Monitoring the photochemical degradation of triclosan in wastewater by UV light and sunlight using solid-phase microextraction

Photo solid-phase microextraction (photo-SPME) is applied for the first time to study the photochemical behavior of an emerging pollutant, triclosan, in real contaminated wastewater samples using a solar simulator. In this study, water samples are extracted by SPME and then, the fiber coating is irradiated for a selected time. This on-fiber procedure, so-called photo-SPME, followed by gas chromatography-mass spectrometry makes it possible to study photodegradation kinetics and the generation of byproducts. Several photoproducts were identified in the real samples including the 2,8-dichlorodibenzo-p-dioxin, dichlorophenols and a compound tentatively identified as other DCDD congener or a dichlorohydroxydibenzofuran. Accordingly, it was possible to postulate main photodegradation mechanisms. Photo-SPME demonstrated slower kinetics in wastewater than in spiked ultrapure water probably due to the presence of dissolved organic matter. This technique was extensively compared with conventional aqueous photodegradation showing high similarity. The influence of pH on the triclosan photolysis and on the triclosan-dioxin conversion was also investigated in wastewater. Photodegradation of triclosan and formation of 2,8-DCDD occurred independently of sample pH. This study represents an advance in the use of photo-SPME to understand the photochemical fate of environmental organic pollutants and demonstrates its clear advantages with real samples.     

Study of chlorothalonil photodegradation in natural waters and in the presence of humic substances

Photodegradation of chlorothalonil was studied in different natural waters (sea, river and lake) as well as in distilled water under natural and simulated solar irradiation. The effect of dissolved organic matter (DOM) such as humic and fulvic substances on the photodegradation rate of chlorothalonil was also studied in simulated sunlight. The presence of DOM enhanced the photodegradation of chlorothalonil with the exception of seawater. The kinetics were determined through gas chromatography electron capture detection (GC/ECD) and the photodegradation proceeds via pseudo-first-order reaction in all cases. Half-life ranged from 1 to 48 h. In natural and humic water chlorothalonil photodegradation gave rise to two different intermediates compared to distilled water demonstrating that the transformation of chlorothalonil depend on the constitution of the irradiated media and especially from DOM. The byproducts identified by GC/MS techniques were: chloro-1,3-dicyanobenzene, dichloro-1,3-dicyanobenzene, trichloro-1,3-dicyanobenzene and benzamide.     

Solar light induced and TiO2 assisted degradation of textile dye reactive blue 4

Aqueous solutions of reactive blue 4 textile dye are totally mineralised when irradiated with TiO2 photocatalyst. A solution containing 4 x 10(-4) M dye was completely degraded in 24 h irradiation time. The intensity of the solar light was measured using Lux meter. The results showed that the dye molecules were completely degraded to CO2, SO4(2-), NO3-, NH4+ and H2O under solar irradiation. The addition of hydrogen peroxide and potassium persulphate influenced the photodegradation efficiency. The rapidity of photodegradation of dye intermediates were observed in the presence of hydrogen peroxide than in its absence. The auxiliary chemicals such as sodium carbonate and sodium chloride substantially affected the photodegradation efficiency. High performance liquid chromatography and chemical oxygen demand were used to study the mineralisation and degradation of the dye respectively. It is concluded that solar light induced degradation of textile dye in wastewater is a viable technique for wastewater treatment.     

太阳光对湖泊中有机污染物降解的研究进展

论述了太阳光对湖泊水体中有机污染物降解作用的研究,就其降解机理、动力学特征、作用对象及降解产物等作了逐一介绍.阐明了太阳光对生物降解湖泊水体中有机污染物具有协同作用,也概述了光降解作用受pH、溶解性有机物(DOM)、水深与水体运动、地理、水文、水质与气候等因素的影响.并对实验室模拟条件下的降解与自然条件下的降解进行对比,提出今后该领域的发展前景与研究方向.     

