Heterotrophic nitrification and related functional gene expression characteristics of Alcaligenes faecalis SDU20 with the potential use in swine wastewater treatment.

A new heterotrophic nitrifying bacterium was isolated from the compost of swine manure and rice husk and identified as Alcaligenes faecalis SDU20. Strain SDU20 had heterotrophic nitrification potential and could remove 99.7% of the initial NH4+-N. Nitrogen balance analysis revealed that 15.9 and 12.3% of the NH4+-N were converted into biological nitrogen and nitrate nitrogen, respectively. The remaining 71.44% could be converted into N2 or N2O. Single-factor experiments showed that the optimal conditions for ammonium removal were the carbon source of sodium succinate, C/N ratio 10, initial pH 8.0, and temperature 30 °C. Nitrification genes were determined to be upregulated when sodium succinate was used as the carbon source analyzed by quantitative real-time polymerase chain reaction (qRT-PCR). Strain SDU20 could tolerate 4% salinity and show resistance to some heavy metal ions. Strain SDU20 removed 72.6% high concentrated NH4+-N of 2000 mg/L within 216 h. In a batch experiment, the highest NH4+-N removal efficiency of 98.7% and COD removal efficiency of 93.7% were obtained in the treatment of unsterilized swine wastewater. Strain SDU20 is promising in high-ammonium wastewater treatment.

Recovery phosphate and ammonium from aqueous solution by the process of electrochemically decomposing dolomite.

The cost-effective recovery of phosphate is of great significance to the mitigation of phosphorus resource depletion crisis. The electrochemical-decomposition of dolomite was developed to recover phosphate and ammonium from aqueous solution. The dolomite ore is mainly composed of CaMg(CO3)2 (53.73%), CaCO3 (28.93%) and SiO2 (16.59%). The continuous release of Mg2+ and Ca2+ were achieved by electrochemically decomposing dolomite ore, accompanied by the generation of base solution (9.0-10.5). The main factors affecting the recovery performance of phosphate (PO4-P) and ammonium (NH4-N) are current, initial concentration of PO4-P and NH4-N, initial pH of feed solution and feed rate. For a 30-d operation, the recovery rate of PO4-P was maintained at 90-97% and that of NH4-N at 50-60% under optimized operating conditions. The recovered product had low water solubility but high citric-acid-soluble, and was proposed as a slow-release fertilizer for crops. The proposed process as a simple, effective and green route may serve as a new strategy for recovering PO4-P and NH4-N from wastewaters.

Efficient ammonium removal through heterotrophic nitrification-aerobic denitrification by Acinetobacter baumannii strain AL-6 in the presence of Cr(VI).

A novel strain AL-6, which was identified as Acinetobacter baumannii, presented an efficient ability to remove ammonium. Nitrogen balance indicates that 55.8% of the initial NH4+-N was ultimately converted to N2 through heterotrophic nitrification and aerobic denitrification, while 30.6% was contributed to assimilation. More interestingly, efficient ammonium removal could be achieved in the presence of Cr(VI) of 0-10 mg L-1 by strain AL-6. Meanwhile, Cr(VI) reduction was observed. The Cr(VI) was mainly reduced to less toxic Cr(III) by strain AL-6 in the culture, while a small part of Cr(VI) might be accumulated in bacterial cells in the formation of Cr(III). The optimal conditions for ammonium removal as well as Cr(VI) reduction was pH of 7 and C/N ratio of 10-15. This study provided a potential prospect for the treatment of Cr(VI)-containing ammonium wastewater.

Chitosan Modified Zeolite Molecular Sieve Particles as a Filter for Ammonium Nitrogen Removal from Water.

