Thailand currently produced about 14.4 million ton/year of the municipal solid waste (MSW), nearly all of which are disposed in landfill. Only 5 disposal sites nationwide truly operate with all the operation practices and environmental controls and conditions expected for a sanitary landfill. The remaining sites incorporate some but not all of these practices and most commonly lack environmental controls. Furthermore, MSW generation would grow 25% by the end of decade. Pollution Control Department (PCD), the national authority that responsible for the MSW management policy and planning, has 2 goals on MSW strategy as:

1. Implementation of feasible and appropriate technical solutions for integrated MSW management focusing on waste-to-energy (WTE) scheme, and

2. Reduction of MSW to be disposed of in landfills in target areas and utilization of MSW as energy generation.

So, Thailand has opportunity to make progress in improving the public health and environment for future generations through better waste management by the large untapped potential of energy recovery from MSW.

To make a resource utilization project by the WTE strategy, incineration technology is developed to perform high-efficiency power generation by reheating the low temperature steam collected from MSW incinerator using petroleum fuel and generate the high temperature steam. Electrical and thermal energy can be utilized from this facility. However, using the combination among landfill, incineration, and composting options for integrated solid waste management (ISWM) system may be necessary for successful waste management. This study addressed the comparative evaluations on the interrelationships among geographic condition, treatment options, economic impact, environmental impact, social impact, and integration framework and legislation requirement under the life cycle concept.

Comprehensive approach on the project feasibility study for the business opportunity of the WTE in Thailand was adopted in the research. Various sources of data were use in the study. Mass burn incineration, such the simple stoker grate WTE plant, was selected for the evaluation in this research. It is a well proven technology and predominant form of MSW incineration because of its simplicity. However, the MSW-fired power cycles have one of the operation limitations resulted from high corrosiveness of the boiler tube at high temperature and consequently very low electrical generating efficiencies. So, incorporation of the MSW boiler as a bottom cycle into a hybrid combined cycles with natural gas (NG) fired topping gas turbine, where the topping exhaust provides superheating, can substantially improve the electrical efficiency of MSW energy utilization using only conventional technology.

From the study of MSW generation, collection, and management policy in Thailand, it was found that BMA (Bangkok Metropolitan Administration) area could be a representative location of the WTE facility and ISWM system proposed in this research. Project site options for the establishment of MSW incineration plant in this research are selected at: 1) Onnuch transfer station, 51 2) Ladkrabang industrial estate, S2, . and 3) Bangpoo industrial estate, S3.

Treatment options in this research covered: 1) Landfilling as business as usual (Landfillbau) that accounted only its operation cost, or operation practice improved with the true cost of investment is covered (Landfilltruct),2) WTE incineration with options combination of the energy recovery as electricity (Incinerationpower) and heat (IncinerationcHP), and the combined cycle technology (IncinerationHcc and IncinerationHybcHP), and 3) Composting: for the organic fraction of the waste. Options of ISWM system as 2,600 ton/day capacity are: 1) dispose all 2,600 ton/day in landfill 2) 1,300 ton/day is disposed in landfill and 1,300 ton/day is incinerated 3) 2,600 ton/day is incinerated 4) 1,300 ton/day is incinerated and 1,300 ton/day is composted and 5) 1,300 ton/day of MSW is disposed in landfill and another 1,300 ton/day is composted. Using the combination of the options for ISWM system, landfill situation, incineration system, and project site; 44 alternatives was established.

In the economic feasibility study, discount cash flow (DCF) model with full cost accounting (FCA) was developed to tackles the planning phase of local ISWM incorporated with WTE technology. The economical beneficial effects of the hybrid combined cycles for WTE incineration in ISWM framework have been confirmed.

