Azo dye reduction by thermophilic anaerobic granular sludge, and the impact of the redox mediator anthraquinone-2,6-disulfonate (AQDS) on the reductive biochemical transformation

Azo dyes are important persistent pollutants of textile industry effluents. Reduction of these dyes to their corresponding aromatic amines under anaerobic conditions can be used to initiate biodegradation. Since electron transfer is suggested to be rate limiting, redox mediators are being considered to improve dye reduction kinetics. This study evaluates the use of riboflavin, the redox active moiety of common occurring enzyme cofactors, as a redox mediator to accelerate the reduction of the azo dye, mordant yellow 10 (MY10). Dye reduction was found to follow zero order kinetics, the total rate constant (Vtotal) could be separated into two components: the rate of reduction due to direct contact between enzymes in the sludge with the dye (Vdirect); and the rate of reduction mediated by riboflavin (Vmediated). Riboflavin increased the Vtotal by 61% at extremely sub-stoichiometric concentrations of 9.1 μmol l-1, which corresponded to a molar riboflavin:dye ratio of 1:60. The accelerating effect of riboflavin displayed saturation kinetics at higher concentrations, with a maximum increase of Vtotal of approximately 2-fold. A model is presented which assumes that Vmediated depends on the activity of riboflavin reductase (RR) and thus follows Michaelis-Menton kinetics with respect to the riboflavin concentration. The half-velocity constant (Km) was very low (6.3 μmol l-1), indicating a high affinity of the sludge RR for riboflavin. Both Vdirect and Vmediated were found to be proportional to the assay sludge concentration. The results taken as a whole indicate that vitamin levels of riboflavin can be utilized to improve the kinetics of azo dye reduction during anaerobic treatment.

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Azo dye decolourisation by anaerobic granular sludge

Chemosphere ◽

10.1016/s0045-6535(00)00270-8 ◽

2001 ◽

Vol 44 (5) ◽

pp. 1169-1176 ◽

Cited By ~ 212

Author(s):

Frank P. van der Zee ◽

Gatze Lettinga ◽

Jim A. Field

Keyword(s):

Azo Dye ◽

Granular Sludge ◽

Anaerobic Granular Sludge ◽

Dye Decolourisation

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The role of sulphate reduction on the reductive decolorization of the azo dye reactive orange 14

Water Science & Technology ◽

10.2166/wst.2006.501 ◽

2006 ◽

Vol 54 (2) ◽

pp. 171-177 ◽

Cited By ~ 15

Author(s):

F.J. Cervantes ◽

J.E. Enriquez ◽

M.R. Mendoza-Hernandez ◽

E. Razo-Flores ◽

J.A. Field

Keyword(s):

Electron Donor ◽

Azo Dye ◽

Redox Mediator ◽

Sulphate Reduction ◽

Anaerobic Sludge ◽

Biological Mechanisms ◽

Azo Reduction ◽

Reactive Orange ◽

The Impact

The aim of this study was to investigate the impact of a broad range of sulphate concentrations (0–10 g SO4−2 L−1) on the reduction of an azo dye (reactive orange 14 (RO14)) by an anaerobic sludge. An increase in the sulphate concentration generally stimulated the reduction of RO14 by sludge incubations supplemented with glucose, acetate or propionate as electron donor. Sulphate and azo dye reductions took place simultaneously in all incubations. However, there was a decrease on the rate of decolorization when sulphate was supplied at 10 g SO4−2 L−1. Abiotic incubations at different sulphide concentrations (0–2.5 g sulphide L−1) promoted very poor reduction of RO14. However, addition of riboflavin (20 μM), as a redox mediator, accelerated the reduction of RO14 up to 44-fold compared to a control lacking the catalyst. Our results indicate that sulphate-reduction may significantly contribute to the reduction of azo dyes both by biological mechanisms and by abiotic reductions implicating sulphide as an electron donor. The contribution of abiotic decolorization by sulphide, however, was only significant when a proper redox mediator was included. Our results also revealed that sulphate-reduction can out-compete with azo reduction at high sulphate concentrations leading to a poor decolorising performance when no sufficient reducing capacity is available.

