High Nitrogen Loading Research Articles

Nitrogen removal and metabolic pathways of nitrifying coal ash propelled by temperature change under high nitrogen loading

Coal ash, owing to its cost-effectiveness and greater adhesion with nitrifiers, has been used as a carrier for immobilizing nitrifiers when treating wastewater with a low C/N ratio and high nitrogen loading. Various environmental conditions significantly affect the nitrogen metabolic pathways of nitrifying coal ash. In this study, the nitrogen metabolic pathways of nitrifying coal ash propelled at different temperatures were investigated to evaluate the impact of seasonal variation on nitrifying coal ash. Results showed average NH<sub>4</sub><sup>+</sup>-N effluent concentrations increased with temperature, and reached 3.37, 5.16, and 76.06 mg N/L with 1158 mg N/L influent under 15 ℃, 25 ℃, and 35 ℃ systems. The total nitrogen removal rate at a cooling temperature of 15 ℃ was higher than that at 25 ℃ and 35 ℃. Further analysis showed <i>Nitrosomonas</i> and <i>Nitrobacter</i> were enhanced, whereas a significant evolution of autotrophic denitrifiers, <i>Acidovorax</i>, was enriched at 15 ℃. An in-depth investigation of N-metabolism pathways suggested higher temperatures of 25 ℃ and 35 ℃ reduced the abundance of key genes involved in ammonia oxidation (amoABC, <i>hao</i>) and nitrite oxidation (<i>nar</i>GH). Network analysis between N-metabolic functional genes and genera presented stronger relevance and richer sources between nitrifiers/denitrifiers and nitrification/denitrification-associated genes under cooler temperatures.

Artificial aeration of an overloaded constructed wetland improves hypoxia but does not ameliorate high nitrogen loads

High organic loadings to constructed wetlands can result in water quality issues such as low dissolved oxygen and high ammonium concentrations, with artificial aeration a potential mitigation option. This study compared baseline (no aeration – NA), continuous aeration (CA), and intermittent aeration (IA) conditions to improve water quality in a tertiary treatment free water surface constructed wetland (FWS CW) with night time hypoxia/anoxia, and high nutrient concentrations. The response variables included dissolved oxygen (DO), total nitrogen (TN), ammonium nitrogen (NH4+-N), nitrate nitrogen (NO3−-N), total phosphorus (TP), phosphate (PO43–-P), and dissolved organic carbon (DOC). In situ aeration and monitoring was performed from April to June 2021 in a large, field-scale FWS CW, the Laratinga wetlands Mount Barker, South Australia.The results demonstrated that DO increased by an average 2.11 mg L−1 from NA to CA during the night and 1.26 mg L−1 and 1.84 mg L−1 from NA to IA during the night and day respectively when averaging over the basins. The C/N ratio was very low and there was no significant influence of DO on DOC concentrations. There was no significant difference in TN concentrations with the application of aeration aside from a decrease in the channel at night from NA to IA, and an increase in NH4+-N resulted under IA compared with NA in Basin 1 and 2 during the day. This implies that the N loadings exceeded the wetland's ability to complete nutrient conversions at a rate that aligns with input rate. The concentrations of NO3−-N increased at night under CA and IA treatments suggesting that some nitrification was promoted, or there was inhibition of dissimilatory nitrate reduction to ammonium. The concentrations of TP and PO43–-P significantly increased with the aeration compared with no aeration, however there was no difference between the aeration treatments. This suggested that increased sediment resuspension during aeration increased P in the water. There was no change in DOC with the application of aeration. Overall, the DO increased with aeration application and may be able to better support the wetland ecology; however, the Laratinga wetland is overloaded and the capacity of the wetland to effectively transform and remove nutrients is inhibited, even with the application of artificial aeration.

