) before starting any development activity
• An EIA enables the government and public at large to evaluate the benefits of the project versus the environmental degradation or modification
• An EIA also enforces regular monitoring to ensure that the project is not damaging the environment  beyond repair
• An EIA is capable of informing the public at large regarding any development activity in an environmentally sensitive area thereby causing public outcry enabling the government to terminate any project with vested interests that damages the livelihood of people (tribes sustaining on the environment).
• An EIA guides the project proponent to study the environment and propose the needed modifications to mitigate the adverse effects of any development activity

LIMITATIONS OF EIA
EIA suffers from the following limitations

• EIA should be undertaken at the project level but it is undertaken at the policy and planning level
• Range of project alternatives inthe project EIA is small
• There is no defined criteria to determine what type of projects undergo an EIA thereby requiring unnecessary expenditure and delay
• Lack of comprehensive environment information base, limitation  of time, manpower and financial resources
• More research and development of improved methodologies is required to overcome limitations related to uncertainities in data
• EIA reports are extremely academic, bureaucratic and lengthy containing too many tables of collected data without data analysis, interpretation and environmental implications
• In actual practice, EIA ends immediately after project clearance and no follow-up action is taken
• It does not incorporate strategies of preventing environmental intervention.
• Project EIAs are limited to the projects direct impacts and this leads to ignoring wide range of impacts including:
• Cumulative impacts
• Global impacts
• Indirect, secondary or induced impacts
• Synergistic impacts

 Finally, the issue of resource conservation, waste minimization, bye-product recovery, and improvement of efficiency of equipment need to be pursued as the explicit goal of EIA.

Objectives of EIA

Objectives of EIA:
EIA is a process that envisions several objectives which are  described below:

• EIA facilitates decision making: EIA provides a systematic systematic investigation of the environmental implications of a proposed project alongwith the suggested alternatives before a decision is taken. The decision along with documents related to the planned activity is called Environmental Impact Statement.
• EIA helps in development: EIA provides a framework for considering location, design and environmental issues together. It helps formulate actions along with indicatons where the project can be modified to eliminate or minimize the adverse effect on the environment. By considering environmental impacts at an early stage in the development activity helps to develop an area in an environmentally sensitive manner. EIA helps improve relations between developer, the planning authority and the local communities.
• An EIA is an instrument for sustainable development: Sustainble development mainly includes
• Maintenance of overall quality of life (QOL)
• Maintainance of continuing access to natural resources.
• Avoidance of extended environmental consequences.

 An EIA can:

• modify and improve design
• ensure efficient resource use
• enhance social aspects
• identify key impacts and measures for mitigating them
• inform decision-making and condition-setting
• avoid serious and irreversible damage to the environment
• protect human health and safety

Streeter-phelps equation

Need for EIA

Need for EIA

• Every anthropogenic activity has some impact on the environment which is often harmful to the environment.
• However, mankind as it is developed today cannot live without taking up these activities for his food, security and other needs. 
• Hence, there is a need to harmonise developmental activities with the environmental concerns. 

Environmental impact assessment (EIA) is one of the tools available with the planners to achieve the above-mentioned goal.

It is desirable to ensure that the development options under consideration are sustainable.
In doing so, environmental consequences must be characterised early in the project cycle and accounted for in the project design. The need or objective of EIA is to foresee the potential environmental problems that would arise out of a proposed development and address them in the project's planning and design stage. The EIA process should then allow for the communication of this information to:

• the project proponent;
• the regulatory agencies; and,
• all stakeholders and interest groups

EIA integrates the environmental concerns in the developmental activities right at the time of initiating for preparing the feasibility report. In doing so it can enable the integration of environmental concerns and mitigation measures in project development.

EIA can often prevent future liabilities or expensive alterations in project design.

Prediction of impacts

PREDICTION OF IMPACTS

An interdisciplinary approach helps in evaluating the impacts of an activity on the potential consequences that may be:

1. Long-term or short-term
2. Direct and indirect
3. Secondary, individual and cumulative
4. Beneficial and adverse

Environmental issues are interdisciplinary, interactive, biological and probablilistic. Indirect or secondary effects can be ignored as they are distant with regard to time from the actual proposed project. Impact prediction and assessment is a major step in environmental assessment process. It involves projection of environmental setting in the future without the proposed action and predicting the impact and assessing the consequences.