Drinking water containing a high amount of ammonium-nitrogen (NH4+-N) is not effectively removed by conventional treatment processes and can cause eutrophication. In this research, a composite adsorbent based on chitosan crosslink with zeolite molecular sieve (CTS-ZMS) was prepared for NH4+-N removal through dynamic adsorption filter experiments. Effect of bed depth (30, 50 and 70 cm), flow rate (32, 49 and 65 mL/min), initial pH value (4.5, 6.5 and 8.5) and influent NH4+-N concentration (3, 5 and 7 mg/L) was examined by using a filter column packed with CTS-ZMS particles. The Thomas model was applied to study the breakthrough curves and adsorption capacity. The optimal process parameters of the aforementioned factors were obtained at bed depth of 70 cm, flow rate of 32 mL/min, pH of 6.5 and initial NH4+-N concentration of 7 mg/L. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and Fourier Transform Infrared Spectroscopy (FTIR) were investigated to analyze the structure and morphology of the CTS-ZMS adsorbents before and after 3 months running. The EDS and FTIR results showed Na+ and the active functional groups of -OH, -NH2 and -COO- on CTS-ZMS adsorbent particles reacted with ammonium nitrogen. The results of this study supported the use of CTS-ZMS to improve drinking water filtration processes by increasing ammonium nitrogen reductions.

Rapid and solvent-free synthesis of pH-responsive graft-copolymers based on wheat starch and their properties as potential ammonium sorbents.

A rapid and cost-effective reactive extrusion (REx) method was employed in this study as an alternative technique for the graft-copolymerization of non-food grade native wheat starch with acrylamide, and 2-acrylamido-2-methylpropane sulfonic acid (AMPS) monomers, with a total starch/monomer ratio of 3:1, using twin-screw extrusion technology. The influence of AMPS content ratio on the REx process was monitored using specific mechanical energy, die pressure and torque values recorded during the extrusion. The as-prepared starch-copolymers were characterized using ATR-FTIR, NMR, TG-DSC, and elemental analysis. An average grafting efficiency and monomer conversion of ~61 and ~86%, respectively, was achieved within 5 min of extrusion at a high starch concentration (0.75:1 w/w starch-water). The copolymer with starch/acrylamide/AMPS weight ratio of 75:20:4 showed the highest swelling capacity in water, while behaving similarly to polyelectrolyte networks in the presence of free ions in both NaCl and NH4Cl solutions. A steady NH4+ adsorption capacity was also recorded for these starch-copolymers within the pH range of ~5.5-8.5, which exceeded those of the natural sorbents. These findings indicate the suitability of the starch-copolymers as potential precursors of effective sorbents, thus confirming the feasibility of using REx to produce pH-responsive hybrid copolymers based on wheat starch at low-cost.

Application of Natural Clinoptilolite for Ammonium Removal from Sludge Water.

Sludge water (SW) arising from the dewatering of anaerobic digested sludge causes high back loads of ammonium, leading to high stress (inhibition of the activity of microorganisms by an oversupply of nitrogen compounds (substrate inhibition)) for wastewater treatment plants (WWTP). On the other hand, ammonium is a valuable resource to substitute ammonia from the energy intensive Haber-Bosch process for fertilizer production. Within this work, it was investigated to what extent and under which conditions Carpathian clinoptilolite powder (CCP 20) can be used to remove ammonium from SW and to recover it. Two different SW, originating from municipal WWTPs were investigated (SW1: c0 = 967 mg/L NH4-N, municipal wastewater; SW2: c0 = 718-927 mg/L NH4-N, large industrial wastewater share). The highest loading was achieved at 307 K with 16.1 mg/g (SW1) and 15.3 mg/g (SW2) at 295 K. Kinetic studies with different specific dosages (0.05 gCLI/mgNH4-N), temperatures (283-307 K) and pre-loaded CCP 20 (0-11.4 mg/g) were conducted. At a higher temperature a higher load was achieved. Already after 30 min contact time, regardless of the sludge water, a high load up to 7.15 mg/g at 307 K was reached, achieving equilibrium after 120 min. Pre-loaded sorbent could be further loaded with ammonium when it was recontacted with the SW.

Enhanced removal of ammonium from water by ball-milled biochar.

Novel biochar was prepared by ball milling using bamboo as raw material. The aim of this study was to find a good alternative way to improve the potentials of biochar for ammonium adsorption from aqueous solution. The sorption performance of ball-milled bamboo biochar (BMBB) was compared with that of bamboo biochar (BB) using batch adsorption experiments. Different adsorption kinetics models proved that the pseudo-second order was the best kinetic model for explanation of the adsorption kinetics characteristics, indicative of the energetically heterogeneous solid surface of the biochar. The Langmuir model could fit the isothermal adsorption data of BMBB well. The maximum adsorption capacity of BMBB (22.9 mg g-1) was much higher than that of BB (7.0 mg g-1). This study offers a relatively cost-effective and efficient methodology for the improvement in the adsorption capacity of biochar for ammonium nitrogen.

