Multi-Criteria Site Selection for Municipal Solid Waste Disposal by Integrating DEMATEL and AHP Methods

Multi-Criteria Site Selection for Municipal Solid Waste Disposal by Integrating DEMATEL and AHP Methods

P. Etraj1, J. Jayaprakasp

Department of Mechanical Engineering,

Dr.MGR Educational and Research Institute University, Chennai 600 095, Tamil Nadu, India.

AbstractThe sanitary landfill has been recognized as the cheapest form of disposing the Municipal Solid Waste (MSW) and also been commonly adopted by every country in the world. However, selecting a suitable Landfill Disposal Sites (LDS) is an extremely complex task mainly due to the fact that the identification and selection process involves many factors and strict regulations. For proper identification and selection of suitable LDS needs very careful and systematic procedures. Wrong sitting may result to environmental degradation and other consequences often lead to public opposition. As the existing LDS has reached its saturation point, the Corporation of Chennai (CoC) is searching for alternate sites for disposing of its MSW for current and future needs. Since, the present method of selection of LDS lack practical applications, the authors made an attempt to develop a Multi Criteria Site Selection for MSW Disposal by Integrating Decision Making Trial and Evaluation Laboratory (DEMATEL) and Analytic Hierarchy Process (AHP) method. The proposed hybrid method is superior to existing methods since it has the capability of representing qualitative data and presenting all possible results with different degrees of priority. The end results also shows that the integrated approach of DEMATRL and AHP method is more precious than that of the individual approach.

KeywordsMunicipal Solid Waste; Corporation of Chennai; Delphi Technique; Decision-Making Trial and Evaluation Laboratory; Analytic Hierarchy Process.

I INTRODUCTION

India generates about 1,33,760 Metric Tones Per Day (TPD) of MSW (MoEF Report). According to the definition from U.S. Environmental Protection Agency (EPA) MSW is composted by everyday items such as product packaging, grass clippings, furniture, clothing, bottles, food scraps, newspapers, appliances, paint, and batteries. Due to increase in population, urbanization, change in life style and consumption pattern, the Municipal Solid Waste Management (MSWM) in urban areas are become a tenacious problem for the waste managers[1]. The arising of MSW in Chennai, the fourth largest metropolitan city in India, has increased from 600 to 4500 TPD during the last 20 years [2]. Urban MSW is considered as one of the burning and serious environmental problems confronting for municipal authorities. As the existing two LDS of CMA namely Kodungaiyur and Perungudi have reached their saturation point, the Corporation of Chennai (CoC) is searching for alternate sites for disposing of its MSW for current as well as future needs.

Sanitary LDS selection needs to address not only the technical issues but also the political, legal, economic, environmental, geological, hydrological as well as socio- economic, socio-political and socio-cultural factors[3]. Choosing the appropriate LDS for MSW has already become a hot point for the decision-maker. This paper applies an effective solution based on an integrated DEMATEL and AHP method[4,5] to assist the expert group for evaluating LDS selection for CMA, since the degree of influence each criterion may differ, depending on the various ecological conditions. The hybrid model of integrated DEMATEL and AHP in combination with Decision Delphi has been found to be a powerful tool to solve the LDS selection problem, since the Decision Delphi Technique will help to converge the criteria and DEMATEL will prioritize the criteria and finally AHP will rank the potential LDS[6].

