Photodegradation of Sulfamethoxazole Applying UV- and VUV-Based Processes

The efficiency of UV- and VUV-based processes (UV, VUV, UV/H₂O₂, and VUV/H₂O₂) for removal of sulfamethoxazole (SMX) in Milli-Q water and sewage treatment plant (STP) effluent was investigated at 20??C. The investigated factors included initial pH, variety of inorganic anions (NO ₃ ^? and HCO ₃ ^? ), and humic acid (HA). The results showed that the degradation of SMX in Milli-Q water at both two pH (5.5 and 7.0) followed the order of VUV/H₂O₂ > VUV > UV/H₂O₂ > UV. All the experimental data well fitted the pseudo-first order kinetic model and the rate constant (k) and half-life time (t _1/2) were determined accordingly. Indirect oxidation of SMX by generated ^?OH was the main degradation mechanism in UV/H₂O₂ and VUV/H₂O₂, while direct photolysis predominated in UV processes. The quenching tests showed that some other reactive species along with ^?OH radicals were responsible to the SMX degradation under VUV process. The addition of 20?mg?L^?1 HA significantly inhibited SMX degradation, whereas, the inhibitive effects of NO ₃ ^? and HCO ₃ ^? (0.1?mol?L^?1) were observed as well in all processes except in UV irradiation for NO ₃ ^? . The removal rate decreased 1.7?C3.6 times when applying these processes to STP effluent due to the complex constituents, suggesting that from the application point of view the constituents of these complexes in real STP effluent should be considered carefully prior to the use of UV-based processes for SMX degradation.     

Photodegradation of 3,5,6-trichloro-2-pyridinol in aqueous solution

A medium-pressure mercury lamp, emitting strongly in the 200–400 nm range was applied for the degradation of 3,5,6-trichloro-2-pyridinol (TCP), a hydrolysis product of chlorpyrifos. Photodegradation of TCP in aqueous solution exhibited pseudo-first order kinetics with a rate constant that was wavelength dependent and increased below 300 nm. The TCP degradation rate and quantum yield increased with solution pH up to a constant maximum value of (6.40 ± 0.046) × 10^?3 cm² mJ^{? 1} and 0.178 ± 0.002 mol E^?1 respectively, at pH 5 and above. Addition of 5 mg L^{? 1} H₂O₂ to generate OH radicals led to an increase in removal rates by a factor of 1.5. Addition of phosphate buffer resulted in decreased photolysis at 3 < pH < 6.     

Photo-Assisted Degradation,Toxicological Assessment,and Modeling Using Artificial Neural Networks of Reactive Gray BF-2R Dye

This work investigates the degradation of Reactive Gray BF-2R dye (a blend of reactive yellow 145, reactive orange 122 and reactive black 5 dyes) using UV/H₂O₂, Fenton, and photo-Fenton-advanced oxidative processes, with artificial sunlight and UV-C radiations. The photo-Fenton process employing UV-C radiation was the most efficient under the conditions studied. The ideal conditions for the degradation of the dye, determined using a factorial design 2³ and a study of the concentration of hydrogen peroxide ([H₂O₂]), were [H₂O₂] equal to 40 mg L^?1, iron concentration [Fe] of 1 mg L^?1, and pH between 3 and 4. The Chan and Chu non-linear kinetic model predicted the kinetic data with a degradation of over 98% for color and 68% for aromatics after 60 min. The behavior of the chemical oxygen demand fitted the first-order kinetic model well, with a degradation of 64% after 60 min. The Multilayer Perceptron 7-11-2 artificial neural network model enabled to model the degradation process of the aromatics and accurately predict the experimental data. Toxicity tests indicated that the post-treatment samples were non-toxic for Escherichia coli bacteria, and Portulaca grandiflora and Basil sabory seeds. However, they inhibited the growth of Lactuca sativa seeds and Salmonella enteritidis bacteria. The photo-Fenton process with UV-C radiation degraded the dye studied efficiently and the degradation percentages were, on average, 7% and 5% higher for color than those observed when employing the Fenton and UV/H₂O₂ processes, respectively. With the aromatic, however, they were 84% and 62% higher, thus justifying the use of this process.     