Removal of High Concentrations of Ammonium from Groundwater in a Pilot-Scale System through Aeration at the Bottom Layer of a Chemical Catalytic Oxidation Filter.

To remove high concentrations of ammonium from groundwater, pure oxygen and compressed air were fed into a chemical catalytic filter and the ammonium removal efficiency was investigated. The experimental results showed that the oxygen content is the critical limiting factor for ammonium removal. Aeration with 40 mL/min pure oxygen or 100 mL/min compressed air from the bottom of the filter supplied adequate oxygen and approximately 4.2 mg/L of ammonium was removed in this process. Moreover, when the aeration device was moved to 1/3 of the height of the filter bed, the required flow rates of pure oxygen and compressed air decreased further and the turbidity removal was improved. Pouring ozone gas into the filter system, which can inactivate bacteria effectively, can also obtain the remarkable ammonium removal, indicating that ammonium removal was mainly due to the chemical catalytic oxidation in this process rather than the biodegradation. This study provides a novel method for removing high concentrations of ammonium from groundwater.

Continuous autotrophic denitrification process for treating ammonium-rich leachate wastewater in bioelectrochemical denitrification system (BEDS).

The reduction of nitrogen compounds in aqueous solution is extremely important for sustainable management of ecosystem and human health. An autotrophic bioelectrochemical denitrification (BED) process was evaluated at various conditions for enhanced treatment of synthetic wastewater (SW) and ammonium-rich leachate. With SW, a decrease in hydraulic retention time (HRT: 41.6 to 8.3 h) resulted in a 370% increase in denitrification rate from 0.026 to 0.096 kg NO3-N/m3. D. An increase in applied voltage (0.7 to 2 V) enhanced nitrate removal (81 to 97% removal), but coulombic efficiency decreased from 74% to 19%. With doubled cathode electrodes, the nitrate removal rate was doubled from 0.056 to 0.114 kg NO3-N/m3. D. Moreover, leachate wastewater was successfully denitrified with the maximum removal rate of 0.121 kg NO3-N/m3. D. These results point towards the practical potential for the combination of nitrification systems with BEDS for reduction of nitrogen for discharge purposes.

Treatment of heavily polluted river water by tidal-operated biofilters with organic/inorganic media: Evaluation of performance and bacterial community.

In this study, biofilters (BFs) packed with inorganic (ceramsite and lava rock) and organic (fibrous carrier and biological ball) materials were applied in a tide-flow mode at three flooded/drained (F/D) time ratios (16/8 h, 12/12 h and 8/16 h) to treat heavily polluted river water. The results showed that higher ammonium and phosphorus removals were achieved with BFs filled with ceramsite (95-97% and 76-77%) and lava rock (87-92% and 84-94%), while fibrous carrier-packed BFs obtained better total nitrogen removal (37-44%). Moreover, the F/D time ratio of 16/8 h was slightly preferable for pollutant removal. High-throughput sequencing analysis illustrated that the relative abundance of potential denitrifiers that developed on organic media was much higher than those on inorganic substrates. The results indicated that the combination of inorganic materials and fibrous carriers as substrates could be an effective strategy for enhancing overall pollutant removal in BFs.

Ion exchange nutrient recovery from anaerobic membrane bioreactor permeate.

Nutrient recovery from municipal wastewater was evaluated using anion exchange media loaded with hydrated ferric oxide (HFO) and copper (Cu2+ ) (Dow-HFO-Cu resin) to selectively capture phosphate, followed by clinoptilolite for ammonium removal and recovery. Nutrients were concentrated in the regenerants and recovered as precipitated struvite. Media exchange capacity after multiple ion exchange cycles was determined using permeate from an anaerobic membrane bioreactor (AnMBR) treating synthetic or actual municipal wastewater from a full-scale water reclamation facility. Regeneration through five ion exchange cycles using relatively low concentration regenerant solution (2% NaCl and 0.5% NaOH) resulted in the highest phosphate exchange capacity and phosphate recovery. This regenerant also provided the most consistent ammonium recovery. Column tests treating AnMBR permeate were performed over five ion exchange cycles; Dow-HFO-Cu resin exchange capacities ranged from 1.6 to 2.8 mg PO4 -P/g dry media. A maximum of 94% of the removed phosphate was recovered during regeneration. The rate and extent of regeneration was insensitive to regenerant salt concentrations in the range investigated. Precipitation using a mixture of the spent regeneration brines from the Dow-HFO-Cu resin and clinoptilolite columns produced low molar ratios of Mg:NH4 :PO4 , suggesting that the recovered product was not pure struvite. PRACTITIONER POINTS: Ion exchange-precipitation for the removal and recovery of PO 4 3 - and NH4 + from AnMBR permeate is a promising technology. 2% NaCl + 0.5% NaOH regeneration solution provided the most consistent exchange performance for both phosphate and ammonium recovery. Regenerated Dow-HFO-Cu resin exchange capacity was consistently less than the virgin resin, likely due to copper leaching during regeneration. Molar ratios in the precipitates suggested that the precipitated material was not pure struvite.

