Mechanical properties of biofilms in water distribution and bioremediation systems
Chair
Aggarwal, SrijanDev, Subhabrata
Committee
Schiewer, SilkeSchuette, Ursel
Keyword
BiofilmsMechanical properties of biofilms
Development of biofilms
Control of biofilms
Industrial applications of biofilms
Acid mine drainage
Metadata
Show full item recordAbstract
This dissertation explores biofilm dynamics in water distribution and acid mine drainage (AMD) treatment, focusing on their roles in resource recovery and public health. Biofilms consist of microbial communities in a self-produced extracellular polymeric substance (EPS) matrix, which influences their mechanical and structural properties based on EPS composition, environmental conditions, and biofilm age. In drinking water distribution systems (DWDS), biofilms pose health hazards as they harbor pathogens and encourage metal corrosion. The composition of extracellular polymeric substances (EPS), particularly its high protein content, is noted in downstream areas, facilitating biofilm development in conditions of reduced chlorine and higher temperature turbidity. Traditional antimicrobial strategies often fail due to the protective EPS matrix, highlighting the need for targeted biofilm control strategies. On the other hand, biofilms show promise in AMD treatment, where biofilm-based bioreactors utilizing sulfate-reducing bacteria (SRB) effectively neutralize acidity and recover valuable metals, including rare earth elements. SRB bioreactors demonstrated sulfate reduction rates of up to 92.8% and near-complete removal of essential metals, showcasing the ability of biofilms to facilitate precipitation and biosorption under extreme conditions. The mechanical properties (as Young’s modulus) of biofilms were observed to vary with environmental conditions and biofilm age, influencing their resilience to mechanical stress. In DWDS, these properties impact biofilm control and removal efforts, while in AMD treatment, increased biofilm stiffness supports structural stability for effective metal removal. Advanced techniques like confocal laser scanning microscopy (CLSM) and atomic force microscopy (AFM) assessed biofilm characteristics, emphasizing the need for site-specific management strategies. Findings indicate that successful biofilm management necessitates an understanding of mechanics, EPS composition, and environmental factors. Future research should enhance biofilm control technologies and explore enzyme-based disruptors, balancing sustainability and public health concerns while optimizing resource recovery.Description
Dissertation (Ph.D.) University of Alaska Fairbanks, 2025Table of Contents
Chapter 1: General introduction -- 1.1 Background -- 1.2 Research objectives -- 1.3 Organizational overview -- 1.4 References. Chapter 2: Understanding biofilm mechanical properties: insights into environmental applications and challenges -- 2.1 Abstract -- 2.2 Background -- 2.2.1 Definition of biofilms -- 2.2.2 Importance of biofilm in different environmental/aquatic systems -- 2.2.3 Significance of studying biofilm mechanical properties -- 2.3 Perspectives of biofilms -- 2.3.1 Biological perspective -- 2.3.2 Chemical perspective -- 2.3.3 Materials perspective -- 2.3.4 Other perspectives -- 2.4 Methods of measuring biofilm mechanical properties -- 2.5 Factors influencing biofilm mechanical properties -- 2.5.1 Microbial community -- 2.5.2 EPS composition -- 2.5.3 Environmental conditions -- 2.5.4 Biofilm age -- 2.5.5 Bulk water chemistry -- 2.5.6 Antimicrobials and detachment-promoting agents -- 2.5.7 Surface properties -- 2.5.8 Quorum sensing -- 2.6 Mechanical properties of biofilms in different environmental systems -- 2.7 Role of mechanical properties in biofilm functions -- 2.8 Conclusions -- 2.9 References -- 2.10 Tables and figures. Chapter 3: Matrix matters: how extracellular substances shape biofilm structure and mechanical properties -- 3.1 Abstract -- 3.2 Background -- 3.3 Research plan and methodology -- 3.3.1 Biofilm growth conditions -- 3.3.2 EPS modifier experiements -- 3.3.3 Mechanical property determination -- 3.3.4 EPS composition analyses -- 3.3.5 Physical characteristics determination -- 3.3.6 Statistical analysis -- 3.4 Results -- 3.5 Discussion -- 3.6 Conclusions -- 3.7 Acknowledgments -- 3.8 References -- 3.9 Tables and figures -- Appendix A: Supplemental materials. Chapter 4: Investigating the properties of in-situ drinking water biofilms in a full-scale water distribution system -- 4.1 Abstract -- 4.2 Background -- 4.3 Methodology -- 4.4 Results and discussion -- 4.5 Conclusion -- 4.6 References -- 4.7 Tables and figures -- Appendix B: Supplemental materials. Chapter 5: Investigating the biofilm properties in sulfidogenic bioreactors removing rare earth elements from acid mine drainage -- 5.1 Abstract -- 5.2 Introduction -- 5.3 Methodology -- 5.3.1 Chemical reagents and nutrient supplements -- 5.3.2 Inoculum -- 5.3.3 Synthetic AMD -- 5.3.4 Sulfidogenic bioreactor -- 5.3.5 Analysis -- 5.3.6 Statistical analysis -- 5.4 Results and discussions -- 5.4.1 Sulfate removal -- 5.4.2 pH -- 5.4.3 Removal/removal of Metals/REE -- 5.4.4 Biofilm characteristics -- 5.4.5 Microbial community composition of bioreactor biofilms -- 5.5 Conclusions -- 5.6 References -- 5.7 Tables and figures -- Appendix C: Supplementary information. Chapter 6: General conclusions -- 6.1 Conclusions -- 6.2 Limitations -- 6.3 Recommendations for future work.Date
2025-05Type
DissertationCollections
Related items
Showing items related by title, author, creator and subject.
