Unsaturated Phase Environmental Processes in MSWI Bottom Ash

Abstract

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.

Abstract (Swedish)

Popular Abstract 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.

• author: Ilyas, Aamir
• supervisor: Magnus Persson
• opponent: Dr. Andreas, Lale, Luleå University of Technology, Luleå, Sweden
• organization: Division of Water Resources Engineering
• publishing date: 2013
• type: Thesis
• publication status: published
• subject: Water Engineering
• keywords: Bottom Ash, Frequency Domain, Hydrogen Recovery, Leaching, Microbial Respiration, Eco-toxicity, Solid Waste
• pages: 157 pages
• defense location: Lecture hall A:B, A-building, John Ericssons väg 1, Lund University Faculty of Engineering
• defense date: 2013-02-18 10:15:00
• ISBN: 978-91-7473-450-8
• language: English
• LU publication?: yes
• id: 9c907d07-1d73-4abe-ae3e-ece2f49eab20 (old id 3409175)
• date added to LUP: 2016-04-04 12:11:06
• date last changed: 2018-11-21 21:09:29