Nitrogen Mass Balance Research Articles

Investigation of nitrogen conversion in ditch-treated greywater: Contributions of biochar and aeration

This study aimed to assess the contribution of different combinations of uninterrupted aeration and tidal flow modes, as well as shallow and deep biochar landfill methods, to nitrogen removal pathways in ditches. Compared to natural ditches, the addition of biochar and aeration resulted in higher water pollution removal rates, lower Greenhouse Gas (GHG) emissions, and reduced sediment leaching. The nitrogen mass balance revealed that Total Nitrogen removal efficiency of each ditch group was 25.33% for CA-C, 43.75% for DBT-C, 49.08% for UBT-C, 30.75% for DBA-C, and 45.16% for UBA-C. Compared to the control group (CA-C), the tidal flow group with deep biochar landfill (DBT-C)demonstrated the highest efficiency in total nitrogen removal. To elucidate the fate of nitrogen elements, potential transformation processes of unexplained nitrogen were explored. The primary outflow pathway of nitrogen pollution in ditches is through liquids. The nitrogen composition in the liquid of each ditch indicated that for shallow biochar configurations (UBT-C/UBA-C), denitrification might be the main factor limiting TN removal efficiency. In contrast, for deep biochar configurations (DBT-C/DBA-C), hydrolysis and nitrification of organic nitrogen were identified as limiting factors, with tidal flow alleviating these limitations. Overall, the combination of shallow biochar and tidal flow aeration in a ditch is the most effective method for removing rural greywater, providing valuable insights for the development of design parameters in greywater removal systems.

144 Assessing economic implications of thermal stress of Bos indicus and Bos taurus species during finishing in northern Colorado

Abstract The objective of this study was to determine the economic implications of thermal stress on climate adaptive capacity, resiliency, and impact of Bos indicus and Bos taurus finishing steers using common finishing systems. The experimental design was a completely randomized design, with a 2 by 2 factorial arrangement of finishing system (‘natural’ or ‘conventional’) and species of cattle (Bos indicus or Bos taurus). Steers [n = 200; body weight (BW) ~450 kg] were housed in 20 feedlot pens (10 steers/pen) for the first 84 d, where cattle were blocked by initial BW. For the remainder of the 180 d (96 d) finishing period, cattle were moved to four Climate Smart Research Pens (50 steers/pen, 1 pen/ treatment, and species combination). Within each Climate Smart Research Pen, five SmartFeed systems were used to evaluate individual animal feed intake, one GreenFeed emission measurement system was used to evaluate individual animal gas emissions flux of enteric CH4, O2, H2, and CO2, and were equipped for nutrient mass balance of carbon, nitrogen, and phosphorus. Animal BW were collected every 28 d for analysis of average daily gain (ADG) and feed efficiency. Thermal stress behaviors were evaluated by one trained personnel on a subset of 7 steers/treatment via the measurement of respiration rate, open mouth breathing, rumen temperature, number of daily water intake events, lying and standing behavior, and pen surface temperature for the last 96 d of the finishing period. At harvest, carcass characteristics, liver scores, and heart scores were collected. Economic analyses were conducted post-hoc to determine the profitability of each species based on economic implications, tradeoffs, carcass quality and quantity, and time to finish. Selection of cattle for climate adaptive features may involve production tradeoffs (e.g., depressed rate of gain, greater yield risk, lower technical efficiency) and adjustment costs (e.g., re-optimizing feed for a new breed), which affect the adoption of less common breeds into the US cattle supply chain. Adding to the complexity of this evaluation, consumers preferences may not adapt quickly, affecting the prospect of Bos indicus cuts of meat in the market. We also, therefore, explore the supply- and demand-side effects of climate change adaptation through breed selection in the beef industry.

Sludge degradation, nutrient removal and reduction of greenhouse gas emission by a Chironomus-Azolla wastewater treatment cascade.

