Monoazo and diazo dye decolourisation studies in a methanogenic UASB reactor

Evaluation of a Microbial Consortium and Selection of a Support in an Anaerobic Reactor Directed to the Bio-Treatment of Wastewater of the Textile Industry

The dyeing processes of the textile industry generate waste products such as unfixed dyes, phenolic surfactants and heavy metals. These constitute an environmental problem for the bodies receiving their wastewater due to the interruption of the lighting in the aquatic environment and the release of toxic molecules by the decomposition of the dyes. There are several treatment methods, of which biological methods are the most feasible. In the current study, the I5-ESPE microbial consortium was obtained and evaluated on the components of textile wastewater, in addition to the selection of a support for an anaerobic reactor that is directed to the treatment of effluents from the textile industry. Two microbial consortia were achieved by exposure to air in Pseudomonas culture medium modified with direct dyes Red 23 and Blue 106, evaluating their removal capacity of the reactive dyes Navy 171, Red 141 and Yellow 84. The consortium I5-ESPE was selected for its greatest action, yielding approximately 95% removal. Its tolerance to phenol was also determined; we reached 98% removal of chromium(VI) and 67% of total chromium under anaerobic conditions and some 25% zinc in aerobiosis. The reduction in the chemical oxygen demand (COD) was evaluated with (57.03%) and without (31.47%) aeration. The species Staphylococcus xylosus, Saccharomyces cerevisiae and Candida tropicalis were identified prior to treatment of textile wastewater, as well as Enterobacter cloacae and Bacillus megaterium after treatment. Bacillus subtilis was present throughout the process. We evaluated coconut shell as a support for an anaerobic reactor, and it demonstrated better physical characteristics than plastic and common rock, in addition to similar results in the reduction in COD of 50%, volatile suspended solids of 2545.46 mg/L and total suspended solids of 282.82 mg/L.

Comparative Anaerobic Decolorization of Azo Dyes by Carbon-Based Membrane Bioreactor

This study used a novel integrated technology of ceramic supported carbon membrane (CSCM) to degrade azo dyes through an anaerobic mixed culture. The CSCM worked simultaneously as biofilm support, redox mediator, and nano-filter to enhance the dye decolorization efficiency. The decolorization of Acid Orange 7 (AO7) was initially investigated with and without microorganisms in both ceramic support (CS) and CSCM reactors. The CSCM bioreactor (B-CSCM), operated with microorganisms, gave a maximum decolorization of 98% using a CSCM evolved from 10% weight (wt.) of Matrimid 5218 solution. To know the influence of permeate flow, feed concentration, and dye structure on the decolorization process, different B-CSCMs for dye removal experiments were studied over monoazo AO7, diazo Reactive Black 5 (RB5), and triazo Direct Blue 71 (DB71). The highest color removal, operated with 50 mg·L−1 feed solution and 0.05 L·m−2·h−1 of permeate flux, was 98%, 82%, and 72%, respectively, for AO7, RB5, and DB71. By increasing these parameters to 100 mg·L−1 and 0.1 L·m−2·h−1, the decolorization rate of dye solution still achieved 37% for AO7, 30% for RB5, and 26% for DB71. In addition, the system was run for weeks without apparent loss of activity. These findings make evident that the combined phenomena taking place in CSCM bioreactor result in an efficient, cost-effective, and ecofriendly azo dye decolorization method.

High-rate anaerobic decolorization of methyl orange from synthetic azo dye wastewater in a methane-based hollow fiber membrane bioreactor

Anaerobic biological techniques are widely used in the reductive decolorization of textile wastewater. However, the decolorization efficiency of textile wastewater by conventional anaerobic biological techniques is generally limited due to the low biomass retention capacity and short hydraulic retention time (HRT). In this study, a methane-based hollow fiber membrane bioreactor (HfMBR) was initially inoculated with an enriched anaerobic methane oxidation (AOM) culture to rapidly form an anaerobic biofilm. Then, synthetic azo dye wastewater containing methyl orange (MO) was fed into the HfMBR. MO decolorization efficiency of ∼ 100 % (HRT = 2 to 1.5 days) and maximum decolorization rate of 883 mg/L/day (HRT = 0.5 day) were obtained by the stepwise increase of the MO loading rate into the methane-based HfMBR. Scanning electron microscopy (SEM) and fluorescence in situ hybridization (FISH) analysis visually revealed that archaea clusters formed synergistic consortia with adjacent bacteria. Quantitative PCR (qPCR), phylogenetic and high-throughput sequencing analysis results further confirmed the biological consortia formation of methane-related archaea and partner bacteria, which played a synergistic role in MO decolorization. The high removal efficiency and stable microbial structure in HfMBR suggest it is a potentially effective technique for high-toxic azo dyes removal from textile wastewater.

