Nitrate-induced photodegradation of atenolol in aqueous solution: kinetics, toxicity and degradation pathways

The extensive utilization of β-blockers worldwide led to frequent detection in natural water. In this study the photolysis behavior of atenolol (ATL) and toxicity of its photodegradation products were investigated in the presence of nitrate ions. The results showed that ATL photodegradation followed pseudo-first-order kinetics upon simulated solar irradiation. The photodegradation was found to be dependent on nitrate concentration and increasing the nitrate from 0.5 mM L⁻¹ to 10 mM L⁻¹ led to the enhancement of rate constant from 0.00101 min⁻¹ to 0.00716 min⁻¹. Hydroxyl radical was determined to play a key role in the photolysis process by using isopropanol as molecular probe. Increasing the solution pH from 4.8 to 10.4, the photodegradation rate slightly decreased from 0.00246 min⁻¹ to 0.00195 min⁻¹, probably due to pH-dependent effect of nitrate-induced OH formation. Bicarbonate decreased the photodegradation of ATL in the presence of nitrate ions mainly through pH effect, while humic substance inhibited the photodegradation via both attenuating light and competing radicals. Upon irradiation for 240 min, only 10% reduction of total organic carbon (TOC) can be achieved in spite of 72% transformation rate of ATL, implying a majority of ATL transformed into intermediate products rather than complete mineralization. The main photoproducts of ATL were identified by using solid phase extraction-liquid chromatography-mass spectrometry (SPE-LC-MS) techniques and possible nitrate-induced photodegradation pathways were proposed. The toxicity of the phototransformation products was evaluated using aquatic species Daphnia magna, and the results revealed that photodegradation was an effective mechanism for ATL toxicity reduction in natural waters.     

Zero valent iron mediated degradation of the pharmaceutical diazepam

Parameters that influence the zero valent iron mediated degradation of the pharmaceutical diazepam (DZP) were evaluated including the iron concentration and its pre-treatment, the effect of complexation with EDTA and oxic versus anoxic condition. It was observed that acid pre-treatment of iron particles is important for degradation efficiency and that H₂SO₄ is a better choice than HCl, resulting in higher degradation of DZP. Under oxic conditions, the degradation of DZP achieved 96% after 60 min using Fe⁰ (25 g L⁻¹) pre-treated with H₂SO₄ in the presence of EDTA (119 mg L⁻¹), while mineralization achieved around 60% after the same time. Under anoxic conditions, degradation occurred, however at lower extent, achieving 67% after 120 min. The addition of EDTA improved the treatment efficiency in 20% leading to 99% DZP degradation after 120 min. The first intermediates formed during DZP degradation were identified using LC/MS analysis and revealed the formation of mono- and di-hydroxylated products from DZP during Fe⁰/EDTA/O₂ degradation, which evidences that OH was the main oxidizing species formed in this process.     

Fate of citalopram during water treatment with O3, ClO2, UV and Fenton oxidation

In the present study we investigate the fate of citalopram (CIT) at neutral pH using advanced water treatment technologies that include O₃, ClO₂ oxidation, UV irradiation and Fenton oxidation. The ozonation resulted in 80% reduction after 30 min treatment. Oxidation with ClO₂ removed >90% CIT at a dosage of 0.1 mg L⁻¹. During UV irradiation 85% reduction was achieved after 5 min, while Fenton with addition of 14 mg L⁻¹ (Fe²⁺) resulted in 90% reduction of CIT. During these treatment experiments transformation products (TPs) were formed from CIT, where five compounds were identified by using high resolution and tandem mass spectrometry. Among these desmethyl-citalopram and citalopram N-oxide have been previously identified as human metabolites, while three are novel and published here for the first time. The three TPs are a hydroxylated dimethylamino-side chain derivative, a butyrolactone derivative and a defluorinated derivative of CIT.     

