Dye-sensitized photodegradation of the fungicide carbendazim and related benzimidazoles

The present work studies the visible-light-promoted photodegradation of the colorless fungicide carbendazim (methyl 2-benzimidazolecarbamate) and several 2-substituted benzimidazoles (SBZ's), in water or water-methanol solution, in the presence of air and, as a photosensitizer, the synthetic xanthene dye Rose Bengal (RB) or the natural pigment riboflavin (Rf). The results indicate that the degradation of each particular SBZ depends on its chemical structure and on the sensitizer employed. In the presence of RB, the degradation always operates via a singlet molecular oxygen (O(2)((1)Delta(g)))-mediated mechanism, through a highly efficient process, as deduced from the comparison of the rate constants for physical and chemical quenching of O(2)((1)Delta(g)). In the presence of Rf, the visible-light irradiation of any of the studied SBZ's produces a series of competitive processes that depend on the relative concentrations of Rf and SBZ. These processes include the quenching of excited singlet and triplet Rf states by the SBZ and the generation of both O(2)((1)Delta(g)) and superoxide radical anion (O(2)(-)), the latter generated by electron transfer from excited Rf species to the dissolved oxygen. The overall result is the photodegradation of the SBZ and the photoprotection of the sensitizer.     

Enhancement of heavy metal accumulation by tissue specific co-expression of iaaM and ACC deaminase genes in plants

The aerobic riboflavin (Rf)-sensitized photodegradation of the endocrine disruptor 4,4'-isopropylidenebisphenol (bisphenol A, BPA), and of the related compounds 4,4'-isopropylidenebis(2,6-dibromophenol) and 4,4'-isopropylidenebis(2,6-dimethylphenol) has been studied in water and water-methanol mixtures through visible-light continuous photolysis, polarographic detection of oxygen uptake, stationary and time-resolved fluorescence spectroscopy, time-resolved near-IR phosphorescence detection and laser flash photolysis techniques. Bisphenols (BPs) quench excited singlet and triplet states of Rf, with rate constants close to the diffusion limit. BPs and dissolved molecular oxygen, employed in similar concentrations, competitively quench triplet excited Rf. As a consequence, superoxide radical anion and singlet molecular oxygen (O(2)((1)Delta(g))) are produced by electron- and energy-transfer processes, respectively, as demonstrated by auxiliary experiments employing selective quenchers of both oxidative species and the exclusive O(2)((1)Delta(g)) generator Rose Bengal. As a global result, the photodegradation of Rf is retarded, whereas BPs are degraded, mainly by an O(2)((1)Delta(g))-mediated mechanism, which constitutes a relatively efficient process in the case of BPA. Oxidation, dimerization and fragmentation products have been identified in the photooxidation of BPA. Results indicate that BPs in natural waters can undergo spontaneous photodegradation under environmental conditions in the presence of adequate photosensitizers.     

Color and COD removal from wastewater containing Reactive Black 5 using Fenton's oxidation process

In this study, Reactive Black 5 (RB5) was removed from synthetic wastewater using Fenton's oxidation (FO) process. Experiments were conducted on the samples containing 100 and 200 mg l(-1) of RB5 to remove the dye toxicity. Seventy-five milligram per litre of RB5 caused 25% toxicity on 24-h born daphnids whereas 100 mg l(-1) of RB5 displayed 100% toxicity on Daphnia magna. The study was performed in a systematic approach searching optimum values of FeSO(4) and H(2)O(2) concentrations, pH and temperature. Optimum pH and temperature for 100 mg l(-1) of RB5 were observed as 3.0 and 40 degrees C, respectively, using 100 mg l(-1) of FeSO(4) and 400 mg l(-1) of H(2)O(2) resulted in 71% chemical oxygen demand (COD) and 99% color removal. For 200 mg l(-1) of RB5, 84% COD removal was obtained using 225 mg l(-1) of FeSO(4) and 1000 mg l(-1) of H(2)O(2) yielding 0.05 molar ratio at pH 3.0 and 40 degrees C. Color removal was also more than 99%. The optimum conditions determined in accordance with the literature data. The H(2)O(2) requirement seems to be related to initial COD of the sample. FeSO(4)/H(2)O(2) ratios found were not changed for both concentrations. The temperature affected the COD removal significantly at high degrees. Toxicity was completely removed for each concentration of RB5 at optimum removal conditions.     

