Dissolved Organic Nitrogen Concentrations Research Articles

Fate of dissolved organic nitrogen in two stage trickling filter process

Dissolved organic nitrogen (DON) represents a significant portion of nitrogen in the final effluent of wastewater treatment plants (WWTPs). Biodegradable portion of DON (BDON) can support algal growth and/or consume dissolved oxygen in the receiving waters. The fate of DON and BDON has not been studied for trickling filter WWTPs. DON and BDON data were collected along the treatment train of a WWTP with a two-stage trickling filter process. DON concentrations in the influent and effluent were 27% and 14% of total dissolved nitrogen (TDN). The plant removed about 62% and 72% of the influent DON and BDON mainly by the trickling filters. The final effluent BDON values averaged 1.8 mg/L. BDON was found to be between 51% and 69% of the DON in raw wastewater and after various treatment units. The fate of DON and BDON through the two-stage trickling filter treatment plant was modeled. The BioWin v3.1 model was successfully applied to simulate ammonia, nitrite, nitrate, TDN, DON and BDON concentrations along the treatment train. The maximum growth rates for ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria, and AOB half saturation constant influenced ammonia and nitrate output results. Hydrolysis and ammonification rates influenced all of the nitrogen species in the model output, including BDON.

Impact of Scots pine admixture in European beech stand on dissolved organic carbon and nitrogen leaching from organic and humic horizons of Dystric Arenosols in Northern Poland

The effect of Scots pine admixture in European beech stand on the leaching of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), nitrate nitrogen (NO<sub>3</sub>-N) and ammonium nitrogen (NH<sub>4</sub>-N) from organic and humic horizons of Dystric Arenosols was studied in northern Poland in 2008–2009. Three zero-tension lysimeters under organic and humic horizons were installed in pure beech and mixed pine-beech stands. Water samples were collected after each rainfall, measured volumetrically, filtered and analysed. In each sample pH and concentrations of DOC, DON, NH<sub>4</sub>-N and NO<sub>3</sub>-N were analysed. Stronger acidification of leachates was observed in mixed stand compared to pure beech. About twice higher concentration of DOC and its fluxes per unit area were determined in mixed stand. The fluxes of DOC from unit mass of soil were less varied. In general, lower concentrations of DON, NH<sub>4</sub>-N and NO<sub>3</sub>-N as well as fluxes of the components (calculated in mg·kg<sup>-1</sup>DM·year<sup>–1</sup> and mg·m<sup>–2</sup>·year<sup>–1</sup>) were observed in mixed stand.  

The distinct nitrogen isotopic compositions of low and high molecular weight marine DON

To constrain the sources and cycling of bulk and size-fractionated marine dissolved organic nitrogen (DON), samples were collected for concentration and isotopic (δ15N) analysis from the western tropical North Atlantic Ocean as well as over the North Australian shelf. Bulk DON concentrations are typically between 4 and 6μM, with low molecular weight (LMW, i.e., <1000Da) DON accounting for 60 to 70% of total DON. The δ15N of both bulk and high molecular weight (HMW, i.e., >1000Da to <0.2μm) DON from the western tropical North Atlantic is similar to previous measurements, as well as to bulk and HMW DON collected off the North Australian Shelf, ~4‰. Here we report the first measurement of marine LMW DON δ15N, and a coherent pattern emerges where LMW DON δ15N<HMW DON δ15N. An analytical concern is that the bulk DON δ15N as calculated from our coupled HMW and LMW measurements is often lower than that measured directly for the bulk DON. Despite this discrepancy, the self-consistency of the data in other regards argues for the robustness of the basic observation of lower δ15N in LMW relative to HMW DON. One explanation for this isotopic difference is considered most likely, based on the model that DON δ15N elevation relative to PON is fundamentally due to DON production from PON without isotopic fractionation, coupled with DON destruction occurring with fractionation. In this model, HMW DON loss must occur predominantly through the breakage of N-containing bonds, for which isotope fractionation should be substantial, whereas LMW DON loss is partly due to direct assimilation by phytoplankton and other microbes, which appears to occur with only minor isotopic fractionation. However, an alternative hypothesis exists: LMW and HMW DON may have distinct sources, for example, prokaryotic and eukaryotic plankton, respectively. In either case, it appears that most LMW DON has not passed through the HMW DON pool, as this would require an unrealistically large isotope fractionation at the HMW to LMW conversion. Finally, neither the concentration nor the δ15N of the bulk or either size fraction of DON varies with in situ N2 fixation rates measured at the time of sample collection. However, the δ15N of both bulk and LMW DON from the western tropical North Atlantic shows significant differences between samples collected six months apart, which may be due to seasonally variable stimulation of primary production by the Amazon River.

