A methodology & software system for developing optimal ...€¦ · A methodology & software system for developing optimal solid wastes management plans ... municipal solid wastes

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A methodology & software system for developing optimal solid wastes management plans

A. P. Economopoulos

Environmental Engineering Department, Technical University of Crete, Chania 731 00, Greece

E-mail: [email protected], Tel +30 28210 37776 & +30 6974430525, Fax: +3028210 37845 Abstract This paper describes a methodology and a software system that can be used for developing optimal municipal solid wastes management plans in large study areas. These plans can satisfy all legal and other requirements with the least cost. The system allows also the performance of sensitivity analy-sis, which comprises the development of alternative optimal plans, each of which meets a set of de-sirable constraints, such as the exclusion or imposition of sites and/or technologies and the applica-tion of capacity limits. The sensitivity analysis provides key technical and economic data to local societies so as to assist them in the select the most appropriate plan, the one that balances best their desires against cost, and not necessarily the least cost one.

Keywords: Waste management plans; waste management costs; biological drying; aerobic MBT; incineration; waste recycling. 1. INTRODUCTION The worldwide realization that the Municipal Solid Wastes (MSW) constitute a valuable source of materials and energy and the growing emphasis on environmental protection results to stringent management requirements for increasing quantities of wastes. As the management costs are escalat-ing, large installations have to be built and the wastes have to be transported over long distances though integrated road, rail and marine transportation networks. Planning is thus evolving into a sophisticated science that needs to combine a multitude of interac-tive measures for the purpose of fulfilling several legal and other requirements. The objective of the present paper is to describe a methodology and a computer software system, that can be used by planners for developing truly optimal waste management plants over large study areas. 2. THE OPTIMIZATION PROBLEM The present paper considers the management of the comingled MSW that remain after the applica-tion of material recovery at the source programs. Planning starts at the point where the packer ve-hicles complete their garbage collection programs and comprises the waste transportation, treatment and disposal.

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The schematic diagrams of Figures 1 to 4 represent typical MSW management plans, that can be developed based on alternative treatment and disposal methods. This list is not exhaustive as addi-tional treatment methods can be considered (e.g. anaerobic MBT, gasification etc.) and each of the treatment methods can be implemented in a number of different ways (e.g. the plan in Fig. 3 with the Aerobic MBT can be implemented so as to recover recyclable materials with/or without RDF). In the above diagrams each Region can comprise a number of Prefectures and each Prefecture a number of Municipalities, as is the case in Greece. The number, the size and the location of installa-tions need to balance, in an optimal way, the economy of scale against the transportation costs, Economopoulou and Economopoulos (2006). The larger the installation and the economy of scale, the larger the area served and the greater the mean normalized transportation cost. Based on the above:

• If landfilling is the sole objective of the MSW management, as in the diagram of Fig. 1, a fair number of landfill sites are required (134 were planned for Greece). This is because landfilling is a low cost operation offering limited economy of scale.

• If the wastes are to be biologically dried and the SRF produced is to be incinerated, as in the diagram of Fig. 2, numerous biological drying plants are required as they offer no economy of scale (they comprise parallel modules, each of which is capable of processing about 50,000 t/y of MSW), few SRF incineration plants as they offer a strong economy of scale and still fewer toxic waste disposal sites, as the toxic wastes quantities generated are li-mited.

• If the wastes are to undergo aerobic Mechanical-Biological Treatment (aerobic MBT), and if the RDF produced is to be incinerated, a limited number of aerobic MBT plants are re-quired, as they offer a fair economy of scale and these have to be combined with fewer RDF incineration plants and still fewer toxic waste disposal sites, as in the previous case.

• If the wastes are to be incinerated, a small number of plants is required as they offer a strong economy of scale and still fewer toxic waste disposal sites as in the previous cases.

From the above it would appear that in each case planners have to define:

• The optimal location and capacity of each plant, the source of their waste input and the des-tiny of their products.

• The optimal transportation system from each municipality to each plant and from each plant to other plants or to final disposal sites. This may involve a combination of road, rail and marine transport modes and is usually implemented through a network of transfer stations.

