Effects of Mg and H on the toxicity of Ni to the unicellular green alga Pseudokirchneriella subcapitata: Model development and validation with surface waters

In this study, increasing Mg concentrations and decreasing pH were observed to decrease Ni toxicity to the green alga Pseudokirchneriella subcapitata. To investigate to what extent the original biotic ligand model (BLM) concept could explain Ni toxicity as a function of water chemistry, the protective effects of Mg²⁺ and H⁺ were modeled as BLM-type single-site competition effects. The model parameters representing these effects were log K_MgBL = 3.3 and log K_HBL = 6.5. The BLM was capable of predicting Ni toxicity by an error of less than a factor of 2 in most synthetic and natural waters used in this study. However, since the relationship between 72-h E_rC50_Ni²⁺ (i.e. the 72-h E_rC50 expressed as Ni²⁺ activity) and H⁺ activity was not linear over the entire tested pH range, only the ‘linear part’ between pH 6.45 and 7.92 was used for derivation of log K_HBL. This nonlinearity indicates that the effect of pH can probably not be attributed to H⁺ competition with Ni²⁺ for a single site alone. When modeling the effect of pH as a linear relation between 72-h E_rC50_pNi²⁺? (= − log (72-h E_rC50_Ni²⁺ corrected for the presence of Mg)) and pH, the applicability of the model was successfully extended to pH levels as low as 6.01. This type of empirical model has also been used in our previous studies on the development of a chronic Ni bioavailability model for Daphnia magna and a long-term Ni bioavailability model for rainbow trout. Finally, we could not detect a statistically significant interactive effect of pH and Mg on the toxicity of Ni²⁺ to P. subcapitata and this is in line with the formulation of our empirical model.     

Application of the Nernst-Planck approach to lead ion exchange in Ca-loaded Pelvetia canaliculata

Ca-loaded Pelvetia canaliculata biomass was used to remove Pb²⁺ in aqueous solution from batch and continuous systems. The physicochemical characterization of algae Pelvetia particles by potentiometric titration and FTIR analysis has shown a gel structure with two major binding groups - carboxylic (2.8 mmol g⁻¹) and hydroxyl (0.8 mmol g⁻¹), with an affinity constant distribution for hydrogen ions well described by a Quasi-Gaussian distribution. Equilibrium adsorption (pH 3 and 5) and desorption (eluents: HNO₃ and CaCl₂) experiments were performed, showing that the biosorption mechanism was attributed to ion exchange among calcium, lead and hydrogen ions with stoichiometry 1:1 (Ca:Pb) and 1:2 (Ca:H and Pb:H). The uptake capacity of lead ions decreased with pH, suggesting that there is a competition between H⁺ and Pb²⁺ for the same binding sites. A mass action law for the ternary mixture was able to predict the equilibrium data, with the selectivity constants α_Ca^H = 9 ± 1 and α_Ca^Pb = 44 ± 5, revealing a higher affinity of the biomass towards lead ions. Adsorption (initial solution pH 4.5 and 2.5) and desorption (0.3 M HNO₃) kinetics were performed in batch and continuous systems. A mass transfer model using the Nernst-Planck approximation for the ionic flux of each counter-ion was used for the prediction of the ions profiles in batch systems and packed bed columns. The intraparticle effective diffusion constants were determined as 3.73 × 10⁻⁷ cm² s⁻¹ for H⁺, 7.56 × 10⁻⁸ cm² s⁻¹ for Pb²⁺ and 6.37 × 10⁻⁸ cm² s⁻¹ for Ca²⁺.     

