Enzymatic NH3-N determination: a specific method for the determination of ammonia in water and sediments

An enzymatic method for the determination of ammonia—nitrogen, not previously applied in water research, is described. The method is specific for NH₃-N, and the risk of hydrolysis of organic nitrogen compounds is very small, because of near neutral pH and low (room) temperature conditions. Differences between results of enzymatic NH₃-N determination and of a distillation method depended on the type of water. The method has been adapted for application in sediment research, where the exchangeable NH₃-N fraction is determined directly, without an extraction procedure. In comparison with this method, direct distillation of sediment samples gave an overestimation of the NH₃-N content of ± 40 per cent.     

Nitrogenous disinfection byproducts formation and nitrogen origin exploration during chloramination of nitrogenous organic compounds

Formation of nitrogenous disinfection by-products (N-DBPs) of cyanogen chloride (CNCl), dichloroacetonitrile (DCAN) and chloropicrin was evaluated during chloramination of several selected groups of nitrogenous organic (organic-N) compounds, including α-amino acids, amines, dipeptides, purines, and pyrimidines, The intermediates generated, reaction pathways, and nitrogen origin in N-DBPs were explored as well. CNCl was observed in chloramination of all tested organic-N compounds, with glycine giving the highest yields. DCAN was formed during chloramination of glutamic acid, cytosine, cysteine, and tryptophan. Chloramination of most organic-N compounds except for cysteine and glutamic acid generated chloropicrin. Aldehydes and nitriles were identified as the intermediates by negative mode electrospray ionization mass spectrometry during reactions of NH₂Cl and organic-N compounds. Labeled ¹⁵N-monochloramine (¹⁵NH₂Cl) techniques showed that nitrogen in N-DBPs may originate from both NH₂Cl and organic-N compounds and the nitrogen partition percentages vary as functions of reactants and pH.     

Source identification of nitrous oxide on autotrophic partial nitrification in a granular sludge reactor

Emission of nitrous oxide (N₂O) during biological wastewater treatment is of growing concern since N₂O is a major stratospheric ozone-depleting substance and an important greenhouse gas. The emission of N₂O from a lab-scale granular sequencing batch reactor (SBR) for partial nitrification (PN) treating synthetic wastewater without organic carbon was therefore determined in this study, because PN process is known to produce more N₂O than conventional nitrification processes. The average N₂O emission rate from the SBR was 0.32 ± 0.17 mg-N L⁻¹ h⁻¹, corresponding to the average emission of N₂O of 0.8 ± 0.4% of the incoming nitrogen load (1.5 ± 0.8% of the converted NH₄⁺). Analysis of dynamic concentration profiles during one cycle of the SBR operation demonstrated that N₂O concentration in off-gas was the highest just after starting aeration whereas N₂O concentration in effluent was gradually increased in the initial 40 min of the aeration period and was decreased thereafter. Isotopomer analysis was conducted to identify the main N₂O production pathway in the reactor during one cycle. The hydroxylamine (NH₂OH) oxidation pathway accounted for 65% of the total N₂O production in the initial phase during one cycle, whereas contribution of the NO₂⁻ reduction pathway to N₂O production was comparable with that of the NH₂OH oxidation pathway in the latter phase. In addition, spatial distributions of bacteria and their activities in single microbial granules taken from the reactor were determined with microsensors and by in situ hybridization. Partial nitrification occurred mainly in the oxic surface layer of the granules and ammonia-oxidizing bacteria were abundant in this layer. N₂O production was also found mainly in the oxic surface layer. Based on these results, although N₂O was produced mainly via NH₂OH oxidation pathway in the autotrophic partial nitrification reactor, N₂O production mechanisms were complex and could involve multiple N₂O production pathways.     

