Solid-state fermentation: tool for bioremediation of adsorbed textile dyestuff on distillery industry waste-yeast biomass using isolated Bacillus cereus strain EBT1

Bioremediation of textile dyestuffs under solid-state fermentation (SSF) using industrial wastes as substrate pose an economically feasible, promising, and eco-friendly alternative. The purpose of this study was to adsorb Red M5B dye, a sample of dyes mixture and a real textile effluent on distillery industry waste-yeast biomass (DIW-YB) and its further bioremediation using Bacillus cereus EBT1 under SSF. Textile dyestuffs were allowed to adsorb on DIW-YB. DIW-YB adsorbed dyestuffs were decolorized under SSF by using B. cereus. Enzyme analysis was carried out to ensure decolorization of Red M5B. Metabolites after dye degradation were analyzed using UV–Vis spectroscopy, FTIR, HPLC, and GC-MS. DIW-YB showed adsorption of Red M5B, dyes mixture and a textile wastewater sample up to 87, 70, and 81 %, respectively. DIW-YB adsorbed Red M5B was decolorized up to 98 % by B. cereus in 36 h. Whereas B. cereus could effectively reduce American Dye Manufacture Institute value from DIW-YB adsorbed mixture of textile dyes and textile wastewater up to 70 and 100 %, respectively. Induction of extracellular enzymes such as laccase and azoreductase suggests their involvement in dye degradation. Repeated utilization of DIW-YB showed consistent adsorption and ADMI removal from textile wastewater up to seven cycles. HPLC and FTIR analysis confirms the biodegradation of Red M5B. GC-MS analysis revealed the formation of new metabolites. B. cereus has potential to bioremediate adsorbed textile dyestuffs on DIW-YB. B. cereus along with DIW-YB showed enhanced decolorization performance in tray bioreactor which suggests its potential for large-scale treatment procedures.     

Acute toxicity, biochemical and gene expression responses of the earthworm Eisenia fetida exposed to polycyclic musks

Phytoremediation is a novel and promising approach for the treatment of pollutants. This study did explore the potential of Aster amellus Linn. to decolorize a sulfonated azo dye Remazol Red (RR), a mixture of dyes and a textile effluent. Induction in the activities of lignin peroxidase, tyrosinase, veratryl alcohol oxidase and riboflavin reductase was observed during RR decolorization, suggesting their involvement in the metabolism of RR. UV-Visible absorption spectrum, HPLC and FTIR analysis confirmed the degradation of RR. Four metabolites after the degradation of the dye were identified as 2-[(3-diazenylphenyl) sulfonyl] ethanesulfonate, 4-amino-5-hydroxynaphthalene-2,7-disulfonate, naphthalene-2-sulfonate and 3-(1,3,5-triazin-2-ylamino)benzenesulfonate by using GC/MS. Textile effluent and mixture of dyes showed 47% and 62% decrease respectively in American Dye Manufacturers Institute value. BOD of textile effluent and mixture of dyes were reduced by 75% and 48% respectively, COD of industrial effluent and mixture of dyes was reduced by 60% and 75% and TOC was reduced by 54% and 69% respectively after the treatment by A. amellus for 60 h; this indicated that the plant can be used for cleaning textile effluents. Toxicity study revealed the phytotransformation of RR into non-toxic products.     

Bacterial assisted phytoremediation for enhanced degradation of highly sulfonated diazo reactive dye

Purpose

Phytoremediation is the exploitation of plants and their rhizospheric microorganisms for pollutants treatment like textile dyes, which are toxic, carcinogenic and mutagenic from the effluent. The purpose of this work was to explore a naturally found plant and bacterial synergism to achieve an enhanced degradation of Remazol Black B dye (RBB).

Methods

In vitro cultures of Zinnia angustifolia were obtained by seed culture method. Enzymatic analysis of the plant roots and Exiguobacterium aestuarii strain ZaK cells was performed before and after decolorization of RBB. Metabolites of RBB formed after its degradation were analyzed using UV?CVis spectroscopy, high-performance liquid chromatography (HPLC), Fourier transform infrared (FTIR) and gas chromatography?Cmass spectrometry (GC-MS). Phytotoxicity studies were performed.

