Robustness of anaerobes exposed to cyanuric acid contaminated wastewater and achieving efficient removal via optimized co-digestion scheme

The impact of various industrial pollutants on anaerobes and the biodegradation potentials need much emphasis. This study aims to investigate the response of anaerobic microbial systems to cyanuric acid (CA) exposure; CA is toxic and possible carcinogen. First, the long-term exposure of mixed culture bacteria (i.e., municipal sludge) to low-strength wastewater containing 20 mg/L CA was conducted in an up-flow anaerobic staged reactor. Stable performance and sludge granulation were observed, and the microbial community structure showed the progression of genus Acinetobacter known as CA degrader. Second, batch-mode experiment was performed to examine the CA biodegradability at higher doses (up to 250 mg/L of CA) in the absence and presence of glucose as a co-substrate; response surface-based optimization was used to design this experiment and to estimate the optimum CA-glucose combination. CA removal of 77-98% was achieved when CA was co-digested with glucose (250-1,000 mg/L), after 7 days-incubation at temperature of 37 °C, compared to 34% when CA was solely digested. Further, the obtained methane yield dropped when CA exceeded over 125 mg/L, though the deterioration was mitigated by addition of higher concentration of glucose. Overall, we conclude that CA is efficiently degraded under anaerobic conditions when being co-digested with readily assimilable substrate.

Transformation of atrazine by photolysis and radiolysis: kinetic parameters, intermediates and economic consideration

Four techniques, UV_{254 nm} photolysis, vacuum ultraviolet (VUV_{172 nm}) photolysis, combined UV_{254 nm}/VUV_{185 nm} photolysis and gamma (γ) radiolysis were used to induce the transformation of atrazine in aqueous solution. The effects of dissolved oxygen (atrazine concentration 1 × 10^-4 mol L^-1 and 4.6 × 10^-7 mol L^-1) and matrix (high purity water/purified wastewater, atrazine concentration 4.6 × 10^-7 mol L^-1) and the electric energy requirements were investigated. The calculation of the energy input in cases of the photolyses was based on the lamp's power. In radiolysis, the absorbed dose (J kg^-1) was the basis. In UV photolysis, atrazine transforms to atrazine-2-hydroxy; this product practically does not degrade during UV photolysis; due to this reason, the mineralisation is very slow. This and some other products of atrazine decomposition degrade only in radical reactions. Dissolved oxygen usually slightly enhances the degradation rate. At 10^-7 mol L^-1 concentration level, the matrix, high purity water/purified wastewater, has not much influence on the degradation rates in UV photolysis and radiolysis. In the VUV and UV/VUV systems, considerable matrix effects were observed. Comparing the electric energy requirements of the four degradation processes, radiolysis was found to be the economically most feasible method, requiring 1-2 orders of magnitude less electric energy than UV/VUV, VUV and UV photolysis.

Identification of intermediates, acute toxicity removal, and kinetics investigation to the Ametryn treatment by direct photolysis (UV254), UV254/H2O2, Fenton, and photo-Fenton processes

This paper reports the degradation of 10 mg L^-1 Ametryn solution with different advanced oxidation processes and by ultraviolet (UV₂₅₄) irradiation alone with the main objective of reducing acute toxicity and increase biodegradability. The investigated factors included Fe²⁺ and H₂O₂ concentrations. The effectiveness of the UV₂₅₄ and UV₂₅₄/H₂O₂ processes were investigated using a low-pressure mercury UV lamp (254 nm). Photo-Fenton process was explored using a blacklight blue lamp (BLB, λ = 365 nm). The UV₂₅₄ irradiation process achieved complete degradation of Ametryn solution after 60 min. The degradation time of Ametryn was greatly improved by the addition of H₂O₂. It is worth pointing out that a high rate of Ametryn removal was attained even at low concentrations of H₂O₂. The kinetic constant of the reaction between Ametryn and HO^● for UV₂₅₄/H₂O₂ was 3.53 × 10⁸ L mol^-1 s^-1. The complete Ametryn degradation by the Fenton and photo-Fenton processes was observed following 10 min of reaction for various combinations of Fe²⁺ and H₂O₂ under investigation. Working with the highest concentration (150 mg L^-1 H₂O₂ and 10 mg L^-1 Fe²⁺), around 30 and 70% of TOC removal were reached within 120 min of treatment by Fenton and photo-Fenton processes, respectively. Although it did not obtain complete mineralization, the intermediates formed in the degradation processes were hydroxylated and did not promote acute toxicity of Vibrio fischeri. Furthermore, a substantial improvement of biodegradability was obtained for all studied processes.

