During the latest decades, there have been indications that the limiting nutrient are changeable in the Bothnian Sea. The current national regulations for wastewater treatment plants which have coastland towards the Gulf of Bothnia have no regulations regarding nitrogen purification, as these basins traditionally has been seen to have phosphorus-limited conditions. The aim of this study was to investigate how the temporal change of phosphorus and nitrogen has developed during the years 1991-2021 in the Bothnian Sea and if there were any differences between coastal and offshore stations. The ultimate goal was to give an overview of the nutrient situation and develop a guideline whether the current regulations for wastewater treatment plants are sufficient. Three coastal and two offshore stations were studied at the depth 0-10 m by investigating data from national monitoring programs, using trend analysis and comparison of means. The result showed that phosphorus is increasing in all the sampling stations. Consequently, the limited nutrient has evolved towards being more nitrogen-limited. The nitrogen load has instead been larger at the coastal compared to the offshore stations, especially for locations affected by river inlets. However, the conclusion according to this study is that the current regulations are sufficiently. This is due to the more recent shift towards nitrogen-limited conditions at the stations affected by river inlets and the high contribution with phosphorus-rich water from the Baltic Proper, as at the same time wastewater treatment plants is not the greatest contributor to the nitrogen load in the Bothnian Sea.

学位授与年月日: 2007-07-23 ; 学位の種類: 新制・課程博士 ; 学位記番号: 工博第2837号 / Perfluorochemicals (PFCs) were produced by industries and consumed “safely” as surfactants, repellents, additives, fire-fighting foams, polymer emulsifiers and insecticides for almost fifty years. However they are now considered as persistent, bioaccumulated and toxic (PBT) chemicals, and ubiquitously distributed in waster, air, human body and biota. Although some efforts were contributed to reduce PFCs in environment, such as development of alternatives and recycling processes, huge amount of persisted PFCs have already been discharged in environment and accumulated in biota including humans. In some industrialized areas, such as Yodo river basin in Japan, water environment and human blood were polluted by some PFCs, and thus reduction and control of PFCs were urgently required for the purpose of environmental safety and human health in these areas. Unfortunately, some studies implied that current water and wastewater treatment processes seemed ineffective to remove PFCs in trace levels. Therefore, this study will try to develop some proper technologies to treat trace level of PFCs in wastewater. In order to achieve this main objective, several works have been accomplished as follows. 　Current available literature has been reviewed to obtain a solid background for this study. Basic information of PFCs was summarized in physiochemical properties, PBT properties, productions and applications, regulations and etc.. Analytical methods for PFCs, especially of LC-ESI-MS/MS, were reviewed including pretreatment processes in diverse matrices, which derived objectives of chapter III. Distributions and behavior of PFCs were briefly discussed in water environments, biota sphere and human bloods. Available control strategies were shown in detail about alternatives, industrial recycling processes, and newly developed treatment processes. Current wastewater treatment processes showed inefficient removal for some PFCs, deriving objectives of chapter IV on the PFC behavior in treatment process. Newly developed treatment technologies seemed able to decompose PFCs completely but unsuitable for application in WWTP. Therefore, granular activated carbon (GAC) adsorption and ultra violet (UV) photolysis were developed in chapter V and VI as removal and degradation processes respectively. 　