Order Degradation Rate Research Articles

Degradative and disinfective properties of carbon-doped anatase–rutile TiO2 mixtures under visible light irradiation

Carbon-doping of TiO2 was performed to improve the visible light response and photocatalytic activity of this catalyst. In this work, the high temperature annealing of TiC was studied and the anatase–rutile doped TiO2 mixtures created were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and ultraviolet–visible light absorption spectrophotometry (UV–Vis). It was found that the TiC fully reacts at 400°C. Transformation of the anatase to rutile phase was observed since the latter form is more heat stable. XPS analysis revealed that the carbon in the sample was present as carbonate species. The UV–Vis spectrum of the doped powders were red shifted compared to P25 TiO2, and a band gap narrowing of 0.2eV was observed. The photocatalytic activity of the powders was quantified by the degradation of methylene blue under visible light irradiation. Langmuir–Hinshelwood kinetics were applied, and the maximum pseudo-first order degradation rate observed was 0.015min−1 for the powder annealed at 400°C for 8h. Disinfection of Escherichia coli K12 was performed using the catalyst in an immobilized configuration under visible light, and up to 80% inactivation was observed, compared to negligible inactivation with P25. The modified Hom disinfection kinetic model was used to describe the data.

광촉매 공정에 따른 이부프로펜의 분해 특성

In this study, Ibuprofen (IBP) degradation by the photo catalytic process was investigated under various parameters, such as UV intensity, optimum dosage of <TEX>$TiO_2$</TEX>, alkalinity, temperature and pH of bulk solution. The pseudo-first order degradation rate constants were in the order of <TEX>$10^{-1}$</TEX> to <TEX>$10^{-4}min^{-1}$</TEX> depending on each condition. The Photocatalytic IBP degradation rate increased with an increase in the applied UV power. At high UV intensity a high rate of tri-iodide (<TEX>$I_3{^-}$</TEX>) ion formation was also observed. Moreover, in order to avoid the use of an excess catalyst, the optimum dosage of catalyst under the various UV intensities (30 and 40 W/L) was examined and ranged from approximately 0.1 <TEX>$gL^{-1}$</TEX>. The photo catalytic IBP degradation rate was changed depending on the alkalinity and temperature and pH in the aqueous solution. This study demonstrated the potential of photo catalytic IBP degradation under different conditions.

Decomposition of cyclohexanoic acid by the UV/H2O2 process under various conditions

Naphthenic acids (NAs) are a broad range of alicyclic and aliphatic compounds that are persistent and contribute to the toxicity of oil sands process affected water (OSPW). In this investigation, cyclohexanoic acid (CHA) was selected as a model naphthenic acid, and its oxidation was investigated using advanced oxidation employing a low-pressure ultraviolet light in the presence of hydrogen peroxide (UV/H2O2 process). The effects of two pHs and common OSPW constituents, such as chloride (Cl−) and carbonate (CO32−) were investigated in ultrapure water. The optimal molar ratio of H2O2 to CHA in the treatment process was also investigated. The pH had no significant effect on the degradation, nor on the formation and degradation of byproducts in ultrapure water. The presence of CO32− or Cl− significantly decreased the CHA degradation rate. The presence of 700mg/L CO32− or 500mg/L Cl−, typical concentrations in OSPW, caused a 55% and 23% decrease in the pseudo-first order degradation rate constants for CHA, respectively. However, no change in byproducts or in the degradation trend of byproducts, in the presence of scavengers was observed. A real OSPW matrix also had a significant impact by decreasing the CHA degradation rate, such that by spiking CHA into the OSPW, the degradation rate decreased up to 82% relative to that in ultrapure water. The results of this study show that UV/H2O2 AOP is capable of degrading CHA as a model NA in ultrapure water. However, in the real applications, the effect of radical scavengers should be taken into consideration for the achievement of best performance of the process.

