Decolorization and toxicity of reactive anthraquinone textile dyes under methanogenic conditions

Reductive decolorization of two anthraquinone reactive dyes (Reactive Blue 4, RB4; Reactive Blue 19, RB19) under methanogenic conditions was performed using a mixed, methanogenic culture. Decolorization of the two anthraquinone dyes was investigated to evaluate the rate and extent of color removal as well as to assess possible toxic effects of the dyes and their decolorization product(s) on the methanogenic culture as a function of initial dye concentration ranging from 50 to 300 mg x L(-1). A dextrin/peptone mixture was used as the carbon and electron source. A high rate and extent of color removal was achieved ranging from 4.3 to 29.9 mg x L(-1)h(-1) and 73-91% for RB4, and 13.0-74.4 mg x L(-1)h(-1) and 90-95% for RB19. Initial RB4 concentrations up to 100 mg x L(-1) did not result in any significant inhibition. Both the 200 and 300 mg x L(-1) RB4-amended cultures, and all RB19-amended cultures resulted in severe inhibition of both acidogenesis and methanogenesis. Sequential dye addition at 300 mg x L(-1) for both RB4 and RB19 resulted in accumulation of volatile fatty acids (VFAs) and a very low methane production at the end of the first dye addition after 44 days of incubation. However, at the end of the second dye addition, after a relatively long incubation (384 days), recovery of methanogens in the RB4-amended culture was observed in contrast to the complete inhibition of methanogenesis in the RB19-amended culture. Therefore, RB19 resulted in a higher degree of inhibition of both acidogenesis and methanogenesis than RB4. Addition of dextrin/peptone to dye-inhibited cultures resulted in acidogenesis and a gradual recovery of methanogenesis (mainly aceticlastic methanogenesis) in the RB4-inhibited culture, and a slow recovery of acidogenesis but no recovery of methanogenesis in the RB19-inhibited culture. In contrast, addition of 80% H(2)-20% CO(2) gas to dye-inhibited cultures resulted in recovery of hydrogenotrophic methanogenesis in both the RB4- and RB19-inhibited cultures. In spite of the relatively severe inhibition of the two anthraquinone dyes on the mixed, methanogenic culture, a high extent of color removal was achieved.     

Bioaugmented membrane bioreactor (MBR) with a GAC-packed zone for high rate textile wastewater treatment

The long-term performance of a bioaugmented membrane bioreactor (MBR) containing a GAC-packed anaerobic zone for treatment of textile wastewater containing structurally different azo dyes was observed. A unique feeding strategy, consistent with the mode of evolution of separate waste streams in textile plants, was adopted to make the best use of the GAC-zone for dye removal. Dye was introduced through the GAC-zone while the rest of the colorless media was simultaneously fed through the aerobic zone. Preliminary experiments confirmed the importance of coupling the GAC-amended anaerobic zone to the aerobic MBR and also evidenced the efficacy of the adopted feeding strategy. Following this, the robustness of the process under gradually increasing dye-loading was tested. The respective average dye concentrations (mg/L) in the sample from GAC-zone and the membrane-permeate under dye-loadings of 0.1 and 1 g/L.d were as follows: GAC-zone (3, 105), permeate (0, 5). TOC concentration in membrane-permeate for the aforementioned loadings were 3 and 54 mg/L, respectively. Stable decoloration along with significant TOC removal during a period of over 7 months under extremely high dye-loadings demonstrated the superiority of the proposed hybrid process.     

