Investigation of the effects of humic acid and H<Subscript>2</Subscript>O<Subscript>2</Subscript> on the photocatalytic degradation of atrazine assisted by microwave

A solution of atrazine in a TiO₂ suspension, an endocrine disruptor in natural water, was tentatively treated by microwave-assisted photocatalytic technique. The effects of mannitol, oxygen, humic acid, and hydrogen dioxide on the photodegradation rate were explored. The results could be deduced as follows: the photocatalytic degradation of atrazine fits the pseudo-first-order kinetic well with k = 0.0328 s^?1, and ·OH was identified as the dominant reactant. Photodegradation of atrazine was hindered in the presence of humic acid, and the retardation effect increased as the concentration of humic acid increased. H₂O₂ displayed a significant negative influence on atrazine photocatalysis efficiency. Based on intermediates identified with gas chromatography-mass spectrometry (GC-MS) and Liquid chromatography-mass spectrometry (LC-MS/MS) techniques, the main degradation routes of atrazine are proposed.     

Effect of humic acids on the Fenton degradation of phenol

We show that the degradation of phenol by Fe(III) and hydrogen peroxide is faster in the presence of humic acids. This is most likely due to faster reduction of Fe(III)-humate complexes by H₂O₂/HO₂^·/O₂^–· when compared with Fe(III)-H₂O complexes. The fact that humic acids, a major class of naturally occurring compounds, favour the Fenton reaction has great relevance in the field of water and soil decontamination, where organic compounds usually have a negative effect. Furthermore, it adds insight into the self-depuration processes of natural aquifers.     

Factors influencing the photodegradation of N-nitrosodimethylamine in drinking water

In order to provide basic data for practical application, photodegradation experiment of N-nitrosodimethylamine (NDMA) in aqueous solution was carried out with a low-pressure Hg lamp. Effects of the initial concentration of NDMA, solution pH, dissolved oxygen, and the presence of humic acid on NDMA photodegradation were investigated. NDMA at various initial concentrations selected in this study was almost completely photodegraded by UV irradiation within 20 min, except that at 1.07 mmol/L, NDMA could be photodegraded almost completely in the acidic and neutral solutions, while the removal efficiency decreased remarkably in the alkaline solution. Dissolved oxygen enhanced the NDMA photodegradation, and the presence of humic acid inhibited the degradation of NDMA. Depending on the initial concentration of NDMA, NDMA photodegradation by UV obeyed the pseudo-first-order kinetics. Dimethylamine, nitrite, and nitrate were detected as the photodegradation products of NDMA. ¹O₂ was found to be the reactive oxygen species present in the NDMA photodegradation process by UV, based on the inhibiting experiments using tert-butanol and sodium azide.     

Decolorisation of Acid Blue 74 by ultraviolet/H<Subscript>2</Subscript>O<Subscript>2</Subscript>

The photodegradation of Acid blue 74 in aqueous solution employing a H₂O₂/ultraviolet system in a photochemical reactor was investigated. The kinetics of decolorization were studied by application of a kinetic model. The results show that the reaction of decolorization followed pseudo-first order kinetics. We demonstrate that there is an optimum H₂O₂ concentration, at which the rate of the decolorization reaction is maximum. Irradiation at 253.7 nm of the dye solution in the presence of H₂O₂ results in complete discoloration after ten minutes of treatment.     

Kinetics of the oxidation of endocrine disruptor nonylphenol by ferrate(VI)

The kinetics of the oxidation of endocrine disruptor nonylphenol (NP) by potassium ferrate(VI) (K₂FeO₄) in water as a function of pH 8.0–10.9 at 25°C is presented. The observed second-order rate constants, k _obs, decrease with an increase in pH 269–32 M^?1 s^?1. The speciation of Fe(VI) (HFeO ₄ ^? and FeO ₄ ^2? ) and NP (NP–OH and NP–O^?) species was used to explain the pH dependence of the k _obs values. At a dose of 10 mg L^?1 (50 μM) K₂FeO₄, the half-life for the removal of NP by Fe(VI), under water treatment conditions, is less than 1 min.     