Significant diethyl phthalate (DEP) degradation by combined advanced oxidation process in aqueous solution

Ultrasound (US) combined with ultraviolet (UV) irradiation and a titanium dioxide (TiO(2)) catalyst was used to effectively remove diethyl phthalate (DEP) from aqueous solutions. Single (sonolysis, photolysis, photocatalysis) and combined (sonophotolysis, sonophotocatalysis) processes were performed to confirm the synergistic effects and DEP degradation mechanism. Using only US, the optimum frequency for DEP degradation was 283kHz. At this frequency a high rate of hydrogen peroxide (H(2)O(2)) formation was observed of approximately 0.32mMmin(-1). The pseudo-first order degradation rate constants were 10(-2)-10(-4)min(-1) depending on the process. Significant degradation and mineralization (TOC) of DEP were observed with the sonophotolytic and sonophotocatalytic processes. Moreover, synergistic effects of 1.29 and 1.95 were exhibited at the sonophotocatalytic and sonophotolytic DEP degradation, respectively. Furthermore, additional advantageous reactions may occur in the heterogeneous sonophotocatalytic process due to interactions between US, UV, and the photocatalyst.

A RP-HPLC-UV Method with Solid Phase Extraction for Determination of Cefepime in Total Nutrient Admixtures: Application to Stability Studies

A simple, specific and selective RP-HPLC – UV method with Solid Phase Extraction (SPE) was developed for the quantification of cefepime in Total Nutrient Admixtures (TNAs). Chromatographic separation was achieved on C18 column using a mobile phase consisting of a mixture of ammonium acetate, acetonitrile and methanol. The flow rate was set to 0.9 mL min-1 and the wavelength was 257 nm. The analyte was extracted from TNAs by using SPE technique. Cefepime calibration curve was linear over a concentration range of 100-1400 μg mL-1 with a correlation coefficient of 0.9994. The intraday accuracy and precision were ≤-4.76% and ≤3.12% respectively. The interday accuracy and precision were ≤-3.90% and ≤4.29% for respectively. The method was successfully applied to stability studies of cefepime in the presence of micronutrients together with low and high concentrations of macronutrients in TNAs. Cefepime was degraded by 42.84% and 58.81 % at room temperature (25±2°C) after 72 hours in low and high macronutrient concentration formulations of TNAs respectively. Cefepime first order degradation rates for low and high macronutrient concentration formulations of TNAs were -0.0032 and -0.0049 hr-1 respectively. These results indicated a higher rate of degradation in TNA formulations with high concentrations of macronutrients.

Improvement of RNA-SIP by pyrosequencing to identify putative 4-n-nonylphenol degraders in activated sludge

Nonylphenols (NP) have estrogenic potential because of their phenolic ring, but the organisms involved in the degradation of this alkylated phenol remain unidentified. Using 16S ribosomal RNA (rRNA)-based stable isotope probing (SIP) and a new method based on pyrosequencing, we identified the bacteria involved in the degradation of the aromatic ring of [U-ring- 13C] 4-n-NP in aerobic sludge. The first order degradation rate of 4-n-NP was 5.5 d −1. Single strand conformation polymorphism of density-separated labeled and unlabeled 16S rRNA showed significant differences and enabled selection of four representative fractions for pyrosequencing. Nineteen phylotypes showed a significant enrichment in the heavy fraction in the labeled pulse. The relative abundances of these phylotypes were combined with the RNA concentration of each fraction to yield a simple model of the distribution of each phylotype across the gradient. This model was used to estimate the percentage of labeling for each phylotype. The sequences showing the highest labeling (11%) were closely related to Afipia sp. but represented only 2 % of the RNA in the heavy fraction of the labeled pulse. The sequences representing the largest proportion of the RNA in the heavy fraction were related to Propionibacterium acnes and Frateuria aurantia, which are known to possess enzymes for phenol degradation. The model shows that despite Afipia having the highest 13C enrichment, other species encoding phenol degradation pathways are responsible for more 13C incorporation. Last, we showed that some species represent 12% of the total RNA but contain only 1% 13C above natural abundance.