Silver nanoparticles in dye effluent treatment: A review on synthesis, treatment methods, mechanisms, photocatalytic degradation, toxic effects and mitigation of toxicity

The current scenario of water resources shows the dominance of pollution caused by the draining of industrial effluents. The polluted waters have resulted in severe health and environmental hazards urging for a suitable alternative to resolve the implications. Various physical and chemical treatment steps currently in use for dye effluent treatment are more time consuming, cost-intensive, and less effective. Alternatively, nanoparticles due to their excellent surface properties and chemical reactivity have emerged as a better solution for dye removal and degradation. In this regard, the potential of silver nanoparticles in dye effluent treatment was greatly explored. Efforts were taken to unravel the kinetics and statistical optimization of the treatment conditions for the efficient removal of dyes. In addition, the role of silver nanocomposites has also experimented with colossal success. On the contrary, studies have also recognized the mechanisms of silver nanoparticle-mediated toxicity even at deficient concentrations and their deleterious biological effects when present in treated water. Hence, the fate of the silver nanoparticles released into the treated water and sludge, contaminating the soil, aquatic environment, and underground water is of significant concern. This review summarizes the current state of knowledge regarding the use of silver nanoparticles and silver-based nanocomposites in effluent treatment and comprehends the recent research on mitigation of silver nanoparticle-induced toxicity.

Degradation of organic pollutants by anaerobic methane-oxidizing microorganisms using methyl orange as example

Anaerobic oxidation of methane (AOM) microorganisms widespread in nature and they are able to utilize methane as electron donor to reduce sulfate, nitrate, nitrite, and high valence metals. However, whether persistent organic contaminants can also be degraded remains unknown. In this study, the organic pollutant methyl orange (MO) was used to address this open question. The initial concentration of MO affected its degradation efficiency and higher concentration (>100 mg/L) caused considerable inhibition. A ¹³CH₄ isotope experiment indicated that methane oxidation was involved in MO degradation, which produced N, N-dimethyl-p-phenylenediamine, and 4-aminobenzenesulfonic acid corresponded stoichiometrically. During the long-term experiment, the maximum degradation rate was 47.91 mg/(L·d). The percentage of Candidatus Methanoperedens and Pseudoxanthomonas significantly increased after 30-d of MO degradation under CH₄ conditions; moreover, Candidatus Methanoperedens dominated (46.83%) the microbial community. Candidatus Methanoperedens, either alone or in combination with Pseudoxanthomonas, utilized methane as the sole carbon source to degrade MO via direct interspecies electron transfer or the syntrophy pathway. This study will add to our understanding of the functions and applications of AOM microorganisms.

Corrugated stainless-steel mesh as a simple engineerable electrode module in bio-electrochemical system: Hydrodynamics and the effects on decolorization performance

The application of bio-electrochemical system (BESs) is strongly depended on the development of the engineering applicable electrode. Here we described an economical and readily processable electrode module with three-dimensional structure, the corrugated stainless-steel mesh electrode module (c-SMEM). This novel developed electrode module was demonstrated to provide a good hydrodynamic characteristic and significantly enhanced the decolorization performance of the BES when serving for treating azo dye (acid orange 7, AO7) containing wastewater. Compared to the conventional planar electrodes module (p-SMEM), c-SMEM was found to prolong the mean residence time (MRT_θ) of AO7 and change the flow pattern closer to the plug flow. As a result, the maximum enhancement of the volumetric decolorization rate (vDR) can reach to 255%, even when the c-SMEM and p-SMEM have the same electrode surface area. In addition, a techno-economic analysis model was established to elucidated the effects of the decolorization performance and the material cost on the initial capital cost, which revealed the BES with c-SMEM could be economically comparable to or even better than the traditional bio-decolorization technologies. These results suggest c-SMEM holds great potential for engineering application, which may help paving the way of applying BES at large-scale.

