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Decolorization of azo dye Acid Black 1 by UV/H2O2 process and optimization of operating parameters
Abstract
An advanced oxidation process, UV/H2O2, was applied for decolorization of a di-azo dye (acid black 1). The effects of operating parameters such as hydrogen peroxide dosage, UV dosage and initial dye concentration, on decolorization have been evaluated. The acid black 1 solution was completely decolorized under optimal hydrogen peroxide dosage of 21.24 mmol/l and UV dosage of 1400 W/l in less than 1.2 min. The decolorization rate followed pseudo-first order kinetics with respect to the dye concentration. The rate increased linearly with volumetric UV dosage and nonlinearly with increasing initial hydrogen peroxide concentration. It has been found that the degradation rate increased until an optimum of hydrogen peroxide dosage, beyond which the reagent exerted an inhibitory effect. For real case application, an operation parameter plot of rate constant was developed. To evaluate the electric power and hydrogen peroxide consumption by UV/H2O2 reactor, 90% color removal was set as criteria to find the balance between both factors.
... On the TiO 2 surface, photogenerated electrons and holes produce various active oxygen species such as O − 2 , OH • , • HO 2 and O • [26]. Shu et al. [27] demonstrated the complete decolorization of azo dye Acid Black 1 (AB1) by the UV/H 2 O 2 processes. They showed that AB1 solution can be completely decolorized under the optimal hydrogen peroxide dosage of 21.24 mmol L −1 and UV dosage of 1400 W/l in less than 1.2 min. ...
... Hydrogen peroxide (H 2 O 2 ), 30% (wt.%) (Certified ACS) was purchased from Fisher Scientific Inc (Pittsburgh, PA, USA). The concentration of H 2 O 2 was chosen following previous studies [27]. Anatase nanopowder titanium dioxide 99% with 10 nm size was purchased from US Research Nanomaterials Inc., (Houston, TX, USA) and was used without further purification. ...
... The UV light radiation was conducted using a 450 W highpressure mercury vapor lamp (Hanovia, AceGlass, Vineland, NJ, USA). Shu et al. [27] reported that the higher UV lamp power may cause the faster formation of OH • free radicals in the presence of oxidants, which promotes the higher removal and degradation rate of azo dyes [27]. The most common use of UV-photolysis in water treatment is for disinfection purposes [47]. ...
... On the TiO 2 surface, photogenerated electrons and holes produce various active oxygen species such as O − 2 , OH • , • HO 2 and O • [26]. Shu et al. [27] demonstrated the complete decolorization of azo dye Acid Black 1 (AB1) by the UV/H 2 O 2 processes. They showed that AB1 solution can be completely decolorized under the optimal hydrogen peroxide dosage of 21.24 mmol L −1 and UV dosage of 1400 W/l in less than 1.2 min. ...
... Hydrogen peroxide (H 2 O 2 ), 30% (wt.%) (Certified ACS) was purchased from Fisher Scientific Inc (Pittsburgh, PA, USA). The concentration of H 2 O 2 was chosen following previous studies [27]. Anatase nanopowder titanium dioxide 99% with 10 nm size was purchased from US Research Nanomaterials Inc., (Houston, TX, USA) and was used without further purification. ...
... The UV light radiation was conducted using a 450 W highpressure mercury vapor lamp (Hanovia, AceGlass, Vineland, NJ, USA). Shu et al. [27] reported that the higher UV lamp power may cause the faster formation of OH • free radicals in the presence of oxidants, which promotes the higher removal and degradation rate of azo dyes [27]. The most common use of UV-photolysis in water treatment is for disinfection purposes [47]. ...
Discharge of dye-containing industrial effluents into natural water bodies causes serious environmental and health problems. In most cases, dyes are toxic, carcinogenic and have a complex structure that is difficult to degrade. Partial degradation of dyes can also produce by-products that are equally harmful to the environment as their parent materials. Therefore, there is a critical need to develop effective and efficient methods to completely remove or make dyes non- toxic before discharging to the environment.
In this research, we investigate the synergistic combination of Advanced Oxidation Processes (AOP) with ultrafiltration polysulfone membrane to provide high performance treatment of dyes and other recalcitrant contaminants.
AOPs cause production of very reactive species such as hydroxyl radicals that can attack organic compounds to degrade and mineralize them. We found 15% and 77.5% decrease in total organic carbon (TOC) also 77% and 95% decrease in concentration of Acid Black 1 as representative synthetic organic dyes from solution by using UV and UV/H2O2 respectively. AOPs Pretreatment approaches can be applied to change the physicochemical properties of organic dyes and reduce the fouling potential. In this study, the effect of pretreatment of solution by AOPs on polysulfone membrane flux ad flux recovery ratio and permeate quality was investigated.
Integration of AOPs by membrane filtration demonstrated to be effective in achieving a more complete removal of organic matter from waste water samples. Ultrafiltration membranes can be used to remove suspended solids, organics and bacteria from the feed of waste water. Membrane fouling is a major obstacle for using membrane in water treatment. However, several modification approaches, such as membrane surface chemical modification, have been used to increase the antifouling ability of membrane. In this work we have used AOPs to drastically reduced membrane fouling.
By using UF eafter AOP not only the water is effectively treated and no /less waste will be producing during the treatment processes but also membrane fouling will be decreased. We used a bench-scale photo reactor, which includes a high-pressure UV lamp (450 W), and cross flow polysulfone ultrafiltration membrane with and without addition of nanoparticles in membrane composition.
... This proved the effectiveness of the PO process for the solution decolorization even under low UV irradiation power. Similar observations of the increase in degradation rate/decolorization percentage with increase in UV irradiation intensity/power were reported by others [17,[44][45][46]. Theoretically, the increase in UV irradiation power promotes the photolysis of H 2 O 2 , which results in a faster formation of HO radicals and, hence, a relatively high decolorization reaction rate and conversion are observed [44,45]. ...
... Similar observations of the increase in degradation rate/decolorization percentage with increase in UV irradiation intensity/power were reported by others [17,[44][45][46]. Theoretically, the increase in UV irradiation power promotes the photolysis of H 2 O 2 , which results in a faster formation of HO radicals and, hence, a relatively high decolorization reaction rate and conversion are observed [44,45]. ...
... The photooxidation of azo dyes in the presence of a large excess of hydrogen peroxide is reported in many studies to follow an apparent first order kinetic model [19,44,[48][49][50][51]. The integrated material balance equation involving a first order rate law is as follows [ ...
A comparative study between the catalytic wet peroxide oxidation (CWPO: Fe(III)–Y zeolite/H2O2) and photooxidation (PO: UV/H2O2) of three different azo dyes—namely, reactive yellow, reactive red, and methyl orange—was conducted. Compared to CWPO, PO demonstrated higher initial reaction rates and final conversions. The contributions of H2O2, UV, UV/H2O2, Fe–Y zeolite, and Fe–Y zeolite/H2O2 to the decolorization of reactive yellow were investigated and the results showed that treatment with UV/H2O2 was the most effective process for the color removal. The effect of [H2O2]0, UV irradiation power, [Fe–Y zeolite], and the reusability of the catalyst were also studied. The catalyst was found to be reusable, but with loss in its catalytic activity. An optimum [H2O2]0 existed in both the PO and CWPO processes. However, this was higher in the latter process. The extent of decolorization increased as the UV irradiation power and [Fe–Y zeolite] increased, but there was a limit in the second case. In addition, the decolorization kinetics of the reactive yellow in both processes were investigated. It was concluded that PO followed an apparent first order kinetic model while CWPO followed the Chu kinetic model. Furthermore, a pseudo-second order rate law, which could be used in continuous flow reactor design equations, was proposed and verified to describe the CWPO rate of reaction.
... This proved the effectiveness of the PO process for the solution decolorization even under low UV irradiation power. Similar observations of the increase in degradation rate/decolorization percentage with increase in UV irradiation intensity/power were reported by others [17,[44][45][46]. Theoretically, the increase in UV irradiation power promotes the photolysis of H 2 O 2 , which results in a faster formation of HO radicals and, hence, a relatively high decolorization reaction rate and conversion are observed [44,45]. ...
... Similar observations of the increase in degradation rate/decolorization percentage with increase in UV irradiation intensity/power were reported by others [17,[44][45][46]. Theoretically, the increase in UV irradiation power promotes the photolysis of H 2 O 2 , which results in a faster formation of HO radicals and, hence, a relatively high decolorization reaction rate and conversion are observed [44,45]. ...
... The photooxidation of azo dyes in the presence of a large excess of hydrogen peroxide is reported in many studies to follow an apparent first order kinetic model [19,44,[48][49][50][51]. The integrated material balance equation involving a first order rate law is as follows [ ...
A comparative study between the catalytic wet peroxide oxidation (CWPO: Fe(III)–Y zeolite/H 2 O 2) and photooxidation (PO: UV/H 2 O 2) of three different azo dyes—namely, reactive yellow, reactive red, and methyl orange—was conducted. Compared to CWPO, PO demonstrated higher initial reaction rates and final conver-sions. The contributions of H 2 O 2 , UV, UV/H 2 O 2 , Fe–Y zeolite, and Fe–Y zeolite/H 2 O 2 to the decolorization of reactive yellow were investigated and the results showed that treatment with UV/H 2 O 2 was the most effective process for the color removal. The effect of [H 2 O 2 ] 0 , UV irradiation power, [Fe–Y zeolite], and the reusability of the catalyst were also studied. The catalyst was found to be reusable, but with loss in its catalytic activity. An optimum [H 2 O 2 ] 0 existed in both the PO and CWPO processes. However, this was higher in the latter process. The extent of decolorization increased as the UV irradiation power and [Fe–Y zeolite] increased, but there was a limit in the second case. In addition, the decolorization kinetics of the reactive yellow in both processes were investigated. It was concluded that PO followed an apparent first order kinetic model while CWPO followed the Chu kinetic model. Furthermore, a pseudo-second order rate law, which could be used in continuous flow reactor design equations, was proposed and verified to describe the CWPO rate of reaction. Electronic supplementary material The online version of this article (doi:10.1007/s11144-014-0810-3) contains supplementary material, which is available to authorized users.