Results

The consortium ZE was found to be more efficient than individual plant and bacteria. Z. angustifolia roots showed significant induction in the activities of lignin peroxidase, laccase, DCIP reductase and tyrosinase during dye decolorization. E. aestuarii showed significant induction in the activities of veratryl alcohol oxidase, azo reductase and DCIP reductase. Analysis of metabolites revealed differential metabolism of RBB by plant, bacteria and consortium ZE. E. aestuarii and Z. angustifolia led to the formation of 3,6-diamino-4-hydroxynaphthalene-2-sulfonic acid, (ethylsulfonyl)benzene, and 3,4,6-trihydroxynaphthalene-2-sulfonic acid and propane-1-sulfonic acid, respectively, whereas consortium ZE produced 4-hydroxynaphthalene-2-sulfonic acid, naphthalene-2-sulfonic acid and 4-(methylsulfonyl)phenol. The phytotoxicity study revealed the nontoxic nature of the metabolites formed after dye degradation.

Conclusion

Consortium ZE was found to be more efficient and faster in the degradation of RBB when compared to degradation by Z. angustifoila and E. aestuarii individually.     

Phytoremediation of textile effluent and mixture of structurally different dyes by Glandularia pulchella (Sweet) Tronc

Plants of Glandularia pulchella (Sweet) Tronc. performed decolorization of structurally different dyes to varying extent because of induction of different set of enzymes in response to specific dyes. Differential pattern of enzyme induction with respect to time was obtained for lignin peroxidase, veratryl alcohol oxidase, tyrosinase and dichlorophenolindophenol reductase during the decolorization of dye mixture, whose combined action resulted in greater and faster decolorization of dyes. HPLC, FTIR and High Performance Thin Layer Chromatography (HPTLC) analysis confirmed degradation of dyes from textile effluent and mixture. HPTLC demonstrated progressive decolorization of dye mixture along with preferential degradation of the dyes. G. pulchella showed reduction in American Dye Manufacturer's Institute from 405 to 21 and 418 to 22, in case of textile effluent and mixture of dyes respectively. The non-toxic nature of the metabolites of degraded textile dye effluent and mixture of dyes was revealed by phytotoxicity studies.     

Decolorization of palm oil mill effluent using growing cultures of Curvularia clavata

Agricultural wastewater that produces color are of environmental and health concern as colored effluent can produce toxic and carcinogenic by-products. From this study, batch culture optimization using response surface methods indicated that the fungus isolated from the pineapple solid waste, Curvularia clavata was able to decolorize sterile palm oil mill effluent (POME) which is mainly associated with polyphenol and lignin. Results showed successful decolorization of POME up to 80 % (initial ADMI [American Dye Manufacturing Index] of 3,793) with 54 % contributed by biosorption and 46 % by biodegradation after 5 days of treatment. Analysis using HPLC and GC-MS showed the degradation of color causing compound such as 3-methoxyphenyl isothiocynate and the production of new metabolites. Ecotoxicity test indicated that the decolorized effluent is safe for discharge. To determine the longevity of the fungus for a prolonged decolorization period, sequential batch decolorization studies were carried out. The results showed that lignin peroxidase and laccase were the main ligninolytic enzymes involved in the degradation of color. Carboxymethyl cellulase (CMCase) and xylanase activities were also detected suggesting possible roles of the enzymes in promoting growth of the fungus which consequently contributed to improved decolorization of POME. In conclusion, the ability of C. clavata in treating color of POME indicated that C. clavata is of potential use for decolorization and degradation of agricultural wastewater containing polyphenolic compounds.     

Decolorization of mixtures of different reactive textile dyes by the white-rot basidiomycete Phanerochaete sordida and inhibitory effect of polyvinyl alcohol

We tried to decolorize mixtures of four reactive textile dyes, including azo and anthraquinone dyes, by a white-rot basidiomycete Phanerochaete sordida. P. sordida decolorized dye mixtures (200 mg l-1 each) by 90% within 48 h in nitrogen-limited glucose-ammonium media. Decolorization of dye mixtures needed Mn2+ and Tween 80 in the media. Manganese peroxidase (MnP) played a major role in dye decolorization by P. sordida. Decolorization of dye mixtures by P. sordida was partially inhibited by polyvinyl alcohol (PVA) that wastewaters from textile industries often contain. This was caused by an inhibitory effect of PVA on the decolorization of Reactive Red 120 (RR120) with MnP reaction system. Second addition of Tween 80 to the reaction mixtures in the presence of PVA improved the decolorization of RR120. These results suggest that PVA could interfere with lipid peroxidation or subsequent attack to the dye.     

