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Fifty years of sewage sludge management research: Mapping researchers' motivations and concerns
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.ORCID iD: 0000-0002-6141-7796
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.ORCID iD: 0000-0002-8758-2079
Department of Thematic Studies, Technology and Social Change at Linköping University, 58183, Linköping, Sweden.
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.ORCID iD: 0000-0002-4597-4082
2023 (English)In: Journal of Environmental Management, ISSN 0301-4797, E-ISSN 1095-8630, Vol. 325, article id 116412Article in journal (Refereed) Published
Abstract [en]

Sewage sludge management is torn between a desire for pollution prevention and reuse of a valuable resource. Reconciling these interests in sustainable management is a challenge for researchers. This study focuses on how research on sewage sludge management practices has evolved and scrutinizes how this research is interlinked with concerns and societal issues such as contaminants, economic efficiency, and legislation. Based on published academic papers on sewage sludge management between 1971 and 2019, this study found four trends in research focused on sewage sludge management: a decreasing interest in disposal (landfilling and sea dumping), a dominant interest in land application, a growing interest in sewage sludge as product, and a stable interest in energy recovery. Research on disposal focuses on increasing sludge volumes, legislative changes, and economic challenges with an interest in waste co-treatment. Research on land application concerns nutrient use and contaminants, mainly heavy metals. Research on sewage sludge as a product focuses on the extraction of certain resources and less on use of sewage sludge specifically. Research on energy recovery of sewage sludge focuses on volume reduction rather than contaminants. Two-thirds of the papers are detailed studies aiming to improve single technologies and assessing single risks or benefits. As management of sewage sludge is multifaceted, the narrow focus resulting from detailed studies promotes some concerns while excluding others. Therefore, this study highlights potential gaps such as the combination of nutrient use and disposal and energy recovery and nutrient use. 

Place, publisher, year, edition, pages
Elsevier, 2023. Vol. 325, article id 116412
Keywords [en]
Land application, energy recovery, phosphorus, legislation, resource recovery, biosolid management
National Category
Energy Systems Environmental Management
Research subject
Energy Engineering; Waste Science and Technology
Identifiers
URN: urn:nbn:se:ltu:diva-93660DOI: 10.1016/j.jenvman.2022.116412ISI: 000877514100006PubMedID: 36274309Scopus ID: 2-s2.0-85140098755OAI: oai:DiVA.org:ltu-93660DiVA, id: diva2:1705028
Funder
Swedish Energy Agency, P46028-1Swedish Research Council Formas, 2018-00194
Note

Validerad;2022;Nivå 2;2022-10-25 (hanlid);

Funder: Bio4Energy

Available from: 2022-10-20 Created: 2022-10-20 Last updated: 2024-04-15Bibliographically approved
In thesis
1. Integrated sewage sludge treatment scenarios – techno-economic analysis on energy and phosphorus recovery
Open this publication in new window or tab >>Integrated sewage sludge treatment scenarios – techno-economic analysis on energy and phosphorus recovery
2022 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Sewage sludge is a by-product of wastewater treatment that simultaneously gathers contaminants, valuable organic matter, and nutrients. The treatment of the increasing amount of sewage sludge is important from both pollution prevention and resource recovery perspectives as i) large shares of mineral phosphorus, listed as a critical raw material, terminate in the sewage sludge, and ii) energy recovery from sewage sludge can cover the energy-intensive demand of the treatment process. Previous research has identified sewage sludge combustion as a suitable treatment approach as it both addresses contaminant destruction and paves the way for efficient phosphorus recovery from the sewage sludge ash. The commercial development of this practice has, however, been slow. Therefore, this thesis aims to investigate the challenges in sustainable sewage sludge management, and to, in more detail, identify the economic viability of energy and phosphorus recovery from sewage sludge through combustion.

The thesis’ aim is divided into two objectives addressed in three papers. First, to investigate how different aspects of sewage sludge management, such as contaminants, economic efficiency, technical aspects, and legislation, evolve and interact. This has been done by a review of sewage sludge management research over fifty years (Paper I). Second, to investigate the economic viability of simultaneous energy and phosphorus recovery from sewage sludge by comparing different technology and market scenarios. This has been done for i) new sewage sludge mono-/co-combustion plants (Paper II), and ii) the integration of treatment technologies, mainly anaerobic digestion, hydrothermal carbonization, and combustion, in an existing wastewater treatment plant (Paper III). 

