Biological treatment of dye wastewaters using an anaerobic-oxic system

Investigation of selected physico-chemical quality parameters in industrial wastewater by electrocoagulation process, Ethiopia

Nowadays, there are more than fourteen major state and private owned textile industries and garment factories in Ethiopia. However, these textile effluents are directly discharged without treatment to the surrounding environment, as a result, the pollutants bring serious problem to the surrounding community including health such as skin diseases, asthma, abortion, carcinogenic effect, biodiversity loss and mutagenic effect on the. The main objective of this study is characterization and treatment of the textile effluent using aluminum electrodes in the electrocoagulation process. EC experimental setups were designed and different parameters were optimized. Electrocoagulation treatment process eliminates physicochemical quality indicators such as pH, electrical conductivity (EC); turbidity, biological oxygen demand (BOD), ammonia; nitrate, nitrite, total nitrogen (TN) and phosphate were determined using standard procedures. From the result, the maximum removal efficiency of phosphate, ammonia, TN, electrical conductivity, turbidity and BOD were obtained 97, 87, 88, 89, 99 and 66%, respectively. Analyses of the electrochemically generated sludge by X-ray Diffraction, Scanning Electron Microscope (SEM), and Fourier Transform Infrared Spectroscopy (FTIR) revealed that the expected crystalline aluminum oxides (bayerite (Al(OH)3 diaspore (AlO(OH)) were found in the sludge. The amorphous phase was also found in the floc. Therefore, a treatment technology was good and encourages the community to apply the technique for the treatment of textile effluent before discharging into the environment.

Gold-selenide quantum dots supported onto cesium ferrite nanocomposites for the efficient degradation of rhodamine B

In this work, different weight percentage of gold-selenide quantum dots (AuSe QDs) (1.0, 2.5, 5.0 and 7.0 wt.%) were successfully synthesized and decorated on cesium ferrite nanocomposite (Cs2Fe2O4 NC). The as-prepared pure AuSe QDs, pure Cs2Fe2O4 NC, and x wt.% AuSe QDs/Cs2Fe2O4 NC photocatalysts were investigated using different characterization techniques such as nitrogen adsorption desorption isotherms (BET), X-ray diffraction patterns (XRD), transmission electron microscopy (TEM), and UV-vis absorption spectroscopy. The results show that AuSe QDs were uniformly distributed on Cs2Fe2O4NCs surface as spherical dots with an average size of 1.0-8.0 nm. While the Cs2Fe2O4 NCs possess an average size between 10 to 35 nm. The photocatalytic performance of x wt. % AuSe QDs/Cs2Fe2O4NCs were measured through the photodegradation of rhodamine B (RhB) dye as a model water pollutant, under a150 W-Mercury lamp with a filter (JB400) as a simulated source of visible light. The results revealed that the % degradation of RhB increased from 50.0 %, 59.1 %, 76.4 %, and to 99.15 % within 150 min for the pure Cs2Fe2O4, 1.0, 2.5 and 5.0 wt.% AuSe QDs/Cs2Fe2O4 NC photocatalysts, respectively. The 5.0 wt.% AuSe/Cs2Fe2O4 NC sample showed highest photocatalytic activity. The effect of recycling also studied. High photocatalytic performance and superior stability confirmed that the prepared nanocomposites act as good photocatalysts.

Facile and Green Synthesis of Silver Quantum Dots Immobilized onto a Polymeric CTS-PEO Blend for the Photocatalytic Degradation of p-Nitrophenol