II LITERATURE REVIEW

An extensive review literature on site-selection process shows that a number of researchers used the Geographical Information System (GIS) to deal with the LDS selection process[7,8]. Identifying the LDS for urban solid waste disposal made easy by using GIS and Remote Sensing(RS) techniques[9]. The article gives the detailed account of optimizing the sitting technique for MSW landfills and its management issues. The assessment of the resident's satisfaction level in MSW system gives more insight to researchers dealing with LDS site selection[10,11]. Selection of LDS for MSW can be treated as one of the Multiple Criteria Decision Making (MCDM) problem, which requires the consideration of a large number of complex criteria[12]. As such the researchers approached this issue by adopting the multi-cretiria technique to improve the selection process [13,14]. A beefy MCDM method needs numerous factors and the RAND Delphi Technique correlate judgments on a topic spanning a wide range of disciplines which aims to achieve a convergence of opinion on a specific real-world issue[15]. A robust MCDM method needs to consider the interactions among the influencing criteria and DEMATEL is one such tool which can evaluate such interaction among the influencing factors[16]. DEMATEL will not only convert the relations between cause and effect of criteria into a structural model, but also can be used as a way to handle the inner dependencies within a set of criteria[17]. AHP is another relatively robust MCDM method which can be dealt with all

kinds of interactions systematically by decomposing the complex decision making problem into a much simpler one by using the paired comparisons to weigh the criteria based on hierarchical structure which provides easiness during decision making[18]. Notably, the AHP method has the advantages of yielding more precise results and verifying consistency of judgments[19]. In the current research work the authors made an attempt to combine all these three methods for LDS selection process to get better solution. The impact of the landfill leachete on ground water is a serious issues and several research papers addressed this issue [20, 21, 22].

III STUDY AREA

Greater Chennai is city of Indian state Tamil Nadu located on the eastern coast (Latitude 13o 07 N and Longitude 80o 16 E). The total area of Greater Chennai city is 174 square kilometer. Presently the CMA covers the CoC and 16 other adjourning local bodies of Municipalities, Town Panchayats and Panchayat Unions. The present population of Greater Chennai City is 6.5 millions and it has been estimated that each individual is generating 700 grams of solid wastes per day. It has been estimated that 4500 TPD of solid waste generated in CMA, which are currently disposed in two LDS viz. Kodungaiyur and Perungudi only. As the existing two LDS have reached their saturation point, the CoC is searching for alternate sites for disposing its MSW for current and future needs. The proposed LDS should adopt a multi- technology approach to deal with different waste streams of MSW as listed below:

• Biological Treatment (BT)- including composting and anaerobic digestion which would treat source- separated biodegradable materials such as food waste;

• Mechanical-Biological Treatment (MBT) – comprising mechanical and biological processes which recover recyclable materials and treat biodegradable fraction from mixed waste;

• Thermal Treatment incinerating the unavoidable mixed waste not handled by biological treatment or MBT and recovering the energy contained

  IV RESEARCH DESIGN

  LDS selection is a difficult, complex, tedious, and protracted process requiring evaluation of many different criteria since it has to combine social, environmental, technical, and financial factors. Economic factors must be considered in the sitting of landfills, which include thecosts associated with the acquisition, development, and operation of the site. Social and political opposition to landfill sitting have been identified as the greatest obstacle for successfully locating the LDS. The not in my backyard (NIMBY) and not in anyones backyard (NIABY) syndrome are becoming a common attitude and creating a tremendous pressure on the decision makers involved in the selection of a LDS. In the first phase literature survey and interview are used for collecting the basic theoretical and practical information. The article demonstrate that how the integration of two or more methods can produce better results than using only one method of site selection[23]. The collected data are presented to an Expert Committee (EC) comprising of 4 academicians, 2 volunteers from NGO, each one MSW

  planners from TNPCB, CoC and private conservancy firm contracted by the CoC. In the next phase Delphi Technique has been applied to identify the influential factors on site selection of LDS for the MSW. In the third phase DEMATEL method has been utilized to prioritize the influential factors. In the fourth phase AHP has been applied with 6 fictitious LDS for the shortlisted factors are par wise compared with the Global weights as well as with the Prioritized factors obtained through the DEMATEL. The consistency of the result is verified by sensitivity analysis. The overall Site Selection Process involves three step procedures:

• Establishing of selection criteria by Delphi Technique.

