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PubMed2002

Nitrogen control of bacterial signal production in Rhizobium meliloti-alfalfa symbiosis.

Under nitrogen-depleted conditions nitrogen-fixing soil bacteria of the family Rhizobiaceae are able to induce symbiotic nodules on the roots of leguminous plants where bacteroids convert atmospheric nitrogen to ammonia. The presence of exogenous nitrogen source inhibits the development and the functioning of bacterium-plant symbiosis. Earlier experiments demonstrated that nitrate inhibited all stages of symbiotic interaction, affecting primarily the host functions. The investigation of the possible involvement of the microsymbiont in nitrogen regulation showed that two signalling steps were controlled by ammonium. The synthesis of the first bacterial signal, the Nod factor was repressed by ammonium. The nitrogen signal is conveyed to nodulation (nod) genes by the general nitrogen regulatory (ntr) system and by the nodD3-syrM self-amplifying system. The fine control also involves a negative regulatory factor, ntrR. When ntrR is mutated, more efficient nodule formation and nitrogen fixation is observed in symbiosis with alfalfa even in the presence of ammonium. The biosynthesis of the second bacterial signal succinoglycan is also controlled by ammonium. SyrM, a common regulatory factor for nod and exo gene expression, may contribute to the adjustment of the amount of succinoglycan and the ratio of its biologically active form.

Genes, Bacterial↗
PubMed2005

Cascading costs: an economic nitrogen cycle.

The chemical nitrogen cycle is becoming better characterized in terms of fluxes and reservoirs on a variety of scales. Galloway has demonstrated that reactive nitrogen can cascade through multiple ecosystems causing environmental damage at each stage before being denitrified to N2. We propose to construct a parallel economic nitrogen cascade (ENC) in which economic impacts of nitrogen fluxes can be estimated by the costs associated with each stage of the chemical cascade. Using economic data for the benefits of damage avoided and costs of mitigation in the Chesapeake Bay basin, we have constructed an economic nitrogen cascade for the region. Since a single tonne of nitrogen can cascade through the system, the costs also cascade. Therefore evaluating the benefits of mitigating a tonne of reactive nitrogen released needs to consider the damage avoided in all of the ecosystems through which that tonne would cascade. The analysis reveals that it is most cost effective to remove a tonne of nitrogen coming from combustion since it has the greatest impact on human health and creates cascading damage through the atmospheric, terrestrial, aquatic and coastal ecosystems. We will discuss the implications of this analysis for determining the most cost effective policy option for achieving environmental quality goals.

Animals↗
PubMed1996

A 15N-leucine-dilution method to measure endogenous contribution to luminal nitrogen in the human upper jejunum.

OBJECTIVE: This study was done to investigate whether an intraveinous infusion of 15N-leucine was accurate to differentiate between endogenous and exogenous nitrogen in the human jejunum after meal ingestion. SUBJECTS: Four healthy human volunteers equipped with an upper jejunal tube. INTERVENTIONS: The jejunal effluents were collected both under fasting conditions and after ingestion of 300g of yoghurt. The nitrogen, amino acid composition and 15N-leucine enrichment were determined in the digesta. RESULTS: During fasting, the jejunal flow rates (mmol/h) of both total nitrogen and amino acids were stable (6.9 +/- 2.7 and 1.88 +/- 0.79, respectively). After yoghurt ingestion, the flow rate of total nitrogen increased to 28.6 +/- 5.8mmol/h at 2h. The 15N-leucine enrichment in plasma reached a plateau at 4.3 mole % excess after one hour and did not vary significantly after meal ingestion. The 15N-leucine enrichment of the endogenous secretion (Ee) in the jejunum was fitted by the equation: Ee = 2.18[1 - 2.05 x exp( - 0.42 x t)]. After yoghurt ingestion, the enrichment in jejunal secretions decreased during the first 80 min. The endogenous nitrogen, calculated from the 15N-enrichment, significantly increased from 20 to 40min after meal ingestion compared to the basal value (P < 0.05). The estimation of the exogenous nitrogen and amino acid yield 300min after yoghurt ingestion indicated that 62 +/- 30% of the exogenous nitrogen and 75 +/- 12% of the amino acids were absorbed in the upper jejunum. CONCLUSIONS: The 15N-leucine-dilution method appears to be a convenient method to differentiate between the exogenous and endogenous contributions to nitrogen fluxes in the intestinal digesta of humans. It can be used in association with dietary protein labelling or in substitution when no labelled dietary proteins are available to compare the digestion as well as the absorption of meals at different levels of the intestine.