Degradation of the antibiotic oxolinic acid by photocatalysis with TiO2 in suspension

In the work presented here, a photocatalytic system using titanium Degussa P-25 in suspension was used to evaluate the degradation of 20 mg L⁻¹ of antibiotic oxolinic acid (OA). The effects of catalyst load (0.2-1.5 g L⁻¹) and pH (7.5-11) were evaluated and optimized using the surface response methodology and the Pareto diagram. In the range of variables studied, low pH values and 1.0 g L⁻¹ of TiO₂ favoured the efficiency of the process. Under optimal conditions the evolution of the substrate, chemical oxygen demand, dissolved organic carbon, toxicity and antimicrobial activity on Escherichia coli cultures were evaluated. The results indicate that, under optimal conditions, after 30 min, the TiO₂ photocatalytic system is able to eliminate both the substrate and the antimicrobial activity, and to reduce the toxicity of the solution by 60%. However, at the same time, ∼53% of both initial DOC and COD remain in solution. Thus, the photocatalytical system is able to transform the target compound into more oxidized by-products without antimicrobial activity and with a low toxicity. The study of OA by-products using liquid chromatography coupled with mass spectrometry, as well as the evaluation of OA degradation in acetonitrile media as solvent or in the presence of isopropanol and iodide suggest that the reaction is initiated by the photo-Kolbe reaction. Adsorption isotherm experiments in the dark indicated that under pH 7.5, adsorption corresponded to the Langmuir adsorption model, indicating the dependence of the reaction on an initial adsorption step.     

Nitrous oxide production kinetics during nitrate reduction in river sediments

A significant amount of nitrogen entering river basins is denitrified in riparian zones. The aim of this study was to evaluate the influence of nitrate and carbon concentrations on the kinetic parameters of nitrate reduction as well as nitrous oxide emissions in river sediments in a tributary of the Marne (the Seine basin, France). In order to determine these rates, we used flow-through reactors (FTRs) and slurry incubations; flow-through reactors allow determination of rates on intact sediment slices under controlled conditions compared to sediment homogenization in the often used slurry technique. Maximum nitrate reduction rates (R_m) ranged between 3.0 and 7.1 μg N g⁻¹ h⁻¹, and affinity constant (K_m) ranged from 7.4 to 30.7 mg N-NO₃⁻ L⁻¹. These values were higher in slurry incubations with an R_m of 37.9 μg N g⁻¹ h⁻¹ and a K_m of 104 mg N-NO₃⁻ L⁻¹. Nitrous oxide production rates did not follow Michaelis-Menten kinetics, and we deduced a rate constant with an average of 0.7 and 5.4 ng N g⁻¹ h⁻¹ for FTR and slurry experiments respectively. The addition of carbon (as acetate) showed that carbon was not limiting nitrate reduction rates in these sediments. Similar rates were obtained for FTR and slurries with carbon addition, confirming the hypothesis that homogenization increases rates due to release of and increasing access to carbon in slurries. Nitrous oxide production rates in FTR with carbon additions were low and represented less than 0.01% of the nitrate reduction rates and were even negligible in slurries. Maximum nitrate reduction rates revealed seasonality with high potential rates in fall and winter and low rates in late spring and summer. Under optimal conditions (anoxia, non-limiting nitrate and carbon), nitrous oxide emission rates were low, but significant (0.01% of the nitrate reduction rates).     

Residual aluminium in water defluoridated using activated alumina adsorption - Modeling and simulation studies

The removal of fluoride from drinking water by the method of adsorption on activated alumina is found superior than other defluoridation techniques mostly due to the strong affinity between aluminium and fluoride. Dissolution of aluminium from the alumina surfaces into its free and hydroxide ions in the aqueous medium is reported to be very low, but the presence of high fluoride concentrations may increase its solubility due to the formation of monomeric aluminium fluoride and aluminium hydroxyl fluoride complexes. An Activated Alumina Defluoridation Model Simulator (AAD) has been developed to represent fluoride adsorption on the basis of the surface complexation theory incorporating aspects of aluminium solubility in presence of high fluoride concentrations and pH variations. Model validations were carried out for residual aluminium concentrations in alumina treated water, by conducting a series of batch fluoride adsorption experiments using activated alumina (grade FB101) treating fluoride concentrations of 1-10 mg/L, at varying pH conditions. The total residual aluminium in the defluoridated water is due to presence of both dissolved and precipitated Al-F complexed forms. The Freundlich adsorption isotherm was found fit for fluoride adsorption capacity versus residual fluoride concentrations for pH = 7.5, and the relationship is given by the linearised equation log (x/m) = log k + (1/n) log C_e with values of k = 0.15 mg/g and 1/n = 0.45 indicating favorable adsorption. The relationship is linear in the region of low fluoride concentrations, but as concentrations of fluoride increased, the formation of the dissolved AlF₃⁰ complexes was favored than adsorption on alumina, and hence makes the isotherm nonlinear. The AAD simulations can predict for operating fluoride uptake capacity in order to keep the residual aluminium within permissible limits in the alumina treated water.     

