Molar Ratio Of Ammonia Research Articles

Microwave-Assisted Hydrothermal Synthesis of Ceric-Ammonium Phosphates (NH4)2Ce(PO4)2⋅H2O and NH4Ce2(PO4)3

The possibility of preparation of crystalline double cerium(IV) phosphates (NH4)2Ce(PO4)2⋅H2O and NH4Ce2(PO4)3 under the conditions of microwave-assisted hydrothermal synthesis has been analyzed. It has been shown that these phosphates in a single-phase state can be obtained in the temperature range of 130–190°С with a synthesis duration of ≥5 min, while the phase composition of the synthesis products is determined by the molar ratio of ammonia and phosphoric acid in the reaction mixture. Short-term (5 min) low-temperature (130°С) hydrothermal synthesis under microwave heating leads to the preparation of (NH4)2Ce(PO4)2⋅H2O and NH4Ce2(PO4)3 with a particle size of ~70 and ~200 nm, respectively. At higher temperatures and treatment times (190°C and 24 h), the particle size of these phases increases to ~200 and ~500 nm, respectively. For the first time, the value of the optical band gap for (NH4)2Ce(PO4)2⋅H2O was determined to be 2.8 and 3.1 eV for indirect and direct transitions, respectively.

Trichloramine and Hydroxyl Radical Contributions to Dichloroacetonitrile Formation Following Breakpoint Chlorination.

Breakpoint chlorination is applied to remove ammonia in water treatment. Trichloramine (NCl3) and transient reactive species can be present, but how they affect the formation of nitrogenous disinfection byproducts is unknown. In this study, the dichloroacetonitrile (DCAN) formation mechanisms and pathways involved during breakpoint chlorination (i.e., free chlorine to ammonia molar ratio ≥2.0) were investigated. DCAN formation during breakpoint chlorination of natural organic matter (NOM) isolates was 14.3-20.3 μg/L, which was 2-10 times that in chlorination without ammonia at similar free chlorine residual conditions (2.1-2.9 mg/L as Cl2). The probe tests and electron paramagnetic resonance spectra supported the presence of •OH, •NO, and NCl3 besides free chlorine in breakpoint chlorination. 15N-labeled ammonium-N tests indicated the incorporation of ammonium-N in DCAN formation though ammonia was eliminated during breakpoint chlorination. Aromatic non-nitrogenous moieties, such as phenols (i.e., none DCAN precursors in the free-chlorine-only system), became DCAN precursors during breakpoint chlorination. The reactions involved in reactive nitrogen species, such as •NO/•NO2 and NCl3, led to additional nitrogen sources in DCAN formation, accounting for 36-84% of total nitrogen sources in DCAN formation from NOM isolates and real water samples. Scavenging •OH by tert-butanol reduced DCAN formation by 40-56%, indicating an important role of •OH in transforming DCAN precursors. This study improves the understanding of breakpoint chlorination chemistry.

Facile synthesis of superparamagnetic thiamine/Fe3O4 with enhanced adsorptivity toward divalent copper ions

The development of environmentally friendly adsorbents has been extensively carried out to overcome the detrimental effects of heavy metal accumulation, which has persistently become a global ecological problem. In pursuit of generating eco-friendly adsorbents, a green method for synthesizing thiamine functionalized-Fe3O4 (FT) was developed in this study. A one-step chemical oxidation and functionalization technique was used to prepare FT using the ammonia-containing solvent. A molar ratio of ammonia:Fe:thiamine of 15:1:1 was shown to produce FT15 with high yield, adsorptivity, and purity. XRD, XPS, FTIR, SEM, and SQUID characterization of FT15 revealed the formation of superparamagnetic thiamine functionalized Fe3O4 in their particles. This superparamagneticity facilitates the easy recovery of FT15 particles from the waste-containing solution by using an external magnetic force. The batch adsorption of Cu(II) onto FT15 showed the best fit with the Sips adsorption isotherm model with a maximum adsorption capacity of 426.076 mg g−1, which is 5.69-fold higher capacity than the control unmodified Fe3O4 (F15). After five adsorption-desorption cycles, the FT15 can maintain up to 1.95-fold higher capacity than the freshly synthesized F15. Observation on the physicochemical properties of the post-adsorption materials showed the contribution of an amine group, pyrimidine ring, and the thiazolium group of thiamine in boosting its adsorption capacity. This study provides important findings to advance the adsorptivity of magnetic adsorbents with promising recoverability from aqueous solution by employing naturally available and environmentally friendly compounds such as thiamine.

