Chemical Denitrification Research Articles

Mixed sulfur-iron particles packed reactor for simultaneous advanced removal of nitrogen and phosphorus from secondary effluent.

A mixed sulfur-iron particles packed reactor (SFe reactor) was developed to simultaneously remove total nitrogen (TN) and total phosphorus (TP) of the secondary effluent from municipal wastewater treatment plants. Low effluent TN (<1.5mg/L) and TP (<0.3mg/L) concentrations were simultaneously obtained, and high TN removal rate [1.03gN/(L·d)] and TP removal rate [0.29g P/(L·d)] were achieved at the hydraulic retention time (HRT) of 0.13h. Kinetic models describing denitrification were experimentally obtained, which predicted a higher denitrification rate [1.98gN/(L·d)] of SFe reactor than that [1.58gN/(L·d)] of sulfur alone packed reactor due to the mutual enhancement between sulfur-based autotrophic denitrification and iron-based chemical denitrification. A high TP removal obtained in SFe reactor was attributed to chemical precipitation of iron particles. Microbial community analysis based on 16S rRNA revealed that autotrophic denitrifying bacteria Thiobacillus and Sulfuricella were the dominant genus, indicating that autotrophic denitrification played important role in nitrate removal. These results indicate that sulfur and iron particles can be packed together in a single reactor to effectively remove nitrate and phosphorus.

Treatment characteristics and effects of nanoparticle zero-valent iron (nZVI) powder on nitrogen removal efficiency for sewage treatment

This study aims at estimating nanoparticle typed zero-valent iron (nZVI) process as an advanced nitrogen removal technique. To focus on investigating characteristics and effects of nZVI on nitrogen removal for sewage treatment, batch reactor experiments were conducted to reduce excessive nitrate nitrogen (NO3-N). To improve NO3-N removal efficiency and to find a supporter or alternative of nZVI, silica sand, synthetic zeolite, and a mixture of silica sand, synthetic zeolite, and nZVI were used in the experiments. As a result of this study, the chemical denitrification by nZVI attracted on the magnet surface may be useful for total nitrogen removal in conventional sewage and wastewater treatment plants under the optimal conditions, and application of silica sand also is an excellent adsorbent or media for N-component removal and a supporter as well. This study concludes the end product in this study may be nitrogen gas (N2) through Fe0 reaction with O2 and NO3− in aerobic nZVI (Fe0)–H2O system. Future study is required to examine the competition of nZVI between nitrate and many other compounds depending upon various experimental conditions for improving the nitrate removal efficiency and impeding the ammonium generation.

Removal Techniques of Nitrate from Water

Nitrate pollution of water is a major environmental problem all over the world. Consequently, numerous techniques have been developed to remove or reduction of nitrate in water. A review of removal techniques of nitrate from water has been carried out in this paper. Recent literatures related to various techniques including reverse osmosis, ion exchange, electrodialysis, biological denitrification, chemical denitrification, adsorption methods using different adsorbents like carbon base, agricultural waste, natural materials are systematically review to assess their performance. The paper reveals that adsorption could be the most promising technique of removal of nitrate from water in near future.

Denitrification of simulated nitrate-rich wastewater using sulfamic acid and zinc scrap

AbstractAn enhanced chemical denitrification process was studied as an alternative treatment of nitrate-rich wastewater which cannot be easily treated using conventional biological methods. To accelerate denitrification and to reduce the conversion to ammonia, nitrite reductants were added. In a batch test with the initial nitrate concentration of 500 mg NO3− -N per L, sulfamic acid and zinc were found to be the best nitrite and metal reductants, respectively. In a column test with the initial nitrate concentration of 500 mg NO3−-N per L, optimum results were experimentally obtained over a zinc scrap column with a 1.0 molar ratio of [NH2SO3H]/[NO3−-N] and the recirculating flow rate of 6 L min−1 at pH 2.5. Approximately 98.8 % of nitrate anions were removed, and the observed reaction rate constant (k) was 0.135 min−1. Zinc consumption was reduced to 46.6 % compared to the procedure without sulfamic acid, and sulfamic acid consumption was reduced to 40 % compared to the results of our previous study. Based on these experimental results, it was concluded that chemical nitrate denitrification using sulfamic acid and zinc scrap is an effective alternative treatment protocol for nitrate-rich wastewater.