Degradation of Di-(2-ethylhexyl) Phthalate (DEHP) by TiO2 Photocatalysis

The photocatalytic degradation of di-(2-ethylhexyl) phthalate (DEHP) in solution using titanium dioxide (TiO₂) was analyzed in this study. It was found that DEHP was completely removed in the solution after 150 min irradiation. The effect of different factors, such as photocatalyst amount, DEHP concentration, light intensity, pH, and temperature on photocatalytic degradation was investigated. The degradation mechanism of DEHP with proton and hydroxyl radicals oxidation were also studied. It is suggested that either ethylhexyl or ester chain scissions of the aliphatic part of DEHP was the dominant degradation mechanism of the process. The photocatalytic degradation process was well described by first-order reaction. The final mineralization product was carbon dioxide and the intermediate products were identified by GC-MS. Thus, the photocatalytic degradation treatment of DEHP in wastewater is a relative simple and fast method.     

Kinetic and Thermodynamic Studies of Chlorinated Organic Compound Degradation by Siderite-Activated Peroxide and Persulfate

The efficacy of two oxidant systems, iron-activated hydrogen peroxide (H₂O₂) and iron-activated hydrogen peroxide coupled with persulfate (S₂O₈ ^2?), was investigated for treatment of two chlorinated organic compounds, trichloroethene (TCE) and 1,2-dichloroethane (DCA). Batch tests were conducted at multiple temperatures (10–50 °C) to investigate degradation kinetics and reaction thermodynamics. The influence of an inorganic salt, dihydrogen phosphate ion (H₂PO₄ ^?), on oxidative degradation was also examined. The degradation of TCE was promoted in both systems, with greater degradation observed for higher temperatures. The inhibition effect of H₂PO₄ ^? on the degradation of TCE increased with increasing temperature for the iron-activated H₂O₂ system but decreased for the iron-activated hydrogen peroxide-persulfate system. DCA degradation was limited in the iron-activated hydrogen peroxide system. Conversely, significant DCA degradation (87% in 48 h at 20 °C) occurred in the iron-activated hydrogen peroxide-persulfate system, indicating the crucial role of sulfate radical (SO₄ ^??) from persulfate on the oxidative degradation of DCA. The activation energy values varied from 37.7 to 72.9 kJ/mol, depending on the different reactants. Overall, the binary hydrogen peroxide-persulfate oxidant system exhibited better performance than hydrogen peroxide alone for TCE and DCA degradation.     

Enhanced dissipation of DEHP in soil and simultaneously reduced bioaccumulation of DEHP in vegetable using bioaugmentation with exogenous bacteria

The widely used plastic film containing di(2-ethylhexyl) phthalate (DEHP) in agriculture has caused serious soil pollution and poses risks to human health through the food chain. An effective DEHP degradation bacteria, Microbacterium sp. J-1, was newly isolated from landfill soil. Response surface methodology was successfully employed for optimization resulting in 96% degradation of DEHP (200 mg L^?1) within 5 days. This strain degraded DEHP by hydrolysis of the ester bond and hydroxylation of the aromatic ring to form 2-ethyl hexanol, mono-(2-ethylhexyl) phthalate, phthalate acid, and protocatechuic acid, and subsequently transformed these compounds with a maximum specific degradation rate (q _max), half-saturation constant (K _s ), and inhibition constant (K _i ) of 1.46 day^?1, 180.2 mg L^?1, and 332.8 mg L^?1, respectively. Bioaugmentation of DEHP-contaminated soils with the strain J-1 greatly enhanced the DEHP dissipation rate (~88%). Moreover, this strain could efficiently colonize the rhizosphere soil of inoculated vegetables and further enhanced DEHP degradation (~97%), leading to a significant decrease (>70%) in DEHP accumulation in shoots and roots of the inoculated vegetables compared to uninoculated vegetables. The results highlighted the roles of the inoculated exogenous bacteria in simultaneously bioremediating contaminated soils and reducing bioaccumulation of DEHP in the edible part of the vegetable for food safety.     