Microporous and Micro-meso-macroporous Y Zeolites in the Synthesis of 2-Methyl-5-ethylpyridine

The study investigates the catalytic properties of microporous (H–Y) and micro-meso-macroporous (H–Y-mmm) FAU-type zeolites in the synthesis of 2-methyl-5-ethylpyridine (MEP) by the reaction of acetaldehyde with ammonia. At 150°C, an acetaldehyde to ammonia molar ratio of 1 : 3, and a catalyst content of 10 wt %, a MEP yield of 58% (0.95H–Y) and 63% (0.95H–Y-mmm) was achieved with a MEP selectivity of 91 and 93%, respectively. The examination of the catalyst stability revealed that hierarchical H–Y-mmm zeolites ensure a 100% MEP selectivity during 4–5 cycles with a slight decline in the catalytic activity, while H–Y zeolites are active during the first cycle only.

Selective Removal of Zinc from BOF Sludge by Leaching with Mixtures of Ammonia and Ammonium Carbonate

The zinc content of basic oxygen furnace (BOF) sludges is too high for direct recycling into the blast furnace via the sinter plant, as excessive zinc concentrations are detrimental for the refractory lining of the blast furnace. However, by partial and selective removal of zinc from the BOF sludge, the residual sludge can be used as a secondary iron resource in the blast furnace. In this paper, BOF sludge was leached with aqueous ammonia, aqueous solutions of ammonium salts (chloride, carbonate, and sulfate), and aqueous mixtures of ammonia and ammonium salt. The mixtures of ammonia and ammonium salt could leach more zinc with respect to either the aqueous ammonia or the aqueous ammonium salt solution. The ammonia–ammonium carbonate (AAC) mixture was selected as the most suitable lixiviant due to the high zinc leaching efficiency in combination with a high selectivity towards iron; furthermore, this combination does not introduce unwanted chloride or sulfate impurities in the residue. The leaching process was optimized in terms of the liquid-to-solid ratio, total ammonia concentration, ammonium:ammonia molar ratio, temperature, and leaching time. The co-dissolved iron was precipitated as a hydroxide after oxidation of ferrous to ferric ions by an air stream, without co-precipitation of zinc, while the dissolved zinc could be easily recovered as zinc sulfide by precipitation with ammonium sulfide. The (almost) closed-loop process was successfully up-scaled from 10 mL to 1 L scale.Graphical

Numerical simulation of flame acceleration and deflagration-to-detonation transition in ammonia-hydrogen–oxygen mixtures

Flame propagation and Deflagration-to-Detonation Transition (DDT) in a two-dimensional obstructed channel filled with stoichiometric ammonia-hydrogen-oxygen mixtures are simulated with detailed chemistry. For mixtures of high ammonia molar ratio (α = 4:1 and 2:1), a hot spot with high temperature appears in the unreacted material, and then DDT is triggered by the reactivity gradient inside a pocket of unreacted material for α = 2:1. However, for α = 4:1, detonative initiation and failure alternatively occur. For mixtures with low ammonia ratios, the DDT is triggered when the flame interacts with the reflected shock waves from either the bottom wall or the obstacle. Furthermore, as the concentration of ammonia decreases, the flame acceleration, the appearance of noticeable shocks and the deflagration-to-detonation transition occur at an earlier instant, and the ultimate propagation velocities of detonation wave increase. The flame cannot propagate stably in premixed ammonia-oxygen mixture without hydrogen with the ignition mode adopted in this study.