Exploring the potential of anaerobic sulfate reduction process in treating sulfonated diazo dye: Microbial community analysis using bar-coded pyrosequencing

Anaerobic decolorization and biotransformation of azo dye was investigated in a sulfate-reducing environment. Batch reactor studies were performed with mixed cultures of anaerobic sulfate-reducing bacteria (SRBs) enriched from anaerobic digester sludge. Complete sulfate and color removal were achieved in batch experiments with different initial dye concentrations (50-2500mg/L) and 1000mg/L of sulfate. Induction of various oxidoreductive enzyme activities such as phenol oxidase, veratryl alcohol oxidase, lignin peroxidase, and azo reductase was studied to understand their involvement in dye metabolism under anoxic environment. The degradation of Cotton Red B was confirmed using high-performance liquid chromatography and gas chromatography-mass spectroscopy. Sulfidogenic sludge demonstrated excellent dye degradation and mineralization ability, producing aniline and 1,4-diamino benzene as metabolites. A barcoded 16S rRNA gene-pyrosequencing approach was used to assess the bacterial diversity in the sludge culture and a phylogenetic tree was constructed for sulfate-reducing bacteria.

Inhibitory effect and mechanism of azo dyes on anaerobic methanogenic wastewater treatment: Can redox mediator remediate the inhibition?

Inhibitory effect of azo dyes on anaerobic methanogenic wastewater treatment (AMWT) has been studied mainly focusing on biological toxicity in the batch test with simulated sole co-substrate. Detailed information on inhibitory effect and mechanism of azo dyes during the long-term operation with real complex co-substrate is limited. Moreover, whether redox mediator (RM) could remediate the inhibition is still unclear in previous studies, especially under the complex scenario. In this study, the real textile wastewater with alternative concentrations of azo dyes (0-600 mg/L) were used to operate a lab-scale high-rate anaerobic methanogenic bioreactor for 127 days, and 50 μM anthraquinone-2-sulfonate (AQS) as RM was added at the last period of operation. Azo dyes with concentration of 600 mg/L could cause significant inhibition on overall (decolorizing and methanogenic) performance of AMWT. Specific methanogenic activity assays showed that acetoclastic methanogens was more susceptible to high concentration azo dyes than hydrogenotrophic methanogens. The spatial distribution of extracellular polymeric substance in the anaerobic granular sludge (AGS) showed that the high biological toxicity of azo dyes was mainly attributed to enrichment effect in tightly bound-EPS (TB-EPS). The channels of AGS was clogged by azo dyes, which was evidenced by the hard release of aromatic amines in EPSs as well as decreased porosity of AGS and scanning electron microscope images. Meanwhile, the settling ability, particle size and strength of AGS all deteriorated after azo dyes concentration exceeded 450 mg/L. The dosing of AQS could mostly remediate overall performance of the bioreactor even if the recovery of acetoclastic methanogens was slow. However, except for the porosity with a part of recovery, physical characteristics of AGS hardly recovered, and washout of sludge from the bioreactor was still happening. It suggested that additional attention should be paid to prevent sludge from washout if RM was practically used to remediate the anaerobic reactor inhibited by azo dyes.

Preparation, characterization and application of Cu–Ni/TiO2in Orange II photodegradation under visible light: effect of different reaction parameters and optimization

A series of mono- and bimetallic Cu–Ni/TiO₂photocatalysts were preparedviawet impregnation. The addition of metal onto the surface of TiO₂led to a better photocatalytic performance for Orange II photodegradation under visible light irradiation.