Metabolism of two dominant epibenthic echinoderms measured at bathyal depths in the Santa Catalina Basin

Metabolism of two abundant echinoderm species constituting 99.6% of the epibenthic megafauna in the Santa Catalina Basin, off southern California, USA was measured at 1 300 m during the 1979 “Bathyal Expedition”. Specimens of the ophiuroid Ophiophthalmus normani and the holothurian Scotoplanes globosa, collected by the submersible “Alvin”, were individually placed in respirometers, and measured in situ for O₂ consumption and ammonium excretion rates. For O. normani, weight-specific O₂ consumption rates decreased with increasing weight and were of comparable magnitude to rates of deep-sea and shallow-water ophiuroids; excretion rates were highly variable. Population O₂ consumption and excretion rates for O. normani (estimated from size-frequency distribution, abundance, and rate regression equations) were 1 129.28 μl O₂ m^-2 h^-1 and 27.30 nmol NH ₄ ⁺ m^-2 h^-1. Weight-specific O₂ consumption and ammonium excretion rates of S. globosa decreased with increasing weight and were of comparable magnitude to rases of shallow-water holothurians. Population O₂ constimption and excretion rates of S. globosa were 1.38 μl O₂ m^-2 h^-1 and 4.86 nmol NH ₄ ⁺ m^-2 h^-1. Combined population O₂ consumption rates for O. normani and S. globosa are of comparable magnitude to that of the sediment community and plankton in the benthic boundary layer (sediment and overlying 50 m water column) of the Santa Catalina Basin.     

Effect of iron speciation on the photodegradation of Monuron in combined photocatalytic systems with immobilized or suspended TiO2

Photodegradation kinetics of Monuron (3-(4-chlorophenyl)-1,1-dimethylurea) in photoreactor with immobilized and suspended TiO₂ photocatalyst were studied. The effect of addition of ferric or ferrous perchlorate was investigated. Whatever the concentration of Fe(III/II) added there is no significant negative effect on the photodegradation rate of pollutants. On the contrary, depending on speciation and concentration of iron salts, slight or marked acceleration of the photodegradation kinetics was observed. This positive influence was more pronounced in the case of TiO₂ suspensions than for TiO₂ layers. Fe(III) was generally more effective than Fe(II).     

Pathway of the ozonation of 2,4,6-trichlorophenol in aqueous solution

The reaction mechanism and pathway of the ozonation of 2,4,6-trichlorophenol (2,4,6-TCP) in aqueous solution were investigated. The removal efficiency and the variation of H₂O₂, Cl^? formic acid, and oxalic acid were studied during the semi-batch ozonation experiments (continuous for ozone gas supply, fixed volume of water sample). The results showed that when there was no scavenger, the removal efficiency of 0.1 mmol/L 2,4,6-TCP could reach 99% within 6 min by adding 24 mg/L ozone. The reaction of molecular ozone with 2,4,6-TCP resulted in the formation of H₂O₂. The maximal concentration of H₂O₂ detected during the ozonation could reach 22.5% of the original concentration of 2,4,6-TCP. The reaction of ozone with H₂O₂ resulted in the generation of a lot of OH? radicals. Therefore, 2,4,6-TCP was degraded to formic acid and oxalic acid by ozone and OH? radicals together. With the inhibition of OH? radicals, ozone molecule firstly degraded 2,4,6-TCP to form chlorinated quinone, which was subsequently oxidized to formic acid and oxalic acid. Two reaction pathways of the degradation of 2,4,6-TCP by ozone and O₃/OH? were proposed in this study.     

Accelerated degradation of orange G over a wide pH range in the presence of FeVO<Subscript>4</Subscript>

In this study, FeVO₄ was prepared and used as Fenton-like catalyst to degrade orange G (OG) dye. The removal of OG in an aqueous solution containing 0.5 g·L^–1 FeVO₄ and 15 mmol·L^–1 hydrogen peroxide at pH 7.0 reached 93.2%. Similar rates were achieved at pH 5.7 (k = 0.0471 min^–1), pH 7.0 (k = 0.0438 min^–1), and pH 7.7 (k = 0.0434 min^–1). The FeVO₄ catalyst successfully overcomes the problem faced in the heterogeneous Fenton process, i.e., the narrow working pH range. The data for the removal of OG in FeVO₄ systems containing H₂O₂ conform to the Langmuir–Hinshelwood model (R² = 0.9988), indicating that adsorption and surface reaction are the two basic mechanisms for OG removal in the FeVO₄–H₂O₂ system. Furthermore, the irradiation of FeVO₄ by visible light significantly increases the degradation rate of OG, which is attributed to the enhanced rates of the iron cycles and vanadium cycles.

