Degradation Of Cyanuric Acid Research Articles

The contribution of mediated oxidation mechanisms in the electrolytic degradation of cyanuric acid using diamond anodes

In this work, the contribution of mediated oxidation mechanisms in the electrolytic degradation of cyanuric acid using boron-doped diamond (BDD) anodes was investigated in different electrolytes. A complete mineralization of cyanuric acid was obtained in NaCl; however lower degrees of mineralization of 70% and 40% were obtained in Na2SO4 and NaClO4, respectively. This can be explained by the nature of the oxidants electrogenerated in each electrolyte. It is clear that the contribution of active chlorine (Cl2, HClO, ClO−) electrogenerated from oxidation of chlorides on BDD is much more important in the electrolytic degradation of cyanuric acid than the persulfate and hydroxyl radicals produced by electro-oxidation of sulfate and water on BDD anodes. This could be explained by the high affinity of active chlorine towards nitrogen compounds. No organic intermediates were detected during the electrolytic degradation of cyanuric acid in any the electrolytes, which can be explained by their immediate depletion by hydroxyl radicals produced on the BDD surface. Nitrates and ammonium were the final products of electrolytic degradation of cyanuric acid on BDD anodes in all electrolytes. In addition, small amounts of chloramines were formed in the chloride medium. Low current density (≤10mA/cm2) and neutral medium (pH in the range 6–9) should be used for high efficiency electrolytic degradation and negligible formation of hazardous chlorate and perchlorate.

Electron beam induced degradation of atrazine in aqueous solution

Herein, the radiolytic degradations of atrazine and cyanuric acid were performed via electron beam irradiation. The results demonstrated atrazine could be completely mineralized without any residue of cyanuric acid in aqueous solution. The degradation of atrazine followed the pseudo-first-order reaction kinetics. The studies in the presence of different radical scavengers (O2 and tert-butanol) indicated hydroxyl radicals were the main species for the decomposition of atrazine into cyanuric acid, while e−aq played vital role in the degradation of cyanuric acid. During the radiolysis processes of atrazine and cyanuric acid, some organic and inorganic intermediates were detected, implying dechlorination, dealkylation, and deamination occurred. On the basis of the effects of radicals and detected products, the potential radiolytic degradation pathways of atrazine via electron beam were proposed.

Investigations on the Degradation of Triazine Herbicides in Water by Photo-Fenton Process

In this work, the degradation of 2-chloro-4,6-diamino-1,3,5-triazine in aqueous solutions by photo-Fenton process has been investigated. The preliminary results have shown that the degradation of 2-chloro-4,6-diamino-1,3,5-triazine by photo-Fenton process is more rapid and more effective than Fenton and UV/H2O2 processes. The effects of certain experimental parameters on kinetics and efficiency of the degradation of 2-chloro-4,6,-diamino-1,3,5-triazine by photo-Fenton process, have been evaluated. Under optimal conditions, photo-Fenton process achieved more than 90% of chloride release and about 30% of nitrate formation. The results of total organic carbon (TOC) and total Kjeldahl nitrogen (TKN) analyses have shown that no carbon dioxide and ammonia are formed during photo-Fenton treatment of aqueous solutions containing 40 mg/L triazine. These results indicate that only substituent groups of triazine ring are released; however, nitrogen atoms of triazine ring remain unaffected. A simple mechanism of degradation of 2-chloro-4,6-diamino-1,3,5-triazine has been proposed. The degradation starts by a rapid release of chlorine atoms as chloride ions to form 2-hydroxy-4,6-diamino-1,3,5-triazine. The amino groups of 2-hydroxy-4,6-diamino-1,3,5-triazine undergo are oxidized into nitro groups by hydroxyl radicals to form 2-hydroxy-4,6-dinitro-1,3,5-triazine which undergoes a slow release of nitro groups and their substitution with hydroxyl groups to form cyanuric acid and nitrate ions. The degradation of cyanuric acid by photo-Fenton process has also been investigated. The results of TOC and TKN analyzes show that no carbon dioxide is formed during the treatment.

