Anaerobic biotransformation of nitroanilines enhanced by the presence of low amounts of carbon materials

Three microporous activated carbons -original (AC0), chemical oxidized with HNO3 (ACHNO3) and thermal treated (ACH2)-, and three mesoporous carbons - xerogels (CXA and CXB) and nanotubes (CNT)-, were tested on the biological reduction of o-, m- and p-nitroaniline (NoA) at a concentration above the half maximal inhibitory concentration (IC50) for a methanogenic consortium degrading a mixture of volatile fatty acids (VFA) containing acetate, propionate and butyrate. NoAs were only partially reduced in the absence of carbon materials (CM). Rates were dependent on the nitro group position, increasing in the order metha>para>ortho. CM lead to NoAs almost total reduction and at higher rates. With AC0 and ACH2, rates increased 3-fold, 4-fold and 8 fold for o-, m- and p-NoA, respectively

Improvement of the upflow anaerobic sludge blanket reactor performance for azo dye reduction by the presence of low amounts of activated carbon

Activated carbon (AC) was investigated as redox mediator of the azo dye Acid Orange 10 (AO10) anaerobic biodegradation in a laboratory scale Upflow Anaerobic Sludge Blanket (UASB). During reactor operation, the effect of AC concentration and the hydraulic retention time (HRT) were investigated and better results were obtained with 0.15 g of AC per g of Volatile Suspended Solids (VSS) and 10 h, respectively. In the mediated reactor, with an HRT of 10 h, high colour and COD removal was obtained, ~70% and ~85%, respectively. In the control, thought similar COD removal, AO10 decolourisation was only 20%, evidencing the ability of AC to accelerate the reduction reactions in continuous reactors

Fate of aniline and sulfanilic acid in UASB bioreactors under denitrifying conditions

Two upflow anaerobic sludge blanket (UASB) reactors were operated to investigate the fate of aromatic amines under denitrifying conditions. The feed consisted of synthetic wastewater containing aniline and/or sulfanilic acid and a mixture of volatile fatty acids (VFA) as the primary electron donors. Reactor 1 (R1) contained a stoichiometric concentration of nitrate and Reactor 2 (R2) a stoichiometric nitrate and nitrite mixture as terminal electron acceptors. The R1 results demonstrated that aniline could be degraded under denitrifying conditions while sulfanilic acid remains. The presence of nitrite in the influent of R2, caused a chemical reaction that led to immediate disappearance of both aromatic amines and the formation of an intense yellow coloured solution. HPLC analysis of the influent solution, revealed the emergence of three product peaks: the major one at retention time (Rt) 14.3 min and two minor at Rt 17.2 and 21.5 min. In the effluent, the intensity of the peaks at Rt 14.3 and 17.2 min was very low and of that at Rt 21.5 min increased (~3-fold). Based on the mass spectrometry analysis, we propose the structures of some possible products, mainly azo compounds. Denitrification activity tests suggest that biomass needed to adapt to the new coloured compounds, but after a 3 days lag phase, activity is recovered and the final (N2 + N2O) is even higher than that of the control.Fundação para a Ciência e a Tecnologia (FCT

Lab-scale bioreactors for aromatic amines reduction under denitrification conditions

