Organic Effluents Research Articles

Spatial and temporal patterns of urea content in a eutrophic stream continuum on the Northern Great Plains

Urea can degrade water quality and stimulate toxic phytoplankton in P-rich lakes, yet little is known of its sources, abundance, or transportation in lotic systems, particularly within the Northern Great Plains. We measured physico-chemical parameters biweekly during May–September 2010–2012 at 16 stations along a 250 km lotic continuum to quantify spatial and temporal variation in urea concentrations and discharge, and to identify potential regulatory processes. Urea concentrations were similar to those in regional prairie lakes (range 5.2–792.1, median 78.6 μg N L−1) with variable seasonal mean (± SD) concentrations (96.6 ± 96.1 μg N L−1) and fluxes (4.22 × 105 ± 257.6 μg N s−1). Landscape analysis with generalized additive models explained 68.3% of deviance in urea concentrations, with high temporal variability predicted mainly by positive relationships with nutrient content and chlorophyte abundance, but not temperature, dissolved organic matter, bacterial abundance, or urban effluent. Seasonal analysis revealed that during spring, urea content was correlated negatively with leguminous forage cover (% area) and positively with stream discharge, oilseed and cereal crops, and shrubs or deciduous plants, while during summer, urea concentrations were correlated negatively with discharge and leguminous crop cover, as well as nutrient levels. Mean porewater urea concentrations (528.5 ± 229.8 μg N L−1) were over five-fold greater than stream concentrations, suggesting that hyporheic production may offset declining influx from terrestrial sources during summer. We conclude that urea may be ubiquitous in eutrophic prairie streams and that management of its export from land may reduce detrimental effects on downstream lakes.

G-C3N4/Ca2Fe2O5 heterostructures for enhanced photocatalytic degradation of organic effluents under sunlight

g-C3N4/Ca2Fe2O5 heterostructures were successfully prepared by incorporating g-C3N4 into Ca2Fe2O5 (CFO). As prepared g-C3N4/CFO heterostructures were initially utilized to photodegrade organic effluent Methylene blue (MB) for optimization of photodegradation performance. 50% g-C3N4 content in CFO composition showed an enhanced photodegradation efficiency (~ 96%) over g-C3N4 (48.15%) and CFO (81.9%) due to mitigation of recombination of photogenerated charge carriers by Type-II heterojunction. The optimized composition of heterostructure was further tested for degradation of Bisphenol-A (BPA) under direct sunlight, exhibiting enhanced photodegradation efficiency of about 63.1% over g-C3N4 (17%) and CFO (45.1%). The photoelectrochemical studies at various potentials with and without light illumination showed significant improvement in photocurrent response for g-C3N4/Ca2Fe2O5 heterostructures (~ 1.9 mA) over CFO (~ 67.4 μA). These studies revealed efficient solar energy harvesting ability of g-C3N4/Ca2Fe2O5 heterostructures to be utilized for organic effluent treatment.

Removal of nutrients from Organic Liquid Agricultural Waste using filamentous algae.

A feasibility analysis of tertiary treatment for Organic Liquid Agricultural Waste is presented using filamentous algae belonging to the genus Cladophora sp. as an alternative to chemical tertiary treatment. The main advantages of tertiary treatments that use biological systems are the low cost investment and the minimal dependence on environmental variables. In this work we demonstrate that filamentous algae reduces the nutrient load of nitrate (circa 75%) and phosphate (circa 86%) from the organic waste effluents coming from dairy farms after nine days of culture, with the added advantage being that after the treatment period, algae removal can be achieved by simple procedures. Currently, the organic wastewater is discarded into fields and local streams. However, the algae can acquire value as a by-product since it has various uses as compost, cellulose, and biogas. A disadvantage of this system is that clean water must be used to achieve enough water transparency to allow algae growth. Even so, the nutrient reduction system of the organic effluents proposed is friendly to the ecosystem, compared to tertiary treatments that use chemicals to precipitate and collect nutrients such as nitrates and phosphates.

Continuous Synthesis and Separation of p-Bromobenzyl Bromide Using Atom-Efficient Bromination of p-Bromotoluene without Any Organic Effluent: Potential for Green Industrial Practice

Continuous Synthesis and Separation of <i>p</i>-Bromobenzyl Bromide Using Atom-Efficient Bromination of <i>p</i>-Bromotoluene without Any Organic Effluent: Potential for Green Industrial Practice

Hydrogen-Bonded Colorimetric and Fluorescence Chemosensor for Fluoride Anion With High Selectivity and Sensitivity: A Review.

