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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Process modelling of the MBBR AS hybrid process

Berry, N. D. January 2000 (has links)
No description available.
2

A comparative study of autotrophic and heterotrophic denitrification using sulphide and acetate

An, Shijie 29 June 2010
Sulphide containing streams must be treated before releases to environment due to the toxicity, corrosivity and unpleasant odour of sulphide. Anaerobic chemolithotrophic desulphurization under denitrifying conditions is the preferred process when compared with others like physicochemical processes, photoautotrophic and aerobic chemolithotrophic desulphurizations as the catalysts, high pressure, high temperature, light energy and oxygen are not needed. Another main advantage of this process is that the denitrification can be achieved with desulphurization simultaneously. In this work, the anaerobic chemolithotrophic desulphurization under denitrifying conditions (autotrophic denitrification) and heterotrophic denitrification processes were studied. Desulphurization under denitrifying conditions was studied in continuous stirred tank bioreactors (CSTB), while batch, continuous stirred tank and biofilm reactors were used to investigate the heterotrophic denitrification. The kinetics of desulphurization, autotrophic and heterotrophic denitrifications obtained in different systems and under various conditions were compared.<p> Using three different feed sulphide concentrations in the range 10-20 mM, a linear relationship between sulphide loading rates and sulphide removal rates was observed in continuous stirred tank reactors, regardless of initial sulphide concentration. The highest sulphide removal rate of 1.79 mM h-1 was obtained in CSTB fed with 15 mM sulphide. In these systems cell washout occurred at lower dilution rates as sulphide concentration in the feed was increased from 10 to 20 mM. The ratio of sulphide to nitrate loading rates influenced the composition of the sulphur oxidation end products where higher ratios favored the formation of elemental sulphur and lower ratios promoted the formation of sulphate.<p> In the batch system initial concentration of nitrate (5 to 50 mM) did not have a notable effect on denitrification process. Nitrate was converted to nitrite first and the produced nitrite was then converted to other gaseous end products such as nitrogen. Increases of temperature in the range of 15 to 35ºC increased the bacterial growth rate significantly with the value of apparent activation energy for specific growth rate being 60.6 kJ mol-1. Using the experimental data generated in two continuous bioreactors operated with feeds containing 10 and 30 mM nitrate biokinetic coefficients for heterotrophic denitrification were determined. The values of µm, Ks, ms, YMX/S, kd for initial nitrate concentrations of 10 and 30 mM were 0.087 and 0.082 h-1, 2.01 and 5.27 mM (NO3-), 1.441 and 1.096 mM (NO3-) (g biomass) -1 h-1, 0.011 and 0.013 g (biomass) (mM NO3-)-1, and 0.016 and 0.014 h-1 respectively. In the biofilm system the linear relationship between nitrate loading rate and nitrate removal rate was observed again for the whole range of tested nitrate loading rate range (up to 183 mM h-1), regardless of the approach used to increase the loading rate (increases in feed flow rate or feed nitrate concentration). The highest nitrate removal rate was 183 mM h-1 which was around 194 times higher than that achieved in the continuous stirred tank bioreactor with free cells.<p> A comparison of the autotrophic and heterotrophic denitrification processes studied in the CSTB system indicated that in case of autotrophic denitrification wash-out occurred suddenly and at a much lower loading rate of 0.75 to 0.96 mM (NO3-) h-1 for initial sulphide concentrations 10 to 20 mM, while in case of heterotrophic denitrification increase of nitrate loading rate did not have such a drastic effect and removal rate of nitrate decreased slowly with the increases of nitrate loading rate. A comparison of the kinetic data obtained in the biofilm reactor in the present work and those generated for autotrophic denitrification in an earlier work conducted at University of Saskatchewan (Tang, 2008) showed that the dependency of nitrate removal rate on its loading rate were linear in either case and somewhat similar. However, the maximum nitrate removal rate obtained in the heterotrophic system (183 mM h-1) was much higher than that obtained in the autotrophic system with sulphide.
3

A comparative study of autotrophic and heterotrophic denitrification using sulphide and acetate

