Nitrogen Discharge Research Articles

Implementation of an Upflow Fixed Bed Bioreactor for Denitrification Coupled to Methane Oxidation: Performance and Biomass Development Under Anoxic Conditions

Denitrification coupled to methane oxidation (DOM) has been shown to be an appropriate process for wastewater treatment applications, since it can reduce greenhouse gas emissions and nitrogen discharges, making wastewater treatment plants more environmentally sustainable. Study of DOM has focused on laboratory-scale application using membrane biological reactors (MBR) or sequency batch reactors (SBR), which have been shown to be able to retain DOM biomass and therefore appropriate for use with this process. However, it is necessary to expand knowledge of the behavior of this process using other configurations, with a view to scaling up. Therefore, in this study, an upflow fixed bed bioreactor (UFBR) was implemented using plastic carriers such as bioballs and Biochips® to carry out the DOM process under anoxic conditions. The reactor reached stable nitrogen removal conditions after approximately 400 days of continuous operation, forming a biomass composed of denitrifying methane-oxidizing microorganisms where the genus Anaerolinea and Methylocystis predominated. Once the biomass was formed and the DOM process was stabilized, maximum nitrite and nitrate removal rates of 17.6 mgN-NO2−/L-d and 8.9 mgN-NO3−/L-d, respectively, and a removal efficiency of methane up to 77% were obtained. This demonstrates the feasibility of the application of the DOM process under anoxic conditions using fixed bed bioreactors, which is promising for further nitrogen removal from wastewater using a varied reactor configuration easily to scaled-up.

Application Research on the Use of Multiple Comparison Methods in The Evaluation of the Effectiveness of Total Nitrogen and Total Phosphorus Reduction Measures

With the problem of water pollution becoming increasingly serious, excessive discharge of nitrogen and phosphorus has become a key factor affecting water quality and ecological balance. In order to evaluate the effectiveness of different pollution reduction measures in total nitrogen and total phosphorus control, this study evaluates multiple best management practices (BMPs) using multiple comparison methods, in particular Tukey HSD testing. The results of the statistical analysis of the reduction effects of the different measures showed that all the treatment groups with measures were significantly better than the control group without measures. In particular, BMP 8, BMP 7 and BMP 6 showed the best reduction effects. This study not only provides a scientific basis for pollution control decisions, but also lays the foundation for follow-up research, highlighting the importance of multiple comparison methods in environmental science.

Filament Formation Mechanism for a Nanosecond Surface Barrier Discharge. Part 2. The Local-Energy Approximation

The development of a surface barrier discharge driven by a negative steplike voltage pulse with an amplitude of V = –8 kV in air at the atmospheric pressure and a pulse with an amplitude of V = –15 kV in nitrogen at a pressure of 6 atm is simulated numerically. Calculations for V = –8 kV were carried out using the local-electric-field and the local-electron-energy approximations. It is demonstrated that both approximations yield similar results on the dynamics of discharge development as a whole, the cathode-layer structure, and the field distribution at the front of the discharge. Substantial differences are observed in parameters of the discharge layer adjacent to the dielectric surface, which allowed to simulate an effect similar to filamentation of the discharge in nitrogen at a pressure of 6 atm and voltage of V = –15 kV in the local-energy approximation.

Dissolved organic nitrogen depresses the expected outcome of wastewater treatment upgrading on effluent eutrophication potential mitigation: Molecular mechanistic insight

Continuously tightening total nitrogen (TN) discharge standards in wastewater treatment plants is a common practice worldwide to mitigate eutrophication. However, given the different bioavailability of effluent dissolved organic nitrogen (DON) and inorganic nitrogen, a great inefficiency of the TN-targeted upgrading might be hidden because of the poor understanding of its impact on effluent eutrophication potential mitigation. Here we show that the tightening TN discharge standards could only considerably promote inorganic nitrogen removal, however, DON concentrations remained constant across different effluent TN levels (p > 0.05, Kruskal-Wallis test). Surprisingly, restricting TN in turn increases the reactivity of DON molecules owing to the accumulation of produced DON by acting on the key biotic and abiotic transformation reactions. The difficulty of removing DON and the increased DON reactivity during wastewater treatment upgrading contribute to the practical elimination effect of effluent eutrophication potential exhibiting lower than expected. This work challenges the rationality of the prevailing pursuit for extreme-low TN discharge, calling for shifting the focus of wastewater treatment upgrading towards the more fundamental eutrophication-targeted perspective.