Photodegradation and volatility of pesticides

BACKGROUND AND OBJECTIVES: Among the factors affecting the environmental fate of surface-applied pesticides several biological as well as abiotic factors, such as volatilization and photochemical transformations are of particular interest. Whereas reliable measurement methods and models for estimating direct photodegradation are already available for the compartments of water and atmosphere and individual subprocesses have already been described in detail, there is still a need for further elucidation concerning the key processes of heterogeneous photodegradation of environmental chemicals on surfaces. METHODS: In order to systematically examine the direct and indirect photodegradation of 14C-labeled pesticides on various surfaces and their volatilization behavior, a new laboratory device ('photovolatility chamber') was designed according to US EPA Guideline 161-3. Model experiments under controlled conditions were conducted investigating the impact of different surfaces, i.e. glass, soil dust and radish plants, and environmental factors, i.e. irradiation and atmospheric ozone (O3), on the photodegradation and volatilization of surface-deposited [phenyl-UL-14C]parathion-methyl (PM). RESULTS AND DISCUSSION: Depending on the experimental conditions, parathion-methyl was converted to paraoxon-methyl, 4-nitrophenol, unknown polar products and 14CO2. With respect to the direct photodegradation of PM (experiments without O3), the major products were polar compounds and 14CO2, due to the rapid photochemical mineralization of 4-nitrophenol to 14CO2. Paraoxon-methyl and 4-nitrophenol formation was mainly mediated by the combination of light, O3, and *OH radicals. In radish experiments PM photodegradation was presumably located in the cuticle compartment, which exhibited a sensitized photodegradation, as more unknown products were yielded compared to the glass and soil dust experiments. This could be explained by intensifying the inherent PM degradation in the dark with the same product spectrum. Due to photochemical product formation, which is an antagonistic process to the volatilization of parent compound, the volatilization of unaltered parathion-methyl from each surface generally decreased in the presence of light, particularly in combination with increasing O3 concentrations and *OH radical production rates. CONCLUSION: First results demonstrated that the photovolatility chamber provides a special tool for the systematic evaluation of (a) photodegradation of surface-located pesticide residues, i.e. measuring qualitative aspects of direct and indirect photodegradation together with relative photodegradation rates, and (b) volatilization of pesticides on surfaces by including and optionally varying relevant parameters such as light, atmospheric O3 concentration, surface temperature, air temperature, air flow rate. OUTLOOK: The experimental facility represents an important complement to lysimeter and field studies, in particular for experiments on the volatilization of pesticides using the wind tunnel system. With the photovolatility chamber special experiments on photodegradation, volatilization and plant uptake can be conducted to study key processes in more detail and this will lead to a better understanding of the effects of certain environmental processes on the fate of released agrochemicals contributing to an improved risk assessment.     

Biological decolorization of reactive anthraquinone and phthalocyanine dyes under various oxidation-reduction conditions.

The decolorization of two anthraquinone dyes (Reactive Blue 4 [RB4] and Reactive Blue 19 [RB19]) and two phthalocyanine dyes (Reactive Blue 7 [RB7] and Reactive Blue 21 [RB21]) was investigated at an initial dye concentration of 300 mg/L using an unacclimated, enrichment culture. The culture was fed a mixture of organic compounds and maintained initially under aerobic conditions, and then progressively developed anoxic/ anaerobic conditions. Biotransformation-related decolorization of the dyes did not take place under aerobic conditions, but use of the feed organic mixture and biomass production by the enrichment culture were not affected. Complete ammonia removal occurred in the control and all dye-amended cultures. The development and extent of nitrification were much lower in the latter cultures, in which ammonia removal via air stripping was the dominant mechanism. Prolonged incubation of the culture under anoxic/anaerobic conditions with multiple carbon source additions resulted in a high decolorization extent of anthraquinone dyes (over 84%) and only partial decolorization of phthalocyanine dyes (49 to 66%). Development of significant methanogenic activity took place in the control and, to a lesser extent, in the two phthalocyanine dye-amended cultures, but the anthraquinone dyes severely inhibited the development of methanogenic activity. The RB4 and RB19 decolorization was attributed to nonreversible, microbially mediated dye transformation(s), demonstrated by the accumulation of decolorization products with absorbance maxima in the 420- to 460-nm region. The decolorization of RB4 and RB19 followed Michaelis-Menten kinetics. At an initial dye concentration of 300 mg/L, the observed maximum decolorization rate per unit biomass was 9.1 and 37.5 mg dye/mg volatile suspended solids x day for the RB4 and RB19, respectively. Thus, partial decolorization of reactive phthalocyanine dyes and extensive biological decolorization of reactive anthraquinone dyes is feasible only under anoxic/anaerobic conditions.     