Immobilization of inorganic metal quantum dots (especially, noble transition metals) onto organic polymers to synthesize nanometal-polymer composites (NMPCs) has attracted considerable attention because of their advanced optical, electrical, catalytic/photocatalytic, and biological properties. Herein, novel, highly efficient, stable, and visible light-active NMPC photocatalysts consisting of silver quantum dots (Ag QDs) immobilized onto polymeric chitosan-polyethylene oxide (CTS-PEO) blend sheets have been successfully prepared by an in situ self-assembly facile casting method as a facile and green approach. The CTS-PEO blend polymer acts as a reducing and a stabilizing agent for Ag QDs which does not generate any environmental chemical pollutant. The prepared x wt % Ag QDs/CTS-PEO composites were fully characterized through X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy (TEM), thermogravimetric analysis, and UV/visible spectroscopy. The characterization results indicated the successful synthesis of the Ag QDs/CTS-PEO composites by the interactions and complexation between x wt % Ag QDs and CTS-PEO blend sheets. TEM images revealed small granules randomly distributed onto the CTS-PEO blend sheets, indicating the immobilization of Ag QDs onto CTS-PEO composites. The presence of a surface plasmon resonance (SPR) band and the shifting of the absorption edge toward higher wavelengths in the UV/vis spectra indicated the formation of x wt % Ag QDs/CTS-PEO composites. The Ag QDs in the polymeric blend matrix led to remarkable enhancement in the optical, thermal, electrical, and photocatalytic properties of x wt % Ag QDs/CTS-PEO composites. The photocatalytic efficiency of the prepared composites was evaluated by the photodegradation of p-nitrophenol (PNP) under simulated sunlight. The maximum photocatalytic degradation reached 91.1% efficiency within 3 h for the 12.0 wt % Ag QDs/CTS-PEO photocatalyst. Generally, the Ag QDs immobilized onto CTS-PEO blend composites significantly enhance the SPR effect and the synergistic effect and reduce the band gap, leading to a high photocatalytic activity.

Biodegradation of acid red 3BN dye in sequential batch reactor: parameters and kinetics studies

Textile and dye industries generate wastewater which is considered as highly polluted and carcinogenic. Due to this, treatment of wastewater is required earlier to discharge or recycle. In the present studies, treatment of dye bearing water (DBW) has been explored. The treatment was performed using activated sludge (mixed culture) for aerobic process in sequential batch reactor (SBR). The fill volume (V F) and fill time (t F) variation in the treatment of DBW was taken place. The initial value of dye concentration, chemical oxygen demand (COD), sludge, and hydraulic retention time (HRT) were found to play important role in the treatment. At optimum condition (HRT = 2.5 d), the 86.84% COD reduction of 190 mg/L COD, and 92.33% dye reduction of 339 mg/L dye were achieved. These values are equal to overall 94.85% dye reduction of 500 mg/L, and 93.15% COD reduction of 380 mg/L. As a result, 500 mg/L dye was reduced to 26 mg/L, and 380 mg/L COD was reduced to 25 mg/L. The biodegradation fitted to Monod kinetics, for which kinetics parameter values of specific growth rate constant of biomass µ = 0.0047 h−1, yield coefficient (Y) = 1.059, and substrate utilization rate (q) = 0.0044 h−1 were evaluated at HRT = 2.5 d. The results show, this process can be applied to treat Acid Red 3BN Dye Water (AR3BNDW).

Impact of solid particles on cavitation behaviors and laser-induced degradation in aqueous suspension

A method for degrading organic pollutants in suspension by applying laser-induced cavitation is presented. Cavitation bubbles are produced remotely by laser beams, achieving a purpose of non-contact degradation. In this work, laser-induced bubble dynamics in SiO₂ sand suspension were studied by high-speed imaging. Pulsating characteristics of cavitaiton bubbles in the infinite domain and near a solid boundary were investigated among various laser energies and sand concentrations. Furthermore, the extent of degradation after processing in suspension and the mechanism were analyzed. Results indicate that solid particles in the liquid medium reduce the extent of degradation. However, the extent of degradation may rebound at a proper sand concentration. In addition, compared to several small bubbles in a bubble string (in the infinite domain), a single larger bubble (near a solid boundary) has a much higher degradation ability.

Photocatalytic and Biological Oxidation Treatment of Real Textile Wastewater

With rapidly growing urbanization and industrialization in developing countries, a large volume of wastewater is produced from industries that contain chemicals generating high environmental risks, which could affect health and socio-economic activities if not treated properly. In this study, the discoloration of wastewater containing azo dyes by chemical oxidation process combined with a biological treatment was evaluated and applied on real textile wastewater generated from one Ethiopian industrial site. The use of TiO2 as a photocatalyst and the effect of the addition of H2O2 on color removal were investigated. Photocatalysis was followed by aerobic biological treatment and their combination resulted in 93.3 and 90.4% removal of color and chemical oxygen demand (COD), respectively. These results revealed that the combination of photocatalytic and biological treatment approach shows a promising potential for the removal of color from real textile wastewater.