Characterising the seasonal cycle of dissolved organic nitrogen using Cefas SmartBuoy high-resolution time-series samples from the southern North Sea

The Cefas SmartBuoy network provides a unique insight into the biogeochemical dynamics of the Northern European shelf seas, particularly the North Sea, through high-resolution automated offshore water sampling. We present total dissolved nitrogen and dissolved organic nitrogen (DON) from the Dowsing SmartBuoy site (53.531° N, 1.053° E) from January to October 2010, the first high resolution seasonal (winter-autumn) cycle of DON from the open North Sea. On top of a refractory background DON concentration of approximately 5 μM, a rapid increase in DON of a further ∼5 μM is observed over the course of the spring bloom. This rapidly produced DON declines at an estimated net decay rate of between 0.6 and 1.8 μM month−1. The slow decay suggests that the majority of the additional DON produced during the spring bloom is of semi-labile nature and has a lifetime of weeks to months. The dataset allows us to tightly constrain the budget for water column nitrogen over the winter, spring and summer of 2010 and clearly demonstrates the ‘sawtooth’ nature of the seasonal cycle of DON in the open North Sea, which has been impossible to resolve with a more traditional ship-based mode of operation. This work highlights the importance of autonomous sampling approaches in better understanding shelf sea biogeochemistry in the future.

Photochemical mineralization of dissolved organic nitrogen to ammonia in prairie lakes

We examined the rate of photoammonifi- cation in 16 lakes from Saskatchewan, Canada. Lakes were selected to encompass a broad range in dissolved organic nitrogen (DON) (269-1,435 l gl -1 ). Lake filtrate (\0.2 lm) was exposed to artificial solar radiation for 4 h. Rates of photoammonification were significant in 7 of the 16 study lakes. Ammonia (NH3) concentrations increased 0.84-2.85 l gl -1 over con- trol values. This is a 4-92% increase in NH3 concen- tration and a conversion of 0.18-0.3% of the DON pool to NH3. We developed an empirical model to predict photoammonification rates across aquatic ecosystems. Photoammonification rates and ancillary parameters (i.e., pH, DOC and DON concentrations, DOC:DON ratios, and a350:DOC) were obtained from published studies to expand our dataset for model development. Model selection was conducted with Akaike's Infor- mation Criterion (AIC). DON concentration and pH were selected as model predictors by AIC. Our model explains 49% of the variance in photoammonification rate across a diverse set of aquatic systems. This model may be useful in estimating photoammonification rates in other aquatic systems.

Dissolved organic nitrogen (DON) in a full-scale drinking water treatment plant

Dissolved organic nitrogen (DON) is currently considered as one of the most important parameters in drinking water treatment due to its potential to form toxic nitrogenous disinfection by-products (N-DBPs). A comprehensive investigation was made in this study on the variation of DON in a full-scale drinking water treatment plant with a treatment train of coagulation/sedimentation, biofiltration and disinfection. The results showed that DON could be removed effectively by coagulation/sedimentation and disinfection, while biofiltration increased the DON concentration significantly. To determine the mechanism of DON increase, DON and other related parameters at different media depths of the biofilter were studied. The results showed that the DON concentration in the biofilter presented a rapid decrease from 0.73 to 0.44 mg l −1 in the top media (0–10 cm), and a slow increase from 0.44 to 1.08 mg l −1 in the bottom media (10–100 cm). Soluble microbial products (SMPs) released by bacterial metabolism might be a main source of the DON in the biofilter. These SMPs contained aromatic protein-like fractions, which were confirmed by EEM analysis.