Rate constants of reactions of ozone with organic and inorganic compounds in water—III. Inorganic compounds and radicals

Second-order rate constants for reactions of ozone with 40 inorganic aqueous solutes are reported. Included are compounds of sulfur (e.g. H₂S, H₂SO₃, HOCH₂SO₃H), chlorine (e.g. Cl⁻, HOCl, NH₂Cl, HClO₂, ClO₂), bromine (e.g. Br⁻, HOBr), nitrogen (e.g. NH₃, NH₂OH, N₂O, HNO₂) and oxygen (e.g. H₂O₂), as well as free radicals (e.g. O₂⁻, OH^•). Most of these compounds exhibit an increase in rate constant with increasing pH corresponding to their degree of dissociation. Rate constants are based on ozone consumption rates measured by conventional batch-type or continuous-flow methods (10⁻³-10⁺⁶ M⁻¹ s⁻¹ range) and determinations of stoichiometric factors. Also listed are data determined by pulse-irradiation techniques using kinetic spectroscopy (10¹⁰ M⁻¹ s⁻¹ range). Additional literature data are reviewed for completeness. Results are discussed with respect to water treatment and environmental processes.     

An automated procedure for the determination of total Kjeldahl nitrogen

A procedure for the determination of total Kjeldahl nitrogen in surface fresh waters and organic wastes is described. Organic nitrogen compounds are converted to ammonium sulphate by a catalytic (red mercuric oxide) acid-sulphate digestion. The digest time is 3 h and allows for a maximum of 36 samples, 2 blanks and 2 standards to be processed simultaneously. There is no pH adjustment required following the digestion. Calibration curves covering the ranges (i) 0.5–100 μg NH₃---Nl⁻¹ and (ii) 10–1000 μg NH₃---Nl⁻¹ were linear within ±2%. The detection limit of the method is 0.5 μg TKNl⁻¹. The concentration range of TKN for which the method is suitable is 0.5 μg Nl⁻¹–40 mg Nl⁻¹. The method displayed a high tolerance to interferences from copper, iron, mercury and hardness. Digest procedure gave a high recovery and reproductibility over a wide range of nitrogen compounds tested.     

Evaluation of a portable bare-electrode amperometric analyzer for determining free chlorine in potable and swimming-pool waters

Chlorine in the forms of HOCl or ClO⁻ was determined rapidly and precisely in the range from 0.10 to 3.0 ppm chlorine, without titration, using a bare-electrode portable amperometric analyzer. The instrument was calibrated with a 1.00 ppm chlorine standard solution or an equivalent permanganate solution which is stable for at least 6 months. The detection limit was 0.10 ppm chlorine, and relative standard deviations (N = 10) were <6.0% in potable or swimming-pool waters containing 0.25, 1.00 and 2.50 ppm or 0.35, 1.40 and 2.70 ppm chlorine respectively. Bromine-, triiodide ion-, and Mn (VII)-generated signals were stoichiometrically equivalent to that of hypochlorite, but MnO₂ suspensions (1.5, 5.0 or 15 ppm) did not produce detectable amperometric signals.Analysis of solutions of hypochlorite with ammonium chloride or selected organic nitrogen compounds indicated that various N-chloro compounds may interfere. In the presence of N-chloroglycine (2.70 ppm chlorine) the amperometric signal was about 5% of that for the equivalent concentration of hypochlorite, but higher relative responses were obtained with NH₂Cl, NHCl₂ or NCl₃ (19, 42 and 70% at 2.60, 1.20 or 1.00 ppm chlorine respectively). Chlorinated urea (2.2 ppm N, 2.90 ppm chlorine), chlorinated bovine albumin (10 ppm albumin, 2.00 ppm chlorine) or monochloroisocyanurate (1.30 ppm chlorine) produced amperometric signals (76, <5 and 50% respectively) which are lower than those obtained by the N,N-diethyl-p-phenylenediamine (DPD) method (100, 12 and 92%).Twenty potable water samples were analyzed for free chlorine by the DPD and amperometric procedures. Statistical analysis showed no significant differences between the two sets of results (P < 0.1). Swimming-pool-water samples were also analyzed by the two methods in the field (22 samples) and in the laboratory (24 samples). In each set of results the mean free-chlorine value by the DPD procedure was significantly higher than that obtained amperometrically (P > 0.005). This discrepancy was associated with the probable presence of chlorinated urea, whose signal by amperometry is lower than that by the DPD method.The advantages of this simple procedure must be weighed against possible inaccurate results in the presence of NH₂Cl, NHCl₂ or NCl₃.     

