Thermophillic treatment by anaerobic granular sludge as an effective approach to accelerate the electron transfer and improve the reductive decolorization of azo dyes in bioreactors
Santos, A.B. dos; Traverse, J. ; Cervantes, F.J. ; Lier, J.B. van - \ 2005
Water Science and Technology 52 (2005)1-2. - ISSN 0273-1223 - p. 363 - 369.
ontkleuring - temperatuur - textielindustrie - kleurstoffen (dyes) - azoverbindingen - afvalwaterbehandeling - anaërobe behandeling - slib - decolorization - temperature - textile industry - dyes - azo compounds - waste water treatment - anaerobic treatment - sludges - redox mediators - reactor - transformation - aqds
The effects of temperature, hydraulic retention time (HRT), and the redox mediator, thraquinone- 2,6-disulfonate (AQDS), on electron transfer and subsequent reductive decolorization of dyes rom textile wastewater was assessed in mesophilic and thermophilic anaerobic bioreactors. The results clearly show that compared to mesophilic anaerobic treatment, thermophilic treatment at 55 8C is an effective approach for increasing the electron transfer capacity in bioreactors, and thus improving the decolorization rates. At an HRT of 2.5 h and in the absence of AQDS, the color removal was 5.3-fold higher at 55 8C compared to 30 8C. Furthermore, similar decolorizations were found at 55 8C between the AQDS-free and AQDSsupplemented reactors, whereas a significant difference (up to 3.6-fold) on dye reduction occurred at 30 8C. Keywords Azo dye; color removal; electron transfer; anaerobic treatment; mesophilic; thermophilic
Reductive decolourisation of azo dyes by mesophilic and thermophilic methanogenic consortia
Cervantes, F.J. ; Santos, A.B. dos; Madrid, M.P. de; Stams, A.J.M. ; Lier, J.B. van - \ 2005
Water Science and Technology 52 (2005)1-2. - ISSN 0273-1223 - p. 351 - 356.
slib - ontkleuring - azoverbindingen - kleurstoffen (dyes) - anaërobe behandeling - redoxreacties - microbiële afbraak - afvalwaterbehandeling - sludges - decolorization - azo compounds - dyes - anaerobic treatment - redox reactions - microbial degradation - waste water treatment - anaerobic sludge - redox mediators - quinone-respiration - anthraquinone dyes - granular sludge - transformation - toxicity - bioreactors - inhibition - reactor
The contribution of acidogenic bacteria and methanogenic archaea on the reductive decolourisation of azo dyes was assessed in anaerobic granular sludge. Acidogenic bacteria appeared to play an important role in the decolourising processes when glucose was provided as an electron donor; whereas methanogenic archaea showed a minor role when this substrate was supplemented in excess. In the presence of the methanogenic substrates acetate, methanol, hydrogen and formate, methane production became important only after colour was totally removed from the batch assays. This retardation in methane production may be due to either a toxic effect imposed by the azo dyes or to the competitive behaviour of azo dyes to the methanogenic consortia for the available reducing equivalents. Keywords Azo dyes; decolourisation; methanogenic consortium; redox mediator; inhibitors
Reductive Decouloristation of Dyes by Thermophilic Anaerobic Granular Sludge
Bezerra Dos Santos, A. - \ 2005
Wageningen University. Promotor(en): Cees Buisman, co-promotor(en): Jules van Lier; F.J. Cervantes. - [S.l.] : S.n. - ISBN 9789085041344 - 176
ontkleuring - kleurstoffen (dyes) - azoverbindingen - textielindustrie - bioreactoren - afvalwaterbehandeling - anaërobe behandeling - decolorization - dyes - azo compounds - textile industry - bioreactors - waste water treatment - anaerobic treatment
The colour removal achieved under anaerobic conditions is also called reductive decolourisation, which is composed of a biological part, i.e. the reducing equivalents are biologically generated, and a chemical part, i.e. the formed electrons reduce chemically the dyes. The overall objective of this research was to explore different strategies to increase the reduction of dyes in bioreactors by using thermophilic anaerobic granular sludge and redox mediators
Effect of different redox mediators during thermophilic azo dye reduction by anaerobic granular sludge and comparative study between mesophilic (30C) and thermophilic (55C) treatments for decolourisation of textile wastewaters
Bezerra Dos Santos, A. ; Bisschops, I.A.E. ; Cervantes, F.J. ; Lier, J.B. van - \ 2004
Chemosphere 55 (2004)9. - ISSN 0045-6535 - p. 1149 - 1157.