Mineralization of Reactive Black 5 in aqueous solution by basic oxygen furnace slag in the presence of hydrogen peroxide

Basic oxygen furnace slag (BOF slag) is a solid waste arisen from the steel making process. FeO is one of the major components of BOF slag. The FeO-containing property of BOF slag makes it possible to catalyze the Fenton reaction. Reactive Black 5 (RB5) dye is chosen as the target compound in this study. This study has investigated the catalytic performance of BOF slag on the Fenton reaction to decompose RB5 in aqueous solution. A first-order kinetic model with respect to TOC was adopted to explain the mineralization of RB5 by the H(2)O(2)/BOF slag process. The experimental results in this study suggested that dosage with 1.49 x 10(-4)M min(-1) H(2)O(2) and 12.5 g l(-1) BOF slag in the solution at pH 2 provided the optimal operation conditions for the mineralization of RB5 yielding a 51.2% treatment efficiency at 100 min reaction time, and complete decoloration can be achieved within 30 min reaction time. The H(2)O(2)/Fe(2+) ratio was then determined to be 6.06:1.     

Photolytic degradation of methyl-parathion and fenitrothion in ice and water: Implications for cold environments

Here we investigate the photodegradation of structurally similar organophosphorus pesticides; methyl-parathion and fenitrothion in water (20 °C) and ice (−15 °C) under environmentally-relevant conditions with the aim of comparing these laboratory findings to limited field observations. Both compounds were found to be photolyzed more efficiently in ice than in aqueous solutions, with quantum yields of degradation being higher in ice than in water (fenitrothion > methyl-parathion). This rather surprising observation was attributed to the concentration effect caused by freezing the aqueous solutions. The major phototransformation products included the corresponding oxons (methyl-paraoxon and fenitroxon) and the nitrophenols (3-methyl-nitrophenol and nitrophenol) in both irradiated water and ice samples. The presence of oxons in ice following irradiation, demonstrates an additional formation mechanism of these toxicologically relevant compounds in cold environments, although further photodegradation of oxons in ice indicates that photochemistry of OPs might be an environmentally important sink in cold environments.     

Quantum yield study of the photodegradation of hydrophobic dyes in the presence of acetone sensitizer.

The photodegradation of hydrophobic disperse dyes with different chromophores in the presence of acetone (ACE) was investigated. In this study, the photodecay of dyes was carried out in the Rayonet RPR-200 merry-go-round photoreactor, with 253.7 nm monochromatic ultraviolet (UV) lamps. A typical azo disperse dye (CI disperse yellow 7--DY7) and an anthraquinone disperse dye (CI disperse orange--DO11) were used as the probe compounds. The results demonstrate that the addition of acetone increases the solubility of hydrophobic disperse dyes and enhances the photosensitization reaction simultaneously. More than ten times of quantum yield enhancement is observed in the presence of ACE photosensitizer than in water alone. The photodegradation of DY7 and DO11 is dominated by photoreduction, which follows pseudo first-order decay, and the rate constants strongly depend on the solvent system (i.e., ACE/H2O ratios) and the initial pH levels. The decay quantum yields of dyes are normally observed with the increase of the ACE/H2O ratio. The optimum quantum yields of DY7 and DO11 were determined at 0.5 (v/v) and 0.25 (v/v), respectively, in alkaline conditions. A further increase in the ACE/H2O ratio reduces the quantum yields, possibly due to light attenuation by excess acetone.     

负载型纳米复合半导体WO_3-TiO_2/AC光催化降解刚果红废水

采用溶胶-凝胶-浸渍-焙烧法制备了负载型纳米复合半导体WO3-TiO2/AC光催化剂,以偶氮染料刚果红为目标降解物,通过正交实验优化了刚果红废水的降解条件,并对其光催化动力学进行了探讨.结果表明,刚果红废水的最佳降解条件为:催化剂投加量10 g/L,pH=7,H2O2用量为3.5 mL/L.在最佳条件下,当刚果红废水起始浓度为40 mg/L时,反应120 min后,刚果红溶液的去除率可达95.21%,较相同条件下TiO2/AC对刚果红染料的降解率提高了19.57%.光催化剂对刚果红的光催化降解符合Langmuir-Hinshelwood(L-H)模型.     