Adult↗
PubMed2026

Isolation and global occurrence of nitrogen-fixing Acidobacteriota in soil environments.

Acidobacteriota, one of the most abundant and ubiquitous bacterial phyla in soils, are well recognized for their role in carbon cycling. In contrast, their roles in soil nitrogen cycling remain largely unexplored, although recent metagenome-assembled genome (MAG) analyses suggest that Acidobacteriota may harbor genes involved in nitrogen cycling. Here, we provide culture-based evidence of diazotrophy within this phylum and demonstrate the widespread occurrence of nitrogen-fixing Acidobacteriota across diverse soil types. From grassland and agricultural soils, we isolated five Acidobacteriota strains representing novel taxonomic lineages, four of which harbor functional nitrogenase (nif) gene clusters. These strains were capable of fixing atmospheric nitrogen in vitro and/or in soil microcosms, as evidenced by acetylene reduction, N2-dependent growth, transcription of nif genes, incorporation of 15N into biomass and soil, and inhibition of nitrogenase activity by ammonium. Furthermore, global-scale meta-analysis of soil metagenomes revealed that nif-harboring Acidobacteriota are widely distributed and locally dominant across soil types. These results demonstrate the nitrogen-fixing capability of Acidobacteriota at the organismal level, complementing MAG-based inferences, and underscore their adaptive capacity in nitrogen-limited environments and their potential contribution to terrestrial nitrogen fixation. We also propose novel taxa within the class Terriglobia of the phylum Acidobacteriota, including diazotrophic strains, comprising one novel family, three novel genera, and four novel species: Koromonadaceae fam. nov., Koromonas soli gen. nov., sp. nov., Koromonas humicola sp. nov., Oryzophilus luti gen. nov., sp. nov., and Humiphilus diazotrophicus gen. nov., sp. nov.

Soil Microbiology↗
PubMed1975

Nitrogen balance in postoperative patients receiving parenteral nutrition.

Fifteen patients were given parenteral nutrition with hyperosmolar glucose during the postoperative period (days 1 to 5): nine received an average of 10.5 gm of nitrogen and 2,340 kilocalories/day, six were given an average of 5.9 gm of nitrogen and 1,600 kilocalories/day. Eight patients (controls) received no nitrogen and 520 kilocalories/day. The results of this study confirm our early findings that total parenteral nutrition is capable of reversing the negative nitrogen balance of the immediate postoperative period; this reversal depends on administration of adequate nitrogen and calories. In patients with moderate surgical procedures, at least 8 gm of nitrogen and 1,800 kilocalories/day are required to correct the negative nitrogen balance. When total parenteral nutrition is instituted, adequate nitrogen and calories should be given even if insulin is required to control hyperglycemia.

Dietary Carbohydrates↗
PubMed2005

Global expression profiling of Bacillus subtilis cells during industrial-close fed-batch fermentations with different nitrogen sources.

A detailed gene expression analysis of industrial-close Bacillus subtilis fed-batch fermentation processes with casamino acids as the only nitrogen source and with a reduced casamino acid concentration but supplemented by ammonia was carried out. Although glutamine and arginine are supposed to be the preferred nitrogen sources of B. subtilis, we demonstrate that a combined feeding of ammonia and casamino acids supports cell growth under fed-batch fermentation conditions. The transcriptome and proteome analyses revealed that the additional feeding of ammonia in combination with a reduced amino acid concentration results in a significantly lower expression level of the glnAR or tnrA genes, coding for proteins, which are mainly involved in the nitrogen metabolism of B. subtilis. However, the mRNA levels of the genes of the ilvBHC-leuABD and hom-thrCB operons were significantly increased, indicating a valine, leucine, isoleucine, and threonine limitation under these fermentation conditions. In contrast, during the fermentation with casamino acids as the only nitrogen source, several genes, which play a crucial role in nitrogen metabolism of B. subtilis (e.g., glnAR, nasCDE, nrgAB, and ureABC), were up-regulated, indicating a nitrogen limitation under these conditions. Furthermore, increased expression of genes, which are involved in motility and chemotaxis (e.g., hag, fliT) and in acetoin metabolism (e.g., acoABCL), was determined during the fermentation with the mixed nitrogen source of casamino acids and ammonia, indicating a carbon limitation under these fermentation conditions. Under high cell density and slow growth rate conditions a weak up-regulation of autolysis genes could be observed as well as the induction of a number of genes involved in motility, chemotaxis and general stress response. Results of this study allowed the selection of marker genes, which could be used for the monitoring of B. subtilis fermentation processes. The data suggest for example acoA as a marker gene for glucose limitation or glnA as an indicator for nitrogen limitation.