Hysteresis in strongly magnetized N2 discharges

A semi-empirical global model for a nitrogen discharge in a strong magnetic field is developed. The model is based upon experimental data from high-resolution Doppler and extreme-ultraviolet vacuum spectroscopy, which establish the plasma composition, discharge parameters, and, most importantly, electronic transitions. This allows the number of required molecular systems and atomic/ionic states to be reduced, thereby retaining only the essential plasma chemistry reactions. The set of 35 stiff non-linear ordinary differential equations is numerically integrated using an unconditionally stable adaptive method. Simulations show the existence of two solution branches with low and high electron temperature, respectively. A distinct hysteresis is exhibited by the discharge and illustrated for three typical N2 mass flow rates. The dependencies of the plasma parameters on the applied power are presented and discussed in detail, including in the vicinity of the bifurcation points. The efficiency of operation in the opposing limits of N2 discharge behavior as either a source of plasma or light emission is examined, with special emphasis on electric propulsion capabilities.

Investigating the Effects of Gliding Arc Plasma Discharge’s Thermal Characteristic and Reactive Chemistry on Aqueous PFOS Mineralization

Per-and Polyfluoroalkyl substances (PFASs) are recalcitrant organofluorine contaminants, which demand urgent attention due to their bioaccumulation potential and associated health risks. While numerous current treatments technologies, including certain plasma-based treatments, can degrade PFASs, their complete destruction or mineralization is seldom achieved. Extensive aqueous PFAS mineralization capability coupled with industrial-level scaling potential makes gliding arc plasma (GAP) discharges an interesting and promising technology in PFAS mitigation. In this study, the effects of GAP discharge’s thermal and reactive properties on aqueous perfluorooctanesulfonic acid (PFOS) mineralization were investigated. Treatments were conducted with air and nitrogen GAP discharges at different plasma gas temperatures to investigate the effects of plasma thermal environment on PFOS mineralization; the results show that treatments with increased plasma gas temperatures lead to increased PFOS mineralization, and discharges in air were able to mineralize PFOS at relatively lower plasma gas temperatures compared to discharges in nitrogen. Studies were conducted to identify if GAP-based PFOS mineralization is a pure thermal process or if plasma reactive chemistry also affects PFOS mineralization. This was done by comparing the effects of thermal environments with and without plasma species (air discharge and air heated to plasma gas temperatures) on PFOS mineralization; the results show that while GAP discharge was able to mineralize PFOS, equivalent temperature air without plasma did not lead to PFOS mineralization. Finally, mineralization during treatments with GAP discharges in argon and air at similar gas temperatures were compared to investigate the role of plasma species in PFOS mineralization. The results demonstrate that treatments with argon (monoatomic gas with higher ionization) lead to increased PFOS mineralization compared to treatments with air (molecular gas with lower ionization), showing the participation of reactive species in PFOS mineralization.