Study on the photodegradation of amidosulfuron in aqueous solutions by LC-MS/MS

Sulfonylurea herbicides are extensively widespread for the protection of a variety of crops and vegetables because of their low application rates, high selectivity and low persistency in the environment; unfortunately, their low persistence does not always correspond to a lower toxicity, since new species potentially more toxic and stable than the precursor herbicides can form, owing to natural degradation processes. Here, the photodegradation of amidosulfuron in aqueous solutions was studied by high-performance liquid chromatography with diode array detection and tandem mass spectrometry to identify the degradation products in order to outline the environmental fate of the molecules generating from the simulation of one of the natural processes that can occur, i.e., photoinduced degradation. The photodegradation process results in a first order kinetic reaction with a t _1/2 value of 276 h (11.5 days) and a kinetic constant of 0.0027 h^?1, and three possible degradation products were identified. The results obtained are then compared to those obtained in previous works carried out in comparable experimental conditions about nicosulfuron and tribenuron-methyl, two sulfonylurea herbicides belonging to different classes, and to literature data: hypotheses on the existence of preferential degradation pathways are then drawn, in consequence of the molecular structure of the sulfonylurea pesticide. In particular, the use of organic solvents to obtain complete solubilization of the sample plays a fundamental role and deeply influences the degradation processes that, therefore, not always fully adhere to the actual natural photodegradation pathways. Moreover, considerations about toxicity were driven since the complete mineralisation of the sample is not reached: even when the parent pesticides are totally degraded, they are, however, transformed into other organic compounds showing, if subject to ecotoxicological tests, at least the same toxicity of the precursor herbicides. The evidence here presented suggests that, at least for the class of sulfonylurea pesticides, their professed low persistence actually does not produce any real advantage.     

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.     

Degradation of carbofuran in water by solar photocatalysis in presence of photosensitizers

The effect of the presence of photosensitizers, methylene blue (MB) and rose Bengal (RB), on the degradation of carbofuran (2,3-dihydro-2,2-dimethylbenzofuran-7-yl methylcarbamate) in water in a solar photocatalytic system was investigated. It was found that as compared to MB, RB generally showed a stronger effect on the decomposition of carbofuran under comparable conditions. Among the conditions studied, adding 2 x 10(-6) M of RB, that corresponding to 2% of the initial concentration of carbofuran solution in the system, rendered the most effective degradation of carbofuran. As a result, a carbofuran removal percentage of 69.9%, a mineralization efficiency of 28.0%, and a microtoxicity reduction of 65.0% could be achieved. The degradation and mineralization of carbofuran was found to follow the pseudo-first order reaction kinetics. The decomposition mechanism of carbofuran was further investigated through identification of the intermediates to elaborate the influence of dye photosensitizer on the solar photocatalysis of carbofuran in water. On the basis of the intermediates identified, including carbofuran phenol, 3-hydroxy carbofuran phenol, and substituted alcohols (3-phenoxy 1-propanol, 2-ethyl 1-hexanol, 2-butoxyl ethanol), it appears that hydrolysis and hydroxylation were the two key mechanisms for decomposing carbofuran during the process of solar photocatalysis with the aid of dye photosensitizer.     

Photooxidation of naphthalenesulfonic acids: comparison between processes based on O(3), O(3)/activated carbon and UV/H(2)O(2)