Photodegradation of Scopoletin in Organic Solvents and Aqueous Solutions: Kinetics and Degradation Pathways

Scopoletin (hereafter SCO), an excellent candidate of acaricides, was discovered and developed in China. Photolysis kinetics of SCO in organic solvents and different aqueous media were investigated under 500W Xe lamp. Effects of five surfactants, nitrate (NO₃^?), nitrite (NO₂^?), and H₂O₂ on SCO photolysis and photodegradation pathways of SCO in aqueous were also studied. The results indicated that photolysis rate of SCO in organic solvents was in the sequence of acetone > ethyl acetate > methanol, and the corresponding half-lives were 9.63, 36.47, and 49.50 h, respectively. Photolysis rate of SCO in different aqueous media was in the sequence of pure water > river water > natural seawater, and the half-lives were 5.68, 6.66, and 7.79 h, respectively. The five kinds of surfactants, NO₃^?, and NO₂^? had significant photoquenching effects on photolysis of SCO, and H₂O₂ had photosensitization effects on photolysis of SCO. By separation and identification of photoproducts using LC/ESI-MS, it could be concluded that SCO was photolyzed through photorearrangement, photohydrolysis, and photooxidation of the molecule itself.     

Effects of soil type and nitrate concentration on denitrification products (N2O and N2) under flooded conditions in laboratory microcosms

Abstract

Denitrification products nitrous oxide ((N₂O) and nitrogen (N₂)) were measured in three flooded soils (paddy soil from Vietnam, PV; mangrove soil from Vietnam, MV; paddy soil from Japan, PJ) with different nitrate (NO₃^–) concentrations. Closed incubation experiments were conducted in 100-mL bottles for 7 d at 25°C. Each bottle contained 2 g of air-dried soil and 25 mL solution with NO₃^– (concentration 0, 5 or 10 mg N L^?1) with or without acetylene (C₂H₂). The N₂O + N₂ emissions were estimated by the C₂H₂ inhibition method. Results showed that N₂O + N₂ emissions for 7 d were positively correlated with those of NO₃^– removal from solution with C₂H₂ (R² = 0.9872), indicating that most removed NO₃^– was transformed to N₂O and N₂ by denitrification. In PJ soil, N₂O and N₂ emissions were increased significantly (P < 0.05) by the addition of greater NO₃^– concentrations. However, N₂O and N₂ emissions from PV and MV soils were increased by the addition of 0 to 5 mg N L^?1, but not by 5 to 10 mg N L^?1. At 10 mg N L^?1, N₂ emissions for 7 d were greater in PJ soil (pH 7.0) than in PV (pH 5.8) or MV (pH 4.3) soils, while N₂O emissions were higher in PV and MV soils than in PJ soil. In MV soil, N₂O was the main product throughout the experiment. In conclusion, NO₃^– concentration and soil pH affected N₂O and N₂ emissions from three flooded soils.     

pH-Based Strategies for an Efficient Addition of H<Subscript>2</Subscript>O<Subscript>2</Subscript> During Ozonation to Improve the Mineralisation of Two Contaminants with Different Degradation Resistances

Ozonation is an efficient process for the primary degradation of most substrates but not for their mineralisation. In this work, the ozonation enhanced with the addition of H₂O₂ was studied for two substrates with very different oxidation resistances: the dye rhodamine 6G (R6G) and the surfactant linear alkylbenzene sulfonate (LAS). With O₃ only, the primary degradation of R6G was completed in less than 10 min but its TOC removal only reached 45% in 1 h. By adding H₂O₂, TOC removal was increased to 70% with a molar ratio (mol H₂O₂/mol substrate) of 10. The analysis of pH decrease served to define the specific basicity loss (SBL). The optimum conditions for the R6G mineralisation were found to be associated with a SBL value between 1 and 10 ((min/g)/L)^?1, through an adequate addition of H₂O₂. Moreover, in the case of LAS, the addition of H₂O₂ for a greater efficiency should occur after the foaming period, above all formed at acid pH. LAS degradation was also considerably improved, and the optimum for primary degradation achieved in 10 min with a TOC removal of over 65% with a molar ratio (mol H₂O₂/mol substrate) of 20.