An, Shijie 29 June 2010 (has links)
Sulphide containing streams must be treated before releases to environment due to the toxicity, corrosivity and unpleasant odour of sulphide. Anaerobic chemolithotrophic desulphurization under denitrifying conditions is the preferred process when compared with others like physicochemical processes, photoautotrophic and aerobic chemolithotrophic desulphurizations as the catalysts, high pressure, high temperature, light energy and oxygen are not needed. Another main advantage of this process is that the denitrification can be achieved with desulphurization simultaneously. In this work, the anaerobic chemolithotrophic desulphurization under denitrifying conditions (autotrophic denitrification) and heterotrophic denitrification processes were studied. Desulphurization under denitrifying conditions was studied in continuous stirred tank bioreactors (CSTB), while batch, continuous stirred tank and biofilm reactors were used to investigate the heterotrophic denitrification. The kinetics of desulphurization, autotrophic and heterotrophic denitrifications obtained in different systems and under various conditions were compared.<p> Using three different feed sulphide concentrations in the range 10-20 mM, a linear relationship between sulphide loading rates and sulphide removal rates was observed in continuous stirred tank reactors, regardless of initial sulphide concentration. The highest sulphide removal rate of 1.79 mM h-1 was obtained in CSTB fed with 15 mM sulphide. In these systems cell washout occurred at lower dilution rates as sulphide concentration in the feed was increased from 10 to 20 mM. The ratio of sulphide to nitrate loading rates influenced the composition of the sulphur oxidation end products where higher ratios favored the formation of elemental sulphur and lower ratios promoted the formation of sulphate.<p> In the batch system initial concentration of nitrate (5 to 50 mM) did not have a notable effect on denitrification process. Nitrate was converted to nitrite first and the produced nitrite was then converted to other gaseous end products such as nitrogen. Increases of temperature in the range of 15 to 35ºC increased the bacterial growth rate significantly with the value of apparent activation energy for specific growth rate being 60.6 kJ mol-1. Using the experimental data generated in two continuous bioreactors operated with feeds containing 10 and 30 mM nitrate biokinetic coefficients for heterotrophic denitrification were determined. The values of µm, Ks, ms, YMX/S, kd for initial nitrate concentrations of 10 and 30 mM were 0.087 and 0.082 h-1, 2.01 and 5.27 mM (NO3-), 1.441 and 1.096 mM (NO3-) (g biomass) -1 h-1, 0.011 and 0.013 g (biomass) (mM NO3-)-1, and 0.016 and 0.014 h-1 respectively. In the biofilm system the linear relationship between nitrate loading rate and nitrate removal rate was observed again for the whole range of tested nitrate loading rate range (up to 183 mM h-1), regardless of the approach used to increase the loading rate (increases in feed flow rate or feed nitrate concentration). The highest nitrate removal rate was 183 mM h-1 which was around 194 times higher than that achieved in the continuous stirred tank bioreactor with free cells.<p> A comparison of the autotrophic and heterotrophic denitrification processes studied in the CSTB system indicated that in case of autotrophic denitrification wash-out occurred suddenly and at a much lower loading rate of 0.75 to 0.96 mM (NO3-) h-1 for initial sulphide concentrations 10 to 20 mM, while in case of heterotrophic denitrification increase of nitrate loading rate did not have such a drastic effect and removal rate of nitrate decreased slowly with the increases of nitrate loading rate. A comparison of the kinetic data obtained in the biofilm reactor in the present work and those generated for autotrophic denitrification in an earlier work conducted at University of Saskatchewan (Tang, 2008) showed that the dependency of nitrate removal rate on its loading rate were linear in either case and somewhat similar. However, the maximum nitrate removal rate obtained in the heterotrophic system (183 mM h-1) was much higher than that obtained in the autotrophic system with sulphide.
4

Two Stage Membrane Biofilm Reactors for Nitrification and Hydrogenotrophic Denitrification

Hwang, Jong Hyuk 09 February 2010 (has links)
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.
5

Two Stage Membrane Biofilm Reactors for Nitrification and Hydrogenotrophic Denitrification

Hwang, Jong Hyuk 09 February 2010 (has links)
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.
6

Simultaneous Nitrification and Denitrification of Wastewater Using a Silicone Membrane Aerated Bioreactor