Bioaugmentation reconstructed nitrogen metabolism in full-scale simultaneous partial nitrification-denitrification, anammox and sulfur-dependent nitrite/nitrate reduction (SPAS)

To enhance nitrogen removal of fermentation pharmaceutical wastewater with high nitrogen load, a full-scale process based on simultaneous partial nitrification-denitrification/ anammox/ sulfur autotrophic denitrification (SPAS) was established via inoculating with bioaugmentation consortia in a modified two-stage AO. More than 93 % TN and 98 % NH4+-N removal were obtained at a rate of 0.8 kg-N/ m3/d in the first A/O stage, in which short-cut SND was involved with 96.05 % ESND when bioaugmented with SND, while S0-SAD could coordinate with anammox to exert further deep denitrification in the second A/O stage. KEGG analysis demonstrated that the SPAS process was synergism of HD, PN/PDN, SND, SAD and anammox metabolism, bioaugmentation could significantly up-regulate genes related to microbial metabolism (TCA cycle, Carbon metabolism, ABC transporters) and environmental adaptation (Two-component system, Quorum sensing) based on the FAPROTAX and Picrust2 functional prediction. This study provided a new perspective in engineering applications.

Anammox in a biofilter reactor to treat wastewater of high strength nitrogen

An anammox biofilter reactor (A-BFR) under high total nitrogen (TN) concentration and high nitrogen loading rate (NLR) was operated for 283 days and the biomass characteristics were investigated at the end of the experiment to discuss the origin of strong impact resistance of A-BFR. The result showed TN removal rate of A-BFR reached 81.76 % averagely under the influent concentration of 525 mg/L and the NLR of 6.30 kg N/m3/d. Furthermore, A-BFR was partitioned as the core zone and the polish zone spontaneously according to the water quality along the height of reactor due to the characteristics of plug flow. Although the core zone bore an actual NLR of 17.71 kg N/m3/d, and an average free ammonia (FA) concentrations of 13.35 mg/L as well as a mean free nitrous acid (FNA) concentrations of 36.89 μg/L, it still obtained the TN removal of >80 %, which could be attributed to the high biomass of 30.67 gVSS/L comprised of biofilm and granular sludge aggregates, the high specific anammox activity up to 49.24 mg N/g VSS/d, and high extracellular polymeric substances of 148.69 mg/gVSS. In addition, the enrichment of anammox bacteria in the core zone attained over 50 %, and the dominant bacteria were unclassified_Candidatus_Brocadiaceae and Candidatus Kuenenia after the operation of 283 days. These findings revealed the unique characteristics of biomass in the core zone decided the robust capacity of A-BFR to resist high NLR and the inhibition of FA and FNA from high TN concentration, which would enrich the knowledge and understanding of anammox with plug flow reactor under higher FA and FNA concentrations, implying BFR was a robust and resilient reactor for anammox.

Enhanced nitrogen and carbon removal in natural seawater by electrochemical enrichment in a bioelectrochemical reactor

Municipal and industrial wastewater discharges in coastal and marine environments are of major concern due to their high carbon and nitrogen loads and the resulted phenomenon of eutrophication. Bioelectrochemical reactors (BERs) for simultaneous nitrogen and carbon removal have gained attention owing to their cost efficiency and versatility, as well as the possibility of electrochemical enrich specific groups. This study presented a scalable two-chamber BERs using graphite granules as electrode material. BERs were inoculated and operated for 37 days using natural seawater with high concentrations of ammonium and acetate. The BERs demonstrated a maximum current density of 0.9 A m−3 and removal rates of 7.5 mg NH4+-N L−1 d−1 and 99.5 mg L−1 d−1 for total organic carbon (TOC). Removals observed for NH4+-N and TOC were 96.2% and 68.7%, respectively. The results of nutrient removal (i.e., ammonium, nitrate, nitrite and TOC) and microbial characterization (i.e., next-generation sequencing of the 16S rRNA gene and fluorescence in situ hybridization) showed that BERs operated with a poised cathode at −260 mV (vs. Ag/AgCl) significantly enriched nitrifying microorganisms in the anode and denitrifying microorganisms and planctomycetes in the cathode. Interestingly, the electrochemical enrichment did not increase the total number of microorganisms in the formed biofilms but controlled their composition. Thus, this work shows the first successful attempt to electrochemically enrich marine nitrifying and denitrifying microorganisms and presents a technique to accelerate the start-up process of BERs to remove dissolved inorganic nitrogen and total organic carbon from seawater.