afvalwater - degradatie - consortia - toxiciteit - waterverontreiniging - ontkleuring - anaërobe behandeling - afvalwaterbehandeling - redoxreacties - azoverbindingen - kleurstoffen (dyes) - slib - waste water - degradation - consortia - toxicity - water pollution - decolorization - anaerobic treatment - waste water treatment - redox reactions - azo compounds - dyes - sludges - waste-water - reactor - carbon - bn6
The impact of different redox mediators on colour removal of azo dye model compounds and textile wastewater by thermophilic anaerobic granular sludge (55 C) was investigated in batch assays. Additionally, a comparative study between mesophilic (30 C) and thermophilic (55 C) colour removal was performed with textile wastewater, either in the presence or absence of a redox mediator
The impact of different redox mediators on colour removal of azo dye model compounds and textile wastewater by thermophilic anaerobic granular sludge (55 degreesC was investigated in batch assays. Additionally, a comparative study between mesophilic (30 degreesC and thermophilic (55 degreesC colour removal was performed with textile wastewater, either in the presence or absence of a redox mediator. The present work clearly evidences the advantage of colour removal at 55 degreesC compared with 30 degreesC when dealing with azo coloured wastewaters. The impact of the redox mediators anthraquinone-2,6-disulfonate (AQDS), anthraquinone-2-sulfonate (AQS) and riboflavin was evident with all dyes, increasing decolourisation rates up to 8-fold compared with the mediator-free incubations. The generation of the hydroquinone form AH(2)QDS, i.e. the reduced form of AQDS, was extremely accelerated at 55 degreesC compared with 30 degreesC. Furthermore, no lag-phase was observed at 55 degreesC. Based on the present results we postulate that the production/transfer of reducing equivalents was the process rate-limiting step, which was accelerated by the temperature increase. It is conclusively stated that 55 degreesC is a more effective temperature for azo dye reduction than 30 degreesC which on the one hand can be attributed to the faster production/transfer of reducing equivalents, but also to the decrease in activation energy requirements. (C) 2004 Elsevier Ltd. All rights reserved.
The contribution of biotic and abiotic processes during azo dye reduction in anaerobic sludge
Zee, F.P. van der; Bisschops, I.A.E. ; Blanchard, V.G. ; Bouwman, R.H.M. ; Lettinga, G. ; Field, J.A. - \ 2003
Water Research 37 (2003)13. - ISSN 0043-1354 - p. 3098 - 3109.
rioolafvalwater - anaërobe behandeling - azoverbindingen - kleurstoffen (dyes) - redoxreacties - afvalwaterbehandeling - sewage effluent - anaerobic treatment - azo compounds - dyes - redox reactions - waste water treatment - redox mediators - decolorization - bacteria - system
Azo dye reduction results from a combination of biotic and abiotic processes during the anaerobic treatment of dye containing effluents. Biotic processes are due to enzymatic reactions whereas the chemical reaction is due to sulfide. In this research, the relative impact of the different azo dye reduction mechanisms was determined by investigating the reduction of Acid Orange 7 (AO7) and Reactive Red 2 (RR2) under different conditions. Reduction rates of two azo dyes were compared in batch assays over a range of sulphide concentrations in the presence of living or inactivated anaerobic granular sludge
Azo dye reduction results from a combination of biotic and abiotic processes during the anaerobic treatment of dye containing effluents. Biotic processes are due to enzymatic reactions whereas the chemical reaction is due to sulfide. In this research, the relative impact of the different azo dye reduction mechanisms was determined by investigating the reduction of Acid Orange 7 (AO7) and Reactive Red 2 (RR2) under different conditions. Reduction rates of two azo dyes were compared in batch assays over a range of sulphide concentrations in the presence of living or inactivated anaerobic granular sludge. Biological dye reduction followed zero order kinetics and chemical dye reduction followed second-order rate kinetics as a function of sulfide and dye concentration. Chemical reduction of the dyes was greatly stimulated in the presence of autoclaved sludge; whereas chemical dye reduction was not affected by living or gamma-irradiated-sludge. Presumably redox-mediating enzyme cofactors released by cell lysis contributed to the stimulatory effect. This hypothesis was confirmed in assays evaluating the chemical reduction of AO7 utilizing riboflavin, representative of the heat stable redox-mediating moieties of common occurring flavin enzyme cofactors. Sulfate influenced dye reduction in accordance to biogenic sulfide formation from sulfate reduction. In assays lacking sulfur compounds, dye reduction only readily occurred in the presence of living granular sludge, demonstrating the importance of enzymatic mechanisms. Both chemical and biological mechanisms of dye reduction were greatly stimulated by the addition of the redox-mediating compound, anthraquinone-disulfonate. Based on an analysis of the kinetics and demonstration in lab-scale upward-flow anaerobic sludge bed reactors, the relative importance of chemical dye reduction mechanisms in high rate anaerobic bioreactors was shown to be small due to the high biomass levels in the reactors. (C) 2003 Elsevier Science Ltd. All rights reserved.