Fifteen kinds of PFCs were included in this study, consisting of twelve kinds of perfluorocarboxylic acids (PFCAs) with 4~18 carbons and three kinds of perfluoroalkyl sulfonates (PFASs) with 4~8 carbons. An integral procedure was developed in chapter III to pretreat wastewater samples. LC-ESI-MS/MS was applied to quantify all PFCs in trace level. Pretreatment methods were optimized between C18 and WAX-SPE processes for aqueous samples, and between IPE, AD-WAX and ASE-WAX processes for particulate samples. Standard spiking experiments were regularly conducted for each wastewater sample to calculate recovery rate and control analytical quality. As the result, WAX-SPE showed better performance on samples with very high organics concentrations, and C18-SPE performed better for long-chained PFCs. ASE-WAX was proposed as the optimum method to pretreat particulate samples because of the simple and time saving operations. 9H-PFNA was used as internal standard to estimate matrix effect in wastewater. 　Behavior of PFCs in a municipal WWTP has been studied in chapter IV by periodical surveys for six times in half a year. All PFCs used in this study were detected in WWTP influent and effluent. According to their carbon chain lengths, all PFCs can be classified into “Medium”, “Long” and “Short” patterns to simplify behavior analysis. PFCs in same pattern showed similar properties and behavior in wastewater treatment facilities. Very high concentrations of PFCs existed in WWTP influent, indicating some point sources of industrial discharge in this area. “Medium” PFCs, such as PFOA(8), PFNA(9) and PFOS(8), were primary contaminants in the WWTP and poorly removed by overall process. Performances of individual facilities were estimated for removal of each PFC. Primary clarification and secondary clarification were helpful to remove all PFCs in both aqueous phase and particulate phase. “Medium” PFCs in aqueous phase were increased after activated sludge process, but other PFCs can be effectively removed. Ozone seemed ineffective to decompose PFCs because of the strong stability of PFC molecules. Sand filtration and biological activated carbon (BAC) filtration in this WWTP can not remove PFCs effectively too, which required further studies. Performances of combined processes were estimated by integrating individual facilities along the wastewater flow. Activated sludge process coupled with clarifiers showed satisfied removal of most PFCs in the investigated WWTP except “Medium” PFCs. 　Adsorption characteristics of PFCs onto GAC have been studied by batch experiments in chapter V. Freundlich equation and homogenous surface diffusion model (HSDM) were applied to interpret experimental data. Isothermal and kinetics experiments implied that PFC adsorption on GAC was directly related with their carbon chain lengths. By ascendant carbon chain length, adsorption capacity for specific PFC was increased, and diffusion coefficient (Ds) was decreased. Ds of GAC adsorption was also decreased gradually in smaller GAC diameters. Coexisted natural organic matters (NOMs) reduced adsorption capacities by mechanism of competition and carbon fouling. Carbon fouling was found reducing adsorption capacity much more intensively than competition by organics. Acidic bulk solution was slightly helpful for adsorption of PFCs. However adsorption velocity or kinetics was not affected by NOM and pH significantly. GAC from Wako Company showed the best performance among four kinds of GACs, and Filtra 400 from Calgon Company was considered more suitable to removal all PFCs among the commercial GACs. Preliminary RSSCT and SBA results implied that background organics broke through fixed GAC bed much earlier than trace level of PFCs. Medium-chained PFCs can be effectively removed by fixed bed filtration without concerning biological processes. 　Direct photolysis process has been developed in chapter VI to decompose PFCAs in river water. Irradiation at UV254 nm and UV254+185 nm can both degrade PFCAs. Stepwise decomposition mechanism of PFCAs was confirmed by mass spectra analysis, and consecutive kinetics was proposed to simulate experimental data. PFASs can also be degraded by UV254+185 photolysis, although the products have not been identified yet. Coexisted NOMs reduced performance of UV photolysis for PFCAs by competition for UV photons. Sample volume or irradiation intensity showed significant influence on degradation of PFCAs. Local river water polluted by PFOA can be cleaned up by UV254+185 photolysis effectively. Ozone-related processes were also studied but ineffective to degrade PFC molecules. However, PFCs could be removed in aeration flow by another mechanism. / 京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第13340号 / 工博第2837号 / 新制||工||1417(附属図書館) / UT51-2007-M963 / 京都大学大学院工学研究科都市環境工学専攻 / (主査)教授 田中 宏明, 教授 藤井 滋穂, 教授 伊藤 禎彦 / 学位規則第4条第1項該当 / Doctor of Engineering / Kyoto University / DFAM