Treatment of grey water (GW) with high linear alkylbenzene sulfonates (LAS) content and carbon/nitrogen (C/N) ratio in an oxygen-based membrane biofilm reactor (O2-MBfR)

Grey water (GW) containing high levels of linear alkylbenzene sulfonates (LAS) can be a threat to the human health and organisms in the environment if not treated properly. Although aerobic treatment may achieve high GW treatment efficacy, conventional aeration can lead to serious foaming. Here, we firstly and systematically evaluated an oxygen-based membrane biofilm reactor (O₂-MBfR) for its capacity to simultaneous remove organics and nitrogen from greywater with high LAS levels and carbon/nitrogen (C/N) ratios. After a five-day startup period, multifarious microorganisms formed multifunctional biofilms and the MBfR achieved high removal rates of chemical oxygen demand (COD), LAS, and total nitrogen (TN) of 88.4%, 95.6%, and 80%, respectively, with a hydraulic retention time of 7.86 h. Higher organics loading (5.53 g TCOD/m²-day) caused cell lysis and damaged the O₂-MBfR system, leading to a discernible and continuous decline of the reactor performance. The O₂-MBfR design completely eliminated foaming formation. LAS -biodegrading-rich genus containing Clostridium, Parvibaculum, Dechloromonas, Desulfovibrio, Mycobacterium, Pseudomonas, and Zoogloea enable the nearly complete removal of LAS even under high C/N conditions. Results demonstrated that the O₂-MBfR technology is feasible for treating GW containing high LAS and C/N ratio, while remaining free of foaming formation, and at a low cost due to high O₂ utilization rates.

Degradation of Rhodamine B in aqueous solution by laser cavitation

A novel method of laser cavitation (LC) was proposed for degrading organic dye wastewater. Rhodamine B (RhB) aqueous solution was employed as the simulated organic dye wastewater, and a LC system was designed to conduct the experiments of degrading RhB. The effects of laser energy, initial concentration and cavitation time on the degradation were investigated. Moreover, the degradation kinetics, degradation mechanism and energy efficiency were analyzed. The experimental results indicate that RhB aqueous solution can be degraded effectively by LC and the degradation follows the pseudo-first-order kinetics. The extent of degradation increases by 27.6% with the rise of laser energy (50-100 mJ) while it decreases by 7.8% with increasing the initial concentration from (20-40 mg/L), but RhB can not be degraded when exceeding 100 mg/L. The degradation extent of RhB at 100 mJ and 20 mg/L for 3 h is 81.11%, and the RhB solution is almost completely degraded at 150 mJ (98.4%). The degradation velocity of RhB rises firstly and then decreases as the cavitation time increases. The degradation of RhB by LC can be attributed to the N-de-ethylation and chromophore cleavage caused by oxidation of hydroxyl (OH) radical and thermal decomposition. LC has a higher energy efficiency compared with other methods and is more energy efficient at lower laser energy.

In-situ synthesis of rGO-ZnO nanocomposite for demonstration of sunlight driven enhanced photocatalytic and self-cleaning of organic dyes and tea stains of cotton fabrics

Recently, research activities are focused on development of 2D reduced graphene oxide (rGO) based semiconductor nanocomposite materials for boosting up its catalytic applications. In this work, a rarely reported green synthesis approach has been envisioned to synthesize in-situ 2D rGO-ZnO (rGZn) nanocomposites from Apple juice and zinc acetate. Also the composition of the samples has been optimized to achieve high photocatalytic and self-cleaning properties by the formation of reactive oxidation species. The samples are characterized for their microstructural, optical absorption and photoluminescence properties. It has been tested that rGZn nanocomposites are capable of removing a test dye, namely methylene blue (MB) from water and achieved the highest dye degradation efficiency of ∼91% within only 60 min under UV-vis light irradiation. A smart cotton fabric (CF) coated with rGZn has been prepared and demonstrated its photocatalytic self-cleaning property by degradation of MB, rhodamine B dyes and tea stains on it even under sunlight irradiation, which is scarcely available in the literature. Therefore, this work may open a new avenue of research for low cost and easy synthesis of rGO-semiconductor nanocomposites with high photocatalytic properties for industrial applications as well as for development of rGO based smart fabric for real-life applications.