The possible changes in the various components of the environment are predicted below:

• Air - degradation due to emissions released and their effect on human beings and the surroundings. Effects of excessive noise due to the project
• Water - degradation of the quality of water and its effect on aquaculture potential and aesthetics of the ecosystem, depletion of groundwater, pollution of nearby water-body by hazardous and toxic substances, effect of temperature and siltation capacity.
• Solid waste - Excess generation of solid wastes cause stress on existing environment
• Vegetation - Destruction of forest cover, depletion of cultivable land, changes in biological productivity, changes in species diversity and rapid disappearance of important species.
• Energy & natural resources - Impact on energy sources in the area due to thermal power generation, natural gas consumption and their effect on local natural resources.
• The action of natural disasters like floods, Earthquake, depositions, stability and air movements.
• Effects on soil and local geology in the form of changes in their physico-chemical characteristics along with an effect on the stability of soil.
• Adverse effects due to man-made facilities and activities like built structures, utility networks, transportation and waste disposal
• Disruption in food chain and spread of diseases due to vectors.

Human aspects affected due to project activities are listed below:

• Economical and occupational aspects involve displacement of population, reaction of population to employment opportunities, services and distribution patterns and change in property values
• Social pattern is affected due to resettlement, rural migration, population density, food, housing, material goods. Another factor to be considered in social pattern is  type of living which can be nomadic or settled, pastoral clubs, recreation, rural or urban lifestyle.
• Social amenities and relationships that are affected by project activities include: family life style, schools, transport, community feelings, disruptions, language spoken, hospitals, clubs and neighbours
• Psychological features include involvement, expectations, stress, work satisfaction, challenges, national or community pride, freedom of chores, company or solution, mobility
• Physical amenities include national parks, wildlife, art galleries, museums, beauty, landscape, wilderness, quiet, clean air and water
• Health includes established medical standards and availability of medical services
• Personal security refers to freedom from molestation and natural disasters
• Regional and traditional belief refers to symbols, values and taboos
• Technology refers to security hazards, safety measures and decomissioning of wastes, congestion and density
• Cultural aspects refer to leisure, fashion and new values
• Political aspects refer to authority, decision making and resource allocation
• Legal aspects are restructuring administrative management, changes in taxes and public policy
• Aesthetic aspects could be visual physical changes, moral conduct and sentimental values
• Statutory laws refer to air and water quality standards, nation building acts and noise abatement bye-laws.

Control of SPM by equipment (gravitation, centrifugation, filtration, scrubbing, electrostatic precipitation)

CONTROL OF SUSPENDED PARTICULATE MATTER BY EQUIPMENT
Suspended Particulate Matter is a collective name given to fine liquid or solid particles added to the atmosphere by processes in the Earth's surface. A few examples of particulate matter are dust, soot, smoke, fumes, mist, pollen, soil particles, etc. SPM may be further classified into RSPM and TSPM based on the average size of particles.
RSPM refers to Respirable Suspended Particulate Matter and it is of size small enough to enter the respiratory tract of human beings and damage the lungs. The average size of RSPM is of the order of 0.1 microns or less.
Particulate matter generates from natural sources like volcanoes, salt sprays, dust storms, grassland fires and living vegetation. Man made sources of SPM is primarily burning of fossil fuels for vehicles, operation of power plants, industrial operations and coal combustion for heating homes and supplying energy.
The composition of SPM depends upon the source. Wind blown mineral dust is composed of mineral oxides and other material blown from Earth's crust. Sea salt is composed of NaCl originates from sea spray.Salt sprays from sea reflect  the composition of sea water and may contain chlorides and sulphates of Magnesium and Potassium. Secondary particles are derived from oxides of primary gases like oxides of Sulphur and Nitrogen. Organic matter may be primary (from anthropogenic or biogenic activities) or secondary (from oxidation of VOCs).
Secondary Organic Aerosols (SOAs) emitted due to internal combustion engines are a danger to human beings.
Control of SPM can be achieved by the equipment listed below.

1. Control of SPM by gravitation 

Equipment used: Gravitational Settling Chamber A typical gravitational chamber is shown below.