Algal Uptake of Hydrophobic and Hydrophilic Dissolved Organic Nitrogen in Effluent from Biological Nutrient Removal Municipal Wastewater Treatment Systems

Dissolved organic nitrogen (DON) accounts for a large fraction of the total nitrogen discharged to surface waters by municipal wastewater treatment plants designed for biological nutrient removal (BNR). Previous research indicates that some but not all of the DON in wastewater effluent is available to bacteria and algae over time scales that are relevant to rivers and estuaries. To separate bioavailable DON from nitrate and less reactive DON species, an XAD-8 resin coupled with an anion exchange treatment was employed prior to chemical analysis and algal bioassays. Analysis of effluent samples from a range of municipal BNR plants (total DON concentrations ranging from 0.7 to 1.8 mg N/L) employing a range of technologies indicated that hydrophilic DON, which typically accounted for approximately 80% of the total DON, stimulated algal growth, whereas hydrophobic DON, which accounted for the remaining DON, remained at nearly constant concentrations and had little or no effect on algal growth during a 14-day incubation period. The hydrophobic DON exhibits characteristics of humic substances, and is likely to persist for long periods in the aquatic environment. The distinct differences between these two classes of DON may provide a basis for considering them separately in water quality models and effluent discharge regulations.

Dissolved organic nitrogen (DON) profile during backwashing cycle of drinking water biofiltration

A comprehensive investigation was made in this study on the variation of dissolved organic nitrogen (DON) during a whole backwashing cycle of the biofiltration for drinking water treatment. In such a cycle, the normalized DON concentration (Ceffluent/Cinfluent) was decreased from 0.98 to 0.90 in the first 1.5h, and then gradually increased to about 1.5 in the following 8h. Finally, it remained stable until the end of this 24-hour cycle. This clearly 3-stage profile of DON could be explained by three aspects as follows: (1) the impact of the backwashing on the biomass and the microbial activity; (2) the release of soluble microbial products (SMPs) during the biofiltration; (3) the competition between heterotrophic bacteria and nitrifying bacteria. All the facts supported that more DON was generated during later part of the backwashing cycle. The significance of the conclusion is that the shorter backwashing intervals between backwashing for the drinking water biofilter should further decrease the DON concentration in effluent of biofilter.

Atmospheric organic nitrogen deposition in China

Abstract Precipitation samples have been collected and analyzed for organic and inorganic nitrogen (N) at 32 sites in China from 2005 to 2009. Our results suggest that dissolved organic nitrogen (DON) accounts for 28% of the total atmosphere bulk N deposition. Average annual DON deposition was 6.84 kg N ha−1 yr−1, ranging from 1.01 to 19.7 kg N ha−1 yr−1. The volume weighted average DON concentration was 77 μmol L−1, ranging from 13 to 190 μmol L−1, which was much higher than results obtained in other regions of the world. Analysis of seasonal variations of DON concentration, deposition, the ratio of DON to total dissolved N (TDN), rainfall and wind frequency roses revealed possible pollution sources in specific regions, e.g. agriculture, oceanic spray and re-suspension. Significant correlations of DON with TDN from results in this study and elsewhere indicate that atmospheric organic N species have similar anthropogenic pollution sources to atmospheric inorganic N species, and that DON deposition is an important part of the TDN deposition.

Interbasin isotopic correspondence between upper-ocean bulk DON and subsurface nitrate and its implications for marine nitrogen cycling