Photochemical and photocatalytic degradation of gaseous toluene using short-wavelength UV irradiation with TiO2 catalyst: comparison of three UV sources

The feasibility of the use of short-wavelength UV (254+185 nm) irradiation and TiO2 catalyst for photodegradation of gaseous toluene was evaluated. It was clear that the use of TiO2 under 254+185 nm light irradiation significantly enhanced the photodegradation of toluene relative to UV alone, owed to the combined effect of photochemical oxidation in the gas phase and photocatalytic oxidation on TiO2. The photodegradation with 254+185 nm light irradiation was compared with other UV wavelengths (365 nm (black light blue lamp) and 254 nm (germicidal UV lamp)). The highest conversion and mineralization were obtained with the 254+185 nm light. Moreover, high conversions were achieved even at high initial concentrations of toluene. Catalyst deactivation was also prevented with the 254+185 nm light. Regeneration experiments with the deactivated catalyst under different conditions revealed that reactive oxygen species played an important role in preventing catalyst deactivation by decomposing effectively the less reactive carbon deposits on the TiO2 catalyst. Simultaneous elimination of photogenerated excess ozone and residual organic compounds was accomplished by using a MnO2 ozone-decomposition catalyst to form reactive species for destruction of the organic compounds.     

Bacterial abundance and community structure in response to nutrients and photodegraded terrestrial humic acids in a eutrophic lake

The exposure of humic substances to solar radiation can alter their concentration and composition and subsequently influences their bioavailability in aquatic food webs. With eutrophication increasingly prominent in lakes, nutrients, such as inorganic N and P, are a prerequisite for heterotrophic bacteria that use organic matter. Here photodegradation of terrestrial humic acids and nutrient addition were performed to investigate the response of bacterial abundance and community structure to photodegraded humic acids and increased nutrient concentrations in a eutrophic lake. Results showed that the decreasing level of absorption coefficient at 460 nm in the treatment irradiated with 40 W UV lamps was more remarkable than that of the treatment irradiated with 20 W UV lamps and the control. This reduced coefficient corresponds to the greatest decrease in humic acid concentration in the 40 W group. Bacteria showed high abundance after incubation with humic acids which underwent strong irradiation intensity. An increased nutrient concentration significantly affected bacterial abundance. The dominant bacteria were Aquabacterium for the irradiated group, Aquabacterium and Limnobacter for the 20 W group and Flavobacterium and Limnobacter for the 40 W group. Armatimonadetes-gp4 and Sediminibacterium showed evident response to high nutrient concentration. Our results showed that the exposure of terrestrial humic acids to UV light and the increasing concentration of nutrients have obviously changed bacterial community.

     

Integrated Waste Management in a Zone of Northern Italy: Compost Production and Use,and Analytical Control of Compost,Soil, and Crop

Agricultural soils of two Italian maize farms were treated for five years with an industrially produced high-quality compost. Cattle manure and the usual mineral fertilizer were used for comparison purposes. The effects of the organic and mineral fertilizer treatments were studied by analyzing the compost and manure, cultured soils, and harvested material. The grain yield was also determined. Organic fertilization improved soil pH, CEC, content of organic matter and NPK. Soil respiration and N mineralization were found to be higher than in the purely mineral-treated soil. Plant K take-up was improved, whereas grain yield was not affected. It was confirmed that organic fertilization, particularly compost use, maintained and increased soil fertility. The study demonstrated the feasibility of using in loco analytical facilities to follow the entire recycling process—from waste to compost production—and the use of the final product in the field.     

Integrated waste management in a zone of northern Italy: compost production and use, and analytical control of compost, soil, and crop

Agricultural soils of two Italian maize farms were treated for five years with an industrially produced high-quality compost. Cattle manure and the usual mineral fertilizer were used for comparison purposes. The effects of the organic and mineral fertilizer treatments were studied by analyzing the compost and manure, cultured soils, and harvested material. The grain yield was also determined. Organic fertilization improved soil pH, CEC, content of organic matter and NPK. Soil respiration and N mineralization were found to be higher than in the purely mineral-treated soil. Plant K take-up was improved, whereas grain yield was not affected. It was confirmed that organic fertilization, particularly compost use, maintained and increased soil fertility. The study demonstrated the feasibility of using in loco analytical facilities to follow the entire recycling process-from waste to compost production-and the use of the final product in the field.     