Removal of methylene blue from aqueous solution by Artist's Bracket fungi: kinetic and equilibrium studies

In this study, adsorption of methylene blue (MB) dye onto Artist's Bracket (AB) fungi was investigated in aqueous solution. Fourier transform infrared and scanning electron microscopy were used to investigate surface characteristic of AB fungi. Influence of operational parameters such as pH, contact time, biosorbent dosage, dye concentration, inorganic salts and temperature was studied on dye removal efficiency. With the increase of pH from 3 to 9, removal efficiency increased from 74.0% to 90.4%. Also, it reduced from 99.8% to 81.8% with increasing initial MB concentration from 25 mg L(-1) to 100 mg L(-1), whereas it increased from 54.7% to 98.7% and from 98.5% to 99.9% with increasing biosorbent dosage from 0.5 g L(-1) to 2 g L(-1) and with increasing temperature from 25 °C to 50 °C, respectively. Isotherm studies have shown adsorption of MB dye over the AB fungi had a better coefficient of determination (R(2)) of 0.98 for Langmuir isotherm. In addition, the maximum monolayer adsorption capacity (qm) was 100 mg g(-1). Also, the MB dye adsorption process followed pseudo-second-order kinetic. In general, AB fungi particles can be favorable for removal of MB dye from dye aqueous solution with natural pH and high temperature.

Removal and recycling of ppm levels of methylene blue from an aqueous solution with graphene oxide

Methylene blue (several ppm) could be efficiently collected and easily recycled by graphene oxide from solution via simple adsorption process.

Degradation and detoxification of methylene blue dye adsorbed on water hyacinth in semi continuous anaerobic–aerobic bioreactors by novel microbial consortium-SB

Combinatorial adsorption–biodegradation treatment of textile wastewater provides a cost effective and ecofriendly alternative to conventional physicochemical treatment methods.

Rapid destruction of the rhodamine B using TiO2 photocatalyst in the liquid phase plasma

Background

Rhodamine B (RhB) is widely used as a colorant in textiles and food stuffs, and is also a well-known water tracer fluorescent. It is harmful to human beings and animals, and causes irritation of the skin, eyes and respiratory tract. The carcinogenicity, reproductive and developmental toxicity, neurotoxicity and chronic toxicity toward humans and animals have been experimentally proven. RhB cannot be effectively removed by biological treatment due to the slow kinetics. Therefore, RhB is chosen as a model pollutant for liquid phase plasma (LPP) treatment in the present investigation.

Results

This paper presents experimental results for the bleaching of RhB from aqueous solutions in the presence of TiO2 photocatalyst with LPP system. Properties of generated plasma were investigated by optical emission spectroscopy methods. The results of electrical-discharge degradation of RhB showed that the decomposition rate increased with the applied voltage, pulse width, and frequency. The oxygen gas addition to reactant solution increases the degradation rate by active oxygen species. The RhB decomposition rate was shown to increase with the TiO2 particle dosage.

Conclusion

This work presents the conclusions on the photocatalytic oxidation of RhB, as a function of plasma conditions, oxygen gas bubbling as well as TiO2 particle dosage. We knew that using the liquid phase plasma system with TiO2 photocatalyst at high speed we could remove the organic matter in the water.

The effects of externally applied pressure on the ultrasonic degradation of Rhodamine B

The present manuscript compares the ultrasonic degradation of Rhodamine B dye under atmospheric (1 bar) and elevated pressures (1.6 and 2 bar). The degradation was studied as a function of the bulk liquid temperature and initial dye concentration at two different values of mechanical amplitudes (ultrasonic intensities). Results indicate that at the low amplitude an increase in the applied pressure increases the dye removal rate, whereas at the high amplitude, the same increase in the pressure has a minimal effect on the degradation of the dye. Furthermore, at low amplitudes an increase in the bulk liquid temperature from 5 to 35 °C increases the dye degradation by 10%. At higher intensities, the same increase in temperature has negative or no effect on the dye removal. An increase in the initial dye concentration by one order of magnitude significantly lowers the dye degradation rate regardless of the applied amplitude. Though these results are caused by numerous physical and chemical processes taking place during ultrasonic cavitation, the number of cavitation sites, bubble temperature and consequently, the amount of oxidative species inside the bubble seem to be the most important ones in determining the extent of the degradation of molecules in the bulk liquid.