Photoelectrochemical Degradation of Cyanuric Acid in TiO<sub>2</sub> Suspension

Photoelectrochemical degradation of cyanuric acid occurred when the applied potential exceeded 2 V by using Ti electrodes and TiO2 suspension in 0.3 M NaCl solution. The removal increased drastically when the applied potential was more than 5 V. The addition of HCO3- ion could accelerate photoelectrochemical degradation of cyanuric acid. An optimum removal of 85% was achieved when HCO3- ion concentration increased to 0.05 M. Further increase of HCO3- ion led to the decrease of removal, due to consumption of hydroxyl radicals and other oxidizing species by excessive bicarbonate. Photocatalytic oxidation had no capacity on degrading cyanuric acid whether in NaHCO3 aqueous solution or in the solution containing both Cl- and HCO3- ions.

Degradation of atrazine in aqueous medium by electrocatalytically generated hydroxyl radicals. A kinetic and mechanistic study

Oxidative degradation of atrazine by hydroxyl radicals ( OH) was studied in aqueous medium. OH were formed in situ from electrochemically generating Fenton's reagent by an indirect electrochemical advanced oxidation process. Identification and evolution of seven main aromatic metabolites and four short-chain carboxylic acids were performed by using liquid chromatography analyses. Total organic carbon (TOC) and ionic chromatography were used in order to evaluate the mineralization efficiency of treated aqueous solutions. A high mineralization rate of 82% (never reported until now) was obtained. The oxidative degradation of cyanuric acid, the ultimate product of atrazine degradation, was highlighted for the first time. The absolute rate constant of the reaction between atrazine and hydroxyl radicals was evaluated by competition kinetics method as (2.54 ± 0.22) × 10 9 M −1 s −1. Considering all oxidation reaction intermediates and end products a general reaction sequence for atrazine degradation by hydroxyl radicals was proposed.

Degradation of cyanuric acid in soil by Pseudomonas sp. NRRL B-12227 using bioremediation with self-immobilization system

The rates of degradation of cyanuric acid, a key intermediate in a metabolic pathway of s-triazine herbicides, were measured for Pseudomonas sp. NRRL B-12227. The rate of degradation was affected by the rate of cyanuric acid transport through cell membranes and the activity of cyanuric acid amidohydrolase inside the cells. At low concentrations of cyanuric acid, the acclimation of cells to cyanuric acid and/or added nutrients effectively enhanced the degradation rate. The strain was also applied to bioremediation using a Bioremediation with Self-Immobilization System (BSIS), in which Pseudomonas sp. NRRL B-12227 cells were co-immobilized with Bacillus subtilis, the latter of which secretes a viscous polymer, in a shallow layer of soil packed in a column. More than 70% of the Pseudomonas sp. NRRL B-12227 cells were co-immobilized with the B. subtilis in a 7.5 cm layer of the packed soil by self-aggregation. More than 60% of the 1 mM cyanuric acid supplied to the packed soil was degraded in this layer during a 72 h period.

Fenton-enhanced γ-radiolysis of cyanuric acid

Degradation of cyanuric acid (OOOT), a stable end product of oxidative decomposition of atrazine, is investigated in a combined field of gamma radiolysis and fenton reaction. The reaction of hydroxyl radical ( OH) at pH 6 was carried out by irradiating N 2O saturated aqueous solutions containing OOOT (1 × 10 −3 mol dm −3), and this resulted only a marginal degradation (20%). However, when the same reaction was carried out in the presence of varying concentrations of ferrous sulfate ((5–10) × 10 −5 mol dm −3), the decay of OOOT has been enhanced to more than 80%. This decay followed a first order kinetics. Nearly similar effects were observed with another triazine derivative, 2,4-dioxohexahydro-1,3,5-triazine (DHT). Two major reaction mechanisms are proposed for the enhanced decay of OOOT. The formation of unstable hydroxyl radical adducts from the reaction of OH which is the result of gamma radiolysis and the Fenton reaction (resulting from the reaction of the added Fe(II) and of the H 2O 2 from the radiolysis of water), is proposed as the first mechanism. The second mechanism, which is likely the major contributor to degradation, is proposed as the reaction of a nucleophilic adduct, Fe(II)OOH, which could directly react with the electron deficient triazine ring. It is highlighted that such degradation reactions must be explored for the complete degradation of the byproducts of the oxidative decomposition of atrazine.

