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

2006 ◽  
Vol 54 (2) ◽  
pp. 171-177 ◽  
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.

The role of (auto)catalysis in the mechanism of an anaerobic azo reduction

2000 ◽  
Vol 42 (5-6) ◽  
pp. 301-308 ◽  
Author(s):  
F.P. van der Zee ◽  
G. Lettinga ◽  
J.A. Field
Keyword(s):  
Chemical Reduction ◽  
Reduction Rate ◽  
Reduction Process ◽  
Anaerobic Sludge ◽  
Acid Orange 7 ◽  
Azo Reduction ◽  
Disulphonic Acid ◽  
Mathematical Evaluation ◽  
The Impact

Azo dyes are non-specifically reduced under anaerobic conditions, but the slow rates at which many dyes react may present a serious problem for the application of anaerobic technology as a first stage in the complete biodegradation of these compounds. Therefore, it is significant to explore the mechanism of anaerobic azo reduction, especially with respect to its kinetics. With that purpose, decolouration of the monoazo dye C.I. Acid Orange 7 (AO7) was studied in batch experiments. Experiments indicated that chemical reduction by sulphide is partially responsible for the anaerobic conversions of AO7. Mathematical evaluation of the experimental results pointed out that autocatalysis played an important role in the chemical reduction of AO7. Further tests made clear that 1-amino-2-naphthol was the dye's constituent aromatic amines that accelerated the reduction process, possibly by mediating the transfer of reducing equivalents. The impact of redox mediation by quinones was further evaluated by testingthe catalysing effects of anthraquinone-2,6-disulphonic acid (AQDS) and of autoclaved sludge. AQDS appeared to be an extremely powerful catalyst, capable of increasing the first-order chemical reduction rate constants by a factor 10 to 100. Also autoclaved sludge, possibly because of mediation by sludge organic matter, accomplished accelerated azo reduction rates. Azo reduction in living sulphidogenic anaerobic sludge environments is 3 times more rapid than the chemically catalysed reaction with sulphide. The exact role of the biological activity remains to be clarified.

Aeration tank odour by dimethyl sulphoxide (DMSO) waste in sewage

2007 ◽  
Vol 55 (5) ◽  
pp. 319-326 ◽  
Author(s):  
D. Glindemann ◽  
J.T. Novak ◽  
J. Witherspoon
Keyword(s):  
Bulk Water ◽  
Sulphate Reduction ◽  
Anaerobic Sludge ◽  
Aeration Tank ◽  
Dimethyl Sulphide ◽  
Reduction Mechanism ◽  
Anaerobic Conditions ◽  
Sludge Flocs ◽  
Oxidation Resistant

Sewage plants can experience dimethyl sulphide (DMS) odour problems by at least one mg/L dimethylsulphoxide (DMSO) waste residue in plant influent, through a DMSO/DMS reduction mechanism. This bench-scale batch study simulates in bottles the role of poor aeration in wastewater treatment on the DMSO/DMS and sulphate/H2S reduction. The study compares headspace concentrations of sulphide odorants developed by activated sludge (closed bottles, half full) after six hours under anoxic versus anaerobic conditions, with 0 versus 2 mg/L DMSO addition. Anoxic sludge (0.1–2 mg/L dissolved oxygen, DO) with DMSO resulted in about 50 ppmv DMS and no other sulphide, while DMSO-free sludge was free of detectable sulphides. Anaerobic sludge (no measurable DO to the point of sulphate reduction) with DMSO resulted in 22/4/37 ppmv of H2S/methanethiol (MT)/DMS, while DMSO-free sludge resulted in 44/8/2 ppmv of H2S/MT/DMS. It is concluded that common “anoxic” aeration tank zones with measurable DO in bulk water but immeasurable DO inside sludge flocs (nitrate reducing) experience DMSO reduction to DMS that is oxidation resistant and becomes the most important odorant. Under anaerobic conditions, H2S from sulphate reduction becomes an additional important odorant. A strategy is developed that allows operators to determine from the quantity of different sulphides whether the DMSO/DMS mechanism is important at their wastewater plant.

Effect of Sulfate and Redox Mediator on Reduction of AO7 in Upflow Anaerobic Filter (UAF)

2014 ◽  
Vol 522-524 ◽  
pp. 584-589
Author(s):  
Li Han ◽  
Yue Wen ◽  
Ning Ding ◽  
Qi Zhou
Keyword(s):  
Reduction Rate ◽  
Redox Mediator ◽  
Health Concern ◽  
Azo Compounds ◽  
Anaerobic Sludge ◽  
Synthetic Dyes ◽  
Acid Orange 7 ◽  
Start Up ◽  
Speed Up ◽  
The Impact

Azo compounds constitute the largest and the most diverse group of synthetic dyes and are widely used. The release of coloured wastewaters represents a serious environmental problem and a public health concern. The aim of this study was to investigate the impact of sulfate and redox mediator on the reduction of an azo dye (Acid orange 7, AO7) by anaerobic sludge. The kinetics showed the AO7 reduction rate can be greatly improved by the addition of sulfate and RF, thus it is possible to speed up the start-up of AO7 reduction system under appropriate condition.

Enhanced reduction of an azo dye using henna plant biomass as a solid-phase electron donor, carbon source, and redox mediator

2014 ◽  
Vol 161 ◽  
pp. 465-468 ◽  
Author(s):  
Jingang Huang ◽  
Shushan Chu ◽  
Jianjun Chen ◽  
Yi Chen ◽  
Zhengmiao Xie
Keyword(s):  
Carbon Source ◽  
Electron Donor ◽  
Azo Dye ◽  
Plant Biomass ◽  
Solid Phase ◽  
Redox Mediator

The production of rice straw-derived biochar and its application for enhanced decolorization of azo dye as the role of redox mediator

2020 ◽  
Vol 201 ◽  
pp. 369-382
Author(s):  
Cong Ding ◽  
Jingjing Yang ◽  
Tianyin Huang ◽  
Wei Wu ◽  
Liming Zhang ◽  
...  
Keyword(s):  
Rice Straw ◽  
Azo Dye ◽  
Redox Mediator

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

2008 ◽  
Vol 57 (7) ◽  
pp. 1067-1071 ◽  
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.

Intergroup Threat and Outgroup Attitudes

2013 ◽  
Vol 44 (5) ◽  
pp. 311-319 ◽  
Author(s):  
Marco Brambilla ◽  
David A. Butz
Keyword(s):  
Gay Men ◽  
Social Group ◽  
Welfare Recipients ◽  
Intergroup Attitudes ◽  
Social Policies ◽  
Intergroup Threat ◽  
Economic Threat ◽  
The Impact ◽  
General Climate

Two studies examined the impact of macrolevel symbolic threat on intergroup attitudes. In Study 1 (N = 71), participants exposed to a macrosymbolic threat (vs. nonsymbolic threat and neutral topic) reported less support toward social policies concerning gay men, an outgroup whose stereotypes implies a threat to values, but not toward welfare recipients, a social group whose stereotypes do not imply a threat to values. Study 2 (N = 78) showed that, whereas macrolevel symbolic threat led to less favorable attitudes toward gay men, macroeconomic threat led to less favorable attitudes toward Asians, an outgroup whose stereotypes imply an economic threat. These findings are discussed in terms of their implications for understanding the role of a general climate of threat in shaping intergroup attitudes.

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