Analyses and assessment of the spatial and temporal distribution of nitrogen compounds in surface waters

The temporal concentration variations and spatial distribution of nitrogen compounds (nitrate, nitrite, ammonium) in the natural surface waters of Stara Zagora Region, Bulgaria, over a period of 1 year were assessed in the present study. Nitrate‐nitrogen concentrations in all surface water samples, except for the December value – 21.8 mg/L in Zetyovo Reservoir, were within the permissible national quality standards. NO₂ ^–‐N could be classified as a priority pollutant of Chirpan and Zetyovo Reservoirs waters. The greatest extent of NH ₄ ⁺‐N pollution was registered in Chirpan Reservoir surface waters. The correlation study revealed appreciable mutual relationship only between NH₄ ⁺‐N and NO ₂ ^–‐N in the surface waters. The hierarchical cluster analysis (HCA) exhibited divergent apportionment of nitrogen compounds in the surface water bodies.     

Nitrous oxide emissions for early warning of biological nitrification failure in activated sludge

Experiments were carried out to establish whether nitrous oxide (N₂O) could be used as a non-invasive early warning indicator for nitrification failure. Eight experiments were undertaken; duplicate shocks DO depletion, influent ammonia increases, allylthiourea (ATU) shocks and sodium azide (NaN₃) shocks were conducted on a pilot-scale activated sludge plant which consisted of a 315 L completely mixed aeration tank and 100 L clarifier. The process performed well during pre-shock stable operation; ammonia removals were up to 97.8% and N₂O emissions were of low variability (<0.5 ppm). However, toxic shock loads produced an N₂O response of a rise in off-gas concentrations ranging from 16.5 to 186.3 ppm, followed by a lag-time ranging from 3 to 5 h ((0.43-0.71) × HRT) of increased NH₃-N and/or NO₂⁻ in the effluent ranging from 3.4 to 41.2 mg L⁻¹. It is this lag-time that provides the early warning for process failure, thus mitigating action can be taken to avoid nitrogen contamination of receiving waters.     

Improved ammonia oxidation by ozone in the presence of bromide ion during water treatment

Ammonia oxidation by ozone proceeds more rapidly in the presence of bromide ion than in its absence. Unlike the direct ozonation of ammonia, the bromide-catalyzed process is little affected by changes in pH. A reaction scheme is proposed in which bromide is oxidized to HOBr, which then brominates ammonia to produce NH₂Br. NH₂Br in turn reacts with O₃ to form NO₃⁻ and also to generate Br⁻, which thus acts as a catalyst. In accordance with the reaction model, zero-order kinetics for ammonia consumption are observed. This work points out once again the importance of Br⁻ as a water quality parameter due to its role as a catalyst in both ozonation and chlorination processes in general.     

Nitrogen inputs to stream water from forests along an elevational gradient in New Mexico

Studies of nitrogen inputs in precipitation and outputs in stream water for a number of terrestrial ecosystems support the hypothesis that undisturbed communities have the ability to reduce losses of nitrogen via stream water. In spite of different levels of biomass, productivity and stream discharge for these communities, net losses of nitrogen were similar. Maintaining nitrogen in an organic or cation form (NH₃, NH₄⁺) is an important factor in minimizing loss. This may be accomplished by slow rates of mineralization, rapid plant uptake, and denitrification through the electron sink pathway. Denitrification by the dissimilatory pathway may also be important.     

The effect of pH on N2O production under aerobic conditions in a partial nitritation system

