Accumulation of Acid Orange 7, Acid Red 18 and Reactive Black 5 by growing Schizophyllum commune

The effect of Acid Orange 7, Acid Red 18 and Reactive Black 5 on the growth and decolorization properties of Schizophyllum commune was studied with respect to the initial pH varying from 1 to 6 and initial dye concentration (10-100 mg/L). The optimum pH value was found to be 2 for both growth and color removal of these azo dyes. Increasing the concentration of azo dyes inhibited the growth of S. commune. It was observed that S. commune was capable of removing Acid Orange 7, Acid Red 18 and Reactive Black 5 with a maximum specific uptake capacity of 44.23, 127.53 and 180.17 (mg/g) respectively for an initial concentration of 100 mg/L of the dye. Higher decolorization was observed at lower concentrations for all the dyes. Finally it was found that the percentage decolorization was more in the case of Reactive Black 5 dye compared to the other two dyes used in the present investigation.     

Decolorization and biosorption for Congo red by system rice hull- Schizophyllum sp. F17 under solid-state condition in a continuous flow packed-bed bioreactor

Synthetic dyes are important chemical pollutants from various industries. This work developed an efficient and relatively simple continuous decolorization system rice hull-Schizophyllum sp. F17 under solid-state condition in a packed-bed bioreactor, for decolorizing Congo red. In the decolorization system, two decolorization mechanisms exist, one is decolorization by Schizophyllum sp. F17, the other is biosorption by rice hull. The decolorization efficiency was greatly affected by dye concentration and hydraulic retention time (HRT), which were quantificationally analyzed and optimized through response surface methodology (RSM). A 2(2) full factorial central composite design (CCD) was performed, and three second order polynomial models were generated to describe the effects of dye concentration and HRT on total decolorization (R2=0.902), decolorization by Schizophyllum sp. F17 (R2=0.866) and biosorption by rice hull (R2=0.890). Response surface contour plots were constructed to show the individual and cumulative effects of dye concentration and HRT, and the optimum values. A maximum total decolorization 89.71% and maximum decolorization by Schizophyllum sp. F17 60.44% was achieved at dye concentration 142.63mg/L, HRT 41h, and dye concentration 110.7mg/L, HRT 29.4h, respectively. Meanwhile, the role of manganese peroxidase (MnP) in the decolorizaion process was investigated. This study proved the feasibility of continuous mode for decolorizing synthetic dyes by white-rot fungi in solid-state fermentation bioreactors.     

Biodecolorization of textile azo dyes by isolated yeast from activated sludge: Issatchenkia orientalis JKS6

An ascomycetous yeast strain isolated from activated sludge could decolorize Reactive Black 5 azo dye at 200 mg l^?1 up to 90 % within 12–18 h under agitated condition. Yeast decolorization ability was investigated at different RB5 concentrations and, at higher dye concentration, 500 mg l^?1, the decolorization was found to be 98 % after 36 h incubation time. Extensive decolorization (95–99 %) was obtained in presence of five other azo dyes, Reactive Orange 16, Reactive Red 198, Direct Blue 71, Direct Yellow 12, and Direct Black 22, by isolated yeast. HPLC analysis, UV–vis spectra and colorless biomass obtained after complete decolorization showed that the decolorization occured through a biodegradation mechanism. Decolorization was occurred during the exponential growth phase which is associated to primary metabolism. Laccase production by the yeast cells was not detected. The isolated yeast was characterized according to phenotypical and molecular procedures and was closely related (99 % identity) to Issatchenkia orientalis.     