... The effectiveness of the treatment is sometimes increased using immense light power and oxidant dosage. Such usage may cause an increase in process cost compared to traditional treatments, namely, coagulation and adsorption (Shu et al., 2004). The UV/H 2 O 2 process has advantages such as strong oxidation ability of dangerous organics, high decomposition efficiency, low reactor volume, no sludge production, and low-toxic intermediates Marechal et al., 1997;Muruganandham & Swaminathan, 2004;Shu et al., 2004). ...
... Such usage may cause an increase in process cost compared to traditional treatments, namely, coagulation and adsorption (Shu et al., 2004). The UV/H 2 O 2 process has advantages such as strong oxidation ability of dangerous organics, high decomposition efficiency, low reactor volume, no sludge production, and low-toxic intermediates Marechal et al., 1997;Muruganandham & Swaminathan, 2004;Shu et al., 2004). ...
Textile industry wastewaters are complex and hazardous because of the variety of dyestuffs and chemicals used in the textile fiber dyeing and finishing processes. Individual wastewater treatment through physical, biological, or chemical methods has its own advantages and disadvantages. Advanced oxidation processes are considered one of the most attractive methods for treating water and wastewater containing toxic and non-biodegradable pollutants. In this study, color and COD removal efficiencies were investigated using advanced oxidation methods Fenton (Fe²⁺/H2O2) and ultraviolet/hydrogen peroxide (UV/H2O2) processes. The optimum values of operational parameters that affect the Fenton and UV/H2O2 treatment of wastewater were determined, such as iron dosage, hydrogen peroxide dosage, process time, and pH. The optimum conditions for the Fenton process were determined as H2O2 and Fe²⁺ concentrations of 1 mg L⁻¹, process time of 30 min, and pH < 3.5. Under these conditions, removal efficiencies of 87.9%, 96.4%, and 98.4% were obtained for COD, color, and turbidity, respectively. In the UV/H2O2 process, optimum conditions were determined as 30 min of processing time, 1 mg L⁻¹ H2O2 concentration, and pH = 3.5 value. Under these conditions, removal efficiencies of 86.7% and 96.5% were obtained for COD and color. The obtained experimental results were also modeled with the nonlinear regression method. When the results were evaluated, it was determined that advanced oxidation methods were very effective in removing color and COD from textile industry wastewater. In addition, based on the finding, the model presented can be used to predict the COD and color removal based on the dependent variables such as Fe²⁺, pH, time, and H202 concentration.
... The amount of UV radiation absorbed by acid orange 8 in solution increases accordingly as the concentration of acid orange 8 increases. As a result, the hydroxyl radicals produced in the reaction system were reduced, and the photolysis rate was decreased (Shu et al., 2004). In addition, an increase in concentration results in more acid orange 8 molecules adsorbed on the surface of NCM, reducing the active site for adsorption of hydroxyl radicals. ...
... In addition, an increase in concentration results in more acid orange 8 molecules adsorbed on the surface of NCM, reducing the active site for adsorption of hydroxyl radicals. The reaction between acid orange 8 and hydroxyl radicals was inhibited, causing a decreased in the photodegradation rate (Shu et al., 2004). ...
Nitrocellulose membranes (NCM) have broad application prospects in the field of organic wastewater treatment. In this research, acid orange 8 was used as the target pollutant, and the effects of factors, such as concentration, light intensity, anions, and cations, on the photodegradation of acid orange 8 were investigated under simulated sunlight by NCM. The results showed that the degradation rate constant of acid orange 8 in the NCM system was 1.94 × 10⁻³ min⁻¹, which was 27.3 times that in the pure water. The photodegradation rate increases with decreasing concentration in the range of 20–120 μmol/L for acid orange 8. The photodegradation rate increased with increasing NCM area. The degradation effect of acid orange 8 increased with the increase of light intensity. Acidic conditions were favorable for the degradation of acid orange 8. The optimal conditions for photodegradation of acid orange 8 were the solution concentration of 20 μmol/L, membrane area of 17.35 cm², light intensity of 481 μmol/(m²s), and pH value of 3.0. The effect of different components in water on the photodegradation of acid orange 8 was different. Ca²⁺, Mg²⁺, and NO3 ⁻ could promote the photodegradation of acid orange 8, while CO3 ²⁻ could inhibit the photodegradation. The effect of degrading acid orange 8 by NCM under light conditions is obvious, which can provide a new method for the removal of acid orange 8 in wastewater.
... Theoretically, it can mineralise any organic compound, reducing it to carbon dioxide and water [7]. It possesses distinct advantages such as high decomposition efficiency, powerful oxidation ability, small requirements for reactor volume and low toxic intermediates production [8]. Therefore, it's become one of the most appropriate AOPs technologies for removing toxic organics from the wastewater because it may occur in nature by itself [9]. ...
... It is possible that azo bonds more easily attacked by hydroxyl radicals. Shu et al. [8] reported that complete Acid Black 1 dye discoloration under the optimum H 2 O 2 concentration of 722.47 mg/L, with a UV dosage of 1,400 W/L in less than 1.2 min. The optimum dosage that leads to the highest dye discoloration was also reported by other researchers [11,13]. ...
In this study, the effect of pH and H2O2 dosage on the treatment of azo dye, Reactive Red 120 (RR120) was evaluated. The experiment was carried out using a cylindrical photochemical reactor, consist of 14 Watt preheated UV lamp. The result shows that UV/H2O2 process can be effectively applied for the treatment of RR120 dye wastewater. The initial pH and H2O2 dosage or concentration played a very important role in the generation of hydroxyl radicals for the dye degradations. Complete decolourization was observed at an initial pH of 3, 5, 7 and 9, except at pH 11. The effect of initial pH on the COD removal clearly confirmed that UV/H2O2 is pH dependent. It seems that a minimal dosage of 0.33 mL/L was sufficient for RR120 discoloration within 120 min reaction. Moreover, the results obtained illustrate that dye mineralization was slower than alterations that took place in chromophore, which led to decolourization. This indicates that the intermediate products formed were more resistant to hydroxyl radical attack than the parent compound during UV/H2O2 process.
... Ghodbane and Hamdaoui (2010) reported that UV-photolysis can change the chemical and biological properties of dyes. However, the decolorization rate increased in the presence of UV/H 2 O 2 compared to UV irradiation alone (Shu et al., 2004). Different physical methods such as membrane filtration processes like ultrafiltration (Zaghbani et al., 2009 ), nanofiltration (Gomes et al., 2005), reverse osmosis (Al-Bastaki, 2004), and adsorption techniques (Mui et al., 2010 ; S ˇ melcerovicétcerovicét al., 2010) are widely used for dye removal. ...
... The initial pH of the solution (pH = 5.2) was measured by using a Fisher scientific accumet Ò model 15 pH meter, according to standard laboratory operating procedures. The concentration of 1 mL of H 2 O 2 , 30% wt.%, was chosen following previous studies (Shu et al., 2004). ...
Performance of a hybrid ultraviolet/hydrogen peroxide (UV/H2O2)–mixed matrix membrane system for an azo dye, acid black 1 [AB1], removal in a water purification process was studied. Different mixed matrix membranes embedded with titanium dioxide (TiO2) nanoparticles, multi-walled carbon nanotubes (MWCNTs), and a mixture of them were fabricated by the phase inversion method. Mixed matrix membranes embedded with MWCNTs resulted in higher pure water flux, and mixed matrix membranes embedded with TiO2 showed lower flux declines in the presence of AB1. However, all the membranes exhibited very low total organic carbon (TOC) rejection and none of the mixed matrix membranes could decolorize the AB1 solution. UV/H2O2 pretreatment of the AB1 solution resulted in enhanced TOC rejection, decolorization, and enhanced antifouling membrane behavior. Combining UV/H2O2 with each type of polysulfone (PSF) mixed matrix membranes (PSF/TiO2, PSF/MWCNT, and PSF/TiO2/MWCNT) resulted in optimal performance in terms of permeation, flux decline, antifouling, rejection, and decolorization. The hybrid process of UV/H2O2-PSF/TiO2/MWCNT mixed matrix membrane resulted in 270 (L/[m2·h]) permeation, 29% flux decline, 90% TOC rejection, 99% decolorization, and 99% flux recovery ratio (FRR%).
... Recent studies have shown that especially azo dyes were very difficult to biodegrade under aerobic conditions because the structure of these organic pollutants cannot be decomposed easily with chemical and biological methods. Although, anaerobic biological treat-* Corresponding author ment processes effectively decolorize the azo dyes, most of the textile industries have traditional activated sludge process for their wastewater treatment [1,2]. ...
... (3) Although •HO 2 promotes radical chain reactions and is an effective oxidant itself, its oxidation potential is much lower than that of •OH [2,20]. Furthermore, at high concentration, H 2 O 2 can also become a scavenger of valence bond holes that would be available for the oxidation of the dye molecule [3,16]. ...
The degradability of an azo dye, Reactive Yellow 81 (RY81), by heterogeneous sonophotocatalytic oxidation process was investigated using simultaneous irradiation of short wave UV-C at 254 nm and power ultrasound at 20 kHz in the presence of a heterogeneous catalyst (ZnO) in this study. The effect of various system parameters i.e. pH, ZnO dose, H2O2 and inital dye concentration was examined on the dye degradation by heterogeneous sonophotocatalytic oxidation process (US/UV/ZnO). The effect of soluble gas (N2, O2 and air) on the dye degradation was assessed to overcome degassing and to enhance the ultrasonic cavity formation. Dye degradation efficiency was evaluated by the abatement in the visible absorbance region. It was found that the decolorization followed non-typical pseudo-first order kinetics, characterized by stabilization of the rate to a non-zero plateau. In two hours oxidation time, almost complete decolorization and partial mineralization were accomplished at 95% and 43.5%, respectively with the rate of 0.0380 min-1.
... doi: 10.1080/19443994.2015.1090915 may often produce secondary pollution by the transfer of the pollutants from one phase to another like adsorption [13]. Consequently, advanced oxidation processes (abbreviated AOPs) are alternative and innovative options for the treatment of the textile wastewater. ...
