Matching Items (4)
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- All Subjects: Biofilms
- Creators: Halden, Rolf
- Creators: Overstreet, Derek
- Resource Type: Text
Description
Intimate coupling of Ti2 photocatalysis and biodegradation (ICPB) offers potential for degrading biorecalcitrant and toxic organic compounds much better than possible with conventional wastewater treatments. This study reports on using a novel sponge-type, Ti2-coated biofilm carrier that shows significant adherence of Ti2 to its exterior and the ability to accumulate biomass in its interior (protected from UV light and free radicals). First, this carrier was tested for ICPB in a continuous-flow photocatalytic circulating-bed biofilm reactor (PCBBR) to mineralize biorecalcitrant organic: 2,4,5-trichlorophenol (TCP). Four mechanisms possibly acting of ICPB were tested separately: TCP adsorption, UV photolysis/photocatalysis, and biodegradation. The carrier exhibited strong TCP adsorption, while photolysis was negligible. Photocatalysis produced TCP-degradation products that could be mineralized and the strong adsorption of TCP to the carrier enhanced biodegradation by relieving toxicity. Validating the ICPB concept, biofilm was protected inside the carriers from UV light and free radicals. ICPB significantly lowered the diversity of the bacterial community, but five genera known to biodegrade chlorinated phenols were markedly enriched. Secondly, decolorization and mineralization of reactive dyes by ICPB were investigated on a refined Ti2-coated biofilm carrier in a PCBBR. Two typical reactive dyes: Reactive Black 5 (RB5) and Reactive Yellow 86 (RY86), showed similar first-order kinetics when being photocatalytically decolorized at low pH (~4-5), which was inhibited at neutral pH in the presence of phosphate or carbonate buffer, presumably due to electrostatic repulsion from negatively charged surface sites on Ti2, radical scavenging by phosphate or carbonate, or both. In the PCBBR, photocatalysis alone with Ti2-coated carriers could remove RB5 and COD by 97% and 47%, respectively. Addition of biofilm inside macroporous carriers maintained a similar RB5 removal efficiency, but COD removal increased to 65%, which is evidence of ICPB despite the low pH. A proposed ICPB pathway for RB5 suggests that a major intermediate, a naphthol derivative, was responsible for most of the residual COD. Finally, three low-temperature sintering methods, called O, D and DN, were compared based on photocatalytic efficiency and Ti2 adherence. The DN method had the best Ti2-coating properties and was a successful carrier for ICPB of RB5 in a PCBBR.
ContributorsLi, Guozheng (Author) / Rittmann, Bruce E. (Thesis advisor) / Halden, Rolf (Committee member) / Krajmalnik-Brown, Rosa (Committee member) / Arizona State University (Publisher)
Created2011
Description
The overall goal of this dissertation is to advance understanding of biofilm reduction of oxidized contaminants in water and wastewater. Chapter 1 introduces the fundamentals of biological reduction of three oxidized contaminants (nitrate, perchlorate, and trichloriethene (TCE)) using two biofilm processes (hydrogen-based membrane biofilm reactors (MBfR) and packed-bed heterotrophic reactors (PBHR)), and it identifies the research objectives. Chapters 2 through 6 focus on nitrate removal using the MBfR and PBHR, while chapters 7 through 10 investigate simultaneous reduction of nitrate and another oxidized compound (perchlorate, sulfate, or TCE) in the MBfR. Chapter 11 summarizes the major findings of this research. Chapters 2 and 3 demonstrate nitrate removal in a groundwater and identify the maximum nitrate loadings using a pilot-scale MBfR and a pilot-scale PBHR, respectively. Chapter 4 compares the MBfR and the PBHR for denitrification of the same nitrate-contaminated groundwater. The comparison includes the maximum nitrate loading, the effluent water quality of the denitrification reactors, and the impact of post-treatment on water quality. Chapter 5 theoretically and experimentally demonstrates that the nitrate biomass-carrier surface loading, rather than the traditionally used empty bed contact time or nitrate volumetric loading, is the primary design parameter for heterotrophic denitrification. Chapter 6 constructs a pH-control model to predict pH, alkalinity, and precipitation potential in heterotrophic or hydrogen-based autotrophic denitrification reactors. Chapter 7 develops and uses steady-state permeation tests and a mathematical model to determine the hydrogen-permeation coefficients of three fibers commonly used in the MBfR. The coefficients are then used as inputs for the three models in Chapters 8-10. Chapter 8 develops a multispecies biofilm model for simultaneous reduction of nitrate and perchlorate in the MBfR. The model quantitatively and systematically explains how operating conditions affect nitrate and perchlorate reduction and biomass distribution via four mechanisms. Chapter 9 modifies the nitrate and perchlorate model into a nitrate and sulfate model and uses it to identify operating conditions corresponding to onset of sulfate reduction. Chapter 10 modifies the nitrate and perchlorate model into a nitrate and TCE model and uses it to investigate how operating conditions affect TCE reduction and accumulation of TCE reduction intermediates.