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? Graphical Abstract

     

Photodegradation of Bisphenol A with ZnO and TiO<Subscript>2</Subscript>: Influence of Metal Ions and Fenton Process

In this study, photocatalytic degradation of bisphenol A (BPA) was investigated using two types of catalysts (TiO₂ and ZnO) with various metal ion concentrations and amounts of added H₂O_2. A kinetic test was performed to observe the changes of BPA over time under UV irradiation in a photocatalytic reactor. Experimental results demonstrated that degradation efficiency of ZnO was higher than that of TiO₂. The degradation rate increased as catalyst dosage increased until reaching optimum dosage, after which degradation rate decreased. The addition of H₂O₂ improved the degradation efficiency of BPA, with the degradation efficiency increasing with the amount of H₂O₂. All metal ions, including Fe²⁺, Ni²⁺, and Cu²⁺, inhibited the degradation of BPA by ZnO at natural pH, whereas Fe²⁺ and Ni²⁺ enhanced degradation efficiency of BPA at acidic pH. Comparison of BPA degradation with H₂O₂ only, ZnO/H₂O₂, Fe²⁺/H₂O₂, and ZnO/Fe²⁺/H₂O₂ revealed that Fe²⁺/H₂O₂ was more efficient than other processes at lower pH (pH?=?3.44), whereas ZnO/H₂O₂ the most efficient at higher pH (pH?=?6.44). These results indicate that ZnO/H₂O₂ process was observed to be the most efficient of all processes. Degradation efficiency of BPA by ZnO was also influenced by additional parameters, including H₂O₂ concentration, metal ions, and solution pH.     

Biodegradability of Di(2-Ethylhexyl) Phthalate by Pseudomonas Fluorescens FS1

Di(2-ethylhexyl)phthalate (DEHP), one of high-molecular weightphthalate esters (PAEs), is used in the manufacturing of polyvinylchloride (PVC) resins, polyvinyl acetate, cellulosics,and polyurethanes, and contributes to environmental pollution. In this article, the characteristics of DEHP biodegradation by aneffective degradation bacterium, Pseudomonasfluorescens FS1 that isolated from the activated sludge at a petrochemicalfactory, was capable of using phthalate esters as the sole carbonand energy source, were investigated. Experimental results showedthat the biodegradation of DEHP by P. fluorescens FS1 could be described by the first-order reaction model, whichcould be expressed as: lnC = –0.0688t + A, and the half-life ofDEHP biodegradation was 10.07 d when the initial concentrations of DEHP were less than 50 mg L^-1. The inhibition effects ofDEHP as a substrate had become predominant above the concentration of 50 mg L^-1. The PAEs-degrading enzyme of P. fluorescens FS1, mainly located in the soluble part andthe particle of cytoplasm, was an intracellular enzyme. The metabolites of DEHP degradation by P. fluorescens FS1, which monoester, phthalic acid, benzonic acid, phenol, wereextracted using dichloromethane at different time intervals and identified by the GC-MS. The tentative pathway proposed for degradation of DEHP by P. fluorescens FS1 under aerobic condition is monoester in the beginning, further enzymatic degradation of the monoester produces phthalic acid, benzonic acid, phenol and finally CO₂ and H₂O.     

EFFECTS OF CALCIUM ON LIGNIFICATION RELATED PARAMETERS IN SODIUM CHLORIDE-STRESSED SOYBEAN ROOTS

The effects of exogenous calcium (Ca²⁺) on root growth and lignification-related parameters – phenylalanine ammonia-lyase (PAL) and peroxidases (POD) activities, hydrogen peroxide (H₂O₂) and lignin contents – in roots of NaCl-stressed soybean seedlings were analyzed. Three-day-old seedlings were cultivated in half-strength Hoagland's solution (pH 6.0) with or without 5 mM calcium nitrate [Ca(NO₃)₂] and 50 to 200 mM sodium chloride (NaCl) in a growth chamber (25°C, 12/12 h light/dark photoperiod, irradiance of 280 μmol m^?2 s^?1) for 24 h. In general, results showed that the absence of Ca²⁺ reduced root growth and increased lignification of soybean seedlings grown in NaCl-free nutrient solution. NaCl reduced the root growth and all lignification-related parameters. Root growth, PAL and POD activities and hydrogen peroxide (H₂O₂) contents were more affected after NaCl treatments without Ca²⁺ in the nutrient solution. At 5 mM, Ca²⁺ did not alleviate the deleterious effects of NaCl on lignification-related parameters.     