Start-up characteristics and microbial nitrogen removal mechanisms in ANAMMOX systems with different inoculations under prolonged starvation

The characteristics of lab-scale ANAMMOX system for efficient nitrogen removal were tested by different inoculations (anaerobic granular sludge (AGS) + anammox sludge (AMS), R1; AGS alone, R2) in continuous flow reactors following start-up under starvation. TN removal rates were above 90 % in both reactors. Microbial community analysis showed that the nitrogen removal was the combined results of anammox and partial denitrification (PD), Higher microbial growth rate triggered by quorum-sensing (QS) caused R1 to secrete more extracellular polymeric substances (EPS) and promoted the growth of its particle size. However, the overproduction of EPS destroyed the particle structure with time, and led to a deterioration of operational stability in R1. R2 showed better nitrogen removal stability to high nitrogen loading rate (NLR). This was due to higher endogenous organics within R2, which inhibited cell aggregation and EPS overproduction. But undeniably, R1 had higher specific anammox activity (SAA) with higher anammox bacteria (AAOB) abundance (The abundance of Planctomycetota in R1 and R2 were 21.2 %, 7.71 %). The results suggest that the operational stability was influenced by a combination of particle properties and microbial metabolism, and that the inoculation of AGS is more conducive to efficient and economic nitrogen removal in wastewater treatment under starvation.

Rapid proliferation of anaerobic ammonium oxidizing bacteria using anammox-hydroxyapatite technology in a pilot-scale expanded granular sludge bed reactor

The practical application of anaerobic ammonium oxidation (anammox) technology was seriously limited by lack of anammox seeding sludge. In this work, a pilot-scale expanded granular sludge bed (EGSB) reactor was used for rapid proliferation of anaerobic ammonium oxidizing bacteria (AnAOB) using anammox-hydroxyapatite (anammox-HAP) technology. The excellent settleability of anammox-HAP granular sludge (with an excellent settling velocity of 395 m/h) supported the up-flow velocity of 9.6 m/h with recirculation ratio of 19. A high nitrogen loading rate (NLR) of 26.4 g N/L/d was achieved in the pilot-scale reactor, with a cell yield of 0.23 g VSS/g NH4+-N. The high recirculation ratio and up-flow velocity brought about the efficient mass transfer for anammox, eliminating free ammonia inhibition, resulting in the high NLR and cell yield. Results of microbial community revealed that the relative abundance of unclassified Brocadiaceae increased from 18.55% to 82.80%, illustrating the rapid proliferation of AnAOB.

The nitrogen budget of an urban watershed: Zeekoevlei, Cape Town

Urban watersheds receive excessively high Nitrogen (N) loads predominantly via N deposition, fertilizer use, stormwater runoff, treated effluent discharge and sewage leaks. Beyond engineered solutions, the capacity of these systems to remove this excess N is largely dependent upon the functioning of riparian and wetland ecosystems, which in urban areas are highly modified, fragmented and increasingly under pressure. Appropriate management of urban watersheds needs to consider N flux and process rates that occur within the urban landscape. This research provides a preliminary quantification of the relative magnitudes of N flux in the context of a small urban watershed comprising key features of cities in the Global South: a mosaic of informal and formal residential, peri-urban agriculture and stressed service delivery. For a watershed system of 88 km2, total N inputs amount to 2.82 Gg N yr−1, 78 % of which is in the form of household food. N outputs amount to 2.35 Gg N yr−1 with 86 % of that coming out of wastewater streams either as treated effluent or during the denitrification process. An estimated 0.17 Gg N yr−1 accumulates in the system as plant biomass, in groundwater, soils and landfill. The Zeekoevlei wetland system is hypothesised to remove 76 % of total N which drains off the urban landscape, indicating an important service provided to the City, in addition to other well documented ecosystem services. In this urban system, our estimates indicate N flux rates almost 3 times higher than what would be here naturally in a nutrient-deplete Fynbos system. This work daylights important monitoring and research needs in order to better understand the role of the urban landscape and wetland ecosystems in a highly human-mediated N cycle.