Remoción anaerobia del colorante azul directo brl en Reactor Anaerobio de Flujo Ascendente UASB (Upflow Anaerobic Sludge Blanket) con carbón activado

<p><strong>Título en ingles</strong>: Anaerobic removal of the brl direct blue dye in Upflow Anaerobic Sludge Blanket (UASB) with activated carbon</p><p>En esta investigación se utilizó el colorante azul directo brl para remoción anaerobia con un consorcio bacteriano aislado de efluentes industriales del Parque Industrial río Seco (PIRS), Arequipa, Perú; en un reactor anaerobio de flujo ascendente UASB con carbón activado. El reactor tuvo una capacidad de 14.4 Lcon lodos y carbón activado del 40% de volumen, con una carga orgánica de 6 KgDQO/m3•día y un tiempo de retención hidráulica de 1 día con un flujo ascendente. El objetivo fue medir la eficiencia de la remoción anaerobia del colorante en un tiempo de 28 días. Los resultados demostraron un incremento del 41% de los Sólidos Suspendidos Volátiles (SSV) de 12894 mg•L-1 a 21546 mg•L-1 bajo las condiciones del experimento, con una remoción del 57% de la Demanda Química de Oxigeno (DQO) de 484 mg•L-1 a 122 mg•L-1 y una remoción del 87% del colorante azul directo brl de 69.61 mg•L-1 a 9 mg•L-1. Los resultados con el carbón activado granular solamente, demostraron una remoción del 61% del colorante azul directo brl de 70.67 mg•L-1 a 27.83 mg•L-1 a los 28 días.</p>

Biodecolorization of recalcitrant dye as the sole sourceof nutrition using Curvularia clavata NZ2 and decolorization ability of its crude enzymes

Extensive use of recalcitrant azo dyes in textile and paper industries poses a direct threat to the environment due to the carcinogenicity of their degradation products. The aim of this study was to investigate the efficiency of Curvularia clavata NZ2 in decolorization of azo dyes. The ability of the fungus to decolorize azo dyes can be evaluated as an important outcome as existing effluent treatment is unable to remove the dyes effectively. C. clavata has the ability to decolorize Reactive Black 5 (RB5), Acid Orange 7 (AO7), and Congo Red azo dyes, utilizing these as sole sources of carbon and nitrogen. Ultraviolet-visible (UV-vis) spectroscopy and Fourier infrared spectroscopy (FTIR) analysis of the extracted RB5's metabolites along with desorption tests confirmed that the decolorization process occurred due to degradation and not merely by adsorption. Enzyme activities of extracellular enzymes such as carboxymethylcellulase (CMCase), xylanase, laccase, and manganese peroxidase (MnP) were also detected during the decolorization process. Toxicity expressed as inhibition of germination was reduced significantly in fungal-treated azo dye solution when compared with the control. The cultivation of C. clavata under sequential batch system also recorded a decolorization efficiency of above 90%. The crude enzyme secreted by C. clavata also showed excellent ability to decolorize RB5 solutions with concentrations of 100 ppm (88-92%) and 1000 ppm (70-77%) without redox mediator. This proved that extracellular enzymes produced by C. clavata played a major role in decolorization of RB5.

Exploiting the efficacy of Lysinibacillus sp. RGS for decolorization and detoxification of industrial dyes, textile effluent and bioreactor studies

Complete decolorization and detoxification of Reactive Orange 4 within 5 h (pH 6.6, at 30°C) by isolated Lysinibacillus sp. RGS was observed. Significant reduction in TOC (93%) and COD (90%) was indicative of conversion of complex dye into simple products, which were identified as naphthalene moieties by various analytical techniques (HPLC, FTIR, and GC-MS). Supplementation of agricultural waste extract considered as better option to make the process cost effective. Oxido-reductive enzymes were found to be involved in the degradation mechanism. Finally Loofa immobilized Lysinibacillus sp. cells in a fixed-bed bioreactor showed significant decolorization with reduction in TOC (51 and 64%) and COD (54 and 66%) for synthetic and textile effluent at 30 and 35 mL h(-1) feeding rate, respectively. The degraded metabolites showed non-toxic nature revealed by phytotoxicity and photosynthetic pigments content study for Sorghum vulgare and Phaseolus mungo. In addition nitrogen fixing and phosphate solubilizing microbes were less affected in treated wastewater and thus the treated effluent can be used for the irrigation purpose. This work could be useful for the development of efficient and ecofriendly technologies to reduce dye content in the wastewater to permissible levels at affordable cost.