... The decolorization process may be expressed by the following relation [13]: ...
The azo dyes are considered as one of the highest toxic compounds of water pollution. Decolorization of these compounds has been carried out via photochemical methods (direct UV photolysis and advanced oxidation processes abbreviated as AOPs) since they are highly resistant to conventional treatment. In this study, direct UV photolysis (under 254, 365, 310 nm, and solar), acetone/UV (254 nm and acetone as a sensitizer), H2O2/UV, (Formula presented.)/UV, (Formula presented.)/H2O2/UV and (Formula presented.)/heat (absence of light), have been investigated in lab-scale experiments for decolorization of Alizarin yellow (abbreviated as AY). From the experimental results, it has been found that color removal followed the increasing order: UV photolysis (negligible) < acetone/UV < (Formula presented.)/heat < (Formula presented.)/H2O2/UV < (Formula presented.)/UV < H2O2/UV. This improvement might be attributed strictly to radicals HO(Formula presented.) in the case of H2O2/UV, HO(Formula presented.) and (Formula presented.) in the case of (Formula presented.)/UV, and heat/(Formula presented.) in absence of light. The effects of parameters like concentrations of H2O2, (Formula presented.) and acetone, and temperature have been studied and the optimum operational conditions were found. In another part, the UV–Vis spectral changes of AY during UV/H2O2 and UV/(Formula presented.) treatments, showed that it was easier to destroy the bonding linkage –N=N– and then the long chain C=C (bathochromic system). Decolorization kinetic followed the pseudo-first-order for all systems.
... Over the past few years, photochemical advanced oxidation processes (PAOPs) have prompted extensive research on the degradation of toxic and biorefractory organic pollutants, especially in industrial wastewater [4,6]. Among PAOPs, H 2 O 2 /UV is considered to be the most common simple system used in sewage treatment plants [6][7][8][9]. It is widely known that hydroxyl radicals ( • OH), with a high oxidation potential of 2.8 V, are produced in this process (Eq.1), as well as in other PAOPs, and act as the primary oxidising agent to degrade and mineralize resistant organic compounds [10,11]. ...
Acetone photolysis was investigated and compared with the UV/H2O2 process for the removal of three com-mercial textile dyes, Reactive Red 184 (RR184), Reactive Orange 4 (RO4), and Direct Red 80 (DR80), in aqueous solution at 254 nm, pH = 6.5–6.8, and T = 20 ± 2 ◦ C. The removal efficiency of RR184, RO4, and DR80 by UV/H2O2 was 35 %, 59 %, and 69 %, respectively, whereas UV/acetone exhibited a removal efficiency of 81 %, 99 %,and 88 %, within 30 min ([Dye]0 = 0.1 mM and [acetone]0 = [H2O2]0 = 50 mM). However, as the initial doses ofH2O2 and acetone were increased, the decolorization increased, and the experimental kinetic data always agreedwith the pseudo-first-order reaction model (R2 = 0.94–0.99). Additionally, UV/acetone was consistently shownto be significantly more efficient than UV/H2O2 under all conditions tested. For instance, the rate constant ratioskUV/acetone/kUV/H2O2 are 3.19, 1.95, and 1.67 for RR184, RO4, and DR80, respectively ([Dye]0 = 0.1 mM and[acetone]0 = [H2O2]0 = 50 mM). Scavenging tests using specific probes revealed that •OH and •CH3 radicalswere the main responsible for dyes degradation (greater than80 %) in the UV/H2O2 and UV/acetone processes,respectively. In both systems, the dyes’ reactivity order was found to be RO4 > DR80 > RR184, indicating thatchemical structure is an important factor in evaluating the efficiency of the degradation process. This reactivityorder was supported by the density functional theory (DFT)-based thermodynamic calculations used to explainthe HO•-initiated degradation of the studied azo dyes in the UV/H2O2 process.
(5) (PDF) Kinetics of three commercial textile dyes decomposition by UV/H2O2 and UV/acetone processes: An experimental comparative study and DFT calculations. Available from: https://www.researchgate.net/publication/371117363_Kinetics_of_three_commercial_textile_dyes_decomposition_by_UVH2O2_and_UVacetone_processes_an_experimental_comparative_study_and_DFT_calculations [accessed Jun 03 2023].
... For higher H 2 O 2 concentrations, MG degradation rate decreases leading to 99%, 98%, and 88% decolorization for 5, 10 and 50 mM, respectively, after 1 h. An optimal H 2 O 2 concentration has already been reported in the Fenton oxidation of dyes [42,43]. Indeed, for high concentrations, H 2 O 2 excess acts as a scavenger of hydroxyl radical ( • OH), resulting in less dye degradation. ...
A novel approach allowing the production of electrical energy by an advanced oxidation process is proposed to eliminate organic micropollutants (MPs) in wastewaters. This approach is based on associating the Galvano–Fenton process to the generation of electrical power. In the previous studies describing the Galvano–Fenton (GF) process, iron was directly coupled to a metal of more positive potential to ensure degradation of organic pollutants without any possibility of producing electrical energy. In this new approach, the Galvano–Fenton process is constructed as an electrochemical cell with an external circuit allowing recovering electrons exchanged during the process. In this study, Malachite Green (MG) dye was used as a model of organic pollutant. Simultaneous MG degradation and electrical energy production with the GF method were investigated in batch process. The investigation of various design parameters emphasis that utilization of copper as a low-cost cathode material in the galvanic couple, provides the best treatment and electrical production performances. Moreover, these performances are improved by increasing the surface area of the cathode. The present work reveals that the GF process has a potential to provide an electrical power density of about 200 W m−2. These interesting performances indicate that this novel Energy-from-Waste strategy of the GF process could serve as an ecological solution for wastewater treatment.
... Table 3 The molecular formula is C22H14N6Na2O9S2. It showed absorption maxima at 615 nm in aqueous medium [15][16][17][18][19]. It displayed red shift on addition of all the four surfactants. ...
The interaction of twenty three dyes with four surfactants was studied by UV absorption spectroscopy.
Out of the ninety two combinations tried, different observations were noted. They include bathochromic,
hypsochromic, hyperchromic and hypochromic shifts and change of pH. Shift of the wavelength value
observed ranged from 0 to 89 nm for various combinations and change of pH from a maximum of about 6.85
to a minimum of about 3.80. Five dyes are recommended to be used with all the four surfactants. Another
five dyes were found suitable with three surfactants. Two dyes are found useful for two surfactants. There are
also few single combinations of dye-surfactants which are noted. Overall forty seven combinations were
found satisfactory out of ninety two. On basis of change of pH use of tween 80 with all the twenty three dyes
is preferred. These readymade observations will be of help to the researchers in selecting dye-surfactant
combinations by cutting on the money and time spent for finding them through experiment.
... Furthermore, although higher pH value could provide a higher concentration of hydroxyl ions to react with valence band holes (h þ ) to form more OH⋅, but the negative surface charge of NPs resulting in electrostatic repulsion, which keep away the hydroxyl ion and oxygen molecule from adsorbing on its surface and thus decreases the availability of hydroxyl and superoxide radical for dye degradation (Choudhury et al., 2012). Again, at higher pH deterioration of H 2 O 2 into oxygen and water rather than hydroxyl radical (OH⋅) become favorable resulting in a decrease in dye degradation (Shu et al., 2004). However, it is shown form the figure that, although more than 75% of the dye (at pH 2) was degraded within 6 hr but it took four more hours for its complete degradation, which means that the degradation become slow after 6 hr. ...
Synthesis of iron oxide nanoparticles by the recently developed green approach is extremely promising because of its non-toxicity and environmentally friendly behavior. In this study, nano scaled iron oxide particles (α-Fe2O3) were synthesized from hexahydrate ferric chloride (FeCl3.6H2O) with the addition of papaya (Carica papaya) leaf extract under atmospheric conditions. The synthesis of iron oxide nanoparticles was confirmed by systematic characterization using FTIR, XRD, FESEM, EDX and TGA studies. The removal efficiency of remazol yellow RR dye with the synthesized iron oxide nanoparticles as a photocatalyst was determined along with emphasizing on the parameters of catalyst dosage, initial dye concentration and pH. Increasing the dose of iron oxide nanoparticles enhanced the decolorization of the dyes and a maximum 76.6% dye degradation was occurred at pH 2 after 6 h at a catalyst dose of 0.8 g/L. Unit removal capacity of the photocatalyst was found to be 340 mg/g at dye concentration of 70 ppm and at a catalyst dose of 0.4 g/L. The synthesized nanoparticles showed moderate antibacterial activity against Klebsiella spp., E.Coli, Pseudomonas spp., S.aureus bacterial strains. Although the cytotoxic effect of nanoparticles against Hela, BHK-21 and Vero cell line was found to be toxic at maximum doses but it can be considered for tumor cell damage because it showed excellent activity against the Hela and BHK-21 cell lines.
... The decolorization was slower under the sole UV irradiation, probably because of the light-resistant nature of most synthetic organic dyes [58]. Furthermore, the lack of the strong oxidizing species (such as HO•) in the UV irradiation may decelerate the reactions [59]. On the other hand, the dye removal efficiency was enhanced in the UV-Fe 2+ system due to the generation of H2O2 and HO• (Eqs. ...
... The decolorization was slower under the sole UV irradiation, probably because of the light-resistant nature of most synthetic organic dyes [58]. Furthermore, the lack of the strong oxidizing species (such as HO·) in the UV irradiation may decelerate the reactions [59]. On the other hand, the dye removal efficiency was enhanced in the UV-Fe 2+ system due to the generation of H 2 O 2 and HO·(equations (20)- (22) ...
... Therefore, the removal of PVA will gradually level off. Although HO· can destroy the long molecular chains of PVA, many intermediate products such as acetone and oxalic acid may still exist in the wastewater [55], as they could not be oxidize further with HO·. ...