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Thermal modification of activated carbon surface chemistry improves its capacity as redox mediator for azo dye reduction

Journal of Hazardous Materials ◽

10.1016/j.jhazmat.2010.08.005 ◽

2010 ◽

Vol 183 (1-3) ◽

pp. 931-939 ◽

Cited By ~ 54

Author(s):

L. Pereira ◽

R. Pereira ◽

M.F.R. Pereira ◽

F.P. van der Zee ◽

F.J. Cervantes ◽

...

Keyword(s):

Activated Carbon ◽

Surface Chemistry ◽

Azo Dye ◽

Thermal Modification ◽

Redox Mediator ◽

Carbon Surface ◽

Dye Reduction

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Utilization of anaerobic granular sludge for chromium (VI) removal from wastewater: optimization by response surface methodology

Water Science & Technology ◽

10.2166/wst.2017.297 ◽

2017 ◽

Vol 76 (5) ◽

pp. 1112-1123

Author(s):

Yifan Hu ◽

Changzhu Yang ◽

Jinfeng Dan ◽

Wenhong Pu ◽

Jiakuan Yang

Keyword(s):

Photoelectron Spectroscopy ◽

Freundlich Isotherm ◽

Granular Sludge ◽

Polynomial Equation ◽

Anaerobic Granular Sludge ◽

Order Kinetic ◽

Chromium Vi ◽

Biosorption Process ◽

Initial Ph ◽

The Impact

In this study, anaerobic granular sludge (AGS) was used as a novel adsorbent for hexavalent chromium (Cr (VI)) removal from aqueous solutions. Factor experiments were conducted to find out the effects of different variables on the biosorption process. Among these terms, the impact of three main independent variables (contact time, initial pH and AGS dosage) on the removal efficiency of Cr (VI) was modeled using a well-fitting polynomial equation (R2 = 0.9044), by conducting 20 batch experiments designed by a central composite. The experimental isotherm data were successfully described by the Freundlich isotherm and the pseudo-second-order kinetic model was more suitable for explaining the kinetics process of adsorption. The AGS can be disposed using 0.1 M NaOH with 96.4% desorption efficiency. The results of the analyses (X-ray photoelectron spectroscopy and Fourier transformed infrared spectroscopy) suggested that Cr (VI) adsorption most likely involved electrostatic adsorption, redox reaction and complexation.

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Biodegradability of N-substituted aromatics and alkylphenols under methanogenic conditions using granular sludge

Water Science & Technology ◽

10.2166/wst.1996.0058 ◽

1996 ◽

Vol 33 (3) ◽

pp. 47-57 ◽

Cited By ~ 19

Author(s):

Elías Razo-Flores ◽

Brian Donlon ◽

Jim Field ◽

Gatze Lettinga

Keyword(s):

Azo Dye ◽

Granular Sludge ◽

The Other ◽

Anaerobic Sludge ◽

Lag Phase ◽

Anaerobic Granular Sludge ◽

Upward Flow ◽

Experimental Conditions ◽

Toxic Concentrations ◽

Biodegradability Test

The biodegradability of seventeen N-substituted aromatic and six alkylphenol compounds were evaluated under methanogenic conditions. Biodegradation was assessed in batch assays inoculated with unacclimated and predigested anaerobic granular sludge at 30°C under agitated conditions over a 150 day period. The compounds were supplied at sub-toxic concentrations in the assays in order to prevent inhibition to the methanogens. The biodegradability test was performed by the measurement of the methane composition in the headspace of the serum flasks. The methanogenic consortia completely mineralized 2-, 3-aminobenzoate, 2-aminophenol and 4-cresol; whereas, 4-aminobenzoate was only partially degraded. The other N-substituted compounds and the alkylphenols tested were not biodegradable under the experimental conditions employed. An additional biodegradability assay was conducted with sludge from an upward-flow anaerobic sludge bed reactor adapted to the degradation of 2-nitrophenol. This sludge mineralized 2-aminophenol without any lag phase while the unadapted sludge required 110 days of acclimation. The three aminobenzoate isomers were fully mineralized by the adapted sludge after similar lag periods observed in the unadapted sludge. The 2-nitrophenol adapted sludge cross-acclimatized to the mineralization of 5-aminosalicylate and 4-aminophenol. This constitutes the first report demonstrating the anaerobic mineralization of 5-aminosalicylate, which indicates that at least some azo dye cleavage products can be degraded in methanogenic consortia.