(Invited) Mixing Elements in 2D Nanostructures Grown by Discharges in Liquids

The synthesis of nanosheets through discharges in liquid nitrogen is observed for certain metals when employed as electrodes [1,2]. Various metals have been examined, with bismuth, lead, or zinc showing a propensity to form nanosheets. Other metals, such as silver or indium, also exhibit sheet formation but with smaller aspect ratios (width/thickness). Mixing metals is not only interesting to create alloys with new properties but also to understand how discharges work to enable the synthesis of these objects.Recently, we demonstrated that these structures can be grown not only in liquid nitrogen but also in water. This is attributed to the discharge primarily originating from the metallic vapor emitted by the electrodes, a consistent process in both liquids, as confirmed by time-resolved optical emission spectroscopy.We showcased that a pre-treatment, involving chemical etching by a Nital solution, significantly enhances the efficiency of nanosheet production, increasing it from almost zero to nearly 100%. We successfully identified the growth mechanism of nanosheets in the case of bismuth electrodes. These structures grow on the cathode with ion assistance, collecting in the bubble formed during the discharge. Upon the collapse of the bubble, they transfer into the liquid phase. Interestingly, the number density of nanoparticles produced under these conditions is either null or too weak to be evaluated.It is feasible to incorporate two different elements into 2D nanostructures by utilizing two electrodes. We achieved a mixture of lead and bismuth oxide by using electrodes composed of the respective elements. This capability is likely associated with the similar melting points and miscibility of both elements. Nanosheets exhibit thicknesses around 5-10 nm for widths ranging in the tens of micrometers.We anticipate that a more comprehensive understanding of the synthesis of these alloys will pave the way for the production of alloyed nanosheets incorporating other elements.[1] A. Hamdan, H. Kabbara, C. Noël, J. Ghanbaja, A. Redjaimia, T. Belmonte, “Synthesis of two-dimensional lead sheets by spark discharge in liquid nitrogen”, Particuology 40 (2018) 152–159[2] H. Kabbara, J. Ghanbaja, C. Noël, T. Belmonte, “Nano-objects synthesized from Cu, Ag and Cu28Ag72 electrodes by submerged discharges in liquid nitrogen”, Materials Chemistry and Physics 217 (2018) 371–378

Nitrogen and Phosphorus Discharges from Cargo Ships’ Black and Grey Waters—A Case Study of a Baltic Sea Port

Shipping is a vital component of global trade. However, shipping activities have negative environmental impacts, including emissions to air and water. The Baltic Sea is severely affected by eutrophication, mainly due to nutrient inputs, especially nitrogen and phosphorus. Understanding the contributions of various nutrient sources is essential for informed environmental regulation. The aim of this research is to quantify the nutrient content of black and grey water discharged from cargo ships in the Baltic Sea in order to assess their contribution to the total nutrient load. Specifically, this research examines the nitrogen and phosphorus loadings from ships calling the port of HaminaKotka and addresses key questions regarding nutrient generation, discharge proportions, emission shares by ship type, and their importance compared to other sources. Using a methodology based on ship data and nutrient production estimates, this study found that 2545 cargo ships generated a total of 781 kg of nitrogen and 134 kg of phosphorus in their effluents during their voyages to the port in 2021. However, only a small fraction (0.5%) of the cargo ships discharged their wastewater at port reception facilities. This study concludes that nutrient discharges from cargo ships’ wastewaters are relatively small, contributing less than 0.06% phosphorus and 0.01% nitrogen to the total load in the area. This result indicates that the impact of cargo ships’ wastewater on the eutrophication of the Baltic Sea is smaller than previously thought. The methodology used in this study can be applied in other ports and regions to assess nutrient discharges from cargo ships’ wastewaters on a wider scale. Further research is recommended to assess the effectiveness of on-board treatment systems, the impact of other contaminants in wastewater, and the development of port reception facilities to facilitate proper wastewater management in the maritime trade.

Improvements in the InVEST water purification model for detecting spatio-temporal changesintotal nitrogen and total phosphorus discharges in the Huai river watershed, China

Improving water quality to provide freshwater is an urgent requirement for regional and even global social development. More accurate simulation of non-point sources pollution, monitored mainly by total nitrogen (TN) and total phosphorus (TP), has always been a challenge for InVEST water purification model, particularly in agricultural areas. This can be attributed to the fact that there is no reference data for TN and TP to rectify the outcomes modelled by this model. This paper provided these data to rectify simulation results of TN and TP to ensure their accuracy. The Huai River watershed (HRW) is an important grain production area with slow economic development, and non-point source pollution has exceeded point-source pollution. There is an urgent need for water management authorities to obtain complete spatio-temporal data on TN and TP loads and their exports to improve water quality. The reference data onloads and exports of TN and TP were estimated for the entire watershed and its sub-watersheds through an investigation-evaluation technique during 1980–2018. TN and TP loads generated from the agricultural sector were the major pollution sources in the HRW and had similar time trends during the same period. The spatial distribution of TN and TP exports was modelled byusingthe InVEST water purification model, and it was found that the temporal trends for the final exports of TN and TP into river systems were similar to those for TN and TP loads in the HRW for 1980–2018. Key driving factors were detected using the Geo-detector method to quantify the contribution rates of factors to the spatiotemporal exports of TN and TP. Our results showed that individual factors, such as precipitation and land use/cover, were the most important factors driving spatio-temporal variations in TN and TP exports in the HRW from 1980 to 2018. Meanwhile, the contribution rates of interactions between land use/cover and other factors were consistently highest in this watershed during the same period. In this study, we estimated the loads and exports of TN and TP, and modelled their spatial patterns in this watershed from 1980 to 2018, providing important information on TN and TP for water-related management authorities. We also provide a method for other river systems to calibrate the parameters in the biophysical table of InVEST water purification model based on final exports of TN and TP.