Ammonia/chlorine synergistic oxidation process applied to the removal of N, N-diethyl-3-toluamide

The ammonia/chlorination process is important for the treatment of ammonia-rich water, such as the ammonia removal, disinfection strategies, and disinfection byproducts controlling. Recently, the simultaneous removal of recalcitrant micropollutants during ammonia/chlorination has attracted attention. In this study, ammonia/chlorination was employed to remove the chlorine-resistant micropollutant N, N-diethyl-3-toluamide (DEET). Using the optimal chlorine to ammonia molar ratio (Cl/N) of 1.6, nearly 60% of DEET was removed by ammonia/chlorination within 15 min, while chlorination or chloramination alone showed minimal DEET removal. The synergistic effect obtained from the combination of ammonia and chlorine is attributed to reactive species generated from the decomposition of chloramine over Cl/N 1.0 to 1.6, being proved by the significantly inhibited performance (almost 95%) by t-butanol. The aqueous matrix was found to affect the results, and acidic/basic solutions reduced DEET removal by 70% to 79%, while the presence of natural organic matter (NOM 6 mg-C/L) suppressed the removal by 33%. The quantity of DEET removed per mole of decomposed chloramine (α) is proposed as a measure of the efficiency of this synergistic oxidation process, and the α values were determined to be 0.034, 0.022 and 0.010 in the synthetic solution, a solution containing 6 mg-C/L NOM and a wastewater effluent, respectively. Trials using high resolution quadrupole time of flight mass spectrometry and 15N isotope labelling, allowed the transformation products to be identified, and hydroxylation was found to be the dominant DEET degradation pathway.

Degradation of lipid regulators by the UV/chlorine process: Radical mechanisms, chlorine oxide radical (ClO•)-mediated transformation pathways and toxicity changes

Degradation of three lipid regulators, i.e., gemfibrozil, bezafibrate and clofibric acid, by a UV/chlorine treatment was systematically investigated. The chlorine oxide radical (ClO•) played an important role in the degradation of gemfibrozil and bezafibrate with second-order rate constants of 4.2 (±0.3) × 108 M−1 s−1 and 3.6 (±0.1) × 107 M−1 s−1, respectively, whereas UV photolysis and the hydroxyl radical (HO•) mainly contributed to the degradation of clofibric acid. The first-order rate constants (k′) for the degradation of gemfibrozil and bezafibrate increased linearly with increasing chlorine dosage, primarily due to the linear increase in the ClO• concentration. The k′ values for gemfibrozil, bezafibrate, and clofibric acid degradation decreased with increasing pH from 5.0 to 8.4; however, the contribution of the reactive chlorine species (RCS) increased. Degradation of gemfibrozil and bezafibrate was enhanced in the presence of Br−, whereas it was inhibited in the presence of natural organic matter (NOM). The presence of ammonia at a chlorine: ammonia molar ratio of 1:1 resulted in decreases in the k′ values for gemfibrozil and bezafibrate of 69.7% and 7%, respectively, but led to an increase in that for clofibric acid of 61.8%. Degradation of gemfibrozil by ClO• was initiated by hydroxylation and chlorine substitution on the benzene ring. Then, subsequent hydroxylation, bond cleavage and chlorination reactions led to the formation of more stable products. Three chlorinated intermediates were identified during ClO• oxidation process. Formation of the chlorinated disinfection by-products chloral hydrate and 1,1,1-trichloropropanone was enhanced relative to that of other by-products. The acute toxicity of gemfibrozil to Vibrio fischeri increased significantly when subjected to direct UV photolysis, whereas it decreased when oxidized by ClO•. This study is the first to report the transformation pathway of a micropollutant by ClO•.

