Abstract

Despite of the improvement through the installation of various schemes, development of new treatment technologies and implementation of economic instruments, solid waste and wastewater problems still impose an increasing pressure on cities and remain one of the major challenges on urban environmental management. There is no single solution to the problem since each city has different set of characteristics and treatment plans. Since Brundtland report, sustainable development has become a prominent and broadly accepted guiding principle in post industrial societies. Current assessment usually aspires to measure economic, ecological and social aspects of waste management system as these areas contemplated to be the basis for sustainable development. There are different realities or circumstances towards this matter. Into a retrospective, treatment systems have improved technologically and managerial but little we know about how different sectors among the society (stakeholders) think about the subject. Integrating waste management and stakeholders' participation within decision making process is a complex situation.

Usually, waste management systems are configured based upon local conditions. For instance, Boston (USA) solid waste treatment system has increasingly suffered from space capacity constrains for the final disposal site and therefore the priority has been towards the development of solutions to reduce the volume of waste to be disposed. On the other hand, Zurich (Switzerland) wastewater treatment system and nutrients recycling issues face a completely different situation where the paradigm of which recycling plans is the most appropriated.

Solid waste and wastewater management systems for these two case study needs to be build in a sustainable manner, reflecting the characteristics of each case and including the complex societal part as preferences of the different stakeholders groups. Consequently, there is a need to develop a systematic approach that integrates these preferences and environmental analysis towards a series of waste treatment plans as a decision support tool for decision making process.

Based on this goal, the dissertation aim was to investigate three constituent components of the decision making, i.e. stakeholder groups, criteria (impact categories) and preferences with regard to solid waste and wastewater treatment plans. In addition, the dissertation analyzes the differences in these decision theoretical components between stakeholders groups (e.g. residents, non governmental organizations and local governmental organization) and its contribution on the final decision scheme. As the stakeholder group's preferences vary according to the problematic, Analytical Hierarchical Process (AHP) was chosen as means of analysis and integration. Specifically, the objectives of this thesis include;

"Study the theoretical aspects of Analytical Hierarchical Process and Life Cycle Assessment (LCA).

"Develop a methodology based on LCA and AHP to evaluate possible treatment plans.

"Application of the developed methodology to evaluate a series of treatment plans for Boston solid waste system and Zurich wastewater system.

"Investigate which assessment criteria (impact categories) were the most relevant on the selection of the best treatment plans from the different stakeholders' perspective.

As the first part of the assessment, it is defined the primary goal of the treatment system where as for Boston case study, it was to propose alternative treatments for the actual household solid waste management system considering the improvement and development of the municipal solid waste system in a sustainable manner. As for Zurich case study, the context is on the wastewater treatment system and the subject of phosphorus and nitrogen recycle. The differences among the treatment plans within each particular study case aims to provide the basis for a challenging decision scheme where the preferences of each stakeholders' groups may differ according to the treatment plan. Under this frame, data gathered and estimated following LCA framework is used to compute the different impact categories defined for each case, reflecting the environmental loadings, energy and resource consumption. The impact categories are parameters that essentially were conceived according to the solid waste or wastewater management situation, independents from each other and with values crucially influenced by each of these treatment plans. Based on the system boundaries and data collected, the chosen impact categories can be estimated through the application of Life Cycle Assessment (LCA) and cost analysis methods. Under this framework, the treatment scenarios were developed aiming to create the basis for the decision problem and the application of AHP to analyze the stakeholders' preferences.

In this study, a framework was proposed for this approach and it is divided into 1) Goal definition and scenario development, 2) Definition of system boundaries, 3) Impact categories selection, 4) Data source analysis, 5) Impact categories estimation (based on LCA and cost analysis), 6) Stakeholders groups' analysis and definition, 7) Survey/questionnaire design, 8) AHP implementation and 9) Stakeholders' preferences analysis. As for the case studies, this procedure was followed to implement the decision problem and analyze the stakeholders' preferences. As for the definition of the impact categories, the concept of sustainability was integrated by analyzing the case study characteristics such as feasibility of the treatment plans and the perception that these stakeholders groups had (refer to chapter 3, section 3.2 and 3.3).

From the analysis conducted in Boston case study solid waste management system, interviews with the stakeholders groups and questionnaire survey, three management plans were proposed. Plan I is defined as the present household solid waste treatment and disposal system. Plan II involves the introduction of biogasification as a treatment option for organic kitchen waste and yard trimming waste in order to divert a fraction of residential solid waste that its landfilled and to produce energy. Plan III combines the concept of Refuse Derived Fuel (RDF) and solid waste export, where approximately fifty percent of MSW that is normally landfilled is transformed into dry RDF pellets (dRDF) that are exported to other states as material for waste to energy plants. These scenarios were compared according to a series of impact categories which are broken-down into Operation Cost, Green House Gases (GHG), Disposal Capacity of local landfills and Health Damage (counted as lost of life expectancy). Each plan represents a solution for the MSW system with a certain degree of trade-off between benefit and its consequences that provides the basis for the decision problem among residents, non governmental organization (NGO) and a local governmental agency.