Polymerization mother liquid (PML) is one of the main sources of wastewater in the chlor-alkali industry. The effective degradation of the PML produced in PVC polymerization using three or five ozone reactors in tandem was designed with a focus on improving the ozonation efficiency. The ozonation efficiency of the tandem reactors for the degradation of PML, along with the effect of ozone concentration, the number of reactors utilized in series, and the reaction time on the chemical oxygen demand (COD) removal were investigated in detail. The results showed that the COD removal increased as the ozone concentration was increased from 10.6 to 60 mg·L−1, achieving 66.4% COD removal at ozone concentration of 80.6 mg·L−1. However, when the ozone concentration was increased from 60 mg·L−1 to 80 mg·L−1, the COD removal only increased very little. The COD decreased with increasing ozone concentration. During the initial degradation period, the degradation rate was the highest at both low and high ozone concentrations. The degradation rate decreased with reaction time. The rate at a low ozone concentration decreased more significantly than at high ozone concentration. Although high ozone concentration is desirable for COD removal and degradation rate, the utilization efficiency of ozone decreased with increasing ozone concentration. The ozone utilization efficiency of the five-reactor device was three times higher than that of three tandem reactors, demonstrating that ozonation utilization efficiency can be improved by increasing the number of tandem reactors. Ozonation in tandem reactors is a promising approach for PML treatment.
... The degradation efficiency was suppressed at higher pH from 7.0 to 11.0 because the repulsive forces operated among the photocatalyst surface and AYR due to net negative charges on both which decreased the adsorption of AYR dye at the surface of the photocatalyst. Moreover, the decomposition of H 2 O 2 into water and oxygen rather than the • OH radical decreased the • OH concentration in solution [77]. The decrease in • OH concentration at higher pH also suppressed the degradation efficiency as the • OH being a strong oxidizing agent tend to oxidize the AYR dye into low molecular weight degradation products. ...
Development of highly robust and solar-light-responsive photocatalysts for the disposal of organic dyes from wastewater is a matter of great significance in order to solve the problems of water pollution. Solar-driven photocatalytic degradation of dyes is considered as a quite efficient, sustainable and cost-effective approach as it involved the inexhaustible and renewable source of energy. In photocatalytic processes, the generation of electron-hole pairs at the surface of the photocatalyst is accomplished by harvesting solar energy. The electron-hole pairs are converted into •OH radicals that are responsible for the degradation of dyes.
Herein, we reported the synthesis of nanosized iron (FeNPs) using the aqueous fruit extract of Actinidia chinensis as a reducing as well as the stabilizing agent. The structure and morphology of synthesized nanoparticles were characterized using various advanced techniques. The TEM micrographs showed that the synthesized FeNPs was predominantly cubic and rod-shaped having the size in the range of 91.78–107 nm. The as-prepared FeNPs were acted as effective photocatalysts and their photocatalytic activity evaluated against alizarin yellow R (AYR) dye. The effect of different reaction conditions such as temperature, pH, time and catalyst loading on photocatalytic degradation of AYR dye was investigated under sunlight irradiation. The FeNPs showed promising photocatalytic activity and up to 93.7% of the dye was degraded in 42 h. The kinetics parameter of the reaction was also evaluated which showed that the photocatalytic degradation of AYR dye followed the pseudo-first-order reaction. In terms of better degradation, the role of FeNPs might be extended for the treatment of different organic dyes from wastewater.
... Consequently, more effectual pre-treatments are required to decolourize the extremely coloured wastewater. Some chemical treatment technologies for dye wastewater have effectively served to remove colour by advanced oxidation processes such as UV/H 2 O 2 , UV/O 3 , or the Fenton reaction (Malik and Saha, 2003;Pirkarami and Olya, 2017;Shu et al., 2005;Shu et al., 2004;Shu and Chang, 2005a, 2005b, 2005c, 2005d. ...
Synthesized iron-nickel (Fe–Ni) bimetallic nanoparticles (NPs) were utilized for the colour removal of C. I. Reactive Blue 21 (RB21) dye. NPs agglomeration was prevented using polyvinyl pyrrolidone (PVP) as a capping agent. The NPs were characterized by nanoparticle size analysis, TEM, XRD and EDX. The operational conditions like pH, NPs concentration and initial dye concentration for decolourization were optimized using mathematical modelling, and its kinetics were studied. Influence of the presence of alkali and salt on dye decolourization was also investigated. Decolourization products were analysed by using FTIR and GCMS analysis. 93.46% of dye decolourization was obtained and a reduction in COD, BOD values was achieved along with minimal sludge generation.
... A very powerful environmental technology family, named advanced oxidation processes (AOPs), with various arrangements including UV irradiation, oxidants (ozone and hydrogen peroxide), Fenton reagents, and photocatalysts (titanium dioxide (TiO 2 ) and zinc oxide (ZnO)), has been developed to degrade all different kinds of pollutants into carbon dioxide, water, and intermediates. The abovementioned AOPs are based on the production of the hydroxyl radical, which is a very strong oxidant and can react with wide range of pollutants non-selectively [13]. Among AOPs, a heterogeneous photocatalytic oxidation process, is very promising in the treatment of environmental pollutants. ...
An advanced oxidation process (AOP) utilizing immobilized zinc oxide (ZnO) photocatalyst was employed to decolorize and mineralize orange G (OG) azo dye in wastewater under solar and visible light irradiation. This AOP employed visible light and ZnO in a so-called Vis/ZnO process. Operating parameters, including ZnO dosage, initial OG concentration, pH, visible-light intensity, catalyst loaded area, and treatment volume were investigated to illustrate their influences on OG degradation and mineralization. From the results, neither visible light alone, nor the ZnO adsorption process could degrade or remove OG from wastewater. However, for the Vis/ZnO process, the higher ZnO dosage and visible light intensity are two major parameters to improve the OG degradation and total organic carbons (TOC) mineralization. The initial pH of 11 was the most effective pH condition on the OG degradation. The first-order rate constant is exponentially decreased from 0.025 to 0.0042 min⁻¹ with the increase of the initial OG concentration and an empirical equation can be derived to estimate the first-order rate constant with a known initial OG concentration. In contrast, the first-order rate constant is linearly increased from 0.0027 to 0.0083 min⁻¹ by increasing the visible light intensity. The results present that the Vis/ZnO process is an effective AOP for the degradation of OG in wastewater.
... Over than 0.7 million tons of organic synthetic dyes are produced and used every year (Jadhav et al., 2007;Han et al., 2009). Decomposition of dye effluents therefore becomes more and more important (Shu et al., 2004;Rauf and Ashraf., 2009). Currently, methods to decompose dyes, such as traditional physical techniques, biological treatment methods and chemical methods, have been developed. ...
A mechano-/photo- bi-catalyst of piezoelectric-ZnO@photoelectric-TiO2 core-shell nanofibers was hydrothermally synthesized for Methyl Orange (10 mg•L-1) decomposition. The mechano-/photo- bi-catalysis in ZnO@TiO2 is superior to mechano- or photo-catalysis in decomposing Methyl Orange, which is mainly attributed to the synergy effect of the piezoelectric-ZnO core’s mechano-catalysis and the thin photoelectric TiO2 shell’s photo-catalysis. The heterostructure of the piezoelectric-ZnO@photoelectric-TiO2 core-shell interface, being helpful to reduce electron-hole pair recombination and to separate the piezoelectrically-/photoelectric ally- induced electrons and holes, may also make a great contribution to the enhanced catalysis performance. The mechano-/photo-bi-catalysis in ZnO@TiO2 core-shell nanofibers possesses the advantages of high efficiency, non-toxicity and tractability and is potential in utilizing mechanical/solar energy to deal with dye wastewater.
... A pseudo-first-order kinetic model is used to describe the decolorization process [37]: ...
The aim of this study is to test the ability of photochemical processes (photolysis, Acetone/UV and H2O2/UV at 254 nm) to eliminate the Methyl Green (MG, cationic structure) and Bromocresol Purple (BCP, anionic structure) in aqueous solution in mono and binary systems. The obtained results show that the rate of decolorization by UV photolysis at 254 nm in single system is weak for BCP (25%) and acceptable for MG (66%). In dark conditions, preliminary experiments show no decolorization of the two dyes in the presence of acetone and in the presence of H2O2 for BCP. However, classical oxidation has been observed for MG in H2O2 for concentrations superior to 5 × 10−4 M. In the presence of light, a real improvement in the decolorization rate of both dyes is obtained using H2O2/UV (acting via (Formula presented.) issued from photolysis of H2O2 at 254 nm) and Acetone/UV (acting via energy transfer from the sensitizer which is Acetone to the dye). In the mixture systems, the Acetone/UV process is more effective than direct UV photolysis and H2O2/UV. In the three photochemical processes used, each dye decreases the removal efficiency of the other. The dyes removal kinetics follows the pseudo-first-order model in Acetone/UV and H2O2/UV systems for both dyes in single and binary systems.
... A pseudo-first-order kinetic model is used to describe the decolorization process [37]: ...
test the ability of photochemical processes (photolysis, Acetone/UV
and H2O2/UV at 254 nm) to eliminate the Methyl Green (MG, cationic structure) and Bromocresol Purple (BCP, anionic structure) in aqueous solution in mono and binary systems.
... These processes have the potential ability to mineralize most of the organic contaminants into carbon dioxide and water. There were reports of successful color removal with final mineralization from azo dye wastewater using advanced oxidation processes (AOPs) such as UV/H 2 O 2 [10][11][12], UV/O 3 [13,14], or the Fenton reaction [15,16]. Additionally, it has been reported that photocatalytic processes such as UV/ZnO system can also be effective in treating dye wastewaters [17][18][19]. ...
