Sustaining the global population depends upon modern agricultural practices reliant on large inputs of nitrogen (N) fertilizer, but export of excess N from agroecosystems has negative environmental consequences, such as accelerated eutrophication and associated water quality degradation. The challenges posed by diffuse and widespread nutrient pollution in agricultural drainage waters necessitate cost-effective, adaptable, and reliable solutions. In this context, enhanced denitrification approaches developed over the last several decades have produced denitrifying bioreactors that harness the ability of ubiquitous soil microorganisms to convert bioavailable N into inert N gas, thereby removing bioavailable N from an ecosystem. Denitrifying bioreactors are edge-of-field structures that consist of organic carbon substrate and support the activity of denitrifying soil bacteria that remove N from intercepted nutrient-enriched drainage waters. The potential to improve bioreactor performance and expand their application beyond the Midwest to the agriculturally significant Mid-Atlantic region was investigated with a three-pronged approach: 1) a pilot study investigating controls on N removal, 2) a laboratory study investigating controls on emission of greenhouse gases nitrous oxide (N2O), methane (CH4), and carbon dioxide (CO2), and 3) a field study of one of the first denitrifying bioreactors implemented in the Atlantic Coastal Plain. The pilot and laboratory studies tested the effect of amending woodchip bioreactors with biochar, an organic carbon pyrolysis product demonstrated to enhance microbial activity. The pilot-scale study provides evidence that either hardwood- of softwood-feedstock biochar may increase N removal in woodchip bioreactors, particularly under higher N loading. The results from the laboratory experiment suggest the particular pine-feedstock biochar tested may induce greater greenhouse gas emissions, particularly of the intermediate product of denitrification and potent GHG nitrous oxide. The field study evaluated performance of a biochar-amended woodchip bioreactor installed on a working farm. Two years of monitoring data demonstrated that the bioreactor successfully removed N from drainage waters, but at relatively low rates constrained by low N loading that occurred in the absence of fertilizer application during continuous soy cropping at the site (10.0 kg NO3--N ha-1 yr-1 or 4.86 g NO3- -N m-3 d-1 on the basis of bed volume reached the bioreactor.) Removal rates averaged 0.41 g m-3 d-1 (8.6% removal efficiency), significantly lower than average rates in systems receiving greater N loading in the Midwest, and more similar to installations in the Maryland Coastal Plain. Greenhouse gas fluxes were within the range reported for other bioreactors, and of the N removed an average of only 0.16% was emitted from the bed surface as N2O. This case study provides useful measurements of bioreactor operation under low N loading that informs the boundaries of bioreactor utility, and may have particular regional relevance. The pilot and field studies suggest that wood-based biochars may enhance N removal and may not produce problematic quantities of greenhouse gases, respectively. However, the laboratory study raises the need for caution when considering the costs and benefits amending woodchip bioreactors with biochar and accounting for the effect on greenhouse gas emissions in this calculation, because the tested pine biochar significantly increased these emissions. / PHD

Conventional nonpoint source pollution policies encourage the adoption of conservation practices to reduce nonpoint source pollutants by paying a portion of the cost to install best management practices. Alternative financial incentive programs, such as payment for environmental services (PES) programs, aim to improve program effectiveness by paying directly for the quantity of environment services provided, but implementing PES programs to reduce nonpoint source pollution has been challenging given the costs and technical feasibility of measuring pollutant outcomes. Bioreactors, engineered sinks that convert biologically available forms of nitrogen into an inert form (N_2), have recently been proposed to treat and remove legacy nitrogen from springs (Easton et al., 2019). Since nitrogen removal can be directly measured, there is potential to implement an outcome-based PES program. Little information exists on the costs and risks sellers face under such a program or the impact of contractual conditions. This research applies Monte Carlo simulation to a case study bioreactor in the Chesapeake Bay Watershed to estimate the financial risks and rewards to N removal service providers under different outcome-based PES contractual conditions. Results indicate that under a fifteen-year contract term and price of $25/lb/yr of nitrogen removal, outcome-based PES for denitrifying bioreactors has a high chance of generating positive financial outcomes for a commercial size case study bioreactor that removes an average of 1,279 lbs of N annually. / Master of Science / Conventional policies to reduce diffuse water pollutants encourage the adoption of conservation practices to reduce diffuse water pollutants by paying a portion of the cost to install remedial practices or technologies. Payment for environmental services (PES) programs, an alternative to conventional policies, aims to improve program effectiveness by paying directly for the quantity of environment services provided. However, implementing PES programs to reduce diffuse water pollution has been challenging given the costs and technical feasibility of measuring pollutants and outcomes of remedial efforts. Bioreactors, engineered sinks that convert the diffuse water pollutant nitrogen into a non-pollutive form, have recently been proposed to remove legacy nitrogen from springs (Easton et al., 2019). Using bioreactors, nitrogen removal can be directly measured, so there is potential for an outcome-based PES program. Little information exists on the costs and risks sellers face under such a program or the impact of contractual conditions. This research applies financial simulation to a case study bioreactor in the Chesapeake Bay Watershed to estimate the financial risks and rewards to N removal service providers under different outcome-based PES contractual conditions. Results indicate that under a fifteen-year contract term and price of $25/lb/yr of nitrogen removal, outcome-based PES for denitrifying bioreactors has a high chance of generating positive financial outcomes for a commercial size case study bioreactor that removes an average of 1,279 lbs of N annually.