Accelerated decolorization of reactive azo dyes under saline conditions by bacteria isolated from Arabian seawater sediment

Presence of huge amount of salts in the wastewater of textile dyeing industry is one of the major limiting factors in the development of an effective biotreatment system for the removal of azo dyes from textile effluents. Bacterial spp. capable of thriving under high salt conditions could be employed for the treatment of saline dye-contaminated textile wastewaters. The present study was aimed at isolating the most efficient bacterial strains capable of decolorizing azo dyes under high saline conditions. Fifty-eight bacterial strains were isolated from seawater, seawater sediment, and saline soil, using mineral salt medium enriched with 100?mg?l^?1 Reactive Black-5 azo dye and 50?g NaCl l^?1 salt concentration. Bacterial strains KS23 (Psychrobacter alimentarius) and KS26 (Staphylococcus equorum) isolated from seawater sediment were able to decolorize three reactive dyes including Reactive Black 5, Reactive Golden Ovifix, and Reactive Blue BRS very efficiently in liquid medium over a wide range of salt concentration (0–100?g NaCl l^?1). Time required for complete decolorization of 100?mg dye l^?1 varied with the type of dye and salt concentration. In general, there was an inverse linear relationship between the velocity of the decolorization reaction (V) and salt concentration. This study suggested that bacteria isolated from saline conditions such as seawater sediment could be used in designing a bioreactor for the treatment of textile effluent containing high concentration of salts.     

Decolorization kinetics of the azo dye Reactive Red 2 under methanogenic conditions: effect of long-term culture acclimation

The biological decolorization of the textile azo dye Reactive Red 2 was investigated using a mixed, mesophilic methanogenic culture, which was developed with mixed liquor obtained from a mesophilic, municipal anaerobic digester and enriched by feeding a mixture of dextrin/peptone as well as media containing salts, trace metals and vitamins. Batch decolorization assays were conducted with the unacclimated methanogenic culture and dye decolorization kinetics were determined as a function of initial dye, biomass, and carbon source concentrations. Dye decolorization was inhibited at initial dye concentrations higher than 100 mg l^-1 and decolorization kinetics were described based on the Haldane model. The effect of long-term culture exposure to the reactive dye on decolorization kinetics, culture acclimation, as well as possible dye mineralization was tested using two reactors fed weekly for two years with an initial dye concentration of 300 mg l^-1 and a mixture of dextrin/peptone. The maximum dye decolorization rate after a 2-year acclimation at an initial dye concentration of 300 mg l^-1 was more than 10-fold higher as compared to that obtained with the unacclimated culture. Aniline and the o-aminohydroxynaphthalene derivative resulting from the reductive azo bond cleavage of the dye were detected, but further transformation(s) leading to dye mineralization were not observed. Reactive Red 2 did not serve as the carbon and energy source for the mixed culture, and dye decolorization was sustained by the continuous addition of dextrin and peptone. Thus, biological decolorization of reactive azo dyes is feasible under conditions of low redox potential created and maintained in overall methanogenic systems, but supply of a biodegradable carbon source is necessary.     

Enhanced decolorization of sulfonated azo dye methyl orange by single and mixed bacterial strains AK1, AK2 and VKY1

Abstract

Methyl orange, a sulfonated azo dye having various industrial applications was decolorized by three bacteria Bacillus sp. strain AK1, Lysinibacillus sp. strain AK2 and Kerstersia sp. strain VKY1. The effect of various factors such as dye concentration, pH, temperature and NaCl concentration on decolorization was investigated. At 200?mg/L methyl orange concentration, the strains AK1, AK2 and VKY1 exhibited maximum decolorizing potential of 93, 95 and 96%, respectively, at temperature 35?°C and pH 7.0 within 18?h of incubation. These strains decolorized the dye over a wide range of pH (5–10), temperature (15–55?°C), and NaCl concentration (5–20?g/L). Further, these strains decolorize up to 800?mg/L concentrations of methyl orange within 24?h. The dye decolorization efficiency was further increased by using different consortia of these three strains which could decolorize the dye completely within 12?h of incubation. The cell-free extracts of the strains AK1, AK2 and VKY1 grown on methyl orange exhibited the azoreductase activity of 0.4794, 1.56 and 1.01?µM/min/mg protein, respectively. HPLC and FTIR analysis of the dye decolorized sample indicated the formation of 4-aminobenzenesulfonic acid and N,N-dimethyl-p-phenylenediamine as breakdown products of azo bond. The high decolorization potential of these bacterial strains individually and in consortia has potential application in remediation of dye effluent.     