Treatment of atrazine by integrating photocatalytic and biological processes

This research examines the degradation of atrazine by photocatalytic oxidation (PCO) under different experimental conditions. Deisopropylatrazine, deethylatrazine and deethyldeisopropylatrazine were formed as major intermediates based on gas chromatography-mass spectrometry. The reaction mixture was found to be toxic towards two bioassays, i.e. the Microtox ® and amphipods survival tests even when atrazine was completely degraded by PCO within 2 h under optimized conditions. The results indicate that adding H 2O 2 could significantly enhance the degradation of atrazine by PCO. Ammeline, ammelide and cyanuric acid (CA) became the major intermediates/products as detected by high performance liquid chromatography from 6th to the 40th h of PCO treatment. After 72 h PCO treatment, only CA was detectable in the reaction mixture. Further degradation of CA was carried out by a newly isolated CA-degrading bacterium, Sphingomonas capsulata. The photochemical pretreatment integrated with microbial degradation lead to the complete degradation and detoxification of atrazine.

Treatment of atrazine by integrating photocatalytic and biological processes

This research examines the degradation of atrazine by photocatalytic oxidation (PCO) under different experimental conditions. Deisopropylatrazine, deethylatrazine and deethyldeisopropylatrazine were formed as major intermediates based on gas chromatography-mass spectrometry. The reaction mixture was found to be toxic towards two bioassays, i.e. the Microtox® and amphipods survival tests even when atrazine was completely degraded by PCO within 2 h under optimized conditions. The results indicate that adding H2O2 could significantly enhance the degradation of atrazine by PCO. Ammeline, ammelide and cyanuric acid (CA) became the major intermediates/products as detected by high performance liquid chromatography from 6th to the 40th h of PCO treatment. After 72 h PCO treatment, only CA was detectable in the reaction mixture. Further degradation of CA was carried out by a newly isolated CA-degrading bacterium, Sphingomonas capsulata. The photochemical pretreatment integrated with microbial degradation lead to the complete degradation and detoxification of atrazine.

Photocatalytic degradation of a cyanuric acid, a recalcitrant species

Degradation of cyanuric acid in aqueous suspensions of Degussa P25 TiO 2 has been achieved by the addition of fluoride ion at low pH. Consistent with the work of Minero and Pelizzetti [Langmuir 16 (2000) 2632, Langmuir 16 (2000) 8964], it is suggested that this is due to the formation of homogeneous phase hydroxyl radicals. Support for this hypothesis is brought from successful degradations using other hydroxyl-generating conditions and the successful degradation of 4- t-butylpyridine, another organic compound previously shown to be resistant to TiO 2-mediated photocatalytic degradation.

Near-quantitative mineralization of two refractory triazines under hydrothermal-supercritical aqueous conditions assisted by ozone and UV/ozone

Refractory atrazine and cyanuric acid were degraded under hydrothermal and supercritical aqueous media (HY-SC) conditions, as well as in the presence of ozone (HY-SC/O3) and UV-illuminated ozone (HY-SC/UV/O3) to assess whether the efficacy of the decomposition process could be enhanced using a single-pass flow-through treatment device under a constant pressure of 23 MPa. The progress of the degradation was evidenced by the extent of removal of total organic carbon (TOC) in solution, by UV absorption spectroscopy (opening of the atrazine and cyanuric acid heterorings), and by the extent of deamination (formation of NH4+) and dechlorination (release of Cl− ions) of the two compounds. Loss of atrazine was confirmed by LC-MSD techniques in the positive ion mode. Formation of various intermediates from the degradation of atrazine was substantiated by positive and negative ion mode MSD analyses. Dechlorination of atrazine occurred around 100 °C under hydrothermal conditions for the HY-SC and HY-SC/O3 processes but not for HY-SC/UV/O3; it did increase rapidly at higher temperatures (beginning at ca. 220–230 °C) for all three methods: HY-SC through HY-SC/UV/O3. Deamination, removal of TOC, and loss of atrazine mass spectral features began around 260–280 °C in hydrothermal aqueous media. Degradation of cyanuric acid showed a similar behavior. For the treated effluent solution in the collector reservoir, ozonation enhanced somewhat both dechlorination and mineralization, but had no significant effect on the deamination of either atrazine or cyanuric acid.

Reaction of Sulphate Radical Anion (SO4•-) with Cyanuric Acid: A Potential Reaction for Its Degradation?

