Browsing by Subject "Denitrification"
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Item Biological treatment of transit mission waste stream(Texas Tech University, 2004-12) Kaparthi, SrikaraThe waste stream on the space mission is recycled to get the potable water. To recover the waste stream, biological (packed-bed and aerated membrane biological reactor) methods are used. Nitrificafion takes place in aerated membrane reactor and denitrification takes place in the packed-bed. The waste stream on space mission is divided into three types based on the technology expected to be available during space missions. The three types of waste streams are transit mission waste stream, early surface mission waste stream, and mature surface mission waste stream. Transit mission waste stream consists of urine, DDI water, and humidity condensate. Little work has been conducted to evaluate the efficiency of the biological treatment of the urine-humidity condensate waste stream. The objectives of this experiment are 50 percent ammonium removal and 95 percent DOC removal. In this experiment four HRTs are used. The objectives of this experiment were met and the performance of the system is not only related to the adequacy of the reactor but also to characteristics of waste stream. Denitrification is limited by DOC and nitrification is kinetically limited. Therefore, to improve the biological treatment efficiency, either DOC or HRT should be increasedItem Comprehensive trade study of bioreactors and advancement of membrane-aerated biological reactors for treatment of space based waste streams(2012-03) Kubista, Kyle; Jackson, Andrew W.; Morse, AudraBiological processes offer an alternative approach to treatment of waste streams for water recycling during long term space missions. The combination of biological pretreatment with downstream physiochemical processes may be able to produce potable water at a lower equivalent system mass (ESM) compared to systems composed of only physiochemical processes. Several biological configurations exist for the removal of carbon and nitrogen. To date, no studies have comprehensively evaluated the relative ESM of each system. The configurations evaluated include: 1) membrane aerated biological reactor for simultaneous nitrification/denitrification, 2) membrane aerated biological reactor for nitrification in sequence with a packed-bed reactor for denitrification and organic carbon removal, 3) a pre-carbon oxidation reactor followed by a membrane aerated biological reactor for nitrification, and 4) an extended membrane aerated biological reactor for nitrification and aerobic carbon oxidation. We report on the systems, analysis and results including a detailed discussion of the inputs of the ESM analysis, methodology for determining reactor size and mass, and the implications of each system on downstream processing and reliability. Ongoing development of microgravity compatible biological reactors is essential to develop full scale flight ready technology. Recently, the first full scale membrane aerated biological reactor (MABR) was developed and evaluated. Despite several shortcomings, the reactor laid the groundwork for future development. To further develop the full scale MABR, a counter-diffusion membrane aerated nitrification denitrification reactor, a new upgraded MABR (CoMANDR) was designed to overcome the limitations experienced by the first generation. The first generation was limited primarily by its ability to transfer oxygen to the bulk liquid and inability to make repairs due to inaccessibility to the various chambers. CoMANDR is designed to overcome oxygen transfer limitations by using a submersible membrane module (SMM) with a pressurized lumen and additional membranes (to provide increased surface area). The SMM has the ability to be completely removed from the bulk liquid chamber allowing for ease of maintenance and repair. Along with the SMM, features like unidirectional gas flow patterns, offset liquid influents, and additional membranes are incorporated into CoMANDR to address the limitations experienced in the first generation. CoMANDR has been designed, constructed and is expected to meet treatment efficiencies of 90 % dissolved organic carbon removal, 70 % nitrification, and 50 % denitrification. CoMANDR will treat mass loadings of 34 g-C/d and 44 g-N/d at a hydraulic loading rate of 40 L/d. The reactors use silicone membranes to provide surface area for bacterial attachment and to supply oxygen to the bacteria. The membranes are the most important feature of MABRs because they provide a unique biofilm stratification that allows for higher removal efficiencies. The counter-diffusion of oxygen and substrate to the bacteria create optimum biofilms. MABR technology has been studied for over 10 years and has recently been designed for full scale applications. The first full scale model experienced oxygen transfer limitations. The next full scale application intends to operate under liquid pressure and lumen pressure (conditions that have not been investigated). This paper investigates benefits of switching to thin walled membranes (1.3 mm thick) from the previously used 2.24 mm thick membranes. The thin walled membranes cannot maintain structural integrity under elevated liquid pressure. Also, the thin membranes only slightly increase the oxygen transfer rate. The thick wall membranes are recommended for the optimization of the new full scale MABR, (CoMANDR).Item Flow, nutrient, and stable isotope dynamics of groundwater in the parafluvial/hyporheic zone of a regulated river during a small pulse(2014-08) Briody, Alyse Colleen; Cardenas, Meinhard Bayani, 1977-Periodic releases from an upstream dam cause rapid stage fluctuations in the Colorado River near Austin, Texas. These daily pulses modulate fluid exchange and residence times in the hyporheic region, where biogeochemical reactions are pronounced. We installed two transects of wells perpendicular to the river to examine in detail the reactions occurring in this zone of surface-water and groundwater exchange. One well transect recorded physical water level fluctuations and allowed us to map hydraulic head gradients and fluid movement. The second transect allowed for water sample collection at three discrete depths. Samples were collected from 12 wells every 2 hours for a 24-hour period and were analyzed for nutrients, carbon, major ions, and stable isotopes. The results provide a detailed picture of biogeochemical processes in the bank environment during low flow/drought conditions in a regulated river. Findings indicate that a pulse that causes a change in river stage of approximately 16-centimeters does not cause significant mixing in the bank. Under these conditions, the two systems act independently and exhibit only slight mixing at the interface.Item Ocean biogeochemistry in the northern Gulf of