Reductive transformation and detoxification mechanism of 2,4-dinitrochlorobenzene in combined zero valent iron and anaerobic-aerobic process

A combined zero valent iron (ZVI) and anaerobic-aerobic process was adopted for the treatment of 2,4-dinitrochlorobenzene (DNCB)-containing wastewater. The transformation pathway, reduction of acute toxicity and enhancement of biodegradability were investigated. After pretreatment by ZVI, DNCB in wastewater could be completely converted into 2,4-diaminochlorobenzene (DACB). The ratio of BOD5/COD increased from 0.005 +/- 0.001 to 0.168 +/- 0.007, while EC(50, 48 hr) (V/V) increased from 0.65% to 5.20%, indicating the enhancement of biodegradability and reduction of acute toxicity with the pretreatment by ZVI. DACB was further dechlorinated to m-phenylenediamine during the anaerobic process using methanol as electron donor, with EC(50, 48 hr) increasing from 5.20% to 48.2%. After the subsequent anaerobic-aerobic process, m-phenylenediamine was degraded completely, with effluent COD of 67.5 +/- 10.8 mg/L. This effluent of the subsequent anaerobic-aerobic process was not toxic to zebrafish. The combined ZVI and anaerobic-aerobic process offers bright prospects for the treatment of chlorinated nitroaromatic compound-containing wastewater.

Post-treatment of anaerobically degraded azo dye Acid Red 18 using aerobic moving bed biofilm process: enhanced removal of aromatic amines

The application of aerobic moving bed biofilm process as post-treatment of anaerobically degraded azo dye Acid Red 18 was investigated in this study. The main objective of this work was to enhance removal of anaerobically formed the dye aromatic metabolites. Three separate sequential treatment systems were operated with different initial dye concentrations of 100, 500 and 1000 mg/L. Each treatment system consisted of an anaerobic sequencing batch reactor (An-SBR) followed by an aerobic moving bed sequencing batch biofilm reactor (MB-SBBR). Up to 98% of the dye decolorization and more than 80% of the COD removal occurred anaerobically. The obtained results suggested no significant difference in COD removal as well as the dye decolorization efficiency using three An-SBRs receiving different initial dye concentrations. Monitoring the dye metabolites through HPLC suggested that more than 80% of anaerobically formed 1-naphthylamine-4-sulfonate was completely removed in the aerobic biofilm reactors. Based on COD analysis results, at least 65-72% of the dye total metabolites were mineralized during the applied treatment systems. According to the measured biofilm mass and also based on respiration-inhibition test results, increasing the initial dye concentration inhibited the growth and final mass of the attached-growth biofilm in MB-SBBRs.

Decolorization of malachite green, decolorization kinetics and stoichiometry of ozone-malachite green and removal of antibacterial activity with ozonation processes

This study aimed to identify degradation intermediates and to investigate the stoichiometry of decolorization and degradation, decolorization kinetics, and removal of antibacterial activity of malachite green (MG) using ozonization processes. The decolorization of MG was optimal at an acidic pH value of 3 based on molecular ozone attack on MG molecules. The stoichiometric ratio of decolorization between ozone and MG was calculated to be 7.0 with a regression coefficient of 0.995, whereas the ratio for degradation was calculated as 13.1 with a regression coefficient of 0.998. With MG concentrations in the range of 0.30-1.82 mM, the concentration of decolorized MG increased with higher initial concentrations of MG, whereas the ozonolytic decolorization rates of MG, decreased with increasing initial concentration. The pseudo-first-order degradation rate constants (k') decreased with the initial concentration and ranged from 0.769 to 0.223 min(-1). Twelve different intermediates were produced during the ozonation of MG with ozonation times between 5 min and 30 min and were identified by GC-MS. Although 86% of MG in the reaction mixture was removed by ozonation after 10 min, the decrease of antibacterial activity was very low (10%) for Bacillus subtilis and Staphylococcus epidermidis because the degradation intermediates, phenol and benzoic acid, also have antibacterial activity. The antibacterial activity of both MG and its intermediates were removed successfully with ozonation times above 26 min.

