|Towards sustainable valorization of sludge : a comprehensive decision-support framework
|Ren, Jingzheng (ISE)
Lee, Carman (ISE)
Ji, Ping (ISE)
|Sewage sludge -- Environmental aspects
Sewage sludge -- Economic aspects
Hong Kong Polytechnic University -- Dissertations
|Department of Industrial and Systems Engineering
|xxi, 456 pages : color illustrations
|The generation of sewage sludge increases year by year with the population growth. Under the current situation of environment and resources and the requirement of sustainable development, it is necessary to conduct effective sludge treatment processes to reduce the negative environmental impacts. During the decade, sludge valorization technologies have attracted wide attention since they can process harmful matters, recover valuable components, and realize energy regeneration simultaneously. There are various sludge treatment technologies which can be applied for value-added products production and these technologies usually have different merits and shortcomings in different aspects. It would be challenging to directly judge their performance and make a suitable choice among all the options, especially when considering multi-criteria. However, analyzing the performance on different perspectives of the technologies is important and necessary under current concerns on sustainable development. Therefore, a comprehensive decision-support framework covering life cycle sustainability assessment and multi-criteria decision-making is needed to guide the decision-making process of sewage sludge.
Although some studies have explored different sludge management technologies, there are still many issues that have not been discussed in-depth or even touched upon, such as the solution for sustainability evaluation under lacking data conditions, sustainability-oriented decision-making considering social and technical aspects, and sustainable supply chain design. Hence, this project aims at constructing a comprehensive decision-support framework to provide insightful reference information and suggestions for related managers, including life cycle sustainability assessment for sludge valorization technologies, sustainability prioritization under different conditions and sustainable supply chain design and optimization. The major results and contributions are presented as follows.
Firstly, in terms of sustainability evaluation, a composite sustainability index is proposed to evaluate the performance of sludge-to-energy technologies from the perspective of energy recovery, carbon emissions and water consumption. The index can also be extended to analyze the footprints of other concerned elements, which can promote the understanding of the features of different sludge management technologies. Results indicate the priority of gasification and melting for sludge treatment and energy recovery. Current challenges and barriers to sustainable sludge management are also figured out by the results.
Secondly, different multi-criteria decision-analysis frameworks are developed to solve decision-making problems under complicated conditions, including performance evaluation and decision-making with insufficient performance data, decision-making problems under multi-data conditions, and group decision-making problems. To deal with the problem of lacking data for sustainability evaluation and prioritization of emerging technologies, process simulation and fuzzy PROMETHEE II approach are applied to analyze sustainability ranking and provide recommendations for stakeholders. Decision-making problems under multi-data conditions are discussed and addressed by Dempster–Shafer theory combined with the fuzzy best-worst method (DS-FBWM), which can effectively process the decision-making problems with crisp numbers, interval numbers, linguistic descriptions, and incomplete information. Afterward, a game theoretical-based multi-criteria decision-analysis method is established to deal with the group decision-making problems considering the conflicting interests and interactions between stakeholders. With the guidance of the decision-making frameworks, stakeholders can find out the effective and suitable alternative for sustainable sludge management under complex situations.
Finally, how to design and optimize the supply chain in the urban area for sewage sludge is discussed by constructing a mix-integer programming model, which can help to decide the proper location of sludge treatment facilities and the technical routes for sludge management. A case study in the context of Hong Kong is conducted and results show relatively good consistency with the practice. Results suggest that centralized management of sewage sludge with proper daily capability and cost-effective technical route adaption can effectively reduce the total costs for sludge treatment.
This research provides useful information on the state-of-arts of current sludge management technologies and analyzes the existing difficulties and challenges of sustainability-oriented evaluation and decision-making under complicated situations. To address these problems, innovative sustainability evaluation approaches and MCDA methods are developed, which can provide effective solutions for practical application as well as reference information to guide future research theoretically. Practical cases are analyzed to demonstrate the feasibility of the proposed methodology frameworks and the results indicate the applicability and reliability of these models, which can also provide insightful suggestions and implications for the experts and policymakers.
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