• Prioritization of selection criteria by DEMATEL and

• Evaluation of weight of criteria and ranking of site selection by AHP.

1. Hybrid DELHI, DEMATEL and AHP

   Research design used in this study using a hybrid Decision Delphi, DEMATEL and AHP methods. The LDS selection process has been structured into three main phases as depicted in Fig. 1. The first is the input stage, where in Factors and Criteria for LDS selection will be established by Decision Delphi. In the next stage Factors and Criteria will be prioritized through DEMATEL method. In the third stage weighting the criteria by AHP and rank the sites.

   Input

   Establishing of SS Factors and Criteria through

   Decision DELPHI

   Input

   Establishing of SS Factors and Criteria through

   Decision DELPHI

   Prioritizing of SS influencing Factors and Criteria by DEMATEL

   Prioritizing of SS influencing Factors and Criteria by DEMATEL

   Determination of relationship between the Criteria and Ranking of LDS by AHP

   Determination of relationship between the Criteria and Ranking of LDS by AHP

   Output

   Recommending the Site with highest Rank

   Output

   Recommending the Site with highest Rank

   Fig. 1. Research Design of Hybrid DEMATEL and AHP

2. Establishment of Factors and Criteria

   The RAND Decision Delphi technique is an important data collection methodology with a wide variety of applications[6]. The EC members are immersed and imbedded in the topic of interest and can provide real-time and real-world knowledge within their domain of expertise. Delphi technique is well suited for consensus-building by multiple iterations on selected data and provides structured alternative anecdotal approach. Firstly factors and criteria obtained from the literature review were presented to the EC to apply the Decision Delphi technique.

   Round 1: The Decision Delphi process traditionally began with an open-ended questionnaire, which served as the cornerstone of soliciting specific information about MSW subjects. The first round was started with 72 criteria under nine factors. After the completion of first round, some criteria which were regarded as unimportant excluded from the list.

   Round 2: During the second round the areas of disagreement and agreement are identified. The second round starts with 7 factors and 59 criteria, and at the end 11 more criteria which were associated with none of the factors were excluded from the list.

   Round 3: In the third and last round, experts came to an agreement on the factors and criteria. More specifically 6 factors and 40 criteria associated with the LDS selection for MSW collected from CMA are determined and depicted in Table I.

   TABLE I, ESTABLISHMENT OF FACTORS AND CRITERIA

3. Priororitzion of Factors and Criteria

   ij

   ij

   The DEMATEL method has been applied in 8 steps procedure as shown as Fig.2, formulating Direct Answer Matrix, Original Average Matrix, Normalizing the Direct Influence Matrix, Deriving the Total Relation Matrix and deciding threshold value to get the Cause and Effect Relationship diagram [16]. The Direct Answer Matrix for each dimensions are to be constructed by the scores awarded by m Decision Makers (DM) with n factors. The degree to which the DM perceived factor i affects on factor "j" is denoted by ak . The integer score of 0 to 4 is assigned for each pairs as per the values given in the Table II.

   Step -1

   Gather EPMs opinion and formulate the Direct Answer Matrix A

   Step -1

   Gather EPMs opinion and formulate the Direct Answer Matrix A

   Step -2 Compute the

   Original Average Matrix B

   Step -2 Compute the

   Original Average Matrix B

   Step -3 Compute the normalized

   Initial Direct Influence Matrix D

   Step -3 Compute the normalized

   Initial Direct Influence Matrix D

   Step -4 Derive the

   Total Relation Matrix T

   Step -4 Derive the

   Total Relation Matrix T

   Step -5 Compute the

   Positions and Relations

   Step -5 Compute the

   Positions and Relations

   Step -6 Compute the

   Threshold Value ()

   Step -6 Compute the

   Threshold Value ()

   Step -7 Construct the

   Cause and Effect Relationship(C&ER) Diagram

   Step -7 Construct the

   Cause and Effect Relationship(C&ER) Diagram

   Re-fix the Threshold value ()