UV-light induced mineralization of organic matter bound chlorine in Lake Bjän,Sweden--a laboratory study

Surface water and aqueous solutions of isolated organic matter from a humic rich lake in southern Sweden were exposed to artificial UV radiation to investigate the UV light induced influence on organic matter bound chlorine in natural systems. It was found that the photodegradation of organic matter bound chlorine was more pronounced than the photodegradation of organic carbon. After 120 h of irradiation of the isolated organic matter, only 35% of the initial organochlorine was still in the solution compared to about 70% of the dissolved organic carbon (DOC). A similar result was obtained for unfractionated surface water. Furthermore, our results indicate that the loss of organic chlorine was mainly due to a mineralization of organic chlorine into chloride ions. The total decrease of organic chlorine after 120 h was 32 microg Cl(org) l(-1), of which the major part disappeared in the initial irradiation phase. A similar increase was observed in the chloride concentration (34 microg Cl(-) l(-1)).     

Remediation of metal contaminated soil with mineral-amended composts

This study examined the use of two composts derived from green waste and sewage sludge, amended with minerals (clinoptilolite or bentonite), for the remediation of metal-contaminated brownfield sites to transform them into greenspace. Soils contaminated with high or low levels of metals were mixed with the mineral-enhanced composts at different ratios and assessed by leaching tests, biomass production and metal accumulation of ryegrass (Lolium perenne L.). The results showed that the green waste compost reduced the leaching of Cd and Zn up to 48% whereas the composted sewage sludge doubled the leachate concentration of Zn. However, the same soil amended with composted sewage sludge showed an efficient reduction in plant concentrations of Cd, Cu, Pb or Zn by up to 80%. The results suggest that metal immobilisation and bioavailability are governed by the formation of complexes between the metals and organic matter. The amendment with minerals had only limited effects.     

Solar photodegradation of dichloroacetic acid and 2,4-dichlorophenol using an enhanced photo-Fenton process

The photo-Fenton process using potassium ferrioxalate as a mediator was investigated for the photodegradation of dichloracetic acid (DCA) and 2,4-dichlorophenol (DCP) in aqueous medium using solar light as source of irradiation. The influence of the solution depth, the light intensity and the effect of stirring the solution during irradiation process were evaluated using DCA as a model compound. A negligible influence of stirring the solution was observed when the concentration of ferrioxalate (FeOx) was 0.8 mM and solution depth was 4.5 or 14 cm. The optimum FeOx concentration determined for solution depths between 4.5 and 14 cm was 0.8 mM considering total organic carbon (TOC) removal during DCA irradiation. The high efficiency of the photo-Fenton process was demonstrated on summer days, when only 10 min of exposition (around noon) were sufficient to completely destroy the organic carbon of a 1.0 mM DCA solution in the presence of 0.8 mM FeOx and 6.0 mM H2O2 using a solution depth of 4.5 cm. It was observed that the photodegradation efficiency increases linearly with the solar light intensity up to values around 15 Wm(-2) but this linear relationship does not hold above this value showing a square root dependence. The photodegradation of a solution of DCP/FeOx showed a lower TOC removal rate than that observed for DCA/FeOx, achieving approximately 90% after 35 min irradiation under 19 W m(-2), while under this light intensity, the same TOC removal of DCA/FeOx was achieved in only 10 min irradiation.     

Photolytic degradation of quinalphos in natural waters and on soil matrices under simulated solar irradiation

The photochemical persistence of quinalphos, one of the most widely used organophosphorous insecticides, was investigated in a variety of environmental matrices such as natural waters and soils of different composition. Simulated solar irradiation was obtained using a xenon arc lamp (Suntest CPS+ apparatus) giving an irradiation intensity of 750 W m(-2) equivalent to a light dose per hour of irradiation of 2,700 kJ m(-2). The phototransformation rates were determined using solid-phase microextraction (SPME) and ultrasonic extraction (USE) coupled to GC-FTD, while the identification of photoproducts was carried out by GC-MS. In water samples, the degradation kinetics followed a pseudo-first-order reaction and photolysis half-lives ranged between 11.6 and 19.0 h depending on the constitution of the irradiated media. Dissolved organic matter (DOM) has a predominant retarding effect, while nitrate ions accelerated the photodegradation kinetics. In soil samples, the degradation kinetics was monitored on 1mm soil layer prepared on glass TLC plates. The kinetic behaviour of quinalphos was complex and characterized by a double step photoreaction, fast in the first 4h of irradiation followed by a slow degradation rate up to 64 h. The photolysis half-life of quinalphos was shorter in sandy soil compared to the rest of the soil samples, varying between 16.9 and 47.5 h, and showing a strong dependence on the composition of the irradiated media. Among the transformation products formed mainly through photohydrolysis and photoisomerization processes, some photoproduct structures were proposed according to their mass spectral information.     