The global nitrogen cycle has been disrupted by large anthropogenic inputs of reactive nitrogen to the environment. Excess nitrogen underlies environmental problems such as eutrophication, and can negatively affect human health. Managing the natural microbial process of denitrification is advocated as a promising avenue to reduce excess nitrogen, and denitrifying bioreactors (DNBRs) are an emerging technology harnessing this biochemical process. Previous DNBR research has established successful nitrate removal, whereas this study examines the potential to expand DNBR functionality to address excess phosphorus and mitigate the production of nitrous oxide, a potent greenhouse gas. Results from a laboratory experiment supported the hypothesis that the addition of biochar, a charcoal-like soil amendment and novel organic carbon source in DNBR research, would increase nitrate and phosphorus removal as well as decrease the accumulation of nitrous oxide, an intermediate product of microbial denitrification. In order more closely examine the ratio of the products nitrous oxide and inert dinitrogen, development of a novel analytical method to quantify dissolved gases in environmental water samples using gas chromatography mass spectrometry was undertaken. Although static headspace analysis is a common technique for quantifying dissolved volatiles, the variation in sample preparation has recently been revealed to affect the determination of dissolved concentrations of permanent gases and convolute comparison between studies. This work demonstrates the viability of internal calibration with gaseous standard addition to make dissolved gas analysis more robust to variable sample processing and to correct for matrix effects on gas partitioning that may occur in environmental samples. / Master of Science

The advent of industrial, fertilizer-intensive agriculture during the 20th century has promoted export of anthropogenic nutrients, spurring degradation of ecosystem biodiversity and water quality. Exported nitrogen and phosphorus are recognized drivers of this deterioration, and require management. In the mid-1990s, denitrifying bioreactors (DNBRs), a subsurface, edge-of-field best management practice (BMP) that intercepts and treats agricultural drainage by supporting nitrate-attenuating denitrification with a saturated, carbon-filled substrate, were developed. Since then, their utility has expanded, and recent studies have unearthed biochar's capability to stimulate simultaneous nitrate (NO3--N) and phosphate (PO43--P) removal in DNBRs. This study investigated biochar's potential as an amendment to the traditional woodchip media by conducting nine, five-day trials on twelve laboratory-scale, horizontal flow-through DNBR columns. Three media types were tested: woodchips (W), 90% woodchips and 10% biochar (B10), and 70% woodchips and 30% biochar (B30). Simulated agricultural drainage with four unique concentration combinations of 16.1 and 4.5 mg L-1 NO3--N and 1.9 and 0.6 mg L-1 PO43--P was delivered at hydraulic retention times (HRTs) of 3, 6, and 12 h. Mean NO3--N removal efficiencies ranged from 16.9%-93.7%, and media type was insignificant at low influent NO3--N concentrations, but B30 was the most effective at high influent NO3--N concentrations. Mean PO43--P removal efficiencies ranged from -122.0%-74.9%, with B10 and B30 significantly worse than W at removing PO43--P. These findings corroborate previous work indicating boosted NO3--N removal with biochar, but contradict studies upholding PO43--P-removing capabilities. / Master of Science

The increasing concentration of nitrates in surface water and groundwater is becoming a global problem. The dissertation thesis is focused on the denitrifying bioreactors with organic fill material designed for the reduction of nitrate input from agricultural areas in the Czech Republic. A set of laboratory experiments was performed – static leaching tests and column tests, including chemical analyses of outflow water and ecotoxicological bioassays. Seven materials common in the Czech Republic, various process parameters, types and lengths of bioreactor shutdown in dry periods and the use of outflow water for irrigation were tested. The thesis deals with both denitrification efficiency and ways of reducing negative effects. An evaluation of the overall effect bioreactors is included along with a prediction regarding leaching over the following years.

