Sustainable Leachate Treatment Plant System at Landfill Site: A Multicriteria Analysis Approach

Leachate generated from Municipal Solid Waste (MSW) landfill may cause various negative impacts, therefore it should be treated properly in a Leachate Treatment Plant (LTP). The paper aims to select a more sustainable LTP system in Indonesia by applying Analytic Network Process (ANP) as multicriteria analysis approach. 5 alternative LTP systems were analyzed using 5 criteria namely economic, environmental, social, technical, and institutional capacity with a total of 25 sub-criteria. Total 36 respondents from municipality staffs, academics, professionals, and LTP operators were interviewed by adopting pair wise comparison. The results from Driving Dependence Power Analysis (DDPA) showed that sub-criteria for operating costs (E2), maintenance costs (E3), processing effectiveness (T1) and monitoring needs (T3) have the highest dependence power value. Sub-criteria of the operational cost (E2) and the availability of regulations (K2) have the highest driving power value. Main considerations for selecting LTP system at a final disposal site by respondents were economic criteria (weight 0.3219) and water protection sub-criteria (L2, weight 0.17). Top priority of the technology chosen by respondents were Alternative#1 consist of Anaerobic, Facultative and Maturation ponds and Biofilter.


Introduction
Every human activity will produce waste that will end up at the Landfill.A landfill is one of the options for waste management that has the potential to pollute three environmental factors, namely soil, air, and water [1].The dump will produce leachate.Leachate is a liquid percolating through the waste containing elements of dissolved and suspended fluid passing through the landfill and mixed and suspended substances or materials in place (Landfill) [2].Leachate produced in Landfills can cause environmental impacts to social conflicts.Therefore, leachate treatment will continue to be a significant concern for landfill managers because of the increasingly stringent water quality limits placed on LTP [3].This indicates that the selection of leachate treatment is complex because it is affected by various aspects (criteria) and the relation between standards.Waste management, including leachate management, is a complex process involving various environmental and socio-economic criteria.Decision makers need a support framework to determine alternatives, choose criteria and sub-criteria with relevant weights, and find appropriate solutions.According to the related review, ANP is the most dominant multicriteria method [4].The criteria considered in decision-making often have links, so the ANP method is appropriate for dealing with problems with the interrelation between standards [5].ANP is a mathematical theory that allows a decision-maker to deal with factors that are interconnected (dependence) and feedback systematically.The ANP method prioritizes the relation between one criterion and another with a dominance of effect from stakeholders.The advantages of the ANP method are its ability to help decision-makers measure and synthesize several factors in a hierarchy or network [6].This study aims to select the LTP system in Indonesia by considering technical and non-technical aspects and adopting the Analytic Network Process (ANP) as a multi-criteria analysis approach so that LTP operations can be more sustainable.

Methodology
Methodology of this research is outlined as illustrated in Figure 1 below.

Identification of Criteria and Sub-Criteria
A long list of sub-criteria was identified based on literature studies (Table 2).All the identified subcriteria had also been confirmed to stakeholders.Determination of the sampling size of the respondents adopted purposive sampling method.The purposive sampling method does not have a minimum amount specified in determining the number of respondents [7] in [8].However, representative of the respondent was selected by considering that the respondent is a decision maker, dealing with or directly involved in the problem.The selected respondents and their numbers are described in Table 3.  [7]; [14] No.

Selection of the Best Alternatives
Questionnaires for the pair wise comparison were carried out using the level of importance between elements with Saaty' scale (1)(2)(3)(4)(5)(6)(7)(8)(9).ANP generalizes the pairwise comparison process to assess each component by including criteria and alternative priorities [17].The questionnaire of each respondent was tested also for the consistency.Inconsistent answers were revised.The result of the pairwise comparison questionnaire was analysed using Super Decision Software through three super-metric stages, namely unweighted super-matrix, weighted super-matrix, and limit super-matrix to obtain the criteria weight and synthesis of the alternatives leachate treatment plant system.4 shows the existing efficiency of BOD resulting from analysis of samples in laboratory and from calculation based on the criteria design from the respective set of treatment processes.It is found that theoretically Alternative#1 has the highest possible BOD efficiency compared to others.However, the existing performance of Alternative#1 generates the lowest efficiency.While Alternative#5 generates the highest one.The differences between the existing performance with the possible criteria design may be affected by the operation of LTP plant itself.From parameter of BOD, only Alternative#5 meets with the leachate standard which is regulated by MoEF Regulation No. 59 year of 2016.It means that all observed LTP systems should improve their existing performance in order to meet the standard.