Evaluation of integrated anaerobic-aerobic biofilm reactor for degradation of azo dye methyl orange

This study was to investigate the mineralization of wastewater containing methyl orange (MO) in integrated anaerobic-aerobic biofilm reactor with coconut fiber as bio-material. Different aeration periods (3h in phase 1 and 2; 3, 6 and 15 h in phase 3; 24 h in phase 4 and 5) in aerobic chamber were studied with different MO concentration 50, 100, 200, 200 and 300 mg/L as influent from phase 1-5. The color removals estimated from the standard curve of dye versus optical density at its maximum absorption wavelength were 97%, 96%, 97%, 97%, and 96% and COD removals were 75%, 72%, 63%, 81%, and 73% in phase 1-5, respectively. The MO decolorization and COD degradation followed first-order kinetic model and second-order kinetic model, respectively. GC-MS analysis indicated the symmetrical cleavage of azo bond and the reduction in aromatic peak ensured the partial mineralization of MO.

Reductive decolourisation of sulphonated mono and diazo dyes in one- and two-stage anaerobic systems

This work assessed the application of one- and two-stage mesophilic anaerobic systems to colour removal of sulphonated mono and diazo dyes with ethanol as electron donor. The dyes Congo Red (CR), Reactive Black 5 (RB5) and Reactive Red 2 (RR2) were selected as model compounds and tested separately in seven different periods. The one-stage system (R(1)) consisted of a single up-flow anaerobic sludge blanket (UASB) reactor, whereas the two-stage system (R(2)) consisted of an acidogenic UASB reactor (R(A)), a settler and a methanogenic UASB reactor (R(M)). For CR and RB5, no remarkable difference was observed between the colour removal performance of both anaerobic systems R(1) and R(2). The experiments with RR2 revealed that R(2) was more efficient on colour removal than R(1), showing efficiencies almost 2-fold (period VI) and 2.5-fold (period VII) higher than those found by R(1). Additionally, R(2) showed a higher stability, giving a good prospect for application to textile wastewaters. Finally, the acidogenic reactor (R(A)) had an important role in the overall decolourisation achieved by R(2) during the experiments with CR and RB5 (>78 %), whereas for RR2, a more recalcitrant dye, R(A) was responsible for up to 38 % of the total colour removal.

Enhanced azo dye wastewater treatment in a two-stage anaerobic system with Fe0 dosing

Azo dye wastewater treatment was enhanced in an acidogenic reactor (A1) by Fe(0) dosing. Both COD (50%) and color (60%) removal in A1 were stable when the dye concentrations were increased from 200 to 800 mg/L. However, the performances of a Fe(0)-free control reactor (A2) showed low COD (34%) and color (32%) removals. The reason was attributed that Fe(0) dosing enhanced the activity of fermentative bacteria, which played an important role in acidogenesis and decolorization. The methanogenic reactor fed with the effluent of A1 exhibited higher removal efficiency and treatment stability. These results suggested that Fe(0) powder dosing was helpful to improve acidogenesis and decolorization to create a favorable feeding condition for the subsequent methanogenic treatment.

Evaluation of impact of exposure of Sudan azo dyes and their metabolites on human intestinal bacteria

Sudan azo dyes are banned for food usage in most countries, but they are illegally used to maintain or enhance the color of food products due to low cost, bright staining, and wide availability of the dyes. In this report, we examined the toxic effects of these azo dyes and their potential reduction metabolites on 11 prevalent human intestinal bacterial strains. Among the tested bacteria, cell growth of 2, 3, 5, 5, and 1 strains was inhibited by Sudan I, II, III, IV, and Para Red, respectively. At the tested concentration of 100 μM, Sudan I and II inhibited growth of Clostridium perfringens and Lactobacillus rhamnosus with decrease of growth rates from 14 to 47%. Sudan II also affected growth of Enterococcus faecalis. Growth of Bifidobacterium catenulatum, C. perfringens, E. faecalis, Escherichia coli, and Peptostreptococcus magnus was affected by Sudan III and IV with decrease in growth rates from 11 to 67%. C. perfringens was the only strain in which growth was affected by Para Red with 47 and 26% growth decreases at 6 and 10 h, respectively. 1-Amino-2-naphthol, a common metabolite of the dyes, was capable of inhibiting growth of most of the tested bacteria with inhibition rates from 8 to 46%. However, the other metabolites of the dyes had no effect on growth of the bacterial strains. The dyes and their metabolites had less effect on cell viability than on cell growth of the tested bacterial strains. Clostridium indolis and Clostridium ramosum were the only two strains with about a 10 % decrease in cell viability in the presence of Sudan azo dyes. The present results suggested that Sudan azo dyes and their metabolites potentially affect the human intestinal bacterial ecology by selectively inhibiting some bacterial species, which may have an adverse effect on human health.

