<p> A half-order kinetic model (8-48 mg NO3+NO2-N/l), coupled with a temperature dependency described by the Arrhenius relationship (4°-27° C), adequately described biological denitrification of municipal wastewater in a pilot scale fluidized bed reactor. Biofilm support media (activated carbon or sand) and hydraulic flux (0.25-1.7 m^3/m^2·min) were not found to be significant factors in controlling denitrification rate within the reactor. Control of biofilm thickness on the support media was essential for satisfactory operation of the process; excess thickness contributed to elutriation of media and attached biofilm. Under similar influent wastewater conditions, the fluidized bed process was capable of equivalent NO3+NO2-N removal in about one-tenth of the time necessary in a suspended growth or a rotating biological contactor (RBC) process. Temperature dependency of the NO3+NO2-N removal rate appeared to be less than the dependency in a suspended growth or a RBC process, but similar to the dependency observed in a packed column.</p> / Thesis / Master of Engineering (MEngr)

<p> This work examines the feasibility of continuous biological nitrification and denitrification for nitrogen removal from municipal wastewater. Pilot plant'studies were conducted using a rotating biological contactor (RBC) for nitrification and upflow packed columns for denitrification. Of primary interest were the effects of temperature on the systems. </p> <P> It was found that an Arrhenius model adequately described nitrification rates measured over a range of temperatures from 7 degrees C to 250 degrees C. Direct comparison of the Arrhenius Activation Energies determined for the RBC and a two stage activated sludge system with intermediate clarification showed that nitrification in the RBC was less temperature sensitive than in the activated sludge process. At 10 degrees C, roughly 20 mg/hr·m^2 (0.10 lb/day•1000 ft^2 ) of ammonia as nitrogen was removed from the system. </p> <p> The rate of denitrification in the packed column reactors displayed great variability. The temperature dependency of the data could not be characterized by an Arrhenius model or any other simple relationship. Although significant nitrate removal was observed at all temperatures between 5°C and 25°C, severe short circuiting due to solids accumulation tended to limit minimum nitrate effluent concentrations to 1 or 2 mg N03^-N/~. </p> / Thesis / Master of Engineering (MEngr)

Increases in impervious surfaces caused by urbanization has led to higher volumes and rates of stormwater runoff that transports urban pollutants directly into natural waterways. Bioretention cells (BRCs) are vegetated soil systems designed to intercept stormwater runoff and reduce loads of water and contaminants discharged to surface waters. Nitrogen removal efficiency is highly variable and improvements are constrained by a poor understanding of the physical, biological, and chemical processes that occur within a BRC. The objectives of this study are to characterize and quantify the microbial communities in a range of existing BRCs, and determine which design factors have the greatest impact on denitrification, a microbial process responsible for removing nitrogen from stormwater. We sampled 23 BRCs throughout MD, VA, and NC, and quantified patterns in populations of denitrifying bacteria, denitrification potential, and microbial community structure within the soil medium. We found the greatest denitrifier populations and denitrification potential in the upper layer of the soil medium, which does not coincide with the internal water storage zone that is engineered to harbor anaerobic conditions favorable to denitrifying bacteria at the bottom of recent BRC designs. Results indicate that BRC vegetative cover, soil media nitrogen, and organic carbon concentrations are among the variables that facilitate nitrifying and denitrifying bacteria populations in BRCs. Bacterial community composition was most different between the top and bottom samples of the BRCs while fungal community composition differed most by BRC vegetative cover. Both fungal and bacterial community compositions were influenced by nitrogen and carbon concentrations. / Master of Science