Decolorization of aqueous solutions of disperse textile dyes by oxidoreductases

The potential of three oxidoreductases, a laccase preparation of Pleurotus sajor-caju PS-2001, horseradish peroxidase (HRP) and a microbial peroxidase (MP) was evaluated for the decolorization of disperse textile dyes (CI Disperse Red 343, CI Disperse Red 167 and CI Disperse Blue 148) used in polyester dyeing. Decolorization was studied in aqueous solutions varying in dye concentration, pH, temperature, enzyme concentration and the addition of mediators HBT and syringaldazine. The best conditions found for Disperse Red 343 with laccase, HRP and MP were: 15 mg L^?1 dye concentration, 50°C, pH 3.0 for laccase and pH 5.0 for peroxidases. Without mediator, the highest decolorizaton results (38.5% and 58.6%) were achieved with the highest tested concentrations of laccase (10 U mL^?1) and HRP (89.7 U mL^?1), respectively, but no significant difference in decolorization was found for the tested MP concentrations (29.9–89.7 U mL^‐1). HBT or syringaldazine increased decolorization with peroxidases significantly, but no effect was observed for the laccase. Decolorization of Disperse Red 167 (up to 15%) and Disperse Blue 148 (up to 25%) was much lower than of Disperse Red 343. With respect to enzyme concentration, the use of mediator and under the selected test conditions the laccase of P. sajor-caju PS-2001 turned out to be more efficient in disperse dye decolorization, than peroxidases HRP and MP.     

绒毛栓孔菌菌丝体在无营养条件下对偶氮染料刚果红的脱色作用

【目的】在无营养条件下,利用白腐真菌绒毛栓孔菌(Trametes pubescens)菌丝体对染料进行脱色可减少试验成本,提高染料处理的实用性。【方法】将该菌株液体培养的菌丝体在无营养条件下对染料进行脱色,并对其中脱色效果较好的偶氮染料刚果红的脱色过程进行分析。在此过程中,测定了该菌株分泌的胞外胞内酶活力,优化影响因子如初始pH值、温度、染料浓度和盐度,同时利用气相色谱-质谱联用技术分析无营养条件下偶氮染料刚果红的降解产物。植物毒性试验测定刚果红经绒毛栓孔菌菌丝体脱色前后的毒性变化。【结果】菌丝体对偶氮染料刚果红有较好的脱色效果,在初始pH值为2.0,温度为30°C,染料浓度为80 mg/L,盐度为2.5%(质量体积比)时,150 r/min转速下培养7 d后脱色率可达80.52%。在此过程中,菌丝体可被连续使用2次,且其所分泌的酶系可降解染料。此外,通过气相色谱-质谱联用分析得到刚果红的降解产物为萘胺、联苯胺和叠氮萘。植物毒性试验显示在无营养条件下的绒毛栓孔菌菌丝体对染料有明显的脱毒作用。【结论】研究发现绒毛栓孔菌菌丝体在无营养条件下的偶氮染料废水处理中具有广阔的应用前景。     

Lab-scale study of an anaerobic membrane bioreactor (AnMBR) for dilute municipal wastewater treatment

Anaerobic bioreactors supplemented with membrane technology have become quite popular, owing to their favorable energy recovery characteristics. In this study, a lab-scale anaerobic Membrane Bioreactor (AnMBR) was assessed in experimental treatments of pre-settled dilute municipal wastewater obtained from a full-scaled wastewater treatment plant. The MBR system was operated in continuous flow mode for 440 days. To evaluate the performance of the AnMBR under various loading rates, the hydraulic retention time (HRT) was reduced in a stepwise manner (from 2 to 0.5 days). Afterward, the mixed liquor suspended solids (MLSS) were reduced from 7,000 to 3,000 mg/L in increments of 1,000 mg/L, resulting in a decrease in solids retention time (SRT) at a constant HRT of 1.0 day. The soluble chemical oxygen demand (SCOD) concentration in the feed varied between 38 and 131 mg/L, whereas the average permeate SCOD ranged between 18 and 37 mg/L, reflecting excellent effluent quality. The AnMBR performance in terms of COD removal proved stable, despite variations in influent characteristics and HRT and SRT changes. The concentration of extracellular polymeric substance (EPS) was reduced with decreases in HRT from 42 to 22 mg VS/mg of MLSS, thereby indicating that the increased biomass concentration biodegraded the EPS at lower HRTs. AnMBR is, therefore, demonstrably a feasible option for the treatment of dilute wastewater with separate stage nitrogen and phosphorus removal processes.     