Identification of Criteria and Sub-Criteria
All criteria and sub-criteria listed from literature review were confirmed and agreed by most of respondents to be included in the further analysis.However, sub-criteria of operational and maintenance costs were chosen by the greatest number of respondents (25 respondents).While, sub-criteria of natural disaster response was chosen by the least number of respondents (2 respondents).Thus, a total of 5 criteria with total 27 sub-criteria were analyzed to find their dependency relation among them.

Driving and Dependence Power Analysis
Determining the dependency relation among sub-criteria was based on the Driving Dependence Power Analysis (DDPA) method as part of ANP's procedure.DDPA is a method used to identify dependency relations and driving forces of related standards.In the DDPA analysis, respondents' responses determine the relationship among sub-criteria (Table 5) and will be processed into the reachability matrix for driving and dependence power (Table 6).The placement of sub-criteria into the 4 DDPA quadrants can be seen in Figure 5 below.Minimum operational costs (E2), minimum maintenance cost (E3), the effectiveness of treatment (T1), and monitoring method (T3) have the value dependence power highest, which means that these subcriteria have the interrelated solid ability.At the same time, sub-criteria of minimum operational cost (E2) and detailed regulation requirement (K2) have the value driving power highest, which means that these sub-criteria have a strong driving force.The sub-criteria above are unstable because the power of linkages and drivers in each sub-criterion are strong.Therefore, the influence of other sub-criteria can cause changes to the requirements themselves and provide feedback.

Influencing elements
Financial Criteria (E) Social Criteria (S)

Social Capacity Building Environmental Technical
Environmental Criteria (L)

Technical Criteria (T)
Affected elements  Among sub-criteria included in Cluster I, sub-criteria of T2 (space/land requirement), T7 (emergency response) and L7 (natural disaster response) have less driving power and less dependency, thus these sub-criteria relatively disconnected from the system with very weak linkage with others.From Cluster II, sub-criteria of budget from municipality (E4), the ease of operation (T4) becomes the most dependent factors which have weak driving power but strong dependence.Among sub-criteria included in Cluster III, sub-criteria of E2 (Operational expenditure), K2 (Detailed regulation requirement), T3 (Monitoring method), E3 (Maintenance cost), and T1 (Effectiveness of treatment) have the strongest driving and dependence power in which any changes to them will significantly affect others.These sub-criteria must be studied carefully because the relation between sub-criteria is not stable, so each treatment on the sub-criteria in this cluster will impact other subcriteria.While the only one sub-criteria namely detailed regulation requirement (K1) becomes a factor which has strong driving power but weak dependence power.Construction of an alternative leachate treatment network model is shown in Figure 4 with predetermined feedback and interdependence clusters.The criteria and sub-criteria that are processed in the ANP method are the sub-criteria that occupy Cluster III.So that the ANP model in the figure only involves a few sub-criteria, which are different from the previous initial model.The sub-criteria included in the ANP model consisted of 3 sub-criteria for economic criteria, 2 sub-criteria for environmental criteria, 1 sub-criteria for social criteria, 3 sub-criteria for technical criteria and 2 sub-criteria for institutional criteria.The ANP model was created using the help of super decisions software version 2.8.
In the construction of the ANP model, criteria that have influence between sub-criteria in the same criterion apply to criteria that have more than 2 sub-criteria.Therefore, only economic criteria and technical criteria have an inner dependence relationship.In the network model, loops are only found in economic and technical criteria.This is because in this criterion there are 3 selected sub-criteria.So, it is still possible to see the effect among sub-criteria in the same criteria.

Selection of the Best Alternatives
Priority determination is carried out in a paired comparison matrix by giving a scale of 1-9 importance to the criteria, sub-criteria, and alternatives compared to subjective respondents.

