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.

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.

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.

Microbial community in anoxic–oxic–settling–anaerobic sludge reduction process revealed by 454 pyrosequencing analysis

2014 ◽  
Vol 60 (12) ◽  
pp. 799-809 ◽  
Author(s):  
Xinqiang Ning ◽  
Wenwen Qiao ◽  
Lei Zhang ◽  
Xu Gao
Keyword(s):  
Microbial Community ◽  
Relative Abundance ◽  
454 Pyrosequencing ◽  
Reduction Rate ◽  
Reduction Process ◽  
Anaerobic Sludge ◽  
Ammonia Oxidizing Bacteria ◽  
Sludge Reduction ◽  
Class Level ◽  
Fermentative Bacteria

Modification of the anoxic–oxic (AO) process by inserting a sludge holding tank (SHT) into the sludge return line forms an anoxic–oxic–settling–anaerobic (A+OSA) process that can achieve a 48.98% sludge reduction rate. The 454 pyrosequencing method was used to obtain the microbial communities of the AO and A+OSA processes. Results showed that the microbial community structures of the 2 processes were different as a result of the SHT insertion. Bacteria assigned to the phyla Proteobacteria and Bacteroidetes commonly existed and dominated the microbial populations of the 2 processes. However, the relative abundance of these populations shifted in the presence of SHT. The relative abundance of Proteobacteria decreased during the A+OSA process. A specific comparison at the class level showed that Sphingobacteria was enriched in the A+OSA process. The result suggested that the fermentative bacteria Sphingobacteria may have key functions in reducing the sludge from the A+OSA process. Uncultured Nitrosomonadaceae gradually became the dominant ammonia-oxidizing bacteria, and the nitrite-oxidizing bacterium Nitrospira was enriched in the A+OSA process. Both occurrences were favorable for stabilized nitrogen removal. The known denitrifying species in the A+OSA process were similar to those in the AO process; however, their relative abundance also decreased.

scholarly journals Acid–Base Catalytic Effects on Reduction of Methanol in Hot Water

Catalysts ◽  
2019 ◽  
Vol 9 (4) ◽  
pp. 373 ◽  
Author(s):  
Satoshi Inaba
Keyword(s):  
Energy Barrier ◽  
Laboratory Experiments ◽  
Catalytic Effect ◽  
Reduction Rate ◽  
Reduction Process ◽  
Hot Water ◽  
Water Molecules ◽  
Acid Base ◽  
Catalytic Effects

We have performed a number of quantum chemical simulations to examine the reduction process of methanol in hot water. Methanol is converted into a methane by capturing a hydrogen molecule and leaving a water molecule behind. The required energy for the reduction is too high to proceed in the gas phase. The energy barrier for the reduction of methanol is reduced by the catalytic effect of water molecules when we consider the reduction in aqueous solution. However, the calculated reduction rate is still much slower than that found experimentally. The ion product of water tends to increase in hot water, even though it eventually decreases at the high temperature of supercritical water. It is valuable to consider the acid–base catalytic effects on the reduction of methanol in hot water. The significant reduction of the energy barrier is accomplished by the acid–base catalytic effects due to hydronium or hydroxyde. Mean collision time between a hydronium and a methanol in hot water is shorter than the reduction time, during which a methanol is converted into a methane. The calculated reduction rate with the acid–base catalytic effects agrees well with that determined by laboratory experiments. The present study reveals a crucial role of the acid–base catalytic effects on reactions in hot water.

scholarly journals Can changes in forest management contribute to the reduction of CO2 in the atmosphere? Literature review, discussion and Polish example

2019 ◽  
Vol 61 (4) ◽  
pp. 299-318
Author(s):  
Krzysztof Adamowicz ◽  
Ljiljana Keca
Keyword(s):  
Fossil Fuels ◽  
Financial Incentive ◽  
Treated Wood ◽  
Reduction Process ◽  
Raw Material ◽  
Scientific Publications ◽  
Organic Carbon Storage ◽  
The Impact ◽  
Positive Effect