Achieving high-level nitrogen removal in mainstream by coupling anammox with denitrifying anaerobic methane oxidation in a membrane biofilm reactor.

To achieve energy neutral wastewater treatment, mainstream anaerobic ammonium oxidation (anammox) has attracted extensive attention in the past decade. However, the relatively high effluent nitrogen concentration (>10 mg N L-1) remains a significant barrier hindering its practical implementation. A novel technology integrating the anammox and denitrifying anaerobic methane oxidation (DAMO) reactions in a membrane biofilm reactor (MBfR) was developed in this study to enhance the mainstream anammox process. With the hydraulic retention time (HRT) progressively decreased from 12 to 4 h, the total nitrogen (TN) removal rate increased stepwise from 0.09 to 0.28 kg N m-3 d-1, with an effluent TN concentration below 3.0 mg N L-1 achieved. Mass balance analysis showed that 30-60% of the nitrate produced by the anammox reaction was reduced back to nitrite by DAMO archaea, and the anammox and DAMO bacteria were jointly responsible for nitrite removal with contributions of >90% and <10%, respectively. Additionally, the established MBfR was robust and achieved consistently high effluent quality with >90% TN removal when the influent nitrite to ammonium molar ratio varied in the range of 1.17-1.55. Fluorescence in situ hybridization (FISH) and 16S rRNA gene sequencing indicated that anammox bacteria, DAMO bacteria and DAMO archaea jointly dominated the biofilm, and were likely the key contributors to nitrogen removal. This is the first study that a high nitrogen removal rate (>0.2 kg N m-3 d-1) and satisfactory effluent quality (∼3 mg TN L-1) were achieved simultaneously by integrating anammox and DAMO reactions in mainstream wastewater treatment.

Stability of partial nitritation in a sequencing batch reactor fed with high ammonium strength old urban landfill leachate

The aim of this study is to investigate the stability of partial nitritation in a lab-scale sequencing batch reactor (PN-SBR) fed with high ammonium strength old municipal landfill leachate without pH adjustment, bicarbonate addition and low dissolved oxygen control. Long sludge retention of over 120 days was applied for the PN-SBR. The PN-SBR, which run over 250 days used the old urban landfill leachate containing 3096 mg NH₄⁺-N l⁻1, 12960 mg HCO₃ l⁻1, and influent HCO₃⁻:NH₄⁺ molar ratio of 1.06. After 75 days of operation, the partial nitritation achieved stability when the effluent nitrite to ammonium molar ratio obtained in the range of 1.0–1.32, which were suitable for feeding to an anammox reactor. The effluent NO₃⁻-N concentration was always below 20 mg N l⁻1. The maximum FA concentration reached 506 mg NH3-N l−1 at hour 26th during the cycle of 73 h. Even though old land fill leachate mainly contained refractory COD, COD removal efficiency achieved about 11%. The OUR tests show that the maximum growth rate μmax, Ko, Ks and yield coefficient YX/N of AOB were 0.12 day−1, 1.35 mg O2 l−1, 53 mg NH4+-N l−1 and 0.26 mgVSS mg−1 NH4+-N, respectively.

Recovery of Cu(II) by chemical reduction using sodium dithionite: effect of pH and ligands.

Wastewaters containing Cu(II) and ligands are ubiquitous in various industrial sectors, and efficacy of copper removal processes, especially precipitation, is greatly compromised by ligands. Chemical reduction, being commonly employed for production of metal nanoparticles, is also effective for metal removal. Adjustment of pH and addition of ligands are important to control the particle size in metallic nanoparticle production. Exploiting the fact that ligands and metals coexist in many wastewaters, chemical reduction was employed to treat ligand-containing wastewater in this study. The experimental result shows that depending on pH, type of ligands, and copper:ligand molar ratio, copper could be removed by either the reduction or precipitation mechanism. Almost complete copper removal could be achieved by the reduction mechanism under optimal condition for solutions containing either EDTA (ethylenediaminetetraacetic acid) or citrate ligands. For solutions containing ammonia, depending on pH and Cu:ammonia molar ratio, copper was removed by both precipitation and reduction mechanisms. At pH of 9.0, formation of nano-sized particles, which readily pass through a 0.45 μm filter used for sample pretreatment before residual copper analysis, results in the lowest copper removal efficiency. Both cuprous oxide and metallic copper are identified in the solids produced, and the possible explanations are provided.