• The dust laden gas enters at the inlet and due to the sudden increase in cross-section the particulate matter settles at the bottom and can be removed from the dust hoppers as shown
• The clean gas free from particulate matter exits  from the outlet

IMPORTANT FACTS:

• Simple to construct and maintain
• Efficient to remove particles of diameter greater than 50 mm from gas streams
• They are used as pre-cleaners before passing gases through high efficiency collection devices
• They rely on gravitational settling and are the simplest and oldest mechanical collectors for removal of particulates from gas streams
• Flow within the chamber must be uniform without macroscopic mixing
• Dust removal system must be sealed to prevent production of turbulence due to air from leaking into chamber
• Efficiency of the equipment increases with increased residence time of the waste gas. Hence, the equipment is operated at lowest possible gas velocity
• The size of the unit depends on:
• gas velocity which should preferably be less than 0.3 m/s

ADVANTAGES

• Low capital and energy cost
• Low maintenance and operating costs
• Low pressure drop
• Reliable
• Equipment is not subjected to abrasion due to low gas velocity
• Equipment provides incidental cooling of gas stream
• Temperature and pressure limitations depend on material of construction
• Pollutants are collected in dry state

DISADVANTAGES

• Low particulate matter collection efficiency
• Unable to handle sticky materials
• Large size
• Trays in multiple tray settling chamber may warp under high temperatures.

2.  Control of SPM by centrifugation

Equipment used: Cyclonic separator

Centrifugation is a process that involves the use of centrifugal force for sedimentation of a heterogeneous mixture with a centrifuge. It involves removal of particulates from air, gas or a liquid stream without use of filters with a vortex separation. When removing particulates from a gaseous stream, a gas cyclone is used while a hydrocyclone is used to remove particulates from a liquid stream. This method can also be used to separate fine droplets of liquid from a gaseous stream. 

A high speed rotating air flow is formed in a cylindrical or conical container called a cyclone.

Air flows in a helical pattern from the top to a narrow bottom as show,

 Cyclones use the principle of inertia to remove particulate matter from a gas stream. Several cyclones operating in parallel is known as multicyclone. In a cyclone separator, dirty gas is fed into a chamber where a spiral vortex exists. The large particles hit the inside walls of the container and drop down into the collection hooper. The clean flue gas escapes from the top of the chamber. Cyclones can be used efficiently to remove particles of size 10 microns or more. High efficiency cyclones can remove particles of dimeter as small as 2.5 microns. They are the least expensive of all particulate collection devices. They are used as rough separators before the gas is passed through fine filtration systems. Their efficiency is between 50-99%. Cyclone separators work best on flue gases that contain large amount of big particulate matter. 

ADVANTAGES:

• Cyclones are less expensive to install or maintain as they do not contain any moving parts
• It is easy to dispose particulate matter as it is collected in the dry state
• Space requirement is very less

DISADVANTAGES:

• They are not efficient in collecting particulate matter smaller than 10 microns
• They cannnot handle sticky material

3.   Control of SPM by filtration

In a fabric filter system, a stream of the polluted gas is made to pass through a fabric that filters out the particulate pollutant and allows the clear gas to pass through. The particulate matter is left in the form of a thin dust mat on the insides of the bag. This dust mat acts as a filtering medium for further removal of particulates increasing the efficiency of the filter bag to sieve more sub mi­cron particles (0.5 µm).

A typical filter is a tubular bag which is closed at the upper end and has a hopper attached at the lower end to collect the particles when they are dislodged from the fabric. Many such bags are hung in a baghouse. For efficient filtration and a longer life the filter bags must be cleaned occasionally by a mechanical shaker to prevent too many particulate layers from building up on the inside surfaces of the bag. A typical bag house filter is shown in the figure below.

ADVANTAGES:

• Bag filter is a high quality performance instrument to effectively control particulate emissions and its efficiency is as high as 99%
• Collection efficiency is not affected by sulphur content in fuel
• It is not sensitive to particle size distribution
• It does not require high voltage
• It can be used to collect flammable dust
• Special fiber or filter aids can be used to sub-micron level smoke and fumes

DISADVANTAGES:

• Fabric life is reduced due to presence of highly acidic or alkaline atmospheres, especially at high temperatures
• Maximum operating temperature is 500 F
• Collection of hygroscopic materials or condensation of moisture can lead to fabric plugging, loss of cleaning efficiency and large pressure losses.
• Certain dusts may require special fabric treatments to aid in reducing leakage or to help in cake removal
• Fabric bags are prone to burning or melting at extreme temperatures.