Investigating the potential role of ammonia in ion chemistry of fine particulate matter formation for an urban environment

To investigate the potential role of ammonia in ion chemistry of PM_2.5 aerosol, measurements of PM_2.5 (particulate matter having aerodynamic diameter < 2.5 µm) along with its ionic speciation and gaseous pollutants (sulfur dioxide (SO₂), nitrogen oxides (NO_x), ammonia (NH₃) and nitric acid (HNO₃)) were undertaken in two seasons (summer and winter) of 2007-2008 at four sampling sites in Kanpur, an urban-industrial city in the Ganga basin, India. Mean concentrations of water-soluble ions were observed in the following order (i) summer: SO₄²⁻ (26.3 µg m^− 3) > NO₃⁻ (16.8) > NH₄⁺ (15.1) > Ca²⁺ (4.1) > Na⁺ (2.4) > K⁺ (2.1 µg m^− 3) and (ii) winter: SO₄²⁻ (28.9 µg m^− 3) > NO₃⁻ (23.0) > NH₄⁺ (16.4) > Ca²⁺(3.4) > K⁺(3.3) > Na⁺ (3.2 µg m^− 3). The mean molar ratio of NH₄⁺ to SO₄²⁻ was 2.8 ± 0.6 (mostly >2), indicated abundance of NH₃ to neutralize H₂SO₄. The excess of NH₄⁺ was inferred to be associated with NO₃⁻ and Cl⁻. Higher sulfur conversion ratio (F_s: 58%) than nitrogen conversion ratio (F_n: 39%) indicated that SO₄²⁻ was the preferred secondary species to NO₃⁻. The charge balance for the ion chemistry of PM_2.5 revealed that compounds formed from ammonia as precursor are (NH₄)₂SO₄, NH₄NO₃ and NH₄Cl. This study conclusively established that while there are higher contributions of NH₄⁺, SO₄²⁻ to PM_2.5 in summer but for nitrates (in particulate phase), it is the winter season, which is critical because of low temperatures that drives the reaction between ammonia and HNO₃ in forward direction for enhanced nitrate formation. In summary, inorganic secondary aerosol formation accounted for 30% mass of PM_2.5 and any particulate control strategy should include optimal control of primary precursor gases including ammonia.     

Potential enzyme toxicity of oxytetracycline to catalase

Oxytetracycline (OTC) is a kind of widely used veterinary drugs. The residue of OTC in the environment is potentially harmful. In the present work, the non-covalent toxic interaction of OTC with catalase was investigated by the fluorescence spectroscopy, UV-vis absorption and circular dichroism (CD) spectroscopy at physiological pH 7.4. OTC can interact with catalase to form a complex mainly by van der Waals' interactions and hydrogen bonds with one binding site. The association constants K were determined to be K_293K = 7.09 × 10⁴ L mol^− 1 and K_311K = 3.31 × 10⁴ L mol^− 1. The thermodynamic parameters (ΔH°, ΔG° and ΔS°) of the interaction were calculated. Based on the Förster theory of non-radiative energy transfer, the distance between bound OTC and the tryptophan residues of catalase was determined to be 6.48 nm. The binding of OTC can result in change of the micro-environment of the tryptophan residues and the secondary structure of catalase. The activity of catalase was also inhibited for the bound OTC. This work establishes a new strategy to probe the enzyme toxicity of veterinary drug residues and is helpful for clarifying the molecular toxic mechanism of OTC in vivo. The established strategy can be used to investigate the potential enzyme toxicity of other small organic pollutants and drugs.     