Under anaerobic conditions, azo dyes are readily decolourised as a result of the reductive transformation of the azo group leading to the formation of aromatic amines which are known to be even more toxic than the original dyes. A logical concept for the removal of azo dyes in biological wastewater treatment systems is based on the combination of anaerobic/aerobic treatment, for the degradation of also aromatic amines. A drawback of aerobic treatment is that many aromatic amines are prone to autoxidation. Nitrate/Nitrite are powerful electron acceptors as alternative to oxygen, avoiding the autoxidation. Our research consisted of operating two bioreactors with the objective to investigate the fate of aromatic amines under denitrifying conditions. The reactors were fed with synthetic wastewater contained aniline and/or sulfanilic acid and a mixture of volatile fatty acids as the primary electron donors. Reactor 1 (R1) contained a stoichiometric concentration of nitrate and Reactor 2 (R2) a mixture of nitrate and nitrite as terminal electron acceptors. The R1 results demonstrated that aniline could be degraded under denitrifying conditions while sulfanilic acid remains. The presence of nitrite in the effluent of R2, at low pH, caused a chemical reaction that led to immediate disappearance of both aromatic amines and the formation of an orange colour solution. HPLC analysis revealed the presence of phenol as a product of aniline. Other compounds were detected by LC_MS. The overall COD removal was always higher in R1 than in R2, suggesting toxicity of nitrite and/or the formed products. Whereas a replacement of amino-groups by hydroxyl-groups holds promise for biodegradability, the results indicate that the chemical reaction is more complex, resulting in the formation of compounds that were not mineralized during the course of the experiment

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

The surface chemistry of a commercial AC (AC0) was selectively modified, without changing significantly its textural properties, by chemical oxidation with HNO3 (ACHNO3 ) and O2 (ACO2 ), and thermal treatments under H2 (ACH2) or N2 (ACN2 ) flow. The effect of modified AC on anaerobic chemical dye reduction was assayed with sulphide at different pH values 5, 7 and 9. Four dyes were tested: Acid Orange 7, Reactive Red 2, Mordant Yellow 10 and Direct Blue 71. Batch experiments with low amounts of AC (0.1 g L−1) demonstrated an increase of the first-order reduction rate constants, up to 9-fold, as compared with assays without AC. Optimum rates were obtained at pH 5 except for MY10, higher at pH 7. In general, rates increased with increasing the pH of point zero charge (pHpzc), following the trend ACHNO3 < ACO2 < AC0 < ACN2 < ACH2 . The highest reduction rate was obtained for MY10 with ACH2 at pH 7, which corresponded to the double, as compared with non-modified AC. In a biological system using granular biomass, ACH2 also duplicated and increase 4.5-fold the decolourisation rates of MY10 and RR2, respectively. In this last experiment, reaction rate was independent of AC concentration in the tested range 0.1–0.6 g L−1.This work was supported by the PTDC/AMB/69335/2006 project grants. L Pereira holds a Pos-Doc fellowship (SFRH/BPD/20744/2004) and R. Pereira holds a fellowship (SFRH/BPD/39086/2007) from Fundacao para a Ciencia e Tecnologia. F.J. Cervantes greatly acknowledges a grant from Council of Science and Technology of Mexico (Grant SEP-CONACYT-C02-55045)

Activated carbon as a redox mediator: effect of AC surface chemistry and solution pH on dye reduction

Azo dyes have a wide application in food, pharmaceutical, textile, leather, cosmetics and paper industries. These are the largest and most versatile classes of dyes used, but are recalcitrant to biodegradation and many are carcinogenic or cytotoxic. Their removal is a major concern when treating dye-containing wastewaters. Under anaerobic conditions, they are non-specifically reduced, a fortuitous but often slow process. Acceleration can be achieved by using electron-shuttling compounds that speed up the reaction, acting as redox mediators. Activated carbon (AC) has been shown as a feasible redox mediator and adsorbent material. In this study, the surface chemistry of a commercial AC (AC0) was selectively modified, without changing significantly its textural properties, by means of chemical oxidation with HNO3 (ACHNO3) (mild acidic surface properties) and thermal treatments under H2 (ACH2) or N2 (ACN2) flow (basic surface properties). Oxidation with 5% O2 (ACO2) ends not only in surface chemistry changes (acidic properties), but also in the textural properties. The effect of modified AC on anaerobic chemical dye reduction was assayed with sulphide as a reducing agent at different pH values: 5, 7 and 9. Four dyes from different classes were tested: Acid Orange 7, Reactive Red 2, Mordant Yellow 10 and Direct Blue 71. Batch experiments with low amounts of AC (0.1 g.L-1) demonstrated an increase of the first-order reduction rate constants (~ 9-fold) for all the dyes tested as compared with assays without AC. The reduction of AO7 and MY10 was highly dependent on the pH, with optimum rates at pH 5 and 7, respectively. Higher rates of RR2 and DB71 reduction were obtained at pH 5. In general, an increase of the rates with increasing the pHpzc was observed, following the trend ACHNO3 < ACO2 < AC0 < ACN2 < ACH2. Comparing the rates of single dyes, MY10 was reduced at the highest rate (12 ± 1 d-1) and RR2 at the lowest (1.3 ± 0.1 d-1)

