Membrane biofilm reactors (MBfR) utilize membrane fibers for bubble-less transfer of gas by diffusion and provide a surface for biofilm development. Nitrogen removal was attempted using MBfR in various configurations - nitrification, denitrification and consecutive nitrification and denitrification. Effects of loading rate and dissolved oxygen on nitrification performance were primarily investigated in a stand-alone nitrifying MBfR. Specific nitrification rate increased linearly with specific loading rate, up to the load of 3.5 g N/m²d. Beyond that load, substrate diffusion limitation inhibited further increase of specific nitrification rate. 100% oxygen utilization was achievable under limited oxygen supply condition. Effects of mineral precipitation, dissolved oxygen and temperature on hydrogenotrophic denitrification were investigated in a stand-alone denitrifying MBfR. Mineral precipitation, caused by intended pH control, caused the deterioration of denitrification performance by inhibiting the diffusion of hydrogen and nitrate. Operating reactor in various dissolved oxygen conditions showed that the denitrification performance was not affected by dissolved oxygen in MBfR. Optimum temperature of the hydrogenotrophic denitrification system was around 28°C. Total nitrogen removal in a two-step MBfR system incorporating sequential nitrification and hydrogen-driven autotrophic denitrification was investigated in order to achieve nitrogen removal by autotrophic bacteria alone. Long-term stable operation, which proved difficult in previous studies due to excessive biofilm accumulation in autotrophic denitrification systems, was attempted by biofilm control. Nitrification performance was very stable throughout the experimental periods over 200 days. Performance of autotrophic denitrification was maintained stably throughout the experimental periods, however biofilm control by nitrogen sparging was required for process stability. Biofilm thickness was also stably maintained at an average of 270 µm by the gas sparging biofilm control. According to the cost analysis of denitrifying MBfR, hydrogenotrophic denitrification can be an economical tertiary treatment option compared to conventional denitrifying filter although its economic feasibility highly depends on the cost of hydrogen gas. Although this study was conducted in a lab-scale, the findings from this study can be a valuable stepping stone for larger scale application and open the door for system modifications in future.

Membrane biofilm reactors (MBfR) utilize membrane fibers for bubble-less transfer of gas by diffusion and provide a surface for biofilm development. Nitrogen removal was attempted using MBfR in various configurations - nitrification, denitrification and consecutive nitrification and denitrification. Effects of loading rate and dissolved oxygen on nitrification performance were primarily investigated in a stand-alone nitrifying MBfR. Specific nitrification rate increased linearly with specific loading rate, up to the load of 3.5 g N/m²d. Beyond that load, substrate diffusion limitation inhibited further increase of specific nitrification rate. 100% oxygen utilization was achievable under limited oxygen supply condition. Effects of mineral precipitation, dissolved oxygen and temperature on hydrogenotrophic denitrification were investigated in a stand-alone denitrifying MBfR. Mineral precipitation, caused by intended pH control, caused the deterioration of denitrification performance by inhibiting the diffusion of hydrogen and nitrate. Operating reactor in various dissolved oxygen conditions showed that the denitrification performance was not affected by dissolved oxygen in MBfR. Optimum temperature of the hydrogenotrophic denitrification system was around 28°C. Total nitrogen removal in a two-step MBfR system incorporating sequential nitrification and hydrogen-driven autotrophic denitrification was investigated in order to achieve nitrogen removal by autotrophic bacteria alone. Long-term stable operation, which proved difficult in previous studies due to excessive biofilm accumulation in autotrophic denitrification systems, was attempted by biofilm control. Nitrification performance was very stable throughout the experimental periods over 200 days. Performance of autotrophic denitrification was maintained stably throughout the experimental periods, however biofilm control by nitrogen sparging was required for process stability. Biofilm thickness was also stably maintained at an average of 270 µm by the gas sparging biofilm control. According to the cost analysis of denitrifying MBfR, hydrogenotrophic denitrification can be an economical tertiary treatment option compared to conventional denitrifying filter although its economic feasibility highly depends on the cost of hydrogen gas. Although this study was conducted in a lab-scale, the findings from this study can be a valuable stepping stone for larger scale application and open the door for system modifications in future.