Migration behavior of landfill leachate contaminants through alternative composite liners

Four identical pilot-scale landfill reactors with different alternative composite liners were simultaneously operated for a period of about 540 days to investigate and to simulate the migration behaviors of phenolic compounds (phenol, 2-CP, 2-MP, 3-MP, 4-MP, 2-NP, 4-NP, 2,4-DNP, 2,4-DCP, 2,6-DCP, 2,4,5-TCP, 2,4,6-TCP, 2,3,4,6-TeCP, PCP) and heavy metals (Pb, Cu, Zn, Cr, Cd, Ni) from landfill leachate to the groundwater. Alternative landfill liners of four reactors consist of R1: Compacted clay liner (10 cm + 10 cm, k = 10⁻⁸ m/sn), R2: Geomembrane (2 mm HDPE) + compacted clay liner (10 cm + 10 cm, k = 10⁻⁸ m/sn), R3: Geomembrane (2 mm HDPE) + compacted clay liner (10 cm, k = 10⁻⁸ m/sn) + bentonite liner (2 cm) + compacted clay liner (10 cm, k = 10⁻⁸ m/sn), and R4: Geomembrane (2 mm HDPE) + compacted clay liner (10 cm, k = 10⁻⁸ m/sn) + zeolite liner (2 cm) + compacted clay liner (10 cm, k = 10⁻⁸ m/sn). Wastes representing Istanbul municipal solid wastes were disposed in the reactors. To represent bioreactor landfills, reactors were operated by leachate recirculation. To monitor and control anaerobic degradation in the reactors, variations of conventional parameters (pH, alkalinity, chloride, conductivity, COD, TOC, TKN, ammonia and alcaly metals) were also investigated in landfill leachate samples. The results of this study showed that about 35-50% of migration of organic contaminants (phenolic compounds) and 55-100% of migration of inorganic contaminants (heavy metals) to the model groundwater could be effectively reduced with the use of bentonite and zeolite materials in landfill liner systems. Although leachate contaminants can reach to the groundwater in trace concentrations, findings of this study concluded that the release of these compounds from landfill leachate to the groundwater may potentially be of an important environmental concern based on the experimental findings.     

The adsorption of saxitoxin to clays and sediments in fresh and saline waters

The adsorption of saxitoxin to Na- and Ca-montmorillonite, kaolin (crystalline and amorphous), kaolinite, Bread and Butter Creek sediment (an estuarine tidal creek), Gulf of Mexico sediment, and Santa Barbara Basin sediment in deionized water and 32‰ salinity simulated seawater (Instant Ocean™) is reported. Adsorption was partially reversible for all cases and best described using a Freundlich isotherm. The corresponding Freundlich constants (K_F) ranged from 8.83 × 10³ μmol/kg to 6.76 × 10⁴ μmol/kg for freshwater and 4.73 × 10³ μmol/kg-1.11 × 10⁴ μmol/kg for seawater. There is a positive linear correlation seen between the K_F values and the cation-exchange capacity of the adsorbents. The release of saxitoxin from previously equilibrated adsorbents was determined in freshwater (0-18%) and seawater (4-53%).     

Nitritation performance and biofilm development of co- and counter-diffusion biofilm reactors: Modeling and experimental comparison