4.  Control of SPM by scrubbing

A scrubber is a system used to remove harmful materials from industrial exhaust gases before they are released into the environment. The two main ways to scrub pollutants out of exhaust are:

1. Dry scrubbing and
2. Wet scrubbing

In dry scrubbing, harmful components of exhausted flue gas are removed by introducing a solid substance (usually in the powdered form) in the gas stream.

Wet scrubbing involves removal of harmful components from exhaust by spraying a liquid substance through the gas.

Both methods work similarly and perform the same process of removing pollutants. The difference lies in the materials they use to remove the pollutant from the gas stream. By removing acidic gases from the exhaust before it is released into the atmosphere, scrubbers help in the prevent the formation of acid rain.

Scrubbing is sometimes referred to as flue gas desulfurization.

Scrubbing is the most effective technique for the removal of oxides of sulphur and is widely used. Scrubbers remove sulphur oxides from flue gases by passing the gases through a spray of water in a wet scrubber that contains many chemicals, mainly calcium carbonate.
If a dry scrubber is used, the flue gas comes in contact with pulverised limestone. The chemical reaction between suphur dioxide and calcium carbonate yields calcium sulphite. The calcium sulphite either falls out of the gas stream or is removed with other particulates.
Scrubbers are highly efficient and remove almost 98% of sulphur from flue gases. However, they are expensive to maintain and install. They are also energy intensive as the flue gas must be reheated after coming into contact with water vapour in the wet scrubber to make the gas buoyant to exit the smoke stacks.

5.  Control of SPM by Electrostatic precipitator
An Electrostatic precipitator is mainly used to control particulate matter. An Electrostatic precipitator uses electrostatic forces to separate dust particles from exhaust gases. A number of high-voltage, direct-current discharge electrodes are placed between grounded collecting electrodes. The contaminated gases flow through the passage formed by the discharge and collecting electrodes as shown in the figure below.

Air borne particles receive a negative charge as they pass through the ionized field between the electrodes. These charged particles are then attracted to the oppositely charged electrode and stick to it. The collected material is then removed by rapping or vibrating the electrodes. Cleaning the electrodes is done without interrupting the air flow.
The main components of all electrostatic precipitators are:

• a power supply unit to supply high voltage DC power
• ionizing section to impart a charge to the particulates in the gas stream
• an attachment to remove the collected particulates
• a housing to enclose the precipitator zone

The following factors influence the collection efficiency of electrostatic precipitators:

• Larger collection surface areas and lower gas flow rates increase efficiency of electrostatic precipitators due to increased time for the electrical activity to collect the dust particles
• The dust particle migration velocity to the collecting electrodes can be increased by:
• Decreasing gas velocity
• Increasing gas temperature and
• Increasing the voltage field

There are two types of precipitators:

• Single-stage precipitators that combine an ionization and collection step also known as cottrell precipitators. It is mainly used in mineral processing operations.
• Low voltage, two stage precipitators that use a similar principle, but in this case, the ionization section is followed by collection plates. It is mainly used for filtration in air-conditioning systems. 

Electrostatic precipitators may be:

1. Plate precipitators in which particles are collected on flat parallel surfaces about 20 to 30 cm apart with a series of discharge electrodes spaced along the centerline of two adjacent plates. The contaminated particles pass through the passage between the plates and the particles get charged and adhere to the collection plates. The particles are eventually removed by rapping the plates and the dust is collected in the hoppers or bins placed at the base of the precipitator.
2. Tubular precipitators consist of cylindrical collection electrodes with discharge electrodes located on the axis of the cylinder. The contaminated gases flow around the discharge electrode and through the inside of the cylinders. The charged particles are collected on the grounded walls of the cylinder. The collected dust is removed from the bottom of the cylinder. They are generally used for collection of mist or fog or for adhesive, sticky, radioactive or extremely toxic materials.

Gaseous pollutant control by absorption, condensation and combustion

GASEOUS POLLUTANT CONTROL BY

1. AbsorptionGaseous pollutants that are soluble in aqueous liquids can be removed by absorption. Absorption is one of the main mechanisms used for the removal of acid gas compounds. (Ex: Sulphur dioxide, Hydrogen Chloride and Hydrogen Fluoride) Water soluble organic compounds like alcohols, aldehydes and organic acids can also be removed by absorption. 
• The contaminant gas or vapour is absorbed from the gas stream as it comes in contact with the liquid
• All absorption processes operate best when gas and liquid temperatures are low.
• Gas and vapour phase contaminants are most soluble in cold conditions.