Influence of hydraulic retention time in a two-phase upflow anaerobic sludge blanket reactor treating textile dyeing effluent using sago effluent as the co-substrate

PURPOSE

Textile dyeing and sago industries are the most polluting industries in South India, especially in industrial cities like Salem, Tamil Nadu, where textile dyeing and sago industries are clumped together geographically. Conventional physicochemical treatment followed by biological processes for the effluent generated from these industries are ineffective, costlier and produce huge quantities of hazardous sludge and harmful by-products which requires further treatment and safe disposal. Hence, the development of an alternative treatment method will become important. The main objective of this investigation is to establish a sustainable biotreatment technology for the treatment of textile dyeing effluent using sago effluent as co-substrate in a two-phase upflow anaerobic sludge blanket (UASB) reactor.

METHODS

In this study, influence of hydraulic retention time (HRT) in a two-phase UASB reactor treating textile dyeing effluent using sago effluent as co-substrate was investigated with different HRTs (36, 30, 24 and 18 h) with an optimum mixing ratio of 70:30 (sago to textile dye wastewaters).

RESULTS

The results revealed that the HRT had a high influence on the chemical oxygen demand (COD) and colour removal. The maximum COD removal efficiency of 39.4% and 88.5% and colour removal efficiency of 43.7% and 84.4% in the acidogenic and methanogenic reactors, respectively was achieved at 24 h of HRT. The biogas production was 312 L/day.

CONCLUSION

The biphasic UASB reactor could be a very feasible alternative, cost-effective, eco-friendly and sustainable treatment system for textile dyeing effluent with sago effluent as a co-substrate.

Effects of an electric field and zero valent iron on anaerobic treatment of azo dye wastewater and microbial community structures

A zero valent iron (ZVI) bed with a pair of electrodes was packed in an anaerobic reactor aiming at enhancing treatment of azo dye wastewater. The experiments were carried out in three reactors operated in parallel: an electric field enhanced ZVI-anaerobic reactor (R1), a ZVI-anaerobic reactor (R2) and a common anaerobic reactor (R3). R1 presented the highest performance in removal of COD and color. Raising voltage in R1 further improved its performance. Scanning electron microscopy images displayed that the structure of granular sludge from R1 was intact after being fed with the high dye concentration, while that of R3 was broken. Fluorescence in situ hybridization analysis indicated that the abundance of methanogens in R1 was significantly greater than that in the other two reactors. Denaturing gradient gel electrophoresis showed that the coupling of electric field and ZVI increased the diversity of microbial community and especially enhanced bacterial strains responsible for decolorization.

Colour removal of dyes from synthetic and real textile wastewaters in one- and two-stage anaerobic systems

Decolourisation of the azo dye model compound, Congo Red (CR), and real textile wastewater, was assessed in one- and two-stage anaerobic treatment systems (R₁ and R₂, respectively). High colour removals were achieved in both treatment systems even when a very high CR concentration (1.2 mM) was applied. However, R₂ presented a slightly better stability, in which the acidogenic reactor (R(2,A)) played a major role on dye reduction, as compared to the methanogenic reactor (R(2,M)), evidencing the role of fermentative microorganisms. The minimum electron donor concentration required to sustain dye reduction was much higher than the stoichiometric amount. Additionally, a decrease on the hydraulic retention time (from 24 to 12 h) did not significantly affect decolourisation, indicating that electron transfer was not a concern. Finally, experiments with real textile wastewater showed low decolourisation efficiencies in both systems, most likely due to the presence of dyes not susceptible to reductive decolourisation under these experimental conditions.