In recent years, the wide application of fluoride materials has grown rapidly, therefore excessive discharge in the surrounding environment, especially in drinking water and organic effluent, has become a potential hazard to humans, and has even resulted in fluorosis disease. The development of a highly effective and convenient method to recognize fluoride anions in surrounding environments seems necessary and urgent. Among which, the development of a colorimetric and fluorescence fluoride chemosensor with obvious color changing allowing for naked-eye detection with high sensitivity and selectivity is more interesting and challenging. In this minireview, current novel colorimetric and fluorescence chemosensors for fluoride anions by hydrogen-bond interaction are introduced, including obvious color changing by naked-eye detection, high sensitivity and selectivity, non-pollution and fluoride extraction ability, aqueous detection, and other additional functions. Finally, the perspective of the fluoride chemosensor design concept and potential evolution trends are pointed out.

High Performance of Biohydrogen Production in Packed-Filter Bioreactor via Optimizing Packed-Filter Position.

In this present investigation, a packed-filter bioreactor was employed to produce hydrogen utilizing an expired soft drink as a substrate. The effects of feeding substrate concentrations ranging from 19.51, 10.19, 5.34, 3.48, to 2.51 g total sugar/L were examined, and the position of the packed filter installed in the bioreactor at dimensionless heights (h/H) of 1/4, 2/4, 3/4, and 4/4 was studied. The results revealed that with a substrate concentration of 20 g total sugar/L and a hydraulic retention time (HRT) of 1 h, a packed filter placed at the half-height position of the bioreactor (h/H 2/4) has the optimal hydrogen production rate, hydrogen yield, and average biomass concentration in the bioreactor, resulting in 55.70 ± 2.42 L/L/d, 0.90 ± 0.06 mol H2/mol hexose, and 17.86 ± 1.09 g VSS/L. When feeding substrate concentrations varied from 20, 10, to 5 g total sugar/L with the packed-filter position at h/H 2/4, Clostridium sp., Clostridium tyrobutyricum, and Bifidobacterium crudilactis were the predominant bacteria community. Finally, it was discovered that the packed-filter bioreactor can produce stable hydrogen in high-strength organic effluent.

Ternary Zn1-xNixSe nanostructures as efficient photocatalysts for detoxification of hazardous Congo red, methyl orange, and chrome yellow dyes in wastewater sources

Water contamination by hazardous organic pollutants poses an extreme threat to the environment and globally endangers aquatic life and human health. Hence, the removal of toxic organic effluents from water sources is necessary to ensure a healthy green environment. To this end, a new class of emerging, visible-light-driven Zn- and Ni-based ternary metal-selenide (Zn1-xNixSe) nanophotocatalysts, with tunable nanostructures via regulation of the stoichiometric ratios of Zn and Ni, were synthesized for efficient water purification by a facile one-pot hydrothermal process. These catalysts exhibit outstanding porous properties, with large surface areas and average particle sizes of around 80 ± 10 nm. The as-prepared ternary Zn1-xNixSe catalysts enable improved optical properties, intrinsic conductivity, bandgap reductions, and large numbers of active sites compared with pristine materials, thereby exhibiting outstanding degradation properties against various dye molecules, including Congo red, methyl orange, and chrome-IV upon visible light irradiation. The improved photodegradation capabilities of the Zn1-xNixSe catalysts may be attributed to the synergistic combinations of Zn and Ni selenides, which in turn minimize the recombination rates of the photogenerated carriers compared to their individual constituents. These findings clearly demonstrate that the proposed ternary Zn1-xNixSe catalysts could be potentially used to remove toxic organic contaminants from industrial wastewater.