Ammonia-oxidising bacteria (AOB) are a major contributor to nitrous oxide (N₂O) emissions during nitrogen transformation. N₂O production was observed under both anoxic and aerobic conditions in a lab-scale partial nitritation system operated as a sequencing batch reactor (SBR). The system achieved 55 ± 5% conversion of the 1 g NH₄⁺-N/L contained in a synthetic anaerobic digester liquor to nitrite. The N₂O emission factor was 1.0 ± 0.1% of the ammonium converted. pH was shown to have a major impact on the N₂O production rate of the AOB enriched culture. In the investigated pH range of 6.0-8.5, the specific N₂O production was the lowest between pH 6.0 and 7.0 at a rate of 0.15 ± 0.01 mg N₂O-N/h/g VSS, but increased with pH to a maximum of 0.53 ± 0.04 mg N₂O-N/h/g VSS at pH 8.0. The same trend was also observed for the specific ammonium oxidation rate (AOR) with the maximum AOR reached at pH 8.0. A linear relationship between the N₂O production rate and AOR was observed suggesting that increased ammonium oxidation activity may have promoted N₂O production. The N₂O production rate was constant across free ammonia (FA) and free nitrous acid (FNA) concentrations of 5-78 mg NH₃-N/L and 0.15-4.6 mg HNO₂-N/L, respectively, indicating that the observed pH effect was not due to changes in FA or FNA concentrations.     

The fate of chlorine and chloramines in cooling towers Henry's law constants for flashoff

Chlorine and chloramines are volatile compounds which are stripped (“flashed off”) from recirculating cooling water systems by the large volumes of air which flow through the water in the cooling tower. The fraction of a volatile gas, such as hypochlorous acid (HOCl), which is removed by stripping is determined by Henry's constant H for that gas: H = X_G/X_L, where X_G is the mole fraction of the gas in the air and X_L is the mole fraction of the gas in the water. We have measured H for HOCl, OCl^?, NH₃, NH₂Cl, NHCl₂ and NCl₃ at 20 and 40°C. We found H = 0.076 for HOCl, compared to 0.71 for NH₃, at 20°C. At 40°C, H was about 2.5-fold larger for HOCl. This means that 10–15% of the HOCl is stripped from cooling water on each passage through a typical cooling tower. The measured flashoff of free available chlorine (HOCl + OCl^?) was markedly pH-sensitive with a pK of 7.5, exactly as expected if HOCl is volatile but OCl^? is not. The data permit a quantitative understanding of the fate of chlorine in cooling systems. The values of H at 40°C for NH₂Cl, NHCl₂ and NCl₃ were 1.28, 3.76 and 1067. This means that all of the chloramines are quickly stripped in a cooling tower.     

Atmospheric NH3 and NO2 concentration and nitrogen deposition in an agricultural catchment of Eastern China

To assess the atmospheric environmental impacts of anthropogenic reactive nitrogen in the fast-developing Eastern China region, we measured atmospheric concentrations of nitrogen dioxide (NO₂) and ammonia (NH₃) as well as the wet deposition of inorganic nitrogen (NO₃⁻ and NH₄⁺) and dissolved organic nitrogen (DON) levels in a typical agricultural catchment in Jiangsu Province, China, from October 2007 to September 2008_. The annual average gaseous concentrations of NO₂ and NH₃ were 42.2 μg m⁻³ and 4.5 μg m⁻³ (0 °C, 760 mm Hg), respectively, whereas those of NO₃⁻, NH₄⁺, and DON in the rainwater within the study catchment were 1.3, 1.3, and 0.5 mg N L⁻¹, respectively. No clear difference in gaseous NO₂ concentrations and nitrogen concentrations in collected rainwater was found between the crop field and residential sites, but the average NH₃ concentration of 5.4 μg m⁻³ in residential sites was significantly higher than that in field sites (4.1 μg m⁻³). Total depositions were 40 kg N ha⁻¹ yr⁻¹ for crop field sites and 30 kg N ha⁻¹ yr⁻¹ for residential sites, in which dry depositions (NO₂ and NH₃) were 7.6 kg N ha⁻¹ yr⁻¹ for crop field sites and 1.9 kg N ha⁻¹ yr⁻¹ for residential sites. The DON in the rainwater accounted for 16% of the total wet nitrogen deposition. Oxidized N (NO₃⁻ in the precipitation and gaseous NO₂) was the dominant form of nitrogen deposition in the studied region, indicating that reactive forms of nitrogen created from urban areas contribute greatly to N deposition in the rural area evaluated in this study.     