abstract: Contamination by chlorinated ethenes is widespread in groundwater aquifers, sediment, and soils worldwide. The overarching objectives of my research were to understand how the bacterial genus Dehalococcoides function optimally to carry out reductive dechlorination of chlorinated ethenes in a mixed microbial community and then apply this knowledge to manage dechlorinating communities in the hydrogen-based membrane biofilm reactor (MBfR). The MBfR is used for the biological reduction of oxidized contaminants in water using hydrogen supplied as the electron donor by diffusion through gas-transfer fibers. First, I characterized a new anaerobic dechlorinating community developed in our laboratory, named DehaloR^2, in terms of chlorinated ethene turnover rates and assessed its microbial community composition. I then carried out an experiment to correlate performance and community structure for trichloroethene (TCE)-fed microbial consortia. Fill-and-draw reactors inoculated with DehaloR^2 demonstrated a direct correlation between microbial community function and structure as the TCE-pulsing rate was increased. An electron-balance analysis predicted the community structure based on measured concentrations of products and constant net yields for each microorganism. The predictions corresponded to trends in the community structure based on pyrosequencing and quantitative PCR up to the highest TCE pulsing rate, where deviations to the trend resulted from stress by the chlorinated ethenes. Next, I optimized a method for simultaneous detection of chlorinated ethenes and ethene at or below the Environmental Protection Agency maximum contaminant levels for groundwater using solid phase microextraction in a gas chromatograph with a flame ionization detector. This method is ideal for monitoring biological reductive dechlorination in groundwater, where ethene is the ultimate end product. The major advantage of this method is that it uses a small sample volume of 1 mL, making it ideally suited for bench-scale feasibility studies, such as the MBfR. Last, I developed a reliable start-up and operation strategy for TCE reduction in the MBfR. Successful operation relied on controlling the pH-increase effects of methanogenesis and homoacetogenesis, along with creating hydrogen limitation during start-up to allow dechlorinators to compete against other microorgansims. Methanogens were additionally minimized during continuous flow operation by a limitation in bicarbonate resulting from strong homoacetogenic activity. / Dissertation/Thesis / Ph.D. Civil and Environmental Engineering 2012

abstract: This study reports on the treatment of ammunition wastewater containing RDX (1,3,5-Trinitro-1,3,5-triazinane), HMX (1,3,5,7-Tetranitro-1,3,5,7-tetrazoctane), and the oxyanion co-contaminants nitrate (NO3-) and perchlorate (ClO4-) in a membrane biofilm reactor (MBfR), a Palladium (Pd)-coated MBfR (Pd-MBfR), and an abiotic Pd-coated film reactor (Pd-film reactor). A consortium of nitrate- and perchlorate-reducing bacteria, continuously fed with synesthetic ammunition wastewater featuring 4 mM nitrate and 0.1-2 mM perchlorate, formed robust biofilms on the membrane surfaces in the MBfR and Pd-MBfR. PdNPs with diameter 4-5-nm auto-assembled and stabilized on the surfaces of membrane and biofilm in MPfR and Pd-MBfR. Nitrate and perchlorate were rapidly reduced by the biofilms in the MBfR and Pd-MBfR, but they were not catalytically reduced through PdNPs alone in the MPfR. In contrast, RDX or HMX was recalcitrant to enzymatic degradation in MBfR, but was rapidly reduced through Pd-catalytic denitration in the MPfR and Pd-MBfR to form ‒N‒NHOH or ‒N‒H. Based on the experimental results, the synergistic coupling of Pd-based catalysis and microbial activity in the Pd-MBfR should be a viable new technology for treating ammunition wastewater. / Dissertation/Thesis / Masters Thesis Civil, Environmental and Sustainable Engineering 2019

abstract: 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. / Dissertation/Thesis / Ph.D. Civil and Environmental Engineering 2012

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