Enhanced biodegradation of Reactive Violet 5R manufacturing wastewater using down flow fixed film bioreactor

The present study emphasizes on the development of bioprocess for biodegradation and bioremediation of Reactive Violet 5R (RV5) manufacturing industry's wastewater in laboratory scale indigenously designed down flow fixed film bioreactor (DFFR). Process was investigated in DFFR, packed with furnace charcoal as a support material. During the batch and continuous operation of DFFR more than 95% degradation, 88% COD reduction and 99% copper remediation was obtained in less than 8h of contact time. Continuous mode treatment gave degradation of more than 2500mg dye in only 1h of contact time. Addition of 0.25% peptone enhanced biodegradation rate more than three-fold. The biologically treated wastewater was found to stimulate the growth of selected soil bacteria. Degradation of major components of the wastewater was confirmed by HPTLC. DFFR was operated successfully for 750d continuously, during which 716 cycles of batch treatment were operated.

A novel adsorbent obtained by inserting carbon nanotubes into cavities of diatomite and applications for organic dye elimination from contaminated water

A novel approach is described for establishing adsorbents for elimination of water-soluble organic dyes by using multi-walled carbon nanotubes (MWCNTs) as the adsorptive sites. Agglomerates of MWCNTs were dispersed into individual tubes (dispersed-MWCNTs) using sodium n-dodecyl itaconate mixed with 3-(N,N-dimethylmyristylammonio)-propanesulfonate as the dispersants. The resultant dispersed-MWCNTs were inserted into cavities of diatomite to form composites of diatomite/MWCNTs. These composites were finally immobilized onto the cell walls of flexible polyurethane foams (PUF) through an in situ PUF formation process to produce the foam-like CNT-based adsorbent. Ethidium bromide, acridine orange, methylene blue, eosin B, and eosin Y were chosen to represent typical water-soluble organic dyes for studying the adsorptive capabilities of the foam-like CNT-based adsorbent. For comparisons, adsorptive experiments were also carried out by using agglomerates of the sole MWCNTs as adsorbents. The foam-like CNT-based adsorbents were found to have higher adsorptive capacities than the CNT agglomerates for all five dyes; in addition, they are macro-sized, durable, flexible, hydrophilic and easy to use. Adsorption isotherms plotted based on the Langmuir equation gave linear results, suggesting that the foam-like CNT-based adsorbent functioned in the Langmuir adsorption manner. The foam-like CNT-based adsorbents are reusable after regeneration with aqueous ethanol solution.

Determination of kinetic constants of hybrid textile wastewater treatment system

The present study is related to treatment of textile wastewater in microaerophilic-aerobic hybrid reactor. The study showed the effectiveness of biological treatment of wastewater involving appropriate microorganism and suitable reactors. COD and color were reduced to 82-94%, and 99% respectively for textile wastewater. The reactor was operated at highest loading of 16.4 g COD g l(-1)d(-1) and obtained 80% COD and 72% color removal. Biokinetic models were applied to data obtained from experimental studies in continuously operated hybrid reactor. Treatment efficiencies of the reactor were investigated at different hydraulic retention times (2.3-9.1d) and organic loading rates (2.6-16.4 g COD l(-1)d(-1)). Second-order and a Stover-Kincannon models were best fitted to the hybrid column reactor. The second-order substrate removal rate constant (k(2(S))) was found as 41.44 d(-1) for hybrid reactor. Applying the modified Stover-Kincannon model to the hybrid reactor, the maximum removal rate constant (U(max)) and saturation value constant (K(B)) were found to be 212 g l(-1)d(-1) and 22.89 g l(-1)d(-1), respectively.

Chemical characterization of a dye processing plant effluent—Identification of the mutagenic components

This work shows the chemical characterization of a dye processing plant effluent that was contributing to the mutagenicity previously detected in the Cristais river, São Paulo, Brazil, that had an impact on the quality of the related drinking water. The mutagenic dyes Disperse Blue 373, Disperse Orange 37 and Disperse Violet 93, components of a Black Dye Commercial Product (BDCP) frequently used by the facility, were detected by thin layer chromatography (TLC). The blue and orange dyes were quantified by high performance liquid chromatography (HPLC/DAD) in a raw and treated effluent samples and their contribution to the mutagenicity was calculated based on the potency of each dye for the Salmonella YG1041. In the presence of S9 the Disperse Blue 373 accounted for 2.3% of the mutagenic activity of the raw and 71.5% of the treated effluent. In the absence of S9 the Disperse Blue 373 accounted for 1.3% of the mutagenic activity of the raw and 1.5% of the treated effluent. For the Disperse Orange 37, in the presence of S9, it contributed for 0.5% of the mutagenicity of the raw and 6% of the treated effluent. In the absence of S9; 11.5% and 4.4% of the raw and treated effluent mutagenicity, respectively. The contribution of the Disperse Violet 93 was not evaluated because this compound could not be quantified by HPLC/DAD. Mutagenic and/or carcinogenic aromatic amines were also preliminary detected using gas chromatograph/mass spectrometry in both raw and treated and are probably accounting for part of the observed mutagenicity. The effluent treatment applied by the industry does not seem to remove completely the mutagenic compounds. The Salmonella/microsome assay coupled with TLC analysis seems to be an important tool to monitor the efficiency of azo dye processing plant effluent treatments.