Enhancement of carotenoids and lipids production by oleaginous red yeast Sporidiobolus pararoseus KM281507

Bioconversion of biodiesel-derived crude glycerol into carotenoids and lipids was investigated by a microbial conversion of an oleaginous red yeast Sporidiobolus pararoseus KM281507. The methanol content in crude glycerol (0.5%, w/v) did not show a significant effect on biomass production by strain KM281507. However, demethanolized crude glycerol significantly supported the production of biomass (8.64?±?0.13?g/L), lipids (2.92?±?0.03?g/L), β-carotene (15.76?±?0.85?mg/L), and total carotenoids (33.67?±?1.28?mg/L). The optimal conditions suggested by central composite design were crude glycerol concentration (55.04?g/L), initial pH of medium (pH 5.63) and cultivation temperature (24.01°C). Under these conditions, the production of biomass, lipids, β-carotene, and total carotenoids were elevated up to 8.83?±?0.05, 4.00?±?0.06?g/L, 27.41?±?0.20, and 53.70?±?0.48?mg/L, respectively. Moreover, an addition of olive oil (0.5???2.0%) dramatically increased the production of biomass (14.47?±?0.15?g/L), lipids (6.40?±?0.09?g/L), β-carotene (54.43?±?0.95?mg/L), and total carotenoids (70.92?±?0.51?mg/L). The oleic acid content in lipids was also increased to 75.1% (w/w) of total fatty acids, indicating a good potential to be an alternative biodiesel feedstock. Meanwhile, the β-carotene content in total carotenoids was increased to 76.7% (w/w). Hence, strain KM281507 could be a good potential source of renewable biodiesel feedstock and natural carotenoids.     

一株高效广谱染料降解细菌的分离鉴定及脱色特性研究

通过梯度驯化,从印染废水长期污染土壤中分离筛选出能以4种不同结构类型的染料(刚果红、美蓝、孔雀绿和活性艳蓝KN-R)为唯一碳源的菌株XSMR,根据其形态学特征和生理生化鉴定及16S rDNA序列分析,初步鉴定为无色杆菌属(Achromobacter sp.)的菌株。菌株XSMR对4种染料均具有强的脱色降解能力,且对染料脱色的同时,自身能够生长繁殖,培养24h菌体干重超过不加染料的对照。在振荡培养条件下对该菌株的脱色反应条件进行研究,结果表明,当刚果红、美蓝、孔雀绿及活性艳蓝KN-R的初始浓度分别小于200mg/L、200mg/L、150mg/L及150mg/L时,在pH7.5、温度35℃、接种量4%(V/V)条件下,接种菌株XSMR脱色14h对4种染料的脱色率均可达到98%以上。通过对降解产物的紫外-可见光谱分析,进一步证明了菌株XSMR能彻底降解染料。菌株XSMR对染料脱色的机理包括生物降解和菌株吸附两方面。     

Production of laccase and manganese peroxidase by Pleurotus pulmonarius in solid-state cultures and application in dye decolorization

