Partial denitrification/anammox (PdNA) is an emerging biological nutrient removal (BNR) process that can be used to remove ammonia (NH3) and NOx from wastewater. This process is a combination of partial denitrification (PdN), which serves to reduce nitrate (NO3) to nitrite (NO2), and anaerobic ammonia oxidation, or anammox (AMX), which uses the nitrite as an electron acceptor to oxidize ammonia. PdNA provides significant aeration and external carbon savings when compared to the conventional nitrification/denitrification biological removal process for nitrogen but has been difficult to implement in mainstream treatment conditions due to many factors. One of these factors is the slow growth rate and startup time of anammox bacteria. This research first focused on determining the required startup time and startup optimization methods for a proposed mainstream polishing PdNA MBBR at Hampton Roads Sanitation District's James River Treatment Plant (JRTP). These two MBBRs were started with either virgin carriers or carriers coated with a preliminary biofilm and were fed secondary effluent The MBBRs were dosed with glycerol based on a feedforward carbon control approach and were not seeded with anammox at any point. Anammox activity was detected in the preliminary biofilm and virgin media MBBRs approximately 52 and 86 days after startup, respectively. Based on these results, starting up a mainstream PdNA reactor without seed is possible, and using preliminary biofilm carriers can speed up startup by approximately one month. A second experiment was conducted to determine the carbon demand and nitrogen removal capabilities of a glycerol fed PdNA MBBR and AMX MBBR in series. A nitrifying MBBR was also added to the MBBR train to test how well residual nitrite leaving the MBBRs could be polished off to limit ozone/disinfectant demand downstream. Additionally, a methanol-fed PdNA integrated fixed-film activated sludge (IFAS) reactor was also operated to determine the carbon demand and nitrogen removal capabilities for a PdNA process in an IFAS reactor. The PdNA and AMX MBBRs had average effluent TIN concentrations of 3.75 ± 1.25 and 2.81 ± 1.21 mg TIN/L, respectively, with a COD dosed per TIN removed ratio (COD/TIN) of 2.42 ± 0.77 g COD/g TIN for the entire process. The PdNA IFAS reactor had average effluent TIN concentrations of 4.07 ± 1.66 mg/L and 3.30 ± 0.96 mg/L at hydraulic retention times (HRTs) of 30 and 25 minutes. At these two HRTs, the PdNA IFAS process had a COD/TIN ratio of 1.08 ± 0.38 and 2.18 ± 0.99 g COD/g TIN, respectively. Overall, this indicated that both the PdNA MBBR and IFAS processes could reach low effluent TIN limits in mainstream conditions with low demand for COD, even with relatively low and unstable PdN efficiencies. Additionally, the nitrifying MBBR managed to keep the effluent nitrite concentration consistently below 0.5 mg/L at ammonia and nitrite influent loadings rates of 0.055 ± 0.035 and 0.379 ± 0.112 g N/m2/day. This research demonstrated that starting a PdNA process in mainstream conditions, without seed, can be accomplished within a reasonable timeframe and provides knowledge that can help engineers better understand the advantages of PdNA and design and startup mainstream polishing PdNA MBBRs and IFAS reactors. / Master of Science / As the human population continues to grow and wastewater discharge requirements continue to become more stringent, researchers and engineers have been exploring new technologies and methods to treat wastewater more efficiently. Once such method that is currently being explored is the integration of anaerobic ammonia oxidation, or anammox (AMX), bacteria with a variety of wastewater treatment technologies to remove nitrogen more efficiently from wastewater. AMX synchronously remove ammonia, which exists naturally in wastewater, and nitrite through an oxidation/reduction reaction in which the nitrogen leaves the wastewater in the form of dinitrogen gas. This process greatly reduces the amount of aeration and external carbon needed for the removal of nitrogen from wastewater compared to the commonly used method of full nitrification and denitrification, which are large operational costs at a wastewater treatment plant. While AMX have found use at full-scale plants in treating concentrated sidestreams with the use of partial nitrification (PN) to produce nitrite for the AMX, little progress has been made to integrate AMX into a full-scale mainstream treatment process where the stream is less concentrated and not ideal for consistent PN. Partial denitrification (PdN), however, has shown some promise in reliably producing nitrite in mainstream conditions for AMX usage. On top of the demand for nitrite, AMX bacteria also grow very slowly compared to most bacteria, which means these processes require relatively large amounts of time to get started. A common strategy for decreasing the startup time of AMX processes has been the addition of AMX biomass to a reactor during startup, but this is not feasible in a full-scale mainstream process due to the large amount of biomass that would be required. Therefore, other methods for startup optimization must be evaluated, which this study sought to do through two startup experiments in separate mainstream polishing moving bed biofilm reactors (MBBRs), which use plastic carriers to develop biofilms of bacteria. These two MBBRs were started with different types of carriers in them, one with carriers coated with a pre-established preliminary biofilm and one with brand-new, virgin carriers, to see what kind of effect these different types of carriers have on AMX startup time. AMX activity was detected in the preliminary biofilm and virgin media MBBRs approximately 52 and 86 days after startup, respectively, which was much quicker than expected. This indicates that starting up a mainstream PdNA reactor without seed is possible and using the preliminary biofilm carriers can speed up startup by approximately one month. After the startup experiment, one of the MBBRs was converted to a PdNA integrated fixed-film activated sludge (IFAS) reactor through the addition of activated sludge. This PdNA IFAS reactor was operated alongside a PdNA MBBR and AMX MBBR to test their nitrogen removal and carbon savings capabilities. Operation of these reactors demonstrated that both a PdNA MBBR or IFAS process are capable of consistently removing nitrogen to low levels with relatively low amounts of external carbon addition, even with inconsistent PdN. Overall, this research provided valuable insight into startup methods and design requirements of PdNA MBBRs and IFAS reactors which will make the implementation of these treatment processes more feasible.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/113208 |
| Date | 26 July 2021 |
| Creators | Macmanus, Justin Edward |
| Contributors | Civil and Environmental Engineering, Pruden, Amy, Bott, Charles B., Wang, Zhiwu |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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