REGIONS LANDFILLS

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Fig. 1 Schematic representation of a management plan involving direct MSW landfill

REGIONS BIODRYING

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SRFINCINERATION

TOXICDISPOSAL

Fig. 2 Schematic representation of a management plan involving biological drying of the MSW and incine-

ration of the SRF produced

REGIONS AEROBIC MBT

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RDFINCINERATION

TOXICDISPOSAL

Fig. 3 Schematic representation of a management plan involving aerobic MBT of the MSW and incineration

of the RDF that could be produced

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REGIONS

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WASTEINCINERATION

TOXICDISPOSAL

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Fig. 4 Schematic representation of a management plan involving mass incineration of the MSW

In the above exercise planners have to develop their management system so as to minimize the sum of the annualized capital investment cost and the annual operating costs of all transportation, treat-ment and disposal operations, taking into consideration the income from the sale of products. This tends to be a rather complex exercise and in practice even more complex as:

• Alternative technology combinations with different products need to be considered and an optimal plan needs to be generated that provides the best overall solution.

• Constraints need to be observed, e.g. landfill site capacities, site-specific limitations in the plant technologies and/or capacities.

• A number of basic parameters, such as the quantities of wastes generated and/or the man-agement requirements, change with time. As a result the system design might have to be dy-namic (evolving with time).

When an optimal solution is produced, the decision makers often wish to know the technical and economic consequences in cases where some limitations were observed (e.g. exclusion or imposi-tion of a technology, exclusion or imposition of some sites, imposition of capacity limits etc.). To cope with these requirements, new optimal management plans have to be generated, each of which meets the desired set of constraints. The comparison of these optimal plans at the Municipal, Pre-fectural and Regional level constitutes the sensitivity analysis. The latter multiplies the design ef-fort, but is valuable to the decision makers helping them to balance social and other preferences against costs and thus to select the most appropriate solution. The above discussion serves to demonstrate the point that in all but the simplest cases, the devel-opment of optimal plans is a fairly complex operation and, for this reason, planners are significnatly assisted use proper methodologies and powerful software tools. 3. INCENTIVES FOR OPTIMIZATION As the management of MSW is becoming increasingly complex and expensive, planners have to develop sophisticated plans, able to combine environmental friendliness and public acceptance with the lowest cost. For this they can be assisted by the methodology and the software tools described elsewhere (Economopoulou et. al, 2005) and outlined in the section that follows. The remainder of

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the present section focuses on the economic impact of the optimal planning exercise. For this, the economic results of a relatively simple and a relatively sophisticated case study are presented. The present methodology and software tools were used in 1995/96 for developing an optimal man-agement plan for the Region of West Macedonia. The latter is located in the North-Western part of the Greek mainland and comprises four Prefectures with a total population of about 450,000. The management requirements were confined to the transportation and the proper disposal of the MSW generated in the Region. The results of the optimization and sensitivity analysis are presented in the diagram of Fig. 5 and can be described as follows (Economopoulou at al., 1999):

Option 1: Optimization of the MSW transportation and final disposal with no constraints imposed. This resulted to the lowest overall management cost, as it could be expected. According to this plan, the use of one or two central landfills in the optimal locations could serve equally well the entire Region. The wastes are optimally transported by the packer vehicles due to the proximity of the largest urban areas to the landfill(s) and the limited quantities of wastes generated by the remaining smaller urban settlements.

Option 2: Optimization of the MSW transportation and final disposal, with the construction of a transfer station near the largest city imposed. This transfer station was desired by the adminis-tration, but it was shown to be uneconomical and for this reason it was not recommended.

Option 3: Simulation of the existing MSW management plan, with the above mentioned transfer station and one landfill per prefecture. This was shown to be considerably more expensive compared to the above optimal plans.