The aim of the present study was to analyze and compare the efficacy of UV photodegradation with that of different advanced oxidation processes (O(3), UV/H(2)O(2), O(3)/activated carbon) in the degradation of naphthalenesulfonic acids from aqueous solution and to investigate the kinetics and the mechanism involved in these processes. Results obtained showed that photodegradation with UV radiation (254 nm) of 1-naphthalenesulfonic, 1,5-naphthalendisulfonic and 1,3,6-naphthalentrisulfonic acids is not effective. Presence of duroquinone and 4-carboxybenzophenone during UV irradiation (308-410 nm) of the naphthalenesulfonic acids increased the photodegradation rate. Addition of H(2)O(2) during irradiation of naphthalenesulfonic acids accelerated their elimination, due to the generation of ()OH radicals in the medium. Comparison between UV photodegradation 254 m and the advanced oxidation processes (O(3), O(3)/activated carbon and UV/H(2)O(2)) showed the low-efficacy of the former in the degradation of these compounds from aqueous medium. Thus, among the systems studied, those based on the use of UV/H(2)O(2) and O(3)/activated carbon were the most effective in the oxidation of these contaminants from the medium. This is because of the high-reactivity of naphthalenesulfonic acids with the *OH radicals generated by these two systems. This was confirmed by the values of the reaction rate constant of *OH radicals with these compounds k(OH), obtained by competitive kinetics (5.7 x 10(9) M(-1) s(-1), 5.2 x 10(9) M(-1) s(-1) and 3.7 x 10(9) M(-1) s(-1) for NS, NDS and NTS, respectively).     

Competitive adsorption of dye metanil yellow and RB15 in acid solutions on chemically cross-linked chitosan beads

One kind of adsorbent with a high adsorption capacity for anionic dyes was prepared using ionically and chemically cross-linked chitosan beads. A batch system was applied to study the adsorption behavior of one acid dye (MY, metanil yellow) and one reactive dye (RB15, reactive blue 15) in aqueous solutions by the cross-linked chitosan beads. The adsorption capacities was 3.56 mmol g(-1) (1334 mg g(-1)) for dye MY and 0.56 mmol g(-1) (722 mg g(-1)) for dye RB15 at pH4, 30 degrees C. The Langmuir model agreed very well with the experimental data (R(2)>0.996). The kinetics of adsorption for a single dye and the kinetics of removal of ADMI color value in mixture solutions at different initial dye concentrations were evaluated by the nonlinear first-order and second-order models. The first-order kinetic model fits well with the dynamical adsorption behavior of a single dye for lower initial dye concentrations, while the second-order kinetic model fits well for higher initial dye concentrations. The competitive adsorption favored the dye RB15 in the mixture solution (initial conc. (mM): MY=1.34; RB15=1.36); while it favored the dye MY in the mixture solution (initial conc. (mM): MY=3.00; RB15=1.34) and the adsorption kinetics for dye RB15 has the tendency to shift to a slower first order model.     

Degradation of Carbofuran in Water by Solar Photocatalysis in Presence of Photosensitizers

The effect of the presence of photosensitizers, methylene blue (MB) and rose Bengal (RB), on the degradation of carbofuran (2,3-dihydro-2,2-dimethylbenzofuran-7-yl methylcarbamate) in water in a solar photocatalytic system was investigated. It was found that as compared to MB, RB generally showed a stronger effect on the decomposition of carbofuran under comparable conditions. Among the conditions studied, adding 2 × 10^?6 M of RB, that corresponding to 2% of the initial concentration of carbofuran solution in the system, rendered the most effective degradation of carbofuran. As a result, a carbofuran removal percentage of 69.9%, a mineralization efficiency of 28.0%, and a microtoxicity reduction of 65.0% could be achieved. The degradation and mineralization of carbofuran was found to follow the pseudo-first order reaction kinetics. The decomposition mechanism of carbofuran was further investigated through identification of the intermediates to elaborate the influence of dye photosensitizer on the solar photocatalysis of carbofuran in water. On the basis of the intermediates identified, including carbofuran phenol, 3-hydroxy carbofuran phenol, and substituted alcohols (3-phenoxy 1-propanol, 2-ethyl 1-hexanol, 2-butoxyl ethanol), it appears that hydrolysis and hydroxylation were the two key mechanisms for decomposing carbofuran during the process of solar photocatalysis with the aid of dye photosensitizer.     

Characterization of photovoltaic performance of the dye-sensitized solar cell with a novel ruthenium complex having a bisdemethoxycurcumin as a ligand

The first example of a ruthenium sensitizer (TUS-22) having a natural dye, bisdemethoxycurcumin, as a ligand has been synthesized. The dye-sensitized solar cell based on this novel dye showed 5.8% conversion efficiency under AM 1.5 (100 mW/cm(2)) irradiation.     