Effect of organic load on decolourization of textile wastewater containing acid dyes in upflow anaerobic sludge blanket reactor

Textile wastewater (TW) is one of the most hazardous wastewater for the environment when discharged without proper treatment. Biological treatment technologies have shown encouraging results over the treatment of recalcitrant compounds containing wastewaters. Upflow anaerobic sludge blanket reactor (UASB) was evaluated in terms of colour and the reduction of chemical oxygen demand (COD) with different organic loads using TW containing dyes belonging to different chemical groups. The study was performed using six different dye concentrations (10mg/L, 25mg/L, 50mg/L, 100mg/L, 150 mg/L, 300 mg/L) with three COD levels ( approximately 1000 mg/L, approximately 2000 mg/L, approximately 3000 mg/L). Decolourization, COD removal and reactor stability were monitored. Over 85% of colour removal was observed with all dye concentrations with three organic loads. Acid Red 131 and Acid Yellow 79 were decolourized through biodegradation while Acid Blue 204 was decolourized due to adsorption onto anaerobic granules. COD removal was high in all dye concentrations, regardless of co-substrate levels. The reactor did not show any instability during the study. The activity of granules was not affected by the dyes. Methanothrix like bacteria were the dominant group in granules before introducing TW, however, they were reduced and cocci-shape microorganism increased after the treatment of textile wastewater.

Behaviour of different anaerobic populations on the biodegradation of textile chemicals

The anaerobic biodegradation of textile chemicals was evaluated with inocula grown under mesophilic (37+/-2 degrees C) or thermophilic (55+/-2 degrees C) conditions, on glucose (glucose-grown) or acetate (acetate-grown) as sole carbon sources. Wool dyebath chemicals (acetic acid, a liposomal surfactant, a synthetic amphoteric surfactant), single or as binary acetate-surfactant mixtures, were used as test carbon sources, in the presence or absence of Acid Orange 7 as model dye. First, the two mesophilic inocula (glucose- or acetate-grown) were compared relatively to lag-phase durations, specific biogas production rates, biogas yields and overall COD removal yields. In some runs, sulphide and/or the model dye were included, to test for inhibition effects. Then, the two glucose-grown inocula (mesophilic and thermophilic) were assessed in batch biodegradation tests with the same carbon feeds. The kinetics for substrate-COD and dye colour removal were described and quantified using a pseudo-first order model. The presence of dye had no effect on performance parameters for all substrates tested. Acetoclastic methanogens seemingly played an important role in biogas production from the liposomal additive, but less so from the synthetic surfactant. The association of acetate and surfactants apparently introduced mutual inhibitory effects on the rates of biogas production, substrate uptake and dye decolourisation.

Effect of influent pH and alkalinity on the removal of chlorophenols in sequential anaerobic-aerobic reactors

This study was carried out to determine the effect of influent pH and alkalinity on the performance of sequential UASB and RBC reactors for the removal of 2-CP and 2,4-DCP from two different simulated wastewaters. The performance of methanogens at low (<6.0) to high (>8.0) pH values and at sufficiently high alkalinity (1500-3500 mg/l as CaCO(3)) is described in this paper. Sequential reactors were capable of handling wastewaters with influent pH, 5.5-8.5. However, with influent pH 7.0+/-0.1 UASB reactor showed best performance for 2-CP (99%) and 2,4-DCP (88%) removals. Increase in alkalinity/COD ratio in the influent (>1.1) caused gradual decrease in the chlorophenol removal in UASB reactors. The UASB reactors could not tolerate wastewater with higher alkalinity/COD ratio (2.6) and showed significant deterioration of its performance in terms of chlorophenols removal achieving only 74.7% 2-CP and 60% 2,4-DCP removals, respectively.