1 2 3500

600

700

800

900

Annual cost (Million Drachmas)

1. Optimal plan with no constraints2. Optimal plan with one transfer station imposed3. Existing plan

Fig. 5 Annual cost of alternative MSW management options for the Region of West Macedonia (1995 cost basis)

The present methodology and software tools were used for developing a master plan for the man-agement of the MSW in Greece, in accordance with the applicable E.U. Directives Economopoulos, 2009). The objective of this study is the analysis of existing Regional plans, the formulation and analysis of a new National plan, and the comparative evaluation of the above alternatives. The Re-gional plans rely on the use of numerous new Integrated Waste Management Facilities (IWMF) and

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on biological drying of the MSW and on the incineration of the SRF produced (see schematic dia-gram of Fig. 2). The results of the analysis show that this scheme is incompatible with the applica-ble EU Directives, as well as overly expensive. In view of these problems, a new National plan is developed, which rely on the use of three new central IWMFs and on the Aerobic Mechanical-Biological Treatment (MBT) with recyclable material recovery and optional RDF recovery and in-cineration (see schematic diagram of Fig. 3) for the treatment of wastes. This plan is formulated so as to be compatible with all applicable EU Directives, as well as cost effective. The results of the economic analysis are presented in the diagrams of Fig. 6 and, as its shown, the existing Regional plans require 4.3 to 4.8 times (3.7 to 4.4 billion €) higher capital investment and their annual cost is at least 2.1 to 2.3 times (577 to 720 million €/y) higher compared to the new National plan.

0 1.000.000.000 2.000.000.000 3.000.000.000 4.000.000.000 5.000.000.000 6.000.000.000

Existing Regional Plans

Proposed New National Plan

Capital investment requirements by the year 2020 [€]

Transportation

Treatment in new plants

Final disposal

0 200.000.000 400.000.000 600.000.000 800.000.000 1.000.000.000 1.200.000.000 1.400.000.000 1.600.000.000

Existing Regional Plans

Proposed New National Plan

Annual cost of transportation, treatment and final disposal [€/y])

Cost of trnaportationCost of treatment in new plantsCost of treatment in existing plantsCost of final disposal

Fig. 6 Capital investment requirements until the year 2020 and annual cost of alternative National

MSW management plans for Greece (2009 cost basis) The above examples serve to demonstrate that the rational planning offers significant economic savings. This is certainly true when planners deal with large study areas and sophisticated manage-ment objectives. This can be also true even when planners are confronted with relatively small Re-gions and simple management objectives. In either case, the cost of proper planning is usually a small part of the savings offered for a single year. 4. METHODOLOGY AND SOFTWARE SYSTEM DESCRIPTION A methodology, which can be followed for the development of effective management plans is illu-strated in the schematic diagram of Fig. 7. According to this, the procedure begins with a prelimi-nary study, the objectives of which are: (a) collection of key data and information, (b) assessment of the minimum number and location of sites for building the treatment and/or disposal installations, (c) definition of the basic management requirements, in accordance with the existing laws and poli-cies, and comparative evaluation of alternative technologies in terms of their compatibility with the management requirements, cost and environmental problems.

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The optimal planning that follows makes use of an advanced software system that is supplied with the necessary data and information (including the ones prepared in the preliminary phase) so as to develop and optimal plan and perform sensitivity analysis. The latter comprises a set of alternative optimal solutions, each of which fulfills a desirable set of constraints (e.g. exclusion or imposition of a technology, exclusion or imposition of some sites, imposition of capacity limits etc.). For each optimal solution there is a detailed cost analysis at the Municipality, Prefectural and/or Regional level, along with visual geographic representations.

Minimum Number of Sites / Selection of

Candidate Sites

SoftwareSystem

Modules for the design and cost estimation of

• Landfills• Transfer stations• Mechanical separation• Aerobic MBT

Cost functions for other installation types

PRELIMINARY STUDY

Optimal plan

Detailed cost analysis

Indicative design of selected installations

Selectedconstraints

Legal Framework / Management Objectives /

Selection of Technologies

Sensitivityanalysis

OPTIMAL DESIGN

Collection of Data and Information

Fig. 7. Methodology and software system for MSW management plan formulation

The preliminary and the detailed study are not mutually independent. The execution of the prelimi-nary study is assisted significantly by the use of the software tools of the detailed study. The de-tailed study in turn, uses the data of the preliminary study and follows its management directions. The latter simplify drastically the optimization problem as they restrict the analysis to a limited number of alternative technologies that suit best the intended purpose. 5. INPUT DATA REQUIREMENTS AND RESULTS The basic data requirements for the formulation of optimal management plans are illustrated in the diagram of Fig. 8 and are summarized as follows:

• Annual quantity of wastes generated by each Municipality during the design period, along with their typical composition.