-
Implications of detachment promoting agents, disinfectants and flow hydraulics on growth and dispersion of bacterial biofilms in drinking water distribution systemsBiofilms in water distribution systems (WDS) can adversely affect the effluent water quality and structural integrity of pipes. Current disinfectants and flushing strategies often prove insufficient to mitigate biofilm growth. Long-term monitoring of biofilm growth under varied WDS flow and disinfection conditions is needed (and often overlooked) for improving biofilm management in the WDS. An alternative approach to counter biofilms in the WDS over the traditional approach of using antimicrobials is to target and weaken the extracellular polymeric substances (EPS) instead of just the microorganisms in the biofilms - via the use of 'detachment promoting agents' (DPAs) to weaken the EPS matrix and cause biofilm dispersion. The growth of fresh biofilm and reattachment of biofilm flocs were investigated by time-lapse imaging in capillary flow cells under varying temperatures, fluid shear, and chlorine dosage. Biofilm disruption efficacy of potential DPAs was investigated for single and multi-species biofilms over varying durations (72 h - 4 months) and on different surfaces (e.g., glass, copper, stainless steel, cement, HDPE). The similar biofilm growth rates with non-chlorinated and 0.2 mg/L chlorine indicate the ineffectiveness of low chlorine dosages for biofilm inhibition. Substantial biofilm growth occurred despite using higher chlorine dosages (0.2-1 mg/L), demonstrating the disinfection resistance of microorganisms in biofilm and detached clusters. The enhanced initial biofilm growth kinetics in the reattachment systems compared to the fresh flow cell reactors indicates the significant role of existing biofilms (and likely their detached clusters) to stimulate biofilm growth in a newer WDS section. The lower reattachment rate at the early stage with hot water (50°C) increased over time likely due to interaction with a high residual chlorine dosage. Multi-species biofilms grown for both long and short duration showed higher resistance to DPA treatment. The maximum dispersal of single-species biofilms was achieved using the DPA agent EDTA (45 ± 32%). The highest observed protein in the effluent with EDTA treatment indicates the effectiveness of DPAs for weakening EPS. Sodium tripolyphosphate (STP) reduced 75% of biomass and half of biofilm thickness on HDPE coupons. However, the formation of disinfection by-products by STP treatment (0.32-0.67 mg/L bromoform) raises regulatory concerns for DBPs. The use of DPAs as anti-EPS agents for biofilm dispersal, rather than the traditional antimicrobial approach yielded promising results for different plumbing materials. Overall, the results from this study demonstrate the potential of non-invasive imaging-based research in understanding the growth mechanisms of biofilm in various flow conditions, highlighting the widespread application of online water monitoring systems. Overall, this research offers new insights and perspectives on the impact of fluid shear and disinfectants on biofilm growth and reattachment, as well as the implications of these processes for water safety and public health.
-
Resource limitation of autotrophs and heterotrophs in boreal forest headwater streamsIn stream biofilms, autotrophs and heterotrophs are responsible for the majority of in stream nutrient transformations. In boreal forest catchments, discontinuous permafrost can lead to variation in nutrient and energy resources, which can control competition for nutrients between autotrophs and heterotrophs within these biofilms. I was interested in determining what resources control nutrient utilization by autotrophs and heterotrophs in headwater streams in the boreal forest of interior Alaska. I hypothesized that the outcome of competition between autotrophs and heterotrophs for inorganic nutrients would be dependent on the availability of (i) organic carbon, (ii) light, or (iii) inorganic nutrients. To measure resource limitation and competition at both patch and reach scales, I deployed nutrient diffusing substrata and conducted nutrient uptake experiments in streams along a permafrost gradient at the Caribou-Poker Creeks Research Watershed in interior Alaska. At the patch scale, autotrophs were light and nutrient limited, whereas heterotrophs were carbon and nutrient limited, and at the reach scale, light had the largest influence on nutrient uptake. Heterotrophs exhibited a larger response to nutrient enrichment when stream ambient carbon stocks were more bioavailable. Autotrophic biomass and productivity was suppressed when labile carbon was available to heterotrophs, suggesting that heterotrophs outcompete autotrophs for nutrients when a labile carbon source is introduced. The positive responses to nutrient and carbon additions suggest that the hypothesized increased nutrient and carbon exports into fluvial networks with permafrost degradation will impact biofilm structure and function, with the potential to influence nutrient export and stream ecosystem function downstream.