Photolytic and photocatalytic degradation of 6-chloronicotinic acid

This work describes for the first time the photolytic and photocatalytic degradation of 6-chloronicotinic acid (6CNA) in double deionised water, which is a degradation product of neonicotinoid insecticides imidacloprid and acetamiprid, and it is known to appear in different environmental matrices. Photolytic experiments were performed with three UVA (ultraviolet A) polychromatic fluorescent lamps with broad maximum at 355 nm, while photocatalytic experiments were performed using immobilised titanium dioxide (TiO₂) on six glass slides in the spinning basket inside a photocatalytic quartz cell under similar irradiation conditions. Photolytic degradation revealed no change in concentration of 6CNA within 120 min of irradiation, while the photocatalytic degradation within 120 min, obeyed first-order kinetics. The observed disappearance rate constant was k = 0.011 ± 0.001 min⁻¹ and t_1/2 was 63.1 ± 5.5 min. Mineralisation rate was estimated through total organic carbon (TOC) and measurements revealed no carbon removal in case of photolysis after 120 min of exposure. However in photocatalytic experiments 46 ± 7% mineralisation was achieved within 120 min of irradiation. Nevertheless, the removal of total nitrogen (TN) was not observed across all experiments. Ion chromatographic analyses indicated transformation of chlorine atoms to chloride and increase of nitrate(V) ions only via photocatalytic experiments. Efficiency of selected advanced oxidation process (AOP) was investigated through toxicity assessment with Vibrio fischeri luminescent bacteria and revealed higher adverse effects of treated samples on bacteria following photocatalytic degradation in spite of the fact that higher mineralisation was achieved. New hydroxylated product generated in photocatalytic experiments with TiO₂, was confirmed with liquid chromatography-electro spray ionisation mass spectrometry (LC-ESI-MS/MS) analyses, gas chromatography-mass spectrometry (GC-MS) and nuclear magnetic resonance spectroscopy (¹H NMR).     

Elimination of diclofenac from water using irradiation technology

The effluents of wastewater treatment plants, usually directly emitted to the environment, often contain the anti-inflammatory drug diclofenac (DCF). The paper investigates DCF elimination using irradiation technology. Hydroxyl radical and hydrated electron reactive intermediates resulting from water radiolysis effectively degrade DCF and strongly reduce the toxicity of the solutions. OH attaches to one of the rings of DCF, and hydroxylated molecules, 2,6-dichloroaniline and quinoid type compounds are the products. Hydrated electron adds to the chlorine atom containing ring, in the reaction quinoid type compounds and 4-chloroacridine form. At a 0.1 mM DCF concentration, a ∼1 kGy absorbed dose is needed for the degradation of DCF molecules, but for mineralization of the products (in presence of O₂) an order of magnitude higher dose is required.For irradiation of wastewater after biological treatment a ∼1 kGy dose is suggested. At this dose DCF and other drugs or metabolites present at μg L⁻¹ level are eliminated together with microorganism deactivation.     

Photolytic and photocatalytic degradation of quinclorac in ultrapure and paddy field water: identification of transformation products and pathways

Quinclorac (QNC) is an effective but rather persistent herbicide commonly used in rice production. This herbicide presents a mean persistence in the environment so its residues are considered of environmental relevance. However, few studies have been conducted to investigate its environmental behavior and degradation. In the present work, direct photolysis and TiO₂ photocatalysis of the target compound in ultrapure and paddy field water were investigated. After 10 h photolysis in ultrapure water, the concentration of QNC declined 26% and 54% at 250 and 700 W m⁻², respectively. However, the amount of quinclorac in paddy field water remained almost constant under the same irradiation conditions. QNC dissipated completely after 40 min of TiO₂ photocatalysis in ultrapure water, whereas 130 min were necessary to degrade 98% of the initial concentration in paddy field water.Possible QNC photolytic and photocatalytic degradation pathways are proposed after structure elucidation of the main transformation products, through liquid chromatography-electrospray ionization-quadrupole time-of-flight mass spectrometry and exact mass measurements. Pyridine ring hydroxylation at C-9 followed by ring opening and/or oxidative dechlorination were the key steps of QNC degradation.     

Ozonation as an advanced oxidant in treatment of bamboo industry wastewater

The present study employed ozonation process to treat the bamboo industry wastewater (BIWW). The impact of ozone dosage and initial organic concentration on color, COD and TOC removal rates were studied along with characterization of the major organics in raw and treated wastewater. The results suggested the ozone dosage of 3.15 g h⁻¹ (concentration 52.5 mg L⁻¹) was suitable for the treatment. After 25 min ozonation of 1 L raw wastewater, the color, COD and TOC removal efficiencies were 95%, 56% and 40%, respectively, with an influent COD concentration of 835 mg L⁻¹. The ratio of kg O₃ kg⁻¹ COD at 3.15 g h⁻¹ was 2.8 (<3), revealing that ozonation was a cost effective process for tertiary treatment of BIWW. Longer oxidization time was required to achieve similar results for raw wastewater with higher COD concentration. The chromatogram from gel permeation chromatography revealed that ozonation resulted in the breakdown of high molecular weight compounds into lower molecular weight components but could not completely mineralize the organic matter. The majority of these compounds were identified in both raw and ozonated samples via GC-MS analysis. In addition to ester derivatives as the main intermediates of ozonation, 1-chloroctadecane, methyl stearate, benzophenone and α-cyperone were identified as the by-products of ozonation.