[1] Measurements to date have shown that both bulk and high molecular weight marine dissolved organic nitrogen (DON) have a 15N/14N that is substantially higher than the 15N/14N of suspended particulate organic nitrogen (PNsusp) found in the same surface waters (with δ15N of ∼4 to 5‰ and ∼−1 to 1‰, respectively). Moreover, the concentration and 15N/14N of DON are much less dynamic than those of PNsusp. These observations raise questions regarding the role of DON in the upper ocean nitrogen (N) cycle. In this study, the concentration and 15N/14N of nitrate and DON was measured in the upper 300 m of the oligotrophic North Atlantic and North Pacific Oceans. Comparing these two regions, the average DON concentration in the upper 100 m is similar, between 4.5 and 5.0 μM, but the average δ15N of DON is significantly different, 3.9‰ versus air in the North Atlantic and 4.7‰ in the North Pacific. This difference parallels a similar isotopic difference between shallow nitrate in these two regions; at 200 m in the North Atlantic, the δ15N of nitrate is 2.6‰, while it is 4.0‰ in the North Pacific. This isotopic correlation between surface DON and subsurface nitrate indicates that DON is actively participating in the upper ocean N cycle of each region. We describe a conceptual model that explains the elevation of the 15N/14N of DON relative to surface ocean PNsusp as well as the interbasin difference in the 15N/14N of DON. In this model, DON is produced from PNsusp without isotopic fractionation but DON is removed by fractionating processes. The ammonium and simple organic N compounds released by DON decomposition reactions are reassimilated by algae into the PNsusp pool, as an integral part of the ammonium-centered cycle that lowers the 15N/14N of PNsusp relative to the nitrate supply from below. This interpretation is consistent with the understanding of the chemical controls on isotope fractionation and is analogous to the previously posed explanation for the 15N/14N elevation of herbivorous zooplankton. In addition, it explains a lack of correlation between in situ N2 fixation rates and DON concentration and 15N/14N on short time scales.

Uptake of dissolved organic nitrogen by size-fractionated plankton along a salinity gradient from the North Sea to the Baltic Sea

The Baltic Sea is known for its ecological problems due to eutrophication caused by high nutrient input via nitrogen fixation and rivers, which deliver up to 70% of nitrogen in the form of dissolved organic nitrogen (DON) compounds. We therefore measured organic nitrogen uptake rates using self produced 15N labeled allochthonous (derived from Brassica napus and Phragmites sp.) and autochthonous (derived from Skeletonema costatum) DON at twelve stations along a salinity gradient (34 to 2) from the North Sea to the Baltic Sea in August/September 2009. Both labeled DON sources were exploited by the size fractions 0.2–1.6 μm (bacteria size fraction) and >1.6 μm (phytoplankton size fraction). Higher DON uptake rates were measured in the Baltic Sea compared to the North Sea, with rates of up to 1213 nmol N l−1 h−1. The autochthonous DON was the dominant nitrogen form used by the phytoplankton size fraction, whereas the heterotrophic bacteria size fraction preferred the allochthonous DON. We detected a moderate shift from >1.6 μm plankton dominated DON uptake in the North Sea and central Baltic Sea towards a 0.2–1.6 μm dominated DON uptake in the Bothnian Bay and a weak positive relationship between DON concentrations and uptake. These findings indicate that DON is an important component of plankton nutrition and can fuel primary production. It may therefore also contribute substantially to eutrophication in the Baltic Sea especially when inorganic nitrogen sources are depleted.

Effect of High Flow Events on In-Stream Dissolved Organic Nitrogen Concentration

Dissolved organic nitrogen (DON) can comprise a large and biologically important fraction of total dissolved N in surface water. Biotic and abiotic processes result in heterogeneous DON concentrations and bioavailability in soils, and as hydrologic connectivity expands and flow paths change in watersheds, novel sources of DON can be mobilized and transported to surface water. Although the relationship between in-stream DOC concentration and stream discharge has previously been examined in the literature, up to now there has not been a synthesis examining how DON concentrations, loads, and composition change during transitions from base flow to pulse flow conditions. We present a meta-analysis examining the effect of high flow on DON concentration ([DON]). The ratio of mean pulse flow [DON] to mean base flow [DON] (P:B) was calculated for individual events and averaged (geometric) within and then across sites to generate an overall effect size. For 47 sites (78 events), mean P:B was 1.58, which was significantly different from unity. This moderate increase in DON concentration contributed to over a more than 10-fold average increase in the rate of DON yield from base flow to high flow. The response of [DON] to high flow was significant in catchments where individual storm events or snowmelt runoff events were responsible for elevated flows, whereas the response was not significant in catchments where high discharge resulted from a mixture of upstream snowmelt and rain events. Additionally, an examination of DOC:DON ratios during high flow indicates that multiple sources of DON may be mobilized during high flow. Finally, current models of annual DON export may be improved by including a positive relationship between discharge and DON.