Synthesis of 3-picoline from acrolein and ammonia through a liquid-phase reaction pathway using SO42−/ZrO2-FeZSM-5 as catalyst

Abstract The synthesis of 3-picoline from the liquid-phase condensation of acrolein and ammonium acetate under atmospheric pressure was conducted by first dissolving ammonium acetate in a C 2 C 6 carboxyl acid medium in the presence of solid acid catalyst, and then, feeding gradually a solution of acrolein in a C 2 C 6 carboxyl acid solvent. It was found that the employment of acetic acid, among various carboxyl acids tested, as both the reaction medium and solvent of acrolein, was most favorable, due to the obvious promotion to the formation of 3-picolind in liquid phase and retarding to the side reaction of acrolein polymerization in gas phase. The SO 4 2− /ZrO 2 -FeZSM-5 catalyst possesses the largest acid acidity and thus exhibited the largest yield of 3-picoline, among various solid acid catalysts. By employing the SO 4 2− /ZrO 2 -FeZSM-5 catalyst and acetic acid as both the reaction medium and solvent of acrolein, the influencing factors, including reaction temperature, molar ratio of ammonium acetate/acrolein/acetic acid, concentration and feeding rate of acrolein solution as well as usage of catalyst, were systematically investigated. The results indicated that an as high as 60% yield of 3-picoline could be achieved from a batch with molar ratio composition acrolein/ammonium acetate/acetic acid = 0.025/0.125/1.8, under the conditions of reaction temperature = 130 °C, concentration of acrolein solution = 14 wt%, feeding speed of acrolein solution = 12 mL/h and catalyst usage = 0.7 g/g (acrolein).

Cationic cellulose and its interaction with chondroitin sulfate. Rheological properties of the polyelectrolyte complex

This work describes the polyelectrolyte complexation between polyquaternium cellulose (PQ-10) and chondroitin 4-sulfate (C-4S), an important structural component of cartilages. The complex shows different behaviors with increasing concentrations of the polyanion. Initially, PQ-10/C-4S interaction forms a soluble, translucent hydrogel that reaches maximum viscosity at a sulfate carboxylate/quaternary ammonium molar ratio lower than 1. After that, the complex begins to aggregate until complete precipitation, and finally, at higher concentrations of C-4S, the resuspension of the aggregate is observed. Further addition of PQ-10 initiates new cycles of precipitation/resuspension for at least seven times.C-4S contains sulfates and carboxylates able to interact with quaternary ammonium of PQ-10. The results of a comparative study with polymers containing only carboxylate or sulfate to evaluate the influence of each group suggest that the phenomena observed involved, essentially, carboxylate groups.

Optimization of partial nitritation in a continuous flow internal loop airlift reactor

In the present study, the performance of the partial nitritation (PN) process in a continuous flow internal loop airlift reactor was optimized by applying the response surface method (RSM). The purpose of this work was to find the optimal combination of influent ammonium (NH4(+)-Ninf), dissolved oxygen (DO) and the alkalinity/ammonium ratio (Alk/NH4(+)-N) with respect to the effluent nitrite to ammonium molar ratio and nitrite accumulation ratio. Based on the RSM results, the reduced cubic model and the quadratic model developed for the responses indicated that the optimal conditions were a DO content of 1.1-2.1 mg L(-1), an Alk/NH4(+)-N ratio of 3.30-5.69 and an NH4(+)-Ninf content of 608-1039 mg L(-1). The results of confirmation trials were close to the predictions of the developed models. Furthermore, three types of alkali were comparatively explored for use in the PN process, and bicarbonate was found to be the best alkalinity source.