The production of ligninolytic enzymes (laccase and Mn-dependent peroxidase) by the white-rot fungus Pleurotus pulmonarius (FR.) Quélet was studied in solid-state cultures using agricultural and food wastes as substrate. The highest activities of laccase were found in wheat bran (2,860?±?250 U/L), pineapple peel (2,450?±?230 U/L), and orange bagasse (2,100?±?270 U/L) cultures, all of them at an initial moisture level of 85 %. The highest activities of Mn peroxidase were obtained in pineapple peel cultures (2,200?±?205 U/L) at an initial moisture level of 75 %. In general, the condition of high initial moisture level (80–90 %) was the best condition for laccase activity, while the best condition for Mn peroxidase activity was cultivation at low initial moisture (50–70 %). Cultures containing high Mn peroxidase activities were more efficient in the decolorization of the industrial dyes remazol brilliant blue R (RBBR), Congo red, methylene blue, and ethyl violet than those containing high laccase activity. Also, crude enzymatic extracts with high Mn peroxidase activity were more efficient in the in vitro decolorization of methylene blue, ethyl violet, and Congo red. The dye RBBR was efficiently decolorized by both crude extracts, rich in Mn peroxidase activity or rich in laccase activity.     

Decolorization of synthetic and real textile wastewater by the use of white-rot fungi

Batch and continuous reactors inoculated with white-rot fungi were operated in order to study decolorization of textile dyes. Synthetic wastewater containing either Reactive Blue 4 (a blue anthraquinone dye) or Reactive Red 2 (a red azo dye) was used during the first part of the study while real wastewater from a textile industry in Tanzania was used in the later part. Trametes versicolor was shown to decolorize both Reactive Blue 4 and Reactive Red 2 if glucose was added as a carbon source. Reactive Blue 4 was also decolorized when the fungus was allowed to grow on birch wood discs in a continuous biological rotating contactor reactor. The absorbance at 595 nm, the wavelength at which the dye absorbs at a maximum, decreased by 70% during treatment. The initial dye concentration in the medium was 200 mg/l and the hydraulic retention time in the reactor 3 days. No glucose was added in this experiment. Changes of the absorbance in the UV range indicated that the aromatic structures of the dyes were altered. Real textile wastewater was decolorized by Pleurotus flabellatus growing on luffa sponge packed in a continuous reactor. The reactor was operated at a hydraulic retention time of 25 h. The absorbance at 584 nm, the wavelength at which the wastewater absorbed the most, decreased from 0.3 in the inlet to approximately 0.1 in the effluent from the reactor.     

Treatability of cheese whey for single-cell protein production in nonsterile systems: Part II. The application of aerobic sequencing batch reactor (aerobic SBR) to produce high biomass of Dioszegia sp. TISTR 5792

This study aimed to investigate the efficiency of an aerobic sequencing batch reactor (aerobic SBR) in a nonsterile system using the application of an experimental design via central composite design (CCD). The acidic whey obtained from lactic acid fermentation by immobilized Lactobacillus plantarum sp. TISTR 2265 was fed into the bioreactor of the aerobic SBR in an appropriate ratio between acidic whey and cheese whey to produce an acidic environment below 4.5 and then was used to support the growth of Dioszegia sp. TISTR 5792 by inhibiting bacterial contamination. At the optimal condition for a high yield of biomass production, the system was run with a hydraulic retention time (HRT) of 4 days, a solid retention time (SRT) of 8.22 days, and an acidic whey concentration of 80% feeding. The chemical oxygen demand (COD) decreased from 25,230 mg/L to 6,928 mg/L, which represented a COD removal of 72.15%. The yield of biomass production and lactose utilization by Dioszegia sp. TISTR 5792 were 13.14 g/L and 33.36%, respectively, with a long run of up to 180 cycles and the pH values of effluent were rose up to 8.32 without any pH adjustment.     

Polyhydroxyalkanoate production using waste vegetable oil and filtered digestate liquor of chicken manure