Results from the analysis of sewage sludge management research (Paper I) show a narrow-focused perspective that often excludes inseparable aspects such as combination of economic consideration and advanced extraction technology. The investment viability of a new mono-/co-combustion of sewage sludge (Paper II) is highly conditional on heat, electricity, and fertilizer price, and external financial support is often a crucial requirement. Sewage sludge co-combustion with potassium-rich biomasses improves sewage sludge quality and forms usable ash as fertilizer without further need for phosphorus recovery technology. In this case, the economic feasibility of the process is independent of usable ash revenue, which stimulates a competitive selling price for the ash, thereby improving the marketing of sludge-based fertilizer. Avoided disposal costs of sewage sludge for a retrofitted wastewater treatment plant by introducing hydrothermal carbonization (Paper III) shows good economic feasibility while recovering phosphorus. Integrating anaerobic digestion, hydrothermal carbonization, and combustion may also improve investment incentives by improving energy outputs and phosphorus recovery. The economic feasibility is contingent on product (hydrochar, heat, electricity) prices and sensitive to added equipment costs, and costs for sludge transportation and disposal. 

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2022
Series
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757
Keywords
Sewage sludge management, techno-economic analysis, phosphorus recovery, thermochemical treatment
National Category
Energy Systems
Research subject
Energy Engineering
Identifiers
urn:nbn:se:ltu:diva-93662 (URN)978-91-8048-196-0 (ISBN)978-91-8048-197-7 (ISBN)
Presentation
2022-12-16, A117, Luleå tekniska universitet, Luleå, 09:00 (English)
Opponent
Supervisors
Available from: 2022-10-21 Created: 2022-10-20 Last updated: 2023-09-05Bibliographically approved
2. Sustainable Sewage Sludge Management: Addressing Multidisciplinary Challenges
Open this publication in new window or tab >>Sustainable Sewage Sludge Management: Addressing Multidisciplinary Challenges
2023 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Hållbar Hantering av Avloppsslam med Fokus på Tvärvetenskapliga Utmaningar och Lösningar
Abstract [en]

This PhD thesis focuses on multidisciplinary challenges in sewage sludge management and how they can be addressed to increase sustainability. 

Sewage sludge is the residual from wastewater treatment. It contains both resources and contaminants making its management challenging. In the past sewage sludge was often used as a fertilizer in agriculture, a practice that is still used in several countries. Today, this practice gets questioned in Europe and especially in Sweden due to the presence of contaminants in the sludge. At the same time, the resources in the sludge get into a stronger focus as society moves towards a circular economy and food production should get more resilient in a world with geopolitical challenges. In sustainable sewage sludge management, the two goals of immobilising/destroying the contaminants and utilizing the resources in the sludge are combined. 

This thesis identifies challenges in various disciplines and provides potential solutions to make sewage sludge management more sustainable. The discussed challenges cover the following areas: legislation (EU and Sweden), perception of sewage sludge (Sweden), research on sewage sludge management (international), and combinations of treatment methods. Results show that outdated legislation in Sweden creates insecurities, while the negative perception of sewage sludge in Swedish society further aggravates these insecurities. Although technical solutions are available or under development, e.g., treatment combinations that can separate resources and contaminants, actors in Sweden remain hesitant due to the aforementioned insecurities. This thesis emphasizes that interdisciplinary approaches, and dialogues between different actor groups and society are essential. The multitude of challenges requires solutions that combine technical and non-technical approaches. Therefore, this thesis provides recommendations for more sustainable sewage sludge management practices, including updating legislation.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2023
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
National Category
Energy Systems Environmental Management
Research subject
Waste Science and Technology
Identifiers
urn:nbn:se:ltu:diva-96680 (URN)978-91-8048-323-0 (ISBN)978-91-8048-324-7 (ISBN)
Public defence
2023-06-16, C305, Luleå tekniska universitet, Luleå, 10:00 (English)
Opponent
Supervisors
Funder
Swedish Energy AgencySwedish Research Council Formas, 2018-00194Swedish Agency for Economic and Regional Growth, 20200905
Available from: 2023-04-20 Created: 2023-04-20 Last updated: 2024-05-21Bibliographically approved
3. Sewage Sludge Treatment Scenarios: Techno-Economic Analyses of Energy and Phosphorus Recovery Focusing on Implementation Challenges
Open this publication in new window or tab >>Sewage Sludge Treatment Scenarios: Techno-Economic Analyses of Energy and Phosphorus Recovery Focusing on Implementation Challenges
2024 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Managing sewage sludge, an inevitable by-product of wastewater treatment processes rich in both contaminants and valuable resources, presents a dual challenge: ensuring pollution prevention by immobilizing or destroying contaminants, and facilitating resource recovery. Balancing these objectives is critical given the growing volumes of sewage sludge and the imperative to both protect the environment and recover valuable resources. The unknown risks of land application of sludge, the currently most common disposal method, make thermal conversion a promising alternative, as it enables energy recovery, the breakdown of potentially harmful organic compounds, and the formation of volume-reduced, sanitized products. Despite the technical feasibility, the commercial development of advanced recovery technologies has been slow. 

