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Dissertation
Novel encapsulation of biofilm-enriched black carbon for polychlorinated biphenyl bioremediation
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Summer 2025
DOI: 10.25820/etd.008157
Abstract
Polychlorinated biphenyls (PCBs) were banned from manufacture in 1979 but persist in the environment and strongly bind to sediments. Lower chlorinated PCBs (LC-PCBs), defined as four or less chlorines per PCB and the most volatile PCBs, more easily transport from sediment into the air than higher chlorinated PCBs. Exposure to PCBs can cause cancers and disorders in humans and animals; thus, LC-PCB exposure poses health threats to nearby communities and ecosystems. Conventional PCB remediation approaches like dredging and the use of geosorbents either relocate PCB mass in sediment to landfills or decrease aqueous PCB mass by sorption, but both approaches do not degrade PCBs; indeed, dredging even mobilizes PCBs from sediment to the water column. Bioremediation is a sustainable approach to biodegrade total PCB mass and mitigate long-term PCB exposure risk. Natural biodegradation processes are often slow, making bioaugmentation an attractive approach to accelerate PCB removal in sediment. Bioaugmenting suspended aerobic PCB-degrading cells in sediment can achieve LC-PCB biodegradation but may not be efficient at sustaining long-term PCB biodegradation due to environmental fluctuations and flow-induced washout that cause cell abundance and viability to decline. Therefore, there is a need to better deliver PCB-degrading cells and protect cells from environmental change impacts. Thus, the overall objective of this research was to develop novel approaches and technologies for bioaugmenting abundant and active PCB-degrading cells to secure long-term biodegradation and thereby improve total LC-PCB removal in sediment under environmentally relevant conditions, breaking the sediment-to-air PCB exposure pathway. This overall objective comprised three objectives, focusing on developing bioaugmentation technology and understanding environmental condition impacts on bioaugmented microbes.The first objective was to characterize cell enrichment and activity on different black carbon surfaces to deliver aerobic PCB-degrading cells into sediments and target LC-PCB biodegradation. We investigated black carbon impacts on cell enrichment and activity using the model aerobic PCB-degrading strain Paraburkholderia xenovorans strain LB400. We discovered black carbon feedstocks significantly influenced LB400 biofilm formation and microbial gene and pathway expression. Pathways related to both PCB biodegradation (box pathway during growth on biphenyl) and biofilm formation (EPS pathway I&II) were upregulated in cells attached on corn kernel biochar compared to granular activated carbon (log2(FC): 0.93–7.5, adj p<0.05). Biphenyl dioxygenase gene, bphA, and the entire bph pathway were more highly expressed in attached cells than suspended cells (bphA transcript per gene: >10 v.s. ~1; bph: log2(FC) > 1.35, p-adj < 0.001), regardless black carbon materials.
The second objective was to develop a novel method for sol-gel encapsulation of biofilm-enriched biochar to improve LB400 biofilm viability and longevity. Although corn kernel biochar enhanced biofilm formation and PCB biodegradation activity, biofilm stability could be interfered by water shear force. Therefore, we systematically tuned sol–gel recipes to encapsulate biofilm-enriched biochar and evaluated the impact of the sol–gel coating on biofilm abundance, cell viability, and pollutant degradation under environmentally relevant conditions. The sol–gel completely encapsulated biofilm-enriched biochar, produced both high porosity and appropriate pore size (glycerol-added gel: >4.6 nm radius, PEG400-added gel: 1.62 nm radius) that allowed pollutant and nutrient transfer, and maintained gel integrity for at least one month under saline condition and continuous water shear force. Sol-gel coated biofilms completely degraded benzoate, a proof-of-concept organic molecule, within 12 days, and sol-gel protected biofilm integrity and cell viability for over three months without a carbon and energy source.
The third objective was to evaluate the impacts of sol-gel coating and environmental conditions on LC-PCB biodegradation performance of sol-gel encapsulated biofilm-enriched biochar. We systematically determined total PCB mass balances, quantified and compared bphA abundance and expression changes, and characterized sol-gel and biofilm integrity over 45 days. We found that sol-gel coating with the combination of benzoate soaking induced and extended bphA activity in biofilms (transcript per gene ratio >2 throughout treatment) under standard environmental conditions (freshwater and room temperature). Lower temperature induced ~2-10 times higher bphA expression on sol-gel coated biofilms but inhibited over 50% of PCB mass removal from biodegradation, potentially because PCB diffusion slowed down through sol-gel at 10C. High salinity (20 g/L) had negative impacts on aqueous PCB biodegradation for PEG400-coated and uncoated biofilms (2-10 times more aqueous PCB mass remaining than baseline), complying to lower bphA expression levels than baseline (0 g/L) at day-45.
To conclude, this research demonstrates that corn kernel biochar and sol-gel coating not only were feasible to deliver PCB-degrading cells and protect biofilm abundance against environmental conditions, but also enhanced biofilm activity to biodegrade LC-PCBs. This research provides practical insights to understand application feasibility of novel bioaugmentation design for long-term in situ bioremediation.
Details
- Title: Subtitle
- Novel encapsulation of biofilm-enriched black carbon for polychlorinated biphenyl bioremediation
- Creators
- Qin Dong
- Contributors
- Gregory H LeFevre (Advisor)Timothy E Mattes (Advisor)Keri C Hornbuckle (Committee Member)Andres Martinez Araneda (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Civil and Environmental Engineering
- Date degree season
- Summer 2025
- DOI
- 10.25820/etd.008157
- Publisher
- University of Iowa
- Number of pages
- xx, 244 pages
- Copyright
- Copyright 2025 Qin Dong
- Grant note
The work was supported by the National Institutes of Environmental Health Sciences (NIEHS) grant NIH P42ES013661. We thank Mary Boes and Einat Snir (IIHG) for helpful RNA sequencing discussions.
(54)- Language
- English
- Date submitted
- 07/17/2025
- Description illustrations
- illustrations (some color)
- Description bibliographic
- Includes bibliographical references.
- Public Abstract (ETD)
Although the manufacture of polychlorinated biphenyls (PCBs) was banned in 1979, these toxic compounds persist in the environment, particularly in sediments. Lower chlorinated PCBs (LC-PCBs) have higher tendency to escape from sediment into the air, causing inhalation exposure risks for nearby communities and ecosystems. Exposure to PCBs can cause cancers and disorders in humans and wildlife. Bioremediation using microorganisms to degrade pollutants offers a sustainable strategy to mitigate PCB contamination. Bioaugmentation, the addition of functional microbes, can accelerate PCB removal in sediment. However, bioaugmentation with free-floating cells in sediment often fails to achieve lasting impact due to unfavorable conditions in the environment and because cells can easily be washed away. To secure long-term LC-PCB biodegradation in sediment, we developed new approaches and technologies to bioaugment abundant and active PCB-degrading cells into natural environments. Using a well-characterized PCB-degrading bacterium, I investigated how black carbon materials, a type of charcoal, affected the survival and activity of this bacterium. I also coated biofilm-enriched black carbon in a gel to protect biofilm abundance and cell viability. I evaluated the impacts of coating and environmental conditions (such as temperature) on PCB biodegradation, bacterial survival, and microbial activity over a 45-day period. This research demonstrates that gel coated bacteria on charcoal effectively support long-term LC-PCB biodegradation, protect bacteria from environmental stress, and offers a feasible approach to break the sediment-to-air PCB exposure pathway. This research contributes valuable insights into the practical application of novel bioaugmentation strategies for long-term in situ bioremediation.
- Academic Unit
- Civil and Environmental Engineering
- Record Identifier
- 9984948427802771
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