Toxicological effect of indole and its azo dye derivatives on some microorganisms under aerobic conditions

Azo dyes are ubiquitous commercial chemicals that present unique environmental problems. The azo dyes in particular can undergo natural anaerobic degradation to potentially carcinogenic amines. They pose a major problem for water-treatment plants downstream. One strategy to remidate polluted surface contaminants is to make use of the degradative capacity of bacteria rather than using destructive chemical reactions. Therefore, pathogenic and non-pathogenic microorganisms namely; Bacillus thuringiensis, Bacillus subtilis, Bacillus megaterium, Proteus vulgaris, Pseudomonas aeruginosa, Staphylococcus aureus, Escherichia coli and Saccharomyces cerevisiae have been chosen and the toxicological effect of indole and its azo dye methyl derivatives on these microorganisms was studied under aerobic conditions. While these compounds have showed remarkable activity against B. megaterium, B. subtilis, B. thuringiensis and S. aureus, they did not exhibit any activity against P. vulgaris. However, indole acted as an inhibitor on all of these compounds specially the Gram negative bacterium P. aeruginosa.

Recent advances in azo dye degrading enzyme research

Azo dyes, which are characterized by one or more azo bonds, are a predominant class of colorants used in tattooing, cosmetics, foods, and consumer products. These dyes are mainly metabolized by bacteria to colorless aromatic amines, some of which are carcinogenic, by azoreductases that catalyze a NAD(P)H-dependent reduction. The resulting amines are further degraded aerobically by bacteria. Some bacteria have the ability to degrade azo dyes both aerobically and anaerobically. Plant-degrading white rot fungi can break down azo dyes by utilizing a number of oxidases and peroxidases as well. In yeast, a ferric reductase system participates in the extracellular reduction of azo dyes. Recently, two types of azoreductases have been discovered in bacteria. The first class of azoreductases is monomeric flavin-free enzymes containing a putative NAD(P)H binding motif at their N-termini; the second class is polymeric flavin dependent enzymes which are studied more extensively. Azoreductases from bacteria represent novel families of enzymes with little similarity to other reductases. Dissociation and reconstitution of the flavin dependent azoreductases demonstrate that the non-covalent bound flavin prosthetic group is required for the enzymatic functions. In this review, structures and carcinogenicity of azo colorants, protein structure, enzymatic function, and substrate specificity, as well as application of the azo dyes and azoreductases will be discussed.

Development of physicochemical nitrogen removal process for high strength industrial wastewater

The biological nitrogen removal (BNR) process is the most common method for removing low quantities of ammonium from wastewater, but this method is not used for wastewater rich with ammonium. In this study, we have developed the physicochemical nitrogen removal process to remove the nitrogen content for a real industrial wastewater. The denitrification was accomplished by the physicochemical denitrification process using zinc powder and sulfamic acid in pH 2-4. The experimental parameters were examined by varying various reaction conditions such as pH, zinc feeding time, amount of sulfamic acid, and amount of nitrate concentration. For each experimental condition, the physicochemical denitrification process was determined by pH, amount of zinc powder and sulfamic acid, zinc feeding time and nitrate concentration.