Alteration of in vitro and acute in vivo toxicity of textile dyeing wastewater after chemical and biological remediation

Introduction

Textile industry is one of the most common and essential sectors in Tunisia. However, the treatment of textile effluents becomes a university because of their toxic impacts on waters, soils, flora, and fauna.

Materials and methods

The aim of this work was to evaluate the ability of Pseudomonas putida mt-2 to decolorize a textile wastewater and to compare the biologic decolorization process to the chemical one currently used by the textile industry.

Results

P. putida exhibited a high decolorizing capacity of the studied effluent, compared to the coagulation?Cflocculation method with decolorization percentage of 86% and 34.5%, respectively. Genotoxicity of the studied effluent, before and after decolorization by P. putida mt-2, was evaluated in vitro, using the SOS chromotest, and in vivo, in mouse bone marrow, by assessing the percentage of cells bearing different chromosome aberrations compared to not treated mice. In addition, textile effluent statistically significant influenced acetylcholinesterase and butyrylcholinesterase activities and lipid peroxidation (p?P. putida is a promising and improved alternative to treating industrial scale effluent compared to current chemical decolorization procedures used by the Tunisian textile industry.     

Phytoremediation of a sulphonated azo dye Green HE4B by <Emphasis Type="Italic">Glandularia pulchella</Emphasis> (Sweet) Tronc. (Moss Verbena)

Purpose  

The dyes and dye stuffs present in effluents released from textile dyeing industries are potentially mutagenic and carcinogenic. Phytoremediation technology can be used for remediating sites contaminated with such textile dyeing effluents. The purpose of the work was to explore the potential of Glandularia pulchella (Sweet) Tronc. to decolorize different textile dyes, textile dyeing effluent, and synthetic mixture of dyes.     

Potential of immobilized bitter gourd (Momordica charantia) peroxidases in the decolorization and removal of textile dyes from polluted wastewater and dyeing effluent

Immobilized peroxidases from Momordica charantia were highly effective in decolorizing reactive textile dyes compared to its soluble counterpart. Dye solutions, 50-200 mg/l, were treated with soluble and immobilized bitter gourd peroxidases (specific activity of 99.0 EU per mg protein). The decolorization of dyes with soluble and immobilized enzyme was maximum in the range of pH 3.0-4.0. The effect of different temperatures on the dye decolorization was monitored and it was observed that all the dyes were maximally decolorized at 40 degrees C. In order to examine the operational stability of the immobilized preparation, the enzyme was repeatedly exploited for the decolorization of the dyes from fresh batch of dye solutions. Even after 10 cycles in each case the immobilized preparation retained nearly 50% of the initial enzyme activity. The immobilized enzyme exhibited more than 90% of the original activity while the soluble enzyme lost 33% of the initial activity when stored for 40 d at room temperature. Mixtures of three, four and eight dyes were prepared and treated with soluble and immobilized bitter gourd peroxidase. Each mixture was decolorized by more than 80% when treated with immobilized enzyme. Dyeing effluent collected from local dyers was treated with both types of enzyme preparations. Immobilized enzyme was capable of removing remarkably high concentration of color from the effluent. TOC content of soluble and immobilized enzyme treated individual dyes, mixture of dyes and dyeing effluent was determined and it was observed that higher TOC was removed after treatment with immobilized enzyme.     

Decolorization of dyes and textile wastewater by potassium permanganate

Decolorization of 10 types of dye solutions by potassium permanganate was studied. Effects of reaction conditions on the decolorization efficiency were examined in batch experiments. The pH value had a significant effect on the decolorization efficiency. When pH value <1.5, the decolorization efficiency was very high. When pH value >4.0, the dye solutions were almost not decolorized. Concentration of potassium permanganate and temperature also showed significant effects on the decolorization efficiency. The decolorization rate of dye solutions by potassium permanganate was rapid, and most of dye solutions can be decolorized effectively. The results of total organic carbon indicated that dye solutions were degraded incompletely by potassium permanganate. The results of treatment of textile wastewater by potassium permanganate indicated that the oxidation with potassium permanganate might be used as a pre-treatment process before biological treatment.     