The effect of sulfide inhibition on the ANAMMOX process

The feasibility of anaerobic ammonium oxidation (ANAMMOX) process to treat wastewaters containing sulfide was studied in this work. Serum bottles were used as experimental containers in batch tests to analyze the short-term response of the ANAMMOX process under sulfide stress. The IC50 of sulfide-S for ANAMMOX biomass was substrates-dependent and was calculated to be 264 mg L−1 at an initial total nitrogen level of 200 mg L−1 (molar ratio of ammonium and nitrite was 1:1). The long-term effects and the performance recovery under sulfide stress were continuously monitored and evaluated in an upflow anaerobic sludge blanket reactor. The performance of the ANAMMOX system was halved at an sulfide-S level of 32 mg L−1 within 13 days; however, the nitrogen removal rate (NRR) decreased by only 17.2% within 18 days at an sulfide-S concentration of 40 mg L−1 after long-time acclimatization of sludge in the presence of sulfide. The ANAMMOX performance recovered under sulfide-S level of 8 mg L−1 with a steady NRR increasing speed, linear relationship between the NRR and operation time. The synchronic reduce in the specific ANAMMOX activity and the biomass extended the apparent doubling time of the nitrogen removal capacity and decreased biomass growth rate.

The influence of fog and airmass history on aerosol optical, physical and chemical properties at Pt. Reyes National Seashore

Abstract This paper presents an analysis of the aerosol chemical composition, optical properties and size distributions for a range of conditions encountered during a field measurement campaign conducted between July 7–29, 2005 at Point Reyes National Seashore, north of San Francisco, CA. The fractional mass loading derived from hourly measurements of an Aerodyne Mass Spectrometer (AMS) during this period are compared with filter-pack measurements from the Pt. Reyes IMPROVE station with good agreement found between the two if it assumed that chloride is primarily from large sea-salt particles (not measured by the AMS). During the first half of the campaign (July 7–17), conditions at the site were largely maritime while flow during the second half of the campaigns (July 18–29) was influenced by a thermal trough that added a cyclonic twist to the incoming marine air, bringing it from the south with a more extensive over-land trajectory. Neither flow regime was associated with air coming from the San Francisco Bay area to the south. The AMS measurements are partitioned into clear and foggy conditions which are then used to calculate the equivalent molar ratio of ammonium to the sum of sulfate, nitrate and chloride. Ratios calculated from measurements made before the onset of the thermal trough on July 18th were associated with acidic or near-neutral particles. Measurements made after July 18th yield ratios that appear to have excess ammonium. Model calculations of the equilibrium gas-phase mixing ratio of NH 3 suggest very high values which we attribute to agricultural practices within the park. Reported as an incidental finding is evidence for the cloud droplet activation of large particles (D P > 0.2 μm) with a corresponding reduction in the single scattering albedo of the non-activated particles, followed by a return in the particle size spectrum to the pre-fog conditions immediately afterwards.

The effect of urban landfill leachate characteristics on the coexistence of anammox bacteria and heterotrophic denitrifiers

Heterotrophic denitrification coexists with the anammox process contributing to N removal owing to the biodegradable organic matter supply from urban landfill leachate and the decay of microorganisms. Both biomasses consumed nitrite increasing the nitrite requirements of the system. The aim of this paper is the study of the causes which induce the system to decrease nitrogen removal efficiency. In this study, urban landfill leachate has been treated in an anammox Sequencing Batch Reactor (SBR) for 360 days. The anammox reactor treated on average 0.24 kgN m(-3) d(-1) obtaining nitrogen removal efficiencies up to 89%. The results demonstrated that i) a suitable influent nitrite to ammonium molar ratio is a crucial factor to avoid troubles in the anammox reactor performance; ii) an excess of nitrite implied nitrite accumulation in the reactor; iii) a lower nitrite supply than the necessary for the system could force a loss of specific anammox activity due to nitrite competition with denitrifiers. These results pointed out the importance of the previous partial-nitritation process control in order to obtain a correct influent nitrite to ammonium molar ratio for the anammox reactor. In addition, sudden variation of the leachate characteristics must be avoided.