A comparative study was conducted on the start-up performance and biofilm development in two different biofilm reactors with aim of obtaining partial nitritation. The reactors were both operated under oxygen limited conditions, but differed in geometry. While substrates (O₂, NH₃) co-diffused in one geometry, they counter-diffused in the other. Mathematical simulations of these two geometries were implemented in two 1-D multispecies biofilm models using the AQUASIM software. Sensitivity analysis results showed that the oxygen mass transfer coefficient (K_i) and maximum specific growth rate of ammonia-oxidizing (AOB) and nitrite-oxidizing bacteria (NOB) were the determinant parameters in nitrogen conversion simulations. The modeling simulations demonstrated that K_i had stronger effects on nitrogen conversion at lower (0-10 m d⁻¹) than at the higher values (>10 m d⁻¹). The experimental results showed that the counter-diffusion biofilms developed faster and attained a larger maximum biofilm thickness than the co-diffusion biofilms. Under oxygen limited condition (DO < 0.1 mg L⁻¹) and high pH (8.0-8.3), nitrite accumulation was triggered more significantly in co-diffusion than counter-diffusion biofilms by increasing the applied ammonia loading from 0.21 to 0.78 g NH₄⁺-N L⁻¹ d⁻¹. The co- and counter-diffusion biofilms displayed very different spatial structures and population distributions after 120 days of operation. AOB were dominant throughout the biofilm depth in co-diffusion biofilms, while the counter-diffusion biofilms presented a stratified structure with an abundance of AOB and NOB at the base and putative heterotrophs at the surface of the biofilm, respectively.     

The interaction between Ag+ and bovine serum albumin: a spectroscopic investigation

By using spectroscopic methods, we probed the interaction of Ag⁺ with bovine serum albumin (BSA) in an aqueous environment. Fluorescence of BSA quenched by Ag⁺ is a dynamic quenching process. Two binding modes-a strong one at low concentration of Ag⁺ and a weak one at high concentration were found. The association constant (K_A) and the number of binding sites (n) were 4.88 × 10³ M^− 1 and 1.17 for strong binding, and 17.6 M^− 1 and 0.547 for weak binding at 293 K. The results of thermodynamic parameters ΔH^θ, ΔG^θ and ΔS^θ for instinct binding modes at different temperatures indicated that the hydrogen bonding and van der Waals interaction play a major role for low Ag⁺/BSA ratio while electrostatic association for high Ag⁺/BSA ratio. Data of UV-Vis and Circular dichroism (CD) suggested that with the increasing amount of Ag⁺, the secondary structure undergoes a decrease in α-helix and an increase in β content and the backbone of BSA experiences a micro-environmental alteration. Furthermore, the distance r between donor (Trp-212) and acceptor (Ag⁺) was evaluated to be 10 nm according to nonradiative energy transfer theory.     

Combined (alkaline + ultrasonic) pretreatment effect on sewage sludge disintegration

The individual effects of alkaline (pH 8-13) and ultrasonic (3750-45,000 kJ/kg TS) pretreatments on the disintegration of sewage sludge were separately tested, and then the effect of combining these two methods at different intensity levels was investigated using response surface methodology (RSM). In the combined pretreatment, ultrasonic treatment was applied to the alkali-pretreated sludge. While the solubilization (SCOD/TCOD) increase was limited to 50% in individual pretreatments, it reached 70% in combined pretreatment, and the results clearly showed that preconditioning of sludge at high pH levels played a crucial role in enhancing the disintegration efficiency of the subsequent ultrasonic pretreatment. By applying regression analysis, the disintegration degree (DD) was fitted based on the actual value to a second order polynomial equation: Y = −172.44 + 29.82X₁ + 5.30 × 10⁻³X₂ − 7.53 × 10⁻⁵X₁X₂ − 1.10X₁² − 1.043 × 10⁻⁷X₂², where X₁, X₂, and Y are pH, specific energy input (kJ/kg TS), and DD, respectively. In a 2D contour plot describing the tendency of DD with respect to pH and specific energy input, it was clear that DD increased as pH increased, but it seemed that DD decreased when the specific energy input exceeded about 20,000 kJ/kg TS. This phenomenon tells us that there exists a certain point where additional energy input is ineffective in achieving further disintegration. A synergetic disintegration effect was also found in the combined pretreatment, with lower specific energy input in ultrasonic pretreatment yielding higher synergetic effect. Finally, in order to see the combined pretreatment effect in continuous operation, the sludge pretreated with low intensity alkaline (pH 9)/ultrasonic (7500 kJ/kg TS) treatment was fed to a 3 L of anaerobic sequencing batch reactor after 70 days of control operation. CH₄ production yield significantly increased from 81.9 ± 4.5 mL CH₄/g COD_added to 127.3 ± 5.0 mL CH₄/g COD_added by pretreatment, and this enhanced performance was closely related to the solubilization increase of the sludge by pretreatment. However, enhanced anaerobic digestion resulted in 20% higher soluble N concentration in the reactor, which would be an additional burden in the subsequent nitrogen removal system.     

