Novel Reactors for Biological Treatment of High Strength Nitrogen and Carbon Wastewater
In this dissertation, we assessed the performance of three different biological systems to achieve near full nitrogen (N) and carbon (C) removal from high-strength N wastewaters with low C/N ratio. The first objective was to demonstrate long-term operation of a simple two-stage partial nitrification-anammox reactor treating separated-source urine wastewater. A membrane aerated biological reactor (MABR) and Pancopia (foam-based) anammox (PAX) reactor were used to accomplish PN and Anammox processes, respectively. The second objective was to modify the configuration of the foam-based anammox (MAX) in order to resolve some potential operational issues observed with PAX systems and to increase N removal efficiency. The third objective was focused on using a combination of nitritation-denitrification and anammox (NDX) processes in a single-stage reactor containing low-density foam media to evaluate the treatment of a space-based wastewater with high N low C/N ratio. The first objective of this research demonstrates the use of MABR-PAXs to reliably treat separated-source urine (urine+ flush water) wastewater with minimal consumables. In MABR systems, gas-permeable hollow fiber membranes were utilized to provide O2 and support bacterial attachment to the membranes’ surface. The PAX reactor is a new type of reactor that contains low-density foams which act to retain anammox bacteria and increase SRT, preventing washout. To accomplish this work, the MABR systems were operated over a range of organic carbon (OC) and total ammonia nitrogen (TAN) loading rates (112-204 g-C/m3-day and 123-246 g-N/m3-day, respectively). The MABR systems achieved OC removal in excess of 108-198 g-C/m3-day, and TAN oxidation rates up to 73-156 g-N/m3-day. OC carbon removal efficiency of MABR reactors was in the range of 94-96 % and independent of OC carbon loading rates. The PAX systems were challenged over the range of 21-83 g-N/m3-d. TAN removal rates of PAX reactors reached up to 80 g-N/m3-d. In general, PAX systems achieved the maximum efficiencies of 85 to 97% TAN removal. In the second objective, we operated a new configuration of anammox reactor to solve PAX operational problems. The MAX reactor is a new anammox reactor configuration which contains low-density foams similar to the PAX reactors but in a new configuration. As with the PAX reactor, the low-density foams act to retain anammox bacteria and increase SRT, preventing washout. The MAX systems were continuously operated for 8 months and removed up to ~98% of the TAN, AN, and NO2-. Maximum TAN, AN, and NO2- removal rates were 211, 126, 114 g-N/m3-d. The main limitation for full TN removal by MAX systems was insufficient NO2- in the influent of MAXs (nonideal ratio of influent NO2-/AN). Compared to the PAX systems, TN removal efficiencies of MAX (89-90 %) were generally higher than PAX (37-97%) at similar loading rates. The new configuration prevented gas build hold up in the system and insured flow through the foam. This resulted in more consistent operation and higher loading rates. The combined system was able to stabilize the urine wastewater and produce N2 gas over long periods and could offer a sustainable alternative to wastewater pretreatment and long-term production of N2 gas. The third objective determines the capacity of a single-stage NDX biological reactor to treat a wastewater with a high N low C/N ratio and organic N concentration ~10X higher than typical municipal wastewater. The wastewater evaluated was based on the composition expected for a Martian Early Planetary Base (EPB), but the EPB wastewater is similar to terrestrial wastewater such as digester effluent and separated-source wastewaters. The NDX system had a working volume of 53 liters including a set of three foam media scaffolds that provide surface area for bacterial growth. The NDX system was intermittently aerated and mixed. The NDX systems were operated over a range of OC and TAN loading rates (38 g/m3-day, and 46 g-N/m3-day, respectively). The NDX systems have achieved organic carbon (OC) removal in excess of 34 g/m3-day, and TAN removal rates up to 42 g-N/m3-day. In general, NDX systems achieved the maximum of efficiency of 78 to 91% TAN removal. OC removal efficiencies of NDX reactors were in the range of 85-96 % and independent of OC carbon loading rates. Compared to past studies, our influent loading rates were lower possibly due to alkalinity and oxygenation limitations on TAN oxidation. TAN removal appears to be due to a combination of both denitrification and anammox resulting in increasing TAN removal efficiency compared to previous studies using nitrification-denitrification systems and the same wastewater. The increase in TAN removal is attributed to the anammox process. Overall, this research supports the use of MABRs-PAX or MAX for terrestrial high strength, low volume wastewaters where complex technology may be unsupportable, such as in rural or developing communities with no centralized treatment for applications where typical two-phase aeration can lead to undesirable off-gassing, and space habitation systems. They are useful for applications that require low maintenance systems, no additional processes (solids management), and simple or no process control systems.