Abstract

The production of polyhydroxyalkanoates (PHA) using digestate of chicken manure combined with waste sunflower oil as no-cost feedstocks in a multi-stage process was investigated. Using Cupriavidus necator H16 in combined culture media, a maximum PHA accumulation of 4.6?±?0.2?g/L at 75.1?±?1.4% of cell dry matter and a residual cell matter yield of 1.5?±?0.1?g/L were obtained after 96?hr of cultivation (30?°C, 160?rpm, pH 7.0) in flask-based experiments. Manure was acidogenically fermented in a continuous stirring tank reactor in fed-batch mode. The bioreactor was operated at varying organic loading rates (OLR) and hydraulic retention times (HRT) ranging from 1–4?g volatile solids (VS)/L/d and 4–8?days, respectively. Optimal operation was observed at an OLR of 4?g VS/L/d and an HRT of 4?days. Analysis showed the presence of significant amounts of ammonia, potassium, magnesium, calcium, and trace elements, i.e. Fe, Cu, Ni, Mn, Co, Zn, Cr in the digestate. The micro-filtered digestate was utilized as a complex culture media base while waste oil served as an additional carbon source and supplemented for effective PHA production. The total volatile fatty acid content of digestate greatly affected the growth performance of the PHA-producing microorganism Cupriavidus necator H16.     

Decolorization of azo dyes by Geobacter metallireducens

Geobacter metallireducens was found to be capable of decolorizing several azo dyes with different structures to various extents. Pyruvate, ethanol, acetate, propionate, and benzoate could support 66.3?±?2.6?93.7?±?2.1 % decolorization of 0.1 mM acid red 27 (AR27) in 40 h. The dependence of the specific decolorization rate on AR27 concentration (25 to 800 μM) followed Michaelis–Menten kinetics (K _m?=?186.9?±?1.4 μΜ, V _max?=?0.65?±?0.02 μmol?mg protein^?1 h^?1). Enhanced AR27 decolorization was observed with the increase of cell concentrations ranging from 7.5 to 45 mgL^?1. AR27 decolorization by G. metallireducens was retarded by the presence of goethite, which competed electrons with AR27 and was reduced to Fe(II). The addition of low concentrations of humic acid (1?100 mgL^?1) or 2-hydroxy–1,4-naphthoquinone (0.5?50 μM) could improve the decolorization performance of G. metallireducens. High-performance liquid chromatography analysis suggested reductive pathway to be responsible for decolorization. This was the first study on azo dye decolorization by Geobacter strain and might improve our understanding of natural attenuation and bioremediation of environments polluted by azo dyes.     

Decolorization of azo dye using PVA-immobilized microorganisms

A microbial consortium having a high capacity for rapid decolorization of azo dye (RED RBN) was immobilized by a phosphorylated polyvinyl alcohol (PVA) gel. The immobilized-cell beads exhibited a color removal capability of 75%, even at a high concentration of RED RBN (500 mg l(-1)) within 12 h using flask culture. The continuous operation was conducted at a hydraulic retention time (HRT) of 5-20 h in which the dye loading rate ranged from 240 to 60 mg dye h(-1). A removal efficiency exceeding 90% was obtained at the HRT higher than 10 h. No recognizable destruction of bead appearance was observed in the 6-month operation. Examination of the mechanism of the decolorization process by cell beads indicated that it proceeded primarily by biological decolorization associated with partial adsorption of the dye onto the entrapped cells and gel matrix. Microscopic observation revealed that the microbial consortium contained in the gel beads was at least made up of three kinds of bacterial species. From the economical viewpoint, alternative cheaper nitrogen sources such as fish meal, soybean meal, pharmamedia and vita yeast powder were examined.     

Azo Dye Decolorization under Microaerophilic Conditions by a Bacterial Mixture Isolated from Anthropogenic Dye‐Contaminated Soil

Soil samples isolated from dye-contaminated sites were exploited for isolation of dye decolorizing microorganisms. A novel bacterial mixture, RkNb1, was selected based on its efficiency, showing maximum and faster decolorization of textile dyes. Seven bacterial strains were isolated and identified from the bacterial mixture as Ochrobactrum intermedium (HM480365), Ochrobactrum intermedium strain M16-10-4 (HM030758), Enterococcus faecalis (HM480367), Arthrobacter crystallopoietes (HM480368), Kocuria flavus (HM480369), Bacillus beijingensis (HM480370), and Citrobacter freundii (HM480371) by 16S rRNA gene sequence analysis. This bacterial mixture showed 98.17% decolorization of Reactive Violet 5 (400 mg L^?1) within 8 h. The culture exhibited good decolorization ability at pH 8 and at a temperature of 37°C. Malt extract and peptone was found to enhance the decolorization rate of Reactive Violet 5. Plackett-Burman experimental design was used for elucidation of medium components affecting Reactive Violet 5 decolorization. Dye degradation products obtained during the course of decolorization were analyzed by high-performance thin-layer chromatography (HPTLC), Fourier transform infrared (FTIR), and nuclear magnetic resonance (NMR). The potential of this bacterial mixture to decolorize Reactive Violet 5 dye from manufacturing industry effluent is to be carried out using appropriate bioreactors.     