Sonophotolytic diethyl phthalate (DEP) degradation with UVC or VUV irradiation

This study investigated the degradation of diethyl phthalate (DEP) by sonolytic, photolytic and sonophotolytic processes. Two types of UV lamps, UVC (254nm) and VUV (185nm+254nm), were combined with ultrasound (283kHz). The pseudo-first order degradation rate constants were in the order of 10−1–10−3min−1 depending on the processes. The sonolytic DEP degradation rate increased with increasing applied power. Photolytic or sonophotolytic degradation of DEP when using a VUV lamp appeared to be effective because the photo ІІ (UVC/VUV) resulted in a significantly faster degradation than the photo І (UVC) processes due to the higher photon energy and higher hydroxyl radical generation by homolysis of water by VUV. Significant degradation and mineralization (TOC) of DEP were observed with the combined sonophotolytic processes. Moreover, synergistic effects of 1.68 and 1.23 were exhibited at DEP degradation of the sonophoto I and sonophoto II processes, respectively. This was attributed to the UV-induced dissociation of hydrogen peroxide (H2O2) generated by the application of US to hydroxyl radicals. Therefore, US in sonophotolytic processes can play an important role in enhancing DEP degradation. Moreover, the sonophoto ІІ process is more effective on the mineralization and biodegradability of DEP.

Catalytic dechlorination of monochlorobenzene by Pd/Fe nanoparticles immobilized within a polymeric anion exchanger

In this study, Pd/Fe bimetallic nanoparticles were immobilized within a macroporous anion exchanger resin D201 through simultaneous NaBH 4 reduction of their chloride-complex precursors, and the properties of the resultant composite for monochlorobenzene (MCB) dechlorination were evaluated in terms of Pd loadings, solution pH, kinetics and cyclic runs. The pseudo-first order degradation rate of MCB was 0.0699 min −1 including partial contribution of adsorption by D201 matrix. However, all MCB was eventually decholorinated to benzene. A rapid and complete dechlorination of MCB by Pd/Fe-D201 was observed within 5 cycles. No Pd dislodge was observed in the process of iron corrosion. The composition of Pd/Fe bimetallic nanoparticles with D201 showed good performance on stability and durability in dechlorination of MCB.

Effect of N-doping on the photocatalytic activity of sol–gel TiO2

In order to study the visible light photocatalytic activity of nitrogen doped titanium dioxide, the interaction between nitrogen dopant sources and titania precursors during sol–gel synthesis is investigated. N–TiO2 was synthesised using the sol–gel method using 1,3-diaminopropane as a nitrogen source. Samples were annealed several temperatures and the percentage of rutile present determined by X-ray diffraction to be 0% (500°C), 46% (600°C), and 94% (700°C). The reducing amounts of anatase at higher temperatures are studied using FTIR, which suggests the absence of any polymeric chains formed by the chelating agents, which would normally extend anatase-to-rutile transformation temperatures. Differential scanning calorimetry shows that crystalliation occurs before 500°C, providing the crystalline form determined by XRD at 500°C. Increased temperature also resulted in diminished visible light absorption capability, with only the 500°C sample showing significant absorption in the visible region. XPS studies revealed that nitrogen remained within the TiO2 lattice at higher temperatures. Consequent with the reduced visible light absorption capacity, photocatalytic activity also reduced with increased annealing temperature. Degradation kinetics of methylene blue, irradiated with a 60W house-bulb, resulted in first order degradation rates constants of 0.40×10−2, 0.19×10−2, and 0.22×10−2min−1 for 500, 600, and 700°C respectively. Degradation of Degussa P25 was minimal under the same conditions, and that of undoped TiO2 was 0.02×10−2min−1. Similarly, using 4-chlorophenol under solar irradiation conditions, the N-doped sample at 500°C substantially out-performed the undoped sample. These results are discussed in the context of the effect of increasing temperature on the nature of the band gap.

Bioremediation of an Experimental Oil Spill in a Coastal Louisiana Salt Marsh

The massive oil release from the Deep Water Horizon disaster has reemphasized the need to remediate oil impacted marshes. Due to the physically fragile nature of salt water marshes, bioremediation is often proposed as an appropriate technology and nutrient amendment is often proposed as a means of accelerating biodegradation of crude oil. However, no information is currently available concerning the efficacy of in situ nutrient amendments in Gulf Coast salt marshes. An experimental crude oil spill (142 l over 100 m2) was conducted to evaluate the efficacy of nitrogen amendment to stimulate bioremediation in a Spartina alterniflora dominated Louisiana salt marsh. A randomized complete block design with replication (n = 10) was utilized to test the hypothesis that additions of fast-release ammonium nitrate (60 g N/m2) and slow-release urea (30 g N/m2) fertilizers could enhance biodegradation of selected crude oil components in the marsh. Crude oil degradation was monitored by analyzing sediment samples for branched and unbranched alkanes over the 180-day study period. The compound/hopane ratio was used to correct for nonbiological losses. No consistent statistically significant effect of fertilizer addition on degradation rates was observed, despite success in increasing the porewater ammonium and NaCl-extractable ammonium over the time frame of the trial. Intrinsic pseudo-first order degradation rates of alkanes in all plots were substantial (0.003–0.008 day−1). Existing, background levels of N did not appear to limit biodegradation rates in Spartina-dominated salt marshes. These results suggest that nutrient amendments will not be successful in stimulation biodegradation of crude oil in these systems.