The comparison study of compost and natural organic matter samples

Sewage sludge is a serious problem facing modern wastewater treatment plants. One of the methods to safely utilize the sludge is through composting and the agricultural use of the final product.In this study the compost samples from municipal sewage sludge are compared to the natural, rich in organic matter samples. Based on physicochemical properties of the material, the maturity indices are obtained to evaluate the quality of organic matter and estimate the similarities between the samples.The study shows that one-dimensional analysis like that based on maturity indices does not provide satisfactory answers concerning the nature of such complex materials. The data set of the analysis naturally possesses a multidimensional character so that the employment of advanced chemometric techniques like cluster analysis show a number of features which were hidden within the ‘data flood’.The major conclusion of this work is that the compost from sewage sludge is similar to peat in the significance of the properties of the organic matter. Moreover, the organic matter of agricultural soil, which is most stable and has been naturally matured over a long period of time, differs substantially from the other samples.     

Experimental measurements and computer predictions of copper complex formation by soluble soil organic matter

Complexing of metals by organic matter can strongly influence their biological activity in the environment. The extent of copper complex formation by soluble organic matter extracted from an organic soil, a clay, and two sandy loams, was measured under identical conditions using two independent experimental methods. The results in every case fitted equations similar to Langmuir two-surface isotherms, but the values of complexing capacity and complexing strength were not the same for the organic matter from the four soils, and so were unsuitable for use in computer programs intended to predict concentrations of individual copper species in soil solutions. These concentrations can, however, be predicted by an empirical relationship between free and total copper at a constant pH and ionic strength.     

Differences in p,p'-DDE bioaccumulation from compost and soil by the plants Cucurbita pepo and Cucurbita maxima and the earthworms Eisenia fetida and Lumbricus terrestris

Two plant species, Cucurbita pepo and Cucurbita maxima, and two earthworm species, Eisenia fetida and Lumbricus terrestris, were exposed to soil and compost with equivalent p,p'-DDE contamination. Pollutant bioconcentration was equal in plant roots in both media, but translocation was higher in C. pepo. Bioaccumulation by E. fetida was approximately 6- and 3-fold higher than that by L. terrestris in the soil and compost, respectively. For all species, p,p'-DDE uptake was significantly greater from soil than from compost; 7- to 8-fold higher for plant roots and 3- to 7-fold higher for worms. Abiotic desorption from soil was approximately twice that from the compost. When all the data are normalized for organic-carbon content of the media, the contaminant is more tightly bound by soil than compost. Although the risk associated with p,p'-DDE is higher in soil than compost, important mechanistic differences exist in contaminant binding to organic carbon in the two media.     

Partitioning and photodegradation of ciprofloxacin in aqueous systems in the presence of organic matter

Ciprofloxacin is an extensively used antibiotic that has been reported to occur in surface water. Previous studies have indicated that ciprofloxacin photodegrades and sorbs to particulate organic material within aquatic systems. The first objective of the current study was to evaluate the influence of organic material on photodegradation rates of ciprofloxacin. Using a bench top experimental design, ciprofloxacin was added to experimental chambers that contained only water or water and fine particulate organic matter (FPOM) followed by exposure to ultraviolet light. Sorption to FPOM was rapid, reducing the amount of ciprofloxacin that was available for photodegradation. Thus, the presence of FPOM initially decreased the ciprofloxacin concentration in the aqueous compartment. However by the end of the 16 h test, 42% of the ciprofloxacin was recovered from the test system with FPOM present, while only 2% of the ciprofloxacin was recovered in systems that did not contain FPOM. The second objective of this study was to compare the sorption coefficients for ciprofloxacin between two types of organic material: FPOM, classified as amphipod processed leaves, and coarse particulate organic matter (CPOM), represented by intact leaf disks. Sorption to FPOM (log Kd of 4.54+/-0.09 l kg(-1)) was 1.6 orders of magnitude greater than sorption to CPOM (log Kd of 2.92+/-0.10 l kg(-1)) potentially resulting in differential toxicity among similar organisms that occupy these different niches and leading to different estimates of environmental fate and effects.     