Bacillus subtilis↗
PubMed1975

Reduction of oxidized inorganic nitrogen compounds by a new strain of Thiobacillus denitrificans.

Denitrification by Thiobacillus denitrificans "RT" strain was investigated using manometry and gas chromatography. 1. From nitrate, resting cells produced only nitrogen anaerobically with thiosulfate as the electron donor. The data suggest that nitrate was assimilated and dissimilated by the same nitrate reductase, assayed with benzyl-viologen as the electron donor. 2. From nitrite, whole cells produced nitric oxide, nitrous oxide and nitrogen, using thiosulfate as the electron donor; nitrogen was the final product of the reduction. Crude extract reduced nitrite to nitrogen with p-phenylene-diamine and dimethyl-p-phenylene diamine as the electron donors, and produced nitric oxide, nitrous oxide and nitrogen with tetramethyl-p-phenylene-diamine as the electron donor. Nitrite was reduced to nitric oxide and nitrous oxide by crude extract using ascorbate-phenazine methosulfate as the electron donor. 3. From nitric oxide, whole cells produced nitrous oxide and nitrogen using thiosulfate as the electron donor, nitrogen was the final reduction product. Nitric oxide was reduced to nitrous oxide by crude extract with the ascorbate-phenazine methosulfate system. 4. Whole cells reduced nitrous oxide to nitrogen with thiosulfate as the electron donor. It was not possible to detect any nitrous oxide reductase activity in crude extract. 5. A scheme was of denitrification by Thiobacillus denitrificans "RT" strain.

Aerobiosis↗
PubMed2006

A cybernetic model to predict the effect of freely available nitrogen substrate on rifamycin B production in complex media.

It is well-known that secondary metabolite production is repressed by excess nitrogen substrate available in the fermentation media. Although the nitrogen catabolite repression has been known, quantitative process models have not been reported to represent this phenomenon in complex medium. In this paper, we present a cybernetic model for rifamycin B production via Amycolatopsis mediterranei S699 in complex medium, which is typically used in industry. Nitrogen substrate is assumed to be present in two forms in the medium; available nitrogen (S(ANS)) such as free amino acids and unavailable nitrogen (S(UNS)) such as peptides and proteins. The model assumes that an inducible enzyme catalyzes the conversion of S(UNS) to S(ANS). Although S(ANS) is required for growth and product formation, high concentrations were found to inhibit rifamycin production. To experimentally validate the model, five different organic nitrogen sources were used that differ in the ratio of S(ANS)/S (UNS). The model successfully predicts higher rifamycin B productivity for nitrogen sources that contain lower initial S(ANS). The higher productivity is attributed to the sustained availability of S(ANS) at low concentration via conversion of S(UNS) to S(ANS), thereby minimizing the effects of nitrogen catabolite repression on rifamycin production. The model can have applications in model-based optimization of substrate feeding recipe and in monitoring and control of fed batch processes.

Actinomycetales↗
PubMed2006

Nitrogen deficiency enhances expression of specific MYB and bHLH transcription factors and accumulation of end products in the flavonoid pathway.

Expression of regulators of the flavonoid pathway was examined in Arabidopsis thaliana wild type and pap1D plants, the latter being a T-DNA activation-tagged line over-expressing the PAP1/MYB75 gene which is a positive regulator of the pathway. Anthocyanin accumulation was induced in plants grown in soil, on agar plates, and hydroponics by withdrawing nitrogen from the growth medium. The agar-grown seedlings and rosette stage plants in hydroponics were further explored, and showed that nitrogen deficiency resulted in the accumulation of not only anthocyanins, but also flavonols. The examination of transcript levels showed that the general flavonoid pathway regulators PAP1 and PAP2 were up-regulated in response to nitrogen deficiency in wild type as well as pap1D plants. Interestingly, PAP2 responded much stronger to nitrogen deficiency than PAP1, 200- and 6-fold increase in transcript levels, respectively, for wild-type seedlings. In rosette leaves the increase was 900-fold for PAP2 and 6-fold for PAP1. At least three different bHLH domain transcription factors promote anthocyanin synthesis, and transcripts for one of these, i.e. GL3 were found to be sixfold enhanced by nitrogen deficiency in rosette leaves. The MYB12 transcription factor, known to regulate flavonol synthesis, was slightly induced by nitrogen deficiency in seedlings. In conclusion, four out of eight regulators involved in the flavonoid pathway showed an enhanced expression from 2 to 1,000 times in response to nitrogen deficiency. Together with MYB factors, especially PAP2, GL3 appears to be the BHLH partner for anthocyanin accumulation in response to nitrogen deficiency.