Removal of veterinary antibiotics from sequencing batch reactor (SBR) pretreated swine wastewater by Fenton's reagent

The large-scale application of veterinary antibiotics in livestock industry makes swine wastewater an important source of antibiotics pollution. This work investigated the degradation of six selected antibiotics, including five sulfonamides and one macrolide, by Fenton's reagent in swine wastewater pretreated with sequencing batch reactor (SBR). The dosing mode and practical dosage of Fenton's reagent were optimized to achieve an effective removal of antibiotics while save the treatment cost. The effects of initial pH, chemical oxygen demand (COD) and suspended solids (SS) of the SBR effluent on antibiotics degradation were examined. The results indicate that the optimal conditions for Fenton's reagent with respect to practical application were as follows: batch dosing mode, 1.5:1 molar ratio of [H₂O₂]/[Fe²⁺], initial pH 5.0. Under the optimal conditions, Fenton's reagent could effectively degrade all the selected antibiotics and was resistant to the variations in the background COD (0-419 mg/L) and SS (0-250 mg/L) of the SBR effluent. Besides, Fenton's reagent helped to not only remove total organic carbon (TOC), heavy metals (As, Cu and Pb) and total phosphorus (TP), but also inactivate bacteria and reduce wastewater toxicity. This work demonstrates that the integrated process combining SBR with Fenton's reagent could provide comprehensive treatment to swine wastewater.     

Biodegradation potential of pure and mixed bacterial cultures for removal of 4-nitroaniline from textile dye wastewater

Environmentally toxic aromatic amines including nitroanilines are commonly generated in dye contaminated wastewater in which azo dyes undergo degradation under anaerobic conditions. The aim of this study was to develop a process for biological treatment of 4-nitroaniline. Three bacteria identified as Acinetobacter sp., Citrobacter freundii and Klebsiella oxytoca were isolated from enrichment cultures of activated sludge on 4-nitroaniline, after which the isolates and the mixed culture were studied to determine optimal conditions for biodegradation. HPLC analyses showed the mixed culture was capable of complete removal of 100 μmol/L of 4-nitroaniline within 72 h under aerobic conditions. There was an inverse linear relationship (R² = 0.96) between the rate of degradation (V) and 4-nitraoaniline concentrations [S] over 100-1000 μmol/L. The bacterial culture was also capable of decolorizing structurally different azo dyes (Acid Red-88, Reactive Black-5, Direct Red-81, and Disperse Orange-3) and also degraded nitrobenzene. Our findings show that enrichment cultures from activated sludge can be effective for the removal of dyes and their toxic intermediates, and that treatment may best be accomplished using an anaerobic-aerobic process.     

Decolorization and biodegradation of methyl red by Klebsiella pneumoniae RS-13

Bacterial strains isolated from dye-contaminated sludge decolorized a toxic azo dye, namely, methyl red (MR). Klebsiella pneumoniae RS-13 was selected because of its better abilities to completely decolorize and degrade MR under aerobic conditions. Effects of physico-chemical parameters, such as: temperature and aeration, concentrations of glucose, ethanol, ammonium sulfate and pH of the culture medium on the MR degradation by the bacterium and a previously isolated aerobic MR-degrading bacterium, Acetobacter liquefaciens S-1, were determined. K. pneumoniae RS-13 had higher MR degradation ability than A. liquefaciens S-1. Under optimal conditions, K. pneumoniae RS-13 completely decolorized and degraded 100 mg l⁻¹ of MR in cultural medium. The high MR degradation ability and low nutrient and environmental requirements of K. pneumoniae RS-13 enable this bacterium to be used in the treatment of industrial effluent containing azo dyes.     

Further treatment of decolorization liquid of azo dye coupled with increased power production using microbial fuel cell equipped with an aerobic biocathode

A microbial fuel cell (MFC) incorporating a recently developed aerobic biocathode is designed and demonstrated. The aerobic biocathode MFC is able to further treat the liquid containing decolorization products of active brilliant red X-3B (ABRX3), a respective azo dye, and also provides increased power production. Batch test results showed that 24.8% of COD was removed from the decolorization liquid of ABRX3 (DL) by the biocathode within 12 h. Metabolism-dependent biodegradation of aniline-like compound might be mainly responsible for the decrease of overall COD. Glucose is not necessary in this process and contributes little to the COD removal of the DL. The similar COD removal rate observed under closed circuit condition (500 Ω) and opened circuit condition indicated that the current had an insignificant effect on the degradation of the DL. Addition of the DL to the biocathode resulted in an almost 150% increase in open cycle potential (OCP) of the cathode accompanied by a 73% increase in stable voltage output from 0.33 V to 0.57 V and a 300% increase in maximum power density from 50.74 mW/m² to 213.93 mW/m². Cyclic voltammetry indicated that the decolorization products of the ABRX3 contained in the DL play a role as redox mediator for facilitating electron transfer from the cathode to the oxygen. This study demonstrated for the first time that MFC equipped with an aerobic biocathode can be successfully applied to further treatment of effluent from an anaerobic system used to decolorize azo dye, providing both cost savings and high power output.     