Three of Hampton Roads Sanitation District's (HRSD's) conventional activated sludge Water Resource Recovery Facilities (WRRFs) add methanol for post-anoxic denitrification: the Virginia Initiative Plant (VIP), Nansemond Plant (NP), and Army Base (AB). From 2017-2020, VIP averaged 0.49 ± 0.03 lb COD/lb N removed, while NP and AB averaged 1.48 ± 0.06 and 2.11 ± 0.15 lb COD/lb N, respectively. Significant methanol savings at VIP may result from post-anoxic denitrification using internal carbon that was stored in the anaerobic zone. An investigation into the factors affecting internal carbon-driven (internal C) denitrification was done via a series of batch tests. The capacity for internal C denitrification was demonstrated with sludge from all three WRRFs, despite not necessarily being used full-scale. For each WRRF, an increase in these rates correlated to higher phosphorus uptake rates, suggesting a dependence on the PAO population. Shorter aerobic times and more acetate in the anaerobic stage were shown to increase internal C denitrification rates to varying degrees, and this type of denitrification was only observed for bio-P biomass that was also nitrifying. Beyond internal carbon, other denitrification factors explored include moving the methanol dose point further into the anoxic zone, longer post-anoxic residence times, plug-flow conditions, solids residence time (SRT), and anoxic conditions prior to methanol dosing. Contributions from slowly biodegradable COD were minimal. Understanding the conditions that promote denitrification with internal carbon or other carbon sources would be required for effective strategies to achieve methanol savings at NP and AB that would rival those at VIP. / Master of Science / Three of Hampton Roads Sanitation District's (HRSD's) Water Resource Recovery Facilities (WRRFs) add methanol to facilitate denitrification in the post-anoxic zone: the Virginia Initiative Plant (VIP), Nansemond Plant (NP), and Army Base (AB). Significant methanol savings at VIP may result from denitrification using carbon that was stored in the biomass earlier in the treatment process. An investigation into the factors affecting this type of denitrification with internal carbon was done via a series of batch tests. All three WRRFs were able to use this internal carbon for denitrification in the batch tests, despite not necessarily using it full-scale. These denitrification rates were shown to relate to the performance of the biomass that is also responsible for phosphorus removal. Shorter aerobic times prior to the anoxic phase and more acetate in the stage where carbon is stored were shown to increase these denitrification rates, and this type of denitrification was only observed for biomass from WRRFs that implement nitrification. Beyond internal carbon, other denitrification factors explored include moving the methanol dose point further into the anoxic zone, longer post-anoxic residence times, plug-flow conditions, solids residence time (SRT), and anoxic conditions prior to methanol dosing. Contributions from carbon pushed downstream from overloading primary clarifiers was minimal. Understanding the conditions that promote denitrification with internal carbon or other carbon sources would be required for effective strategies to achieve methanol savings at NP and AB that would rival those at VIP.

Bioretention cells (BRCs) are low-impact development stormwater management structures that integrate water quantity and quality management. Although BRCs have a predicted design life of about 25 years, most current research focuses on performance of cells less than two years old. This project evaluated the effectiveness of a BRC installed in 2007 to treat a 0.16-ha parking lot in Blacksburg, VA. After installation, this BRC was monitored for five months to determine initial flow reduction and total suspended solids, and nutrient removal. By monitoring for the same parameters, changes in cell performance since installation were quantified. ISCO automated stormwater samplers collected inflow and outflow composite samples from the cell, which were then analyzed for fecal indicator bacteria (total coliforms, E. coli, and enterococci), total suspended solids (TSS), total nitrogen (TN), and total phosphorus (TP). To determine if denitrification is occurring within the BRC, media samples taken throughout the cell were analyzed using qPCR. The bioretention media was also sampled to quantify changes in media nutrient content and particle size over the past seven years. Results indicate the bioretention media has not accumulated nitrogen and phosphorus since installation, and that the BRC remains effective at reducing flow volume and peak flow rates, as well as TSS, TN, TP, total coliforms, E. coli, and enterococci loads. Bacterial analysis of the media show most of the denitrifiers are present in the top layers of the bioretention media, despite an internal water storage layer and the bottom of the cell designed specifically for denitrification. / Master of Science