In case of Zurich case study, three management plans involving nutrient recycling were proposed. Plan I is defined as the present wastewater and sludge treatment system. Plan II involves the introduction of a separation scheme at the user level with the aim to separate the urine which is source of a series of nutrients from the wastewater stream. Plan III combines the actual wastewater system and sludge treatment through incineration with the phosphorus recovery from chemical precipitation. The nutrient recycling scenarios were compared according to a series of impact categories as green house gases (GHG), euthrophication, acidification, operation cost and nutrient recycling. Each plan besides the actual treatment system presents a different approach for nutrient recycling as the basis for the decision problem focused to residents in the area of Zurich, NGOs and; federal office for environment and agriculture.

The rank or weight of the management plans for Boston case study shows that for the resident group, Plan II and III were ranked first and second respectively. Despite Plan II involved kitchen and yard trimming waste sorting, residents choice of this plan could be motivated by the actual yard waste separation program in the city of Boston and the home composting carried out by some of the residences. In case of Plan III, the possibility to obtain a benefit by creating RDF pellets from solid waste and to increase the landfill capacity may also played a relevant role, as well as the reduction of local air emissions. In case of the NGO group, plan III and II are ranked first and second respectively which stress the importance the NGO gives the management constrains, especially to the landfill space capacity. Plan III represented the export of solid waste to other states in the form of RDF pellets as source of energy. Even though solid waste separation is not applied at the household level as in plan II, the amount of solid waste disposed in the local landfill site is expected to decrease by the export of RDF. Local governmental agency rank distribution for plan II and III is first and second respectively. The selection of Plan II where Biogasication is introduced could respond to its contribution to separate Kitchen and Yard solid waste from the main stream and consequently extending the landfill capacity, which also answer to the choice of management capacity as the most preferred impact category by this group; following the state policy for implementing solid waste diversion programs.

Despite the low return rate for the questionnaire survey carried out for Zurich case study, residents' preferences towards plan II ( based on urine separation scheme) are higher than the rest of the treatment plans, although this plan requires the cooperation of every member in the household by the use of a special toilet. As for treatment plan I which represents the actual wastewater and sewage sludge treatment, most of the respondents rated this plan the second or even the most preferable options rather than plan III which it may leads us to assume the possible bias the term of sewage sludge may have on the respondent. As nutrient recycling through different schemes is currently being analyzed in Switzerland by the governmental institution, there are no clear policy issues towards these plans at this moment. However, it is possible to highlight that no further development is expected until the health risk associated to micropollutants and heavy metals on nutrients recycled from wastewater and sludge treatment cycle is improved, and market is open to the use of vegetables grown with this kind of fertilizers.

In summary, solid waste and wastewater management involves complex decision making situations that require the understanding of different sectors within the society. This research presents AHP based methodology as a decision making support tool that allows the consideration of several stakeholders' groups preferences during the multicriteria evaluation of different treatment plans. From the case studies, it was proven that in combination with other methods to characterize the different treatment plans (such as LCA), AHP is a useful technique to distinguish the preferences of several sectors and support the decision scheme. However, both the availability and credibility of data plays an important role on characterizing the different plans. Although the impact categories defined on this study represent somehow relevant issues towards solid waste and wastewater treatment systems, there is still a need for a better selection and representation of these categories. From the perspective of the decision problem and stakeholders participation, the results of this analysis may not only provide an starting point for the development of suitable treatment plans according to stakeholders preferences but as well a better understanding to improve it acceptance.

Regarding the dissertation structure; chapter 1 refers to the introduction the solid waste and wastewater management decision problem, the questions and objectives of this work are presented. Chapter 2 is a literature review highlighting the role of multicriteria based methods and AHP. Chapter 3 describes the methodological framework applied on this study where it combines evaluation approaches as LCA and AHP. Chapter 4 analyze how the solid waste management in Boston has changed over the past 15 years and what kind of issues will become relevant on the next 15 years, a comparison with the city of Yokohama is also carried out. Based on the results of this analysis, the decision problem for Boston case study is presented considering how solid waste management would develop in the coming years. According to the decision problem, the impact categories for the different treatment scenarios are calculated through the LCA framework and the related stakeholder groups are described. Chapter 5 introduces the decision scheme for wastewater treatment for Zurich case study where the calculation of the impact categories for the treatment scenarios follows the same approach as chapter 4, as well as the analysis of stakeholder groups.