Effects of external recirculation on a two-stage mainstream anaerobic-anammox treatment system.

Nitritation-anammox treatment can be a potentially energy- and resource-efficient technology for treating mainstream wastewater. However, the issue of nitrate residue from anammox treatment remains to be addressed. Herein, external recirculation of the anammox effluent to a hybrid anaerobic reactor (HAR), which was also to provide a continuous flow with low COD/N for the nitritation-anammox reactor, was employed to decrease the residue compounds. The recirculation ratio of 50% was observed to be the optimal to achieve the best overall performance with potential savings in energy demand. Specifically, in the operation scenario of R = 50%, the highest COD removal of ~90% by the HAR was achieved. Meanwhile, the lowest COD/NH4 + -N ratio of ~2.0 in the HAR effluent ensured the lowest observed NO3 - -N/NH4 + -N ratio of ~14% in the nitritation-anammox reactor. These results have demonstrated the feasibility of applying external recirculation for nitrate residue removal via denitrification in the anaerobic pretreatment stage. PRACTITIONER POINTS: Nitritation-anammox treatment is an attractive method for mainstream wastewater treatment. Nitrate residue from anammox processes contributes to total nitrogen in the final effluent. Recirculation of anammox effluent to an anaerobic reactor can decrease nitrate residue. A recirculation ratio of 50% results in a low COD/NH4 + ratio of 2 that benefits the subsequent anammox.

Arsenite removal from groundwater by iron-manganese oxides filter media: Behavior and mechanism.

Arsenic, a common contaminant in groundwater environments, usually coexists with other contaminants, for example, ammonium, iron, and manganese. In our previous studies, an iron-manganese (Fe-Mn) oxides filter media was developed for catalytic oxidation removal of ammonium, iron, and manganese. In this study, batch oxidation/adsorption kinetic experiments revealed that the filter media could easily oxidize arsenite (As(III)) to arsenate (As(V)). And the sorption kinetics was found to follow the pseudo-second-order kinetic model. X-ray powder diffraction (XRD) and Fourier transform infrared spectra (FTIR) along with X-ray photoelectron spectroscopy (XPS) were used to analyze the surface change in the Fe-Mn oxides. Based on sorption and spectroscopic measurements, the mechanism of As(III) removal by the Fe-Mn oxides filter media was found to be an oxidation coupled with sorption approach. As(III) in the aqueous solution was firstly oxidized to As(V) on the surfaces of the Fe-Mn oxides filter media. Then the converted As(V) was attracted to the Fe-Mn oxides filter media surfaces and bounded with the active sites (-OH groups), through weak intermolecular H-bondings. Our results indicated that the novel Fe-Mn oxides filter media could be applied for the simultaneous removal of ammonium, iron, manganese, and As(III) in drinking water treatment and environmental remediation. PRACTITIONER POINTS: A novel iron-manganese oxides filter for efficient As(III) removal was established. The exhausted filter media could be easily regenerated by NaHCO3 solution. Mn(III) related to surface lattice oxygen species was responsible for As(III) oxidation. The oxidation and adsorption processes were involved in As(III) removal. The filter media could be successfully applied to simultaneous removal of ammonium, manganese, iron, and arsenic.

Combination of heterotrophic nitrifying bacterium and duckweed (Lemna gibba L.) enhances ammonium nitrogen removal efficiency in aquaculture water via mutual growth promotion.