The figure below illustrates the removal of pollutants from a gas stream using a scrubbing liquid. This technique explains the removal of gaseous pollutant by absorption

Water can be used for recovery of water-soluble compounds such
as acetone and low molecular weight alcohols, which can later be separated from water using distillation. Additives are often used to increase the effective mass transfer rate of the pollutant from the gas phase into the liquid phase, affecting the surface tension, reducing interfacial resistance and increasing the apparent solubility.

Gas absorption can be expensive, however it is generally used only to recover VOCs that have a secondary market value. Gas absorption techniques are used for the recovery of a variety of chemicals in the coke manufacturing industry. They are often called scrubbers.

2.   Condensation: Condensation and gas absorption are most commonly used for highly concentrated VOC (Volatile Organic Carbon) streams that are advantageous to recover and the relatively large expense is justified. It employs a drop in temperature and/ or increase in pressure to cause the VOCs in the emission stream to condense. The cleaned air stream is separated from the condensate containing target pollutants. In many cases, very large temperature drops are required to achieve effective condensation, requiring significant energy investment to accomplish cooling.

Condensation is used to recover gasoline and fuel vapors at gasoline loading terminals and in gasoline dispensing facilities. It is also used in the adsorbent regeneration process to separate solvents from the stream to separate solvents from the stream used to regenerate the activated carbon.

3.   Combustion: Incineration or combustion is a commonly used technology to control VOCs. Complete combustion of hydrocarbons produces carbon dioxide and water. Flares, thermal oxidisers and catalytic converters use oxidation chemistry to treat VOC emissions. For example, by using catalytic converters, thermal oxidation of by-products of incomplete combustion can be safely achieved at temperatures much lower than what would be required without the aid of catalysts. Sometimes the gases are moved over a bed of copper oxide, which reacts with oxides of sulphur to form copper sulphate. Copper sulphate acts as a catalyst for reducing NOx to ammonia (NH3). Ammonia may be added to flue gas before passing it over a catalyst. The catalyst enables ammonia to react with Oxides of Nitrogen (NOx) converting it into molecular nitrogen and water. Staged combustion processes significantly reduce NOx emissions

Stack sampling and analysis of air pollutants

STACK SAMPLING AND ANALYSIS OF AIR POLLUTANTS

Stack sampling poses a problem due to the varying composition of pollutants in the flue gas thereby making the process of obtaining a representative sample difficult. The important factors in obtaining a representative sample are:

• selection of the sampling site and
• number of sampling points required
• The sampling site should be located at least eight stack or duct diameters downstream and tro diameters upstream from any source of flow disturbance such as bends, fittings or constrictions. The gas stream in a stack is normally under turbulent flow conditions and any flow disturbance causes non-uniform and unstable gas flow profiles along with non-uniform particle concentration patterns.

The above problems can be minimized by providing proper distance so that adequate mixing may occur. Sometimes it is not possible to ensure uniform flow. Hence, multiple samples are used to acquire a representative sample.

• Actual sampling must be performed at a number of points in the stack.
• Two sets of reading, at right angles should be taken at the same plane for circular stacks.
• The traverse points required is at least six or the number of points depends on location of upstream and downstream disturbances.
• For rectangular stacks, the sampling site is located by calculating the equivalent diameter using the equation: D_eq = 4 * Cross-sectional area of flow / Wetted perimeter

Other problems associated with stack sampling are:

• High temperature
• Collection of additional parameters like
  • moisture content
  • pressure
  • temperature
  • flow rate of gas
  • composition of flue gas

Accurate measurements of ALL these factors is essential for valid sampling.

Stack sampling is carried out by diverting part of the gas stream through a sampling train. The sampling train consists of a nozzle, a sampling probe, particulate collection devices, a flow measuring device and a prime mover such as a vaccum pump or an ejector.

The devices used for collection of particulates in gases in stack sampling are:

• Filtration devices
• Devices for wet or dry impingement
• Devices for impaction, electrostatic and thermal precipitation
• Devices for collecting particulates
• Adsorption, Absorption and freeze-out devices for collecting gases.