Fed-batch bioreactor strategies for microbial decolorization of azo dye using a Pseudomonas luteola strain

A Pseudomonas luteola strain possessing azoreductase activity was utilized to decolorize a reactive azo dye (C. I. Reactive Red 22) with fed-batch processes consisting of an aerobic cell growth stage and an anaerobic fed-batch decolorization stage. The fed-batch decolorization was conducted with different agitation and aeration rates, initial culture volumes, dye loading strategies, and yeast extract to dye (Y/D) ratios, and the effect of those operation parameters on azo dye decolorization was evaluated. Dissolved oxygen strongly inhibited the azo reduction activity; thus aeration should be avoided during decolorization but slight agitation (around 50 rpm) was needed. With the periodical feeding strategy, the specific decolorization rate (v(dye)) and overall decolorization efficiency (eta(dye)) tended to increase with increasing feeding concentrations of dye, whereas substrate inhibition seems to arise when the feeding concentration exceeded 600 mg dye/L. In the continuous feeding mode, higher initial culture volume resulted in better eta(dye) due to higher biomass loading, but lower v(dye) due to lower dye concentration in the bioreactor. With a volumetric flow rate (F) of 25 mL/h, both v(dye) and eta(dye) increased almost linearly with the increase in the loading rate of dye (F(dye)) over the range of 50-200 mg/h, while further increase in F(dye) (400 mg/h) gave rise to a decline in v(dye) and eta(dye). As the F was doubled (50 mL/h), the v(dye) and eta(dye) increased with F(dye) only for F(dye) < 80 mg/h. The best v(dye) (113.7 mg dye g cell(-)(1) h(-)(1)) and eta(dye) (86.3 mg dye L(-)(1) h(-)(1)) were achieved at F(dye) = 200 mg/h and F = 25 mL/h. The yield coefficient representing the relation between dye decolorized and yeast extract consumed was estimated as 0.8 g/g. With F(dye) = 75 mg/h, the Y/D ratio should be higher than 0.5 to ensure sufficient supply of yeast extract for stable fed-batch operations. However, performance of the fed-batch decolorization process was not appreciably improved by raising the Y/D ratio from 0.5 to 1.875 but was more sensitive to the changes in the dye loading rate.     

Decolorization of reactive dyes by mixed cultures isolated from textile effluent under anaerobic conditions

In the present study mixed cultures that could grew in the molasses media were isolated from textile dye effluent and its decolorization activity was studied in a batch system under anaerobic conditions, in order to determine the optimal conditions required for the highest decolorization activity. The optimum pH value for decolorization was determined as 8 for all the dyes tested. In the experiment with pH 8 dye decolorizations by mixed cultures were investigated at about 96.2–1031.3 mg l⁻¹ initial dye concentrations. The highest dye removal rates of mixed cultures were 94.9% for Reactive Red RB, 91.0% for Reactive Black B and 63.6% for Remazol Blue at 953.2, 864.9 and 1031.3 mg l⁻¹ initial dye concentrations respectively within 24 h incubation period. When the Reactive Red RB was used, approximately 82–98% total color removal was obtained at between 96.2 and 953.2 mg l⁻¹ initial dye concentrations after 12 h of incubation at 35 °C. These results show that our enriched mixed cultures have the potential to serve as an excellent biomass for the use in reactive dye removal from wastewaters under anaerobic conditions.