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UV-C light-enhanced photo-Fenton oxidation of methyl parathion

The photodegradation of aqueous solutions containing 0.2 mM methyl parathion has been studied through the optimization of the [H₂O₂]/[Fe³⁺] ratio in a Fe³⁺/H₂O₂/UV-C flow system of 1.3 L capacity. The decay kinetics and TOC abatement have been analyzed for the experiments performed at pH 3.0 and room temperature. All experiments lead to the total methyl parathion destruction after a few minutes, following a pseudo-first-order decay kinetics. Total mineralization can be reached after 120 min at the optimum ratio found, due to the synergistic effect of the very oxidizing hydroxyl radical (^·OH) produced via the Fenton reagent and the effective photodecarboxylation at 253.7 nm.     

Removal of acid yellow 36 using Box–Behnken designed photoelectro-Fenton: a study on removal mechanisms

Photoelectro-Fenton was applied for the removal of acid yellow 36 (AY36) from synthetic aqueous solution using iron electrodes. A Box–Behnken design was used for optimization of the effects of pH, H₂O₂ concentration, current density, and reaction time. Individual effects of these variables were more important than their interaction effects. The derived model was in good agreement with the experimental results. Total organic carbon was determined in solution and sludge in order to clarify the removal mechanism. Increase of H₂O₂ concentration and current density led to domination of oxidation and coagulation mechanisms, respectively. The effects of scavenging and inhibiting agents were also investigated: (1) presence of alcohols can reduce the efficiency through competition with dye for reaction with hydroxyl radicals; (2) anions (NO₃^?, HCO₃^?, and H₂PO₄^?) scavenged hydroxyl radicals and reduced decolorization of AY36.     

五氧化二钒类Fenton降解邻苯二甲酸二乙酯的机制研究

发展了基于五氧化二钒(V_2O_5)和过氧化氢(H_2O_2)的新型类Fenton体系,探索了此体系产生羟基(·OH)的机制及降解邻苯二甲酸二乙酯(DEP)的效率;并考察了V_2O_5投加量、H_2O_2浓度,以及草酸对DEP降解的影响。结果表明,当V_2O_5投加量为0.1 g·L-1,H_2O_2浓度为2.0 mmol·L-1,反应24 h后,对DEP(25 mg·L-1)的降解率可达61.1%,增加或降低V_2O_5投加量和H_2O_2浓度均不利于DEP的降解。利用电子顺磁共振技术(Electron Paramagnetic Resonance,EPR)耦合5,5-二甲基-1-吡咯啉氮氧化物(DMPO)为捕获剂对反应体系中的主导自由基进行鉴定,发现·OH是体系降解DEP的主要活性物种,利用苯甲酸作为探针分子实现了·OH的间接定量,并初步推测了V_2O_5活化H_2O_2的过程。     

水体酸化条件下Cu(II)对斑马鱼胚胎的毒性效应

为评价由酸雨、酸性矿山排水等环境污染导致的水体酸化及水体重金属联合作用对水生生物的生态毒性效应,研究了不同pH值(pH=3、4、5、6、7和7.8)条件下Cu2+对斑马鱼胚胎发育的影响。结果表明,酸性水体及Cu2+单一存在时,酸对斑马鱼胚胎24h半数效应浓度值EC50为pH=3.65,Cu2+(pH=7.8)对斑马鱼胚胎24h-EC50为0.267mg·L-1;当水体酸化及水体中的Cu2+共存时,较低的pH对Cu2+的生物毒性起协同作用,表现为随溶液pH的降低,各浓度Cu2+对斑马鱼胚胎的24h凝结率显著增高(P24h致死率=0.001),而斑马鱼胚胎96h孵化率显著降低(P96h孵化率=0.002),且不同浓度的Cu2+之间的生物毒性效应存在显著性差异(P24h致死率=0.0321;P96h孵化率=0.0028)。这说明酸性水体和Cu2+都显著影响斑马鱼胚胎的发育,且Cu2+在酸性水体中对斑马鱼胚胎的毒性显著增强。因此,在受重金属Cu2+污染的地区,如同时受到酸雨或酸性矿山排水等较低pH值和Cu2+的双重胁迫,较低浓度的Cu2+就能够对水生生物的生殖发育及水生生态系统产生严重的影响和危害。     

Allelopathic inhibition on red tide microalgae Skeletonema costatum by five macroalgal extracts