Fate of pharmaceuticals--photodegradation by simulated solar UV-light

The fate of pharmaceuticals in surface waters under solar irradiation was investigated. Photodegradation of pharmaceuticals caused by sun irradiation may be of major significance in the natural elimination process. Based on a data compilation from the literature, the lipid lowering agent metabolite clofibric acid, the iodinated X-ray contrast media iomeprol, which contribute to the adsorbable organic halogen compounds, and the antiepileptic drug carbamazepine were selected. The irradiation experiments were carried out in batch experiments with simulated UV–sunlight. The photodegradation of the pharmaceuticals showed a pseudo-first-order kinetics. The objective of this investigation was to demonstrate that the extent of photoinduced degradation of pharmaceuticals can vary significantly for the different pharmaceuticals and it strongly depends on the water constituents present in solution. The influences of different initial pharmaceutical concentrations, the presence of other pharmaceuticals like carbamazepine or clofibric acid and the presence of natural organic matter on the photochemical degradation rate of pharmaceuticals in aqueous solutions were investigated. Analyses of the pharmaceuticals and their photodegradation products were carried out by high performance liquid chromatography with diode-array and fluorescence detection.     

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

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

Effect of short-term sunlight irradiation on absorbance spectra of chromophoric organic matter dissolved in coastal and riverine water

Samples of riverine and coastal, filtered (filter pore size 0.2 μm) water were exposed to short-term sunlight irradiation which reduced their absorbance in the UV and visible regions. Absorbance losses in coastal chromophoric dissolved organic matter (CDOM) were up to 10-fold smaller than those in riverine CDOM. Accompanying changes of absorbance spectra shapes (increased slope parameter) were, probably, a result of decrease of the mean molecular size of light absorbing organic matter. The potential of coastal CDOM to photodegradation was smaller and was exhausted during the course of a day-long experiment. A distinctive feature of spectral changes after sunlight exposure was a maximum absorbance decrease which appeared at 300 nm in riverine and at 280 nm in coastal water. That selective absorbance loss has been ascribed in both cases to the disappearance of chromophores of terrestrial origin which, in coastal water, had a lower mean molecular size (due to flocculation and/or prior photodegradation) but, nevertheless, retained their molecular properties.     

Use of 15N-depleted artificial compost in bound residue studies

Association of bound residues to soil humic matter may be accomplished by different binding mechanisms such as sequestration in hydrophobic interiors of the organic material or covalent linkage to the organic matter. The structures and chemical environments of compounds can be observed by NMR spectroscopy. We applied 15N-NMR spectroscopy to study the soil-bound residues of 15N-labeled simazine. As the 15N-isotope has a low sensitivity and natural abundance 15N-NMR experiments require long measurement times and often result in low signal-to-noise (S/N) ratios. Therefore, in addition to the use of 15N-labeled simazine, 15N-depleted compost was used to reduce the amount of background signal and enhance the sensitivity. The compost was produced from maize and wheat plants grown on sand with 15N-depleted NH4NO3 as sole nitrogen source. The plants were freeze-dried, ground and mixed with sand for composting. After a composting period of 224 days analysis of the compost revealed a 15N-content of 267 ppm as opposed to a natural abundance of 3650 ppm. Characterization of this artificial compost produced parameter values similar to those of a natural compost. The 13C-NMR-spectra of the humic and fulvic acids during different stages of maturity showed that there was a shift from single-bond functional groups to more complex double-bond and aromatic structures. Experiments with this compost showed an increased signal intensity. The improved sensitivity made it possible to obtain interpretable NMR signals in contrast to experiments with 15N-simazine on native soil where no signals were detectable. The data indicated that the bound residues of simazine are composed of metabolites resulting from N-dealkylation and triazine ring destruction. Silylation of the bound residues showed a very strong binding of the residues to the matrix as only a small fraction could be solubilized.