Selective Nitrate Synthesis by Plasma/Liquid Water Reaction: An Enhanced Oxidative Strength Mechanism in Nitrogen Discharge

Selective Nitrate Synthesis by Plasma/Liquid Water Reaction: An Enhanced Oxidative Strength Mechanism in Nitrogen Discharge

Optical emission characterization of an atmospheric pressure dielectric barrier discharge in nitrogen: Evolution of CN emissions during PTFE etching

AbstractThe present work investigates the etching of coated polytetrafluoroethylene (PTFE) films using an atmospheric pressure dielectric barrier discharge operating in nitrogen in a filamentary regime. For different treatment durations, the optical emission spectra were recorded over time. Most of the emissions are attributed to the N2 second positive system. The presence of CN is also observed, and its emissions rise with the exposure time of PTFE. This rise is attributed to the density of CN produced. The X‐ray photoelectron spectroscopy surface characterization suggests two etching regimes. This is linked with a change in slope in the intensity evolution of the optical emissions of the CN. At longer times, a fluorinated deposit on the electrode is observed, confirming a different nature of the etched material.

Jump and hysteresis of plasma density in the spatial afterglow of inductively coupled plasmas

In this work, jump and hysteresis of plasma density between low-density (LD) and high-density (HD) in the spatial afterglow of inductively coupled plasmas are experimentally studied for different gas discharges. A quartz plate with a micropore is used to independently control the pressures in the active plasma and spatial afterglow. The plasma density jump from LD to HD vs the pressure in the spatial afterglow only exists in a larger micropore diameter. By adjusting the pressure back and forth, a hysteresis loop in plasma density is formed. The light intensity and excitation rate vs the pressure corresponds well to the jump and hysteresis of plasma density. Therefore, the abrupt changes in ionization rate are responsible for the jump and hysteresis of plasma density. Compared with argon discharges, the critical pressure for the jump from LD to HD is higher in nitrogen discharges, forming a larger hysteresis loop. For hydrogen discharges, the jump from LD to HD is less significant and the hysteresis loop almost disappears. In argon–hydrogen mixed gas discharges, there is no hysteresis loop in plasma density. Experimental results obtained using Langmuir double probes and spectrometer achieve qualitative agreement in gas discharges mentioned above.

Role of charge exchange collision on generation of active species for cold plasma food processing

Charge exchange collision (CXC) is well known in solar and space plasmas. In this work, we present how the CXC between N2+ and N2 can be exploited to overcome major challenges in cold plasma food processing (CPFP). CPFP is an emerging application of glow discharge plasmas for physicochemical modifications to achieve shelf-life enhancement, preservation, surface activation for germination, antimicrobial treatment, surface cleaning, etc. The commercial application of CPFP is in its infancy and it faces two major challenges. The first challenge is the difficulty in generating the desired active species for the required modification, and the second is the very high processing cost. In this paper, with the help of numerical modeling for nitrogen discharge, we show that the CXC between N2+ and N2 can be utilized to generate active species selectively, enhance energy efficiency, and possibly eliminate the processing gas cost. The modeling is followed by experimental demonstration and validation of the proposed concept. This work may lead to a new direction of transdisciplinary research towards the commercial application of CPFP.