Wastewater treatment plants (WWTPs) are a point source of nutrients, emit greenhouse gases (GHGs), and produce large volumes of excess sludge. The use of aquatic organisms may be an alternative to the technical post-treatment of WWTP effluent, as they play an important role in nutrient dynamics and carbon balance in natural ecosystems. The aim of this study was therefore to assess the performance of an experimental wastewater-treatment cascade of bioturbating macroinvertebrates and floating plants in terms of sludge degradation, nutrient removal and lowering GHG emission. To this end, a full-factorial experiment was designed, using a recirculating cascade with a WWTP sludge compartment with or without bioturbating Chironomus riparius larvae, and an effluent container with or without the floating plant Azolla filiculoides, resulting in four treatments. To calculate the nitrogen (N), phosphorus (P) and carbon (C) mass balance of this system, the N, P and C concentrations in the effluent, biomass production, and sludge degradation, as well as the N, P and C content of all compartments in the cascade were measured during the 26-day experiment. The presence of Chironomus led to an increased sludge degradation of 44% compared to 25% in the control, a 1.4 times decreased transport of P from the sludge and a 2.4 times increased transport of N out of the sludge, either into Chironomus biomass or into the water column. Furthermore, Chironomus activity decreased methane emissions by 92%. The presence of Azolla resulted in a 15% lower P concentration in the effluent than in the control treatment, and a CO2 uptake of 1.13 kg ha-1 day-1. These additive effects of Chironomus and Azolla resulted in an almost two times higher sludge degradation, and an almost two times lower P concentration in the effluent. This is the first study that shows that a bio-based cascade can strongly reduce GHG and P emissions simultaneously during the combined polishing of wastewater sludge and effluent, benefitting from the additive effects of the presence of both macrophytes and invertebrates. In addition to the microbial based treatment steps already employed on WWTPs, the integration of higher organisms in the treatment process expands the WWTP based ecosystem and allows for the inclusion of macroinvertebrate and macrophyte mediated processes. Applying macroinvertebrate-plant cascades may therefore be a promising tool to tackle the present and future challenges of WWTPs.

Nitrogen removal and carbon reduction of mature landfill leachate under extremely low dissolved oxygen conditions by simultaneous partial nitrification anammox and denitrification

In this study, a SNAD-SBBR process was implemented to achieve ammonia removal and carbon reduction of mature landfill leachate under extremely low dissolved oxygen conditions (0.051 mg/L) for a continuous operation of 266 days. The process demonstrated excellent removal performance, with ammonia nitrogen removal efficiency reaching 100 %, total nitrogen removal efficiency reaching 87.56 %, and an average removal rate of 0.180 kg/(m3·d). The recalcitrant organic compound removal efficiency reached 34.96 %. Nitrogen mass balance analysis revealed that the Anammox process contributed to approximately 98.1 % of the nitrogen removal. Candidatus Kuenenia achieved a relative abundance of 1.49 % in the inner layer of the carrier. In the SNAD-SBBR system, the extremely low DO environment created by the highly efficient partial nitrification stage enabled the coexistence of AnAOB, denitrifying bacteria, and Nitrosomonas, synergistically achieving ammonia removal and carbon reduction. Overall, the SNAD-SBBR process exhibits low-cost and high-efficiency characteristics, holding tremendous potential for landfill leachate treatment.

Nitrogen removal and nitrous oxide emission from moving bed biofilm reactor (MBBR) under different loads and airflow

Total nitrogen (TN) removal by sewage treatment required the development of nitrifying and denitrifying activities; however, these metabolite activities can produce and emit nitrous oxide (N2O), one of the greenhouse gases (GHG). With the expansion of sewage treatment in the world, compact systems such as moving bed biofilm reactor (MBBR) may be promising, mainly in more populated cities. However, little is known about N2O emission by the MBBR. This work investigated the N-NHx and TN removal, N2O production and emission and nitrogen mass balance in a MBBR under organic load and airflow variation. The highest TN removal (47%) was observed under higher load and higher aeration rate. Meanwhile, the MBBR under lower load and lower airflow had the lowest efficiency of TN and N-NHx removal probably due to a lower nitrifying activity. The N2O emission factors were lower than 1.6% (value estimated by the IPCC for sewage aerobic treatment systems). In addition, in the essay with higher load and lower airflow, half of removed TN was released by settled sludge and there is little research about this subject. Therefore, the MBBR showed to be a promising process for nitrogen removal with little emission of N2O even under different operational conditions that normally can occur in sanitary sewage system in cities around the world.