Agro-industrial Wastes as Bioactive Molecules Source

Sustainable use of renewable natural resources, through value addition, using biological life processes, is an ideal transition from an oil-based economy to bioresource economy. Addressing climate change, renewable resources such as agro-industrial wastes, currently seen as low value materials, are in fact natural sources of value-added compounds that can be used, for example, as economic sources of bioactive substances of high interest for chemical, pharmaceutical and food industries. Moreover, agro-industrial by-products such as most of organic effluents have a high organic load content and can be vaporizable through a gaseous energy carrier production (methane/hydrogen) and a digested flow for agricultural purposes, using anaerobic digestion techniques. Once adopted, biological processes of these materials may contribute to reduce the environmental pollution burden.The present work refers to different procedures and methodologies applied to wastes valorisation that, within a biorefinery concept, had the achievement of valuable biomolecules as a core of the entire recovery line system. Several wastes/wastewaters mainly produced in the Mediterranean area were under study.

Effective Dye Degradation Using Sol-Gel Synthesized Titania Nanostructures

Background: The organic effluents from industry remain one of the reasons for water contamination. By the natural degradation process, it is difficult to remove this; hence finding an effective solution for this is inevitable. TiO2-based materials have received enormous attention in the area of semiconductor photocatalysis, particularly for the degradation of organic dyes. This work emphasizes on the degradation of two industrial dyes methylene blue and rhodamine blue by visible light irradiation of TiO2 based nanoparticles. Methods: In the present study, pristine and La3+ and Ce3+ doped nanotitania were synthesized by the sol-gel method. The samples under investigation were characterized using X-ray diffraction, Transmission electron microscopy to study the variation of crystallite size and UV-Visible absorption spectroscopy. Results: The increase in crystallite size for the pristine samples calcined at various temperatures confirms the effect of calcination temperature. Also, the doping reduced the size of the synthesized nanotitania. Visible light extended absorption spectra have been observed for the calcined samples and Ce3+ doped nanotitania. The La3+ doped sample showed a blue shift in the absorption confirming quantum confinement. The photocatalytic activity in the context of degradation of certain industrial dyes such as methylene blue and rhodamine blue has been investigated for the samples. Conclusion: The studies found that nanotitania consisting of mixed anatase-rutile phase exhibits higher degradation efficiency than that of pure anatase or rutile samples. Besides, photocatalytic dye degradation has been significantly improved for Ce3+ doped nanotitania compared to the pristine sample.

Ferric ion-ascorbic acid complex catalyzed calcium peroxide for organic wastewater treatment: Optimized by response surface method

Hydrogen peroxide (H2O2) disproportionation, iron precipitation, and narrow pH range are the drawbacks of traditional Fenton process. To surmount these barriers, we proposed a ferric ion (Fe3+)-ascorbic acid (AA) complex catalyzed calcium peroxide (CaO2) Fenton-like system to remove organic dyes in water. This collaborative Fe3+/AA/CaO2 system presented an obvious improvement in the methyl orange (MO) decolorization, and also effectively eliminated other dyes. Response surface method was employed to optimize the running parameters for this coupling process. Under the optimized arguments (2.76 mmol/L Fe3+, 0.68 mmol/L AA, and 4 mmol/L CaO2), the MO removal achieved 98.90% after 15 min at pH 6.50, which was close to the computed outcome of 99.30%. Furthermore, this Fenton-like system could perform well in a wide range of pH (3–11), and enhance the H2O2 decomposition and Fe ions recycle. The scavenger experiment result indicated that hydroxyl radical, superoxide anion free radical, and singlet oxygen were acted on the dye elimination. Moreover, electron spin resonance analysis corroborated that the existences of these active species in the Fe3+/AA/CaO2 system. This study could advance the development of Fenton-like technique in organic effluent disposal.

Controlled synthesis of photoactive gallium based sillenite single crystal and its application in environmental remediation

Among the numerous photocatalytic materials studied for potential application in degradation of organic effluents and antibiotic wastes, sillenite materials emerge as important candidates. In the present work, Ga based sillenite has been used to degrade aqueous persistent organic pollutants such as bisphenol (BPA) and Norfloxacin (NF) in presence of natural solar irradiation. Sillenite based oxides have exhibited various physico chemical applications due to their photocatalytic nature. Here, gallium based sillenite, Bi24Ga2O39, has been successfully synthesized through two different techniques, hydrothermal route (HY) and solid state reaction (SS) method. X-Ray Diffraction patterns and Rietveld refinement of same revealed the occurrence of sillenite single phase. Morphological investigation by Scanning Electron Microscopy revealed regular tetrahedral morphology of HY sample. X-ray photoelectron and Raman spectroscopy were performed to analyze the chemical composition and its environment. UV–Visible spectroscopy on sillenites was used to analyze and calculate the effective optical band gap energy ~2.55 eV (HY) and ~2.76 eV (SS) respectively. Photoelectrochemical measurements performed on the samples showed appreciable photocurrent response (~1.9 μA/cm2 for HY sample). The photoactivity of samples have been utilized for degradation of aqueous persistent organic pollutants, such as methylene blue, norfloxacin and bisphenol A in presence of visible light degrading upto 92%, 82% and 84% (HY) respectively.