For the environmental feasibility study, it was aimed to understand the overall environmental impact of the waste treatment alternatives for municipal solid waste management (MSWM) planning with life cycle assessment (LCA). The result from life cycle impact assessment (LCIA) showed the environmental benefit of implementing the WTE incineration with heat recovery. The study also pointed out the environmental impact from current operation of landfill disposal. Integrated weighting indicator was established for the decision maker, so that the decision makers could base their judgment on the complete view provide by environmental impact assessment from various impact categories.

Public preferences for MSWM alternatives using contingent valuation method (CVM) in Bangkok were conducted as social feasibility study. People's concerns towards MSWM and their relation with the preferences to facilities were analyzed. Questionnaires were used in face-to-face interviews with the residents in Bangkok. A questionnaire was designed based on major concerns of willing to accept (WTA) and willing to pay (WTP) of the proposed ISWM alternatives. Results revealed the considerable preference in incineration with combined cycle technology, and affordability in the combined cycle incineration with heat utilization over the other treatment methods.

Economic, environmental, and social aspects have to be considered to measure the sustainability of project development. Driving forces of the project were examined and decision indicators were identified. Multi-criteria analysis (MCA) technique for comparing and ranking different outcomes that evaluated from non-monetary objectives and indicators was applied. Result from the calculation of sustainability indicator showed that combined cycle incineration with heat utilization alternative gave the optimal performance.

Panel weighting by face-to-face interviews was conducted. Weighting value that reflected durability of the sustainability was based on the qualitative consideration from stakeholder situation. Result showed slightly different weights received from the panel compared with the equal weighting. Increasing weight in economic domain from the panel resulted decreasing in attraction of the ISWM alternatives engaged with incineration. Integrated evaluation combined both optimality and durability provided final result for sustainable development of the MSWM to the decision maker.

From this study, the following conclusions were withdrawn: The position of Thailand is on the decisive steps to address the unfinished agenda by focusing on MSW reduce and recycling; improving treatment and safe disposal; enhancing the supporting institutional, regulatory, and financing framework; and expanding public and civil society participation.

A framework has been developed to assess impacts, especially economic, social, and environmental impacts of technologies. Research on improving the framework is required, considering on the reduction of uncertainties and expanding of the treatment methods and criteria pollutants for impact assessment. It is recommended that the best available data be used to minimize the discrepancies between the model and reality.

The policy implications of the results presented in this research depend on the aim of policy. The discussion here tasks as a starting point that one aim of the policy is to establish central solid waste disposal facilities with integrated concept of appropriate technology and beneficial utilization of waste such as energy recovery.

In the system studied here, combined cycle incineration with heat utilization alternative gives the most attractive performance. If MSW can replace fossil fuel energy sources, a policy promoting incineration will be success. Application of the methodology in this research may be useful to other developing country in MSWM to utilize the valuable potential as an alternative resource.

本論文は「Evaluation of Waste-to-Energy Technology Incorporated into the Integrated Solid Waste Management Systems in Thailand (タイにおける統合的固形廃棄物管理システムに組み込んだ廃棄物エネルギー変換技術の評価)」と題し、発展途上国の中で比較的経済発展が顕著なタイのようなに国において、今後重要となるであろうごみ焼却発電などの廃棄物からのエネルギー利用技術について、それが統合的廃棄物管理システムに組み込まれたときの評価方法の枠組みを示し、首都バンコクにある地区を選定したケーススタディーにおいて、ごみ焼却発電を組み入れる廃棄物管理政策が様々なステークホルダーにも受け入れられ、またごみ焼却発電事業が環境ビジネスとして成り立つことを示した研究である。

第1章は「序論」である。研究の背景、問題意識、それを受けた研究の必要性、目的と位置づけ、及び論文構成等を述べている。

第2章は「既往の研究」である。廃棄物エネルギー変換技術、ごみからのエネルギー回収の現状、一般廃棄物処理プロセス等に関する経済的分析手法、環境影響評価手法、社会的受容性評価方法に関する既往の知見をまとめている。