Criteria assessment
The criteria weight results of respondents' preferences, as shown in Figure 5, show that economic criteria are the top priority in alternative leachate treatment, with a weight of 0.3219.Compared with the results of the DDPA analysis, the economic aspects also have the most sub-criteria, which are included in quadrant 3, namely investment costs (E1), operational costs (E2), and maintenance costs (E3).The value of the Consistency Ratio (CR) of 0.0972 (9.72%) shows that the criteria weight is relatively consistent and is within the inconsistency ratio of <10%.There are five scenarios for leachate treatment, namely a combination of biological and chemical processing.Based on the preferences of all respondents, the processing that has the highest priority for leachate treatment is the Alternative#1 (Anaerobic, Facultative, Maturation, and Biofilter) with the highest weight, which is 0.4893.The results of the synthesis of alternative priorities for processing organic waste can be seen in Figure 7 below.The resulting consequence is quite far when compared to other alternatives.The ANP analysis results are the same as the evaluation results based on design criteria which shows that Alternative#1 has the highest BOD removal efficiency.

Conclusion
In order to operate properly in a sustainable manner, Leachate Treatment Plant (LTP) must be designed by considering multicriteria, including through the application of ANP for LTP cases in Indonesia.MoPW of Indonesia provided alternatives of LTP as guideline design to establish LTP in a final disposal site.Ideally, all alternatives listed in the MoPW guideline can achieve the LTP effluent standards regulated by MoEF.However, due to lack of various resources, including limited operational costs and operator capabilities, based on the sampling procedure not all observed LTPs met these effluent standards.From 5 criteria (financial, environmental, social, technical, and capacity building) with a total of 27 sub-criteria selected, stakeholders considered operational and maintenance costs, detailed regulation requirement, monitoring method, and effectiveness of treatment as subcriteria having the most vital driving and dependence power.Among the criteria available, financial has the highest weight.Thus, the LTP system with simpler technology was deemed the most suitable to be adopted in Indonesia.

2
Alternative technologies for leachate treatment are listed in Appendix III of Minister of Public Works Regulation No. 03 of 2003 concerning the Implementation of Solid Waste Infrastructure and Facilities in Household Waste Management and Household Waste.The choice of technology alternatives will be made by multicriteria analysis, which facilitates the selection of the best options among the existing alternatives and assesses the various criteria that affect them.

Figure 1 .
Figure 1.Methodology of the Research

Figure 2 .
Figure 2. Initial Model Consists of 5 Criteria and 27 Sub-Criteria 3. Result and Discussion 3.1.Evaluation of Representative LTP System in Indonesia Analysis of existing conditions carried out at LTP locations that represent alternative leachate treatment guided by MoPW Regulation No. 03 year of 2003.Table4shows the existing efficiency of BOD resulting from analysis of samples in laboratory and from calculation based on the criteria design from the respective set of treatment processes.It is found that theoretically Alternative#1 has the highest possible BOD efficiency compared to others.However, the existing performance of Alternative#1 generates the lowest efficiency.While Alternative#5 generates the highest one.The differences between the existing performance with the possible criteria design may be affected by the operation of LTP plant itself.From parameter of BOD, only Alternative#5 meets with the leachate standard which is regulated by MoEF Regulation No. 59 year of 2016.It means that all observed LTP systems should improve their existing performance in order to meet the standard.

Fig. 4
Fig.4 Driving and Dependence Power in the Reachability Matrix

Figure 4 .
Figure 4. Network Model for Alternative Leachate Treatment

Table 1 .
An evaluation was conducted by sampling and analysing the sample of the LTP effluent to laboratory and comparing the effluent to leachate quality standards.The effluent standard of leachate generated from final disposal site refers to according to Ministry of Environmental and Forestry (MoEF) Regulation No. 59 year of 2016 (Table1).In this study, parameter of BOD has been chosen as the most crucial parameter to determine the performance of LTP system because all LTP technology alternatives guided by MoPWH Regulation No. 3 year of 2003 put the biological process as primary treatment.Effluent Standard of Leachate from Waste Processing Facility in Indonesia

Table 2 .
Identification of Criteria and Sub-Criteria

Table 3 .
Representative Respondents and the Number of Selected Respondents 2.3.Driving and Dependence Power AnalysisAs part of Analytic Network Process (ANP) method, Dependence and Driving Power Analytic (DDPA) was used to determine relationship among criteria and sub-criteria and to explain the strength of the hanging of sub-criteria categorized into 4 dominant sectors, namely:Quadrant I : Autonomous Cluster (weak dependence -weak driving) Quadrant II : Dependence Cluster (strong dependence -weak driving) Quadrant III : Linkage Cluster (strong dependence -strong driving)

Table 4 .
Efficiency of LTP System

Table 5 .
Dependency Relationship among Sub-Criteria