Influence of solution pH on degradation of atrazine during UV and UV/H2O2 oxidation: kinetics, mechanism, and degradation pathways

The kinetics, degradation mechanism and degradation pathways of atrazine (ATZ) during sole-UV and UV/H₂O₂ processes under various pH conditions were investigated; the effects of UV irradiation time and H₂O₂ dose were also evaluated.

Enhanced photocatalytic degradation of atrazine by platinized titanium dioxide under 352 nm irradiation

Simply coating 1 wt.% of platinum on titanium dioxide (TiO₂) surface resulted in simple preparation of platinized TiO₂ (Pt-TiO₂). This study demonstrated the photodegradation of atrazine (ATZ) using either Pt-TiO₂ or TiO₂ as a photocatalyst under 352 nm light irradiation. The Pt-TiO₂-catalyzed ATZ degradation reached 76% in 3 hours without adding H₂O₂ solution or aeration, which was more than 10% higher than the TiO₂-catalyzed reaction. The decomposition product of Pt-TiO₂-catalyzed ATZ degradation was mainly cyanuric acid. Thus, Pt-TiO₂ as an effective photocatalyst has three main advantages in the photodegradation of ATZ under 352 nm irradiation. First, the coated Pt can facilitate the generation of appropriate amounts of OH radicals, so it can prevent the formation of over-oxidized TiO₂. Second, aeration was not needed. Third, the excited electrons were mainly uni-directionally transferred to the catalyst surface to avoid recombination of electron-hole pairs.

Degradation of florfenicol in water by UV/Na2S 2O 8 process

UV irradiation-activated sodium persulfate (UV/PS) was studied to degrade florfenicol (FLO), a phenicol antibiotic commonly used in aquaculture, in water. Compared with UV/H2O2 process, UV/PS process achieves a higher FLO degradation efficiency, greater mineralization, and less cost. The quantum yield for direct photolysis of FLO and the second-order rate constant of FLO with sulfate radicals were determined. The effects of various factors, namely PS concentration, anions (NO3 (-), Cl(-), and HCO3 (-)), ferrous ion, and humic acid (HA), on FLO degradation were investigated. The results showed that the pseudo-first-order rate constant increased linearly with increased PS concentration. The tested anions all adversely affected FLO degradation performance with the order of HCO3 (-) > Cl(-) > NO3 (-). Coexisting ferrous ions enhanced FLO degradation at a Fe(2+)/PS molar ratio under 1:1. HA significantly inhibited FLO degradation due to radical scavenging and light-screening effect. Toxicity assessment showed that it is capable of controlling the toxicity for FLO degradation. These findings indicated that UV/PS is a promising technology for water polluted by antibiotics, and the treatment is optimized only after the impacts of water characteristics are carefully considered.

Water quality parameters controlling the photodegradation of two herbicides in surface waters of the Columbia Basin, Washington

The water quality parameters nitrate-nitrogen, dissolved organic carbon, and suspended solids were correlated with photodegradation rates of the herbicides atrazine and 2,4-D in samples collected from four sites in the Columbia River Basin, Washington, USA. Surface water samples were collected in May, July, and October 2010 and analyzed for the water quality parameters. Photolysis rates for the two herbicides in the surface water samples were then evaluated under a xenon arc lamp. Photolysis rates of atrazine and 2,4-D were similar with rate constants averaging 0.025 h(-1) for atrazine and 0.039 h(-1) for 2,4-D. Based on multiple regression analysis, nitrate-nitrogen was the primary predictor of photolysis for both atrazine and 2,4-D, with dissolved organic carbon also a predictor for some sites. However, at sites where suspended solids concentrations were elevated, photolysis rates of the two herbicides were controlled by the suspended solids concentration. The results of this research provide a basis for evaluating and predicting herbicide photolysis rates in shallow surface waters.