To solve the environmental challenge of textile wastewater, a UV/ZnO photocatalytic system was proposed. The objective of this study was to prepare a photocatalytic system by utilizing both cold cathode fluorescent light (CCFL) UV irradiation and steel mesh supported ZnO nanoparticles in a closed reactor for the degradation of azo dye C.I. Orange G (OG). Various operating parameters such as reaction time, preparation temperature, mixing speed, ZnO dosage, UV intensity, pH, initial dye concentration, and service duration were studied. Results presented efficient color and total organic carbon (TOC) removal of the OG azo dye by the designed photocatalytic system. The optimal ZnO dosage for color removal was 60 g m-2. An alkaline pH of 11.0 was sufficient for photocatalytic decolorization and mineralization. The rate of color removal decreased with the increase in the initial dye concentration. However, the rate of color removal increased with the increase in the UV intensity. The steel mesh supported ZnO can be used repeatedly over 10 times without losing the color removal efficiency for 120 min reaction time. Results of Fourier transform infrared (FTIR) and ion chromatography (IC) indicated the breakage of N=N bonds and formation of sulfate, nitrate, and nitrite as the major and minor products. The observation indicated degradation of dye molecules.
In the world’s rapidly expanding economy, textile industries are recognized as a substantial contributor to economic growth, but they are one of the most significant polluting industrial sectors. Dye-contaminated water sources can pose serious public health concerns, including toxicity, mutagenicity, and carcinogenicity among other adverse health effects. Despite a limited understanding of efficacious decolorization methodologies, the pursuit of a sustainable strategy for the treatment of a wide spectrum of dyes remains a formidable challenge. This article conducted an exhaustive review of extant literature pertaining to diverse physical, chemical, biological, and hybrid processes with the aim of ascertaining their efficacy. It also elucidates the advantages and disadvantages, cost considerations, as well as scalability impediments of the treatment methodologies, thereby facilitating the identification of optimal strategies for establishing techno-economically efficient processes in the sustainable handling of these effluents. The hybrid configuration exhibited superior efficiency and was documented to surmount the limitations and constraints inherent to individual techniques. The study also revealed that most of the proven and established dye removal techniques share a common limitation viz., the generation of secondary pollution (i.e., sludge generation, toxic intermediates, etc.) to the ecosystem.
Biological stains are widely used in biomedical research laboratories and also for diagnostic purposes. Dyes of similar structures are used industrially. Some stains can be removed from aqueous solution using the polymeric resin Amberlite XAD‐16. In some cases, the resins Amberlite XAD‐2, XAD‐4, and XAD‐7 can also be used. The decontaminated solution may be disposed of with the nonhazardous aqueous waste and the resin with the hazardous solid waste. Ethidium bromide in H 2 O and buffer solution may be degraded by reaction with sodium nitrite and hypophosphorous acid in an aqueous solution. Many hazardous compounds, such as pesticides and polychlorinated biphenyls, contain halogen atoms. The halogenated compounds are reductively dehalogenated with nickel–aluminum alloy in a dilute base to give the corresponding compound without the halogen. Hypochlorites, in general, and sodium hypochlorite solutions, in particular, tend to deteriorate with time, so they should be periodically checked for the amount of active chlorine they contain.
Water is a precious natural resource and its quality and availability is essential for the survival of living creatures on the earth. However, rapid industrialization is continuously degrading the quality of water due to the incontrolable discharge of large amounts of pollutants into the water bodies. Water pollutants have appeared as threats for the entire biosphere, so their removal has become essential. The different types of water pollutants along with their sources and impact are ellucidated. The fundamental requirements for water purification are appropriate materials with high separation capacity, low cost, porosity, and reusability. Taking this into consideration, nanotechnology provides an opportunity to develop advanced materials for effective water purification by optimizing their properties like hydrophillicity, hydrophobicity, porosity, mechanical strength, and dispersibility. Nanoparticles having high surface area, can contribute a lot in water purification but its agglomeration restricts its use. However, agglomeration can be minimized by converting nanomaterials to nanocomposites. In this chapter, different types of nanocomposites, their preparation and properties are discussed.
Using the pump-probe method, the short-lived induced and long-lived absorption capacity of a crystal violet (CV) dye is studied in various solvents. The solvents selected for this study are water, dimethyl sufoxide (DMSO), and isopropyl and ethyl alcohols. The formation of triplet-triplet states of CV is observed in these solvents under excitation by the 4-th harmonic nanosecond radiation of a Nd:YAG-laser (wavelength 266 nm, average power 25.5 mW, pulse repetition frequency 3 Hz, pulse duration 10 ns, and peak power 10−12 MW/cm2). It is shown that the nonstationary spectra of induced absorption of CV in ethanol contain two bands at 400 and 485 nm. In isopropyl alcohol, both singlet-singlet and long-lived triplet-triplet absorption of CV > 17.2 ns is recorded at room temperature in the region of 400–500 nm.
Three dimeric-triphenylmethane dyes were designed and synthesised for enhancing the rigidity of triphenylmethane moiety and three water-soluble dyes were prepared from them in order to manufacture water-based inks for high-speed ink-jet printing technology. The geometrical characteristics of the synthesised dyes were investigated by carrying out density functional theory calculations. Because of their highly twisted chemical structures and hydrophilic substituents, the synthesised dyes showed efficiently enhanced water solubility when formulated into water-based inks. All the prepared dyes exhibited superior molar extinction coefficients and photo stability than the commercially available acid blue dye. The prepared water-based inks showed the excellent long-term storage stability by optimising the physical and rheological properties of the inks. Moreover, they exhibited good ejection performance and well-ordered pattern arrays when applied to high-speed inkjet printing tests.
Photocatalysis is a versatile phenomenon that finds expressions in many applications in the field of energy and environmental remediation, such as hydrogen production, conversion of carbon dioxide into hydrocarbon fuels, pollutant degradation, pathogen disinfection, biomass conversion, organic synthesis, transformation reactions, etc. The effective utilization of such multifaceted phenomenon demands suitable materials in order to conduct the reactions with enhanced quantum efficiencies. The meticulous understanding of the photocatalytic phenomenon reveals that an ideal photocatalyst, for various reasons, should hold appropriate band edge positions, narrow band gap energy, abundant catalytic sites, enhanced charge transfer characteristics, improved surface adsorption, and excellent stability. Of the various materials available, with their own pros and cons, the metal–organic framework compounds (MOFs) play an important role and provide room to suitably engineer the materials for various photocatalytic applications. The unique structure of MOFs involves inorganic cluster junctions, organic linkers, and guests in the pores. Together, these structures provide more features to MOFs and enable them to integrate both heterogeneous and homogeneous catalytic functions. MOFs can be a promising candidate for versatile and simultaneous photocatalytic applications. In this context, this chapter has been constructed to provide insights into the structural features, synthesis, characterizations, mechanisms, and photocatalytic applications of MOFs in the field of environmental remediation. Finally, it concludes by providing the concepts derived from MOFs for the effective utilization of photocatalytic phenomenon and future prospects of MOFs in the field of photocatalytic science and technology.
The degradation of crystal violet (CV) by the ultraviolet/persulfate (UV/PS) process was investigated in this study. The degradation processes of CV by PS and UV/PS could be appropriately described by second-order degradation kinetics, with kinetics rate constants of 3.57×10⁻³ and 9.58×10⁻³ g⋅mg⁻¹min⁻¹, respectively (UV lamp at 0.346 mW/cm², CV0=10 mg/L, PS = 0.5 mmol/L, pH = 7.0, and temperature = 20 °C). An increases in PS dosage and temperature can both promote the degradation of CV. However, an excessive PS dosage (≥1 mmol/L), too high a temperature (≥25 °C) and too low an initial CV concentration may not be desirable options with respect to the economic cost. In addition, better degradation efficiencies were obtained both under neutral conditions (pH = 7) and the presence of an appropriate amount of metal ions (0.1 mmol/L), such as Cu2+, Zn2+, and Fe2＋. Economical cost comparison revealed that UV/PS has a better economy as compared to UV/H2O2 and UV/TiO2. Free radical quenching experiments revealed that the contributions of ⋅OH and SO⋅4− to the CV removal by UV/PS process were 19.7% and 26%, respectively (UV lamp at 0.346 mW/cm², CV0=10 mg/L, PS = 0.5 mmol/L, pH = 7.0, and temperature = 20 °C). The CV degradation pathways of UV/PS were proposed and can be summarized as follows: demethylation, decarboxylation, deamination and ring-opening reaction following the oxidative cleavage of the double bond of CV, after which small molecules such as H2O, CO32−, NO3− were eventually generated.
The concept of augmenting UV/H2O2 reactor with impinging jet atomization to achieve highly efficient mixing and thin fluid sheet formation capability was investigated. The collision of two jets forming a free-standing thin liquid sheet allowed the establishment of an effective UV/ H2O2 advanced oxidation setting. The response surface methodology (RSM) was applied to model and optimize the photochemical degradation process, which provides three level designs for RSM fitting. Three variables namely, Re (15000–31000), impingement angle (60–120 degree) and H2O2 dosage (1000−3000 mg L⁻¹) were applied in BBD to model and optimize the effects of three key operational parameters. The optimum methyl orange (MO) removal percentage (after 90 min) and the apparent first order rate constant were 93.6% and 2.438 min⁻¹, respectively. The influences of initial dye concentration, UV radiation power, and jet diameter were also investigated as the other main operating parameters. ANOVA analysis indicated that the Re number has the highest impact of the three considered parameters and additional experiments showed that the jet diameter does not have any significant effect on MO degradation. A pseudo-first-order kinetic model was applied for the prediction of contaminant degradation and rate coefficients. The good agreements between the model predictions and experimental results indicate that the proposed model could successfully describe the effectiveness of the augmented UV/H2O2 reactor due to the maximum degradation of the model contaminant.
A facile and useful approach to the removal of possible health and environmental hazardous organic dye Alizarin Yellow R was completed by utilizing copper nanoparticles synthesized from Ficus Carica fruit extract. The polyphenols, proteins, and biomolecules present in the fruit extract were involved in the bio-reduction of Copper nanoparticles. The photocatalytic activity of the Copper nanoparticles was examined by the degradation of toxic organic dyes such as Alizarin Yellow R. These results displayed that photocatalytic capacity of Copper nanoparticles towards Alizarin Yellow R dye was more significant and maximum degradation performance of Alizarin Yellow R was 89.71%, respectively. Different parameters that affect the degradation performance were also studied to determine the ideal conditions for maximum photocatalytic efficiency. The chemical kinetics and possible photocatalytic degradation mechanism were also described. Due to the high degradation performance and stability, it could be possible that copper nanoparticles may have some beneficial effects in organic dyes removing from different industries wastewater in the future.