Synthesis and Characterisation of Novel-Activated Carbon from Waste Biomass Pine Cone and Its Application in the Removal of Congo Red Dye from Aqueous Solution by Adsorption

The present study deals with the synthesis and subsequent application of Fe₃O₄@n-SiO₂ nanoparticles for the removal of Cr(VI) from aqueous solutions. Rice husk, an agrowaste material, was used as a precursor for the synthesis of nanoparticles of silica. Synthesized nanoparticles were characterized by XRD and SEM to investigate their specific characteristics. Fe₃O₄@n-SiO₂ nanoparticles were used as adsorbent for the removal of Cr(VI) from their aqueous solutions. The effects of various important parameters, such as initial Cr(VI) concentration, adsorbent dose, temperature, and pH, on the removal of Cr(VI) were analyzed and studied. A pH of 2.0 was found to be optimum for the higher removal of Cr(VI) ions. It was observed that removal (%) decreased by increasing initial Cr(VI) concentration from 1.36?×?10^-2 to 2.4?×?10^-2 M. The process of removal was found to be endothermic, and the removal increased with the rise in temperature from 25 to 45 °C. The kinetic data was better fitted in pseudo-second-order model in comparison to pseudo-first-order model. Langmuir and Freundlich adsorption capacities were determined and found to be 3.78 and 1.89 mg/g, respectively, at optimum conditions. The values of ΔG ⁰ were found to be negative at all temperatures, which confirm the feasibility of the process, while a positive value of ΔH ⁰ indicates the endothermic nature of the adsorption process. The present study revealed that Fe₃O₄@n-SiO₂ nanoparticles can be used as an alternate for the costly adsorbents, and the outcome of this study may be helpful in designing treatment plants for treatment of Cr(VI)-rich effluents.     

A Stable Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>/Expanded Perlite Composite Catalyst for Degradation of Rhodamine B in Heterogeneous Photo-Fenton System

A stable and efficient Fe₂O₃/expanded perlite (Fe₂O₃-Ep) composite catalyst was synthesized by a simple hydrothermal method for degradation of refractory contaminants in heterogeneous photo-Fenton system. X-ray diffraction and FT-IR analyses confirmed the presence of the Fe₂O₃ in the synthesized catalyst. The catalytic activity of the Fe₂O₃-Ep catalyst was evaluated by the degradation of rhodamine B (RhB, 5 mg/L) and metronidazole (MET, 5 mg/L) in the presence of H₂O₂ under visible light irradiation. The Fe₂O₃-Ep catalyst exhibited high efficiency for degradation of RhB at a wide pH range from 2 to 10 and showed excellent catalytic property for decomposition of MET as well. The degradation ratio of RhB was achieved 99%, and the removal ratio of COD was 62% within 90 min at the best experimental conditions (0.5 g/L of Fe₂O₃-Ep catalyst, 2 mL/L of H₂O₂). Furthermore, iron leaching of the Fe₂O₃-Ep catalyst during the catalytic degradation reaction was negligible and the catalyst still exhibited high catalytic activity and stability after five cycles. These results show that the catalyst can be used as a highly efficient heterogeneous photo-Fenton catalyst for the degradation of non-biodegradable refractory pollutants in water.     