Role of charge exchange collision on generation of active species for cold plasma food processing

Charge exchange collision (CXC) is well known in solar and space plasmas. In this work, we present how the CXC between N2+ and N2 can be exploited to overcome major challenges in cold plasma food processing (CPFP). CPFP is an emerging application of glow discharge plasmas for physicochemical modifications to achieve shelf-life enhancement, preservation, surface activation for germination, antimicrobial treatment, surface cleaning, etc. The commercial application of CPFP is in its infancy and it faces two major challenges. The first challenge is the difficulty in generating the desired active species for the required modification, and the second is the very high processing cost. In this paper, with the help of numerical modeling for nitrogen discharge, we show that the CXC between N2+ and N2 can be utilized to generate active species selectively, enhance energy efficiency, and possibly eliminate the processing gas cost. The modeling is followed by experimental demonstration and validation of the proposed concept. This work may lead to a new direction of transdisciplinary research towards the commercial application of CPFP.

Full-Scale Demonstration of Nitrogen Removal from Mature Landfill Leachate Using a Two-Stage Partial Nitritation and Anammox Process

The excessive discharge of nitrogen leads to water eutrophication. The partial nitritation and anammox (PN/A) process is a promising technology for biological nitrogen removal in wastewater treatment. However, applying it to mature landfill leachate (MLL) faces challenges, as the toxic substances (e.g., heavy metal) within MLL inhibit the activity of anammox bacteria. Therefore, most previous studies focused on diluted, pretreated, or chemically adjusted MLL. This study demonstrated at full scale that the two-stage PN/A process can treat raw MLL. Initially, the operational issue of sludge floatation resulted in rapid biomass loss with overflow discharging, which selectively suppresses nitrite-oxidizing bacteria (NOB), promoting the achievement of nitrite accumulation. After that, the NOB suppression was self-sustained by the high in situ free ammonia concentration, i.e., 26.2 ± 15.9 mg N/L. In the subsequent anammox tank, nitrogen removal primarily occurred via the anammox process, complemented by denitrification, achieving total nitrogen removal efficiency exceeding 72%. In addition, the nitrogen removal capacity of this system was significantly influenced by temperature with the nitrogen-loading rate above 0.4 kg N/m3/d at 38 °C and approximately 0.1 kg N/m3/d at 21 °C. The optimization of system operation, such as gradually increasing MLL content, remains necessary to enhance nitrogen removal capacity further.

Optical characterization of nanosecond-pulsed discharge in liquid nitrogen

We report the optical characterization of nanosecond-pulsed plasma ignited directly in liquid nitrogen. Using imaging and optical emission spectroscopy, we estimate neutral temperatures and densities, as well as local electric field values, and the obtained results indicate that the discharge develops via streamer (‘electronic’) mechanism. We show that millimeter-scale plasma propagates in liquid nitrogen at velocities of ∼500 km s−1 with the corresponding required local electric fields as high as 25 MV cm−1, while the estimated local electric fields in the ‘core’ of the discharge are around 6–8 MV cm−1 (corresponding to reduced electric field values of 600–1000 Td). The neutral and electron densities in the ‘main body’ of the discharge were estimated using broadened argon lines, indicating that the neutral densities in the near-electrode region are around 1020 cm−3 (tens of atmospheres), while the maximum recorded temperature is just a few tens of degrees above the surrounding liquid. Electron densities were estimated to be ∼1017 cm−3, about two orders of magnitude lower than those measured for water discharge.

Post-treatment of high-rate activated sludge effluent via zeolite adsorption and recovery of ammonium-nitrogen as alternative fertilising products

This study investigates the potential to connect nutrient flows between wastewater treatment and agriculture through a two-stage nitrogen (N) recovery system composed of high-rate activated sludge treatment in contact stabilisation mode (HRAS/CS) and column adsorption with zeolite. The HRAS/CS process removes organic matter and suspended solids in wastewater, leaving N behind in the effluent. The N was successfully recovered with the zeolite column under different scenarios, generating N and K-rich by-products. The regeneration effluent from the zeolite column with KCl contained 60–845 mg NH4+-N/L and 1.6–14.3 g K/L, having potential for use as fertigation water. The N-saturated zeolite contained 1.5–8.4 mg N/g and 14.3–19.3 mg K/g of the product fresh weight and low contaminant content, making it potentially eligible as various fertilising products. Adsorption can thus concentrate N from HRAS/CS effluent and produce by-products with potential agricultural value while meeting chemical oxygen demand and total nitrogen discharge standards.

