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Doctoral Thesis
Process Innovations in Applied Smouldering of Sewage Sludge: Dry Biomass-Aided Ignition, Co-Smouldering with Rice Husk, and Oxy-Fuel Operation
Doctor of Philosophy (PhD), Murdoch University
2025
Abstract
Self-sustaining smouldering combustion is emerging as a sustainable solution for treating high-moisture organic waste like sewage sludge. By reducing dewatering needs and overall energy consumption, it offers a cost-effective alternative for sludge management. However, efficient ignition at high moisture levels remains challenging. To address this, a dry biomass layer beneath the sludge can be used to significantly enhanced ignition. Experiments with rewetted sludge (50–70 wt% moisture) mixed with silica sand (sand-to-fuel ratios of 3–5 g/g) demonstrated that lower heating values facilitated smouldering propagation. A subsequent series using thicker biomass layers (2–5 cm) and wider sand-to-fuel ratios (10–25 g/g) reduced ignition energy by up to 38.7% through lowered moisture content and improved thermal conductivity.
To further advance smouldering performance, particularly waste destruction rate, co-smouldering with rice husk was then examined for sludge at 80 wt% moisture. Replacing inert media with rice husk provided structural support and additional fuel, achieving higher temperatures, faster propagation, and greater waste destruction. Rice husk ash further stabilized the fuel bed and promoted uniform combustion. These findings highlight the potential of replacing purely inert media with biomass-based materials, thereby reducing reliance on auxiliary fuel and improving the overall energy balance of the process.
Finally, oxy-fuel smouldering was investigated to simplify carbon capture by raising the CO2 level in the flue gas. Substituting nitrogen with carbon dioxide (under 21% O₂/79% CO₂ and 30% O₂/70% CO₂) only slightly affected peak temperatures yet boosted combustion front speed at higher oxygen levels. The resulting biochar exhibited increased reactivity, indicating altered reaction pathways. Leaching tests confirmed that the residues under both air and oxy-fuel conditions satisfied landfill disposal regulations. Collectively, these innovations (dry biomass-aided ignition, co-smouldering with rice husk, and oxy-fuel operation) enhance the viability and energy efficiency of self-sustaining smouldering for high-moisture sewage sludge treatment.
Details
- Title
- Process Innovations in Applied Smouldering of Sewage Sludge: Dry Biomass-Aided Ignition, Co-Smouldering with Rice Husk, and Oxy-Fuel Operation
- Authors/Creators
- Jiadong Teng
- Contributors
- Xiangpeng Gao (Supervisor) - Murdoch University, Centre for Water, Energy and WasteParisa A. Bahri (Supervisor) - Murdoch University, Centre for Water, Energy and WasteFang Xia (Supervisor) - Murdoch University, Centre for Water, Energy and Waste
- Awarding Institution
- Murdoch University; Doctor of Philosophy (PhD)
- Identifiers
- 991005786083807891
- Murdoch Affiliation
- School of Engineering and Energy
- Resource Type
- Doctoral Thesis
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