Photochemistry for pollution abatement

Sunlight is a clean, cheap, and abundant reagent. Many light-initiated reactions can be carried out in water, making photochemistry an ideal tool for pollution abatement and/or elimination. We studied the photoreactivity of different families of common organic micropollutants: light-initiated processes in the absence or presence of co-oxidants, and photocatalyzed reactions using different photocatalysts and composites. Based on the experimental evidences found, detailed transformation mechanisms have been proposed that help understand the reactivity of organic micropollutants and predict their environmental fate. Our approach includes the study of the photophysics for each family of compounds, its reactivity upon direct photolysis, adsorption onto photocatalysts, photocatalytic reactivity, thermodynamics, and kinetics of the processes involved (pKa, Eº, rate constants, etc.), product analysis, and ecotoxicological assessment. Different commonly overlooked problems, related to the kinetics of the process, are reported, and a model is proposed that includes the possibility of adsorption on different types of active sites, leading to different reactivities.

Fast atrazine photodegradation in water by pulsed light technology

Pulsed light technology consists of a successive repetition of short duration (325μs) and high power flashes emitted by xenon lamps. These flashlamps radiate a broadband emission light (approx. 200-1000 nm) with a considerable amount of light in the short-wave UV spectrum. In the present work, this technology was tested as a new tool for the degradation of the herbicide atrazine in water. To evaluate the presence and evolution with time of this herbicide, as well as the formation of derivatives, liquid chromatography-mass spectrometry (electrospray ionization) ion trap operating in positive mode was used. The degradation process followed first-order kinetics. Fluences about 1.8-2.3 J/cm(2) induced 50% reduction of atrazine concentration independently of its initial concentration in the range 1-1000 μg/L. Remaining concentrations of atrazine, below the current legal limit for pesticides, were achieved in a short period of time. While atrazine was degraded, no chlorinated photoproducts were formed and ten dehalogenated derivatives were detected. The molecular structures for some of these derivatives could be suggested, being hydroxyatrazine the main photoproduct identified. The different formation profiles of photoproducts suggested that the degradation pathway may include several successive and competitive steps, with subsequent degradation processes taking part from the already formed degradation products. According to the degradation efficiency, the short treatment time and the lack of chloroderivatives, this new technology could be considered as an alternative for water treatment.

Oxidative decomposition of atrazine in water in the presence of hydrogen peroxide using an innovative microwave photochemical reactor

The simultaneous application of microwave (MW) power and UV light leads to improved results in photochemical processes. This study investigates the oxidative decomposition of atrazine in water using an innovative MW and UV photochemical reactor, which activates a chemical reaction with MW and UV radiation using an immersed source without the need for a MW oven. We investigated the influence of reaction parameters such as initial H(2)O(2) concentrations, reaction temperatures and applied MW power and identified the optimal conditions for the oxidative decomposition of atrazine. Atrazine was completely degraded by MW/UV/H(2)O(2) in a very short time (i.e. t(1/2) = 1.1 min for 20.8 mg/L in optimal conditions). From the kinetic study, the disappearance rate of atrazine can be expressed as dX/dt = k(PH)[M](0)(b-X)(1-X), where b ≡ [H(2)O(2)](0)/[M](0)+k(OH)[·OH]/k(PH)[M](0), and X is the atrazine conversion, which correlates well with the experimental data. The kinetic analysis also showed that an indirect reaction of atrazine with an OH radical is dominant at low concentrations of H(2)O(2) and a direct reaction of atrazine with H(2)O(2) is dominant when the concentration of H(2)O(2) is more than 200 mg/L.

Photolytic destruction of endocrine disruptor atrazine in aqueous solution under UV irradiation: products and pathways

The ultraviolet (UV) photolysis of atrazine in aqueous solution was investigated at wavelength of 254 nm in this study. This paper was mainly focused on the identification of atrazine degradation intermediates by HPLC-MS/MS and its degradation mechanisms. The photodegradation products included the following seven classes: dechloro-hydroxylated products, chloro-dealkylated products, dechloro-dealkylated products, alkylic-oxidated products, delamination-hydroxylated products, olefinic products, and dechloro-hydrogenated products which were never reported in direct photolytic process, 4-isopropylamino-6-ethylamino-s-triazine (IEST), 4,6-dihydroxy-s-triazine (OOST). The main degradation products were 2-hydroxy-4-acetamido-6-ethylamino-s-triazine (OIET), 2-chloro-4-isopropyl-amino-6-methylamino-s-triazine (CIMT), 2-chloro-4,6-divinylamino-s-triazine (CVVT), 2-chloro-4-ethylamino-6-amino-s-triazine(CEAT), 2-methoxy-4-isopropyl-amino-6-methylamino-s-triazine (OIMT), 2-hydroxy-4-acetamindo-6-ethylamino-s-triazine (ODET), etc. Finally, the possible degradation mechanism was also proposed here.

