Tang'an, Diret Bitrus
(2024)
Remediation of petroleum hydrocarbon contaminated soils using microwave processing systems.
PhD thesis, University of Nottingham.
Abstract
The rise in the world’s energy demand has led to an increase in oil and gas exploitation and exploration activities. During these processes, spillages from crude oil and its refined products occur, resulting in major environmental problems such as land pollution. In Nigeria’s Niger Delta, Total Petroleum Hydrocarbons (TPH) is identified as a key land contaminant from these spillages that has led to the destruction of vegetation, posing severe health risks to the local population. This research carried out a robust and systematic technology evaluation for removing TPH from the contaminated soils.
A decision matrix was developed to choose the remediation technology classification with the best potential to address this challenge. Important remediation criteria like remediation efficiency, speed, environmental impact, cost, and suitability for TPH removal were selected and assigned weights based on the peculiarity of contaminated site characteristics of the Niger Delta. Thermal methods emerged as a viable technology option with the best potential to contribute towards addressing this problem. Out of the nine thermal technologies evaluated, ex-situ microwave heating (MW) and ex-situ thermal desorption (TD) scored the highest. However, there were uncertainties about how these technologies would perform with varying soil type and composition. This could potentially impact their overall effectiveness and the technology selection decision. Therefore, investigating the viability of ex-situ microwave heating was the primary focus of this study which was also compared with ex-situ TD.
Selected heavy and light oil-contaminated solids from the United Kingdom and Nigeria’s Niger Delta were collected and used. These materials were characterised for dielectric properties, moisture content, oil content, contaminant composition, and particle size distribution. The dielectric properties indicated that the dipolar and ionic/conductive loss mechanisms played a role in heat generation between 20 and <200°C (drying stage). However, ionic/conductive loss was the dominant loss mechanism between ≥450 and 700°C (char formation stage).
The soils were subjected to the microwave ‘dry’ heating system at various specific energies using 2.45 GHz to understand how they would interact with microwave energy. Oil removal up to 94% (at 3.8 kJ/g and 6 minutes), 37% (at 1.5 kJ/g and 3 minutes), 44% (at 4.2 kJ/g and 8 minutes), and 30% (at 4 kJ/g and 10 minutes) were achieved for filter cake, road planings, Bodo and K-Dere soils respectively. The hydrated clay layers and texture of the filter cake played a significant role in the high oil removed as temperatures >250°C were attained which enhanced oil removal via the steam stripping mechanism. To improve oil removal, contaminated materials were wetted with 5% ethylene glycol and treated (wet microwave heating system). This significantly increased oil removal in road planings to 87%. However, its effect on the other materials was insignificant.
Thermal runaway was a significant challenge that limited material processing, degraded contaminated materials, and damaged equipment during the dry and wet microwave treatments. To overcome this, the solids were treated in an inert liquid system that submerged the materials in hexane before microwave processing. For the first time, the inert liquid system addressed thermal runaway in all the materials and increased the oil removal yields of road planings, Bodo and K-Dere soils compared with the dry heating system due to the combined effect of microwave heating and the inert liquid (hexane). However, it came with a trade-off as higher specific energy inputs were required.
The overall re-evaluation of the initial technology selection decision showed that the remediation of road plainings, filter cake, Bodo and K-Dere soils were best achieved using the microwave wet heating system, microwave dry heating system, thermal desorption, and inert liquid system respectively. The inert liquid system successfully reduced the hydrocarbon contamination in Bodo and K-Dere soils to concentrations within acceptable limits set by the Environmental Guidelines and Standards for the Petroleum Industry in Nigeria (EGASPIN). While the wet microwave heating system reduced the concentrations in road planings to the set guideline, thermal desorption reduced the contamination of all the materials to acceptable limits.
| Item Type: |
Thesis (University of Nottingham only)
(PhD)
|
| Supervisors: |
Binner, Eleanor
Adam, Mohamed |
| Keywords: |
Microwave processing technology, Microwave heating, land contamination, Total petroleum hydrocarbon (TPH), Soil remediation, Thermal runaway, Thermal desorption |
| Subjects: |
T Technology > TD Environmental technology. Sanitary engineering |
| Faculties/Schools: |
UK Campuses > Faculty of Engineering > Department of Chemical and Environmental Engineering |
| Item ID: |
79951 |
| Depositing User: |
Tang'an, Diret
|
| Date Deposited: |
04 Nov 2024 11:39 |
| Last Modified: |
10 Dec 2024 04:40 |
| URI: |
https://eprints.nottingham.ac.uk/id/eprint/79951 |
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