Mikroplastik (MPs) Partikel die kleiner als 5 mm sind, werden weltweit als neu identifizierte Gefahr auf die Umwelt betrachtet. Um geeignete Minderungsstrategien entwickeln zu können, werden diese neuartigen Umweltschadstoff hinsichtlich möglicher Eintragsquellen und potentieller Transportwege in der Umwelt zunehmend diskutiert. Gründe für eine notwendige Reduzierung von MPs in der Umwelt gibt es viele. Es werden dabei insbesondere das Transportverhalten in der Umwelt sowie deren Toxizität auf das System Mensch und Umwelt als Schlüsselkomponenten angesehen. Die in den letzten zehn Jahren gestiegene Nachfrage an synthetischen Textilien und der daraus resultierenden Produktionssteigerung hat zur Folge, dass diese Textilien eine Hauptquelle der MP-Verschmutzung im aquatischen System darstellen. Jedoch fehlen aktuell spezifische Informationen über die Größe und den Verbleib von faserigen Mikroplastikpartikeln (FMP), die aus gewaschenen Textilien des täglichen Lebens freigesetzt werden, wenn sie die Kläranlagen passieren und schließlich in Ökosysteme gelangen. Ziel dieser Arbeit ist es, die prävalent vorkommenden Größenfraktionen aus Polyethylenterephthalat (PET) FMPs, die aus synthetischen Fleecejacken beim Waschen in einer kommerziellen Waschmaschine freigesetzt werden, zu identifizieren und anschließend zu quantifizieren. Dabei soll ihr Vorkommen und ihr Verbleib in konventionellen Kläranlagen unter Berücksichtigung verschiedener Behandlungsstufen untersucht werden. Um den potenziellen Einfluss der PET-Faserlänge auf das Transportverhalten in Kläranlagen zu untersuchen, wurden zwei unterschiedlichen Größenfraktionen (1500 – 500 µm und 150 – 50 µm) in Batchtests miteinander verglichen. Darüber hinaus wurde in dieser Studie die Wirksamkeit der Koagulation, einem etablierten Verfahren aus der chemischen Abwasserbehandlung, auf die Eliminierung von FMP-PET-Fasern aus Abwässern untersucht. Unter Verwendung eines aus einer städtischen Kläranlage stammenden Inokulums wurde die biologische Abbaubarkeit von FMPs (PET) im Labormaßstab im Vergleich zu natürlichen (Baumwolle), regenerierten (Viskose), PET/Baumwoll-Mischgewebe und oxo-abbaubaren PET-Fasern untersucht. Zusätzlich wurde der Einfluss verschiedener Ausrüstungsverfahren (z.B. Reaktivfarbstoffe, Weichmacher und antimikrobielle Zusätze) auf die biologische Abbaubarkeit von Viskosefasern getestet. Der Waschtest ergab, dass die höchste Freisetzung von FMPs beim ersten Waschen auftrat und mit einer schrittweisen Reduzierung der Faseremission in weiteren Versuchen einherging. Bei einer Gesamtverteilung der PET-Faserlänge zwischen >1500 - 5 µm deckte die am häufigsten vorkommende massenbezogene Größenfraktion einen Bereich von 500 µm bis 50 µm ab. In einer Kläranlage konnte festgestellt werden, dass die Mehrheit der PET-Fasern unabhängig von der Größenverteilung mit partikulären Feststoffen abgeschieden werden (>90 % für Belebtschlamm und >99 % für Primärschlamm). Es konnte jedoch beobachtet werden, dass ein erhöhter Anteil kleiner Fasern (150 – 50 μm) in der flüssigen Phase verbleiben, was darauf hindeutet, dass kleineren Fasern nicht durch Kläranlagen zurückgehalten werden und schließlich in die Gewässer gelangen. Darüber hinaus konnte gezeigt werden, dass die Zugabe einer Koagulationschemikalie die Entfernung von großen PET Fasern (1500 – 500 μm) aus Abwässern geringfügig verbessern könnte; der Effekt war jedoch nicht signifikant. Die biologische Abbaubarkeit von Fasern in aquatischen Matrices nahm mit folgender Reihenfolge ab: Baumwolle ≥ Viskose > PET/Baumwollmischung > oxo-abbaubares PET ≥ PET. Dabei wiesen mit bestimmten Ausrüstungsmitteln behandelte Fasern im Vergleich zu unbehandelten Fasern einen niedrigeren Mineralisierungsgrad auf. Dieses zentrale Ergebnis unterstreicht die Bedeutung zur Berücksichtigung der Textilausrüstung bei der Bewertung des Umweltverhaltens von FMP. Dies ist die erste Studie, in der sich in der Abwasserbehandlung ausschließlich auf das Verhalten von PET-Fasern als eins der am häufigsten