Replenishment of landscape water with reclaimed water: threshold of hydraulic retention time employing transparency as a control indicator

ABSTRACT There exists a significant risk of water blooms during the utilization of recycled water in landscape environments. The nitrogen and phosphorus discharge standards of sewage treatment plants are very low. Controlling hydraulic retention time (HRT) is currently the most effective means to control water bloom. This article proposes a new method for determining the HRT threshold based on water transparency as a control indicator. The following results were obtained: (1) with the nitrogen and phosphorus concentrations of 15 and 0.5 mg/L, respectively, the threshold for HRT under high temperature and strong light is 4.6 days, while the threshold under low temperature and low light is 11.5 days. (2) With the nitrogen and phosphorus concentrations of 10 and 0.3 mg/L, respectively, the threshold for HRT under high temperature and strong light is 5 days, while the threshold under low temperature and low light conditions is 12.3 days. (3) The HRT threshold obtained under high temperature and strong light is lower than that obtained under low temperature and low light conditions. (4) The higher the concentrations of nitrogen and phosphorus, the smaller the HRT threshold obtained. (5) Blue algae have stronger adaptability than green algae and diatoms.

The impact of elevated nutrients on the Holocene evolution of the Great Barrier Reef

The initiation of the Holocene Great Barrier Reef coincided with rapid environmental change as sea level rose and inundated the shelf. Core data from One Tree Reef (southern Great Barrier Reef) shows coral growth started by ∼8.2 ka, but accretion between 8 and 7 ka was slower, occurred in deeper water, and comprised more sediment-tolerant coral communities compared to growth following sea-level stabilization. It has been postulated that environmental stressors (e.g. increased turbidity and nutrients) suppressed and delayed reef growth, however direct data supporting this hypothesis are scarce. Here we combine the isotopic composition of skeletal bound organic nitrogen (δ15N) and Ba/Ca ratios of coral skeletons with published geochemical proxies of terrestrial sediment discharge to constrain Holocene water conditions at One Tree Reef. Between 8 and 7 ka the skeletal δ15N values from multiple corals and genera were elevated (average of 8.45 ± 0.89‰) relative to the early transgression and following sea-level stabilization (average of 7.04 ± 0.82‰). We propose that elevated δ15N in corals reflects the discharge of deep terrestrial soil nitrogen resulting from high runoff. This is supported by Ba/Ca measurements and published rare earth element and yttrium (REE + Y) geochemical proxies in coral and reefal microbialites from the same cores. These data suggest that increased terrigenous discharge of sediment and nutrients did not inhibit reef growth, rather led to the establishment of slower-growing, deeper and more sediment-tolerant coral communities. Understanding the capacity for reef growth under adverse environmental conditions provides insight into thresholds and resilience of the GBR over centennial-millennial timescales.

Power measurement analysis of moderate pressure capacitively coupled discharges

This study examines the transition of 13.56 MHz, capacitively coupled plasmas (CCP) from low to intermediate pressure regimes. Here, we investigate power deposition/plasma production in argon, nitrogen, and oxygen discharges as a function of pressure. These three feed gases were chosen as they provide a set of electropositive and electronegative gases and they are widely discussed in the existing literature. Experiments were conducted for all combinations of pressures: 0.5, 1.5, and 2.5 Torr, and nominal power density between 0.1 and 0.7 W/cm2 for each feed gas at a fixed electrode gap of 24 mm, a commonly employed gap in many industrial processes. Our study shows that increasing pressure results in an increase in current at a given electrode bias in argon and oxygen discharges, while there is no discernible pressure-induced change in nitrogen discharges. We attribute this increase to an increase in plasma density, which might result from a change in power deposition or ionization processes. It is likely that heating via secondary electrons becomes more important at intermediate pressures, resulting in increased plasma density and current. Specifically, based on our measurements, it appears that the mechanisms through which power is deposited into the plasma change with increasing pressure for both argon and oxygen discharges but not for nitrogen discharges. Our experimental results align with the outcomes of our simulations and the simulation results of CCP discharges conducted by other researchers under similar conditions.