Simultaneous nitrification and denitrification process in a new Tubificidae-reactor for minimizing nutrient release during sludge reduction

Nutrient release is reported as one of the main disadvantage of sludge reduction induced by aquatic worm. In this study, a Static Sequencing Batch Worm Reactor (SSBWR) was proposed with novel structure of perforated panels, combined aeration system and cycle operation. Effective simultaneous nitrification and denitrification were obtained owing to the stratified sludge layer containing aerobic and anoxic microzone formed on each carrier during most of the operation time in the SSBWR, which created suitable conditions for remarkable sludge reduction and nutrient removal. The results showed that the total nitrogen (TN) concentration, NO₃^?–N + NO₂^?–N concentration and NH₄⁺–N release could be reduced by 67.5%, 98.5% and 63.0%, respectively. And the soluble chemical oxygen demand (sCOD) released by sludge predation was also proved to provide a carbon source for denitrification leading to carbon release control and substantial cost savings. A schematic diagram of the stratified sludge layer and the mass balance of the nitrification–denitrification cycle were given, providing further insight into the nutrient (sCOD and nitrogen compounds) transformation during the worm predation in the SSBWR. For the mixed sludge liquid of 3000 mg TSS/L, 30 mg/L sCOD and 40 mg/L NO₃^?–N, the NO₃^?–N and NO₂^?–N came close to zero, and the sludge concentration, NH₄⁺–N release and sCOD release was reduced by 33.6%, 63.0% and 72.5%, respectively, during 48 h’ predation.     

Investigation of Lake Sapanca water pollution,Adapazari, Turkey

Lake Sapanca has been the only source of drinking and recreational water for the city of Adapazari, Turkey. This paper reports a study of the variation of nutrient loading and trophic state of the lake, and also water quality parameters of Lake Sapanca compared to those of the neighbouring Lake Iznik. Through one year, samples were taken every three months from 15 different points on the streams feeding and draining off the lake. Nitrate, NO₂‐N, NH₃‐N, TKN, PO₄‐P concentrations on the 12 streams fe and three draining off points were determined. Then, loading, discharge, and accumulation amounts of nitrogen and phosphorus causing eutrophication were calculated and the trophic state of the lake was determined. A simple model was used to analyse the response of Lake Sapanca when the phosphorus loading rate was changed. Through this model, the variation of different parameters (t, M, K, Q, V and A) with respect to phosphorus concentration (C) was studied to identify effects and results. The consequences of an eutrophic state and measures to protect the lake are also discussed.     

Moisture effects on greenhouse gases generation in nitrifying gas-phase compost biofilters

Gas-phase compost biofilters are extensively used in concentrated animal feeding operations to remove odors and, in some cases, ammonia from air sources. The expected biochemical pathway for these predominantly aerobic systems is nitrification. However, non-uniform media with low oxygen levels can shift biofilter microbial pathways to denitrification, a source of greenhouse gases. Several factors contribute to the formation of anoxic/anaerobic zones: media aging, media and particle structure, air velocity distribution, compaction, biofilm thickness, and moisture content (MC) distribution. The present work studies the effects of media moisture conditions on ammonia (NH₃) removal and greenhouse gas generation (nitrous oxide, N₂O and methane, CH₄) for gas-phase compost biofilters subject to a 100-day controlled drying process. Continuous recordings were made for the three gases and water vapor (2.21-h sampling cycle, each cycle consisted of three gas species, and water vapor, for a total of 10,050 data points). Media moisture conditions were classified into three corresponding media drying rate (DR) stages: Constant DR (wetter media), falling DR, and stable-dry system. The first-half of the constant DR period (0-750 h; MC = 65-52%, w.b.) facilitated high NH₃ removal rates, but higher N₂O generation and no CH₄ generation. At the drier stages of the constant DR (750-950 h; MC = 52-48%, w.b.) NH₃ removal remained high but N₂O net generation decreased to near zero. In the falling DR stage (1200-1480 h; MC = 44-13%) N₂O generation decreased, CH₄ increased, and NH₃ was no longer removed. No ammonia removal or greenhouse gas generation was observed in the stable-dry system (1500-2500 h; MC = 13%). These results indicate that media should remain toward the drier region of the constant DR (in close proximity to the falling DR stage; MC = 50%, approx.), to maintain high levels of NH₃ removal, reduced levels of N₂O generation, and nullify levels of CH₄ generation.     