Nitrogen transformation in acid soils subjected to pH value changes

The aim of this investigation was to determine which application of fertilizer and lime material does not form toxic quantities of nitrite nitrogen and when the losses by denitrification are the lowest in the examined acid soils. Investigations were performed on pseudogley soils of different acidity. Changes of available nitrogen forms were examined by the method of short-term incubation experiments. Experimental treatments were without the use of mineral fertilizers and with application of (NH4)2SO4 (100 ppm of NO3-N) and KNO3 (100 ppm of NO3-N); with and without addition of Ca(OH)2 (50% of full neutralization and full neutralization). When (NH4)2SO4 was used, nitrites occurred in both examined soils as a result of decelerated nitrification and when KNO3 was added as a result of chemical denitrification. Application of Ca(OH)2 caused the intensification of mineralization, nitrification and biological denitrification processes. When a higher dose of lime material was used (full neutralization), nitrites occurred in larger quantities as a result of the strengthening of nitrification and denitrification processes. Application of a lower lime dose caused nitrite occurrence in smaller quantities. Therefore, in these soils as well as in soils of similar chemical properties, application of lower doses of lime material can be recommended (&lt;50% of full neutralization) as well as the application of ammonium fertilizer, bearing in mind that in such conditions losses of added fertilizer in the denitrification process are reduced and the occurrence of nitrites as an intermediate product of this process is prevented.

The Chemistry of Drying an Aqueous Solution of Salts

The fate of salts in drying aqueous solution was investigated. In the drying of acidic solutions, weak acid ions and chloride ions combine with protons and evaporate, depending on the proton concentration. In the drying of alkaline solutions, weak acid ions evaporate or remain as salts depending on the ratio of the concentrations of excess nonvolatile cations (the difference between concentrations of nonvolatile cation and nonvolatile anion) to volatile anions defined as DeltaCA. Under neutral and alkaline conditions, the fate of nitrite depends not only on DeltaCA but also on the drying speed. Nitrite is converted to N2, which is formed by reacting nitrite with ammonium (denitrification), NO and NO2, HONO and salts. In urban areas, nitrite and ammonium can appear in high concentrations in dew. HONO in the atmosphere affects the ozone concentration, but dew formation decreases the concentration of HONO. If chemical denitrification occurs, nitrogen species will decrease in the environment, and as a result, the ozone concentration could decrease. Ozone levels show an ozone depression when dew formed, and a Box model simulation showed an ozone depression by decreasing HONO levels.

Specific transformations of mineral forms of nitrogen in acid soils

Investigations were performed on soils of different acidity, ranging in the pH interval 4.65-5.80 (in water). Changes of the mineral nitrogen forms in the examined soils were studied by applying short-term incubation experiments performed under aerobic conditions, with a humidity of 30 % and a temperature of 20?C, both with and without the addition of 100 and 300 ppm NH4-N. The results of the incubation experiments showed that retarded nitrification was present in all the examined soils. Increased and toxic quantities of nitrites (35.7 ppm) were formed during the incubation, which remained in the soil solution for several days, and even weeks, in spite of favorable conditions of moisture, aeration and temperature for the development of the process of chemoautotrophic nitrification. Decelerated chemoautotrophic nitrification was the source of the occurrence of nitrite in the examined less acid soil (soil 1), while in soils of higher acidity (soils 2 and 3) after addition of 100 and 300 ppm NH4-N, nitrite occurred due to chemical denitrification (chemodenitrification). Nitrites formed in the process of chemodenitrification underwent spontaneous chemical oxidation resulting in nitrate formation (chemical nitrification). The content of mineral nitrogen (NH4 + NO3 + NO2-N) decreased during the incubation period, proving gaseous losses from the examined soils. Application of lower doses of nitrogen fertilizers could decrease nitrogen losses by denitrification as well as the occurrence of nitrite in toxic quantities in the investigated pseudogley soil.

Activated Sludge Diffusion for Odour Removal - Effects of H2S on the Biomass

The removal of odours from wastewater treatment plants through diffusion of odour-containing air volumes into the aerated basins was investigated in a bench scale experimental campaign which lasted more than 200 days. Hydrogen sulphide was selected as a model odorous compound and its removal efficiencies were experimentally evaluated along with its effects on the biomass and on the main biochemical processes. Two bench scale sequencing batch reactors were fed in parallel on real primary sewage and monitored for chemical oxygen demand removal, nitrification and denitrification. The balance of H2S was also monitored after adding to one of them a Na2S liquid solution of 17 mgS lreactor −1 d−1, corresponding to a gas-phase concentration of 240 mgS (Nm3)−1. Results showed an average sulphide removal of 94% in the reactor supplied with Na2S. Moreover, microbial composition did not show relevant variations after the addition of sulphide, and the good features of activated sludge flocs were maintained also in terms of sludge settleability. No relevant effects of sulphide were detected on carbon and nitrogen metabolism and chemical oxygen demand removal, nitrification and denitrification efficiencies were always above 75%, 95%, and 50% respectively, and comparable across the two reactors.