Activated Carbon as an Electron Acceptor and Redox Mediator during the Anaerobic Biotransformation of Azo Dyes
Zee, F.P. van der; Bisschops, I.A.E. ; Lettinga, G. ; Field, J.A. - \ 2003
Environmental Science and Technology 37 (2003)2. - ISSN 0013-936X - p. 402 - 408.
slib - koolstof - redoxreacties - verontreinigende stoffen - azoverbindingen - kleurstoffen (dyes) - anaërobe behandeling - oxidatie - afvalwaterbehandeling - sludges - carbon - redox reactions - pollutants - azo compounds - dyes - anaerobic treatment - oxidation - waste water treatment - sp strain bn6 - oxidative dehydrogenation - catalytic-oxidation - hydrogen-sulfide - fluidized-bed - reduction - sludge - decolorization - degradation - quinones
The role of AC as redox mediator in accelerating the reductive transformation of pollutants as well as a terminal electron acceptor in the biological oxidation of an organic substrate is described. This study explores the use of AC as an immobilized redox mediator for the reduction of a recalcitrant azo dye in laboratory-scale anaerobic bioreactors, using volatile fatty acids as electron donor
Activated carbon (AC) has a long history of applications in environmental technology as an adsorbent of pollutants for the purification of drinking waters and wastewaters. Here we describe novel role of AC as redox mediator in accelerating the reductive transformation of pollutants as well as a terminal electron acceptor in the biological oxidation of an organic substrate. This study explores the use of AC as an immobilized redox mediator for the reduction of a recalcitrant azo dye (hydrolyzed Reactive Red 2) in laboratory-scale anaerobic bioreactors, using volatile fatty acids as electron donor. The incorporation of AC in the sludge bed greatly improved dye removal and formation of aniline, a dye reduction product. These results indicate that AC acts as a redox mediator. In supporting batch experiments, bacteria were shown to oxidize acetate at the expense of reducing AC. Furthermore, AC greatly accelerated the chemical reduction of an azo dye by sulfide. The results taken as a whole clearly suggest that AC accepts electrons from the microbial oxidation of organic acids and transfers the electrons to azo dyes, accelerating their reduction. A possible role of quinone surface groups in the catalysis is discussed.
Anaerobic azo dye reduction
Zee, F.P. van der - \ 2002
Wageningen University. Promotor(en): G. Lettinga; J.A. Field. - S.l. : S.n. - ISBN 9789058086105 - 142
anaërobe behandeling - azoverbindingen - kleurstoffen (dyes) - redoxreacties - antrachinonen - anaerobic treatment - azo compounds - dyes - redox reactions - anthraquinones
Azo dyes, aromatic moieties linked together by azo (-N=N-) chromophores, represent the largest class of dyes used in textile-processing and other industries. The release of these compounds into the environment is undesirable, not only because of their colour, but also because many azo dyes and their breakdown products are toxic and/or mutagenic to life. To remove azo dyes from wastewater, a biological treatment strategy based on anaerobic reduction of the azo dyes, followed by aerobic transformation of the formed aromatic amines, holds promise. However, the first stage of the process, anaerobic azo dye reduction, proceeds relatively slow. Therefore, this thesis research aimed at optimising anaerobic azo dye reduction, by studying the reaction mechanism and by consequently applying the obtained insights.