Background & objectives: Acid black 1 dye is one of the major dangers for human health and environment due to its benzene rings, poisonousness, mutagenicity, carcinogenicity and late degradability. The current research was aimed at determining optimum conditions for removing AB-1 from aqueous solutions through synthesized nZVI nanoparticles using green method. Methods: The structure and morphology of nanocomposites was investigated using FTIR and SEM techniques. The dye density was determined using spectrophotometer in the wavelength of 618nm. The reaction time of the variables, pH of the solution, absorption amount and the dye's density were all evaluated in this study. To determine the isotherm and absorption kinetic, two isotherm models of Langmuir and Freundlich as well as pseudo-first and second order kinetic models were utilized. Results: Having synthesized nZVI nanoparticles through green method, the correctness of the produced nanoparticles' structure was evaluated using physical-chemical analyses. During optimum conditions, the removal efficiency for AB-1 with the density of 50 mg/L, the dose of nanoparticle of 1g/L, the pH equal to 3 and the time of reaction as 60 min, was 96.3%. The results of investigating isotherm and absorption kinetic for AB-1 indicated that absorption process followed Freundlich's isotherm and pseudo-second order kinetics. The maximum absorption capacity of the nanoparticles determined to be 76.34mg/g using Langmuir model. Conclusion: The present research showed that nZVI nanoparticles could be used as an effective absorbent for the removal of AB-1 dye from aqueous solutions.
Weakly coordinating anions (WCAs) offer two succinct advantages when they are introduced as counter anions in a dye. First, replacing strong electrostatic attraction between a cationic dye and its counter anion with the relatively weak electrostatic attraction from a WCA can improve photo-stability of the dye due to charge distribution. Second, the steric hindrance due to the WCAs forms a spatial obstacle between the unstable charged site of the cationic dye and an external element that may degrade the dye. In this study, WCAs are introduced as counter anions in basic dyes to improve their photostability. Basic Yellow 1, Rhodamine 6G, and Rhodamine B were selected as dyes due to their particularly low photostabilities among cationic dyes. Three WCAs were investigated, where two were composed of anions surrounded by fluorine moieties (hexafluorophosphate and bis(trifluoromethane)sulfonimide), and one is surrounded by oxygen moieties (bis(oxalate)borate) Upon dissolving these dyes in three different organic solvents (Chloroform, Methylene Chloride, and Dimethylformamide), the photostabilities of almost all the WCA-substituted dyes were comparatively improved. The photo-stability of each WCA-substituted dye was especially improved in low polarity solvents and the bis(trifluoromethane)sulfonamide-basic dye pairs showed the highest photo-stabilities among four anion-dye pairs including the unsubstituted dyes.
A series of cobalt substituted zinc aluminium chromite nanoparticles were synthesized by simple, cost effective sol–gel auto-combustion method. The synthesized samples were characterized by different sophisticated techniques. The thermal properties of chromite nanoparticles were evaluated using thermogravimetric analysis and differential thermal analysis. X-ray diffraction analysis reveals the formation of single cubic spinel phase with an average crystallite size 25 nm. Morphological studies were carried out by scanning electron microscopy and transmission electron microscopy. The chemical compositions of chromites have been examined by energy dispersive spectroscopy and X-ray photoelectron spectroscopy technique which reveals the purity of the prepared samples. The photocatalytic performance of the synthesized material was studied towards decomposition of aqueous Rhodamine B dye solution. We systematically investigated the effect of various parameters such as irradiation time of UV light, palladium doping and kinetic parameters of photocatalysis with chromites. The catalytic performance of the samples was studied for the two-component coupling reaction of aryl halide and phenyl boronic acid. The effects of solvent, temperature, and palladium loading on the material were also discussed.
Colorless crystals of the coordination polymer (CP) [Cd(EIN)2(SCN)2], 1, and pink crystals of the coordination complex [Co(EIN)4(SCN)2], 2 were prepared by the reaction of metal nitrate salt with ethyl isonicotinate (EIN) and thiocyanate anion as bridged ligand. The structures of 1 and 2 were characterized by elemental analyses, electronic, FT-IR, ¹H-NMR spectroscopy, thermal analysis and X-ray diffraction measurements. The structure of the CP 1 consists of cyclic (CdSCN)n building blocks which exhibit chair conformation creating 1D-chain decorated by the coordinated EIN on both sides. The network structure of 2 contains discrete units of [Co(SCN)2(EIN)4] connected by extensive H-bonds to form 1D-chain. The free ethyl carboxylate groups play the essential role in the formation of the H-bonds extending the structures of 1 and 2 to 3D-network. The catalytic behavior of 1 and 2 was utilized for degradation of acid blue 92 dye (AB-92). The kinetic data indicated that 1 and 2 are effective catalysts for degradation of AB-92 while irradiation enhances significantly the rate of degradation. Disodium salt of terephthalic acid photoluminescence probing technology was carried out to identify the reactive oxygen species. Moreover, the efficiency of recycled the catalysts and the mechanism of degradation of AB-92 dye were also investigated.
In this project, degradation and mineralization of ortho-toluidine (OT) were investigated by UV/H2O2 process in a batch recirculating photo reactor. The full factorial design and response surface methodology were applied for evaluating the effects of experimental variables such as amount of H2O2, initial concentration of pollutant and pH on the removal of the OT and chemical oxygen demand (COD). Analysis of variance (ANOVA) showed a high determination coefficient value (R² = 0.9291, R²adj = 0.9122 for removal of OT and R² = 0.9751, R²adj = 0.9677 for removal of COD) and satisfactory prediction second-order regression model. The results showed a good agreement with the experimental values. The graphical counter plots and response surface were employed to determine the optimum conditions. Based on the optimum results, maximum efficiency for removal of the OT was achieved in initial pH of 10, dosage of H2O2 at 30 mM and initial concentration of the OT at 40 mg l–1. According to the kinetic study, the pseudo-first-order rate constant (k = 4.95 × 10–2 min–1) was obtained for the removal of the OT. The degradation and mineralization of the OT were estimated by HPLC and COD tests, respectively.
对水环境中染料光降解的基础、染料分子的直接光降解和间接光降解进行了综述。重点介绍了染料在Fe(III)体系、腐殖酸体系、NO3- 体系、光催化体系(以TiO2为例)中的光降解。 Photolysis bases of dyes, the direct and indirect photodegradation of dyes in aqueous solution were reviewed. Photodegradation of dyes in solution containing Fe(III), humic acid, NO3- , and catalyst (e.g. TiO2) were summarized.
Sulfate radical-based advanced oxidation processes (SR-AOPs) are powerful technologies to treat various pollutants. Among these SR-AOPs, UV/persulfate (UV/PS) and UV/Oxone were chosen to degrade and mineralize Acid Blue 113 (AB113) wastewater for their strong reactivity. The experimental setup was designed identical to compare two processes. Operating parameters such as oxidant dosage, UV intensity, initial dye concentration, and pH were studied to evaluate their effects on degradation and mineralization of AB113. The results demonstrated powerful degradation of AB113 and mineralization rate for both UV/PS and UV/Oxone processes. However, reaction with either UV irradiation alone or persulfate alone can reach low removal efficiency of AB113. But Oxone oxidation alone can achieve about 95% of AB113 removal efficiency. For both UV/PS and UV/Oxone processes, the higher the oxidant dosage applied, the higher the AB113 and TOC removal efficiencies can be obtained up to the optimal dosage. On the other hand, the AB113 removal efficiency and reaction rate constant decreased with increasing in the initial AB113 concentration. The initial pH showed no significant effect on AB113 removal efficiency. UV/Oxone process was observed to be more sensitive to UV intensity and pH on TOC mineralization. The lower UV power conducted lower TOC mineralization.
The paper describes the production of copper nanoparticles through the reduction of copper chloride (CuCl2·2H2O) by hydrazine in the aqueous cetyle trimethyl ammonium bromide (CTAB) solution. The copper nanoparticles were then supported on chemically activated Montmorillonite clay (MMT). The native and modified clays as well as synthesized Cu-nanoparticle-clay were structurally and texturally characterized by XRD, FTIR, BET, SEM and TEM in addition to the estimation of exchange capacity parameters. BET surface characterization revealed a decrease in surface area of the clay support after the incorporation of Cu nanoparticles. Cu/clay was then utilized as a catalyst for the degradation of aqueous solutions containing methylene blue (MB) over a wide pH range. Diverse kinetics models were employed to examine the degradation process revealing a better fit with pseudo-first-order model. The present study offers a novel modified clay based catalysts for the degradation of methylene blue dye contaminant from wastewater.
Background and Aim: One of the important sources of environmental pollution existing in different industrial wastewater, including loom wastewater are dyes which are harmful for human health and environment. The purpose of this study was to investigate the efficiency of photochemical and sonochemical processes combined with hydrogen peroxide in removal of DB71 from aqueous solution. Material and Methods: This study was an experimental - laboratory study. At first, a reactor was designed and made. Then, optimum pH was determined which was 7 for photochemical and 3 for sonochemical process in constant condition. The effects of initial concentration of hydrogen peroxide, DB71 and contact time were studied at the constant optimum pH. Then data were interpreted and analyzed by use of Excel software and regression coefficient. Result: The results of this study showed that with increased initial concentration of DB71, its removal decreased. But removal efficiency of DB71 increased by increasing contact time and initial concentration of hydrogen peroxide. In addition, kinetic parameters were obtained by application of first-order (Langmuir-Hinshelwood) equations. Conclusion: The results showed that UV/ H2O2 and US/H2O2 processes can be effective in the removal of DB71 from aqueous solutions. Considering dye removal efficiency and availability, photochemical process combined with hydrogen peroxide can be recommended as a fast effective method for removal of dyes from aqueous solutions. Key word: Direct Blue 71, Photochemical process, Sonochemical process, Aqueous solution.