Utilisation de la clinoptilolite en potabilisation des eaux—elimination de l'ion NH4+Clinoptilolite in drinking water treatment for NH4+ removal

The objective of this study is to develop a technique to remove ammonium ion from water intended for potable purposes. An ion exchange method is used with a selective ion exchanger, a natural cation zeolite, clinoptilolite. Glass columns (Fig. 1) are used for laboratory experiments. These experiments show that the NH₄⁺ exchange capacity is very small compared to its total capacity 2.17 meq g^?1; its value depends essentially on the NH₄⁺ initial concentration and less on the Ca²⁺ concentration in the influent water. Figure 3 illustrates the practical exchange capacity relative to the initial concentration of ammonium ion for a soft water (Ca²⁺ = 35–50 mg l^?1). We were particularly interested in waters weak in ammonium ion concentration (NH₄⁺ = 1–3 mg l^?1). In this case and for ～1 and 2 mg l^?1 NH₄⁺ concentration in water, the practical capacity is only 0.06 and 0.108 meq g^?1 respectively. The leakage is smaller than the ECC limit (European Community Council) for drinking waters (NH₄⁺ ? 0.5 mg l^?1) and the treated volume of water to breakthrough, defined at 0.5 mg l^?1 of NH₄⁺, is ?720 BV (BV = bed volume) in both cases.In another way Fig. 6 shows that hard waters (due to Ca²⁺ ions) are more difficult to treat than soft waters. The practical capacity is smaller than before and the NH₄⁺-leakage is greater. To lessen NH₄⁺-leakage to less than 0.5 mg l^?1 for soft waters down-flow and up-flow, regeneration is used. Figure 7 shows that up-flow regeneration is more attractive than down-flow regeneration.Cycle reproducibility (Figs 4 and 5) shows that the regeneration conditions satisfied our requirements: in this case, the salt consumption is 180 eq of salt per eq of NH₄⁺ eliminated. This prompted us to try to reuse the regenerant (with NH₄⁺ ion). An increase of NH₄⁺-leakage is noticed in the presence of an NH₄⁺-residual in the regenerant. This increase is more significant with down-flow regeneration.After these laboratory experiments, we carried out a semi-industrial pilot-plant. Our objective was first to verify the laboratory results and secondly to study clinoptilolite behaviour relative to the time it was used. Two plexiglass columns comprise the pilot-plant shown in Fig. 9; soft water is used for these experiments. The first column is regenerated with fresh salt solution. The cycles obtained, considering their initial NH₄⁺-concentration, are reproduced in Fig. 10. For 2 mg l^?1 NH₄⁺ in the influent water, the leakage is about 0.2 mg l^?1 and the treated volume to breakthrough (0.5 mg l^?1 of NH₄⁺) is about 750 BV. The second column is regenerated with a recycled solution. The quality of the cycles decreases with the number of reuse of the regenerant as shown in Fig. 11. Nevertheless, it is interesting to note that after 3 reuses, the performance decrease is only 25% and the leakage, although it increases is smaller than 0.5 mg l^?1.Pilot results allowed us to propose a treatment of 30,000 m³ day^?1; the cost per cubic meter water treated, relative to NH₄⁺-removal, is about 0.165 FF (0.033 US $) for a plant and 0.77 FF (0.014 US $) for the same plant at the seaside. Using two serial columns decreased the cost by about 40–50%.     

Summer fluxes of atmospheric greenhouse gases N2O, CH4 and CO2 from mangrove soil in South China

The atmospheric fluxes of N₂O, CH₄ and CO₂ from the soil in four mangrove swamps in Shenzhen and Hong Kong, South China were investigated in the summer of 2008. The fluxes ranged from 0.14 to 23.83 μmol m⁻² h⁻¹, 11.9 to 5168.6 μmol m⁻² h⁻¹ and 0.69 to 20.56 mmol m⁻² h⁻¹ for N₂O, CH₄ and CO₂, respectively. Futian mangrove swamp in Shenzhen had the highest greenhouse gas fluxes, followed by Mai Po mangrove in Hong Kong. Sha Kong Tsuen and Yung Shue O mangroves in Hong Kong had similar, low fluxes. The differences in both N₂O and CH₄ fluxes among different tidal positions, the landward, seaward and bare mudflat, in each swamp were insignificant. The N₂O and CO₂ fluxes were positively correlated with the soil organic carbon, total nitrogen, total phosphate, total iron and NH₄⁺-N contents, as well as the soil porosity. However, only soil NH₄⁺-N concentration had significant effects on CH₄ fluxes.     