The technique used for sampling particulate laden gases is called “isokinetic technique”. Under isokinetic conditions, the static pressure at the tip of the probe is equal to the static pressure in the free stream and hence the sampling velocity is equal to the free stream velocity. Under these conditions, the flow pattern in front of the probe is not disturbed.

The process for obtaining a gas sample from a stack is similar to that used in sampling particulates. However, the sampling is easier as it is not necessary to sample under isokinetic conditions.

• Gas sample is withdrawn from stack at a constant rate independent of the flow rate in the stack.
• Precautions to be followed in gas sampling are as follows:
  • Particulate matter must be filtered upstream of collection system to:
    • prevent downstream line plugging
    • minimize loss of gaseous pollutants due to reaction with particulates on cooling
• To minimize amount of particulates that are pulled into sampling line, the probe must be pointed downstream.
• If a straight probe is used, it should be fitted with a filter such as glass or pyrex wool.
• Moisture present in stack gases can condense in the sampling line and dissolve gaseous constituents of interest.
• To prevent losses due to condensation the sampling line should be heated.
• The preferred material for the probe is usually stainless steel and teflon is preferred in some special applications.
• The rate and duration of sampling are important in determining the amount of constituent gas collected and it depends on the technique used for collection.

ANALYSIS OF AIR POLLUTANTS

• Air quality measurements are done by continuous automatic analysers.
• Conventional laboratory techniques for for analysis of discrete samples is done for spot checking.
• For measurement of gaseous pollutants procedures are physical and chemical principles of measurement
• In chemical methods, the pollutant being measured undergoes chemical transformation and the product is analysed using an appropriate chemical technique.
  • In wet chemical analysis, the chemical is absorbed in a liquid for a specific time and then treated with a reagent causing a formation of another product indicated by a change of colour. The intensity of colour is related to the concentration of the original pollutant.
• In physical methods of measurement, a physical property of the pollutant is exploited – such as the ability of the gas to absorb infrared radiation. Its concentration is given by amount of radiation absorbed.

SO2

• The most common methods for measuring atmospheric SO2 are based on colorimetry, iodimetry or turbidimetry.
• The West and Gaeke colorimetric procedure is the reference or standard method. In this method, SO2 from a measured quantity of air is absorbed in a solution of sodium tetrachloromercurate. This forms stable and non-volatile dichlorosulphitomercurate complex. This is reacted with formaldehyde and para-rosaniline to yield a magenta coloured para-rosaniline sulphonic acid product. Photometric methods are used to detect the colour intensity of this acid. This is proportional to the concentration of SO2. EDTA is added to prevent interferences due to Iron and other heavy metals.
• The automatic instruments for monitoring sulphur dioxide are based on conductometric, colourimetric and flame photometric principles. In the conductometric method the sampled air containing SO2 is passed through a dilute solution of H2O2 and dilute sulphuric acid. SO2 is oxidised to H2SO4 with an increase in electrical conductivity of the solution which is proportional to the concentration od SO2 in the sample. However, acidic gases like HCl give positive errors while NH3 interferes negatively.
• Coulometry is used for automatic monitoring of SO2. In this process, SO2 is drawn continuously through an electrolytic cell containing and acidified bromine solution and two sets of electrodes. SO2 in the air sample is oxidised by bromine causing a reduction in the concentration of bromine. This causes a potential difference between the indicator electrode and the reference electrode. The current flow is a measurement of the SO2 concentration in the air stream.
• Flame photometric analyser works on the principle that when an air stream containing sulphur is ignited in a hydrogen rich flame, a characteristic flame emission spectrum is produced at 394 μm. This wavelength is monitored by a narrow band pass filter and a photomultiplier tube. The amount of light emitted is proportional to concentration of sulphur within the flame.
• In the electrochemical method, the SO2 gas diffuses through a semi permeable membrane and a thin electrolyte layer to get absorbed at the sensing electrode where it undergoes an electrochemical reaction. The current generated is proportional to the SO2 concentration. Electrochemical analysers are sensitive and stable for SO2 monitoring. Moreover, they are simple, portable, have a low cost and give immediate results.
• Infrared and ultraviolet spectrophotometry are based on selective absorption of light at a given wavelength by SO2. Degree of absorption is proportional to SO2 concentration.
• Spectrophotometric analysers
  • require small particle filtration
  • water removal
  • removal of sulphuric acid mist
  • are bulky and difficult to transport

Because of the above reasons, spectrophotometric analysers are least advantageous for field application.