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Debojit_Thesis (1st revision)4.86 MB
Embargoed Access, Embargo ends: 08/28/2027
Dissertation
Encapsulating sorptive materials and biodegrading microorganisms in composite alginate bead geomedia to capture and remove stormwater trace organics and nutrients
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Summer 2025
DOI: 10.25820/etd.008154
Abstract
Urban areas covered with impervious surfaces generate rapid and intense runoff during rain events and/or after snowmelts. Urban stormwater runoff is known to contain complex mixtures of both dissolved phase and particle-bound pollutants that degrade water quality of receiving waterbodies. The mixture of pollutants frequently includes various nutrients, metals, microplastics, and trace organic contaminants. Green stormwater infrastructure such as bioretention cells (also called raingardens) are increasingly being applied in urban areas to remove stormwater contaminants. Even though bioretention cells can effectively remove particle-bound pollutants, most hydrophilic compounds generally pass through conventional bioretention cells without treatment. Thus, there is a growing need to amend bioretention cells to enable the removal of hydrophilic stormwater pollutants. Bioretention amendment with different sorbent materials (e.g., black carbon materials, such as granular activated carbon [GAC], powdered activated carbon [PAC], biochar) can temporarily enable removal of different hydrophilic stormwater contaminants in bioretention cells. Even the amendment of sorptive material in bioretention cells, however, does not provide a complete solution because the cells would become ineffective over extended time periods when the sorption capacities would get consumed. As such, there is a need to develop an improved media amendment for bioretention cells that would not only enable contaminant sorption but also biodegrade the captured contaminants in situ to renew bioretention sorption capacities.In the first study, I developed and characterized a novel biologically active compound alginate bead geomedia (called “BioSorp Beads”) that could be used to bioaugment bioretention cells and enable contaminant capture during infiltration and biodegradation during antecedent dry periods. I thoroughly mixed powdered activated carbon (sorbent), iron water treatment residual (sorbent, increases bead density), white rot fungi (a representative biodegrading microorganism), wood flour (maintenance substrate for the encapsulated microbes), and AQDS (a model electron shuttle) in sodium alginate. The mixture was then added dropwise into a divalent/trivalent cationic crosslinker solution (CaCl2 or FeCl3) using a peristaltic pump to produce wet beads. Finally, the instantaneously formed wet beads were air-dried to produce the BioSorp Beads. I investigated the effects of different bead compositions on various physical properties of the beads, such as mechanical strength, swelling, surface area, pore volume, leaching, pH. Bead properties could be customized to cater for specific application needs. For example, BioSorp Beads could be produced using FeCl3 as crosslinkers instead of CaCl2 if the encapsulated microbes need a more acidic environment (the case for fungi). Additionally, the encapsulated white rot fungi remained viable in the dried beads at room temperature over an extended period (3 months) and could grow from the beads when nutrients were present, demonstrating the bioaugmentation potentials of the BioSorp Beads.
In the second study, I investigated the beads’ capacity to remove nutrients and trace organic compounds. I quantified the sorption of one nutrient (phosphate), one insecticide and one of its common environmental metabolites (imidacloprid and desnitro-imidacloprid, respectively), three PFAS (one long chain PFAS—PFOA, two short chain PFAS—PFBA, PFBS), and one tire wear compound—acetanilide. This study demonstrated coupled sorption and biodegradation of acetanilide as proof-of-concept of the developed bead technology. Beads crosslinked with FeCl3 demonstrated higher phosphate sorption than the beads crosslinked with CaCl2 (up to 42.12 mg/g vs 13.01 mg/g). The presence of PAC was crucial to achieve trace organic sorption. Alginate encapsulation increased desnitro-imidacloprid (more toxic to mammals than the parent compound) sorption onto PAC. BioSorp Beads exhibited higher removal of long-chain PFAS than short-chain PFAS (13.1 mg PFOA per g, 5.2 mg PFBA per g, and 5.1 mg PFBS per g). Fungal encapsulation in alginate beads also improved fungal viability by providing protection from harsh environmental conditions. Thus, BioSorp Beads could be used to amend bioretention cells to achieve in situ contaminant sorption and biodegradation.