Environmental photodegradation of mefenamic acid

Pharmaceuticals and personal care products are an emerging class of environmental pollutants. Photolysis is expected to be a major loss process for many of these compounds in surface waters, including the common non-steroidal anti-inflammatory drug mefenamic acid. The direct photolysis solar quantum yield of mefenamic acid was observed to be 1.5+/-0.3x10(-4). Significant photosensitization was observed in solutions of Suwanee River fulvic acid and Mississippi River water, as well as for the model photosensitization compounds 3'-methoxyacetophenone, 2-acetonaphthone and perinaphthenone. Quenching, sparging and light-filtering experiments suggested a direct reaction of mefenamic acid with excited triplet-state dissolved organic matter as the major photosensitization process. The persistence of the model photosensitizer suggests that the photosensitization by perinaphthenone occurs either by triplet-energy transfer or an electron transfer followed by rapid regeneration of the sensitizer. Due to its low quantum yield, the loss of mefenamic acid in sunlit natural waters is expected to depend on both direct and indirect photodegradation processes.     

The role of carbonate radical in limiting the persistence of sulfur-containing chemicals in sunlit natural waters

Carbonate radical (*CO3-) is a selective oxidant that may be important in limiting the persistence of a number of sulfur-containing compounds in sunlit natural waters. Thioanisole, dibenzothiophene (DBT), and fenthion were selected to investigate the degradation pathway initiated by *CO3-; electron-rich sulfur compounds are particularly reactive towards the *CO3-. Using HPLC, GC, GC-MS and LC-MS for structural confirmation, the major photodegradation products of thioanisole and DBT were the corresponding sulfoxides. The sulfoxide products were further oxidized through reaction with *CO3- to the corresponding sulfone derivatives. Fenthion showed a similar pathway with appearance of fenthion sulfoxide as the major product. The proposed mechanism involves abstraction of an electron on sulfur to form a radical cation, which is then oxidized by dissolved oxygen. Each of the sulfur probes were further investigated in a sunlight simulator under varying matrix conditions. The highest rate constants occurred in the *CO3- matrix, and the lowest occurred in a matrix of dissolved organic carbon (DOC) and bicarbonate. In synthetic and natural field water, thioanisole photodegraded faster than under direct photolysis, with half-lives of 75.1 and 85.8 min, respectively. Fenthion photodegraded more rapidly than thioanisole. DBT photodegraded rapidly in a *CO3- matrix with a half-life of 24.8 min, while the half-life of direct photolysis was 350 min. Photodegradation products of each compound were also investigated. Ultimately, *CO3- was found to contribute toward the photodegradation of sulfur-containing compounds in natural waters.     

A batch kinetic study on decolorization and inhibition of Reactive Black 5 and Direct Brown 2 in an anaerobic mixed culture

Decolorization and inhibition kinetic characteristics of two azo dyes namely Reactive Black 5 (RB 5) and Direct Brown 2 (DB 2) were investigated with partially granulated anaerobic mixed culture using glucose (3000 mg l(-1) COD) as carbon source and electron donor during batch incubation. Monod, zero-, first-, and second-order reaction kinetic models were tested in order to determine the most suitable rate model of substrate and color removal kinetic. The course of the decolorization and substrate removal process approximates to first-order kinetic model under batch conditions. Decolorization, and substrate removal were achieved effectively under test conditions but ultimate removal of azo dyes and substrate were not observed at high dye concentrations. Aromatic amine and volatile fatty acid accumulation were observed proportionally at a higher azo dye concentration. A competitive kinetic model that describes the anaerobic co-metabolism of increasing RB 5 and DB 2 dye concentrations with glucose as co-substrate has been developed based on the experimental data.     

Ferric citrate-induced photodegradation of dyes in aqueous solutions

The photooxidation of dye solutions containing Fe(III)-citrate complexes was studied. The photodegradation under near-UV light of the five dyes, C. I. reactive red 2, C. I. reactive blue 4, C. I. reactive black 8, C. I. basic red 13 and C. I. basic yellow 2, in aqueous solutions at pH2.0 containing Fe(III)-citrate complexes was found to follow pseudo-first order kinetics. The photodegradation rates of the dye, C. I. reactive red 2, decreased with increasing the initial dye concentration in range of 20 – 60 mg/L . A comparatively higher photodegradation efficiency of the dye was gained under the condition of pH2.0 and the Fe(III) to citrate ratio 1:2.