A method development for the determination of an aromatic amine degraded from an azo dye in cloths was carried out. Sodium dithionite was used to cleave the azo bond of Sudan I into its aromatic amines, and the amines, mainly aniline were analyzed using high performance liquid chromatography (HPLC) with UV detection. The efficiency of the reduction process of Sudan I, based on the degree of decolorization of dye, was measured using the spectrophotometer. The optimized values of the reduction process was found effective when 1:1 ratio of 0.30% sodium dithionite to Sudan I (dit/Sud) was used at pH 8. The recovery percentage and relative standard deviation (R.S.D.) of this method was found to be 62.9 - 88.4% and 7.6 - 21.5%, respectively. The proposed method was tested on self-dyed cloth samples with Sudan I. Aniline released from the reduction of Sudan I was detected in the self-dyed cloth samples. The results of this study demonstrate the applicability of sodium dithionite for the reduction of the azo dye in the cloth samples.
In this research, degradation of Ortho-Toluidine (OT) that is considered toxic and carcinogenic in the wastewater of petrochemical industries was investigated by advanced oxidation processes in circulating photoreactor. The effect of some operational parameters such as pH, flow rates of ozone, dosage of the OT, and concentration of hydrogen peroxide pollutant was investigated. The degradation and relative mineralization of the OT were estimated by HPLC and COD tests, respectively. Optimal conditions were determined by using a factor at the time. The maximum reduction in COD was 57 and 70.2% for ozonation (initial pH 9) and UV/O3 (initial pH of 11), respectively. In H2O2/O3 (initial pH 9, initial concentration of H2O2 = 40 mM) and UV/O3/H2O2 processes (initial pH of 10, initial concentration of H2O2 = 20 mM), 65.5 and 82.5% of COD removed, respectively. Reaction time for COD removal of OT solution in all processes was 120 min. Optimal dosage of ozone was 0.5 l/min for all processes based on ozone. Also, after 40 min of reaction, the degradation percent of OT was 100, 90.7, 89.5, and 85.5% for UV/O3/H2O2, UV/O3, O3/H2O2, and O3 processes, respectively. The optimum concentration of the OT was obtained at 100 mg/l in all processes. From the kinetic study, it was clear that the mineralization was slower than the degradation and the best process was the UV/O3/H2O2, since it achieved the highest degradation and mineralization efficiency.
Several problems are involved the treatment plants of textile effluents, mainly the low efficiency of color removal. This paper presents an alternative of post-treatment by UV/H2O 2 process, for color removal in biologically treated textile effluents. The tests were performed in a photochemical reactor and samples were taken at different times to perform analyses. Using 250 mgH2O 2.L -1, 96% removal of color was verified, indicating the dyes degradation. A reduction of 84% of aromatics compounds, 90% of TSS removal, and a further reduction of the organic fraction were observed, demonstrating that the process is effective as a post-treatment of effluents from textile industries.
In this research, titanium dioxide (TiO2) nano-fibers with a well-organized anatase structure were synthesized by a hydrothermal method. Their structural properties were characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), and transmission electron microscope (TEM) analysis, respectively. Subsequently, the TiO2 nano-fibers were optically excited under the ultraviolet (UV) irradiation to decolorize the reactive dye solution. The influences of initial pH, concentrations of reactive dye and TiO2 nano-fibers as well as irradiation time on rate of photocatalytic decolorization were investigated. Based on their excellent photocatalytic performance, a novel method for achieving the synchronized wash-off of reactive-dyed cotton and decolorization of resultant wastewater was developed. It was found that the wash fastness of reactive-dyed cotton after TiO2-based wash-off was equal to that after standard way. The influences of TiO2-based wash-off on the properties of cotton substrates were determined by Fourier transform infrared spectroscopy (FTIR), XRD, and scanning electron microscope (SEM) analysis, respectively, which indicated that this new synchronized method would exert few damages to the cotton substrate.
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The 3D-supramolecular coordination polymer (SCP) (3)∞[ Cu2(CN)3(Me3Pb)(qox)], 1, as the first example of the CuCN SCP containing the (Me3Pb) fragment, was explored to investigate its catalytic and photo-catalytic activities. The structure of 1 contains two chemically identical but crystallographically different [Cu2(CN)3⋅Me3Pb⋅qox]2 units with four Cu(I) sites assuming distorted TP-3 geometry. Two non-linear chains of equal abundance are formed producing corrugated parallel chains which are connected laterally by quinoxaline creating 2D-layers which are arranged parallel in an (AB⋯AB⋯AB)n fashion forming 3D-network. IR, mass, electronic absorption and fluorescence spectra are also investigated. The SCP 1 is diamagnetic and exhibits good catalytic and photo-catalytic activities for the degradation of methylene blue (MB). The reaction is first order with respect to MB dye. The irradiation of the reaction with UV-light enhanced the rate of MB mineralization. The efficiency of recycled the 1 and the mechanism of degradation of MB dye were investigated.
Environmental pollution and in particular contaminated waste due to polycyclic aromatic hydrocarbons (PAHs) are of current environmental concern. In an effort to find solutions, bioremediation techniques have shown promising results in the treatment of contaminated wastes. Composting approaches as a bioremediation technology to treat contaminated waste were first reported in the 1980s. This article provides a comprehensive review of research to date on the use of composting approaches for bioremediation of PAH-contaminated waste. It critically evaluates the existing research in an effort to assess the relative effectiveness of different composting approaches, determine optimal composting operation conditions, and identify the limitations and advantages of using composting approaches relative to other solutions, and recommends areas of further research effort.
The photodegradation of three non hydrolysed reactive azo dyes (Reactive red 120, Reactive black 5, Reactive yellow 84) in aqueous solution was investigated in a laboratory-scale batch photoreactor equipped with an immersed low-pressure mercury lamp. Six different doses of hydrogen peroxide, at constant initial concentration of the substrate (100 mg/l) were used. The pseudo-first order rate constants have been calculated from the experimental kinetic curves, for the three azo dyes. These rate constants have extreme values of the order of 0.1 min−1 at a H2O2 dose of 24.5 mmol/l. The effectiveness of the UV/H2O2 process has been evaluated by the degree mineralization of the total organic carbon (TOC), as a complementary indicator of the treatment efficiencies. Our results confirm the suitability of the UV/H2O2 process as a textile wastewater pre-treatment step, once optimum operating conditions and cost effectiveness of the method are established.
Eighty-seven dyestuffs have been tested in short-term aerobic biodegradation tests. The results confirmed that dyestuffs are most unlikely to show any significant biodegradation in such tests. With many dyestuffs a substantial colour removal was observed which may be attributed to the elimination of the dyes by adsorption. In some cases DOC (Dissolved Organic Carbon) removal did not correlate with colour removal and this is attributed to the presence of non-coloured organic components in the dyestuff.
Most of the published studies on azo dye colour removal involve anaerobic mixed cultures and there is some interest in the knowledge of how dye reduction occurs, if by facultative, strictly anaerobic or both bacterial trophic groups present in classic anaerobic digestors. This paper describes the behaviour of methanogenic and mixed bacteria cultures on the colour removal in batch systems, of a commercial azo dye, C.I. Acid Orange 7, used in paper and textile industries. The aim of this study is to demonstrate, by analysing dye decolourisation, that it occurs with mixed cultures as well as with strictly anaerobic (methanogenic) cultures. Tests were performed with a range of dye concentrations between 60 and 300 mg x l(-1). The influence of dye concentration on the carbon source removal and decolourisation processes was studied. The effect of carbon source concentration on colour removal was also analysed for both cultures. The degradation rates in mixed and methanogenic cultures were compared. The consumption of carbon source was monitored by COD analysis and dye degradation by ultraviolet-visible spectrophotometry and thin layer chromatography.
The wastewater from textile dyeing facilities is difficult to treat satisfactorily because of high compositional variability and high color intensity. To reduce colored effluents discharged into watercourses, the government of Taiwan adopted the Effluent True Color Standard in 1998. The true color discharge limit is 400 American Dye Manufactures Institute (ADMI) units. The adopted analytical method is the ADMI Tristimulus Filter Method (3 wavelength (WL) method), and the 31 WL ADMI method might be also adopted as an alternative for color value measurement. The refractory nature of textile dyes and the introduction of this new regulation present an environmental challenge to the Taiwanese textile industry. The main objectives of this study were to (1) evaluate the efficacy of current wastewater treatment systems for controlling the colored textile wastewater discharges, and (2) evaluate the correlations between 3 and 31 WL ADMI methods. Ten representative textile wastewater treatment facilities employing biological and chemical coagulation treatment technologies were selected to perform a 10-consecutive-day effluent sampling and analysis. Results show that a significant difference between 3 and 31 ADMI methods was observed. These two ADMI methods cannot be substituted for each other, and the discharge standard should be determined based on the selected testing method. Investigation results also suggest that the commonly used wastewater treatment technology (biological + chemical coagulation) fails to effectively remove dye from the colored textile wastewater. Sodium hypochlorite (NaOCl) addition was applied by most facilities as the temporary post-polishment step to comply with the color discharge standard.
Analytical methods for residual hydrogen peroxide and coablt-bicarbonate-H//20//2-method for the determination of H//2O//2 are described.
Chemical oxidation technologies are useful in the oxidative degradation or transformation of a wide range of pollutants for the treatment of drinking water, groundwater, wastewater, and contaminated soils. The application status and potential of three chemical oxidation treatment methods which generate powerful oxidants (hydroxyl radicals): ultraviolet light (uv)/hydrogen peroxide (H[sub 2]O[sub 2]) process, Fenton's reagent treatment, and titanium dioxide (TiO[sub 2])-assisted photocatalytic degradation, are described and discussed. These oxidation methods are known to effectively degrade and, in several cases, mineralize contaminants ranging from inorganic compounds (such as cyanides) to chlorinated aliphatic compounds and complex aromatic compounds in reaction times on the order of a few minutes to a few hours. Of the three oxidation systems discussed, the technology for the uv/H[sub 2]O[sub 2] process is the most advanced, with numerous successful full-scale treatment units already in existence. Applications of both the Fenton's reagent and TiO[sub 2]-assisted photodegradation processes are currently being developed, with the concepts proven in numerous laboratory-scale studies for a wide range of contaminants. However, both of these processes have only been studied at the pilot/field scale to a limited extent. The application of Fenton's reagent as a pretreatment step prior to biological treatment for industrial wastes and contaminated soils appears promising. Improved system configuration and quantum efficiency of photoreactors are likely to improve the economics of TiO[sub 2]-assisted photodegradation for groundwater treatment, especially with the use of solar illumination. 203 refs., 6 figs., 4 tabs.