Enhanced nitrogen and phosphorus removal from eutrophic lake water by Ipomoea aquatica with low-energy ion implantation

Ipomoea aquatica with low-energy N⁺ ion implantation was used for the removal of both nitrogen and phosphorus from the eutrophic Chaohu Lake, China. The biomass growth, nitrate reductase and peroxidase activities of the implanted I. aquatica were found to be higher than those of I. aquatica without ion implantation. Higher NO₃-N and PO₄-P removal efficiencies were obtained for the I. aquatica irradiation at 25 keV, 3.9 × 10¹⁶ N⁺ ions/cm² and 20 keV 5.2 × 10¹⁶ N⁺ ions/cm², respectively (p < 0.05). Moreover, the nitrogen and phosphorus contents in the plant biomass with ion implantation were also greater than those of the controls. I. aquatica with ion implantation was directly responsible for 51-68% N removal and 54-71% P removal in the three experiments. The results further confirm that the ion implantation could enhance the growth potential of I. aquatica in real eutrophic water and increase its nutrient removal efficiency. Thus, the low-energy ion implantation for aquatic plants could be considered as an approach for in situ phytoremediation and bioremediation of eutrophic waters.     

Study on the adsorption of Neutral Red from aqueous solution onto halloysite nanotubes

Halloysite nanotubes (HNTs), a low-cost available clay mineral, were tested for the ability to remove cationic dye, Neutral Red (NR), from aqueous solution. Natural HNTs used as adsorbent in this work were initially characterized by XRD, FT-IR, TEM and BET. The effect of adsorbent dose, initial pH, temperature, initial concentration and contact time were investigated. Adsorption increased with increase in adsorbent dose, initial pH, temperature and initial concentration. The equilibrium data were well described by both the Langmuir and Freundlich isotherm models. The maximum adsorption capacity was 54.85, 59.24 and 65.45 mg/g at 298, 308 and 318 K, respectively. Batch kinetic experiments showed that the adsorption followed pseudo-second-order kinetic model with correlation coefficients greater than 0.999. Thermodynamic parameters of ΔG⁰, ΔH⁰ and ΔS⁰ indicated the adsorption process was spontaneous and endothermic. The results above confirmed that HNTs had the potential to be utilized as low-cost and relatively effective adsorbent for cationic dyes removal.     

Degradation of fifteen emerging contaminants at μg L initial concentrations by mild solar photo-Fenton in MWTP effluents

The degradation of 15 emerging contaminants (ECs) at low concentrations in simulated and real effluent of municipal wastewater treatment plant with photo-Fenton at unchanged pH and Fe = 5 mg L⁻¹ in a pilot-scale solar CPC reactor was studied. The degradation of those 15 compounds (Acetaminophen, Antipyrine, Atrazine, Caffeine, Carbamazepine, Diclofenac, Flumequine, Hydroxybiphenyl, Ibuprofen, Isoproturon, Ketorolac, Ofloxacin, Progesterone, Sulfamethoxazole and Triclosan), each with an initial concentration of 100 μg L⁻¹, was found to depend on the presence of CO₃²⁻ and HCO₃⁻ (hydroxyl radicals scavengers) and on the type of water (simulated water, simulated effluent wastewater and real effluent wastewater), but is relatively independent of pH, the type of acid used for release of hydroxyl radicals scavengers and the initial H₂O₂ concentration used. Toxicity tests with Vibrio fisheri showed that degradation of the compounds in real effluent wastewater led to toxicity increase.     