Cross-shore transport and eddies promote large scale response to urban eutrophication

A key control on the magnitude of coastal eutrophication is the degree to which currents quickly transport nitrogen derived from human sources away from the coast to the open ocean before eutrophication develops. In the Southern California Bight (SCB), an upwelling-dominated eastern boundary current ecosystem, anthropogenic nitrogen inputs increase algal productivity and cause subsurface acidification and oxygen (O2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{2}$$\\end{document}) loss along the coast. However, the extent of anthropogenic influence on eutrophication beyond the coastal band, and the physical transport mechanisms and biogeochemical processes responsible for these effects are still poorly understood. Here, we use a submesoscale-resolving numerical model to document the detailed biogeochemical mass balance of nitrogen, carbon and oxygen, their physical transport, and effects on offshore habitats. Despite management of terrestrial nutrients that has occurred in the region over the last 20 years, coastal eutrophication continues to persist. The input of anthropogenic nutrients promote an increase in productivity, remineralization and respiration offshore, with recurrent O2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{2}$$\\end{document} loss and pH decline in a region located 30–90 km from the mainland. During 2013 to 2017, the spatially averaged 5-year loss rate across the Bight was 1.3 mmol m-3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{-3}$$\\end{document} O2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{2}$$\\end{document}, with some locations losing on average up to 14.2 mmol m-3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{-3}$$\\end{document} O2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{2}$$\\end{document}. The magnitude of loss is greater than model uncertainty assessed from data-model comparisons and from quantification of intrinsic variability. This phenomenon persists for 4 to 6 months of the year over an area of 278,40 km2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{2}$$\\end{document} (∼\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim$$\\end{document}30% of SCB area). These recurrent features of acidification and oxygen loss are associated with cross-shore transport of nutrients by eddies and plankton biomass and their accumulation and retention within persistent eddies offshore within the SCB.

Ammonia emissions related to black soldier fly larvae during growth on different diets

Abstract Black soldier fly (Hermetia illucens) is considered a farmed animal. The larvae live in a moist substrate, which leads to a complex interaction with the microbial community. As such the combined metabolism of the insects and that of the microbial community can ultimately lead to all sorts of emissions such as ammonia and greenhouse gases. For ammonia emissions and associated depositions, it is known that this can lead to eutrophication of local ecosystems and the formation of particulate matter which can affect human health. This issue is known for intensive livestock farming where in some Western European countries this has led to specific regulations, for example limited number of livestock per farm, to control ammonia emissions. The production of black soldier fly larvae is a novel activity that could similarly lead to ammonia emissions. This study introduces a new method to quantify ammonia emissions in an industrial setting using an accumulation chamber and validates the findings with a nitrogen mass balance. Additionally, different feed substrates (Gainesville diet, chicken feed, artificial supermarket waste and brewers spent grains) were assessed with varying crude protein concentrations, hypothetically one of the driving factors affecting emissions. Results indicate significant ammonia emissions, the total emissions during larval growth ranged from 2.6 up to 83.6 g N/kg larvae (dry matter basis) and depend strongly on the diet. The rates at which these emissions are produced are negligible during the first three days. In the following days all diets emitted ammonia at a varying rate. The highest observed hourly emission rate for test substrates could be as low as 6.8 mg N/kg initial substrate (dry matter basis) and as high as 306 mg/kg. Different properties of the feed, such as the initial crude protein concentration, but also how the pH changes throughout larval growth, will affect emissions.

Towards an industrial perspective for urea-to-hydrogen valorization by electro-oxidation on nickel(III): Real effluents and pilot-scale proof of concept