Decolorization and detoxification of two textile industry effluents by the laccase/1-hydroxybenzotriazole system

The aim of this work was to determine the optimal conditions for the decolorization and the detoxification of two effluents from a textile industry—effluent A (the reactive dye bath Bezactive) and effluent B (the direct dye bath Tubantin)—using a laccase mediator system. Response surface methodology (RSM) was applied to optimize textile effluents decolorization. A Box–Behnken design using RSM with the four variables pH, effluent concentration, 1-hydroxybenzotriazole (HBT) concentration, and enzyme (laccase) concentration was used to determine correlations between the effects of these variables on the decolorization of the two effluents. The optimum conditions for pH and concentrations of HBT, effluent and laccase were 5, 1 mM, 50 % and 0.6 U/ml, respectively, for maximum decolorization of effluent A (68 %). For effluent B, optima were 4, 1 mM, 75 %, and 0.6 U/ml, respectively, for maximum decolorization of approximately 88 %. Both effluents were treated at 30 °C for 20 h. A quadratic model was obtained for each decolorization through this design. The experimental and predicted values were in good agreement and both models were highly significant. In addition, the toxicity of the two effluents was determined before and after laccase treatment using Saccharomyces cerevisiae, Bacillus cereus, and germination of tomato seeds.     

沼泽红假单胞菌W12对活性黑5的厌氧脱色和降解作用

从处理印染废水的厌氧移动床生物膜反应器（moving bed biofilm reactor, MBBR）中分离到一株具有高效脱色活性的沼泽红假单胞菌W12。经实验确定W12对活性黑5（reactive black 5，RB5）脱色的适宜条件为：pH＜10；有光照；谷氨酸盐或乳酸盐作为碳源，当乳酸钠为碳源时浓度应＞500 mg/L；盐度不超过5％；RB5浓度不大于700 mg/L。紫外可见光谱扫描结果表明，RB5的脱色和降解过程生成芳香胺类化合物，这些中间产物可进一步降解。此外发现，RB5诱导生成的胞外代谢物能提高W12的脱色活性。     

Decolorization does not always mean detoxification: case study of a newly isolated Pseudomonas peli for decolorization of textile wastewater

The textile industry is a favor to the Tunisian economy by offering several job positions. However, it’s not environmentally friendly. In fact, textile industries discharge high volumes of wastewater which contain several toxic pollutants such as dyes, fixator, and whiteness. In our study, Pseudomonas peli, isolated and characterized from Oued Hamdoun (center of Tunisia), was found able to decolorize textile effluent about 81 % after 24 h shaking incubation. On the other hand, the in vitro antiproliferative effects of the untreated and treated effluent was evaluated by their potential cytotoxic activity using the MTT colorimetric method against three human cancer cell lines (A549, lung cell carcinoma; HT29, colon adenocarcinoma; and MCF7, breast adenocarcinoma). Results showed that intact textile effluent and its content azo dyes didn’t inhibit the proliferation of all tested cell lines. However, the cytotoxic effect was remarkable when we tested effluent obtained after treatment by P. peli in a dose-dependent manner. This activity was attributed to the presence, in our treated effluent, of some azo products of dyes which are responsible for inhibition of human cell lines proliferation. Thus, the use of this strain for testing on the industrial scale seems impossible and disadvantageous.     

Biosorption and biodegradation of Acid Orange 7 by Enterococcus faecalis strain ZL: optimization by response surface methodological approach

Reactive dyes account for one of the major sources of dye wastes in textile effluent. In this study, decolorization of the monoazo dye, Acid Orange 7 (AO7) by the Enterococcus faecalis strain ZL that isolated from a palm oil mill effluent treatment plant has been investigated. Decolorization efficiency of azo dye is greatly affected by the types of nutrients and the size of inoculum used. In this work, one-factor-at-a-time (method and response surface methodology (RSM) was applied to optimize these operational factors and also to study the combined interaction between them. Analysis of AO7 decolorization was done using Fourier transform infrared (FTIR) spectroscopy, desorption study, UV–Vis spectral analysis, field emission scanning electron microscopy (FESEM), and high performance liquid chromatography (HPLC). The optimum condition via RSM for the color removal of AO7 was found to be as follows: yeast extract, 0.1 %?w/v, glycerol concentration of 0.1 %?v/v, and inoculum density of 2.5 %?v/v at initial dye concentration of 100 mg/L at 37 °C. Decolorization efficiency of 98 % was achieved in only 5 h. The kinetic of AO7 decolorization was found to be first order with respect to dye concentration with a k value of 0.87/h. FTIR, desorption study, UV–Vis spectral analysis, FESEM, and HPLC findings indicated that the decolorization of AO7 was mainly due to the biosorption as well as biodegradation of the bacterial cells. In addition, HPLC analyses also showed the formation of sulfanilic acid as a possible degradation product of AO7 under facultative anaerobic condition. This study explored the ability of E. faecalis strain ZL in decolorizing AO7 by biosorption as well as biodegradation process.     