Insights into rapidly recovering the autotrophic nitrogen removal performance of single-stage partial nitritation-anammox systems: Reconstructing granular sludge and its functional microbes synergy

Partial nitritation-anammox (PNA) deteriorates easily and is difficult to recover. After an airlift inner-circulation partition bioreactor was impacted by low NH4+–N wastewater containing organic matter, Nitrospira and Denitratisoma propagated rapidly, granular sludge disintegrated, and the total nitrogen removal efficiency (TNRE) decreased from 68.27 % to 5.97 %. This study used a unique strategy to recover deteriorated single-stage PNA systems and explored the mechanism of rapid performance recovery. The TNRE of the system recovered up to 61.77 % in 43 days. The high nitrogen loading rate and hydraulic shear force from the airlift caused the sludge in the reactor to granulate again. The microbial community structure recovered, with a decrease in the abundance of Nitrospira (0.05 %) and enrichment of Candidatus Brocadia (8.82 %). A favorable synergy among functional microbes in the reactor was thus re-established, promoting the rapid recovery of the nitrogen removal performance. This study provides a feasible recovery strategy for PNA processes.

Applying the Nernst Equation to Control ORP in Denitrification Process for Uranium-Containing Nuclear Effluent with High Loads of Nitrogen and COD

Several reviews of denitrification have shown it to be an efficient process for treating high nitrate-loaded effluents from nuclear industries. However, stressful conditions adversely affect biological kinetic parameters and performance. Additionally, actual nuclear effluents contain multiple pollutants and radioactive emissions that could render implementation difficult. The objective of this study was to treat and recycle water from nuclear industries by using a mixture of blended real nuclear wastewater (BRNW). The process was carried out under physicochemical parameters control in a biological model to established a technical setup and to model the denitrification process in a real nuclear wastewater effluent. Denitrification processes were carried out in the wastewater sample under controlled ORP conditions by the Hill model to establish the kinetic model. The results show a complete elimination of nitrate by the bacteria. Indicators of biochemical reactions were used to obtain a model based on Monod and controlled ORP. The good fit of the proposed model was verified under empirical and simulated conditions. To establish optimal performance, it was necessary to add 3% v/v of methanol, as a carbon source, to remove the nitrate in BRNW. Isolation techniques confirmed that Pseudomonas spp. was the dominant bacteria. Gene expression demonstrated the lack of inhibition of the NosZ gene responsible for the reduction in nitric oxide, a “greenhouse gas”. Finally, COD and uranium were removed from the liquid by precipitation. At the end of the process, the treated effluent could potentially be reused in industrial processes, recycling most of the wastewater effluents.

Catchment controls of denitrification and nitrous oxide production rates in headwater remediated agricultural streams

Heavily modified headwater streams and open ditches carry high nitrogen loads from agricultural soils that sustain eutrophication and poor water quality in downstream aquatic ecosystems. To remediate agricultural streams and reduce the export of nitrate (NO3−), phosphorus and suspended sediments, two-stage ditches with constructed floodplains can be implemented as countermeasures. By extending hydrological connectivity between the stream channel and riparian corridor within constructed floodplains, these remediated ditches enhance the removal of NO3− via the microbial denitrification process. Ten remediated ditches were paired with upstream trapezoidal ditches in Sweden across different soils and land uses to measure the capacity for denitrification and nitrous oxide (N2O) production and yields under denitrifying conditions in stream and floodplain sediments. To examine the controls for denitrification, water quality was monitored monthly and flow discharge continuously along reaches. Floodplain sediments accounted for 33 % of total denitrification capacity of remediated ditches, primarily controlled by inundation and stream NO3− concentrations. Despite reductions in flow-weighted NO3− concentrations along reaches, NO3− removal in remediated ditches via denitrification can be masked by inputs of NO3−-rich groundwaters, typical of intensively managed agricultural landscapes. Although N2O production rates were 50 % lower in floodplains compared to the stream, remediated ditches emitted more N2O than conventional trapezoidal ditches. Higher denitrification rates and reductions of N2O proportions were predicted by catchments with loamy soils, higher proportions of agricultural land use and lower floodplain elevations. For realizing enhanced NO3− removal from floodplains and avoiding increased N2O emissions, soil type, land use and the design of floodplains need to be considered when implementing remediated streams. Further, we stress the need for assessing the impact of stream remediation in the context of broader catchment processes, to determine the overall potential for improving water quality.