   Re-fix the Threshold value ()

   F4

   Sl.No.	Factors	F-Code	Criteria	C-Code
   1.	Receptor	F1	Site capacity	F1C1
   			Technical and operational	F1C2
   			Lateral expansion	F1C3
   			Type of approach road	F1C4
   			Traffic nuisance	F1C5
   2.	Distance	F2	From waste generating zone.	F2C1
   			Nearest residential locality	F2C2
   			Nearest drinking water sources	F2C3
   			Nearest public utility facility	F2C4
   			Nearest religious sites	F2C6
   			Nearest archaeological sites	F2C7
   			Nearest coastal precinct	F2C8
   3.	Environment	F3	Odor, dust and noise nuisance	F3C1
   			Threat to ecology	F3C2
   			Risk of leachete leaking	F3C3
   			Risk of explosive gases	F3C4
   			Weather and Climate	F3C5
   			Threat to Flora and Fauna	F3C6
   			Risk to contiguous area	F3C8
   			Vector vulnerability	F3C9
   			Spoil of vicinities air quality	F3C10
   			Fire hazard and wind path	F3C11
   4.	Hydrology and hydrogeolog y	Ground water contamination	F4C1
   		Wetlands	F4C2
   		Floodplains	F4C3
   		Soil permeability	F4C4
   		Soil erosion risk	F4C5
   		Slope pattern	F4C6
   		Geomorphology	F4C7
   		Topography	F4C8
   5.	Social, Legal and Political	F5	Vicinitys aesthetics	F5C1
   			Public tolerability	F5C2
   			Agreement with pressure group	F5C3
   			Synchronize with local bodies	F5C4
   			Concord with UNEP	F5C5
   			Compliance to EPA 1986.	F5C6
   6.	Financial	F6	Land cost	F6C1
   			Transportation costs	F6C2
   			Operation and maintenance	F6C3
   			Cost for after care	F6C4

   Sl.No.	Factors	F-Code	Criteria	C-Code
   1.	Receptor	F1	Site capacity	F1C1
   			Technical and operational	F1C2
   			Lateral expansion	F1C3
   			Type of approach road	F1C4
   			Traffic nuisance	F1C5
   2.	Distance	F2	From waste generating zone.	F2C1
   			Nearest residential locality	F2C2
   			Nearest drinking water sources	F2C3
   			Nearest public utility facility	F2C4
   			Nearest religious sites	F2C6
   			Nearest archaeological sites	F2C7
   			Nearest coastal precinct	F2C8
   3.	Environment	F3	Odor, dust and noise nuisance	F3C1
   			Threat to ecology	F3C2
   			Risk of leachete leaking	F3C3
   			Risk of explosive gases	F3C4
   			Weather and Climate	F3C5
   			Threat to Flora and Fauna	F3C6
   			Risk to contiguous area	F3C8
   			Vector vulnerability	F3C9
   			Spoil of vicinities air quality	F3C10
   			Fire hazard and wind path	F3C11
   4.	Hydrology and hydrogeolog y	F4	Ground water contamination	F4C1
   			Wetlands	F4C2
   			Floodplains	F4C3
   			Soil permeability	F4C4
   			Soil erosion risk	F4C5
   			Slope pattern	F4C6
   			Geomorphology	F4C7
   			Topography	F4C8
   5.	Social, Legal and Political	F5	Vicinitys aesthetics	F5C1
   			Public tolerability	F5C2
   			Agreement with pressure group	F5C3
   			Synchronize with local bodies	F5C4
   			Concord with UNEP	F5C5
   			Compliance to EPA 1986.	F5C6
   6.	Financial	F6	Land cost	F6C1
   			Transportation costs	F6C2
   			Operation and maintenance	F6C3
   			Cost for after care	F6C4

   Is the C & ER

   Diagram represents the required

   data? No

   Yes

   Apply the factors

   as per the priority indicated by the Cause and Effect Relationship Diagrams

   Apply the factors

   as per the priority indicated by the Cause and Effect Relationship Diagrams

   Fig. 2 DEMATEL application procedure

   TABLE II, SCORE FOR PAIR WISE COMPARISONS [16].