Abstract A novel reaction between sulfate radical anion (SO4•-) and cyanuric acid (CA), a non-degradable end product of the oxidative degradation of the triazine based herbicide, atrazine, is presented using laser flash photolysis and steady state radiolysis techniques at pH 5. A second order rate constant of 1.9×107 dm3 mol-1 s-1 has been determined and the transient intermediate (λmax=330 nm) is assigned to a radical cation of CA (CA•+). The degradation profile indicated that about 76% of CA have been decomposed after an absorbed γ-radiation dose of 18 kGy. It is therefore proposed that the reaction of SO4•- could be utilised for the degradation of CA in aqueous medium which is normally stable to any Advanced Oxidation Processes.

Direct electrochemical degradation of organic wastes in aqueous media

The goals of research reported here include the discovery of optimal electrocatalytic materials and electrolysis conditions for rapid degradation of organic compounds to CO 2(g). Concepts of the designated procedure are summarized with emphasis on the carboxylic acids generated as intermediate products during anodic degradation of 4-chlorophenol and benzoquinone. Data are summarized for various electrode materials including oxide-covered Pt, as well as PbO 2 and SnO 2 films that are heavily doped with altervalent metallic cations. The anodic degradation reactions have in common the fact that they involve transfer of O-atoms from H 2O in the solvent phase to the oxidation products. Therefore, variations in reactivity of electrode materials are ascribed to differences in the extent of electrocatalytic participation of these electrode surfaces within the anodic O-transfer mechanisms. Results are explained on the basis of the following mechanistic speculations: (1) a prerequisite of the required anodic O-transfer reactions is the discharge of H 2O to generate adsorbed hydroxyl radicals; (2) a co-requisite is preadsorption of the reactant species; (3) the O-transfer step occurs from (OH) ads to (R) ads; and (4) an inevitable but undesirable concomitant reaction is the anodic evolution of O 2(g). The expected benefit of elevated anode temperature is verified for degradation of acetic acid at a Pt anode. Also, cyanuric acid generated as a stable product of photocatalytic degradation processes is demonstrated to be degraded by anodic reaction at a Pt electrode. Recovery of nitrate is approximately 70% during degradation of cyanuric acid and it is speculated that some volatile N-species is lost during the procedure.

Preparation of cyanuric and isocyanic acids in a fluidized bed reactor

We found out that the reactor suggested for pyrolysis in fluidized bed conditions, with indirect heating of the stock, proved to be convenient for the preparation of cyanuric and isocyanic acids. Under optimal conditions the yield of cyanuric acid from urea was 95% with 96% selectivity, i.e. the content of by-products is considerably lower than in case of processing in the static bed reactor. In the same reactor we prepared isocyanic acid from cyanuric acid in quantitative yield. The amount of gaseous isocyanic acid emitted was up to 50%. The isocyanic acid obtained was utilized in a reaction with aromatic and aliphatic amines to get mono- and disubstituted ureas. In connection with these experiments we studied the kinetics of the degradation of cyanuric acid and trimerization of isocyanic acid to obtain a quantitative description of the process.

Anaerobic Degradation of Cyanuric Acid, Cysteine, and Atrazine by a Facultative Anaerobic Bacterium

A facultative anaerobic bacterium that rapidly degrades cyanuric acid (CA) was isolated from the sediment of a stream that received industrial wastewater effluent. CA decomposition was measured throughout the growth cycle by using a high-performance liquid chromatography assay, and the concomitant production of ammonia was also measured. The bacterium used CA or cysteine as a major, if not the sole, carbon and energy source under anaerobic, but not aerobic, conditions in a defined medium. The cell yield was greatly enhanced by the simultaneous presence of cysteine and CA in the medium. Cysteine was preferentially used rather than CA early in the growth cycle, but all of the CA was used without an apparent lag after the cysteine was metabolized. Atrazine was also degraded by this bacterium under anaerobic conditions in a defined medium.

Rapid degradation of cyanuric acid by Sporothrix schenckii

Summary A strain of Sporothrix schenckii was isolated which rapidly degraded cyanuric acid. The specific rate of degradation amounted to 30 mg cyanuric acid × h−1 × (g dry weight of cells)−1. During growth the strain was able to utilize cyanuric acid as its sole nitrogen source, with a concomitant release of carbon as carbon dioxide. Resting cells degraded the compound to carbon dioxide and ammonia. The action of the degrading enzymes was induced primarily by cyanuric acid, whereas ammonia and biuret resulted in a reduction of the specific rate of cyanuric acid degradation.