Two stage biological treatment of a diazo reactive textile dye and the fate of the dye metabolites

A two stage anaerobic/aerobic bacterial process was used to decolorize and partially mineralize a reactive vinyl sulfone diazo dye C.I. Reactive Black 5 (RB5) in a synthetic wastewater. Since the anchor group of reactive dyes reacts during the dyeing process, the effect the degree of hydrolysis of the vinyl sulfone dye had on decolorization, mineralization and toxicity in each stage was investigated. An overall color removal of approximately 65% was found for both the fully and partially hydrolyzed dye. Partial mineralization of the fully hydrolyzed RB5 was achieved in the two stage rotating disc reactors. While the anchor group metabolite p-aminobenzene-2-hydroxyethylsulfonic acid (p-ABHES) was mineralized, an oxidized form of the center metabolite (1,2-ketimino-7-amino-8-hydroxynaphthalene-3,6-disulfonic acid) remained in the aerobic stage effluent, causing the effluent to be colored although no RB5 was present. Partially hydrolyzed dye in the influent with vinyl forms of the anchor group caused cessation of biogas production and a reduction in decolorization efficiency in the anaerobic stage. No evidence for mineralization of the partially hydrolyzed dye or its metabolites was found. A method for evaluating dye mineralization using lumped parameters is presented.     

Biodegradation of C.I. Acid Red 1 by indigenous bacteria <Emphasis Type="Italic">Stenotrophomonas</Emphasis> sp. BHUSSp X2 isolated from dye contaminated soil

A significant proportion of xenobiotic recalcitrant azo dyes are being released in environment during carpet dyeing. The bacterial strain Stenotrophomonas sp. BHUSSp X2 was isolated from dye contaminated soil of carpet industry, Bhadohi, India. The isolated bacterial strain was identified morphologically, biochemically, and on the basis of 16S rRNA gene sequence. The isolate decolorized 97 % of C.I. Acid Red 1 (Acid RED G) at the concentration of 200 mg/l within 6 h under optimum static conditions (temperature ?35 °C, pH 8, and initial cell concentration 7?×?10⁷ cell/ml). Drastic reduction in dye degradation rate was observed beyond initial dye concentration from 500 mg/l (90 %), and it reaches to 25 % at 1000 mg/l under same set of conditions. The analysis related to decolorization and degradation was done using UV-Vis spectrophotometer, HPLC, and FTIR, whereas the GC-MS technique was utilized for the identification of degradation products. Phytotoxicity analysis revealed that degradation products are less toxic as compared to the original dye.     

Batch and continuous biodegradation of Amaranth in plain distilled water by P. aeruginosa BCH and toxicological scrutiny using oxidative stress studies

Bacterium Pseudomonas aeruginosa BCH was able to degrade naphthylaminesulfonic azo dye Amaranth in plain distilled water within 6 h at 50 mg?l^?1 dye concentration. Studies were carried out to find the optimum physical conditions and which came out to be pH?7 and temperature 30 °C. Amaranth could also be decolorized at concentration 500 mg?l^?1. Presence of Zn and Hg ions could strongly slow down the decolorization process, whereas decolorization progressed rapidly in presence of Mn. Decolorization rate was increased with increasing cell mass. Induction in intracellular and extracellular activities of tyrosinase and NADH-DCIP reductase along with intracellular laccase and veratryl alcohol oxidase indicated their co-ordinate action during dye biodegradation. Up-flow bioreactor studies with alginate immobilized cells proved the capability of strain to degrade Amaranth in continuous process at 20 ml?h^?1 flow rate. Various analytical studies viz.—HPLC, HPTLC, and FTIR gave the confirmation that decolorization was due to biodegradation. From GC-MS analysis, various metabolites were detected, and possible degradation pathway was predicted. Toxicity studies carried out with Allium cepa L. through the assessment of various antioxidant enzymes viz. sulphur oxide dismutase, guaiacol peroxidase, and catalase along with estimation of lipid peroxidation and protein oxidation levels conclusively demonstrated that oxidative stress was generated by Amaranth.     