Agar↗
PubMed2005

Dynamics of leaf area and nitrogen in the canopy of an annual herb, Xanthium canadense.

We studied leaf area and nitrogen dynamics in the canopy of stands of an annual herb Xanthium canadense, grown at a high (HN)- and a low-nitorgen (LN) availability. Standing leaf area increased continuously through the vegetative growth period in the LN stand, or leveled off in the later stage in the HN stand. When scaled against standing leaf area, both production and loss rates of leaf area increased but with different patterns: the production rate was retarded, while the loss rate was accelerated, implying an upper limit of standing leaf area of the canopy. The rate of leaf-area production was higher in the HN than in the LN stand, which was caused by the higher rate of leaf production per standing leaf area as well as the greater standing leaf area in the HN stand. Although the rate of leaf-area loss was higher in the HN than in the LN stand, it was not significantly different between the two stands when compared at a common standing leaf area, suggesting involvement of light climate in determination of the leaf-loss rate. On the other hand, the rate of leaf-area loss was positively correlated with nitrogen demand for leaf area development across the two stands, suggesting that leaf loss was caused by retranslocation of nitrogen for construction of new leaves. A simple simulation model of leaf and nitrogen dynamics in the canopy showed that, at steady state, where the rate of leaf-area loss becomes equal to the production rate, the standing leaf area was still greater in the HN than in the LN stand. Similarly, when the uptake and loss of nitrogen are equilibrated, the standing nitrogen was greater in the HN than in the LN stand. These results suggest that leaf-area production is strongly controlled by nitrogen availability, while both nitrogen and light climate determine leaf-loss rates in the canopy.

Analysis of Variance↗
PubMed2025

Hyperspectral imaging of grains uncovers the genetic architecture of nitrogen response of development in bread wheat.

UNLABELLED: Unraveling the genetic architecture of nitrogen response of development is critical for improving wheat productivity while reducing nitrogen inputs. In this study, hyperspectral imaging (HSI) was applied to wheat grains obtained from nitrogen-deficient and normal conditions, combined with genome-wide association studies (GWAS), to investigate the nitrogen response of development in a diverse wheat panel. The 1,792 i-traits were acquired via hyperspectral imaging system, which reflect detailed phenotypic assessments of wheat development, capturing subtle variations in nitrogen response. A total of 3,556 significant loci and 3,648 candidate genes were identified. Key candidate genes involved in nitrogen uptake and utilization were identified by integrating agronomic traits with i-traits, including TaARE1-7A, TaPTR9-7B, TaNAR2.1, and Rht-B1. This approach underscores the potential of combining HSI on grains with GWAS to dissect complex traits like nitrogen response, offering valuable genetic insights for breeding nitrogen-efficient wheat varieties and enhancing sustainability in crop production. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s11032-025-01609-6.

Bread wheat↗
PubMed1985

Effects of vegetable diets on nitrogen metabolism in cirrhotic subjects.

This study compared the effect of a vegetable diet with an animal protein diet on various aspects of nitrogen metabolism to identify what components of the vegetable diet might be causing beneficial therapeutic effects in hepatic encephalopathy. Vegetable diets contained 4.5-fold greater amounts of fiber (56 +/- 3 g/day) and reduced amounts of methionine, tyrosine, and tryptophan. In 6 stable cirrhotic subjects without encephalopathy, vegetable diets caused a significant reduction in the urea production rate from 106 +/- 5 to 89 +/- 5 mg X kg-1 X 24 h-1 of urea nitrogen. This was mainly accounted for by a fall in urinary urea output. Vegetable diets also caused a fall in total urinary nitrogen, which was accounted for by the fall in urea nitrogen, and a comparable increase in fecal nitrogen from 12 +/- 2 to 28 +/- 5 mg X kg-1 X 24 h-1. The fecal bacterial fraction contained 63% of the increase in stool nitrogen. Most plasma amino acids, including methionine, tyrosine, phenylalanine, as well as total and free tryptophan, were unchanged. The effect of vegetable diets on nitrogen metabolism can be mainly accounted for by the increased intake of dietary fiber and increased incorporation and elimination of nitrogen in fecal bacteria.