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Impact of Microaeration and the Redox Mediator Anthraquinone-2,6-Disulfonate on Azo Dye Reduction and By-Products Degradation

CLEAN - Soil Air Water ◽

10.1002/clen.201700518 ◽

2018 ◽

Vol 46 (8) ◽

pp. 1700518

Author(s):

Amanda N. de Barros ◽

Marcos E. R. da Silva ◽

Paulo I. M. Firmino ◽

Eduardo A. F. de Vasconcelos ◽

André B. dos Santos

Keyword(s):

Azo Dye ◽

Redox Mediator ◽

Dye Reduction ◽

By Products

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Effect of nitrate on the reduction of Reactive Red 2 by mesophilic anaerobic sludge

Water Science & Technology ◽

10.2166/wst.2008.047 ◽

2008 ◽

Vol 57 (7) ◽

pp. 1067-1071 ◽

Cited By ~ 4

Author(s):

A. B. Dos Santos ◽

C. H. C. Braúna ◽

S. Mota ◽

F. J. Cervantes

Keyword(s):

Azo Dye ◽

Catalytic Properties ◽

Redox Mediator ◽

Anaerobic Sludge ◽

Redox Mediators ◽

Anaerobic Conditions ◽

Anaerobic Reactors ◽

Nitrate Addition ◽

Dye Reduction ◽

Reactive Red 2

This research aimed to evaluate the effect of nitrate on anaerobic azo dye reduction by using mesophilic bioreactors, in the absence (reactor R2) and in the presence (reactor R1) of redox mediators. The azo dye Reactive Red 2 (RR2) and the redox mediator anthraquinone-2,6-disulphonate (AQDS) were selected as model compounds. The results showed that the bioreactors were efficient on RR2 reduction, in which ethanol showed to be a good electron donor to sustain dye reduction under anaerobic conditions. The redox mediator AQDS increased the rates of reductive decolourisation, but its effect was not so remarkable compared to the previous experiments conducted. Contrary to the raised hypothesis that the nitrate addition could decrease decolourisation rates and catalytic properties of the redox mediators, no effect of nitrate was observed in the bioreactors, suggesting that the presence of nitrate in textile wastewaters will not decrease the capacity of anaerobic reactors supplemented or not with redox mediators to decolourize azo dyes.

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Toxicity of Sulfite and Cadmium to Anaerobic Granular Sludge

Water Quality Research Journal ◽

10.2166/wqrj.1994.037 ◽

1994 ◽

Vol 29 (4) ◽

pp. 581-598

Author(s):

C.F. Shew ◽

N. Kosaric

Keyword(s):

Granular Sludge ◽

Upflow Anaerobic Sludge Blanket ◽

Shock Load ◽

Anaerobic Sludge ◽

Anaerobic Granular Sludge ◽

Scanning Electron Micrographs ◽

Bacterial Growth Rate ◽

Digestion Rate ◽

Sulfate Reducing ◽

Load Conditions

Abstract Toxicity of sulfite (Na2SO3) and cadmium (CdCl2) ions to anaerobic granular sludge was investigated in 1.2 litre bench-scale upflow anaerobic sludge blanket (UASB) reactors during process acclimation and shock load conditions. Minimal sulfite toxicity was observed under gradual and shock load conditions at sulfite concentrations of up to 1000 mg S/L if proper acclimation was allowed to occur. No long-term toxic effects were observed although the COD digestion rate was temporarily inhibited by shock load of sulfite. Scanning electron micrographs indicated that more sulfate-reducing bacteria were present in the granules developed in the reactors with sulfite supplement although rod-shaped Methanosaeta-like bacteria were still dominant. High bacterial growth rate was observed in the reactors which were supplied with the feed containing sulfite. The COD digestion rate was inhibited at a cadmium loading rate of 2.4 g Cd per day under both acclimation and shock load conditions. Acclimation did not seem to improve the bacteria to tolerate the toxicity of cadmium. The concentration of free cadmium was very low in the reactors under normal conditions, but increased rapidly when the COD digestion in the reactors ceased. The bacteria could not be reactivated after inhibited by cadmium. When reactors were operated at low specific COD loading rates, more inorganic precipitates were formed inside the granules which consequently settled faster.

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