Spatio-temporal variability of the dissolved organic carbon and nitrogen in a coastal area affected by river input: The north eastern shelf of the Gulf of Cádiz (SW Iberian Peninsula)

Four surveys (June and November 2006; February and May 2007) were carried out in the north eastern shelf of the Gulf of Cádiz (southwest Iberian Peninsula) to investigate the dynamics of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) in a coastal area affected mainly by river input, but also by primary production/respiration, resuspension from the sediments, and mixing. In the period of the present study, DOC values ranged from 42 to 198 μM, while DON ranged from 0 to 20 μM. The seasonal variations showed high mean surface concentrations of DOC (106.2 ± 25.6 μM-C) and DON (8.6 ± 3.1 μM-N) in May, shifting to low DOC (89.1 ± 26.4 μM-C) and DON (4.2 ± 2.8 μM-N) in February. In spring, DOC and DON released by phytoplankton are likely to be the most significant source of organic matter. Low DOC and DON concentrations during winter are probably due to the uptake of DOC and DON by bacteria and to the strong mixing of the water column. The spatial variations showed the highest mean concentrations of dissolved organic matter (DOM) in the lower part of the Guadalquivir Estuary and the lowest mean concentrations of DOM in the bottom water of the oceanic zone. The very high mean DOC and DON concentrations measured off the Guadalquivir Estuary may be due to river input and/or re-suspension of the organic matter from the bottom sediments. The very low mean DOC and DON concentrations measured in the bottom water of the continental shelf may be due to mineralization and a surplus of more refractory organic carbon.

Dissolved Organic Nitrogen in Mediterranean Ecosystems

Dissolved organic nitrogen (DON) in soils has recently gained increasing interest because it may be both a direct N source for plants and the dominant available N form in nutrient-poor soils, however, its prevalence in Mediterranean ecosystems remains unclear. The aims of this study were to i) estimate soil DON in a wide set of Mediterranean ecosystems and compare this levels with those for other ecosystems; ii) describe temporal changes in DON and dissolved inorganic nitrogen (DIN) forms (NH + 4 and NO − 3), and characterize spatial heterogeneity within plant communities; and iii) study the relative proportion of soil DON and DIN forms as a test of Schimel and Bennett's hypothesis that the prevalence of different N forms follows a gradient of nutrient availability. The study was carried out in eleven plant communities chosen to represent a wide spectrum of Mediterranean vegetation types, ranging from early to late successional status. DON concentrations in the studied Mediterranean plant communities (0–18.2 mg N kg −1) were consistently lower than those found in the literature for other ecosystems. We found high temporal and spatial variability in soil DON for all plant communities. As predicted by the Schimel and Bennett model for nutrient-poor ecosystems, DON dominance over ammonium and nitrate was observed for most plant communities in winter and spring soil samples. However, mineral-N dominated over DON in summer and autumn. Thus, soil water content may have an important effect on DON versus mineral N dominance in Mediterranean ecosystems.

Examining the coupling of carbon and nitrogen cycles in Appalachian streams: the role of dissolved organic nitrogen