Photocatalytic Activity of Combustion Synthesized Nanocrystalline CeAlO3

AbstractThe photocatalytic activity of combustion synthesized nanocrystalline CeAlO3 was determined for the degradation of four anionic and four cationic dyes. The perovskite oxide showed high‐photocatalytic activity and a complete degradation of all the dyes was possible within 2 h. The photocatalytic activity of the compound was comparable with the activity of the commercial Degussa P‐25 TiO2 catalyst. The degradation of dyes was found to follow first order kinetics and the first order degradation rate constants were determined.

Monitoring and Modeling Nitrate Persistence in a Shallow Aquifer

A modeling study on fertilizer by-products fate and transport was performed in an unconfined shallow aquifer equipped with a grid of 13 piezometers. The field site was located in a former agricultural field overlying a river paleochannel near Ferrara (Northern Italy), cultivated with cereals rotation until 2004 and then converted to park. Piezometers were installed in June 2007 and were monitored until June 2009 via pressure transducer data loggers to evaluate the temporal and spatial variation of groundwater heads, while an onsite meteorological station provided data for recharge rate calculations via unsaturated zone modeling. The groundwater composition in June 2007 exhibited elevated nitrate (NO 3 − ) and chloride (Cl−) concentrations due to fertilizer leaching from the top soil. The spatial distribution of NO 3 − and Cl− was heterogeneous and the concentration decreased during the monitoring period, with NO 3 − attenuation (below 10 mg/l) after 650 days. A transient groundwater flow and contaminant transport model was calibrated versus observed heads and NO 3 − and Cl− concentrations. Cl− was used as environmental tracer to quantify groundwater flow velocity and it was simulated as a conservative species. NO 3 − was treated as a reactive species and denitrification was simulated with a first order degradation rate constant. Model calibration gave a low denitrification rate (2.5e−3 mg-NO 3 − /l/d) likely because of prevailing oxic conditions and low concentration of dissolved organic carbon. Scenario modeling was implemented with steady state and variable flow time discretization to identify the mechanism of NO 3 − attenuation. It was shown that transient piezometric conditions did not exert a strong control on NO 3 − clean up time, while transient recharge rate did, because it is the main source of unpolluted water in the domain.

The role of activated carbon as a catalyst in GAC/iron oxide/H 2O 2 oxidation process

The catalytic properties of granular activated carbon (GAC) in GAC/iron oxide/hydrogen peroxide (H 2O 2) system was investigated in this research. Batch experiments were carried out in de-ionized water at the desired concentrations of ethylene glycol and phenol. Rate constants for the degradation of hydrogen peroxide and the formation rate of iron species were determined and correlated with mineralization of ethylene glycol at various GAC concentrations. The observed first order degradation rate of hydrogen peroxide in the absence of iron oxide and organic matter increases linearity with the increasing of the GAC concentration. The decomposition rate of hydrogen peroxide was suppressed significantly as the solution pH became acidic or by reducing the surface area of the GAC. The reduction of the surface area was obtained by loading an organic compound (such as phenol) on the GAC or by using the oxidizing agent (H 2O 2). The addition of both chemicals, phenol and H 2O 2, affects mainly the surface area of the small pores, resulting in reducing the catalytic activity inside the micropores. The catalytic properties of the GAC were used to accelerate the formation rate of the ferrous ions, which is known in the literature to be the limiting rate reaction in the classic Fenton like reagent. It was shown that the ethylene glycol mineralization rate was increased by more than 50%. Finally, optimization of the GAC consumption leading to the fastest mineralization of the ethylene glycol, resulting in decreasing of the decomposition rate of H 2O 2 while enhancing the generation rate of ferrous ions.