We created a combined system using duckweed and bacteria to enhance the efficiency of ammonium nitrogen (NH4+-N) and total nitrogen (TN) removal from aquaculture wastewater. Heterotrophic nitrifying bacterium was isolated from a sediment sample at an intensive land-based aquaculture farm. It was identified as Acinetobacter sp. strain A6 based on 16S rRNA gene sequence (accession number MF767879). The NH4+-N removal efficiency of the strain and duckweed in culture media and sampled aquaculture wastewater at 15°C was over 99% without any accumulation of nitrite or nitrate. This was significantly higher than strain A6 or duckweed alone. Interestingly, the presence of NO3- increased NH4+-N removal rate by 35.17%. Strain A6 and duckweed had mutual growth promoting-effects despite the presence of heavy metals and antibiotics stresses. In addition, strain A6 colonized abundantly and possibly formed biofilms in the inner leaves of duckweed, and possessed indoleacetic acid (IAA)- and siderophore-producing characteristics. The mutual growth promotion between strain A6 and duckweed may be the reason for their synergistic action of N removal.

Ammonium removal characteristics of an acid-resistant bacterium Acinetobacter sp. JR1 from pharmaceutical wastewater capable of heterotrophic nitrification-aerobic denitrification.

A new acid-resistant bacterium Acinetobacter sp. JR1 was isolated, and its feasibility in nitrogen removal was investigated under acidic condition. Results show that JR1 indicated excellent ammonium and nitrate removal abilities with no accumulation of intermediates, and the maximum ammonium and nitrate removal efficiencies were 98.5% and 91.1%, respectively. Further experiments demonstrated that JR1 preferred to use ammonium with ammonium and nitrate as the mixed N-sources. For JR1, ammonium was assimilated directly as nutrients into cells and also converted into N2 through heterotrophic nitrification-aerobic denitrification. Under acidic condition, JR1 performed comparable nitrogen removal abilities to other strains under neutral or weak alkaline environment, and the efficient removal of ammonium occurred at pH 4.5-10, C/N 12-24, 20-40 °C, DO ≥4.72 mg/L, 0-1.5% of salinity, 10 mg/L Zn2+ or 20 mg/L Mn2+. All these make JR1 a promising candidate for treating acidic wastewater containing nitrogen.

Characteristics of heterotrophic nitrification and aerobic denitrification bacterium Acinetobacter sp. T1 and its application for pig farm wastewater treatment.

A novel heterotrophic bacterium was isolated from activated sludge of a pig farm wastewater treatment plant and identified as Acinetobacter sp. T1. It exhibited efficient heterotrophic nitrification and aerobic denitrification capability to utilize ammonium, nitrate or nitrite as the sole nitrogen source, and their removal rates were 12.08, 5.53 and 1.69 mg/L/h, respectively. Furthermore, the optimal conditions for the heterotrophic nitrification process were sodium citrate as the carbon source, C/N mass ratio of 10, pH of 8.5 and dissolved oxygen (DO) concentration of 5.1 mg/L. Only trace amounts of nitrate and nitrite were observed during the process. When the aerobic tank of the A2O process of a pig farm wastewater treatment plant was inoculated with traditional activated sludge, the average removals of COD, NH4+- N and TN in the effluent were 30%, 15% and 16%, respectively, which was much lower than that of inoculated with strain T1, the increase was statistically significant, indicating a great potential of strain T1 for full-scale applications.

Adsorption characteristics of ammonium ion onto hydrous biochars in dilute aqueous solutions.

This research aims at studying the characteristics of ammonium adsorption onto hydrous bamboo biochar. Results showed that pH played the most important role in ammonium adsorption. High ionic strength enhanced the ammonium adsorption capacity of bamboo biochar. Ammonium adsorption was exothermic and spontaneous. FTIR results showed shift, disappearance, or appearance of specific functional groups on the bamboo biochar surface. Surface precipitation and complex formation contributed to the adsorption of ammonium onto hydrous bamboo biochar. Biochar can be an effective adsorbate for ammonium removal from water. Additionally, the formation of nitrogen containing precipitates on the biochar surface, potentially, leads to the in-situ synthesis of slow-release fertilizer.

The simultaneous removal of ammonium and manganese from surface water by MeOx: Side effect of ammonium presence on manganese removal.