This paper presents an investigation into urea-to-hydrogen valorization through electro-oxidation on nickel(III). The study has dual objectives: (i) to gain a better understanding of the effects of organic compounds (other than urea) in human urine on UEO and (ii) to upscale the process to pilot-scale. Initial voltammetric studies at lab-scale using real human urine showed that urea adsorption on nickel(III) sites, followed by its electro-oxidation, competes with molecules such as creatinine, histidine, and creatine. Notably, creatinine reduced the nickel(II) oxidation signal by up to 20 %, indicating its reaction precedence over urea. Additionally, the oxidation rate of urea by nickel(III) in urine exhibited a much lower partial order (0.1), as opposed to 0.3 in KOH solution, confirming the impact of competitive adsorption. Subsequently, UEO experiments were upscaled using a specially designed 1 L undivided tubular EC reactor operating in multi-pass mode. Potentiostatic electrolysis of a urea synthetic solution was conducted over 70 h, achieving nitrogen and carbon species mass balances of over 97 %—a milestone previously unreported at this scale. The study further examined the influence of operating parameters such as anode surface area, flow rate and applied potential on the EC process. This investigation underscored the impact of factor like reactor geometry, controlled potential and temperature on process efficiency. Parameters for optimal N2 production, highest urea conversion rate, etc., were also defined. Finally, the electrolysis of human urine at pilot-scale unveiled new challenges distinct from those encountered with urea synthetic solutions.

Closing Dichloramine Decomposition Nitrogen and Oxygen Mass Balances: Relative Importance of End-Products from the Reactive Nitrogen Species Pathway.

In drinking water chloramination, monochloramine autodecomposition occurs in the presence of excess free ammonia through dichloramine, the decay of which was implicated in N-nitrosodimethylamine (NDMA) formation by (i) dichloramine hydrolysis to nitroxyl which reacts with itself to nitrous oxide (N2O), (ii) nitroxyl reaction with dissolved oxygen (DO) to peroxynitrite or mono/dichloramine to nitrogen gas (N2), and (iii) peroxynitrite reaction with total dimethylamine (TOTDMA) to NDMA or decomposition to nitrite/nitrate. Here, the yields of nitrogen and oxygen-containing end-products were quantified at pH 9 from NHCl2 decomposition at 200, 400, or 800 μeq Cl2·L-1 with and without 10 μM-N TOTDMA under ambient DO (∼500 μM-O) and, to limit peroxynitrite formation, low DO (≤40 μM-O). Without TOTDMA, the sum of free ammonia, monochloramine, dichloramine, N2, N2O, nitrite, and nitrate indicated nitrogen recoveries ±95% confidence intervals were not significantly different under ambient (90 ± 6%) and low (93 ± 7%) DO. With TOTDMA, nitrogen recoveries were less under ambient (82 ± 5%) than low (97 ± 7%) DO. Oxygen recoveries under ambient DO were 88-97%, and the so-called unidentified product of dichloramine decomposition formed at about three-fold greater concentration under ambient compared to low DO, like NDMA, consistent with a DO limitation. Unidentified product formation stemmed from peroxynitrite decomposition products reacting with mono/dichloramine. For a 2:2:1 nitrogen/oxygen/chlorine atom ratio and its estimated molar absorptivity, unidentified product inclusion with uncertainty may close oxygen recoveries and increase nitrogen recoveries to 98% (ambient DO) and 100% (low DO).

Enhanced denitrification performance in iron-carbon wetlands through biomass addition: Impact on nitrate and ammonia transformation

This study investigated the influence of biomass addition on the denitrification performance of iron-carbon wetlands. During long-time operation, the effluent NO3−-N concentration of CW-BFe was observed to be the lowest, registering at 0.418 ± 0.167 mg/L, outperforming that of CW-Fe, which recorded 1.467 ± 0.467 mg/L. However, the effluent NH4+-N for CW-BFe increased to 1.465 ± 0.121 mg/L, surpassing CW-Fe's 0.889 ± 0.224 mg/L. Within a typical cycle, when establishing first-order reaction kinetics based on NO3−-N concentrations, the introduction of biomass was found to amplify the kinetic constants across various stages in the iron-carbon wetland, ranging between 2.4 and 5.4 times that of CW-Fe. A metagenomic analysis indicated that biomass augments the reduction of NO3−-N and NO2−-N nitrogen and significantly bolsters the dissimilation nitrate reduction to ammonia pathway. Conversely, it impedes the reduction of N2O, leading to a heightened proportion of 2.715 % in CW-BFe's nitrogen mass balance, a stark contrast to CW-Fe's 0.379 %.

