Unsaturated Phase Environmental Processes in MSWI Bottom Ash
Author
Summary, in English
Every year, Sweden produces 1.5 million tons of incineration residues from waste to energy
plants. Among these residues bottom ash(BA) due to its large volume and good geotechnical
quality can be reused as an alternative construction material. However there are some
negative environmental impacts of this practice such as leaching of salts and metals to soils
and groundwater. Environmental processes occuring in the unsaturated phase can determine
BA’s environmental impacts as well as provide interesting insights into improving its reuse.
However, due to dominant conceptualisation of BA’s environmental impacts as a saturated
phase phenomenon, very little work has been done on understanding the usaturated phase
environmental processes. There is virtaully nothing known about BA’s dielectric properties
which can be an impediment in the development of innovative tools e.g. microwave based
monitoring and metal recovery systems. Similarly, release of hydrogen gas in anaerobic
phase is considered a problem and its recovery for beneficial use has not been considered yet.
Finally, residual organic matter is known to degrade and support microbial respiratory
processes in BA. However, little work has been done on exploring its impact on leaching of
metals and eco-toxicity of ash leachates.Therefore, the objective of this thesis was to
explorethese unsaturated enviromental processes and highlight their role in envrionmental
monitoring, reuse and resource recovery.To achieve this objective, the thesis was divided
into three subdomains; 1) physical-dielectrics and non invasive monitoring , 2) chemicalanaerobic
corrosion and hydrogen production, and 3) biological-microbial respiration and its
impacts on the ash quality. During this work, methods such as frequency domain
relectometry, respiration tests, hydrogen evolution experiments, batch leaching and
ecotoxicity tests were employed. Methods such as gas chromatocgraphy and scanning
electron microscopy(SEM) were also used when needed. For data analysis, statistical
techniques such as polynomial regression, hierarchical clustering and principal components
analysis (PCA) were used. Moreover, during the work on dielectrics, physical models were
also used to establish the relationship between dielectric permittivity and volumetric water
content.
The results of dielectrics showed that in dry state BA acts a non conductor with strong
dispersion tendencies especially at high frequencies.From the measured dielectric spectra, it
was possible to estimate the moisture content as well as the effective electrical conductivity
of BA.The dielectric properties of BA indicate the potential use of microwaves in noninvasive
monitoring of moisture,weathering, residual metal contentand wet metal
recovery.The results of hydrogen gas formation showed that the gas production from fresh
BA was possible at mild conditions of temperature and pressure, and it showeda promise for
commercial development. Comparison of hydrogen production with metal recovery showed
that as compared to metal recovery,the reaction of metallic Al with alkaline solutions, to
generate hydrogen , was more efficient. From the results on respiration tests, it was found
that the respiration in fresh ash played a positive role by lowering the pH, reducing the
leaching of critical metals and modifying the ash leachate eco-toxicity. However in case of
the weathered ash, the microbial respiration negatively affected the ash quality by increasing
the leaching heavy metals. The leaching of metals(Cu, Cr, Mo, Ni, Pb, & Zn) and total
organic carbon was further enhanced by the addition of external organic matter. Further work
on a bench scale hydrogen recovery system, the use of substrate induced respiration in fresh
BA for carbonation and the use of microwaves in environmental monitoring and wet metal
recovery is suggested.
plants. Among these residues bottom ash(BA) due to its large volume and good geotechnical
quality can be reused as an alternative construction material. However there are some
negative environmental impacts of this practice such as leaching of salts and metals to soils
and groundwater. Environmental processes occuring in the unsaturated phase can determine
BA’s environmental impacts as well as provide interesting insights into improving its reuse.
However, due to dominant conceptualisation of BA’s environmental impacts as a saturated
phase phenomenon, very little work has been done on understanding the usaturated phase
environmental processes. There is virtaully nothing known about BA’s dielectric properties
which can be an impediment in the development of innovative tools e.g. microwave based
monitoring and metal recovery systems. Similarly, release of hydrogen gas in anaerobic
phase is considered a problem and its recovery for beneficial use has not been considered yet.
Finally, residual organic matter is known to degrade and support microbial respiratory
processes in BA. However, little work has been done on exploring its impact on leaching of
metals and eco-toxicity of ash leachates.Therefore, the objective of this thesis was to
explorethese unsaturated enviromental processes and highlight their role in envrionmental
monitoring, reuse and resource recovery.To achieve this objective, the thesis was divided
into three subdomains; 1) physical-dielectrics and non invasive monitoring , 2) chemicalanaerobic
corrosion and hydrogen production, and 3) biological-microbial respiration and its
impacts on the ash quality. During this work, methods such as frequency domain
relectometry, respiration tests, hydrogen evolution experiments, batch leaching and
ecotoxicity tests were employed. Methods such as gas chromatocgraphy and scanning
electron microscopy(SEM) were also used when needed. For data analysis, statistical
techniques such as polynomial regression, hierarchical clustering and principal components
analysis (PCA) were used. Moreover, during the work on dielectrics, physical models were
also used to establish the relationship between dielectric permittivity and volumetric water
content.
The results of dielectrics showed that in dry state BA acts a non conductor with strong
dispersion tendencies especially at high frequencies.From the measured dielectric spectra, it
was possible to estimate the moisture content as well as the effective electrical conductivity
of BA.The dielectric properties of BA indicate the potential use of microwaves in noninvasive
monitoring of moisture,weathering, residual metal contentand wet metal
recovery.The results of hydrogen gas formation showed that the gas production from fresh
BA was possible at mild conditions of temperature and pressure, and it showeda promise for
commercial development. Comparison of hydrogen production with metal recovery showed
that as compared to metal recovery,the reaction of metallic Al with alkaline solutions, to
generate hydrogen , was more efficient. From the results on respiration tests, it was found
that the respiration in fresh ash played a positive role by lowering the pH, reducing the
leaching of critical metals and modifying the ash leachate eco-toxicity. However in case of
the weathered ash, the microbial respiration negatively affected the ash quality by increasing
the leaching heavy metals. The leaching of metals(Cu, Cr, Mo, Ni, Pb, & Zn) and total
organic carbon was further enhanced by the addition of external organic matter. Further work
on a bench scale hydrogen recovery system, the use of substrate induced respiration in fresh
BA for carbonation and the use of microwaves in environmental monitoring and wet metal
recovery is suggested.
Department/s
Publishing year
2013
Language
English
Full text
Document type
Dissertation
Publisher
Lund University (Media-Tryck)
Topic
- Water Engineering
Keywords
- Bottom Ash
- Frequency Domain
- Hydrogen Recovery
- Leaching
- Microbial Respiration
- Eco-toxicity
- Solid Waste
Status
Published
Supervisor
ISBN/ISSN/Other
- ISBN: 978-91-7473-450-8
Defence date
18 February 2013
Defence time
10:15
Defence place
Lecture hall A:B, A-building, John Ericssons väg 1, Lund University Faculty of Engineering
Opponent
- Lale Andreas (Dr.)