In the last study, I present the adaptability of BioSorp Beads by tuning the materials and microorganisms to enable nitrate nutrient removal. Nitrate is not particle-associated (similar to trace organics) and thus, difficult to capture in bioretention cells—however, nitrate can be biodegraded. I encapsulated anion exchange resin (AER) and denitrifying microorganisms (enriched from wastewater treatment plant sludge) in the bead geomedia to effectively capture and biodegrade nitrate from stormwater. Beads containing no AER did not sorb any nitrate whereas beads containing AER exhibited up to 1.32 mg/g NO3-N sorption capacity. Our proposed beads (containing live denitrifying microorganisms, AER, PAC, iron minerals, and wood flour) removed nitrate below detection within a week under anaerobic conditions (initial concentration=10 mg/L NO3-N; bead load=10 g/L), demonstrating coupled nitrate sorption and biodegradation. The proposed beads also exhibited nitrate biodegradation under bulk aerobic conditions, which would be critical for post-construction bioretention amendments.
Altogether, this thesis highlights the urgent need to amend green stormwater infrastructure (GSI) with biologically active geomedia with enhanced sorption capacity to enable sustained hydrophilic pollutant removal. Hydrophilic pollutants are not particle-associated and likely to pass through GSI systems. Additionally, GSI systems are generally designed with high hydraulic conductivity to minimize extended ponding. BioSorp Beads may address the difficulties associated with hydrophilic pollutant removal by: (a) sorbing the pollutants during rapid infiltration, and (b) keeping the sorbed pollutants in close proximity to biodegrading microbes and enabling biodegradation during antecedent dry period. Thus, BioSorp Beads may enhance stormwater treatment in GSI by decoupling the hydraulic residence time from the pollutant residence time, in the similar way activated sludge decouples hydraulic residence time from solids retention time in wastewater treatment. The thesis demonstrates that the developed BioSorp Beads could be customized according to the needs and used in GSI to capture and biodegrade various stormwater relevant hydrophilic pollutants, in situ, to improve receiving water quality and ensure public safety.
Details
- Title: Subtitle
- Encapsulating sorptive materials and biodegrading microorganisms in composite alginate bead geomedia to capture and remove stormwater trace organics and nutrients
- Creators
- Debojit S Tanmoy
- Contributors
- Gregory LeFevre (Advisor)Craig Just (Committee Member)David Cwiertny (Committee Member)Timothy Mattes (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.008154
- Publisher
- University of Iowa
- Number of pages
- xix, 191 pages
- Copyright
- Copyright 2025 Debojit S Tanmoy
- Grant note
This work was supported by NSF CBET CAREER under Grant 1844720. The authors would like to thank Dr. Drew E. Latta (University of Iowa), Dr. Alexei V. Tivanski (University of Iowa), the UI CMRF, and the UI MATFab Facility.
(54)- Language
- English
- Date submitted
- 07/28/2025
- Description illustrations
- color illustrations
- Description bibliographic
- Includes bibliographical references.
- Public Abstract (ETD)
Because people build many buildings, roads, and parking lots in urban areas and heavily change the original land, rainwater and snowmelt cannot easily go into the ground in most cities and towns. As a result, the water keeps flowing on the city/town surface and risks flooding. This excess water is called stormwater runoff. Different man-made and natural chemicals also mix in the stormwater runoff and pollute the receiving waters. Now-a-days, Green Stormwater Infrastructure (GSI) is becoming popular for managing stormwater runoff and removing different harmful chemicals. However, chemicals that can easily dissolve in water (known as hydrophilic chemicals) do not get removed in GSI effectively. For this reason, there is a need to modify the GSI so that hydrophilic chemicals can get captured and biodegraded (broken down) by microbes (different bacteria or fungi) in the GSI systems. In the first study of this thesis, I developed a bead filter media about the size of large sand grains that hold chemical eating microbes (a type of wood eating fungi in this case) in GSI systems. I named the filter media BioSorp Beads. In the second study, I tested the capabilities of the developed geomedia to remove different representative hydrophilic chemicals including a phosphorus nutrient, two insecticides, three PFAS forever chemicals , and a tire wear compound. In the last study, I investigated the adaptability of the BioSorp Beads by installing materials and microbes that can capture and biodegrade another major stormwater pollutant nitrate (nitrogen nutrient).
- Academic Unit
- Civil and Environmental Engineering
- Record Identifier
- 9984948738402771
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