Quantification of liquid nitrogen injection efficiency and phase change expansion boost laws in coal seam borehole

The implementation of liquid nitrogen injection into coal seam boreholes is a prerequisite for its application to increase coal seam permeation. Exploring the efficiency of liquid nitrogen injection is of great significance in optimizing the settings of key injection parameters, thereby reducing costs. By using high-pressure liquid nitrogen tank, flowmeter, endoscope, thermocouple and mass balance, experiments of different liquid nitrogen injection rates were carried out in 1 m long coal seam borehole. The rules for changing the liquid nitrogen net level in the borehole at different injection rates were obtained: slow growth-linearly growth-slowly growth to stability, and the maximum net liquid level could reach 60 cm. The effective convection coefficient and radiation coefficient during the transient film boiling at the early stages of liquid nitrogen injection were calculated, and it was found that convective heat transfer dominated this stage. The liquid nitrogen injection efficiency at different injection rates was quantitatively investigated, and the maximum efficiency was 8.75 %, and the injection efficiency increases with the increase of injection rate. After stopping the injection, the net liquid nitrogen level in the borehole was analyzed, and they all decreased exponentially. A liquid nitrogen phase change expansion boost model was established and experimental verification passed. Further, it was calculated that the maximum value of liquid nitrogen phase change expansion pressure in a closed borehole of 1 m long coal seam was 45.8 MPa. The expansion pressure can play a dominant role in fracture propagation during the fracturing process, and combined with the damaging effects of liquid nitrogen cold shock on coal, it has a great development prospect in the field of coal seam permeability enhancement.

Sustainable in situ ammonia recovery from municipal solid waste leachate in a single-stream microbial desalination cell

Municipal solid waste (MSW) leachate is one of the most hazardous waste streams leading to great potential risk to environment, and a renewable resource with high concentrations of organic contaminant and ammonia. High energy consumption and chemical input are still the challenges for ammonia recovery from MSW leachate. Here, a single-stream microbial desalination cell (SMDC) was successfully developed for simultaneous energy extraction from organic contaminant and in-situ energy utilization for ammonia recovery. 70% of the organic contaminant from the actual MSW leachate was removed, and 24.9% of the total ammonia was recovered as high-purity (NH4)2SO4. The additional desalination chamber introduced into the SMDC can potentially enhance the NH4+ migration that was determined by the NH4+ concentration gradient and electric field. More than 30% of the total nitrogen was lost, as revealed by nitrogen mass balance analysis, probably resulting from the anodic denitrification process driven by denitrifying microorganisms, e.g., Thauera, which thrived in the anode chamber. Concomitantly, the chemical input for ammonia stripping can be reduced by up to 68% due to the relatively low buffer capacity of the catholyte and the OH− production from the cathode reaction. This SMDC can be an effective and environmentally sustainable solution for MSW leachate treatment and resource recovery.

Electrocatalytic Nitrate Reduction to Ammonia at Atomically Dispersed Titanium Sites on Carbon Nanoflowers