In this thesis it is shown that non-adapted anaerobic granular sludge has the capacity to non-specifically reduce azo dyes. As there was no correlation between a dye's reduction rate and its molecular characteristics (i.e. its size and its number of sulphonate groups and other polar substituents), it is unlikely that the mechanism of azo dye reduction involves cell wall penetration. Moreover, the presence of bacteria is not a prerequisite: azo dyes can also be reduced by sulphide in a purely chemical reaction. As dye containing wastewater usually contains sulphate and other sulphur species that will be biologically reduced to sulphide during treatment in anaerobic bioreactors, azo dye reduction will be a combination of biotic and abiotic processes. However, it was demonstrated that under normal conditions in high-rate anaerobic bioreactors (high sludge content, moderate sulphide levels), chemical azo dye reduction by sulphide hardly contributes to the overall reaction. Anaerobic azo dye reduction is therefore mainly a biological process, either a direct enzymatically catalysed reaction involving non-specific enzymes or a reaction with enzymatically reduced electron carriers. Azo dye reduction by sludge that had not earlier been exposed to dyes was found to relate to the oxidation of endogenous substrate and, especially, to the oxidation of hydrogen when present in bulk concentrations. Enrichment was required for the utilisation of electrons from volatile fatty acids for dye reduction.
Examination of the reduction of twenty chemically distinct azo dyes by anaerobic granular sludge revealed a large variation in the reaction rates. Especially reactive azo dyes with triazyl reactive groups were slowly reduced. For these common occurring reactive dyes, long contact times may be necessary to reach a satisfying extent of decolourisation. Consequently, they pose a serious problem for applying high-rate anaerobic treatment as the first stage in the biological degradation of azo dyes. However, this problem can be overcome by using redox mediators, compounds that speed up the reaction rate by shuttling electrons from the biological oxidation of primary electron donors or from bulk electron donors to the electron-accepting azo dyes.
It was observed that one of the constituent aromatic amines of the azo dye Acid Orange 7 had an autocatalytic effect on the dye's reduction, probably by acting as a redox mediator. Other compounds, e.g. the artificial redox mediator anthraquinone-2,6-disulphonate (AQDS), a compound that is known to catalyse the reductive transfer of several pollutants, and the commonly occurring flavin enzyme cofactor riboflavin, were found to be extremely powerful catalysts, capable of raising the pseudo first-order reaction rate constants by orders of magnitude. Moreover, a large stimulatory effect was found for autoclaved sludge, presumably due to the release of internal electron carriers, e.g. enzyme cofactors like riboflavin, during autoclaving.
AQDS was successfully applied to improve the continuous reduction of Reactive Red 2 (a reactive azo dye with a triazyl reactive group) in a lab-scale anaerobic bioreactor that was operated under moderate hydraulic loading conditions. Without AQDS, the reactor's dye removal efficiency was very low, which gave rise to severe dye toxicity towards the biological activity. Addition of catalytic concentrations of AQDS to the reactor influent caused an immediate increase of the dye removal efficiency and recovery of the methane production. Eventually, almost complete RR2 colour removal could be reached.
Though effective AQDS dosage levels are low, continuous dosing has disadvantages with respect to the costs and the discharge of this biologically recalcitrant compound. Therefore, the feasibility of activated carbon (AC), which is known to contain quinone groups at its surface, to act alternatively as an insoluble/immobilised redox mediator was explored. Incorporation of AC in the sludge of lab-scale anaerobic bioreactors that treated Reactive Red 2 in synthetic wastewater containing volatile fatty acid as primary electron donor resulted in enhanced continuous dye reduction as compared to the control reactors without AC. The effect of AC was in large excess of its dye adsorption capacity. In addition, it was shown that bacteria could utilise AC as terminal electron acceptor in the oxidation of acetate. Moreover, AC catalysis of chemical azo dye reduction by sulphide was demonstrated. These results clearly suggest that AC accepts electrons from the microbial oxidation of organic acids and transfers the electrons to azo dyes, thereby accelerating their biological reduction.
The research presented in this thesis makes clear that the reduction of azo dyes can be optimised by utilising redox mediators, i.e. either by continuous dosing of soluble quinones or by incorporation of AC in the sludge blanket. The potential of using redox mediators is probably not limited to enhancing azo dye reduction but may be extrapolated to other non-specific reductive (bio)transformations, e.g. reduction of halogenated or nitroaromatic compounds. The potential of using redox mediators is furthermore probably not limited to wastewater treatment but may also apply to bioremediation of soils polluted with e.g. polychlorinated solvents or nitroaromatic pesticides.