Toxicity of 2,4-dinitrotoluene to terrestrial plants in natural soils

The presence of energetic materials (used as explosives and propellants) at contaminated sites is a growing international issue, particularly with respect to military base closures and demilitarization policies. Improved understanding of the ecotoxicological effects of these materials is needed in order to accurately assess the potential exposure risks and impacts on the environment and its ecosystems. We studied the toxicity of the nitroaromatic energetic material 2,4-dinitrotoluene (2,4-DNT) on alfalfa (Medicago sativa L.), barnyard grass (Echinochloa crusgalli L. Beauv.), and perennial ryegrass (Lolium perenne L.) using four natural soils varying in properties (organic matter, clay content, and pH) that were hypothesized to affect chemical bioavailability and toxicity. Amended soils were subjected to natural light conditions, and wetting and drying cycles in a greenhouse for 13 weeks prior to toxicity testing to approximate field exposure conditions in terms of bioavailability, transformation, and degradation of 2,4-DNT. Definitive toxicity tests were performed according to standard protocols. The median effective concentration (EC₅₀) values for shoot dry mass ranged from 8 to 229 mg kg^− 1, depending on the plant species and soil type. Data indicated that 2,4-DNT was most toxic in the Sassafras (SSL) and Teller (TSL) sandy loam soils, with EC₅₀ values for shoot dry mass ranging between 8 to 44 mg kg^− 1, and least toxic in the Webster clay loam soil, with EC₅₀ values for shoot dry mass ranging between 40 to 229 mg kg^− 1. The toxicity of 2,4-DNT for each of the plant species was significantly (p ≤ 0.05) and inversely correlated with the soil organic matter content. Toxicity benchmark values determined in the present studies for 2,4-DNT weathered-and-aged in SSL or TSL soils will contribute to development of an Ecological Soil Screening Level for terrestrial plants that can be used for ecological risk assessment at contaminated sites.     

Degradation of selected pharmaceuticals in aqueous solution with UV and UV/H2O2

The degradation of four pharmaceutical compounds (PhACs), ibuprofen (IBU), diphenhydramine (DP), phenazone (PZ), and phenytoin (PHT) was investigated via ultraviolet (UV) photolysis and UV/H₂O₂ process with a low-pressure (LP) UV lamp. For each PhAC tested, direct photolysis quantum yields at 254 nm were found to be ranging from 6.32 × 10⁻² to 2.79 × 10⁻¹ mol E⁻¹ at pH 7. The second-order rate constants of the reaction between the PhACs and OH were determined to be from 4.86 × 10⁹ to 6.67 × 10⁹ M⁻¹ s⁻¹ by using a competition kinetic model which utilized para-chlorobenzoic acid (pCBA) as a reference compound. The overall effect of OH radical scavenging from humic acid (HA) and anions HCO₃⁻, NO₃⁻ was measured utilizing R_OH,UV method through examining the aqueous photodegradation of pCBA as a probe compound. Moreover, these fundamental direct and indirect photolysis parameters were applied in the model prediction for oxidation rate constants of the PhACs in UV/H₂O₂ process. It was found that the predicted oxidation rate constants approximated the observed ones. The results indicated that the new R_OH,UV probe compound method was applicable for measuring background OH radical scavenging effects in water treatment process of UV/H₂O₂. Furthermore, by GC-MS analysis, most of the intermediates created during the photodegradation of the selected PhACs in UV/H₂O₂ process were identified. For the photodegradation of PZ, a competition mechanism existed between the direct UV photolysis and the oxidation of OH. An appropriate dosage of H₂O₂ could hinder the occurrence of the direct photolysis.     