Active nitrogen species are widely acknowledged as pollutants that are both harmful to the environment as well as human health. Emissions from wastewater and agricultural applications contain nitrogen in many forms, but in soils and waterways nitrate (NO3 -) predominates due to the presence of nitrifying bacteria. In comparison to more reduced forms of nitrogen such as total ammonia (NH3/NH4 +), nitrate is not only a less versatile species from a chemical manufacturing and energy standpoint; it is also more difficult to selectively separate from wastewater streams. For instance, we have conducted considerable work on electrochemical ammonia stripping, achieving high selectivities and even enabling concentration of ammonia in the form of strong ammonium salt solutions.1 Moreover, it is estimated that recovery of active nitrogen species from municipal and agricultural wastewaters could offset the need for ~30% of Haber-Bosch ammonia synthesis. From this perspective, it is desirable to develop catalysts that are active and selective for the conversion of nitrate to ammonia. Titanium metal has been demonstrated as a relatively active and selective catalyst for nitrate reduction to ammonia in acid;2 however, similarly active and selective catalysts under neutral-to-alkaline conditions are a subject of active research.3–6 Here we report on the performance of atomically dispersed titanium sites on carbon nanoflowers7 for the reduction of nitrate to ammonia under alkaline conditions. The dispersity of these catalysts was supported by XAS (little/negligible Ti-Ti scattering, putative Ti-N and Ti-N-C scattering), STEM (visual confirmation of atoms), and XRD (no crystalline Ti phases observed). We contrast the performance of these atomically dispersed catalysts with that of bulk titanium foil, which shows comparably low activity and selectivity for nitrate reduction at similar pHs and potentials. In addition, we compare the atomically dispersed titanium catalysts with titanium nanoparticles, as a first-order check for catalyst aggregation under reductive reaction conditions. Moreover, the performances of all of these catalysts are compared with the baseline/controls of bare carbon paper, as well as carbon nanoflowers supported on carbon paper without titanium dopant. Additional control experiments include tests conducted in the absence of nitrate. These lines of evidence, together with the relatively high rate of ammonia production (>0.01 mmol / cmgeo 2 / h, >10 mmol / mg Ti / h), support the notion that atomically dispersed titanium is uniquely active and selective for NO3RR under alkaline conditions.Further, for the above catalysts at pH ~13, we show the impacts of potential on the product distribution, including nitrogen mass balance and Faradaic efficiency. As a best practice, we demonstrate consistent closure of both metrics. Potential was varied between -0.4 V and -0.85 V vs. RHE. Partial current toward NO3RR increases with increasing overpotential, as another sanity check supporting the findings. Notably, in addition to observing ammonia and nitrite as products of NO3RR, we also checked for other stable intermediates (in addition to N2) along the 8-electron reaction pathway – and as a result, we are able to report small amounts (FE ~5-10%) of hydroxylamine (NH2OH) product.In the specific case of atomically dispersed titanium on carbon nanoflowers, we also report on certain observed electrolyte effects, such as the incorporation of perchlorate vs. sulfate as a supporting electrolyte. We demonstrate the role of supporting salt both in modifying selectivity – e.g. sulfate suppressing HER, possibly via site-blocking – as well as in altering the carbon support itself. These observations contribute to a growing body of work that will enable the engineering of these catalysts for high-rate reduction of nitrate to ammonia, aiding both wastewater remediation and the decarbonization of ammonia synthesis.

Nitrogen mass balance and uptake velocity for eutrophic reservoirs in the Brazilian semiarid region.

The nitrogen (N) cycle from the catchment to the downstream reservoir is complex, particularly the quantification of N losses. However, in order to assess the nitrogen impact in a reservoir ecosystem, simplified models may be applicable regarding the TN load production and the magnitude of lake TN removal. This study presented a methodology to perform and validate a TN mass balance to further calibrate a simplified coefficient for TN losses (vf.) in 29 tropical semiarid reservoirs. The study reservoirs were highly productive ecosystems with an average total nitrogen (TN) concentration, accounting for all measurements in all reservoirs, ranging from 0.59 to 3.84 mg L-1. Regarding the production of TN load, the median values ranged from 4.35 to 2,499.43 t year-1 with median of 80.34 t year-1. The TN loads were estimated through an annual mass balance over a 24-year period. The median of the estimates was compared with reference values obtained by using the export modelling coefficient. The correlation between the median estimated and reference loads resulted in satisfactory agreement (r2 0.88) and reinforced the reliability of the mass balance alternative. From the validated TN loads, the TN uptake velocity (vf) was estimated for all reservoirs (44.9 ± 20.1 m year-1) and could be described as a general function of the water residence time. The reservoirs of the study region have demonstrated higher vf than temperate lakes and reservoirs and similar vf with Latin America/Caribbean ones. As expected, reservoirs of warmer climates tend to present intensified N loss processes compared to lakes and reservoirs of temperate regions. The methodology proposed in the present study can be used to potentially improve water quality management in tropical semiarid reservoirs.

Performance, community dynamics and network of an aerobic denitrifying consortium from a coastal mariculture area