Treatment of textile dyeing wastewaters by conventional methods have recently proved to be inadequate. Such methods consist of various combinations of biological, physical and chemical methods including coagulation/flocculation and carbon adsorption. The study described herein is an investigation of the treatability of a commonly used azo dye in the textile dyeing and finishing operations, Reactive Black 5, by an advanced oxidation process, to achieve an acceptable degree of destruction of the target pollutant. The research was focused on a UV/H2O2 oxidation process, where the individual effects of H2O2 concentration, initial dye concentration, and alkalinity under neutral pH on the pseudo-first order reaction rate constant were investigated. Relative removal rates of color with respect to chemical oxygen demand and total organic carbon in dye-distilled water mixture were compared; effect of bicarbonate alkalinity at neutral pH was tested. Pseudo-first order reaction rate constants and electrical energy requirements per order of magnitude removal were determined.
Literature regrading azo dye carcinogenicity was examined to establish, if possible, guidelines to predict the human health risks of new azo dyes. Three different mechanisms for azo dye carcinogenicity were identified, all involving metabolic activation to reactive electrophilic intermediates that covalently bind DNA. In the order of decreasing number of published references, these mechanisms are 1. Azo dyes that are toxic only after reduction and cleavage of the azo linkage to give aromatic amines, mostly via intestinal anaerobic bacteria. The aromatic amines are met‐abolically oxidized to reactive electrophilic species that covalently bind DNA.2. Azo dyes with structures containing free aromatic amine groups that can be meta‐bolically oxidized without azo reduction.3. Azo dyes that may be activated via direct oxidation of the azo linkage to highly reactive electrophilic diazonium salts.Each mechanism may be compound specific, thus azo toxicity is probably caused by more than one mechanism. Although it is not possible to predict azo dye carcinogenicity with absolute certainty, it is possible to establish certain guidelines. Because some species of intestinal anaerobic bacteria (and in some cases, hepatic azo reductases) may reduce any azo compound to aromatic amines, those containing aromatic amine subgroups known to be carcinogenic, such as benzidines, must be suspect. Information about human carcinogenicity of other specific aromatic amines is scant, and various short‐term mutagenicity tests may provide some guidance. Other in vitro tests can directly assay new azo dyes. Although it is unlikely that azo dyes can be developed that can be guaranteed not to generate constituent aromatic amines, it may be possible to select aromatic amines that are not toxic.
The decolorization and mineralization of some azo and anthraquinone dyes by photoactivated hydrogen peroxide has been studied. The degradation process seems to occur according to a similar mechanism for all the selected dyes. Decolorization is complete in a relatively short time and follows apparent first order kinetics, whereas mineralization requires longer irradiation times. Initially fluorescent intermediates are generated in all cases by hydroxylation of the studied compounds. A simple kinetic model, describing adequately the process, has been proposed; pH does not influence significantly the process in the range going from 3 to 9.
During the past few years attention has been drawn on chemical techniques that could be used to discolour textile wastewaters. We have studied the photooxidation of several aqueous monoazodyes solutions in the presence of hydrogen peroxide. Irradiation was carried out with a low-pressure mercury lamp. We observed that the reaction is pseudo-first-order with respect to the dye concentration. The effects of hydrogen peroxide and dye dosages, temperature, pH, and chemical structure of the organic matter were also investigated. Results suggest that molecules, hydrazone form of which predominates, are the most sensitive to °OH oxidation. If a labile hydrogen atom is present in the chromophore, it is the primary target of the attack.
Tertiary or pretreatment of dyeing effluents by advanced oxidation processes (AOP) catalyzed by a source of UV light and a powerful oxidant is a promising alternative for the effective removal of color and refractory organics from the effluent. A crucial feature in designing such systems is the optimization of operating conditions (such as UV and oxidant dosages), which yield maximum removal at acceptable costs. The present study describes a modeling approach to keep the oxidant dosage at the most “effective” level to sustain maximum rate of dye removal at the selected experimental conditions. The method of study involved monitoring the rate of dye degradation in a synthetic azo dye solution of nearly constant concentration during irradiation by a medium pressure light source and varying H2O2 dosages, followed by predicting a mathematical relation between the pseudo-first order rate constant and the “effective H2O2 level” in the photoreactor. It was found that this “effective level” can be set by controlling the initial mass ratio of H2O2 to dye, or the light fraction absorbed by hydrogen peroxide within the UV emission spectra of the light source.
The chemical oxidation of eight non-biodegradable azo dyes by ozonation and photooxidation process was studied in a pilot scale photochemical (UV/ozone) reactor. In experiments with ozone bubbling, the degradation of eight azo dyes was found to occur in the absence of UV light. The degradation rate of azo dyes was observed to be first order with respected to both azo dye and ozone concentrations. The pH of the solution decreased while the azo dyes degraded. UV light did not significantly enhance the degradation ability of the ozonation reaction under various conditions. No degradation was observed when the azo dye solution was irradiated by UV light alone. Effects of ozone dosage, and initial concentrations of azo dyes are discussed. Time for removal of 50 % of azo dye and rate constants can be used to determine the decomposition rate of each azo dye by different oxidation processes as a function of various conditions.
Advanced Oxidation Processes (AOPs) have been used as emerging wastewater treatment technologies which can effectively handle various hazardous organics in wastewater and groundwater. The photooxidation of two non-biodegradable azo dyes, acid red 1 and acid yellow 23, were studied in an UV/hydrogen peroxide photochemical reactor with a 5 kW low pressure mercury lamp. It was observed that the decomposition of both azo dyes were pseudo-first order reactions with respect to the azo dye concentrations. Simultaneously, the effects of hydrogen peroxide dosage, pH, initial concentration of the azo dyes and intensity of UV light were also studied. Moreover, the time required for the 50% removal of azo dyes and observed pseudo-first order rate constants were used as parameters to show the efficiency of azo dye treatment.
The objective of this study was to determine the partitioning of water soluble azo dyes in the activated sludge process (ASP). Azo dyes are of concern because some of the dyes, dye precursors, and/or their degradation products such as aromatic amines (which are also dye precursors) have been shown to be, or are suspected to be, carcinogenic. Specific azo dyes were spiked at 1 and 5 mg/L to pilot-scale treatment systems with both liquid and sludge samples collected. Samples were analyzed by high performance liquid chromatography (HPLC) with an ultraviolet-visible detector.Mass balance calculations were made to determine the amount of the dye compound in the waste activated sludge (WAS) and in the activated sludge effluent (ASE). Of the 18 dyes studied, 11 compounds were found to pass through the ASP substantially untreated, 4 were significantly adsorbed onto the WAS, and 3 were apparently biodegraded.
Decolorization studies of simulated wastewater containing vat dye (C.I. vat blue 1: indigo) and azo dyes (Reactive blue H3R and Reactive red HE 7B) have been carried out under anaerobic conditions using mixed bacterial cultures with long hydraulic retention times (HRT). Laboratory scale semicontinuous reactors were operated using simulated cotton dyeing wastewater at ambient temperatures (24–28 °C) by maintaining 10-day HRT for azo dyes and 5-day HRT for indigo dye. Influent dye concentration in wastewater was maintained at 100 mg/l and the reactors were operated for a period of 58 days. The performance of the bioreactors was evaluated by monitoring oxidation–reduction potential (ORP) in the reactor, color and chemical oxygen demand (COD) removal. COD removal of up to 95, 90 and 92% was achieved in a control (no dye), blue and red dye containing reactors. Color removal of 98–99% could be achieved in both the azo dye containing reactors. In the indigo dye containing reactor COD removal of 90% and color removal of up to 95% could be achieved. The results indicated the usefulness of semi-continuous reactors for the degradation of recalcitrant compounds like azo and vat dyes.
A detailed investigation of the photochemical and photocatalytic degradations of the indigoid dye AB74 is presented. H2O2 and C-UV light have negligible effect when they are used on their own. However, joint UV/H2O2 treatment more efficiently decomposes this organic compound. Surprisingly, reaction order depends strongly on the initial dye concentration. On the other hand, NMR analysis reveals that the original dye is first converted into isatinsulfonic acid, then into aliphatic acids. Under band gap excitation of semiconductors, AB74 undergoes irreversible oxidation too. The photodegradation kinetics, on various catalysts, are discussed in term of the Langmuir–Hinshelwood model. NMR, UV–VIS and FTIR spectroscopic techniques provide an insight into the nature of the photoproducts. It was possible then to present a more complete degradation mechanism than supposed until now.
An advanced oxidation treatment, UV/H2O2, was applied to an azo dye, Hispamin Black CA, widely used in the Peruvian textile industry. Rates of color removal and degradation of the dye have been evaluated. A strongly absorbing solution was completely decolorized after 35 min of treatment, and after 60 min an 82% reduction of the total organic carbon (TOC) was obtained. It has been found that the degradation rate increased until an optimum value, beyond which the reagent exerted an inhibitory effect. The degradation rate was also function of pH.
A kinetic model for the decolorization of C.I. Reactive Black 5 by the combination of hydrogen peroxide and UV radiation was developed based on experimental results and known chemical and photochemical reactions. The observed kinetic reaction coefficient was determined and correlated as a function of hydrogen peroxide concentration and UV intensity. The validity of the rate expression was tested experimentally in a parameterization study. The decolorization rate follows pseudo-first order kinetics with respect to dye concentration. The rate increases linearly with UV intensity and nonlinearly with increasing hydrogen peroxide concentration, going from a linear relationship at low H(2)O(2) concentrations to a maximum as hydrogen peroxide concentration continues to increase. The decolorization rate expression derived from the proposed reaction mechanism was reconciled with that used for correlating the experimental data.