• Temporal distribution of the collected waste loads (weekly, daily and hourly loads).

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• Location of existing installations, along with key data about their operation. The latter are collected through specialized questionnaires, depending on the type of installation.

• Location of candidate sites for the location of transfer, treatment and final disposal installa-tions, along with key characteristics (e.g. size of available area, holding capacity of land-fills).

• Definition of alternative routes that connect municipalities to sites and sites to sites with re-levant data about distances and mean transportation times. This information is normally produced through the use of GIS.

• Definition of the desirable sets of constraints. For each such set, an optimal plan is to be formulated, which will fulfill all relevant constraints.

Quantities & Composition

Temporal Distributions

Candidate Sites

Alternative Transportation Links

Existing Infrastructure

InputDatabase

Plan Optimization Software System

OutputDatabase

GIS RepresentationsOptimal PlansDesign of PlantsSensitivity Analysis

MIS/GIS

Alternative Constraints

Fig. 8. Input and output of the management optimization software system

As illustrated in the diagram of Fog. 7, the software system comprises modules that estimate the capital investment and the annual operating cost of the installations involved. The required cost data for transfer stations, aerobic MBT plants and landfills are estimated analytically by sophisticated plant design and cost estimating modules. The cost data for other types of installations are com-puted from cost functions, Economopoulos (2010). The software system comprises a cost database, which yields valid predictions for plants in E.U. countries. This database may have to be modified so as to yield valid preditions in other countries. The results comprise graphical presentations of the optimal solutions, as well as a number of reports (with material flows and cost analysis), which define the optimal solutions and allow comparison of the optimal solutions at the Municipality, Prefectural and Regional level (sensitivity analysis). In

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addition, reports can be generated that define the optimal design and operation of transfer stations, Aerobic MBT plant and Landfills. 6. DISCUSSION AND CONCLUSIONS With the application of the present methodology and software tools, planners can develop optimal waste management plans that meet all legal and other objectives with the least cost. The sensitivity analysis allows the development of optimal plans that meet desirable constraints, such as the exclu-sion or imposition of sites and/or technologies and the application of capacity limits. This helps lo-cal societies to select, among the alternative plans, the one that balances best their desires against cost. The application procedure is well organized so as to allow the fastest possible development of plans. The time required for this purpose normally ranges from 6 to 24 months, depending on the size of the study area, the complexity of the management objectives, the extend of the sensitivity analysis and, above all, the availability of the required input data. The execution of a project is carried out by our study team, which can be assisted significantly by local scientists and engineers. The latter can collect, crosscheck and preprocess the required data under the directions of the study team. REFERENCES 1. Economopoulos, A. P. (2010). “Technoeconomic aspects of alternative municipal solid wastes

treatment technologies”. Waste Management. To appear.

2. Economopoulos, A. P. (2009). Formulation and comparative evaluation of rational MSW man-agement plans for Greece. Keynote paper. Proceedings, 2nd International Conference on Envi-ronmental Management, Engineering, Planning and Economics, June 21 to 26, Mykonos is-land.

3. Economopoulou A. A. and A. P. Economopoulos, (2005). Transport distances versus econo-mies of scale for municipal solid wastes treatment and disposal installations. Conference pro-ceedings. 9th International Conference on Environmental Science and Technology. Rodos, Sept. 3 to 6, 2005.

4. Economopoulou, M. A., A. A. Economopoulou, P. P. Economopoulos and A. P. Economopou-los, (2005). “Optimal Solid Wastes Management / Part I: Methodology and Software Infra-structure”. Proceedings of the 5th International Exhibition and Conference on Environment “HELECO ’05”, Paper O-C31. Technical Chamber of Greece, Feb. 3 to 6, Athens, Greece..

5. Economopoulou M.A., P.P. Economopoulos and A.P. Economopoulos. (1999). “Optimum mu-nicipal solid waste management and sensitivity analysis for the region of W. Macedonia.” Pro-ceedings, of the 3rd International Exhibition and Conference on Environment “HELECO’ 99”, Vol. II p. 31-41. Technical Chamber of Greece, June 3 to 6, Thessalonica, Greece.