Chemical denitrification of water by zero-valent magnesium powder

A laboratory-scale study was conducted in batch mode to investigate the feasibility of using zero-valent magnesium (Mg 0), for removal of nitrate from aqueous solution. Reaction pH, dose of Mg 0, initial nitrate concentration and temperature were considered variable parameters during the study. Strong acidic condition enhanced nitrate reduction and in absence of external proton addition, reaction pH increased rapidly above ten and insignificant nitrate removal (7–16%) was achieved. At Mg 0:NO 3 −–N molar ratio of 5.8 and controlled reaction pH of 2, 84% denitrification efficiency was achieved (initial NO 3 −–N 50 mg/L) under ambient temperature and pressure and total nitrogen removal was 70% with 3.2% and 10% conversion of initial NO 3 −–N to NO 2 −–N and NH 4 +–N, respectively. The reaction was first order with respect to nitrate concentration. Nitrate removal rate decreased with solution pH and increased linearly with Mg 0 dose. Nitrate removal was coupled with 96–100% removal of dissolved oxygen and 85–90% generation of soluble Mg 2+ ion. An activation energy ( E a) of nitrate reduction over the temperature range of 10–50 °C was observed as 17.7 kJ mol −1.

Chemical denitrification for nitrogen removal from landfill leachate

A new system that removes nitrogen from landfill leachate and other waste waters with similar properties has been proposed with nitritation (i.e. oxidation of ammonium to nitrite) of half of the influent ammonium followed by chemical denitrification with a reaction between equal amounts of ammonium and nitrite to form nitrogen gas. Chemical denitrification occurs at high concentrations and the reactions were studied in combination with a concentration step. Studied concentration methods were freezing/thawing and evaporation/drying. Chemical denitrification is well-known in inorganic chemistry and has been observed in natural systems. Studies in laboratory were focused on chemical denitrification and showed that nearly complete removal of soluble nitrogen can be obtained in evaporation/drying of water solutions or leachate with equal amounts of ammonium and nitrite. Freezing/drying was less efficient with a removal of about 50-60% at high initial concentrations. Chemical denitrification is much influenced by concentration, pH-value, temperature and some compounds in leachate have an inhibiting effect on the reaction. Factors as safety (ammonium nitrite as a salt is explosive above 60 degrees C) and possible side-reactions as formation of ammonia and nitrogen oxides must be carefully evaluated before use in full-scale. Conductivity is a suitable parameter to follow-up the chemical denitrification process.

Kinetics of reductive denitrification by nanoscale zero-valent iron

Zero-valent iron powder (Fe 0) has been determined to be potentially useful for the removal of nitrate in the water environment. This research is aimed at subjecting the kinetics of denitrification by nanoscale Fe 0 to an analysis of factors affecting the chemical denitrification of nitrate. Nanoscale iron particles with a diameter in the range of 1–100 nm, which are characterized by the large BET specific surface area to mass ratio (31.4 m 2/g), removed mostly 50, 100, 200, and 400 mg/l of nitrate within a period of 30 min with little intermediates. Compared with microscale (75–150 μm) Fe 0, endproduct is not ammonia but N 2 gas. Kinetics analysis from batch studies revealed that the denitrification reaction with nanoscale Fe 0 appeared to be a pseudo first-order with respect to substrate and the observed reaction rate constant ( k obs) varied with iron content at a relatively low degree of application. The effects of mixing intensity (rpm) on the denitrification rate suggest that the denitrification appears to be coupled with oxidative dissolution of iron through a largely mass transport-limited surface reaction (<40 rpm).