   Sl.No.	Degree of influence	Score
   1.	No influence	0
   2.	Low influence	1
   3.	Medium influence	2
   4.	High influence	3
   5.	Very high influence	4

   The sum of rows and the sum of columns of the total relation matrix T are denoted as vector r and vector c. The sum (ri+cj) gives an index called the Position representing the total effects both given and received by the

   ith factor, ie, (ri+cj) shows the degree of importance that the ith factor plays in the system (total sum of effects given and received). The difference (ri-cj) gives an index called the Relation shows the net effect, the ith factor contributes to the system. If (ri-cj) is positive, then ith factor is a net causer and if (ri-cj) is negative, then ith factor is a net receiver. The Cause and Effect Relationship diagram is constructed by mapping all coordinate sets of (ri+cj, ri-cj) to judge the significant factors and their influence on other factors.

4. Ranking of Factors and Criteria.

   Principle of Decomposition, Principle of Comparative Judgment and Principle of Synthesis of Priorities are the three basic principles of AHP. In this article AHP is applied in nine steps as follows[19]:-

   Step 1: Set-up Hierarchy: The basic linear hierarchical structure shown in Fig.3 is a top down approach consisting of Goal (Level-1), Criteria (Level-2) and Alternatives (Level-3).

   Level 1

   Goal

   Selection of Suitable LDS for MSW

   Level 1

   Goal

   Selection of Suitable LDS for MSW

   Level 2

   Criteria

   Influencing Factors and Criteria

   Level 2

   Criteria

   Influencing Factors and Criteria

   Level 3

   Alternatives

   Alternative LDS locations

   Level 3

   Alternatives

   Alternative LDS locations

   Fig. 3, Model Linear Hierarchy of AHP

   In this current research the Goal is to select an alternative LDS for CMA by pair-wise comparison with Factor/Criteria shown in Fig. 4.

   Suitable LDS for MSW

   Let C1,.., Cn are elements of some level in a hierarchy and w1,, wn, are weights of influence on some elements in the next level to be found. The elements of the matrix are selected representing judgment of pair-wise comparisons. If aij is the element of row i" and column j of the matrix, then 1/aij is the element of row j and column i of the matrix. ie aji=1/aij. If the element aij indicate the strength of C1 when compared with Cj. This matrix is denoted by matrix A. When aji=1/aij, matrix A becomes reciprocal. If judgment is perfect in all comparisons, then aik = aij* ajk., for all i,j,k and the matrix A becomes consistent. The matrix A has been shown as Fig. 5.

   Fig. 5, Comparison Reciprocal Matrix

   Step 3: Priority Vector for Criteria: The pair-wise comparison reciprocal matrix is obtained by:-

   1. Sum the values in each column of the pair-wise comparison reciprocal matrix.

   2. Divide each value by the corresponding column sum to get the Normalized Matrix.

   3. Average the values in each row of the normalized matrix and compute the Priority Vector.

Step 4: Compare Alternatives: Repeat the step i" to iii for each alternatives.

Step 5: Priority Vector for Alternatives: Compute the

Fx or FxCy

Location

A

Fx or FxCy

Location

B

Fx or FxCy

Location

C

Fx or FxCy

Location

D

overall score for each decision alternatives.

Step 6: Overall Priority Vector: Rank the decision alternatives, according to the magnitude.

Step 7: Consistency Index: CI=( max n)/(n-1), where, max is the Principal Eigen value and n is the order of the matrix.

