Groundwater should be considered a complex system with several polluting inputs that may simultaneously affect its quality. Agriculture plays a key role among the various anthropogenic activities that may cause multiple groundwater contamination. It can, directly and indirectly, influence the concentrations of a large number of inorganic substances in groundwater, including nitrate. In several geographical areas, nitrates exceed the quality standards for drinking water consumption (over 50 mgNO3- L-1) recommended by the World Health Organisation (WHO). Reverse osmosis, electrodialysis, and ion exchange are considered the most recommended technologies for treating nitrates in groundwater. However, these conventional technologies are energy-intensive, chemicals dosage are sometimes required, and the nitrates are concentrated in a waste brine that is difficult to dispose of. Biological denitrification partly would solve this issue through harmful nitrate reduction into dinitrogen gas (N2). However, conventional heterotrophic denitrification generates an excess of biomass and requires an electron donor (organic matter), usually not present in groundwater. The possible release of residual organic matter into the treated water would make it unusable for drinking purposes. Bioelectrochemical systems are emerging as sustainable alternatives for treating nitrate contaminated groundwater, thanks to the autotrophic denitrifying bacteria that can use a cathode electrode as the electron donor. This process implies a negligible generation of sludge, low energy consumption and, no chemicals addition. However, the complexity of real groundwater is not only due to nitrate contamination, and can strongly influence the behaviour of BES and its scaling-up. One of the most intriguing challenges that researchers are currently facing is the application of BES to the bioremediation of multi-contaminated groundwater. This PhD thesis aims to evaluate the applicability of BES for the removal of nitrate, coupled with other typical saline groundwater contaminants. In particular, the objectives and activities of this PhD thesis are largely in line with the “SARdNAF” project, which aims to apply BES to the treatment of groundwater from the nitrate vulnerable zone of Arborea (Sardinia, Italy), characterised not only by high nitrate concentrations but also by high salinity and high calcium and manganese concentrations. Firstly, the effect of elements typically found in groundwater (mainly calcium and manganese) was evaluated on a conventional bioelectrochemical system configuration to evaluate the effects on the denitrification process. Furthermore, a novel 3-compartment BES configuration was developed to test a proof-of-concept for bioelectrochemical denitrification with groundwater desalination. The system was initially operated in batch mode to study its feasibility. Subsequently, its performance was reinforced in terms of denitrification and desalination once continuous mode operation was applied. Finally, the operation with decreasing hydraulic retention times was tested to investigate the effect on overall process performance and energy consumption. In conclusion, the results presented in this PhD thesis support the application of the bioelectrochemical system as a potential alternative technology for the treatment of multi-contaminated groundwater.

REMEDIATION OF MULTI-CONTAMINATED GROUNDWATER USING BIOELECTROCHEMICAL SYSTEMS

PUGGIONI, GIULIA
2022-04-20

Abstract

Groundwater should be considered a complex system with several polluting inputs that may simultaneously affect its quality. Agriculture plays a key role among the various anthropogenic activities that may cause multiple groundwater contamination. It can, directly and indirectly, influence the concentrations of a large number of inorganic substances in groundwater, including nitrate. In several geographical areas, nitrates exceed the quality standards for drinking water consumption (over 50 mgNO3- L-1) recommended by the World Health Organisation (WHO). Reverse osmosis, electrodialysis, and ion exchange are considered the most recommended technologies for treating nitrates in groundwater. However, these conventional technologies are energy-intensive, chemicals dosage are sometimes required, and the nitrates are concentrated in a waste brine that is difficult to dispose of. Biological denitrification partly would solve this issue through harmful nitrate reduction into dinitrogen gas (N2). However, conventional heterotrophic denitrification generates an excess of biomass and requires an electron donor (organic matter), usually not present in groundwater. The possible release of residual organic matter into the treated water would make it unusable for drinking purposes. Bioelectrochemical systems are emerging as sustainable alternatives for treating nitrate contaminated groundwater, thanks to the autotrophic denitrifying bacteria that can use a cathode electrode as the electron donor. This process implies a negligible generation of sludge, low energy consumption and, no chemicals addition. However, the complexity of real groundwater is not only due to nitrate contamination, and can strongly influence the behaviour of BES and its scaling-up. One of the most intriguing challenges that researchers are currently facing is the application of BES to the bioremediation of multi-contaminated groundwater. This PhD thesis aims to evaluate the applicability of BES for the removal of nitrate, coupled with other typical saline groundwater contaminants. In particular, the objectives and activities of this PhD thesis are largely in line with the “SARdNAF” project, which aims to apply BES to the treatment of groundwater from the nitrate vulnerable zone of Arborea (Sardinia, Italy), characterised not only by high nitrate concentrations but also by high salinity and high calcium and manganese concentrations. Firstly, the effect of elements typically found in groundwater (mainly calcium and manganese) was evaluated on a conventional bioelectrochemical system configuration to evaluate the effects on the denitrification process. Furthermore, a novel 3-compartment BES configuration was developed to test a proof-of-concept for bioelectrochemical denitrification with groundwater desalination. The system was initially operated in batch mode to study its feasibility. Subsequently, its performance was reinforced in terms of denitrification and desalination once continuous mode operation was applied. Finally, the operation with decreasing hydraulic retention times was tested to investigate the effect on overall process performance and energy consumption. In conclusion, the results presented in this PhD thesis support the application of the bioelectrochemical system as a potential alternative technology for the treatment of multi-contaminated groundwater.
20-apr-2022
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11584/333141
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