Although regional and global models of nitrogen (N) cycling typically focus on nitrate, dissolved organic nitrogen (DON) is the dominant form of nitrogen export from many watersheds and thus the dominant form of dissolved N in many streams. Our understanding of the processes controlling DON export from temperate forests is poor. In pristine systems, where biological N limitation is common, N contained in recalcitrant organic matter (OM) can dominate watershed N losses. This recalcitrant OM often has moderately constrained carbon:nitrogen (C:N) molar ratios (approximately 25-55) and therefore, greater DON losses should be observed in sites where there is greater total dissolved organic carbon (DOC) loss. In regions where anthropogenic N pollution is high, it has been suggested that increased inorganic N availability can reduce biological demand for organic N and therefore increase watershed DON losses. This would result in a positive correlation between inorganic and organic N concentrations across sites with varying N availability. In four repeated synoptic surveys of stream water chemistry from forested watersheds along an N loading gradient in the southern Appalachians, we found surprisingly little correlation between DON and DOC concentrations. Further, we found that DON concentrations were always significantly correlated with watershed N loading and stream water [NO3-] but that the direction of this relationship was negative in three of the four surveys. The C:N molar ratio of dissolved organic matter (DOM) in streams draining watersheds with high N deposition was very high relative to other freshwaters. This finding, together with results from bioavailability assays in which we directly manipulated C and N availabilities, suggests that heterotrophic demand for labile C can increase as a result of dissolved inorganic N (DIN) loading, and that heterotrophs can preferentially remove N-rich molecules from DOM. These results are inconsistent with the two prevailing hypotheses that dominate interpretations of watershed DON loss. Therefore, we propose a new hypothesis, the indirect carbon control hypothesis, which recognizes that heterotrophic demand for N-rich DOM can keep stream water DON concentrations low when N is not limiting and heterotrophic demand for labile C is high.

Marine Macrophyte Wrack Inputs and Dissolved Nutrients in Beach Sands

We investigated the role of sandy beaches in nearshore nutrient cycling by quantifying macrophyte wrack inputs and examining relationships between wrack accumulation and pore water nutrients during the summer dry season. Macrophyte inputs, primarily giant kelp Macrocystis pyrifera, exceeded 2.3 kg m−1 day−1. Mean wrack biomass varied 100-fold among beaches (range = 0.41 to 46.43 kg m−1). Mean concentrations of dissolved inorganic nitrogen (DIN), primarily NO x − -N, and dissolved organic nitrogen (DON) in intertidal pore water varied significantly among beaches (ranges = 1 to 6,553 μM and 7 to 2,006 μM, respectively). Intertidal DIN and DON concentrations were significantly correlated with wrack biomass. Surf zone concentrations of DIN were also strongly correlated with wrack biomass and with intertidal DIN, suggesting export of nutrients from re-mineralized wrack. Our results suggest beach ecosystems can process and re-mineralize substantial organic inputs and accumulate dissolved nutrients, which are subsequently available to nearshore waters and primary producers.

Behavior of Dissolved Organic Matter in Coral Reef Waters in Relation with Biological Processes

Behavior of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) in coral reef waters in relation with biological processes was studied with incubation experiments and field observations in May 2008 and 2009 at the fringing reef of Sesoko Island, Okinawa, Japan. Reef sea water (RSW) and coral mucus added RSW collected from Acropora digitifera (AcrRSW) and Montipora digitata (MonRSW) were incubated for one day in situ and then for 77 days in the laboratory under dark condition. The results indicated that the behavior of DON was different compared to that of DOC in RSW and mucus added (AcrRSW and MonRSW) during dark incubation. Concentration of DON increased from 8.3 µM to 11.8 µM for AcrRSW and 4.0 µM to 15.4 µM for MonRSW during dark incubation period. The increasing rates for DON in AcrSRW and MonRSW were 0.05 µM day-1 and 0.1 µM day-1 respectively. On the other hand DOC concentration decreased from 129.0 µM to 75.0 µM for AcrRSW and 75.1 µM to 64.7 µM for MonRSW, with decreasing rates of 0.7 µM day-1 and 0.1 µM day-1 respectively. We assume that the increase of DON may be determined by difference between rates of inputs of organic matter mainly from mucus and rate of degradation of dissolved organic matter in the water column. These results suggest that recycling of DON is slow than that of DOC in coral reef ecosystem.