Step 8: Consistency Ratio: CR = CI/RI, where RI is the

Fig. 4, The Proposed Hierarchy Structure of AHP

Step 2: Compare Criteria: The pair-wise comparison elements of one level with another level in their strength of influence are made by collecting the data through survey conducted in MTC. The pair wise comparisons are rated by nine point Saatys scales for pair wise comparisons[18] as given in Table III.

TABLE III, THE SAATYS SCALE [18].

Random Index as given in Table V.

TABLE V, VALUES FOR RANDOM INDEX [18].

Step 9: Check for Consistency: If 0 CR 0.1, then the judgment is perfectly consistent and the criteria/alternative can be accepted and if CR>0.1, the judgment is inconsistent and untrustworthy. Hence it need to revise the subjective judgment.

V. AN ILLUSTRATIVE CASE APPLICATION The proposed hybrid model is demonstrated with the

help of 6 conjured LDS to show that how suitable sites could be identified and ranked by the combination of DEMATEL

and AHP methods. MS-Excel spread sheet has been used for all numerical calculations throughout this research work. This

TABLE VIII, PREFERENCE (PAIR-WISE COMPARISON) NORMALIZED MATRIX FOR FACTORS BY DM GROUP

proposed technique allowed for an often qualitative assessment of site selection to be replaced by a more quantitative, informed and unbiased method.

A. Applying DEMATEL on six Factors

Each Expert Committee members performed the pair-

Factors F1

F2 F3

F4 F5

F6 Sum Priority

Vector

wise comparisons of 6 Factors and hence nine Direct Answer Matrix are formulated as per the Step-1 of Fig.2. and Original Average Matrix B has been computed as per Step-2. The Normalized Initial Direct Influence Matrix D has been computed by as per Step-3 and Total Relation Matrix T has been computed as per Step-4 and presented in Table VI, VII and VIII.

TABLE VI, POSITIONS AND RELATIONS AMONG FACTORS.

F5 0.19 0.31 0.19 0.11 0.16 0.17 1.13 0.221

F6 0.06 0.03 0.10 0.11 0.08 0.08 0.47 0.09

Principal eign value max= 6.35 Consistency index (I) 0.07

Consistency Ratio (CR) 0.06 < 0.1

Initially the ranking of LDS was formulated by applying the global weight obtained from AHP and results are presented in Table IX.

The Cause and Effect Relationship (CER) among the six factors are constructed and shown in Fig.6.

F4

F3

F4

F3

F5

F5

Site C 0.26 0.26 0.24 0.31 0.22 0.25 0.34 25.52%

Site D 0.19 0.14 0.20 0.15 0.19 0.10 0.20 17.43%

Site E 0.22 0.18 0.20 0.23 0.26 0.28 0.21 22.42%

Site F 0.10 0.21 0.11 0.07 0.10 0.14 0.09 11.14%

Next the CER computed from the DEMATEL has been synthesized and applied to AHP as global weight to rank the LDS. The results are presented in Table X.

TABLE X, RANKING OF LDS BY DEMATEL GLOBAL WEIGHT

2

1.5

1

0.5

0

-0.5 15

-1

-1.5

-2

2

1.5

1

0.5

0

-0.5 15

-1

-1.5

-2

16

16

17

F2 F1

17

F2 F1

18

18

19

19

20

20

Global

Global

F1 F2 F3 F4 F5 F6 DEMATEL Priority

Vector

F6

F6

Weight Site A 0.09 0.07 0.06 0.08 0.06 0.06 0.05 06.47%

Site B 0.14 0.15 0.18 0.16 0.17 0.17 0.06 16.30%

The AHP has been applied on the six factors and the Expert Committee members are acted upon the role of Decision Makers (DM). Since AHP technique can be applied using different methods i.e. Eigen Vector/Value Method, Geometric Mean Method and Arithmetic Mean Method. In this current research work Geometric Mean Method has applied and MS-Excel spread sheet was used for arithmetic calculations.