Treatment of olefin plant spent caustic by combination of neutralization and Fenton reaction

Spent caustic from olefin plants contains much H2S and some mercaptans, phenols and oil. A new treatment process of spent caustic by neutralization followed by oxidation with Fenton's reagent (Fe2+/H2O2) was successfully developed. Over 90% of dissolved H2S were converted to gas phase by neutralization at pH = 5 and T = 70 degrees, and the vent gas stream could be introduced to sulfur recovery plant. The neutralized liquid was oxidized with OH. free radical, which was provided by a Fenton's reagent. The residual sulfides in the neutralized spent caustic were oxidized to less than 0.1 mg/L. The total COD removal of spent caustic is over 99.5% and the final COD value of the effluent can be lower than 100 mg/L under the following oxidation conditions: reaction time = 50 min, T = 90 degrees, Fe2+ = 100 mg/L, and a stoichiometric H2O2/COD = 1.1. The value is better than the 800 mg/L value obtained by common WAO process. The optimum pH of the Fenton reaction is around 2 for this process, and the oxidation step can maintain a pH value in the range of 1.8-2.4. Moreover, the iron catalyst can be recycled without affecting process effectiveness thus preventing secondary pollution.     

Fenton oxidation of cork cooking wastewater--overall kinetic analysis

In the present work, the possibility of using chemical oxidation through Fenton's reagent for the pre-treatment of cork cooking wastewaters was exploited. Aiming both the selection of the best operating conditions (pH, Fe2+:H2O2 ratio and initial H2O2 concentration) and the evaluation of the overall reaction kinetics, trials were performed in a batch reactor. Operating at pH = 3.2, H2O2 concentration = 10.6 g/L and Fe2+:H2O2 ratio = 1:5 (by weight), about 66.4% of total organic carbon (TOC), 87.3% of chemical oxygen demand (COD) and 70.2% of biochemical oxygen demand (BOD5) were removed and an increase of the BOD5/COD ratio from 0.27 to 0.63 was achieved. In the temperature range 20-50 degrees C, the best performance was obtained at 30 degrees C. The kinetic study was undertaken at different initial TOC concentrations and temperatures. Overall kinetics can be described by a second-order followed by a zero-order rate equation and the apparent kinetic constants at 30 degrees C are k = 2.3 x 10(-4) L/mg min and k0 = 26.0 mg/L min, respectively. The experiments performed at different temperatures confirmed the global kinetic model and allowed to calculate the global activation energy for the second-order reaction (70.7 kJ/mol).     

Comparative studies on potential of consortium and constituent pure bacterial isolates to decolorize azo dyes

The decolorization potential of the consortium HM-4 constituted by mixing four laboratory isolates identified as Bacillus cereus (BN-7), Pseudomonas putida (BN-4), Pseudomonas fluorescens (BN-5) and Stenotrophomonas acidaminiphila (BN-3) was compared with that of individual isolates. Six different azo dyes viz., C.I. Acid Red 88 (AR-88), C.I. Acid Red 119 (AR-119), C.I. Acid Red 97 (AR-97), C.I. Reactive Red 120 (RR-120), C.I. Acid Blue 113 (AB-113) and C.I. Acid Brown 100 (AB-100) were used in this study. The individual bacterial isolates were not able to completely decolorize these dyes, except for dyes AR-119 and AB-113. The consortium HM-4 was able to decolorize all the dyes used at an initial dye concentration of 20 mg L⁻¹ at a significantly higher rate as compared to that achieved by individual isolates.     