Magnetic carbon composites as recycling electron shuttles on anaerobic biotransformations

Book of Abstracts of CEB Annual Meeting 2017[Excerpt] The unique properties of magnetic nanoparticles (MNP), such as high surface area, magnetic, sorption and catalytic characteristics, make them very versatile for many applications in different areas including environmental remediation, as catalysts, adsorbents, immobilising agents for microorganisms and enzymes, and as supports for biofilm growth and water disinfectants. In order to improve their stability and to introduce additional surface properties and functionalities, MNP can be coated with carbon materials (CM) due to their chemical stability, biocompatibility and possibility of tailoring their textural and surface chemical properties for specific applications [1]. We have previously proved that various CM, including activated carbon, carbon xerogels and carbon nanotubes (CNT), can be used as redox mediators (RM) in anaerobic biotransformation, accelerating the electron transfer and, consequently, the reduction rates of organic compounds [1,2]. The combination of CM with MNP offers the possibility of creating magnetic carbon composites with synergistic properties: the adsorptive and catalytic properties of both and the magnetic character of MNP, improving the material performance and rendering it easier to be retained and recovered, by applying a magnetic field. [...]info:eu-repo/semantics/publishedVersio

Soybean (Glycine max) as a versatile biocatalyst for organic synthesis

A series of aliphatic and aromatic aldehydes and ketones were reduced using plant cell preparations of Glycine max seeds (soybean). The biotransformation of five aromatic aldehydes in water, at room temperature afforded the corresponding alcohols in excellent yields varying from 89 to 100%. Two prochiral aromatic ketones yielded the alcohol in very low conversion, 1% and to 4%; however with good enantiomeric excess (ee) of 99 and 79%, respectively. Additionally, three prochiral and one cyclic aliphatic ketones produced the corresponding alcohols in moderate yields varying from 10 to 58% and ee varying from 73 to 99%. Hydrolysis of two aromatic esters yielded the expected carboxylic acids in 49 and 66%. Most of the obtained alcohols have commercial value as cosmetic fragrances. Although, the enzymes present in soybean (reductase/lipase) has not been defined, the reaction is an important route for the preparation of pure alcohols and carboxylic acid, with low cost and environmental impact.Keywords: Glycine max, biocatalysis, bioreduction, aldehydes and ketones, ester hydrolysi

A wide perspective of carbon materials as catalysts for bioremediation of emerging pollutants and methanogenesis

Biotransformation of emerging pollutants under anoxic conditions can be accelerated by carbon materials (CM) acting as redox mediators. CM have been also extensively reported as facilitating external electron transfer in methanogenic processes. Here, different CM including magnetic carbon materials (C@MNP), were prepared, characterized and applied as RM on the biological reduction of Acid Orange 10 (AO10) and ciprofloxacin (CIP). CIP could be biologically removed in the presence of CNT and CNT@2%Fe, and AO10 decolourisation rates were 79-fold higher in the assays with CNT@2%Fe. The effect of carbon nanotubes (CNT) on the activity of several pure cultures of methanogens was also investigated, demonstrating that CNT could accelerate up to 17-fold the methane production rate. It is evident from this work that carbon materials with different chemical and textural characteristics can accelerate significantly bioremediation and methanogenic processes. The fact that concentrations as low as 0.1 g/L were used with positive effects, is remarkable in terms of economic feasibility of using CM as efficient catalysts in both processes.info:eu-repo/semantics/publishedVersio