This thesis aims to expand knowledge on different sewage sludge treatment and disposal scenarios under varying conditions; thereby shedding light on implementation challenges, local opportunities, and the financial dynamics critical for phosphorus and energy recovery from the perspectives of wastewater treatment plants, investors, and policymakers. The aim is primarily addressed by performing techno-economic analysis of sewage sludge treatment scenarios, covering the entire sludge treatment process from sludge treatment to end products and disposal (Paper II-V). The techno-economic analysis is supplemented by a review of academic research on sewage sludge management from 1971 to 2019 (Paper I). 

Results from the analysis of sewage sludge management research (Paper I) show a narrow-focused perspective that often misses the broader, interconnected aspects of sewage sludge management, leading to research that, while detailed, fails to capture the complexity of the field. The investment viability of a new mono-/co-combustion plant for sewage sludge (Paper II) is highly conditional on heat, electricity, and fertilizer prices, and external financial support is often a crucial requirement. Cocombustion of sludge (in low ratios) with K-rich agricultural biomass requirement in and energy demand of a thermal dryer, and by yielding ash that contains phosphorus in a plant-available form. Utilizing existing heat facility (Paper III) and co-combustion to mitigate investment costs and energy demand in sludge management showed the potential to offer a cost-effective alternative to land application. However, the viability of co-combustion hinges on both a high heat market price (Paper II) and the proximity of affordable biomass resources (Paper III). Without these conditions, co-combustion may increase the financial burden of sludge management on wastewater treatment plants and policymakers. 

Retrofitting a wastewater treatment plant by integrating hydrothermal carbonization in sludge treatment (Paper IV), demonstrated good economic feasibility, primarily due to the avoided disposal costs, while also recovering phosphorus. However, integrating hydrothermal carbonization in a system designed for a thermal dryer may cause a significant reduction in electricity production.

Given the high moisture content of sludge and the low market prices for fertilizer, the potential revenue from energy and phosphorus recovery is inadequate to solely drive investment in advanced sewage sludge treatment technologies (Papers II-V). This issue is exacerbated by the fact that most wastewater treatment plants are small in scale. Collaborative sludge management across neighboring wastewater treatment plants (Paper V) increases phosphorus recovery capacity and leverages economies of scale, fostering investment in advanced technology. This strategy presents a significant opportunity to lower the treatment costs and offers a competitive alternative to land application, while encompassing energy and phosphorus recovery into the sludge treatment.

In conclusion, resource recovery and pollution prevention in sludge management is a complex task that necessitates simultaneous consideration of technical aspects, product quality, site-specific conditions, and profitability to ensure a comprehensive and viable approach. Leveraging local infrastructure and resources in sewage sludge management is crucial, highlighting the ecessity for strategies to be tailored to the local opportunities and limitations. Such an approach outperforms mono-combustion by eliminating the investment ensures that solutions are not only environmentally sustainable but also economically viable and socially acceptable. 

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2024
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
Keywords
Sewage sludge management, techno-economic analysis, phosphorus recovery, energy recovery, thermochemical treatment
National Category
Energy Engineering Energy Systems
Research subject
Energy Engineering
Identifiers
urn:nbn:se:ltu:diva-105083 (URN)978-91-8048-534-0 (ISBN)978-91-8048-535-7 (ISBN)
Public defence
2024-06-14, A117, Luleå University of Technology, Luleå, 09:00 (English)
Opponent
Supervisors
Available from: 2024-04-15 Created: 2024-04-15 Last updated: 2024-05-24Bibliographically approved

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Bagheri, MarziehBauer, TorbenWetterlund, Elisabeth

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