Influence of temperature on aerobic granular sludge formation and stability treating municipal wastewater with high nitrogen loadings

This study investigated the influence of temperature (20 and 30 °C) on the formation and stability of aerobic granules in sequential batch reactors (SBR). Therefore, two lab-scale SBRs operated at 20 and 30 °C (SBR20 and SBR30) were used. The reactors were fed with municipal wastewater (CODt:TN:TP 100:15:1.7), leading to mean organic loading rates (OLR) of 1.3 ± 0.4 kgCODt m−3 day−1. Both reactors had the same height/diameter ratio of 4.2 and were inoculated with activated sludge from a municipal wastewater treatment plant. The operational conditions were also the same for both temperatures and lasted in stable process parameters for over 100 days. By optimizing the aeration and oxygen concentration, a high removal efficiency of NH4–N (∼99%) and COD (∼90%) was achieved in both reactors, despite the poor C:N:P ratio at the influent. Furthermore, a relatively low oxygen concentration of 2 mg L−1 was defined as the set point for the control strategy. Nevertheless, granulation at 30 °C was significantly faster, resulting in more stable sludge volume index (SVI) values (SVI10/SVI30 < 1.1). The granules formed at 30 °C were also larger, more compact, and considerably more stable against system disturbances. However, at higher temperatures, larger granules might be required for nitrate removal because of the increased oxygen diffusion rates. Finally, microbiological 16S rRNA gene amplicon analysis for both systems indicated major differences relatively to the inoculum sludge only for nitrogen-degrading organisms.

Recovery of anammox process performance after substrate inhibition: Reactor performance, sludge morphology, and microbial community

Most of the current studies have focused on the inhibition of anaerobic ammonium oxidation (anammox) by substrates, however, little attention has been paid to the recovery process of the reactor after inhibition. Therefore, we investigated the changes in reactor performance, granular sludge structure, and microbial community during the recovery phase after being inhibited by a high nitrogen load for 15 d. The nitrogen removal rate of the reactorwasrestored to pre-inhibition levels after 75 d of recovery, and the stoichiometric ratio converged to the theoretical value. The surface of the granular sludge developed into a broccoli-like structure, and the Ca and P contents of the granules increased from 6.88% and 4.39% to 24.42% and 13.88%, respectively. The abundance of the anammox bacterium Candidatus brocadia increased from 5.86% to 12.10%, and network analysis indicated that SMA102 and SBR1031 were positively correlated with the occurrence of Candidatus brocadia.

Riverine dissolved organic matter (DOM) as affected by urbanization gradient

Rapid urbanization has considerably altered carbon biogeochemical cycle and river hydrology. However, the influences of urban land use and urban-induced nutrient increase on dissolved organic matter (DOM) characteristics are poorly understood. Here we hypothesize that the alterations significantly change sources and levels of DOM in river systems that drain the urban areas. To test the hypothesis, we investigated DOM in headwater rivers with varied urban intensities in the Three Gorges Reservoir Area (TGRA), China, through field sampling conducted in the dry and wet seasons. We found positive relationships of urban land (%Urban) with DOC concentration and chromophoric DOM (CDOM) absorption coefficients a254, a280 and a350, as well as fluorescence index (FI370), indicating the significantly increased levels of DOM and autochthonous sources along an urbanization gradient. A stepwise regression analysis demonstrated that occurrences of DOC and CDOM can be predicted by %Urban, while increasing autochthonous source is predictable by the increase in riverine nitrogen. Moreover, a254, a280 and FI370 values showed distinct seasonal variations, with significantly higher CDOM concentration in the wet season and with much higher autochthonous signal in the dry season with high nitrogen loading. Based on the findings, we conclude that urbanization influences occurrences and sources of DOM, with increasing urbanization making an important and direct contribution to DOM, and an indirect effect of urban induced nutrient enrichment, i.e., enhanced nutrient loadings increase autochthonous DOM production in rivers.