Climatologies of lower stratospheric NOy and O3 and correlations with N2O based on in situ observations

This paper presents NOy and O3 seasonal mean distributions as a function of equivalent latitude and height from more than 140 ER‐2 flights. The observations span a height range of 360–530 K (∼150‐45 hPa) and have nearly pole‐to‐pole coverage in most seasons. These climatologies are intended to support efforts to evaluate the chemistry and dynamics of assessment models. Reasonable model representations of NOy, O3, and their seasonal variations are necessary to assess the effects of aircraft exhaust on the stratosphere. ER‐2 measurements of N2O are combined with the NOy data to examine their lower stratospheric relationship and to identify regions of denitrification. Measurements of these species above ER‐2 altitudes in the Arctic vortex support the interpretation of some of the ER‐2 NOy‐N2O data, which suggest that transport rather than chemical denitrification causes deviations from the normally linear relationship. This places constraints on the use of a linear relationship to calculate denitrification. The observed relationship between N2O and O3 is also presented. The spatial gradients in lower stratospheric O3 photochemistry are used to explain observed variations in the N2O‐O3 relationship. The N2O‐O3 relationship above ER‐2 altitudes in the Arctic vortex, much like the case of NOy‐N2O, also differs in slope from lower altitudes. This points to the difficulties in using tracer correlations to infer O3 values in the vortex prior to polar stratospheric cloud processing. It is necessary to understand the photochemical and transport history of the air that descends into the lower stratospheric vortex in order to correctly quantify O3 depletion.

Natural Denitrification in Drying Process of Dew

This report is the first observation of natural chemical denitrification in the drying process of dew. Nitrogen compounds released in the atmosphere are considered to be subjected to oxidation to form nitric acid by the chemical process so far. The results here show that nitrous acid is reduced to N2 by drying of dew. Dew was collected at Osaka Prefecture University in Sakai City, Japan from 1996 to 1997. Concentrations of ammonium and nitrite ions in dew were very high related to those in rain, and pHs of dew were relatively high, pH ca. 6.5. We found that when dew was dried, most nitrite and ammonium ions included in dew were decomposed. It is well-known that concentrated ammonium nitrite aqueous solution is unstable and decomposes to N2 and H2O. During the drying process of dew, nitrite and ammonium would be concentrated and react to form N2, and as a result, nitrite and ammonia in the dried dew are lost, that is, natural denitrification occurs in the drying process of dew. We report here results of th...

アミド硫酸による工場排水中の亜硝酸性窒素の処理効果

Chemical denitrification of NO2-N conducted with amido sulfonic acid was studied to treat NO2-N in both bench and in situ experiments. In bench experiments, following optium conditions for NO2-N removal were obtained. The dosage of amide sulfate was 6.9 times equivalent to NO2-N load, pH value and stirring rate were 2.5 and 50 r.p.m., respectively in the bench reactor, and the period for reaction was more than 60 minutes. Nitrogenous gases like NOx and N2O, which are causative materials for air pollution and global warming, were not detected in the gas exhaust.In situ experiment was made with wastewater containing NO2-N discharged from a factory and with its operating parameters same as the optimum conditions obtained in the bench experiment. It ran in batch style and was controlled automatically. Results showed that efficient chemical dentrification could be conducted through continuously striring during treated wastewater discharging, and through covering nitrite sensor to keep it from the nitrogenous gases generated in the reaction.

Nitrate Removal From Drinking Water—Review

Nitrate concentrations in surface water and especially in ground water have increased in Canada, the United States, Europe, and other areas of the world. This trend has raised concern because nitrates cause methemoglobinemia in infants. Several treatment processes including ion exchange, biological denitrification, chemical denitrification, reverse osmosis, electrodialysis, and catalytic denitrification can remove nitrates from water with varying degrees of efficiency, cost, and ease of operation. Available technical data, experience, and economics indicate that ion exchange and biological denitrification are more acceptable for nitrate removal than reverse osmosis. Ion exchange is more viable for ground water while biological denitrification is the preferred alternative for surface water. This paper reviews the developments in the field of nitrate removal processes.

Fluxes of nitric oxide from soils following the clearing and burning of a secondary tropical rain forest