Use of aerobic denitrifying consortia, as a new efficient tool for nitrogen removal, has attracted widespread attention because of their stable and efficient nitrogen removal ability. Yet, little attention has been given to highly efficient aerobic denitrifying consortia from mariculture environments. In this study, a natural aerobic denitrifying consortium, named C3, was obtained by an enrichment technique from a coastal mariculture area of Dongshan Bay of Fujian Province, China. In culture, it exhibited good and stable nitrate removing performance. Nitrogen mass balance indicated that 49.30% of the initial TN was converted into gaseous nitrogen and 49.63% was assimilated to biomass nitrogen. High-throughput sequencing and network analysis revealed that Pseudomonas and Fusarium were putative dominant aerobic denitrifying bacterial and fungal species, respectively, cooperating with Exophiala, Penicillium, Mortierella, Neocamarosporium, Neocosmospora, Sterigmatomyces, Thelebolus, Thermomyces, Cutaneotrichosporon and Gymnopilus to perform aerobic denitrification. In addition, four Pseudomonas strains have been successfully isolated from consortium C3, which supported the inference that Pseudomonas was the dominant contributor in the aerobic denitrifying consortium C3. These results will offer novel insights into aerobic denitrifying consortia in mariculture environments for biotechnological nitrogen pollution removal.

Visualization of Productivity Zones Based on Nitrogen Mass Balance Model in Narragansett Bay, Rhode Island.

Primary productivity in the coastal regions, linked to eutrophication and hypoxia, provides a critical understanding of ecosystem function. Although primary productivity largely depends on riverine nutrient inputs, estimation of the extent of riverine nutrient influences in the coastal regions is challenging. A nitrogen mass balance model is a practical tool to evaluate coastal ocean productivity to understand biological mechanisms beyond data observations. This study visualizes the biological production zones in Narragansett Bay, Rhode Island, USA, where hypoxia frequently occurs, by applying a nitrogen mass balance model. The Bay is divided into three zones - brown, green, and blue zones - based on primary productivity, which are defined by the mass balance model results. Brown, green, and blue zones represent a high physical process, a high biological process, and a low biological process zone, depending on river flow, nutrient concentrations, and mixing rates. The results of this study can better inform nutrient management in the coastal ocean in response to hypoxia and eutrophication.

Phenol and nitrogen removal in microalgal–bacterial granular sequential batch reactors

AbstractBACKGROUNDMicroalgal–bacterial systems work on the principle of the symbiotic relationship between algae and bacteria. The ability of algal–bacterial photobioreactors for the treatment of wastewater containing ammonia and phenol has been poorly addressed. In this work a self‐sustaining synergetic microalgal–bacterial granular sludge process was thus developed to treatment of industrial wastewater based upon the low cost of photosynthetic oxygenation and the simultaneous phenol and nitrogen removal. The performance of a conventional sequential batch reactor (SBR) based on aerobic bacterial communities (SBRB) and a microalgal–bacterial granular SBR (SBRMB) were comparatively assessed. The major challenges associated with microalgal–bacterial systems were discussed.RESULTSA complete removal of phenol (100 mg L−1) was achieved in both reactors. The reactors SBRB and SBRMB showed similar performance in term of removal of inorganic nitrogen. Nitrogen mass balances estimated nitrogen assimilation, nitrification and denitrification. Higher simultaneous nitrification and denitrification (70% SND) occurred in SBRB as determined by mass balances. The higher nitrogen assimilation (17.9%) by the microalgal–bacterial biomass compensated the lower denitrifying activity in SBRMB (54% SND), resulting in a removal of inorganic nitrogen (61%) similar to that obtained in SBRB (66%). N2O was not detected in the headspace of any system.CONCLUSIONGranular microalgal–bacterial consortia implemented in SBR constitute an efficient method for industrial wastewater treatment achieving complete removal of ammonia and phenol. The application of SBRMB would be more cost effective than SBRB mainly due to the significant energy savings in SBRMB resulting in a sustainable system that contributes to the circular bioeconomy. © 2023 The Authors. Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).

The effect of calcium hydroxide addition on enhancing ammonia recovery during thermophilic composting in a self-heated pilot-scale reactor