Aged↗
PubMed1994

Hepatic conversion of amino-nitrogen to urea in thyroid diseases. II. A study in hyperthyroid patients.

Conflicting data have been reported on the influence of thyroid hormones on hepatic nitrogen metabolism and on liver metabolic activity. We studied the urea-nitrogen synthesis rate (UNSR) and the kinetics of the process of hepatic amino-nitrogen to urea-nitrogen conversion in response to constant alanine infusion (ie, the functional hepatic nitrogen clearance [FHNC]) in five hyperthyroid female patients before and after the achievement of a stable euthyroid status. In the same patients, galactose elimination capacity and antipyrine clearance were also measured as quantitative indices of hepatic function. The basal urea synthesis rate was nearly doubled in hyperthyroid patients (35.6 +/- 8.5 mmol.h-1 v 17.6 +/- 7.7 in euthyroid patients, P < .05) and increased linearly with increasing alpha-amino-nitrogen (alpha-AN) concentrations in both conditions. The urea synthesis rate during alanine infusion was still higher by approximately 30 mmol.h-1 in hyperthyroid subjects. The FHNC, calculated as the slope of the linear relation between the UNSR in each time interval and the corresponding average alpha-AN concentration, was not different (hyperthyroidism, 30.6 +/- 7.2 L.h-1; euthyroidism, 28.5 +/- 4.4; normal values > 25). The hepatic microsomal and cytosolic activities (antipyrine clearance and galactose elimination) were normal in hyperthyroid patients and did not change significantly after therapy. Our data show that the hepatic nitrogen metabolism of hyperthyroid patients is characterized by an upregulation of amino-nitrogen catabolism and loss of the sparing mechanism at low plasma amino acid levels, without any change in different metabolic activities.

Adult↗
PubMed1996

Formation of recombinant proteins in Escherichia coli under control of a nitrogen regulated promoter at low and high cell densities.

The use of a modified Escherichia coli glnAP2 promoter results in the formation of both homologous and heterologous, cytoplasmic and periplasmic recombinant proteins in a nitrogen concentration dependent manner. As in the E. coli nitrogen regulatory system, glnAP2 controlled gene expression is induced when ammonium concentration in the growth medium is below 1 mM (nitrogen limitation), otherwise only extremely low expression of recombinant genes is observed. Both high cell density cultivations (HCDC) and low cell density cultivations (LCDC) gave similar results for inducibility and formation of the following recombinant proteins: chloramphenicol-acetyltransferase, phosphorylcholine binding mini-antibodies (scFv-dhlx of McPC603) and K1-streptokinase. Recombinant proteins were formed in quantities of about 2-3% of total cellular protein. At low cell densities, slightly higher quantities resulted under partial nitrogen limitations than under total nitrogen limitation. In contrast, high cell density cultivations resulted in lower product concentrations at partial nitrogen limitation compared with total nitrogen limitation. These lowered product concentrations were probably due to the very high amounts of K+ or Na+ ions which accumulated during pH-regulation, thereby disturbing growth. HCDC under partial nitrogen limitation decreased proteolysis of recombinant proteins, therefore reduced amounts of proteases are considered to be responsible.

Cell Division↗
PubMed1988

Creatinine and inulin clearance at the different nitrogen and energy intake in sheep.

1. Renal creatinine and inulin clearances were compared between sheep fed (a) high nitrogen and high energy diet; (b) low nitrogen and high energy diet and (c) low nitrogen and low energy diet. 2. Inulin clearance was significantly lower in sheep on both low nitrogen diets vs the group with high nitrogen intake. Differences were not ascertained between the groups on low nitrogen diets. 3. No significant differences were found in the creatinine clearance. The creatinine inulin clearance ratio was higher when animals were fed low nitrogen diets, vs the group on a high nitrogen diet. 4. Results suggest that the endogenous creatinine is not suitable for the GFR measurement in sheep under the different conditions of nutrition.

Animals↗
PubMed2006

Application of global analysis techniques to Corynebacterium glutamicum: new insights into nitrogen regulation.