On chapter 6, a questionnaire survey for each case study was designed based on the characteristics of the treatment scenarios (such as the calculated value for the impact categories). Through the implementation of AHP of the survey results, the preferences of the different stakeholders groups are estimated for the treatment plans and impact categories; considering the analysis of the stakeholder's role on the decision scheme. Conclusions and further recommendations are presented on chapter 7.

廃棄物や下水管理の問題は資源循環と環境負荷削減の観点から世界各地で大きな課題となっている。これらの問題の場合に特徴的なことは、市民、NGO、行政などのステイクホルダーによって意見が異なるという点である。実際の問題を解決し廃棄物や下水のマネジメントを前進させるためにはステイクホルダーの意見を把握し、合意形成を進めていくことが求められており、そのための手法の開発が待ち望まれている。

本論文はこのような背景の元に行われた研究の成果をまとめたもので、Application of Analytical Hierarchical Process to analyze stakeholders' preferences for municipal solid waste and sewage management systems(一般廃棄物および下水管理システムにおけるステイクホルダ-の選好分析への階層分析法の適用)と題し、7章からなる。

第1章は序論であり、廃棄物および下水管理に伴う今日的な課題を述べると共に、これらの課題解決にあたって対象となるステイクホルダーとその関与の重要性を指摘し、本研究の目的を述べている。

第2章は既往の研究の整理である。

第3章は方法論の全体像について整理したものである。本研究ではアメリカ・ボストンにおける一般廃棄物に関する詳細な現地調査およびスイス・チューリヒにおける新たな方式の資源回収型の下水処理についての調査、ステイクホルダーごとの意見の相違を明らかにするための調査と階層分析法を適用したそれらの結果の解析を行っている。これらの一連の方法の中で、本研究が優れている点は、詳細な聞き取り調査に基づいてこれまでの経緯と現状を把握し、それにもとづいて将来シナリオを設定していることと、それぞれのシナリオに対してライフサイクルアセスメントを行うことによって種々の環境側面への負荷を定量的に評価している点にある。更に、これらの定量的な情報を示した上で各ステイクホルダーの意見を調査し、解析している点も優れた点である。

第4章は、ボストンの廃棄物を対象にした調査と解析をまとめたもので、本研究の中心的な章となっている。

まず、廃棄物問題に関する枠組みを解析し、どのようなドライバー(原動力)が働いて廃棄物管理が促進されるかという点をまとめている。その中では、技術的な側面、社会科学的な側面、法的な側面、またさらには国際的な側面が重要であることを指摘し、廃棄物管理計画への反映についてその姿を明らかにしている。

次いで、ボストンの抱えている固有の問題に関して、詳細な現地調査に基づく解析の結果を示している。廃棄物の各成分の量の動向とその変化の背景になっている要因について、1990年から今日、更に将来に向けての姿を示している。また、このボストンと対比する意味で横浜市の廃棄物管理についても同様の方法で解析を行っている。そして、これら両都市の廃棄物管理に関して、1990年から未来にわたる変化の動向を比較検討している。

これらの検討に基づいてボストンの廃棄物管理について、3つの将来シナリオを設定した。すなわち、現状維持、バイオガス化、燃料にして域外に移出、である。一方、意見を求めるステイクホルダーとして、地方政府、住民の他、2つのNGOを選定した。これらのステイクホルダーに対し、各シナリオのライフサイクルアセスメントの結果とコスト、健康影響を定量的に示した上で、それぞれの意識と選好を調査した。

第5章は現在新たに検討されている資源回収型の下水処理について、チューリヒで調査を行った結果をまとめたものである。現状の下水処理システム、屎尿分離型トイレの導入、下水汚泥焼却灰からのリンの回収のそれぞれのシナリオに対して、ライフサイクルアセスメント、費用計算を行い、定量的な比較を可能にした。

第6章は、階層分析法の適用である。第4章で詳細に検討したボストンの廃棄物管理に関し、各ステイクホルダーが各シナリオに下した評価を定量化し、ステイクホルダー同士の重み付けを変化させた場合の総合的な評価について解析を行っている。

第7章は結論であり、結果を総括すると共に、今後の課題を述べている。

本研究は、それぞれの地域によって状況が異なる廃棄物と下水管理に関して、アメリカ、スイス、日本の比較研究を行いその相違を浮き彫りにしただけでなく、ステイクホルダーによる選好の相違を定量的かつ客観的に評価する方法を提案した点に意義がある。本論文で提案している手法は、環境政策に限らず、各ステイクホルダーによって意見が相違するような政策に対して、その評価を与えまた合意形成に資することができるという点で将来の発展性を有している。

以上、本研究において得られた成果には大きなものがある。本論文は環境工学の発展に大きく寄与するものであり、博士(工学)の学位請求論文として合格と認められる。