Waltz, Kirk Hjelte 01 April 2009 (has links)
The purpose of this thesis is to investigate the use of a single reactor to biologically treat wastewater by simultaneously oxidizing ammonia, and reducing nitrate and nitrite. The Environmental Protection Agency (EPA) places strict discharge restrictions on these compounds due to their inherent toxicity to humans, wildlife, and ecosystems. The use of a simultaneous system can assist the conventional wastewater treatment technology that requires separate systems, by creating a system that needs less time and smaller size to reach effluent requirements. To conduct this research, a bench-scale membrane aerated biofilm reactor was built using silicone tubing for aeration. Batch and continuous-flow experiments were conducted to investigate the reactor’s capability to oxidize ammonia using a defined growth media and monitor nitrate production and reduction. Also, wastewater from a local reclamation facility was used to determine the reactor’s ability to nitrify ammonia and denitrify nitrate concentrations within wastewater. The wastewater was taken from different locations within the reclamation facility, and combinations of primary and nitrified effluent were used to monitor ammonia and nitrate concentration changes. The batch experiments showed the greatest changes, and one batch experiment showed a 79% decrease in ammonium concentrations, and followed a first-order kinetics rate constant of -0.0284 hrs-1. The continuous-flow experiments showed much greater fluctuations in results, but one of the experiments showed an ammonia oxidation efficiency of 86%. The wastewater experiments had even greater fluctuations, and the effluent concentrations of ammonia, nitrate and nitrite showed no changes when compared to the influent.
7

Experimental Investigation of the Effects of Coagulant Dose and Permeate Flux on Membrane Fouling in a Moving Bed Biofilm Reactor-Membrane Process

Karimi, Masoomeh 20 April 2012 (has links)
The application of membrane bioreactors (MBRs) to wastewater treatment is increasing due to their ability to operate at high biomass concentrations and to deliver effluents of high quality. The major challenges associated with the application of MBRs is fouling which can shorten the useful life of the membrane, increase in the amount of energy consumed, and the cost for membrane cleaning. The main reasons for fouling are the deposition of solids as a cake layer, pore plugging by colloidal particles, adsorption of soluble compounds and biofouling. Fouling is a particular problem for activated sludge membrane bioreactors (AS-MBRs) since this process deals with liquors having a high concentration of total solids as well as dissolved compounds such as extracellular polymeric substances (EPS). The combination of a moving bed biofilm reactor and a membrane reactor (MBBR-MR) has significant potential. It may be considered as a compact wastewater treatment process which can compensate for the drawbacks of AS-MBRs. Readily biodegradable COD is removed in the MBBR while particulate matter is separated by the membrane. To further reduce the membrane fouling the effects of adding an intermediate coagulation stage was investigated critically on membrane fouling. The present study includes an overall assessment of the performance of a combined MBBR-MR system, based on the chemical oxygen demand (COD) removal efficiency and membrane fouling mechanism. The required test runs were conducted using pilot-scale MBBR and ultra filtration membrane. The pilot MBBR had a working volume of 1.8 m3 with a 60% carrier fill fraction. The MBBR was operated with loading rate of 78 ± 21 g/m2/d (HRT of 4 h). The ultra-filtration was spiral wound and composed of polyethersulfone (PES) with a pore size of 0.03 microns. The MBBR feed was obtained from a final treated wastewater effluent in a food processing plant located in SW Ontario. In this research, ferric chloride was also employed as a coagulant and influences of different coagulant doses and permeate fluxes on membrane fouling were studied. Based on the experimental results, it was found that the combination of MBBR with membrane filtration can produce a constant high quality permeate that is appropriate for water reuse purposes. The composition analysis of permeate showed that the stream is free of suspended solids and the average COD turns to 75 ± 25 mg/l. In addition, the MBBR had a SCOD removal of 76% ± 7% which is considered as a reasonable efficiency for a single reactor. Operating the membrane without adding coagulant caused rapid fouling in a short time period and the Trans Membrane Pressure (TMP) reached the maximum allowable pressure of 10 psi. However, addition of coagulant was found to decrease the fouling of the membrane as well as increasing the filtration time. The extent of the pre-coagulation effect on membrane fouling was found to strongly depend on the dosage of the coagulant and the MBBR effluent characteristics. A coagulant dose of 400 mg/l with a permeate flux of 7.6 LMH performed the best at reducing membrane fouling. Colloidal fouling was found to be a significant fouling mechanism at low coagulant dose (e.g. 200 mg/l), while cake formation appeared to be mainly responsible for fouling at higher coagulant doses. Permeate flux was found to have a significant effect on the fouling of the membrane. The presence of colloidal matters at low fluxes and TSS at higher fluxes were responsible for fouling of the membrane by blocking the pores and formation of the cake layer on the membrane surface, respectively. Then later addition of Dissolved Air Flotation (DAF) inside the factory had a noticeable effect on wastewater characteristics and consequently on fouling of the membrane. A 22% and 31% improvement in TCOD and TSS in the wastewater was observed leading to reduction in the fouling.
8