The regulation of nitrogen metabolism in the amino acid producer Corynebacterium glutamicum was subject of research for several decades. While previous studies focused on single enzymes or pathways, the publication of the C. glutamicum genome sequence gave a fresh impetus to research, since a global investigation of metabolism and regulation networks became possible based on these data. This communication summarizes the advances made by different studies, in which global analysis approaches were used to characterize the C. glutamicum nitrogen starvation response. A combination of bioinformatics approaches, transcriptome and proteome analyses as well as chemostat experiments revealed new insights into the nitrogen control network of C. glutamicum. C. glutamicum reacts to a limited nitrogen supply with a rearrangement of the cellular transport capacity, changes in metabolic pathways for nitrogen assimilation and amino acid biosynthesis, an increased energy generation and increased protein stability. With the aid of chemostat experiments, in which different growth rates were obtained by nitrogen limitation, general starvation effects could be distinguished from specific nitrogen limitation-dependent changes. The core adaptations on the level of transcription are controlled by the master regulator of nitrogen control, the TetR-type protein AmtR. This global regulator governs transcription of at least 33 genes via binding to a palindromic consensus motif (AmtR box). Genes with AmtR box-containing promoters were identified by genome-wide screening and validated, besides by other methods, by transcriptome analyses using DNA microarrays.

Bacterial Proteins↗
PubMed2006

Dynamic transformations of nitrogen during mechanical-biological pre-treatment of municipal solid waste.

Mechanical-biological pre-treatment (MBP) of municipal solid waste (MSW) has gained evidence as a practice capable of accomplishing the requirements for environmental sustainable landfilling. In particular, MBP is effective in reducing the ammoniacal nitrogen content in the leachate. However, few data are available on the modifications of the nitrogen forms occurring during MBP and on the role played by processes such as nitrification and generation of refractory organic compounds. The dynamic transformations of nitrogen were investigated during the MBP. MSW was mechanically and biologically pre-treated; samples were collected at different stages of the process and analysed to investigate the evolution of nitrogen forms; batch and column leaching tests were performed as well. The results indicate that nitrification is negligible and volatilization can only partially explain the low ammoniacal nitrogen content in the leachate. Incorporation of ammoniacal nitrogen into a refractory organic form was assessed and is likely to play an important role. The maximum content of refractory organic nitrogen in the solid waste was achieved after about 60 days of aerobic pre-treatment; therefore, the minimal duration of the MBP should be about 8-9 weeks in order to optimize the ammoniacal nitrogen incorporation, unless the waste is characterized by a low C/N ratio.

Ammonia↗
PubMed2004

Enhanced ammonia nitrogen removal using consistent biological regeneration and ammonium exchange of zeolite in modified SBR process.

The modified zeo-SBR is recommended for a new nitrogen removal process that has a special function of consistent ammonium exchange and bioregeneration of zeolite-floc. Three sets of sequencing batch reactors, control, zeo-SBR, and modified zeo-SBR were tested to assess nitrogen removal efficiency. The control reactor consisted of anoxic-fill, aeration-mixing, settling, and decanting/idle phases, meaning that nitrogen removal efficiency was dependent on the decanting volume in a cycle. The zeo-SBR reactor was operated in the same way as the control reactor, except for daily addition of powdered zeolite in the SBR reactor. The operating order sequences in the zeo-SBR were changed in the modified zeo-SBR. Anoxic-fill phase was followed by aeration-mixing phase in the zeo-SBR, while aeration-mixing phase was followed by anoxic-fill phase in the modified zeo-SBR to carry NH4(+)-N over to the next operational cycle and to reduce total nitrogen concentration in the effluent. In the modified zeo-SBR, nitrification and biological regeneration occurred during the initial aeration-mixing phase, while denitrification and ammonium adsorption occurred in the following anoxic-fill phase. The changed operational sequence in the modified zeo-SBR to adapt the ammonium adsorption and biological regeneration of the zeolite-floc could enhance nitrogen removal efficiency. As a result of the continuous operation, the nitrogen removal efficiencies of the control and zeo-SBR were in 68.5-70.9%, based on the 33% of decanting volume for a cycle. The zeo-SBR showed a consistent ammonium exchange and bio-regeneration in the anoxic-fill and aeration-mixing phases, respectively. Meanwhile, the effluent total nitrogen of the modified zeo-SBR showed 50-60 mg N/L through ammonium adsorption of the zeolite-floc when the influent ammonium concentration was 315 mg N/L, indicating the T-N removal efficiency was enhanced over 10% in the same HRT and SRT conditions as those of control and zeo-SBR reactors. The ammonium adsorption capacity was found to be 6-7 mg NH4(+)-N/g FSS that is equivalent to 40 mg NH4(+)-N/L of ammonium nitrogen removal.

Adsorption↗