ContributorsTang, Youneng (Author) / Rittmann, Bruce E. (Thesis advisor) / Westerhoff, Paul (Committee member) / Krajmalnik-Brown, Rosa (Committee member) / Halden, Rolf (Committee member) / Arizona State University (Publisher)
Created2012
Description
This report provides information concerning qualities of methylcellulose and how those properties affect further experimentation within the biomedical world. Utilizing the compound’s biocompatibility many issues, ranging from surgical to cosmetic, can be solved. As of recent, studies indicate, methylcellulose has been used as a physically cross-linked gel, which cannot sustain a solid form within the body. Therefore, this report will ultimately explore the means of creating a non-degradable, injectable, chemically cross-linking methylcellulose- based hydrogel. Methylcellulose will be evaluated and altered in experiments conducted within this report and a chemical cross-linker, developed from Jeffamine ED 2003 (O,O′-Bis(2-aminopropyl) polypropylene glycol-block-polyethylene glycol-block-polypropylene glycol), will be created. Experimentation with these elements is outlined here, and will ultimately prompt future revisions and analysis.
ContributorsBundalo, Zoran Luka (Author) / Vernon, Brent (Thesis director) / LaBelle, Jeffrey (Committee member) / Overstreet, Derek (Committee member) / Barrett, The Honors College (Contributor) / Harrington Bioengineering Program (Contributor)
Created2013-05
Description
Biofilm derived orthopedic infections are increasingly common after contamination of an open bone fracture or the surgical site pre- and post-orthopedic prosthetic insertion or removal. These infections are usually difficult to eradicate due to the resistant nature of biofilms to antimicrobial therapy. Difficulty of treatment of biofilm derived infections is also partly due to the presence of persister cells in the biofilm matrix. Persister cells are tolerant to antimicrobial therapy delivered via the systemic route. It is thus possible for these cells to repopulate their environment once systemic antimicrobial delivery is discontinued. The antimicrobial concentration required to eradicate bacterial biofilms, minimum biofilm eradication concentration (MBEC), can be determined in vitro by exposing biofilms to different regimens of antimicrobial solutions. Previous studies have demonstrated that values of the MBEC vary depending on the material and surface the biofilm grows on. This study investigated the relationship between antimicrobial susceptibility and antimicrobial exposure time, and the effects of surface material type on the antimicrobial susceptibility of staphylococcal biofilms. It was concluded that antimicrobial susceptibility increases with increased antimicrobial exposure time, and that the investigated surface and material properties did not have an effect on the susceptibility of staphylococcal biofilms to antimicrobial therapy. Further investigation is however necessary to confirm these results due to some inconsistent data obtained over the course of the trials.
ContributorsTavaziva, Gamuchirai Clinton (Author) / Vernon, Brent (Thesis director) / Overstreet, Derek (Committee member) / Castaneda, Paulo (Committee member) / Harrington Bioengineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2016-05