Excess nutrient pollution and eutrophication are widespread problems that must be solved at watershed scales, and stream restoration is increasingly implemented as a solution. Yet few studies evaluate the cumulative effects of multiple individual restoration projects on watershed-scale nutrient loading. We constructed a HEC-RAS model of stream restoration implemented throughout a generic 4th order watershed typical of the Piedmont physiographic province of the eastern USA. We simulated restoration of hyporheic exchange as one increasingly popular technique that receives dissolved nitrate-nitrogen (NO3--N) mitigation credit under the Chesapeake Bay TMDL. We populated the model with hyporheic exchange (0.3% of surface flow per hyporheic-exchange inducing in-stream restoration structure) and NO3--N removal (supply-limited denitrification removes all NO3--N that enters the hyporheic zone) values from prior literature on in-stream structures and related restoration techniques. We then varied the percentage of stream channels in the watershed in which restoration occurred. For watersheds with less than 100% of stream channels restored, we also varied where in the watershed (i.e. stream order) that restoration occurred. We found that hyporheic restoration in our 4th order watersheds has the potential to reduce NO3--N loading to downstream waterbodies by up to 83%, but that a maximum of <100% reduction exists given certain watershed characteristics. Model results revealed a nonlinear relationship between percent of stream channels restored and percent NO3--N loading reduction that occurred at the watershed outlet. This indicates that the effects of individual projects are not linearly additive, and must be evaluated in the context of how much of the watershed has already been restored. We also found that restoration was more effective at reducing NO3--N loading when it occurred in higher order streams (e.g., 3rd and 4th order), yielding load reductions upward of 30% compared to < 10% in lower order streams (e.g., 1st and 2nd order). Thus, the location of an individual restoration project within a watershed is important in determining its effect on NO3--N. Overall, our results indicate that hyporheic restoration can have significant effects on watershed NO3--N loading to downstream waterbodies, yet the watershed must be viewed as a whole to understand the potential impacts of any particular project under consideration. / Master of Science / Nutrient pollution and harmful algal blooms are widespread problems that must be solved at watershed scales, and stream restoration is increasingly implemented as a solution. Yet few studies evaluate the cumulative effects of multiple individual restoration projects on watershed-scale nutrient loading. We constructed a HEC-RAS model of stream restoration implemented throughout a generic watershed typical of the mid-Atlantic USA. We simulated restoration of nutrient-reducing groundwater flow cells along a stream corridor (hyporheic exchange) as one increasingly popular technique that is emphasized under the Chesapeake Bay TMDL. We populated the model with hyporheic exchange and nitrate-nitrogen (NO3--N) removal values from prior literature on in-stream structures and related restoration techniques. We then varied the percentage of stream channels in the watershed in which restoration occurred. For watersheds with less than 100% of stream channels restored, we also varied where in the watershed (i.e. stream order) that restoration occurred. We found that hyporheic restoration in our watershed has the potential to reduce NO3--N loading to downstream waterbodies by up to 83%, but that a maximum of less than 100% reduction exists given certain watershed characteristics. Model results revealed a nonlinear relationship between percent of stream channels restored and percent NO3--N load reduction that occurred at the watershed outlet. This indicates that the effects of individual projects are not linearly additive, and must be evaluated in the context of how much of the watershed has already been restored. We also found that restoration was more effective at reducing NO3--N loading when it occurred in larger streams, yielding load reductions upward of 30% compared to less than 10% in smaller streams. Thus, the location of an individual restoration project within a watershed is important in determining its effect on NO3--N. Understanding the maximum possible degree of NO3--N reducing hyporheic exchange is an important step for practitioners and policy-makers in choosing the most effective location for a stream restoration based on a project's goals, and cannot be done without analyzing the watershed as a whole. With more watershed-scale planning and a better understanding of certain physical characteristics, we can choose restoration locations and strategies that will ultimately work more efficiently toward reaching a nutrient reduction goal.

We investigated variations in resource availability (nitrate and labile organic carbon, LOC) as determinants of denitrification in sediments of streams in the southern Appalachian Mountains, USA. Stream water and sediments were sampled seasonally in two streams of contrasting nitrate availability, Noland Creek (high NO₃-N) and Walker Branch (low NO3-N). Eight additional streams with varying nitrate levels were sampled once during summer. Stream sediments were incubated at ambient stream temperatures, and nitrous oxide accumulation was quantified following acetylene inhibition of nitrous oxide reduction. Denitrification potential was greater in Noland Creek than Walker Branch and was generally greater in sediments from the higher-nitrate streams. In autumn and spring, nitrate and LOC amendments indicated that denitrification potential in Walker Branch sediments was nitrate limited, with temperature having no effect on rates. Denitrification potential in Noland Creek sediments was not limited by nitrate, but temperature had a significant effect. When Noland Creek seasonal data were corrected to a common temperature, no seasonal differences in denitrification potential were detected. Nitrate-N in the 10 surveyed streams ranged from 10 to 549 mg/L, with the highest NO₃-N levels and denitrification rates generally occurring in the higher elevation streams in the GSMNP. We found that nitrate availability, more than LOC availability, controls potential denitrification in these streams. / Master of Science