Abstract Both COP21 and COP22 stressed the role of forests in climate protection as a natural CO2 sink. With this in mind, the study reviewed some literature findings related to afforestation, stand level management, forest soils, peatland management and storage yards to increase the amount of CO2 absorbed by the forest ecosystem. It was shown that some of the assumptions, for example, afforestation or improved water relations in soils, may contribute to reduced CO2 levels in the atmosphere. Our research was of a review nature and consisted in seeking information in various scientific publications. For a better interpretation of the results, we have divided our research into several parts. In the first part, we analysed the importance of deforestation and afforestation in the context of CO2 accumulation. We discussed the results of research on these issues giving specific examples. We have analysed the possibility of afforestation of new land. Using the example of Poland, we have indicated problems related to this issue. We have analysed the possibility of afforestation of new land. On the example of Poland, we have indicated problems related to this problem. We have come to the conclusion that in today’s Europe, the obstacle to such efforts is the lack of land that can be afforested and the financial incentive to abandon farming for forestry is too low. In the second part, we discussed the role of forest stands in the process of CO2 accumulation and reduction. We discussed breeding treatments that can be performed on racks. We noticed their importance in the CO2 reduction process. We noticed that when the density of forests increased, this has a positive effect on organic carbon storage. We presented and discussed examples of different rotation strategies in the context of their impact on CO2 accumulation. We analysed issues related to obtaining wood raw material and possible further storage of coal or its release into the atmosphere. We have recognized that proper forest soil management is important for CO2 accumulation. Therefore, another part of the research was devoted to the discussion on the role of soil in the process of CO2 accumulation. We discussed examples of using soil for forest and non-forest purposes, looking for the answer: how does this affect CO2 accumulation? In addition, we analysed the impact of soil moisture on processes related to CO2 storage. In our research, we critically treated wood storage as a method of reducing CO2. We also discussed the problem of treating wood as a source of bioenergy. We came to the conclusion that wood as an energy source can have a positive effect on CO2 reduction. The condition is, however, that energy produced from wood replaces energy from fossil fuels. Finally, we presented and discussed financial and legal issues related to CO2 reduction activities involving forests. We have found that attempts to commercialize CO2 emission reduction units for emissions generated in forests should be linked to the environmental responsibility of companies, and as such, should not be included in the current emissions’ trading policies. In the article, we also present a Polish proposal to run coal farms. We discuss their importance in the context of the issues discussed in this article.

scholarly journals The impact of the confinement of reactants on the metal distribution in bimetallic nanoparticles synthesized in reverse micelles

2014 ◽  
Vol 5 ◽  
pp. 1966-1979 ◽  
Author(s):  
Concha Tojo ◽  
Elena González ◽  
Nuria Vila-Romeu
Keyword(s):  
Exchange Rate ◽  
Reverse Micelles ◽  
Reaction Rate ◽  
Reduction Potential ◽  
Bimetallic Nanoparticles ◽  
Chemical Reduction ◽  
Reduction Rate ◽  
Reaction Rates ◽  
Confined Media ◽  
The Impact

A kinetic study on the formation of bimetallic nanoparticles in microemulsions was carried out by computer simulation. A comprehensive analysis of the resulting nanostructures was performed regarding the influence of intermicellar exchange on reactivity. The objects of this study were metals having a difference in standard reduction potential of about 0.2–0.3 V. Relatively flexible microemulsions were employed and the concentration of the reactants was kept constant, while the reaction rate of each metal was monitored as a function of time using different reactant proportions. It was demonstrated that the reaction rates depend not only on the chemical reduction rate, but also on the intermicellar exchange rate. Furthermore, intermicellar exchange causes the accumulation of slower precursors inside the micelles, which favors chemical reduction. As a consequence, slower reduction rates strongly correlate with the number of reactants in this confined media. On the contrary, faster reduction rates are limited by the intermicellar exchange rate and not the number of reactants inside the micelles. As a result, different precursor proportions lead to different sequences of metal reduction, and thus the arrangement of the two metals in the nanostructure can be manipulated.

scholarly journals Foreign Aid Reduction and Local Civil Society: Recent Research and Policy Guidance for Donors and International NGOs

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Christopher L. Pallas ◽  
Mark Sidel
Keyword(s):  
Civil Society ◽  
Foreign Aid ◽  
Reduction Process ◽  
Legal Framework ◽  
Civil Society Organizations ◽  
Government Support ◽  
Policy Guidance ◽  
Development Objectives ◽  
The Impact

AbstractThe impact of foreign aid reduction on local civil society organizations has gained a growing amount of scholarly attention over the past several years. However, most research has focused on the experiences of local CSOs and their adaptations to reduced donor support. In this piece, we review the extant literature to offer a comprehensive perspective on the role of donors in the aid reduction process. We highlight the ways that donor planning and management of aid reduction can enhance or undermine civil society sustainability and offer six prompts for donors, designed to improve the aid reduction process. These include inventorying donors’ original development objectives; leaving behind an appropriate legal framework; facilitating local philanthropy; developing a framework for government support of CSOs; communicating aid reduction plans transparently; and supporting local adaptions to funding withdrawal.

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.

Sign in / Sign up

Export Citation Format

Share Document