TABLE VII, PREFERENCE (PAIR-WISE COMPARISON) NORMALIZED MATRIX FOR FACTORS BY SINGLE DM

Factors F1 F2 F3 F4 F5 F6 Sum Priority

Vector

F1 0.08 0.07 0.09 0.06 0.07 0.09 0.46 0.08

F2 0.08 0.07 0.09 0.06 0.05 0.18 0.53 0.09

F3 0.31 0.30 0.35 0.39 0.39 0.27 2.01 0.34

F4 0.23 0.22 0.18 0.19 0.20 0.18 1.20 0.20

F5 0.23 0.30 0.18 0.19 0.20 0.18 1.28 0.21

F6 0.08 0.04 0.12 0.10 0.10 0.09 0.52 0.09

Principal eign valuemax= 6.21

Consistency index (I) 0.04

Consistency Ratio (CR) 0.03 < 0.1

Site F 0.10 0.21 0.11 0.07 0.10 0.14 0.08 10.01%

The comparative analysis among the six locations chosen for the study to select the best suitable LDS as per the local conditions has been depicted in Table XI.

TABLE XI, FINAL RANKING OF LDS

The results are also been presented graphically as bar chart in Fig. 7.

30%

25%

20%

15%

10%

5%

0%

AHP DAHP

Site A Site B Site C Site D Site E Site F

Fig. 7, Final Ranking of LDS

VI RESULTS AND DISCUSSION

uniqueness of the current study stems from the fact that the Environmental Factors were consider as the crucial governing factors for selection of suitable LDS for MSW. Even though the AHP method and the integrated DEAMTEL and AHP methods are yielding to the identical results, the integrated approach converged into more precisely distinguished the goals. This helps the waste planners from pitfall of selecting a wrong LDS which follows very close to the best one with marginal difference. The superiority of the proposed integrated MCDM method stems from its inherent flexibility in its application to dissimilar sites with diverse local conditions[24].

REFERNCES

1. Prioritization of factors by DEMATEL

   The analysis of Total Relation Matrix depicted as Table VI and CER diagram given in Fig.6 shows that Environmental Factor (F3) is the most important factor having the largest (r+c) value ie. 19.47, wheeas Financial Factor (F6) is least important factor having the smallest (r+c) value ie. 15.88. According to the degree of significance, the magnitude of the factors are recognized as F3>F4>F5>F2>F1>F6. And also the (r-c) values helps to classify the factors into:- (1) Cause Group and (2) Effect Group.

   1. Cause Group Factors

      Factors with positive (r-c) value are classified as Net Causer or Cause Group which directly affects other factors and their degree of impact are proportionate to their numerical values. The CER diagram shown as Fig.6, reveals that, Environmental Factor (F3), Hydrology and Hydrogeology Factor (F4), Social, Legal and Political Factors (F5) are fall into the Cause Group, since their (r-c) values are 1.63, 1.61 and 0.75.

   2. Effect Group

      Factors with negative (r-c) value are classified as Net Receiver or Effect Group and largely influenced by other factors. Accordingly Transport Factor (F2), Receptor Factor (F1) and Financial Factor (F6) are fall into the Effect Group, since their (r-c) values are -0.92, -1.25 and-1.82.

2. Ranking of sites by AHP

Ranking of sites by AHP has been worked out separately with global weight obtained from AHP method as well the DEMATEL method. The end results of both the methods agree that Site 'C' is most preferred and Site A is least preferred. The order of preference is Site 'C' > Site 'E' > Site 'D > Site 'B' > Site 'A.

VII CONCLUSIONS

This paper presents a hybrid model of MCDM approach by integrating DEMATEL and AHP to identify the most suitable site for disposing of MSW from Greater Chennai Metropolitan Area. The study was based upon a set of factors and key criteria, which were selected based upon the already available knowledge from research literature as well as the pre-existing local level factors of the area. Even though the basic factors to be assessed for LDS are universally the same, different area may have different sets of local conditions. The

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