Denitrification is a microbially-catalyzed reaction which reduces nitrate to N2 through a series of intermediate nitrogen compounds. Nitrate is a nutrient and its release into the environment may lead to eutrophication, depending on the amount that is released and the state of the recipient. The release of nitrate from the mining industry in Kiruna (Sweden) has been identified as an eutrophication risk, and a denitrifying bioreactor is to be constructed at the site to reduce the nitrate release.Since the denitrification rate decreases with temperature and the temperature in Kiruna during large parts of the year drops below 0˚C, the denitrifying bioreactor therefore has to be designed for the site-specific environment in terms of flow rate and hydraulic residence time. Laboratory column studies are used to study and determine the nitrate removal rate in a low temperature environment (5˚C) with pine wood chips as reactive matrix/ electron donor; the input solution had an average concentration of 35 mg NO3-N/L and a high sulfate concentration. Nitrate removal was studied as a function of hydraulic residence time and temperature. Parameters that were monitored include pH, alkalinity and concentrations of ammonium, nitrite and sulfate in the effluent from the columns. On three occasions, samples were gathered along the flow path in the columns (concentration profiles) such that changes in nitrate, nitrite, and occasionally ammonium concentration could be studied in relation to each other. The study concluded that a denitrifying bioreactor utilizing pine wood chips as the reactive matrix is a suitable option for nitrate treatment in a low temperature (5˚C) environment. Under the conditions of the study, effluent nitrate, nitrite, and ammonium concentrations are below limits established in legislation. Nitrate removal rates are given for zero-order nitrate reduction and overall first-order nitrate reduction, as the concentration profiles revealed a decrease in nitrate removal rate as nitrate concentration dropped below 3 mg NO3-N/L. / Nitrat är ett näringsämne som kan orsaka övergödning vid utsläpp, beroende på halterna och recipienten. Växterna som tar upp kväve kommer så småningom att dö och sjunka mot botten där de förmultnar. Förmultningen kräver syre, och vid ökad växtlighet så ökar även konsumtionen av syre då det finns mer organiskt material att bryta ned. Detta leder i slutändan till syrefria områden, där djurliv och växtlighet är mer begränsade. Nitratutsläpp från gruvindustrin i Kiruna har blivit identifierad som en potentiell övergödningsrisk och en denitrifierande bioreaktor ska därmed installeras för att minska utsläppen. Denitrifikation är en mikrobiell reaktion som reducerar nitrat till kvävgas genom en serie av intermediära kväveföreningar. En denitrifierande bioreaktor använder sig utav denitrifikation för att minska nitratkoncentrationer i vatten som passerar genom bioreaktorn som består av huvudsakligen; (1) bakterierna som sköter denitrifikationen, och (2) en kolkälla som fungerar som ”mat” till de denitrifierande bakterierna, Hastigheten varvid nitrat omvandlas till kvävgas genom denitrifikation, minskar med temperatur och den denitrifierande bioreaktorn måste därmed anpassas till omgivningen där den ska placeras med avseende på uppehållstid i reaktorn. Uppehållstiden måste vara tillräcklig för att minska nitratkoncentrationen till önskad nivå, men samtidigt så får uppehållstiden inte vara för lång då andra ämnen kan reagera och bilda ofördelaktiga produkter vid låga nitratkoncentrationer. Kolonnstudier i en låg-tempererad miljö (5˚C) är ett första steg för att studera hastigheten av nitratförbrukning i en sådan omgivning, och används i detta arbete med träflis av tall som kolkälla. Parametrar som påverkar, och varierar som ett resultat av, denitrifikation (exempelvis pH och sekundära föroreningar) övervakas. Hastigheten av nitratförbrukning som fås från kolonnstudierna kan sedan används som riktlinjer för konstruktionen av en denitrifierande bioreaktor i fältskala i Kiruna. Studiens slutsats är att en denitrifierande bioreaktor med träflis av tall som reaktivt medium är ett fungerande alternativ för nitrat reducering i en lågtempererad miljö (5˚C) då nitrat effektivt reduceras till under gränsvärden fastslagna i lag. Även andra potentiella biprodukter (exempelvis nitrit och ammonium) som kan resultera från den miljö som den denitrifierande bioreaktorn ger upphov till är under de gränsvärden som finns fastslagna i lag.