Ammonium nitrogen removal from coking wastewater by chemical precipitation recycle technology

Ammonium nitrogen removal from wastewater has been of considerable concern for several decades. In the present research, we examined chemical precipitation recycle technology (CPRT) for ammonium nitrogen removal from coking wastewater. The pyrolysate resulting from magnesium ammonium phosphate (MAP) pyrogenation in sodium hydroxide (NaOH) solution was recycled for ammonium nitrogen removal from coking wastewater. The objective of this study was to investigate the conditions for MAP pyrogenation and to characterize of MAP pyrolysate for its feasibility in recycling. Furthermore, MAP pyrolysate was characterized by scanning electron microscope (FESEM), transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FTIR) as well as X-ray diffraction (XRD). The MAP pyrolysate could be produced at the optimal condition of a hydroxyl (OH −) to ammonium molar ratio of 2:1, a heating temperature of 110 °C, and a heating time of 3 h. Surface characterization analysis indicated that the main component of the pyrolysate was amorphous magnesium sodium phosphate (MgNaPO 4). The pyrolysate could be recycled as a magnesium and phosphate source at an optimum pH of 9.5. When the recycle times were increased, the ammonium nitrogen removal ratio gradually decreased if the pyrolysate was used without supplementation. When the recycle times were increased, the ammonium nitrogen removal efficiency was not decreased if the added pyrolysate was supplemented with MgCl 2·6H 2O plus Na 2HPO 4·12H 2O during treatment. A high ammonium nitrogen removal ratio was obtained by using pre-formed MAP as seeding material.

Long-term operation of a partial nitritation pilot plant treating leachate with extremely high ammonium concentration prior to an anammox process

The goal of this work was to demonstrate the feasibility of treating leachate with high ammonium concentrations using the SBR technology, as a preparative step for the treatment in an anammox reactor. The cycle was based on a step-feed strategy, alternating anoxic and aerobic conditions. Results of the study verified the viability of this process, treating an influent with concentration up to 5000 mg N– NH 4 + L −1. An effluent with about 1500–2000 mg N– NH 4 + L −1 and 2000–3000 mg N– NO 2 - L −1 was achieved, presenting a nitrite to ammonium molar ratio close to the 1.32 required by the anammox. Furthermore, taking advantage of the biodegradable organic matter, the operational strategy allowed denitrifying about 200 mg N– NO 2 - L −1. The extreme operational conditions during the long-term resulted on the selection of a sole AOB phylotype, identified by molecular techniques as Nitrosomonas sp. IWT514.

Enhanced Nitrogenous Disinfection ByProduct Formation near the Breakpoint: Implications for Nitrification Control

Increasing the chlorine to ammonia molar ratio and breakpoint chlorination are two control strategies practiced by drinking water treatment utilities experiencing nitrification during chloramination. The first strategy will increase dichloramine formation, which increases nitrosamine formation. Moreover, our results indicate that dichloramine is also an important factor for nitrile formation. Near the breakpoint, nitrosamine formation is over an order of magnitude higher than that observed during chloramination. We propose that there are two nitrosamine formation pathways active in the breakpoint chlorination region: (i) a relatively slow reaction of dichloramine with amine precursors in the presence of dissolved oxygen and (ii) a fast reaction involving reactive breakpoint chlorination intermediates. Lastly, in the presence of nitrite, if breakpoint chlorination is conducted to achieve a significant free chlorine residual, nitrosamines and nitramines will form through a reaction with nitrite and hypochlorite. However, nitrosamine formation will be much lower than when breakpoint chlorination is conducted with no significant free chlorine residual.