Mexico, the East/Japan Sea, and the South Pacific with a focus on denitrification(2012-05) Kim, Il Nam, 1976-; Min, Dong-Ha; Macdonald, Alison M.; McClelland, James W.; Gardner, Wayne S.; Liu, ZhanfeiOcean nitrogen fixation and denitrification are crucial nitrogen source and sink mechanisms for the global ocean environment. While recent studies have reported that oceanic denitrification has increased over the last few decades, others have suggested that global ocean nitrogen fixation rates have been underestimated, and still others that anthropogenic perturbations have altered the global nitrogen cycle. This implies that the current estimates of the oceanic nitrogen inventory are incomplete and they need to be revised with more information. In addition, current denitrification estimates need to be reexamined due to their large associated uncertainties. Thus, I have conducted research estimating denitrification rates in three different locations: the northern Gulf of Mexico (GOM), the East/Japan Sea (EJS), and the South Pacific: from coastal to marginal to open ocean scale in different oceanographic conditions. Denitrification rates in the bottom layer (including bottom waters+sediments) at the shallow and often hypoxic northern GOM ranged from 103-544 [mu]mol N m⁻² d⁻¹ (=1.4 to 7.4 Gg N mon⁻¹ with area=3.24x10¹⁰m²), and were controlled not only by biogeochemical factors (i.e. organic matter supply and remineralization), but also by physical factors (i.e. stratification and relative contributions from different water masses). Despite high dissolved oxygen concentrations, the significant decrease in nitrate concentrations below the expected levels, low N/P ratio (<12.4), and deep nitrite peak in the bottom layer indicate a presence of denitrification in EJS, confined at the Tatar Strait and the Ulleung Basin areas. The estimated denitrification rates range from 0.3 to 33.2 [mu]mol N m⁻² d⁻¹, and was comparable to the directly measured denitrification rates from sediment samples. The high-quality repeat hydrographic datasets observed at 32°S of the South Pacific Ocean offer an opportunity to estimate water column denitrification rates on a basin-scale in the open ocean away from the Eastern Tropical Pacific oxygen minimum zones. The mean water column denitrification rates in the oxygen minimum layer of P06 line (32°S) were estimated to range between 7.1 and 18.5 [mu]mol N m⁻² d⁻¹. The results imply that, although very small at any particular site, once integrated over a basin-scale, the open ocean water column denitrification can be a significant component of the oceanic nitrogen budget. Denitrification is subject to seasonal, decadal and possibly climate scale variations. While it is commonly estimated at the oxygen minimum zones or sediments, denitrification is not merely confined to such regions only, and small amounts of denitrification occur in other oceanic parts. Once integrated, it may be quantitatively significant for the world's oceans. Denitrification is playing a significant role in local, regional, and global ocean scales. In the future, we need to consider variability of denitrification in coastal regions, and to investigate denitrification in unexpected and unexplored regions, in order to improve our knowledge on global oceanic mass balance.Item Optimizing denitrification at Austin’s Walnut Creek Wastewater Treatment Plant(2010-08) Hughes, Mark Patrick, 1986-; Lawler, Desmond F.; Malina, Joseph F., 1935-In natural waters, high concentrations of ammonia are toxic to fish, and the oxidation of ammonia to nitrate (NO₃-) consumes large quantities of dissolved oxygen. The influent to municipal wastewater treatment plants in the United States typically contains approximately 40 mg/L of ammonia nitrogen (NH₃₋ N). Almost all of this ammonia must be removed in a wastewater treatment process before the effluent is discharged to the natural environment. This dramatic decrease is accomplished by the aerobic biological process of nitrification, in which ammonia is oxidized to nitrate Biological denitrification is an anoxic biological process in which nitrate (NO₃-) is reduced to nitrogen gas (N₂). Denitrification can increase the alkalinity in activated sludge aeration basins and decrease the concentration of filamentous organisms. The staff at the City of Austin Water Utility decided to implement a denitrification system at Walnut Creek Wastewater Treatment Plant to control filamentous organisms and increase the alkalinity within the aeration basins. The denitrification configuration that the staff implemented was unconventional because no structural changes were made to the aeration basins to encourage denitrification. However, the system functioned well and allowed operators to turn off one of the two air blowers, which saves the plant a significant amount of energy. The current operation has occasional problems, where the alkalinity in the aeration basin decreases or the effluent ammonia increases. When the alkalinity decreases to the point where the pH drops to near 6.0, operators are forced to add chemicals to increase the alkalinity. When the effluent ammonia increases to near the permitted concentration (2.0 mg NH₃-N/L),operators are forced to turn back on the second blower which eliminates the anoxic zone. These problems occur most often during the winter, when the wastewater is the coldest. The wastewater temperature at Walnut Creek varies from a high of 30°C during the summer to a low of 18°C during the winter. The goal of this research was the identification of ways to make the operation more robust which would prevent the need for chemical addition and minimize the use of the second blower. Laboratory-scale reactors were operated to assess possible improvements that could be made to the operation and configuration of the denitrification system at Walnut Creek. The data observed in the laboratory scale experiments showed that the population of denitrifying bacteria limits denitrification and is especially important during the winter. Increasing the solids retention time to 20 days appeared to be the best way to increase the population of denitrifying bacteria and improve denitrification. Improvements can also be made by increasing the volume of the anoxic zone. Increasing the volume of wastewater and biomass recycled will most likely not benefit denitrification until other improvements have been made. Recommendations to the City of Austin Water Utility include the following: 1) increase the solids retention time at Walnut Creek, 2) Increase the volume of the anoxic zone, 3) Separate the anoxic zone from the aerobic section of each aeration basin, 4) During the winter, operate the flow equalization basins to reduce the dissolved oxygen entering the anoxic zone, 5) Continually mix some of the effluent from the aeration basins with the primary effluent in the flow equalization basins.