verwendeten Materialien in der Bekleidungsindustrie konzentriert wurde. Es konnte gezeigt werden, dass das Verhalten von textilbasierten FMPs bei der Abwasserbehandlung größenabhängig sein kann. Darüber hinaus wurde beobachtet, dass die Textilveredelung, je nach Haltbarkeit und Art des verwendeten Additivs, die Halbwertszeit von Faserschuppen in der Umwelt verlängern kann. Beide Erkenntnisse sind von großer Bedeutung, um nachhaltige Textilprodukte mit einer deutlich geringeren FMP-Emission in die Umwelt und im Hinblick auf eine funktionierende Kreislaufwirtschaft zu entwerfen. / Microplastics (MPs), plastic particles <5 mm, have been considered as global emerging environmental contaminants, triggering discussions regarding their sources, transport pathways and possible mitigation strategies, while fate and toxicity are recognized as key issues, including their potential threats to human health. The increased production and use of synthetic clothes over the last decade have placed synthetic textiles as one of the main sources of MP pollution in aquatic environments. However, there is still lack of information specifically on the size and fate of Fibrous Microplastic Particles (FMPs) released from washed daily-life products when they pass through Wastewater Treatment Plants (WWTPs) and eventually end up in the ecosystems. This thesis aims to investigate the amount and the dominant size fractions of polyethylene terephthalate (PET) FMPs released from synthetic fleece jackets during washing and to understand their occurrence and fate in conventional WWTPs, by considering different treatment stages. The potential influence of fibre length on the removal of PET fibres in WWTP was also investigated in batch tests, with two size fractions being compared, i.e. 1500 – 500 μm and 150 – 50 μm. Additionally, this study examined the efficacy of the coagulation, an established process of chemical treatment, on the elimination of FMP PET fibres from wastewaters. Finally, the present study evaluated the biodegradability of FMPs (PET) compared to natural (cotton), regenerated (viscose), PET/cotton blend and oxo-degradable PET fibres under laboratory conditions, by using inoculum from a WWTP, as well as the influence of different finishing processes (i.e. reactive dyes, softener and antimicrobial agent) on the biodegradability of viscose fibres. The washing test revealed that the highest release of PET fibres occurred in the first wash, with a consequent reduction of fibres’ emissions in sequential trials. PET fibre sheds collected with the aid of a filter cascade ranged from >1500 – 5 μm, with the most dominant size fraction in terms of mass ranging from 500 μm to 50 μm. Microscopic and gravimetric analysis revealed that when present in a WWTP, the majority of PET fibres were found to be associated to solids (>90% for activated and >99% for primary sludge), irrespective of their size fraction. However, small fibres (150 – 50 μm) were demonstrated to be retained in the liquid phase to a higher extent, indicating the likelihood of smaller fibres to pass through the WWTPs, entering eventually the water bodies. Moreover, our results showed that the addition of the coagulant chemical could slightly enhance the removal of large PET fibres (1500 – 500 μm) from wastewater effluents; however the effect was not significant. The biodegradability of fibres in aquatic environments decreased with the following order: cotton ≥ viscose > PET/cotton blend > “oxo-degradable” PET ≥ PET, while fibres treated with certain finishing agents displayed a lower mineralization level compared to the untreated, highlighting the importance of considering the textile finish when assessing the environmental behavior of FMPs. This is the first study giving emphasis solely on the behavior of PET fibres, one of the most common materials used in apparel industry, demonstrating that the performance of FMPs originated from textiles in wastewater treatments may be size-dependent. Moreover, it was shown that textile finishing might prolong the environmental half-lives of fibre sheds, depending on the durability and type of additive applied. Both findings are important when aiming at designing sustainable textile products with respect to a circular economy and considerably less FMPs emissions in the environment.