Integrated and sequential anaerobic/aerobic biodegradation of azo dyes
Tan, N.G.C. - \ 2001
Wageningen University. Promotor(en): G. Lettinga; J.A. Field. - S.l. : S.n. - ISBN 9789058083746 - 104
biodegradatie - bioremediëring - kleurstoffen (dyes) - azoverbindingen - biodegradation - bioremediation - dyes - azo compounds
Azo dyes constitute a major class of environmental pollutants accounting for 60 to 70% of all dyes and pigments used. These compounds are characterized by aromatic moieties linked together with azo groups (-N=N-). The release of azo dyes into the environment is a concern due to coloration of natural waters and due to the toxicity, mutagenicity and carcinogenicity of the dyes and their biotransformation products. Therefore, considerable attention has been given to evaluating the fate of azo dyes during wastewater treatment and in the natural environment. Azo dyes require an anaerobic and an aerobic phase for their complete biodegradation. Therefore, the aim of this thesis was to evaluate the mineralization of azo dyes under integrated and sequential anaerobic/aerobic conditions. These conditions were applied on three azo dyes, Mordant Orange 1 (MO1), 4-phenylazophenol (4-PAP) and Mordant Yellow 10 (MY10). Since many azo dyes are substituted with a sulfonic acid group, special attention was paid to the sulfonated azo dyes and their biodegradation products, the sulfonated aromatic amines.
The first step in the biodegradation of azo dyes is the azo dye reduction resulting in the formation of the aromatic amines. The influence of oxygen on the azo dye reduction of MO1 was tested in order to evaluate the integrated anaerobic/aerobic conditions. The co-substrate ethanol was successfully applied as electron donor for azo dye reduction and also created anaerobic microniches to facilitate anaerobic azo dye reduction in the presence of oxygen. Increasing oxygen concentrations showed decreasing azo dye-reduction rates with ethanol as co-substrate. These rates were higher when applying acetate as co-substrate. Moreover, Nedalco granular sludge could withstand better with the applied integrated anaerobic/aerobic conditions than Shell granular sludge.
Since none of the expected aromatic amines from MO1 was degraded, further research was conducted to evaluate the aerobic biodegradation of aromatic amines. MY10 and 4-PAP were tested under integrated anaerobic/aerobic conditions. All aromatic amines were removed if sufficient oxygen was present. Oxygen was primarily used to oxidize co-substrate and if sufficient oxygen was available the formed aromatic amines were further degraded. The removal of 4-aminobenzenesulfonic acid (4-ABS) was only possible after bioaugmentation of a 4-ABS-degrading enrichment culture. The results from the biodegradation study of 4-AP indicated that 4-aminophenol was removed due to autoxidation. Degradation of azo dyes is possible under integrated anaerobic/aerobic conditions if co-substrate and oxygen are in balance.
In the sequential anaerobic/aerobic bioreactor, the azo dye MY10 was successfully mineralized. Its constituent aromatic amines, 5-aminosalicylic acid (5-ASA) and 4-ABS, were both recovered in the anaerobic stage and degraded in the aerobic stage. Biodegradation of the 4-ABS was only possible after bioaugmentation with a 4-ABS-degrading enrichment culture. High recovery of sulfate indicated mineralization of 4-ABS. After long-term exposure to 5-ASA, the anaerobic granular sludge showed the ability to degrade this compound.
It was observed that the degradation of the sulfonated aromatic amine 4-ABS only proceeded after bioaugmentation of a specialized enrichment culture. Therefore, the ultimate biodegradability of the sulfonated aromatic amines is questionable. To investigate this matter, the fate of sulfonated aromatic amines with natural mixed cultures was evaluated in aerobic and anaerobic batch assays and bioreactor experiments. None of the ten tested compounds was degraded under anaerobic conditions and only 2-ABS and 4-ABS were aerobically mineralized. This was observed in batch as well as in bioreactor experiments. Degradation of the 2-ABS and 4-ABS was found with inoculum sources that were historically polluted with sulfonated aromatic compounds. At concentrations up to 1.0 g l -1 , none of the tested sulfonated aromatic amines showed any toxicity towards anaerobic and aerobic biomass.
The results of this research demonstrated that azo dyes are mineralized under integrated and sequential anaerobic/aerobic conditions. Due the difficulties with balancing the supply of co-substrate and oxygen in integrated anaerobic/aerobic systems, the sequential anaerobic/aerobic conditions are recommended for the mineralization of azo dyes. However, during the degradation of sulfonated azo dyes, many different sulfonated aromatic amines will be formed and these compounds are not likely to be degraded aerobically. Therefore, special attention should be paid on the removal of these compounds