Manganese and ammonium pollution in surface water sources has become a serious issue. In this study, a pilot-scale filtration system was used to investigate the effect of ammonium on manganese removal during the simultaneous removal of ammonium and manganese from surface water using a manganese co-oxide filter film (MeOx). The results showed that the manganese removal efficiency of MeOx in the absence of ammonium was high and stable, and the removal efficiency could reach 70% even at 5.5 °C. When the influent ammonium concentration was lower than 0.7 mg/L, ammonium and manganese could be removed simultaneously. However, at an ammonium concentration of 1.5 mg/L, the manganese removal efficiency of the filter gradually decreased with time (from 96% to 46.20%). Nevertheless, there was no impact of manganese on ammonium removal. The mechanism by which ammonium negatively affected manganese removal was investigated, demonstrating that ammonium affected manganese removal mainly through two possible mechanisms. On one hand, the decreased pH caused by ammonium oxidation was unfavorable for the oxidation of manganese by MeOx; on the other hand, the presence of ammonium slowed the growth of new MeOx and retarded the increase in the specific surface area of the MeOx-coated sand, and induced changes in the morphology and crystal structure of MeOx. Consequently, the manganese removal efficiency of the filter decreased when ammonium was present in the inlet water.

Investigating the effect of copper and magnesium ions on nitrogen removal capacity of pure cultures by modified non-competitive inhibition model.

Copper, a common heavy metal, may be beneficial for or poisonous to microbial activity. The objective of this study was to determine the effect of different copper ion concentrations on the nitrogen removal performance of Arthrobacter arilaitensis strain Y-10 and Pseudomonas taiwanensis strain J488. The non-competitive inhibition model was employed to evaluate the 50% inhibition concentrations (IC50 values) of copper ions toward the pure strains. In the absence of magnesium ions, a low concentration of copper (0.1 mg/L) significantly enhanced the ammonium removal ability of strain Y-10 and its removal efficiency increased by 10.88% compared with the control treatment. Copper ranging from 0 to 0.1 mg/L had no significant effect on the ammonium removal capacity of strain J488. After adding 9.90 mg/L of magnesium to the basal medium, the effects of copper on nitrification of ammonium or denitrification of nitrate or nitrite were also assessed. In these conditions, 0.25 mg/L copper ions could strongly inhibit the ammonium, nitrate and nitrite removal activities for strain Y-10. For strain J488, no clear deterioration in ammonium removal efficiency was observed at copper ion concentrations below 0.5 mg/L, but 0.25 mg/L copper ions significantly inhibited nitrate and nitrite removal efficiencies, which were only 45.88% and 6.35%, respectively. The IC50 values of copper ions for nitrate and nitrite removal by strain Y-10 were 0.195 and 0.090 mg/L respectively; for strain J488, the IC50 values were 0.175 and 0.196 mg/L. The magnesium ions could improve the cell growth, nitrogen removal efficiency and copper ion resistance of bacteria.

Treatment of Sewage Using a Constructed Soil Rapid Infiltration System Combined with Pre-Denitrification.

The activated sludge process of the anaerobic/oxic (A/O) process has a good denitrification performance because it can make full use of the carbon source in the original sewage, and the denitrification can provide alkalinity for aerobic nitrification. The traditional constructed soil rapid infiltration (CSRI) system, on the other hand, has a poor nitrogen removal effect. Dividing the traditional CSRI system into two sections, one performs denitrification as an anoxic section, while the other performs nitrification as an aerobic section and is placed after the anoxic section. The nitrification liquid of the effluent from the aerobic section is mixed with the original wastewater and enters the anoxic section for denitrification. We expected that this would be improved by combining CSRI with a pre-denitrification step that would make full use of the carbon source in the original sewage. In a small-scale experimental model, the removal efficiencies of nitrogen, in the form of ammonium, nitrate, and total nitrogen (TN), as well as chemical oxygen demand (COD), were determined. The hydraulic load was varied, while the backflow reflux capacity was kept constant, to determine the effect on the pre-denitrification process. An average removal rate of 95.4% for NH4⁺-N and 96% for COD could be obtained when a hydraulic load of 80 cm³(cm²·d)-1 and a reflux ratio of 75% were applied. Under these conditions, the average removal rate of TN was 77.4%, which is much higher than what can be typically achieved with conventional CSRI systems.