Ultrafast and selective adsorption of anionic dyes with amine-functionalized glucose-based adsorbents

Synthesis of biomass-based carbonaceous adsorbents with high adsorption performance, reusability, environmental-friendliness as well as low cost for water treatment remains a challenge. In this study, a glucose-based amine-functionalized carbon microsphere (AF-CMS) was synthesized via hydrothermal method and amine functional modification for the removal of organic dye. The results of materials characterization demonstrated an efficient amine functionalization of AF-CMS with a high nitrogen loading of 25.0 wt.% and strong positive charge under acidic conditions. Batch adsorption studies showed that the maximum adsorption capacities of AF-CMS for methyl orange (MO) and tartrazine (TTZ) were up to 1487.29 and 699.30 mg g−1, and the adsorption equilibrium was reached within 30 min with the 500 mg L−1 of dye solution. It could also quickly and completely capture dye molecule within 8 min for the TTZ dye solution of 100 mg L−1. The adsorption data of AF-CMS on anionic dyes was correlated with the pseudo-second-order kinetic and the Langmuir isotherm model. The adsorption capacity of AF-CMS for MO and TTZ dye still reached 1234.55 mg g−1 (83.01% of Qmax) and 618.65 mg g−1 (88.47% of Qmax), respectively, after five cycles of regeneration. More importantly, superior adsorption selectivity was demonstrated by the investigation of mixture of anionic dye and cation dye. Comprehensive analysis revealed that the good adsorption performance of AF-CMS was contributed to the strong electrostatic interaction between dye molecular and amine groups. Based on its simple preparation, low cost and excellent adsorption properties, the AF-CMS possesses a promising candidate for separating organic dyes from wastewater.

Morphological, kinetic, and microbial community characterization of anammox bacteria with different inoculations and biofilm types for low-ammonium wastewater treatment

Granular anammox sludge treating high-ammonium wastewater and biofilm anammox sludge treating low-ammonium wastewater were inoculated in two identical reactors to treat low-ammonium wastewater. The morphological and microbial community characterizations were investigated. Kinetic models were applied to understand kinetic characterizations and predict reactor performances. Both types of sludge adapted well in 10 and 5 days with the average total inorganic nitrogen removal efficiencies >85%. The average particle size of the granular sludge decreased from 843 μm to 515 μm. The biomass and thickness of the biofilm sludge increased by 17% and 66% when NH4+-N, NO2−-N and temperature increased from 10 mg/L to 33 mg/L, <0.5 mg/L to 41 mg/L, and circa 13 °C to 35 °C, respectively. The granular sludge had higher maximum utilization rate constant and saturation value constant (16.393 and 12.934 mg/(L·h)) than biofilm sludge (1.017 and 0.080 mg/(L·h)), indicating the inherent difference of inoculations. The granular sludge inoculated from high nitrogen loading rate (NLR) (0.36 g-N/(g-VSS·d)) condition had the potential to withstand a higher NLR than that in present reactor (0.14 g-N/(g-VSS·d)). The results of Grau second-order model indicated that both reactors performed good nitrogen removal efficiency despite inoculations and types differences, and can predict the nitrogen removal efficiency well. Microbial community diversities deceased, but granular bacteria richness increased due to the lower free ammonium and free nitrous acid. The dominant anammox bacteria in the granular sludge shifted from Candidatus Kuenenia to Candidatus Brocadia. Candidatus Kuenenia was always the dominant anammox bacteria in the biofilm sludge.