A chromatography-free and aqueous waste-free process for thioamide preparation with Lawesson's reagent.

After completing the thio-substitution with Lawesson’s reagent, ethanol was found to be effective in the decomposition of the inherent stoichiometric six-membered-ring byproduct from the Lawesson’s reagent to a highly polarized diethyl thiophosphonate. The treatment significantly simplified the following chromatography purification of the desired thioamide in a small scale preparation. As scaling up the preparation of two pincer-type thioamides, we have successfully developed a convenient process with ethylene glycol to replace ethanol during the workup, including a traditional phase separation, extraction, and recrystallization. The newly developed chromatography-free procedure did not generate P-containing aqueous waste, and only organic effluents were discharged. It is believed that the optimized procedure offers the great opportunity of applying the Lawesson’s reagent for various thio-substitution reactions on a large scale.

Emerging Hexagonal Mo2C Nanosheet with (002) Facet Exposure and Cu Incorporation for Peroxymonosulfate Activation Toward Antibiotic Degradation.

The catalyst with a special exposed active facet and multivalent element synergism is much desired for advanced oxidation progress (AOP) reaction. Herein, an emerging substrate, Cu-incorporated Mo2C, with an active (002) facet exposed was developed by one-step calcination to activate peroxymonosulfate (PMS) toward antibiotic degradation. Combining the multivalent Cu-Mo synergistic effect and Cu complexing interaction, Cu was incorporated onto the Mo2C surface to further enhance its antibiotic removal through PMS activation. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) measurements indicated the 5% Cu-Mo2C exhibited in the hexagonal nanosheet with Cu uniformly dispersed on the surface. Moreover, 5% Cu-Mo2C displayed excellent PMS activation which could fully degrade the tetracycline (TC) within 20 min, and the degradation rate was found to be at least 20 times higher than those of pure Mo2C, classical Fe2O3 and Co3O4, and Fenton reaction of 5% Cu-Mo2C. The results were found to be ascribed to enhanced electrical conductivity, multivalent Cu-Mo synergism, and increased generation of active radicals which contributed in the sequence SO4•- > •OH > O2•-. Surface chemical analysis combined with density functional theory (DFT) calculations confirmed that both Cu2+/Cu+ and Mo6+/Mo4+/Mo2+ redox cycles occurred on the (002) plane of Mo2C, which dominated more free electrons and mainly accounted for facilitating PMS activation. Meanwhile, systematically conditional experiments uncovered that the 5% Cu-Mo2C exhibited superb catalysis even under a wide pH and temperature, various natural polluted waters and coexisting ions, and long-time recycle. In addition, the as-prepared catalyst presented excellent adaptability for the degradation of different organic effluents originated from medical, dyeing, and beneficiation wastewaters. Considering its great performance, stability, and applicability, 5% Cu-Mo2C would be a capable candidate for PMS activation toward large-scale practical application in environmental remediation.

Agro and industrial residues: Potential raw materials for photocatalyst development