Speciation of Phosphorus and Cadmium in a Contaminated Soil Amended with Bone Char: Sequential Fractionations and XANES Spectroscopy

In this work, photocatalytic degradation of two reactive dyes, Reactive Yellow 84 (RY 84) and Reactive Black 5 (RB 5), on FeTiO₃/TiO₂ heterojunction in the presence of UV–visible radiation and H₂O₂ has been reported. FeTiO₃/TiO₂ heterojunction has been prepared from ilmenite FeTiO₃ and anatase TiO₂ by employing oxalic acid as an organic linker. FeTiO₃/TiO₂ ratios have been varied from 1 to 5 wt.%, and the materials were characterized by X-ray diffraction, scanning electron microscope and diffused reflectance UV–visible spectroscopic analysis. The photocatalytic activity of FeTiO₃/TiO₂ heterojunction for the degradation of the organic dyes RY 84 and RB 5 in the presence of UV–visible light was found to be higher than that of pure TiO₂. The addition of H₂O₂ increases the rate of degradation of both dyes on FeTiO₃/TiO₂ heterojunction. It facilitates the fast degradation of dye solutions even when their concentration was above 100 mg/l, which is otherwise very slow due to the low transmittance of light by the dye solution. The extent of mineralisation of the reactive dye during photocatalytic degradation was estimated from chemical oxygen demand analysis. FeTiO₃/TiO₂ heterojunction photocatalyst was also found to have good photostability; the material retains almost 97 % of its initial activity even in the fifth cycle.     

Distribution Coefficient and Adsorption–desorption Rates of di (2-ethylhexyl) Phthalate (DEHP) onto and from the Surface of Suspended Particles in Fresh Water

The commonly used plastic softener, di (2-ethylhexyl) phthalate (DEHP), also a known Endocrine Disrupting Compound, was found contaminated in various aquatic environments, including river water in Thailand. The data of adsorption kinetics from this study indicated that DEHP can adsorb onto pure bentonite and natural suspended sediment with average adsorption rate constants of 0.0056 and 0.0039 min^?1 respectively. The average distribution coefficients between suspended particles and water found in this study for pure bentonite and natural suspended sediment were 0.045 and 0.043 l g^?1 respectively. Although the studies were carried out in pH 4.0, 7.0 and 10.0, there were no obvious influences of pH on adsorption rates and distribution coefficients of DEHP onto both pure bentonite and natural suspended particles. The desorption rate was very small and was estimated to be less than 0.03 μg min^?1. The results indicated that suspended sediment could become a long term release of DEHP and facilitate the transport of DEHP mainly due to fast adsorption rate and relatively high adsorption capacity.     

Application of Adjoint-based Forecast Sensitivities to Asian Dust Transport Events in Korea

Phytoremediation is an attractive, economic alternative to soil removal and burial methods to remediate contaminated soil. However, it is also a slow process. The effect of humic acid in enhancing B and Pb phytoextraction from contaminated soils was studied (pot experiment) using transplanted vetiver grass (Vetiveria zizanioides (L.) Nash). Boron was applied at 0, 45, 90 and 180 kg B ha^?1 soil (as H₃BO₃) in 16 replicates. Of the 64 pots, four pots each were treated with 0, 100, 200 and 400 kg ha^?1 humic acid (HA) solution. In a separate experiment, Pb was applied (as Pb(NO₃)₂) at 0, 45, 90 and 180 kg Pb ha^?1 prior to addition of HA solutions at levels identical to the B experiment. Experiments were conducted using a randomized complete block design with four replicates. Vetiver grass was harvested 90 days after planting. Lead addition beyond 45 kg Pb ha^?1 decreased Pb uptake mostly due to a yield decline. Humic acid application increased Pb availability in soil and enhanced Pb uptake while maintaining or enhancing yield. An application of 200 kg HA ha^?1 was optimal for maintaining yield at elevated Pb levels. Boron application did not impact yield but greatly increased B content of roots and shoot. Boron uptake was greatest upon addition of 400 kg HA ha^?1. We conclude that HA addition to vetiver grass can be an effective way to enhance phytoremediation of B and Pb but optimum rates differ depending on soil B and Pb contamination levels.     