This study aims to identify effective antialgal allelochemicals from marine macroalgae that inhibit the growth of red tide microalgae. Practically, new algicidal agents were developed to control red tide. The growth inhibitory effects of 5 marine macroalgae Porphyra tenera, Laminaria japonica, Ulva pertusa, Enteromorpha clathrata, and Undaria pinnatifida on Skeletonema costatum were evaluated by adding crude seawater extracts of macroalgal dry tissue into the culture medium containing S. costatum. The half-effective concentrations at 120 h (EC_{50, 120 h}) of the seawater extracts were 0.6, 0.9, 1.0, 1.0, and 4.7 g/L for the five macroalgae above, respectively. E. clathrata, L. japonica and U. pertusa showed strong allelopathic effect on the growth of S. costatum. There have been no previous reports with regard to the allelopathic effects of the former two macroalgae so far. The possible allelochemicals of 21 compounds of the E. clathrata were detected using Gas chromatography-mass spectrometry (GC-MS) analysis. Unsaturated fatty acids, acrylic acid (C₃H₄O₂), and linolenic acid (C₁₈H₃₀O₂) were the most likely allelochemicals in E. clathrata.     

High-valent iron-based oxidants to treat perfluorooctanesulfonate and perfluorooctanoic acid in water

Perfluoroalkyl and polyfluoroalkyl substances are occurring in consumer and industrial products. They have been found globally in the aquatic environment including drinking water sources and treated wastewater effluents, which has raised concern of potential human health effects because these substances may be bioaccumulative and extremely persistent. The saturated carbon–fluorine bonds of the substances make them resistant to degradation by physical, chemical, and biological processes. There is therefore a need for advanced remediation methods. Iron-based methods involving high-valent compounds are appealing to degrade these substances due to their high oxidation potentials and capability to generate environmentally friendly by-products. This article presents for the first time the oxidation ability of tetraoxy anions of iron(V) (Fe^VO₄ ^3?, Fe(V)), and iron(IV) (Fe^IVO₄ ^4?, Fe(IV)), commonly called ferrates, in neutral and alkaline solutions. Solid compounds of Fe(V) (K₃FeO₄) and Fe(IV) (Na₄FeO₄) were added directly into buffered solution containing perfluorooctansulfonate and perfluorooctanoic acid at pH 7.0 and 9.0, and mixed solutions were subjected to analysis for remaining fluoro compounds after 5 days. The analysis was performed by liquid chromatography–mass spectrometry/mass spectrometry technique. Fe(IV) showed the highest ability to oxidize the studied contaminants; the maximum removals were 34 % for perfluorooctansulfonate and 23 % for perfluorooctanoic acid. Both Fe(V) and Fe(IV) had slightly higher tendency to oxidize contaminants at alkaline pH than at neutral pH. Results were described by invoking reactions involved in oxidation of perfluorooctansulfonate and perfluorooctanoic acid by ferrates in aqueous solution. The results demonstrated potentials of Fe(V) and Fe(IV) to degrade perfluoroalkyl substances in contaminated water.     

Availability of colloidal ferric oxides to coastal marine phytoplankton

Cell growth of a coastal marine diatom, Phaeodactylum tricornutum (stock cultures), and two red tide marine flagellates, Heterosigma akashiwo and Gymnodinium mikimotoi (stock cultures), in the presence of soluble chelated Fe(III)-EDTA (1:2) and of four different phases of ferric oxide colloids were experimentally measured in culture experiments at 20°C under 3000 lux fluorescent light. Soluble Fe(III)-EDTA induced the maximal growth rates and cell yields. The short-term uptake rate of iron by H. akashiwo in Fe(III)-EDTA medium was about eight times faster than that in solid amorphous hydrous ferric oxide (Fe₂O₃·xH₂O) medium. In culture experiments supplied with four different ferric oxide forms, the orders of cell yields are amorphous hydrous ferric oxide>-FeOOH (lepidocrocite)>Fe₅O₇(OH)·4H₂O (hydrated ferric oxyhydroxide polymer >-FeOOH (goethite). The specific growth rates () at logarithmic growth phase in Fe(III)-EDTA, amorphous hydrous ferric oxide and -FeOOH media were significantly greater than those in Fe₅O₇ (OH)·4H₂O and -FeOOH media. The thermodynamically stable forms such as Fe₅O₇(OH)·4H₂O and -FeOOH supported a little or no phytoplankton growth. The iron solublities and/or proton-promoted iron dissolution rates of these colloidal ferric oxides in seawater at 20°C were determined by simple filtration techniques involving -activity measurements of ⁵⁹Fe. The orders of solubilities and estimated dissolution rate constants of these ferric oxides in seawater were consistent with that of cell yields in the culture experiments. These results suggest that the availability of colloidal iron to provide a source of iron for phytoplankton is related to the thermodynamic stability and kinetic lability of the colloidal ferric oxide phases, which probably control the uptake rate of iron by phytoplankton.     