Wastewater treatment plants (WWTPs) are originally not constructed to remove pharmaceuticals from the wastewater. Biological treatment technologies used in many WWTPs today, e.g., activated sludge, MBBR and trickling filters, can, however, remove some pharmaceuticals well. Advanced treatment technologies, like ozonation, can be used as a complement to biological treatment for an even better removal. Käppala WWTP is not required to remove pharmaceuticals today, but is obligated to follow the development of advanced treatment technologies and prepare to implement one in the future. Additionally, a new wastewater treatment directive is under development with stronger regulations of pharmaceutical removal. Because of this, it is important to gather information about removal efficiencies for different treatment technologies in Käppala and other WWTPs. In this project, direct injection-UHPLC-Orbitrap-MS/MS was used to analyze wastewater from seven different WWTPs, including Käppala, with the aim to detect as many pharmaceuticals as possible. The removal efficiencies for 59 identified compounds, most of them pharmaceuticals, were used to evaluate the WWTPs and their treatment technologies. 55 of these compounds were detected in Käppala WWTP while 48 were detected in all seven WWTPs. In Käppala WWTP, around half of all compounds were removed with less than 20 %, including most of the compounds that is proposed to be regulated in the new wastewater treatment directive. This highlights the need for Käppala WWTP to introduce new treatment technologies. Two Swiss plants with ozonation had a removal efficiency &gt; 80 % across the whole plant for 79 % and 67 % of the compounds respectively. In the WWTPs that lacked advanced treatment technologies only 12-33 % of the compounds had a removal &gt; 80 %. One compound, chlorothiazide, did however increase 30 times across the plants with ozonation treatment. The trickling filter in one WWTP barely removed any compound with more than 20 % and was thereby the biological treatment technology with lowest removal efficiency. Activated sludge without N-removal also had a slightly lower removal of pharmaceuticals compared to activated sludge with N-removal and MBBR, possibly due to a shorter hydraulic retention time (HRT) and sludge retention time (SRT).

This research demonstrates the use of two novel methodologies to evaluate energy autarky status of wastewater treatment plants (WWTPs) in two steps. Step I (analysis 1 and 2) focuses on overall energy performance evaluation of a conventional activated sludge process (CAS) using a quantitative mass balance model. Step II involves development of a dynamic model that simulates a future wastewater resource recovery facility (WRRF). The step I (analysis 1) focused on small WWTPs with treatment capacities less than 5 MGD. The results revealed that a CAS process can achieve energy autarky or energy-positive status when old technology equipment is replaced with new, high efficiency equipment to save 10-12% energy; aeration energy is reduced by installing nitritation/anammox nitrogen removal process; and energy production is enhanced with the addition of FOG for co-digestion. Analysis 2 of step I focusing on large plant capacities (i.e., > 20 MGD) evaluated the effect of influent wastewater strength (IWWS), primary treatment COD removal efficiency (PT-COD), and proper design of combined heat and power (CHP) systems on the overall energy performance. The results showed that energy autarky is feasible when PT-COD is 60% for low IWWS, 40% or greater for medium IWWS, and 30% or greater for high IWWS. In step II analysis, a new and dynamic model was developed by integrating high rate algal pond (HRAP) and anaerobic digester (AD) systems. The model was calibrated using the experimental data from recent studies. The results showed that this system can achieve energy autarky when advanced solids separation and co-digestion systems are included. Solids separation efficiency was increased from 75 to 90% to reduce the winter effluent COD concentrations from HRAP (by 20%). Similarly, nitrogen effluent concentrations were reduced by increasing the solids retention time. Future studies should focus on techno-economic and environmental life cycle impact analysis of these novel process configurations.

No description available.

No description available.

