Electrokinetic process in soil remediation for lead removal / Ng Yee Sern
Soil washing is one of the popular soil remediation methods which is widely studied for treating heavy metal contaminated land. However, this method suffers from high wash solution consumption, which eventually increases treatment cost. In order to solve this problem, a study on the incorporation...
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| Format: | Thesis |
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2016
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| Online Access: | http://studentsrepo.um.edu.my/6180/ http://studentsrepo.um.edu.my/6180/4/Thesis_KHA120057.pdf |
| Summary: | Soil washing is one of the popular soil remediation methods which is widely studied for
treating heavy metal contaminated land. However, this method suffers from high wash
solution consumption, which eventually increases treatment cost. In order to solve this
problem, a study on the incorporation of electrokinetic process into soil washing as soil
remediation method was carried out, as electrokinetic process can transport metal ions
using electricity in the absence of hydraulic gradient. In this study, two-stage
electrokinetic washing was introduced as a novel soil remediation method in treating
lead (Pb) contaminated soil at low wash solution consumption. This process consists of:
i) initial soil washing to provide desorption condition in the soil, and ii) electrokinetic
process to transport desorbed Pb from the soil. The study revealed that two-stage
electrokinetic washing could enhance Pb removal efficiency by 4.98-20.45% in
comparison to normal soil washing. Among the wash solutions, 0.1M citric acid
emerged as the best wash solution as it not only yielded high removal efficiency at low
power consumption compared to 0.01M NaNO3, 0.1M HNO3 and 0.01M EDTA but
also maintained a stable system, low solution: soil ratio and low effluent generation.
A further study on the effect of operating parameters using citric acid as the
wash solution revealed that the increase in electric potential difference and wash
solution concentration enhanced the removal efficiency and the interaction between
these two parameters was significantly positive whereby low pH and high current
density were the most important criteria in the removal process. However, unfavourable
high effluent generation and power consumption were also observed under these
conditions. An optimisation study on these parameters showed that an optimum removal
efficiency of 84.14% with negligible extra effluent generation and low power
consumption of 2.27kWh/kg Pb removed could be achieved under 7.58V and 0.057M
citric acid concentration. The study proved that two-stage electrokinetic washing
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process could enhance the soil remediation efficiency by ≈16% than normal soil
washing under similar low consumption of wash solution at <0.8mL:1g soil and
operating conditions.
Other than incorporating into soil washing, the ability of electrokinetic process
as soil pretreatment method in contaminated soil volume reduction was also
investigated for single Pb contaminated soil and Pb/Cr co-contaminated soil. The results
showed that electrokinetic process could provide soil volume reduction by
concentrating Pb and Cr into smaller soil volume in both types of soils via
electromigration without hydraulic flow. The study also suggested that the performance
of electrokinetic process was strongly dependent on the types of wetting agents, types of
contaminants and soil conditions, whereby 0.1M citric acid was suitable for single Pb
contaminated soil while 0.1M EDTA showed better performance in treating Pb/Cr cocontaminated
soil. Further study on the application of approaching electrode technique
in electrokinetic process revealed that this technique did not enhance the
electromigration significantly in the present study. Nevertheless, approaching electrode
was found to reduce the power consumption by 18% to 42% for single Pb contaminated
soil and 22.5% for co-contaminated soil. |
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