Effect of dissolved oxygen on the photodecomposition of monochloramine and dichloramine in aqueous solution by UV irradiation at 253.7 nm

The effect of dissolved oxygen on the photodecomposition of monochloramine (7.5 < pH < 10) and dichloramine (pH = 3.7 ± 0.2) at 253.7 nm has been investigated. The kinetic study shows that the rate of photodecomposition of monochloramine is about two times faster in the absence of oxygen than in the presence of oxygen, is not significantly affected by pH and by the presence of hydroxyl radical scavengers (hydrogenocarbonate ion and tert-butanol). The apparent quantum yields of photodecomposition of monochloramine at 253.7 nm ([NH₂Cl]₀ ≈ 1.5-2 mM, ?_{253.7 nm} = 371 M⁻¹ cm⁻¹) were equal to 0.28 ± 0.03 and 0.54 ± 0.03 mol E⁻¹ in oxygenated-saturated and in oxygen-free solutions, respectively. The photodecomposition rates or the apparent quantum yields of photodecomposition of dichloramine ([NHCl₂]₀ ≈ 1.5-2 mM, pH = 3.7 ± 0.2) in oxygen-free and in oxygen-saturated solutions were quite identical (Φ = 0.82 ± 0.08 mol E⁻¹; ?_{253.7 nm} = 126 M⁻¹ cm⁻¹). Under O₂ saturation, UV irradiation of NH₂Cl leads to the formation of nitrite (≈0.37 mol/mol of NH₂Cl decomposed), nitrate (≈0.073 mol/mol) and does not form ammonia (<0.01 mol/mol). In oxygen-free solutions, monochloramine decomposes to form ammonia (≈0.37 mol/mol). Photodecomposition of dichloramine did not lead to significant amounts of nitrite and nitrate in the presence and in the absence of oxygen. The nitrogen mass balances also indicate the formation of other nitrogen species (probably N₂ and/or N₂O) during the photodecomposition of monochloramine and dichloramine by UV irradiation at 253.7 nm.     

Floc-based sequential partial nitritation and anammox at full scale with contrasting N2O emissions

New Activated Sludge (NAS^®) is a hybrid, floc-based nitrogen removal process without carbon addition, based on the control of sludge retention times (SRT) and dissolved oxygen (DO) levels. The aim of this study was to examine the performance of a retrofitted four-stage NAS^® plant, including on-line measurements of greenhouse gas emissions (N₂O and CH₄). The plant treated anaerobically digested industrial wastewater, containing 264 mg N L⁻¹, 1154 mg chemical oxygen demand (COD) L⁻¹ and an inorganic carbon alkalinity of 34 meq L⁻¹. The batch-fed partial nitritation step received an overall nitrogen loading rate of 0.18-0.22 kg N m⁻³ d⁻¹, thereby oxidized nitrogen to nitrite (45-47%) and some nitrate (13-15%), but also to N₂O (5.1-6.6%). This was achieved at a SRT of 1.7 d and DO around 1.0 mg O₂ L⁻¹. Subsequently, anammox, denitrification and nitrification compartments were followed by a final settler, at an overall SRT of 46 d. None of the latter three reactors emitted N₂O. In the anammox step, 0.26 kg N m⁻³ d⁻¹ was removed, with an estimated contribution of 71% by the genus Kuenenia, which constituted 3.1% of the biomass. Overall, a nitrogen removal efficiency of 95% was obtained, yielding a dischargeable effluent. Retrofitting floc-based nitrification/denitrification with carbon addition to NAS^® allowed to save 40% of the operational wastewater treatment costs. Yet, a decrease of the N₂O emissions by about 50% is necessary in order to obtain a CO₂ neutral footprint. The impact of emitted CH₄ was 20 times lower.