Azadirachta indica (Neem) leaf powder as a biosorbent for removal of Cd(II) from aqueous medium

A biosorbent, Neem leaf powder (NLP), was prepared from the mature leaves of the Azadirachta indica (Neem) tree by initial cleaning, drying, grinding, washing to remove pigments and redrying. The powder was characterized with respect to specific surface area (21.45 m2g(-1)), surface topography and surface functional groups and the material was used as an adsorbent in a batch process to remove Cd(II) from aqueous medium under conditions of different concentrations, NLP loadings, pH, agitation time and temperature. Adsorption increased from 8.8% at pH 4.0 to 70.0% at pH 7.0 and 93.6% at pH 9.5, the higher values in alkaline medium being due to removal by precipitation. The adsorption was very fast initially and maximum adsorption was observed within 300 min of agitation. The kinetics of the interactions was tested with pseudo first order Lagergren equation (mean k(1)=1.2x10(-2)min(-1)), simple second order kinetics (mean k2=1.34x10(-3) gmg(-1)min(-1)), Elovich equation, liquid film diffusion model (mean k=1.39x10(-2)min(-1)) and intra-particle diffusion mechanism. The adsorption data gave good fits with Langmuir and Freundlich isotherms and yielded Langmuir monolayer capacity of 158mgg(-1) for the NLP and Freundlich adsorption capacity of 18.7 Lg(-1). A 2.0 g of NLP could remove 86% of Cd(II) at 293 K from a solution containing 158.8 mg Cd(II) per litre. The mean values of the thermodynamic parameters, DeltaH, DeltaS and DeltaG, at 293 K were -73.7 kJmol(-1), -0.24 Jmol(-1)K(-1) and -3.63 kJmol(-1), respectively, showing the adsorption process to be thermodynamically favourable. The results have established good potentiality for the Neem leaf powder to be used as a biosorbent for Cd(II).

The contribution of azo dyes to the mutagenic activity of the Cristais River

To verify whether dyes emitted within the discharge of a dye processing plant were contributing to the mutagenicity repeatedly found in the Cristais River, Sao Paulo, Brazil, we chemically characterized the following mutagenic samples: the treated industrial effluent, raw and treated water, and the sludge produced by a Drinking Water Treatment Plant (DWTP) located approximately 6 km from the industrial discharge. Considering that 20% of the dyes used for coloring activities might be lost to wastewaters and knowing that several dyes have mutagenic activity, we decided to analyze the samples for the presence of dyes. Thin layer chromatographic analysis indicated the presence of three prevalent dyes in all samples, except for the drinking water. This combination of dyes corresponded to a commercial product used by the industry, and it tested positive in the Salmonella assay. The structures of the dye components were determined using proton magnetic resonance and mass spectrometric (MS) methods, and the dyes were tested for mutagenicity. The blue component was identified as the C.I. Disperse Blue 373, the violet as C.I. Disperse Violet 93, and the orange as C.I. Disperse Orange 37. The dyes showed mutagenic responses of 6300, 4600, and 280 revertants/microg for YG1041 with S9 respectively. A bioassay-directed fractionation/chemical analysis showed that the C.I. Disperse Blue 373 contributed 55% of the mutagenic activity of the DWTP sludge. We showed that these dyes contributed to the mutagenic activity found in the Cristais River environmental samples analyzed and are indirectly affecting the quality of the related drinking water. Therefore, we believe that this type of discharge should be more thoroughly characterized chemically and toxicologically. Additionally, human and ecological risks associated with the release of dye processing plant effluents should be more fully investigated, especially where the resultant water is taken for human consumption.

Combined anaerobic-aerobic treatment of azo dyes--a short review of bioreactor studies

The most logical concept for the removal of azo dyes in biological wastewater treatment systems is based on anaerobic treatment, for the reductive cleavage of the dyes' azo linkages, in combination with aerobic treatment, for the degradation of the products from azo dye cleavage, aromatic amines. Since the 1990s, several research papers have been published on combined, sequential or integrated, anaerobic-aerobic bioreactor treatment of azo dye-containing wastewater. The extent of azo dye reduction in the anaerobic phase of those bioreactor systems was generally high, albeit the process often required long reaction times, a limitation that can easily be remedied by making use of the property of redox mediators to speed up the process. The consequent removal of aromatic amines under aerobic conditions was less unequivocal. Although analytical data indicate that many of the aromatic amines were removed from the wastewater, and although the limited amount of available toxicity data all show far-reaching detoxification during aerobic treatment, it is clear that not all aromatic amines can be completely mineralized.

Removal of synthetic dyes from wastewaters: a review

The more recent methods for the removal of synthetic dyes from waters and wastewater are complied. The various methods of removal such as adsorption on various sorbents, chemical decomposition by oxidation, photodegradation, and microbiological decoloration, employing activated sludge, pure cultures and microbe consortiums are described. The advantages and disadvantages of the various methods are discussed and their efficacies are compared.