Measurement of dissolved organic nitrogen in a drinking water treatment plant: Size fraction, fate, and relation to water quality parameters

This paper investigates the characteristics of dissolved organic nitrogen (DON) in raw water from the Huangpu River and also in water undergoing treatment in the full-scale Yangshupu drinking water treatment plant (YDWTP) in Shanghai, China. The average DON concentration of the raw water was 0.34 mg/L, which comprised a relatively small portion (~ 5%) of the mass of total dissolved nitrogen (TDN). The molecular weight (MW) distribution of dissolved organic matter (DOM) was divided into five groups: > 30, 10–30, 3–10, 1–3 and < 1 kDa using a series of ultrafiltration membranes. Dissolved organic carbon (DOC), UV absorbance at wavelength of 254 nm (UV254) and DON of each MW fraction were analyzed. DON showed a similar fraction distribution as DOC and UV254. The < 1 kDa fraction dominated the composition of DON, DOC and UV254 as well as the major N-nitrosodimethylamine formation potential (NDMAFP) in the raw water. However, this DON fraction cannot be effectively removed in the treatment line at the YDWTP including pre-ozonation, clarification and sand filtration processes. The results from linear regression analysis showed that DON is moderately correlated to DOC, UV254 and trihalomethane formation potential (FP), and strongly correlated to haloacetic acids FP and NDMAFP. Therefore, DON could serve as a surrogate parameter to evaluate the reactivity of DOM and disinfection by-products FP.

Fate of Organic Nitrogen in Four Biological Nutrient Removal Wastewater Treatment Plants

This study investigated the fate of nitrogen species, especially organic nitrogen, along the mainstream wastewater treatment processes in four biological nutrient removal (BNR) wastewater treatment plants (WWTPs). It was found that the dissolved organic nitrogen (DON) fraction was as high as 47% of soluble nitrogen (SN) in the low-SN effluent plant, which limited the plant's capability to remove nitrogen to very low levels. A lower DON fraction was observed in high-SN effluent plants. Effluent DON concentrations from the four plants ranged from 0.5 to 2 mg N/L and did not vary significantly, even though there was a large variation in the influent organic nitrogen concentrations. Size fractionation of organic nitrogen by serial filtration through 1.2-, 0.45-, and 0.22-microm pore-sized membrane filters and the flocculation-and-filtration with zinc sulfate (ZnSO4) method was investigated. The maximum colloidal organic nitrogen (CON) fractions found were 68 and 45% in the primary effluent and final effluent, respectively. The experimental results showed that effluents after filtration through the 0.45-microm pore-sized filter contain significant colloidal fractions; hence, the constituents, including organic nitrogen, are not truly dissolved. A high CON fraction was observed in wastewater influents and was less significant in effluents. The flocculation and filtration method removed the colloidal fraction; therefore, the true DON fraction can be determined.

Size fractionation and molecular composition of water‐soluble inorganic and organic nitrogen in aerosols of a coastal environment

This study reports the first high and low molecular weight measurements of dissolved organic nitrogen (DON) in size‐fractionated atmospheric particles. The variations in concentration of nitrogen species corresponded to varying sources and weather conditions. The results indicate that continental, local, and marine origins are the key factors controlling the particle size distribution of inorganic and organic nitrogen species. For dissolved inorganic nitrogen and DON, relatively high concentrations and fine‐mode particle (particle diameter &lt;1 μm) enrichment were significantly affected by continental and locally derived sources, which were mainly attributable to anthropogenic activities. However, the coarse/fine ratios indicate that DON was derived from a coarse particle (particle diameter &gt;1 μm) source that may be sea salt particles. To investigate the possible sources of DON, an ultrafiltration method was used to separate DON into high (HMW) and low (LMW) molecular weight categories. The results indicate that HMW‐DON and LMW‐DON contributed 57 ± 9% and 43 ± 9%, respectively, to the total DON concentration. Correlations and positive matrix factorization analysis of HMW‐DON and LMW‐DON levels with major and non‐sea‐salt ions indicated that HMW‐DON and LMW‐DON in coarse particles may be generated from continental soil dust and sea spray, respectively, whereas, in fine particles, DON may originate from aerosols derived from combustion processes. The annual fluxes of HMW‐DON and LMW‐DON were estimated to be 11.0 and 11.3 mmol m−2 yr−1, respectively. Consequently, the inputs of HMW‐DON and LMW‐DON appear to make equal contributions to DON in aerosols over the studied coastal area.