Eutrophication is one of the major threats to the marine environment in the Baltic Sea. The human pressure on the sea by nutrient input from agriculture, industry, public sewage facility and small sewage treatment plants causes excessive algal blooms leading to oxygen depleted seabed and an ecosystem out of balance. The objective of this study is to investigate how local legitimacy and fairness is addressed in the multilevel and complex issue of reducing Baltic Sea eutrophication. The main results show that there is a great challenge and uncertainty in dealing with the problem of eutrophication. Furthermore, there is an unfair distribution of costs and responsibilities related to wastewater treatment in the municipal planning documents and nearly total exclusion of the individual property owners from participating in the decision-making processes related to the expansion plans for public sewage facility. This in turn risks the legitimacy and the democratic aspects of the plans. Previous studies related to public and simple sewage plants have investigated different issues related to the legislation and practical planning as possible reasons for a sluggish progress in the measures to reduce nutrient discharges to the sea. However, the fairness aspects and the participatory processes of the plans have not been studied. The implications of this study are to invite to a more inclusive and fair planning process with the use of alternative solutions to the compulsory expansion of public sewage facility. Modifications in the legislation to include economic instruments creating incentives for the property owners can be a way of increasing participation and thus the legitimacy of the system.

The increasing amount of microplastics found in the environment have underscored the urgency to identify, develop and deploy scenarios in which municipal wastewater treatment plants (MWWTPs) limit the release of urban microplastics into the environment. Simultaneously, the global trend towards a circular economy has defined the conditions for these scenarios in relation to the water-energy- nutrient nexus. This study has created a novel framework between studies into treatment technologies for microplastics removal in wastewater streams and circular economic objectives from policymakers with regard to the water-energy-nutrient nexus. The results of this study build on the existing evidence that MWWTPs release significant amounts of microplastics to both terrestrial and aquatic environments. This study has demonstrated how Multi-criteria Analysis (MCA) can be applied to analyse wastewater treatment scenarios for their ability to limit microplastic pollution from MWWTPs, whilst taking the water-energy- nutrient nexus into account. The MCA has identified MBR inci-eco as the best performing circular economic scenario for limiting microplastic pollution from MWWTPs in to be constructed plants. This scenario includes a Membrane Bioreactor (MBR) with Anaerobic Digestion, energy recovery through incineration and Phosphorus recovery through Ecophos. If already existing MWWTPs aim to upgrade their facility to limit microplastic pollution, CASPACUF with Pyreg as an energy-nutrient recovery is seen as the best performing scenario. The powder activated carbon with ultra filtration (PAC-UF) system would then be installed as an additional polishing step to an existing conventional activated sludge (CAS) system, significantly reducing upfront investment costs. Academia can build upon these results to initiate additional research into novel microplastic filtration specific technologies, business model innovation for wastewater treatment and microplastic pollution prevention at the source and in stormwaters. National and international policymakers should ban the distribution and sale of biosolids for direct land application to limit the pollution of microplastics from bio-solids. Furthermore, efforts should be put in place to limit microplastic pollution at the source by stimulating policies for a ban on the use of microbeads, limit tyre wear and improving design for e.q. washing machines. / Den ökande mängden mikroplast som finns i miljön har understrukit brådskan i att identifiera, utveckla och tillämpa strategier där kommunala avloppsreningsverk (MWWTP) begränsar utsläpp av urbana mikroplaster. Samtidigt har den globala trenden mot en cirkulär ekonomi definierat villkoren för dessa scenarier i förhållande till vatten-energi-näring-näxan. Denna studie har tagit fram ett nytt ramverk mellan studier om reningsteknologier för avlägsnande av mikroplast i avloppsvattenströmmar och cirkulära ekonomiska mål från beslutsfattare med avseende på water-energy-nutrient