Isolation, identification and application of novel bacterial consortium TJ-1 for the decolourization of structurally different azo dyes

A novel bacterial consortium (TJ-1), which could decolorize Acid Orange 7 (AO7) and manyother azo dyes, was developed. In TJ-1 three bacterial strains were identified as Aeromonas caviae, Proteus mirabilis and Rhodococcus globerulus by 16S rRNA gene sequence analysis. AO7 decolorization was significantly higher with the use of consortium as compared to the use of individual strains, indicating complementary interactions among these strains. AO7 decolorization was observed under microaerophilic condition in the presence of organic carbon source. Either yeast extract (YE) alone or a combination of YE and glucose resulted in much higher decolorization of AO7 as compared to glucose alone, peptone or starch. Kinetic studies with different initial AO7 concentrations showed that more than 90% decolorization could be achieved even at 200mg/l within 16h. Fed-batch studies showed that AO7 decolorization required 10h during the first cycle and 5h in the second and third cycles, showing that bacterial cells could be used for multiple cycles. The consortium also decolorized fifteen other azo dyes individually as well as a simulated wastewater containing a mixture of all the sixteen azo dyes, thus, conferring the possibility of application of TJ-1 for the treatment of industrial wastewaters.

Evaluation of the efficacy of upflow anaerobic sludge blanket reactor in removal of colour and reduction of COD in real textile wastewater

The upflow anaerobic sludge blanket (UASB) reactor was evaluated for its efficacy in decolourization and reduction in chemical oxygen demand (COD) of real textile wastewater (RTW) under different operational conditions. The efficiency of UASB reactor in reducing COD was found to be over 90%. Over 92% of colour removal due to biodegradation was achieved. The activities of the anaerobic granules were not affected during the treatment of textile wastewater. Cocci-shaped bacteria were the dominant group over Methanothrix like bacteria in textile wastewater treatment. Alkalinity, volatile fatty acids (VFA) content and pH in effluents indicated that the anaerobic process was not inhibited by textile wastewater. It is concluded that UASB reactor system can effectively be used in the treatment of textile wastewater for the removal of colour and in the reduction of COD.

Algal decolorization and degradation of monoazo and diazo dyes

This study is to inspect how the variation of molecular structures and functional groups present in our models, monoazo dye (Tartrazine) and diazo dye (Ponceau), affects decolorization capabilities of green algae, cyanobacteria and diatoms. The results revealed that the removal of azo dyes was rapid at the initial period of study (3 days) and became slowly with the time (6 days). The maximum decolorization was observed at 5 ppm Tartrazine with S. bijugatus (68%) and N. muscourm after 6 days incubation. The reduction of color removal appears to be related to the molecular structure of the dyes and species of algae used. The culture of the diatom Nitzschia perminuta was completely died after 2 days of incubation. Azo reductase of algae, which is responsible for degradation of azo dyes into aromatic amine by breaking the azo linkage, was estimated. IR spectra represented a new peak at 3300 cm(-1) and a reduction in the azo band at 1642-1631 cm(-1). In order to investigate the sorption behavior of algae, Langmuir equilibrium model was tested.

Decolorization and partial degradation of monoazo dyes in sequential fixed-film anaerobic batch reactor (SFABR)

Decolorization of two monoazo dyes, acid orange 6 (AO6) and acid orange 7 (AO7), were studied in sequential fixed-film anaerobic batch reactor (SFABR) with varying dye concentrations and 500 mg/L glucose as the co-substrate. More than 90% dye decolorization could be achieved, even at 300 mg/L, with both AO6 and AO7 and dye decolorization rates were 168 mg/L/d and 176 mg/L/d, respectively. COD removals with these two monoazo dyes were significantly different, as 75% and 35% decrease were observed with AO6 and AO7, respectively. UV-visible spectral as well as HPLC analysis of SFABR treated effluent showed the accumulation of 4-aminobenzenesulfonate (4-ABS) from AO6 and AO7. Aminoresorcinol (AR) formed from AO6 decolorization could not be detected at the end of SFABR cycle. This along with high COD removal indicated its further degradation. Formation of pink coloration on exposure to air indicated the presence of 1-amino-2-naphthol (AN) in AO7 fed reactor effluent. Thus both 4-ABS and AN were resistant to further degradation under anaerobic conditions. Presence of nitrate did not decrease the observed decolorization at the end of 24h SFABR cycle, although initial rate was decreased. This indicates the suitability of SFABR configuration for the treatment of azo-dye containing wastewaters in the presence of nitrate.