Carbon, hydrogen, and nitrogen isotope fractionation during light-induced transformations of atrazine

The 13C, 2H, and 15N fractionation associated with light-induced transformations of N-containing pesticides in surface waters was investigated using atrazine as a model compound. In laboratory model systems, bulk isotope enrichment factors epsilonC, epsilonH, and epsilonN were determined during the photooxidation of atrazine by excited triplet states of 4-carboxybenzophenone ((3)4-CBBP*), by OH radicals, and during direct photolysis at 254 nm. Moderately large 2H fractionations, quantified by EH values of -51.2 +/- 2.5% per hundred and -25.3 +/- 1.7% per hundred, were found for the transformation of atrazine by (3)4-CBBP* and OH radicals, respectively. 13C and 15N enrichment factors were rather small (-0.3% per hundred > epsilon(C, N) > -1.7% per hundred). The combined delta(13)C, delta(2)H, and delta(15)N analysis suggests that isotope effects are most likely due to H abstraction at the N-H and C-H bonds of the N-alkyl side chains. Direct photolysis of atrazine yielding hydroxyatrazine as main product was characterized by inverse 13C and 15N fractionation (epsilonC = 4.6 +/- 0.3% per hundred, epsilonN = 4.9 +/- 0.2% per hundred) and no detectable 2H fractionation. We hypothesize that isotope effects from photophysical processes involving the excited states of atrazine as well as magnetic isotope effect originating from the magnetic interactions of spin-carrying C and N nuclei have contributed to the observed inverse fractionation. Our study illustrates how compound-specific isotope analysis can be used to differentiate between important direct and indirect phototransformation pathways of agrochemicals in the environment.

Photolytic treatment of atrazine-contaminated water: products, kinetics, and reactor design

This study investigates the products, kinetics, and reactor design of atrazine photolysis under 254-nm ultraviolet-C (UVC) irradiation. With an initial atrazine concentration of 60 microg/L (60 ppbm), only two products remain in detectable levels. Up to 77% of decomposed atrazine becomes hydroxyatrazine, the major product. Both atrazine and hydroxyatrazine photodecompose following the first-order rate equation, but the hydroxyatrazine photodecomposition rate is significantly slower than that of atrazine. For atrazine photodecomposition, the rate constant is proportional to the square of UVC output, but inversely proportional to the reactor volume. For a photochemical reactor design, a series of equations are proposed to calculate the needed UVC output power, water treatment capacity, and atrazine outlet concentration.

Fragmentation and gas phase aggregation processes in the laser desorption ionization of chlorodiaminotriazines

Fragmentation and supramolecular aggregation induced during the laser desorption/ionization (LDI) of four chlorodiaminotriazines (simazine, atrazine, terbutylazine and propazine) have been investigated. The laser wavelength employed (266 nm) lies within the first absorption band of the four triazines. The main fragmentation channel observed involves the prompt cleavage of the Cl atom, followed by partial or total fragmentation of the side alkyl chains. Breakage of the triazinic ring becomes efficient at moderate laser powers; however, the deamination of the triazine is not observed to take place. In addition, the formation of both covalent and non-covalent triazinic aggregates in the desorption plume is found to be particularly efficient. Aggregates as large as heptamers are neatly detected, with the observation that those with the most intense signal involve the dechlorinated triazinic fragment. Both aggregation and fragmentation are largely suppressed upon dilution of the triazine under matrix-assisted laser desorption/ionization conditions.

On the Low-Lying Excited States ofsym-Triazine-Based Herbicides

We report a joint computational and luminescence study on the low-lying excited states of sym-triazines, namely, 1,3,5-triazine (1) and the ubiquitous herbicides atrazine [6-chloro-N2-ethyl-N4-isopropyl-1,3,5-triazine-2,4-diamine (2)] and ametryn [6-methylthio-N2-ethyl-N4-isopropyl-1,3,5-triazine-2,4-diamine (3)]. Geometrical structures, energetics, and transition and state properties of I and 2 were computed at the TD-DFT, CASSCF, and CASPT2 levels of theory. The fluorescence and phosphorescence emission spectra, lifetimes, and fluorescence quantum yields were measured for the three compounds, and from these, the energies of the lowest excited states and their corresponding radiative rates were determined. The predictions from CASPT2 calculations are in good agreement with the experimental results obtained from the luminescence studies and allow the interpretation of different absorption and emission features.