At sites in the Atlantic Lowlands of Costa Rica, clearing and burning of a secondary tropical rain forest caused a significant increase in soil nitric oxide (NO) emissions. Soil‐atmosphere NO fluxes averaged 0.5 ng N cm−2 hr−1 prior to clearing and increased to 4.1 ng N cm−2 hr−1 following clearing and to greater than 12.0 ng N cm−2 hr−1 following burning. Soil NO emissions were elevated for a period of 3–4 months following clearing, and fluxes peaked for 1–3 days following burning. We conducted a series of experiments with intact soil cores to determine the probable mechanism responsible for elevated NO emissions from soils. In one set of experiments we added substrates for microbial nitrification (ammonium), denitrification (nitrate), and chemical denitrification (nitrite) to autoclaved (killed) and nonautoclaved (live) soil cores. Water‐only additions were used as controls. Compared to water or nitrate additions, ammonium caused a significant increase in NO emissions from live cores. Water, ammonium, and nitrate additions had no effect on emissions from autoclaved cores. Nitrite solution additions resulted in highly significant increases in NO emissions from both autoclaved and nonautoclaved soil cores. In a second set of experiments we treated intact soil cores with acetylene (1 kPa C2H2) to selectively inhibit nitrification and oxygen to inhibit denitrification. The oxygen treatment had no effect on NO production while acetylene significantly reduced NO emissions. The results from the substrate addition and inhibition experiments demonstrate that microbial denitrification is not a major pathway for NO production in these soils. In contrast, microbial nitrification appears to be a critical process responsible for NO emissions throughout the clearing and burning period. Field experiments with acetylene as an inhibitor show that immediately following burning, chemical denitriflcation of nitrite deposited in ash supports a large peak in NO fluxes.

Essai de valorisation agricole de déchets industriels contenant de l'azote nitreux et nitrique

Summary — Trial on agricultural use of industrial waste containing nitrous and nitric nitrogen. Two batches of industrial waste containing 10-15% oxidized inorganic N, half of which was in nitrite form, were used as N source for wheat and maize crops. In laboratory incubation the conversion of nitrite to nitrate varied from 22-52 mg N.kg soil wk at temperatures of 10, 15 and 20 °C in soil with a neutral pH. In acid soil at least one-third of the nitrite N was lost by chemical denitrification and the functioning of part of the microflora appeared to be perturbed: there was an increased mineralization of C and production of ammonia. In the field, the rate of conversion corresponded with laboratory results when the waste was applied as a solution, but halved with solid products. Persistance of nitrite in the soil was a function of the dose added. Application to wheat at the beginning of stem elongation slightly reduced grain yield (- 5%), with nitrites slowing down N assimilation of the plants. Applied to maize at sowing, germination was strongly affected by nitrites, resulting in a diminution of grain yield which reached 30% depending on the application dose. When soil temperature had attained 10 °C, an application of 50 kg.ha of oxidized N to the growing crop (wheat) allowed the 2 batches of waste to be used in agriculture.

Biofilm Reactors: A Compact Solution for the Upgrading of Waste Water Treatment Plants

In order to obtain compact plants and to assure a greater treatment reliability, fixed film reactors have been developed. This biofiltration has been applied and proved for over a decade for carbon removal. Today, new applications appear in nitrogen and phosphate removals, which are able to respond to the upgrading of aging waste water treatment plants. Full scale plant results are presented in nitrification. The use of two stages of biofilm reactors (C + N) permits high effluent quality. Chemical phosphate removal and denitrification results obtained on pilot tests are also discussed. Some plants are now been built with such processes. The VEAS concept, in Oslo, which includes four steps of fixed film reactors is discussed as an example of this present upgrading tendency.

Denitrification en reacteur garni en pyrite de fer: Etudes de laboratoire

Abstract The authors study the chemical and/or biological denitrification of water flowing through a column packed with pyrite. This laboratory pilot unit simulates the denitrification of groundwater occuring during its flow through some soils. The mass balance and the biological reactions are given. Besides, the profiles of nitrate removal are given and a mathematical equation modelizes these phenomena.

Effect of Temperature on Consecutive Denitrification Reactions in Brookston Clay and Fox Sandy Loam

The kinetics of several steps in the microbial denitrification process in Brookston clay and Fox sandy loam, two soils common to Southwestern Ontario, were studied in the temperature range of 5 to 25 degrees C. The extent of chemical denitrification was also determined in otherwise identical but sterilized soils at temperatures up to 80 degrees C. A gas flow system was used in which soil gases were continuously removed from anaerobic soil columns by argon carrier gas. Net steady-state rates of NO and N(2)O production, rates of loss of NO(3), and production and loss of NO(2) were measured over periods of up to 5 days. Arrhenius activation energies for the zero-order process NO(3) --> NO(2) were calculated to be 50 +/- 9 kJ mol for Brookston clay and 55 +/- 13 kJ mol for Fox sandy loam. The overall reaction, NO(2) --> NO (chemodenitrification), in both sterile soils was accurately first order with respect to NO(2); the activation energy was 70 +/- 2.8 kJ mol in Brookston clay and 79 +/- 1.2 kJ mol in the sandy loam, and the preexponential factors were (2.3 +/- 1.2) x 10 and (5.7 +/- 1.2) x 10 min, respectively.