通过土壤泥浆中的过氧化氢处理三氯乙烯污染的土壤

Chlordecone, one of the most persistent organochlorine pesticides, was applied between 1972 and 1993 in banana fields in the French West Indies, which results in long-term pollution of soils and contamination of waters, aquatic biota, and crops. As human exposure to chlordecone is mainly due to food contamination, early research was focused on chlordecone transfer to crops. Field trials were conducted to investigate chlordecone contamination of yam, sweet potato, turnip, and radish grown on a ferralic Nitisol polluted by chlordecone. We also carried out trials on yam, courgette, and tomato under greenhouse conditions with homogenized Andosol and Nitisol, polluted by chlordecone to various extents. Our results indicated that i) all tubers were contaminated in accordance with the chlordecone content of the soils; ii) the contamination capacity of the Nitisol was greater than that of the Andosol; and iii) whatever the soil type, tuber contamination was related to the soil volumetric content of dissolved chlordecone. Nevertheless, no tubers showed sufficient chlordecone uptake for efficient soil decontamination by means of plant extraction. Soil contact accounted for most of the root crop contamination, which was inversely proportional to the tuber size. Internal transfer might also increase root crop contamination when the root central cylinder contained raw sap flow, as in the case of turnip or radish. Courgette fruits showed high contamination without soil contact. Thus, further research is needed to explore the pattern of both below- and aboveground plant chlordecone contamination and assess the hypothesis of its correlation with sap flow. Finally, we used our results to build a decision-making tool for farmers, relating soil pollution with the maximal contamination of the harvested organs to predict crop contamination and thus assisting farmers in making crop choices at planting in order to conform with the European Union’s regulations.     

Characteristics of Raindrop Acidification by Co-Washout of SO2(G)-H2O2(G)-HNO3(G)

In order to investigate the acid rain formation under the coexistence of SO₂(g), H₂O₂(g), and HNO₃(g) in the air, a mathematical model has been built and some numerical simulations have been carried out with use of the model. The simulation reveals that SO₂(g) absorbed into a raindrop is released and then re-absorbed as the fall distance increases. The desorption and re-absorption processes of SO₂(g) are caused by: (1) the fact that the equilibrium concentration of H₂O₂(aq) and HNO₃(aq) in raindrops are much higher than that of SO₂(aq), and (2) the fact that the oxidation reaction rate of HSO₃ ^? with H₂O₂(aq) increases with H⁺ concentration in raindrops. The degree of acidification of the rainwater has been estimated by introducing a raindrop size distribution. The acidification is mainly caused by the adsorption of SO₂(g) in the usual case where the atmospheric concentration of SO₂(g) is much higher than that of HNO₃(g). With the increase in the atmospheric concentration of HNO₃(g), the concentration of H⁺ generated from SO₂(g) decreases and the contribution of HNO₃(g) to the generation of H⁺ becomes dominant.

     

Evaluation of a Quasi-steady-state Respiration Test in a Full-scale Biopile

A quasi steady state respiration test based on Fick’s law with a correction term for advective flux, for estimating petroleum hydrocarbon degradation rates, was evaluated in a full-scale (3,000 m³) biopile study. A contaminated clayey sand soil with an average TPH content of 1,421?±?260 mg kg^?1 soil was treated in a biopile with a fixed venting and heating system. Temperature in the biopile ranged from 12.1 to 36.6°C and soil water content from 15.2 to 35.8 m³ H₂O m^?3 soil. Oxygen concentrations in the biopile showed a rapid decrease with depth, before venting and reached constant atmospheric concentration during venting. Measured oxygen consumption in the biopile ranged from ?0.04 to ?0.68 mol O₂ m^?3 soil day^?1. Average oxygen consumption rates calculated with the quasi-steady-state method were significantly (P?<?0.05) lower then the oxygen consumption rates calculated with the transient method. It was suggested that the oxygen diffusion was underestimated by the diffusivity models used and that further research is needed to determine relative effective diffusion coefficients in biopiles. Although both respiration testing and petroleum hydrocarbon concentration showed a decrease of oxygen consumption in time, the estimated degradation rate was low compared to the actual decrease in petroleum hydrocarbon concentration. Additional work will have to be done to acquire a more precise knowledge of the relationship between respirometrically determined degradation rates and the actual change in petroleum hydrocarbon concentration in the soil.