Contamination by organic effluents is currently one of the most serious environmental problems and, as a result, the elimination of these pollutants has been widely studied, mainly with organic phenolic pollutants. Photocatalysis have been showing an interesting process in order to optimize the conventional wastewater treatments. Thus, agroindustrial waste (exhausted bark acacia) and Ziegler–Natta catalyst slurry waste were used as supports for photocatalysts. The morphology and chemical composition of the catalysts were determined by scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX) and the X-ray photoelectron spectroscopy (XPS). Band-gaps were determined using UV diffuse reflectance spectroscopy (DRS). Multiscale structural characterization, pore analysis and specific surface area were determined by small-angle X-ray scattering (SAXS) and N2 porosimetry 77 K. Zeta potential (ζ) measurements were carried out to verify the stability of catalyst suspensions. The photocatalysts contained Al, Mg, Si and Ti. Metallic content ranged from 0.01 to 0.83 wt%. Ti-samples showed specific surface area between from 27.3 562.30 m g-to 562.30 m² g−1, a band gap energy (2.55–3.65 eV), negative surface potential and the presence of mass and surface fractals. The prepared photocatalytic systems (catalyst with support) were evaluated for phenol photodegradation, where the greatest percentage of phenol degradation was 68.4% under UV-V % under UV–vis radiation, while industrial standard Degussa P25 showed 43.8 % degradation. Therefore, (agro)industrial waste can be used as precursors or catalytic supports of photocatalysts for application in the treatment of wastewater meeting sustainable development.

Structure of Microbial Communities When Complementary Effluents Are Anaerobically Digested

Olive oil and pig productions are important industries in Portugal that generate large volumes of wastewater with high organic load and toxicity, raising environmental concerns. The principal objective of this study is to energetically valorize these organic effluents—piggery effluent and olive mill wastewater—through the anaerobic digestion to the biogas/methane production, by means of the effluent complementarity concept. Several mixtures of piggery effluent were tested, with an increasing percentage of olive mill wastewater. The best performance was obtained for samples of piggery effluent alone and in admixture with 30% of OMW, which provided the same volume of biogas (0.8 L, 70% CH4), 63/75% COD removal, and 434/489 L CH4/kg SVin, respectively. The validation of the process was assessed by molecular evaluation through Next Generation Sequencing (NGS) of the 16S rRNA gene. The structure of the microbial communities for both samples, throughout the anaerobic process, was characterized by the predominance of bacterial populations belonging to the phylum Firmicutes, mainly Clostridiales, with Bacteroidetes being the subdominant populations. Archaea populations belonging to the genus Methanosarcina became predominant throughout anaerobic digestion, confirming the formation of methane mainly from acetate, in line with the greatest removal of volatile fatty acids (VFAs) in these samples.

Anaerobic digestion of dairy wastewater: effect of different parameters and co-digestion options—a review

Increasing demand for dairy products resulted in the development of a large number of dairy industries, generating wastewater of high pollution potential. Main wastes generated include whey residues, milk fat and proteins, dairy sludge, and liquid effluents produced through different lines (cleaning, processing, and sanitary). Anaerobic digestion technology has got wide acceptance in recent times for treating highly organic effluents like dairy wastes due to its added benefits like energy recovery and high waste stabilisation with less energy requirement. This review paper is aimed at studying the effects of different key parameters (pH, carbon-to-nitrogen ratio, temperature, organic loading rate, solid retention time, hydraulic retention time, alkalinity, and mixing) on the successful operation of an anaerobic digester and thereby enhancing biogas production efficiency. Different waste streams generated in the dairy industry are identified along with their important characteristics. The process chemistry of anaerobic degradation of various effluents generated from the dairy industry is discussed. The need for pre-treatment technologies and the scope of co-digestion of dairy wastewater with other organic wastes are also covered. This critical review is intended to summarise the present knowledge on the application of anaerobic methods for treating dairy wastes most efficiently with proper control over operational parameters while maximising the biogas yield.

Insight into the adsorption kinetics, mechanism, and thermodynamics of methylene blue from aqueous solution onto pectin-alginate-titania composite microparticles

In the present study, pectin-alginate-titania (PAT) composites were synthesized and the adsorptive removal behavior of methylene blue (MB) from aqueous solution, as a model of synthetic organic effluents, onto the prepared PAT composites were investigated by monitoring the effect of contact time, initial MB concentration, and temperature. The adsorption isotherm data were fitted well with the Freundlich isotherm model, suggesting the surface heterogeneity of the PAT composites and that the MB adsorption occurred on the active sites on multilayer surface of the composites. The adsorption kinetics of MB was demonstrated to be pseudo-second order, governed by two intraparticle diffusion rates, and the adsorption process was exothermic, spontaneous, and more disorder. The Langmuir isotherm model suggested that the maximum adsorption capacity of MB on the PAT composites was in the range of 435–637 mg g–1. In general, it increased with the TiO2 NPs content in the PAT composites, due most likely to the increase in surface area exposing more functional groups of the pectin and alginate to interact with the synthetic dye. The adsorptive removal of MB by the PAT composites was found to be more efficient compared with many other reported adsorbents, such as graphene oxide hybrids, pectin microspheres, magnetite-silica-pectin composites, clay-based materials, chemically treated minerals, and agricultural waste. The present study therefore demonstrated for the first time that PAT composites are not only promising to be utilized as an adsorbent in wastewater treatment, but also provide an insight into the adsorption mechanism of the synthetic dyes onto the biopolymers-titania composites.Graphic abstractInsight into the adsorption kinetics, mechanism, and thermodynamics of methylene blue from aqueous solution onto pectin-alginate-titania composite microparticles.