第3章は「研究の方法、基礎となる情報、シナリオ」である。本研究の方法論を述べ、ケーススタディーのために選定した地区に関する基礎情報や研究に使用した基礎データを示し、またバンコク首都圏庁の廃棄物管理に関する将来計画を参照してリサイクルする廃棄物を設定し、基本的には、エネルギー回収型焼却とコンポストの中間処理と衛生埋立てを組み合せる処理プロセスのシナリオを設定している。

第4章は「経済的フィージビリティ」である。本章では、IRR(Internal rate of return)を評価指標として、プロジェクトとしての事業収益性を評価し、各シナリオの経済面での実現可能性を評価している。焼却施設は建設コストが高いことも発展途上国で敬遠される大きな要因であるが、本研究では、既存の天然ガスパイプラインを有効に利用できる位置を選定すれば、「コンポスト‐埋め立て」シナリオより収益性は劣るが、ガス複合発電を導入しても十分経済的に成立する魅力的なIRR値を与えることを示した。限界IRRを7.5%とすると、熱需要先として近くに工業団地が十分に確保されない選定地シナリオでは、熱供給を含むコジェネレーション(熱電供給)事業は成立しない場合が生じるが、逆に発電事業を中心とするシナリオではより広い範囲の条件で収益性を確保できることを定量的に示した。

第5章は「環境影響評価」である。本章では、GWP(Global Warming Potential),AP(Acidification Potential),NP(Nitrification Potential)を基本評価指標として、各シナリオの環境影響面での評価を行なっている。焼却を導入することにより埋め立てからのメタン生成は削減されるため、また窒素対策が十分になされる焼却技術ではNPの面でアンモニアを揮散させるコンポストよりも有利になり、総合的に焼却技術を導入する方が環境影響面で有利となることを示している。なお明確に定量的に評価するため重み付けEIP(Environmental Impact Factor)を用いると、熱電供給及びガス複合発電シナリオが最もインパクトの低いシナリオであることを示した。また、重み付けの感度解析からも評価順位の変動は上記2シナリオでは生じず、頑健な評価となっていることが示された。

第6章は「社会的選好」である。如上の章の結果を基にインタビューとアンケート調査を実施し、CVM(Contingent Valuation Method)を用いて、WTA(Willing to Accept) 及び(Willing to Pay)を算出し、社会的選好指標として各シナリオを評価している。400通の調査票のうち51%の回収率で解析に使用しうる回答を得た。WTAを指標すると、ガス複合発電に最も高い選好が示された。また、ガス複合発電や熱電供給に対するWTPでは、現在のごみ処理料金より高い料金を払っても良いという受容性が認められた。逆に埋め立てのみのシナリオでは、現在のごみ処理料金よりも低い支払い意志しか得られないことがわかった。

第7章は「総合的評価」である。前章までの結果を総合し、経済的フィージビリティ(IRR)、環境影響(EIP)、社会的選好(WTA)の3指標を統合した指標(SI, Sustainability Index)を提案している。上記3指標の重み付けのため、ステークホルダーごとのインタビュー調査を実施した。全体的には、重み付けの有無に関わらず、ガス複合発電と熱電供給事業が高い評価となることが示された。ただし、熱電供給事業では事業収益性から成立しない場合があり、そのことを考慮するために、総合的評価を行なう前に限界IRRに達しない事業は除くという評価の方法論が重要であることが確認された。

第8章は「結論と今後の課題」である。本研究で得られた結論及び評価の方法の枠組みを提示し、今後の研究課題について述べている。

以上要するに、本論文は、タイ・バンコクにおける廃棄物エネルギー変換技術としてのごみ焼却発電の導入を具体例として、事業収益性を担保しつつ地球のサステイナビリティの貢献する先進技術の発展途上国への適用性の評価の枠組みを示したものであり、本研究で得られた知見は、都市環境工学の学術の発展に大きく貢献するものである。

よって本論文は、博士(工学)の学位請求論文として合格と認められる。