Partial denitrification anammox (PdNA) is an emerging wastewater treatment technology with the potential to increase process capacity and save on energy and carbon. PdNA circumvents potential issues with stability of the more familiar mainstream partial nitritation anammox (PNA) process. The PdNA process can be used to effectively remove ammonia, nitrate, and nitrite from mainstream municipal waste streams. To retain slow growing anammox, some sort of retention system is needed with media being a common solution to this problem. PdNA has been successfully implemented in mainstream full-scale systems in sand filters and with moving media. The goal of this study was to assess the denitrifying capabilities, anammox treatment capacity, and effective surface area to volume of two types of fixed media. A nitrifying pilot was set up to assess the effective surface area to volume. To assess the nitrifying and anammox ammonia removal capabilities of the fixed media, a fixed media PdNA system was installed in the second anoxic zone of a full-scale municipal wastewater treatment plant. The fixed media system consisted of three modules of sheets modified to mimic a plug flow system. After accounting for the estimated nitrate removal from mixed liquor, denitrification rates normalized to media surface area were 0.52 +/- 1.9 g/m2-day in the first module, 0.62 +/- 0.91 g/m2-day for the second module, and 0.56 +/- 0.90 g/m2-day for the third module. In ex situ batch testing it was found that maximum ex-situ anammox ammonia removal rates for the / Master of Science / Urban population growth has created a two-pronged problem for wastewater treatment plants. Plants in populated areas are seeing increases in flow along with growing space restrictions that limit new infrastructure construction. Additionally, rising environmental awareness from the public has spurred regulatory agencies to impose tighter limits on the quality of water leaving plants and entering sensitive watersheds. These factors have driven a need for treatment techniques that allow plants to operate better with their existing equipment. Overall, this concept is known as process intensification. One such method that treatment plants are using to intensify wastewater treatment is the addition of plastic media into their existing tanks. This media provides additional surfaces for the microorganisms that biodegrade the pollutants in the wastewater to grow and allows waste to be treated faster in the same area. It also allows slow growing organisms to be retained in the system that would otherwise not have time to grow. Such slow-growing microbes are especially critical for the removal of ammonia, a toxic form of nitrogen that occurs in high concentrations in wastewater. The partial denitrification-anammox process is an intensification process that leverages microbial metabolisms to convert nitrate to nitrite instead of denitrifying the nitrate all the way to nitrogen gas. Plants then let more ammonia pass through the aeration zone, where ammonia is converted to nitrate. The bleed through ammonia and the nitrite generated from partial denitrification is used by microbes called anammox, which denitrify without the addition of carbon. The full denitrification process requires externally added carbon, which is energy intensive to produce and expensive, and aeration requires energy to run the aeration blowers. Bypassing the full denitrification process using PdNA results in two-fold cost and energy savings. The plastic media help slow-growing anammox bacteria attach and grow to achieve this aim. Most of the plants that use plastic media use media that is free floating in the tank. However, certain plants cannot use this floating plastic media because it can either plug up the system, or flow to the end of the treatment tank and have no way to get back to the front. In instances such as these it could be beneficial to use a type of media that is fixed in place. One potential use of fixed media that has never been tried before is with partial denitrification with anammox. This research sets out to evaluate the effectiveness of fixed media with use in a partial denitrification anammox process and compare it to a treatment tank of moving media that is present at the same plant to find out whether it may be a viable option for retrofitting plants that cannot use moving media.

The CE-QUAL-W2 model has been selected as a tool for use in water quality management studies of the Occoquan Reservoir. In order for the model to achieve its best possible predictive capability, additional quantitative information on denitrification rates in the reservoir was required. A microcosm operating protocol was developed to obtain such information and also to enhance the understanding of complex nitrate-sediment-phosphorus interactions. The microcosm system developed was a biphasic system, consisting of a single continuous stirred tank reactor (CSTR), or a series of CSTRs containing representative sediment and water samples from the reservoir. The system was configured to simulate the bottom waters in the upper reaches of the reservoir during anoxic conditions. Nitrate concentrations in the microcosm system were monitored, and first-order denitrification-rate constants calculated to be used as an input to the reservoir water quality model CE-QUAL-W2. Other water chemistries were also monitored to investigate the nitrate effects on water quality. From the investigation results, it appears that the first-order denitrification-rate constant of the model should be set at 0.22 day-1 instead of the model default value. Nitrate was also observed to be removed by chemical and/or biologically mediated reduction by reduced forms of manganese. Once the nitrate was depleted, soluble manganese was released from the sediment first, followed by soluble iron. The release of phosphorus was not observed in this study after the depletion of nitrate, but nevertheless, was believed to occur. The absence of the release was attributed to phosphorus adsorption to the Plexiglas reactor walls. / Master of Science

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.