Hyperammonemia Post Lung Transplant: A Rare and Fatal Complication

Introduction Among the extra pulmonary complications associated with lung transplantation, severe hyperammonemia has been reported as a rare and fatal complication with an incidence of up to 4% and a fatality rate of 67% in some case series. We present a case report of a patient who underwent bilateral lung transplantation and developed severe hyperammonemia in his immediate post-operative course. Case Report A 66 year old male with past medical history of idiopathic pulmonary fibrosis was referred to our center for evaluation for bilateral lung transplantation. He underwent a technically uncomplicated successful procedure and his immediate post-operative course was complicated by metabolic acidosis and acute renal failure. On post op day 4 he developed mental status changes and was noted to have elevated plasma ammonia of 154 mcmol/L. Laboratory and imaging studies were negative for acute hepatic dysfunction. A head CT was negative for cerebral edema or acute findings. He was started on rifaximin, lactulose enemas and via nasogastric tube, in addition to empiric macrolide therapy. Despite these interventions his mental examination and ammonia level did not improve in the following 24 hours. He was initiated on L-arginine, sodium benzoate and levocarnitine for possible undiagnosed glutathione synthase deficiency. Continuous renal replacement therapy (CRRT) for more rapid ammonia clearance was also started. He required CRRT for 5 days with gradual improvement in mental status. CRRT was discontinued once plasma levels normalized. He was slowly weaned off the above pharmacological interventions in the ensuing 3 weeks. He was discharged to inpatient rehabilitation without the need of any medical therapies for hyperammoenmia on post op day 30. He remained well for a period of 4 years post-transplant and eventually succumbed to chronic lung allograft dysfunction. Summary The primary underlying mechanism for post transplant hyperammonemia remains unknown, but several risk factors have been linked to this condition. The most commonly reported are disseminated opportunistic infection with ureaplasma or mycoplasma, high nitrogen loads, pulmonary hypertension and hepatic glutamine synthetase deficiency. Treatment regimens are multimodal but overall aimed at reducing ammonia levels and providing neuroprotection. Early initiation of treatment is paramount for improving survival and outcomes. Among the extra pulmonary complications associated with lung transplantation, severe hyperammonemia has been reported as a rare and fatal complication with an incidence of up to 4% and a fatality rate of 67% in some case series. We present a case report of a patient who underwent bilateral lung transplantation and developed severe hyperammonemia in his immediate post-operative course. A 66 year old male with past medical history of idiopathic pulmonary fibrosis was referred to our center for evaluation for bilateral lung transplantation. He underwent a technically uncomplicated successful procedure and his immediate post-operative course was complicated by metabolic acidosis and acute renal failure. On post op day 4 he developed mental status changes and was noted to have elevated plasma ammonia of 154 mcmol/L. Laboratory and imaging studies were negative for acute hepatic dysfunction. A head CT was negative for cerebral edema or acute findings. He was started on rifaximin, lactulose enemas and via nasogastric tube, in addition to empiric macrolide therapy. Despite these interventions his mental examination and ammonia level did not improve in the following 24 hours. He was initiated on L-arginine, sodium benzoate and levocarnitine for possible undiagnosed glutathione synthase deficiency. Continuous renal replacement therapy (CRRT) for more rapid ammonia clearance was also started. He required CRRT for 5 days with gradual improvement in mental status. CRRT was discontinued once plasma levels normalized. He was slowly weaned off the above pharmacological interventions in the ensuing 3 weeks. He was discharged to inpatient rehabilitation without the need of any medical therapies for hyperammoenmia on post op day 30. He remained well for a period of 4 years post-transplant and eventually succumbed to chronic lung allograft dysfunction. The primary underlying mechanism for post transplant hyperammonemia remains unknown, but several risk factors have been linked to this condition. The most commonly reported are disseminated opportunistic infection with ureaplasma or mycoplasma, high nitrogen loads, pulmonary hypertension and hepatic glutamine synthetase deficiency. Treatment regimens are multimodal but overall aimed at reducing ammonia levels and providing neuroprotection. Early initiation of treatment is paramount for improving survival and outcomes.