nexus. Resultaten av denna studie bygger på befintliga bevis på att kommunala avloppsreningsverk släpper ut betydande mängder mikroplast i både mark- och vattenmiljöer. Denna studie har visat hur Multi-Criteria Analysis (MCA) kan användas för att analysera avloppsreningsscenarier utifrån deras förmåga att begränsa mikroplastföroreningar från reningsverk, samtidigt som man tar hänsyn till vatten-energi-näring-näxan. MCA har identifierat MBR-inci-eco som det bäst presterande cirkulära ekonomiska scenariot för att begränsa mikroplastföroreningar från nya verk. Detta scenario inkluderar en Membrane Bioreactor (MBR) med anaerobisk nebrytning, energiåtervinning genom förbränning och fosforåtervinning genom Ecophos. Om redan befintliga verk ska uppgradera sin anläggning för att begränsa mikroplastföroreningar, ses CASPACUF med Pyreg som energi-näringsåtervinning som det bästa scenariot. Det pulveraktiverade kolet med ultrafiltreringssystemet (PAC-UF) skulle sedan installeras som ett ytterligare poleringssteg till ett befintligt konventionellt system för aktiverat slam (CAS), vilket avsevärt minskar investeringskostnaderna. Framtida forskning kan använda dessa resultat för att undersöka nya mikroplastfiltreringsspecifika tekniker, affärsmodellinnovation för avloppsrening och förebyggande av mikroplastförorening vid källan och i stormvatten. Nationella och internationella beslutsfattare bör förbjuda distribution och försäljning av biosolids för direkt markanvändning för att begränsa mikroplastföroreningar från biosolids. Vidare bör åtgärder vidtas för att begränsa mikroplastföroreningar vid källan genom att stimulera policyer för ett förbud mot användning av mikrokulor, begränsa däckslitage och förbättra designen för e.q. tvättmaskiner.

Urbanization affects in-stream biogeochemical processes that control nutrient export. Attempts to restore urban streams will not be successful unless the biological and physical controls on water quality are thoroughly understood. The objective of this study was to identify the relative influences of tributary dilution, groundwater discharge, and biological processing on nitrate concentrations in an urban stream during high and low flow periods. A wastewater treatment plant (WTP) on Pennypack Creek, an urban stream near Philadelphia, PA, increases nitrate concentrations to a mean of 8.5 mg-l-1 (as N). Concentrations decrease to 5.5 mg-l-1 about 7.5 km downstream. Reaches along this distance were sampled for nitrate concentration and delta-15N at fine spatial intervals to determine the reasons for this decrease. To quantify the effects of dilution, samples were collected from tributaries, groundwater springs, and upstream and downstream of tributaries or groundwater discharge zones identified through terrain analysis and continuous temperature modeling. These methods were also used to identify and sample reaches along which hyporheic flow occurred, where nitrate biological processing is often concentrated. In addition, loggers were installed at closely spaced sites to monitor daily fluctuations in nitrate, dissolved oxygen, and related parameters, which provided further indications of biological processing. Longitudinal sampling revealed decreases in nitrate concentration of 2 and 6.5 mg-l-1 during high and low flow, respectively. During high flow, delta-15N varied from 9.5 to 10.5 per mille downstream of the WTP, while delta-15N varied from 10.14 to 11.06 per mille throughout this reach during low flow. Mixing analysis indicated that groundwater discharge and biological processing both control nitrate concentration during both flow periods. Larger declines in nitrate concentration were observed during low flow than during high flow, and delta-15N fell between biological and groundwater signatures, indicating that both processes were enhanced. Continuous nitrate concentrations displayed distinct diurnal cycles often out-of-phase with dissolved oxygen cycles, indicating autotrophic processing. However, shifts occurred in nitrate cycle timing at a weekly scale wherein daily maximum concentrations were observed as many as 6 hours closer to noon than previously. These shifts were comparable to shifts observed across seasons in other studies, and by the end of the summer, nitrate and dissolved oxygen cycles were in-phase. Furthermore, shifts in nitrate cycles could not be linked to shifts in daily fluctuations of WTP discharge. Longitudinal sampling and continuous monitoring suggest that biological processing is an important control on nitrate concentrations in urban systems, though documenting its signature may be complicated by groundwater discharge and anthropogenic inputs. / Geology