Microbial decolorization of synthetic dyes and reactive dyes of industrial effluents by using a novel fungus Aspergillus proliferans

A decolorizing fungal strain was isolated and identified by the morphology and genotypic characterization as Aspergillus proliferans. The effect of A. proliferans on decolorization of synthetic dyes (70 mg ml(-1)) and colored effluent was evaluated in liquid culture medium. A. proliferans expressed their effective decolorization activity in effectual decolorization of synthetic dyes and industrial effluent. Synthetic dyes were decolorized by 76 to 89% within 6 days of treatment and 73.5% of color was removed in industrial effluent within 8 days. The addition of optimum carbon and nitrogen sources were effectively stimulated the decolorization activity. The high concentration of glucose repressed the decolorization activity and supplementation of yeast extract has significantly enhanced the effluent decolorization at p < 0.05. Laccase enzyme was isolated from liquid state fermentation, which showed significant enzyme activity (10,200 Uml(-1)) at p < 0.005. The crude enzyme decolorizes the dyes aniline blue and congo red in 14 hours (40.9 to 70%) and the effluent in 14 hours (88.6%). Moreover, the culture free supernatant without the fungal biomass has also effectively decolorized the effluent and synthetic dyes. The fungi Aspergillus proliferans was used not only for decolorization but also for better bioremediation of industrial effluent.     

A novel thermotolerant Pediococcus acidilactici B-25 strain for color, COD, and BOD reduction of distillery effluent for end use applications

The present study was aimed to characterize physico-chemical and microbial population of distillery effluent and isolate a novel thermotolerant bacterium for color, COD, and BOD reduction of spentwash. The level of alkalinity, TSS, DO, COD, BOD, TN, ammonical nitrogen, nitrate nitrogen, phosphorous, potassium, chloride, and calcium of spentwash (SW), bioreactor effluent (BE), and secondary treated effluent (STE) were well above the permissible limits. The level of color, TS, and TDS were under the permissible limits for STE but not for SW and BE. The microbial population was higher in BE. The results revealed that effluent was highly polluted and require suitable treatment before discharge. A novel thermotolerant bacterium, identified as Pediococcus acidilactici, was isolated which exhibited maximum 79 % decolorization, 85 % COD, and 94 % BOD reduction at 45 °C using 0.1 %, glucose; 0.1 %, peptone; 0.05 %, MgSO4; 0.05 %, K₂HPO₄; pH 6.0 within 24 h under static condition. The ability of this strain to decolorize melanoidin at minimum carbon and nitrogen supplementation warrants its possible application for effluent treatment at industrial level. In addition, it is first instance when melanoidin decolorization was reported by P. acidilactici. This study could be an approach towards control of environmental pollution and health hazards of people in and around the effluent distillery unit.     

Influence of operational key parameters on the photocatalytic decolorization of Rhodamine B dye using Fe2+/H2O2/Nb2O5/UV system

The present research deals with the development of a new heterogeneous photocatalysis and Fenton hybrid system for the removal of color from textile dyeing wastewater as Rhodamine B (RhB) solutions by using Fe²⁺/H₂O₂/Nb₂O₅ as a photocatalytic system. The application of this photocatalytic system for the decolorization of dye contaminants is not reported in the literature yet. Different parameters like dye concentration, Nb₂O₅/Fe²⁺ catalyst amount, pH, and H₂O₂ concentration have been studied. The optimum conditions for the decolorization of the dye were initial concentration of 10 mg L^?1 of dye, pH 4, and Nb₂O₅/Fe²⁺ catalyst concentration of 0.5 g L^?1/50 mg L^?1. The optimum value of H₂O₂ concentration for the conditions used in this study was 700 mg L^?1. Moreover, the efficiency of the Nb₂O₅/photo-Fenton hybrid process in comparison to photo-Fenton alone and a dark Fenton process as a control experiment to decolorize the RhB solution has been investigated. The combination of photo-Fenton and Nb₂O₅ catalysts has been proved to be the most effective for the treatment of such type of wastewaters. The results revealed that the RhB dye was decolorized in a higher percent (78 %) by the Nb₂O₅/photo-Fenton hybrid process (Fe²⁺/H₂O₂/Nb₂O₅/UV) than by the photo-Fenton process alone (37 %) and dark Fenton process (14 %) after 120 min of treatment. Moreover, the Nb₂O₅ catalyst as a heterogeneous part of the photocatalytic system was demonstrated to have good stability and reusability.