Low-temperature anaerobic digestion of chicken manure at high organic and nitrogen loads - strategies for controlling short chain fatty acids

Objective of this work was to investigate the technical feasibility of low-temperature, closed-loop two-stage (liquid–solid) anaerobic digesters to treat chicken-manure (TS:68%; NH3:8 g/L) as a sole-feedstock. Effect of pH, temperature, treatment-duration, organic loading rate (OLR) and inoculum-recirculation ratio on short chain fatty acids (SCFA) production was studied. Digesters were operated at 20 ± 1 °C for 282-d over 4 batch-runs (∼70-d/batch) at an OLR of 8.78–4.3 gVS/L/d. Results showed that specific methane yield above 0.6 LCH4/gVS was feasible with a methane concentration > 60%. SCFA speciation of the entire system was monitored through the liquid-digester. Among SCFA indicators, the ratios of propionic-to-acetic acids, (butyric + valeric)-to-acetic acids, and total SCFA-to-alkalinity were observed within the limit, i.e., below 1.4, 0.3 and 0.8, respectively, indicating high-digester stability. This strategy allowed early detection, diagnosis of process failures in high-solids digester in fed-batch mode, and re-evaluation of operating protocol to enrich performance with economic-benefits.

The Inhibitory Effect of Free Nitrous Acid and Free Ammonia on the Anoxic Phosphorus Uptake Rate of Polyphosphate-Accumulating Organisms

The purpose of this study is to investigate the effect of free nitrous acid (FNA) and free ammonia (FA) on the anoxic phosphorus uptake rate (PUR) of polyphosphate-accumulating organisms (PAOs) via the utilization of nitrite. With this goal, upon developing a PAO-enriched culture in a sequential batch reactor, a series of batch experiments were conducted to examine the effects of nitrite and ammonium on the anoxic phosphorus uptake rate at different pH levels. According to the results, both free nitrous acid and free ammonia were found to inhibit anoxic PUR to a degree similar to their respective effects on aerobic PUR reported in previous studies, suggesting that phosphorus removal via the anoxic pathway may be just as susceptible as that via the aerobic pathway. The effect of FNA on anoxic PUR is optimally described by a non-competitive inhibition model with a KiFNA value of 1.6 μg N L−1, while the Levenspiel model with an SFA* value of 37 mg N L−1 provided the best fit for the FA effect on PAOs anoxic activities. The results of this study provide new insights regarding the viability of EBPR under high nitrogen loading conditions.

Effects of aquatic nitrogen pollution on particle-attached ammonia-oxidizing bacteria in urban freshwater mesocosms.

Ammonia-oxidizing bacteria (AOB) attached to aquatic particles are important participants in ammonia oxidation within hypereutrophic urban river systems. To explore the effects of aquatic nitrogen pollution on particle-attached AOB in urban river, we utilized laboratory mesocosms to investigate the responses of abundances and community structure of particle-attached AOB to ammonium (NH4+) and glycine (C2H5NO2) amendments. The abundance and community structure of particle-attached AOB were determined with quantitative real-time polymerase chain reaction (qRT-PCR) analysis and high-throughput sequencing based on the AOB amoA gene, respectively. Most of the bacterial amoA sequences from different treatments were affiliated with uncultured Nitrosomonadaceae bacterium, uncultured Nitrosomonadales bacterium, and uncultured Nitrosomonas sp., which are closely associated with organic pollution. The species richness and diversity of particle-attached AOB communities increased with increasing NH4+ and glycine concentrations. Treatment effects contributed significantly to the variance in particle-attached AOB communities. Although, glycine was completely transformed to ammonium within a few days and ammonium amendments would change the community structure of particle-attached AOB, the effect of glycine on the particle-attached AOB community was regulated by both the resulting ammonium concentration, as well as organic matter availability to the heterotrophic bacteria. Results suggested that high anthropogenic nitrogen loadings appeared to promote higher particle-attached AOB richness and diversity in the hypereutrophic urban river, but the effect of organic nitrogen on the particle-attached AOB community was different from the effect of inorganic nitrogen. This study informs ammonia oxidization mechanisms in the hypereutrophic urban rivers, which contributes to remediation/restoration strategies.