Degradation of polycyclic aromatic hydrocarbons: Model simulation for bioavailability and biodegradation

AbstractA mathematical model for a one‐dimensional convective‐dispersive solute transport in a soil matrix is presented. The interplay of linear equilibrium sorption and first order degradation were incorporated into the formulation of the model. The model took into consideration the overall effects of the solid and liquid phase mass transfer resistances. Data from experiments were analysed using the temporal moments method (MOM) and CXTFIT curve‐fitting technique. The functional parameters; dispersion coefficient, first order degradation rate constant and the retardation factor were estimated using both first and second normalised moments. The solution to the model equations was achieved by the use of the backward finite difference scheme. Results obtained showed that naphthalene was more selectively degraded than pyrene and anthracene with a residual concentration of naphthalene 1.12E − 5 mg/L, 1.48 mg/L; pyrene 3.11E − 4 mg/L, 1.58 mg/L; and anthracene 7.67E − 4 mg/L, 1.61 mg/L in the axial and radial directions, respectively. Concisely, the modeling results showed the occlusion of these compounds within the fissures and cavities of the soil particles, which renders them not readily bioavailable and thus inaccessible to microbial degradation.

Assessing the microbial bioavailability and degradation rate constants of dissolved organic matter by fluorescence spectroscopy in the coastal upwelling system of the Ría de Vigo

The time course of colored dissolved organic matter (CDOM) absorption and fluorescence were monitored during 50 to 70 days of laboratory incubations with water collected in the coastal upwelling system of the Ría de Vigo (NW Iberian Peninsula) under contrasting hydrographic conditions. CDOM fluorescence at peak-T (Ex/Em, 280/350 nm), characteristic of protein-like materials, decayed at a 1st order degradation rate constant ( k T) of 0.28 ± 0.13 day − 1 (average ± SD). k T covaried ( R 2 = 0.86, p < 0.0002) with the degradation rate of the bulk DOC ( k DOC), but the protein-like materials degraded 72 ± 23% faster than DOC. Therefore, this study confirms that the CDOM fluorescence at peak-T can be used as a proxy to a DOM fraction significantly more labile than the bulk bioavailable DOC. In parallel with the decay of DOC and protein-like fluorescence, an increase in CDOM fluorescence at peak-M (Ex/Em, 320/410 nm) during the course of the incubations verified the production of marine humic-like substances as a by-product of the microbial metabolism. CDOM fluorescence at peak-M built-up at a production rate ( k M) of 0.06 ± 0.01 day − 1 (average ± SD) in the Ría de Vigo. Furthermore, the slope of the linear regression between k DOC and k M ( R 2 = 0.64, p < 0.001) revealed that the formation of marine humic-like substances occurred at about one fifth of the rate of net DOC consumption.

Microcystin Elimination During Sediment Contact

Microcystins (MCYSTs) are a group of structurally similar toxic peptides produced by cyanobacteria ("blue-green algae") which occur frequently in surface waters worldwide. Reliable elimination is necessary when using these waters as drinking water sources. Bank filtration and artificial groundwater recharge utilize adsorption and degradation processes in the subsurface, commonly through sand and gravel aquifers, for the elimination of a wide range of substances during drinking water (pre-) treatment. To obtain parameters for estimating whether MCYST breakthrough is likely in field settings, we tested MCYST elimination in laboratory experiments (batch experiments, column experiments) under a range of conditions. Adsorption coefficients (k(d)-values) obtained from batch studies ranged from 0.2 mL/g for filter sand to 11.6 mL/g for fine grained aquifer materials with 2% fine grains (<63 microm) and 0.8% organic matter. First order degradation rates in column studies reached 1.87 d(-1) under aerobic conditions and showed high variations under anoxic conditions (<0.01-1.35 d(-1)). These results show that, next to sediment texture, redox conditions play an important role for MCYST elimination during sediment passage. Biodegradation was identified as the dominating process for MCYST elimination in sandy aquifer material.