A modified outdoor large-scale nutrient recycling system was developed to compost organic sludge and aimed to recover clean nitrogen for the cultivation of high-value-added microalgae. This study investigated the effect of calcium hydroxide addition on enhancing NH3 recovery in a pilot-scale reactor self-heated by metabolic heat of microorganisms during thermophilic composting of dewatered cow dung. 350 kg-ww of compost was prepared at the ratio of 5: 14: 1 (dewatered cowdung: rice husk: compost-seed) in a 4 m3 cylindrical rotary drum composting reactor for 14 days of aerated composting. High compost temperature up to 67 °C was observed from day 1 of composting, proving that thermophilic composting was achieved through the self-heating process. The temperature of compost increases as microbial activity increases and temperature decreases as organic matter decreases. The high CO2 evolution rate on day 0–2 (0.02–0.08 mol/min) indicated that microorganisms are most active in degrading organic matter. The increasing conversion of carbon demonstrated that organic carbon was degraded by microbial activity and emitted as CO2. The nitrogen mass balance revealed that adding calcium hydroxide to the compost and increasing the aeration rate on day 3 volatilized 9.83 % of the remaining ammonium ions in the compost, thereby improving the ammonia recovery. Moreover, Geobacillus was found to be the most dominant bacteria under elevated temperature that functions in the hydrolysis of non-dissolved nitrogen for better NH3 recovery. The presented results show that by thermophilic composting 1 ton-ds of dewatered cowdung for NH3 recovery, up to 11.54 kg-ds of microalgae can be produced.

Integrating a manganese ores-filled module with a submerged plants cathode sediment fuel cell: In-situ remediation of ammonium pollution in surface water

Ammonium removal from contaminated surface water depends highly on electron acceptors like dissolved oxygen (DO), which was limited in eutrophic water bodies. In this study, a small ecological module was constructed with manganese ores (MO) and used to remove ammonium for the overlying water by integrating sediment microbial fuel cells (SMFC) and submerged plants. Nine different microcosms were operated to assess the pollutants removal performances. Compared with the 44.1 % of the control, ammonium removal of microcosms with MO addition increased to 79.1 %. Moreover, ammonium removal of the SMFC coupling system and submerged plant SMFC coupling system reached 83.3 % and 97.1 %, respectively. Besides, under the two coupling modes mentioned above, the degradation of chemical oxygen demand (COD) and the total organic carbon (TOC) was enhanced. The maximum power density was 390.63 mW/m3. The mass balance of nitrogen indicated the introduction of SMFC increased the contribution of denitrification to nitrogen removal. By contrast, plants promoted the release of oxygen and regulated community structure for intensifying simultaneous nitrification and denitrification (SND). Additionally, the effects of storage by substrates and sediments and plant uptake were also important. Heterotrophic and autotrophic denitrifying bacteria were enriched on the substrates around electrodes. Besides, electrochemically active bacteria (EAB) and Mn cycle related bacteria triggering the enhancement of nitrogen conversion. The Mn cycle in different valence states, electron transport between electrodes and substrates, and oxygen-producing submerged plants conspired to help excellent contaminant removal performance. This study promises a new thought for remediation of surface water and sediments in situ.

Relationship between denitrification and anammox rates and N2 production with substrate consumption and pH in a riparian zone

ABSTRACT Denitrification and anaerobic ammonium oxidation (anammox) are the key processes to quantitatively remove nitrate (NO3 −) and balance the nitrogen (N) budget of the ecosystem. In this paper, a slurry-based 15N tracer approach was used to study the correlation and quantitative relation of substrate consumption and pH with rates of denitrification and anammox in a riparian zone. The results showed that the fastest rates of 0.93 µg N h−1 and 0.32 µg N h−1 for denitrification (Denitrif-N2) and anammox (Denitrif-N2), respectively. N2 produced by denitrification occupied 74.04% and produced by anammox occupied 25.96% of the total N2, proving denitrification is the dominant process to remove NO3 −. The substrate content (NO3 −, NH4 + and TOC) and pH varied during incubation and were significantly correlated with Dentrif-N2 and Anammox-N2. Nitrate and TOC as the substrates of denitrification demonstrated a significant correlation with Anammox-N2, which was associated with the products of denitrification involved in the anammox process. This proved a coupling of denitrification and anammox. A quantitative relationship was observed between Dentrif-N2 and Anammox-N2 in the range of 2.75–2.90 when TOC, NH4 + and NO3 − consumption per unit mass or pH changed per unit. Nitrogen mass balance analysis showed that 1 mg N substrate (NO3 −+NH4 +) consumption in the denitrification and anammox can produce 1.05 mg N2 with a good linear relationship (r 2 = 0.9334). This could be related to other processes that produced extra N2 in denitrification and anammox system.