Sensors for Structural Health Monitoring of Agricultural Structures.

The health diagnosis of agricultural structures is critical to detecting damages such as cracks in concrete, corrosion, spalling, and delamination. Agricultural structures are susceptible to environmental degradation due to frequent exposure to water, organic effluent, farm chemicals, structural loading, and unloading. Various sensors have been employed for accurate and real-time monitoring of agricultural building structures, including electrochemical, ultrasonic, fiber-optic, piezoelectric, wireless, fiber Bragg grating sensors, and self-sensing concrete. The cost–benefits of each type of sensor and utility in a farm environment are explored in the review. Current literature suggests that the functionality of sensors has improved with progress in technology. Notable improvements made with the progress in technology include better accuracy of the measurements, reduction of signal-to-noise ratio, and transmission speed, and the deployment of machine learning, deep learning, and artificial intelligence in smart IoT-based agriculture. Key challenges include inconsistent installation of sensors in farm structures, technical constraints, and lack of support infrastructure, awareness, and preference for traditional inspection methods.

Studies on the structural, optical and photocatalytic properties of CuO/MgO nanocomposite prepared by facile chemical co-precipitation

Several semiconducting materials have gained paramount attention as photocatalysts in the treatment of toxic organic effluents. Among them metal oxides play a major role in photodegradation of dye effluents. In the present work, CuO/MgO nanocomposite has been prepared by chemical co-precipitation. The structural, morphological and optical properties were studied using X-ray diffraction, Scanning Electron microscopy and Uv–Visible spectroscopy. X-ray diffraction analysis confirms the formation of CuO/MgO nanocomposite. Scanning Electron microscope images shows spherical particles with homogeneous morphology. Composition studies has been carried out by EDAX analysis. HRTEM images further confirms the presence of spherical particles and the structure of CuO-MgO. Bandgap value of the prepared composite is determined to be 1.67 eV. Photocatalytic degradation of Methylene Blue (MB) using the prepared CuO-MgO composite has been investigated. The results of photocatalytic activity reveal 87% degradation of MB for a time period of 60 min.

Photocatalytic Degradation of Organic Pollutants: The Case of Conductive Polymer Supported Titanium Dioxide (TiO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;) Nanoparticles: A Review

In recent years development of different type of industries are enlarged and these industries are connected with the discarding of organic pollutants which are harmful to aquatic system and the human health. The presence of those organic pollutants in the aquatic system can result in pollution of wastewater which affects the ecosystem. Therefore, the removals of pollutants have become an ecological concern and they are vital for the environmental sustainability. Many practices have been widely applied in the treatment of organic effluent such as biological treatment, reverse osmosis, ozonation, filtration, adsorption on solid phases, incineration, and coagulation. However, each of the methodologies has its own advantages and limitations. The recent research demonstrates that advanced oxidation processes (AOPs) based on photocatalysts are valuable and this method benefits complete mineralization of organic molecules into nontoxic CO2 and H2O at the atmospheric conditions by generating active species such as hydroxyl radicals (•OH) which can remove even non-biodegradable organic compounds from wastewater. These review papers give an overview of the enhanced photocatalytic activities of titanium dioxide (TiO2) based photocatalyst. An effort has also been made to give an overview of expedient photocatalytic activity of these supported nanoparticles for their potential application in environmental remediation. In this review article also, various methods used to enhance the photocatalytic characteristics of TiO2 including doping, coupling and other supporting are discussed. It is observed that the degradation of dyes depends on several parameters like pH, catalyst load, dye concentration, reaction temperature and scavengers on the degradation of dyes.