Dynamic changes in radial oxygen loss and iron plaque formation and their effects on Cd and As accumulation in rice (Oryza sativa L.)

Temporal variations and correlations between radial oxygen loss (ROL), iron (Fe) plaque formation, cadmium (Cd) and arsenic (As) accumulation were investigated in two rice cultivars at four different growth stages based upon soil pot and deoxygenated solution experiments. The results showed that there were significant differences in ROL (1.1–16 μmol O₂ plant^?1 h^?1), Fe plaque formation (4,097–36,056 mg kg^?1), Cd and As in root tissues (Cd 77–162 mg kg^?1; As 49–199 mg kg^?1) and Fe plaque (Cd 0.4–24 mg kg^?1; As 185–1,396 mg kg^?1) between these growth stages. ROL and Fe plaque increased dramatically from tillering to ear emergence stages and then were much reduced at the grain-filling stage. Furthermore, significantly positive correlations were detected between ROL and concentrations of Fe, Cd and As in Fe plaque. Our study indicates that increased Fe plaque forms on rice roots at the ear emergence stage due to the increased ROL. This stage could therefore be an important period to limit the transfer and distribution of Cd and As in rice plants when growing in soils contaminated with these toxic elements.     

Microwave and Fenton's reagent oxidation of wastewater

We compared two H₂O₂ oxidation methods for the treatment of industrial wastewater: oxidation using Fenton's reagent [H₂O₂/Fe(II)] and microwave irradiation. Both methods were applied to the treatment of synthetic phenol solutions (100 mg L⁻¹) and of an industrial effluent containing a mixture of ionic and non-ionic surfactants at high load (20 g L⁻¹ of COD). The effects of initial pH, initial H₂O₂ concentration, Fenton catalyst amount and irradiation time were assessed. According to the oxidation of phenol, it has been found that the oxidation by Fenton's reagent is dependent on the pH, contrary to the microwave system, which is not influenced by this parameter. For both systems, a limiting amount of oxidant has been found; above this point the oxidation of phenol is not improved by a further addition of peroxide. The oxidation of the industrial surfactant effluent has only been successful with the Fenton's reagent. In this case, large amounts of ferrous ions are necessary for the precipitation of the ionic surfactants of the effluent, followed by the oxidation of the non-ionic constituents of the solution. Electronic Publication     

Diffusive boundary layers and photosynthesis of the epilithic algal community of coral reefs

The effects of mass transfer resistance due to the presence of a diffusive boundary layer on the photosynthesis of the epilithic algal community (EAC) of a coral reef were studied. Photosynthesis and respiration of the EAC of dead coral surfaces were investigated for samples from two locations: the Gulf of Aqaba, Eilat (Israel), and One Tree Reef on the Great Barrier Reef (Australia). Microsensors were used to measure O₂ and pH at the EAC surface and above. Oxygen profiles in the light and dark indicated a diffusive boundary layer (DBL) thickness of 180–590 μm under moderate flow (~0.08 m s^?1) and >2,000 μm under quasi-stagnant conditions. Under light saturation the oxygen concentration at the EAC surface rose within a few minutes to 200–550% air saturation levels under moderate flow and to 600–700% under quasi-stagnant conditions. High maximal rates of net photosynthesis of 8–25 mmol O₂ m^?2 h^?1 were calculated from measured O₂ concentration gradients, and dark respiration was 1.3–3.3 mmol O₂ m^?2 h^?1. From light–dark shifts, the maximal rates of gross photosynthesis at the EAC surface were calculated to be 16.5 nmol O₂ cm^?3 s^?1. Irradiance at the onset of saturation of photosynthesis, E _k, was <100 µmol photons m^?2 s^?1, indicating that the EAC is a shade-adapted community. The pH increased from 8.2 in the bulk seawater to 8.9 at the EAC surface, suggesting that very little carbon in the form of CO₂ occurs at the EAC surface. Thus the major source of dissolved inorganic carbon (DIC) must be in the form of HCO₃ ^?. Estimates of DIC fluxes across the DBL indicate that, throughout most of the daytime under in situ conditions, DIC is likely to be a major limiting factor for photosynthesis and therefore also for primary production and growth of the EAC.