Experimental Investigation of the Effects of Coagulant Dose and Permeate Flux on Membrane Fouling in a Moving Bed Biofilm Reactor-Membrane Process

Karimi, Masoomeh 20 April 2012 (has links)
The application of membrane bioreactors (MBRs) to wastewater treatment is increasing due to their ability to operate at high biomass concentrations and to deliver effluents of high quality. The major challenges associated with the application of MBRs is fouling which can shorten the useful life of the membrane, increase in the amount of energy consumed, and the cost for membrane cleaning. The main reasons for fouling are the deposition of solids as a cake layer, pore plugging by colloidal particles, adsorption of soluble compounds and biofouling. Fouling is a particular problem for activated sludge membrane bioreactors (AS-MBRs) since this process deals with liquors having a high concentration of total solids as well as dissolved compounds such as extracellular polymeric substances (EPS). The combination of a moving bed biofilm reactor and a membrane reactor (MBBR-MR) has significant potential. It may be considered as a compact wastewater treatment process which can compensate for the drawbacks of AS-MBRs. Readily biodegradable COD is removed in the MBBR while particulate matter is separated by the membrane. To further reduce the membrane fouling the effects of adding an intermediate coagulation stage was investigated critically on membrane fouling. The present study includes an overall assessment of the performance of a combined MBBR-MR system, based on the chemical oxygen demand (COD) removal efficiency and membrane fouling mechanism. The required test runs were conducted using pilot-scale MBBR and ultra filtration membrane. The pilot MBBR had a working volume of 1.8 m3 with a 60% carrier fill fraction. The MBBR was operated with loading rate of 78 ± 21 g/m2/d (HRT of 4 h). The ultra-filtration was spiral wound and composed of polyethersulfone (PES) with a pore size of 0.03 microns. The MBBR feed was obtained from a final treated wastewater effluent in a food processing plant located in SW Ontario. In this research, ferric chloride was also employed as a coagulant and influences of different coagulant doses and permeate fluxes on membrane fouling were studied. Based on the experimental results, it was found that the combination of MBBR with membrane filtration can produce a constant high quality permeate that is appropriate for water reuse purposes. The composition analysis of permeate showed that the stream is free of suspended solids and the average COD turns to 75 ± 25 mg/l. In addition, the MBBR had a SCOD removal of 76% ± 7% which is considered as a reasonable efficiency for a single reactor. Operating the membrane without adding coagulant caused rapid fouling in a short time period and the Trans Membrane Pressure (TMP) reached the maximum allowable pressure of 10 psi. However, addition of coagulant was found to decrease the fouling of the membrane as well as increasing the filtration time. The extent of the pre-coagulation effect on membrane fouling was found to strongly depend on the dosage of the coagulant and the MBBR effluent characteristics. A coagulant dose of 400 mg/l with a permeate flux of 7.6 LMH performed the best at reducing membrane fouling. Colloidal fouling was found to be a significant fouling mechanism at low coagulant dose (e.g. 200 mg/l), while cake formation appeared to be mainly responsible for fouling at higher coagulant doses. Permeate flux was found to have a significant effect on the fouling of the membrane. The presence of colloidal matters at low fluxes and TSS at higher fluxes were responsible for fouling of the membrane by blocking the pores and formation of the cake layer on the membrane surface, respectively. Then later addition of Dissolved Air Flotation (DAF) inside the factory had a noticeable effect on wastewater characteristics and consequently on fouling of the membrane. A 22% and 31% improvement in TCOD and TSS in the wastewater was observed leading to reduction in the fouling.
9

Linking Structure and Function to Manage Microbial Communities Carrying Out Chlorinated Ethene Reductive Dechlorination

January 2012 (has links)
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
10

Treating Energetics-contaminated Wastewater

January 2019 (has links)
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

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