Anatoxin-a degradation by Advanced Oxidation Processes: Vacuum-UV at 172 nm, photolysis using medium pressure UV and UV/H2O2

Two Advanced Oxidation Processes, namely vacuum-ultraviolet (VUV) photolysis at 172 nm and ultraviolet/hydrogen peroxide (UV/H₂O₂) were investigated for the degradation of anatoxin-a in aqueous solutions. Solutions of anatoxin-a-fumarate were treated with VUV light at 172 nm with a UV dose of 200 mJ/cm², where fumaric acid served as a reference compound for a competition kinetics analysis. The second-order rate constant for the reaction between anatoxin-a and the hydroxyl radical was found to be (5.2 ± 0.3) × 10⁹ M⁻¹ s⁻¹ and was independent of pH, temperature, and initial concentration of anatoxin-a. The direct photolysis of anatoxin-a using a medium pressure (MP) UV lamp was also investigated, in which case a UV dose of 1285 mJ/cm² was required to degrade anatoxin-a by 88% and 50% at concentrations of 0.6 mg/L and 1.8 mg/L of toxin, respectively. Treatment of anatoxin-a with a low pressure (LP) UV lamp in the presence of 30 mg/L of H₂O₂ was examined, where it was found that more than 70% of toxin could be degraded at a UV dose of 200 mJ/cm². The degradation arises from the oxidation of the toxin by hydroxyl radicals. The addition of H₂O₂ clearly enhanced the degradation of anatoxin-a, up to a concentration of 40 mg/L, after which addition of more H₂O₂ had little effect on the degradation kinetics of anatoxin-a. The effect of background constituents in the water on the degradation of anatoxin-a was also investigated using natural and synthetically produced model waters.     

Photolytic reaction mechanism and impacts of coexisting substances on photodegradation of bisphenol A by Bi2WO6 in water

Bi₂WO₆ displayed great photolytic degradation efficiency to bisphenol A (BPA) under simulated solar light irradiation but its reaction mechanism and the impacts of coexisting substances on the degradation remain unclear. In present study, the reaction mechanism was investigated using DMPO spin-trapping ESR spectra and experiments with scavengers of hydroxyl radicals (OH) and holes. The results supported that hole oxidation mainly governed the photodegradation process. As a common humic substance in natural water, humic acid accelerated the degradation of BPA when its concentration was 1 mg/L, while the photodegradation was impeded with the increase of humic acid concentration in the range of 5-20 mg/L. Almost all anions, including NO₃⁻, HCO₃⁻, Cl⁻, SO₄²⁻ inhibited the degradation of BPA by Bi₂WO₆ and their inhibition effects followed the order of SO₄²⁻ > Cl⁻ > HCO₃⁻ > NO₃⁻. Cations of Na⁺, K⁺, Ca²⁺ and Mg²⁺ displayed slight suppressing effect on BPA degradation mainly due to the impact of Cl⁻ coexisting in the solution. However, Cu²⁺ hindered the BPA photodegradation heavily. Fe³⁺ and H₂O₂ affected the photodegradation in a complicated way: they suppressed or promoted the photodegradation depending on their concentrations. This could be the result of competition between photolyitc hole generated by Bi₂WO₆ and OH produced by Fe³⁺ or H₂O_2.     

Aerobic degradation of acid orange 7 in a vertical-flow constructed wetland

Biological, aerobic degradation of an azo dye and of the resultant, recalcitrant, aromatic amines in a constructed wetland (CW) was demonstrated for the first time. A vertical-flow CW, planted with Phragmites sp. was fed with 127 mg l⁻¹ of acid orange 7 (AO7) at hydraulic loads of 28, 40, 53 and 108 l m⁻²day⁻¹. Color removal efficiencies of up to 99% clearly demonstrate cleavage of the azo bond, also confirmed by the similar AO7 removal and SO₄²⁻ release rates revealing that adsorption onto the matrix was constant. The positive redox potential at the outlet demonstrates that aerobic conditions were present. Chemical oxygen demand and total organic carbon removal efficiencies of up to 93% were also indicative of AO7 mineralization. The degradation of sulfanilic acid was confirmed by the presence of NO₃⁻, SO₄²⁻ and secondary metabolites, which suggest at least two degradation pathways leading to a common compound, 3-oxoadipate.