Biotreatment and bioassessment of heavy metal removal by sulphate reducing bacteria in fixed bed reactors

In this work a batch-optimised mixture (w/w %: 6% leaves, 9% compost, 3% Fe(0), 30% silica sand, 30% perlite, 22% limestone) was investigated in a continuous fixed bed column reactor for the treatment of synthetic acid-mine drainage (AMD). A column reactor was inoculated with sulphate-reducing bacteria and fed with a solution containing sulphate and heavy metals (As(V), Cd, Cr(VI), Cu and Zn). At steady state, sulphate abatement was 50±10%, while metals were totally removed. A degradation rate constant (k) of 0.015±0.001h−1 for sulphate removal was determined from column data by assuming a first order degradation rate. Reduction of AMD toxicity was assessed by using the nematode Caenorhabditis elegans as a test organism. A lethality assay was performed with the toxicants before and after the treatment, showing that only 5% of the animals were still alive after 48h in presence of the contaminants, while the percentage increased to 73% when the nematodes were exposed to the solution eluted from the column.

Photo-induced environmental depletion processes of β-blockers in river waters

In order to improve the understanding of the fate and behaviour of pharmaceuticals in the environment there is a need to investigate in-stream depletion mechanisms, e.g. phototransformation of active pharmaceutical ingredients (APIs) in natural surface waters. In this study, abiotic and biotic degradation of selected beta-blockers was measured simultaneously in non-sterilised and sterilised river waters and deionised water (DIW) under simulated sunlight (lambda: 295-800 nm) and dark conditions, and at environmentally relevant concentrations, i.e.<or= ppb levels. Results suggested that the overall degradation followed pseudo first order kinetics under the solar simulation conditions and was between two and ten times faster in river waters than in DIW. There was a significant correlation (p < 0.07) between dissolved organic carbon (DOC) and overall first order degradation rate constants for the tested beta-blockers (n = 4-6), suggesting coloured DOC triplet-induced or reactive transient mediated oxidation mechanisms in river waters. Phototransformation was the main depletion mechanism for the beta-blockers tested over a 2 to 7 day period. Slow hydrolysis was observed for metoprolol only. Loss due to biodegradation in river waters was not observed for propranolol but was found for metoprolol and atenolol at a very slow rate within the study period. However, biodegradation of metoprolol was accelerated under the light conditions, implying that photo-induced intermediates could be more easily biodegraded in river waters.

Comparative efficiencies of the decolourisation of Methylene Blue using Fenton’s and photo-Fenton’s reactions

The decolourisation and mineralization of Methylene Blue azo dye (MB) under Fenton's and photo-Fenton's conditions have been studied. Some parameters, such as initial concentrations of iron (Fe(2+)) and fixed hydrogen peroxide (H(2)O(2)), were evaluated to find the optimal conditions for the efficient degradation of azo dye. The experimental assays showed better efficiency for the photo-Fenton's system. Pseudo-first order degradation rate constants were obtained from batch experimental set up. It is suggested that photo-Fenton's reactions are viable processes for treatment of azo dye MB, according to the high levels of colour (UV(665)) and total organic carbon (TOC) removal.

The aqueous photodegradation of fenitrothion under various agricultural plastics: Implications for pesticide longevity in agricultural ‘micro-environments’

Plastic cladding is increasingly used in agriculture to create micro-environments to improve crop yield/growth. Many of these plastics can alter the solar light spectrum by inhibiting or reducing the transmittance of certain parts of the solar spectrum. In this study, we investigated the aqueous photolysis of fenitrothion, under a selection of different plastic films commonly used in agriculture. Three different grades of polyethylene film were used: ‘standard’, ‘transparent’ and ‘opaque’. The transmittance of light wavelengths in the UV region (290–400 nm), measured with a spectroradiometer, was found to decrease in the order of transparent > standard > opaque. Fenitrothion, an organophosphorothioate insecticide possesses molar absorptivity in the solar wavelength range of 290–400 nm. Aqueous first order degradation rate constants for fenitrothion determined over a 12 h period were found to be considerably less for those experiments conducted under the standard and opaque plastic films, compared to the transparent film and no-film control. The experiments were conducted in an Atlas Suntest solar simulator using a UV-filtered Xenon arc lamp to simulate sunlight. The first order half-life for fenitrothion was 100 and 250 h under the standard and opaque films, respectively, compared to ∼10 h for the transparent film and no-film experiments. Our results suggest that pesticide longevity could be greatly extended within these plastic micro-environments, especially for those chemicals which may degrade/transform via photolytic or photochemical pathways.