Combined anaerobic-aerobic treatment of azo dyes--a short review of bioreactor studies

The most logical concept for the removal of azo dyes in biological wastewater treatment systems is based on anaerobic treatment, for the reductive cleavage of the dyes' azo linkages, in combination with aerobic treatment, for the degradation of the products from azo dye cleavage, aromatic amines. Since the 1990s, several research papers have been published on combined, sequential or integrated, anaerobic-aerobic bioreactor treatment of azo dye-containing wastewater. The extent of azo dye reduction in the anaerobic phase of those bioreactor systems was generally high, albeit the process often required long reaction times, a limitation that can easily be remedied by making use of the property of redox mediators to speed up the process. The consequent removal of aromatic amines under aerobic conditions was less unequivocal. Although analytical data indicate that many of the aromatic amines were removed from the wastewater, and although the limited amount of available toxicity data all show far-reaching detoxification during aerobic treatment, it is clear that not all aromatic amines can be completely mineralized.     

Chromium (VI) reduction in activated sludge bacteria exposed to high chromium loading: Brits culture (South Africa)

A mixed-culture of bacteria collected from a wastewater treatment plant in Brits, North-West Province (South Africa) biocatalytically reduced Cr(VI) at much higher concentrations than previously observed in cultures isolated in North America. Cr(VI) reduction rate up to 8 times higher than the rate in previous cultures was achieved by the Brits culture under aerobic conditions. Near complete Cr(VI) reduction was observed in batches under initial concentrations up to 200 mg Cr(VI)/L after incubation for 65 h in aerobic cultures. Under anaerobic conditions up to 150 mg Cr(VI)/L was completely removed after incubating for 130-155 h. In the previous cultures, complete removal was only achieved in cultures at an initial Cr(VI) concentration lower than 30 mg/L after incubation for 96-110 h. Consortium cultures were characterised using 16S rRNA partial sequence analysis. Results showed that the Gram-positive Bacillus genera predominated under aerobic conditions with a small composition of the Gram-negative Microbacterium sp. More biodiversity was observed in anaerobic cultures with the marked appearance of Enterococcus, Arthrobacter, Paenibacillus and Oceanobacillus species. Experiments run on purified individual species did not achieve the same level of Cr(VI) reduction as observed in the original consortium from sludge indicating possible existence of interspecies interactions necessary for optimum Cr(VI) reduction. All Cr(VI) reduced was accounted for as Cr(III) with a small error range (2-6%).     

厌氧(IC反应器)/好氧联用处理淀粉生产废水

针对淀粉废水有机物浓度高、可生化性好的特点,选择内循环厌氧反应器(IC)/好氧处理工艺.IC反应器可去除大部分有机物,减轻后续好氧处理的压力.运行结果表明,原水COD为4 500～5 300 mg/L,出水COD为220～300 mg/L,达到<污水综合排放标准(GB 8978-1996)的三级标准,产生的沼气可用于原水加热.     

Detection of tannic acid at trace level in industrial wastewaters using a highly sensitive chemiluminescence method

A novel flow injection procedure was developed for the determination of tannic acid in industrial wastewaters based on the enhancement by tannic acid of the chemiluminescence from luminol-K3Fe(CN)6-OH- system. The method has the merits of higher sensitivity, higher selectivity, wider linear range, simpler instrumentation. It is applicable for the determination of tannic acid in the range of 3.0 x 10(-10)-1.0 x 10(-7) mol/L with a detection limit of 1.0 x 10(-10) mol/L. The relative standard deviation is 2.7% for the determination of 1.0 x 10(-8) mol/L tannic acid (n = 11). The method has been successfully used to determine tannic acid at trace level in industrial wastewaters from brewery and tannery.     

Optimisation of process parameters for bioreduction of azo dyes using Bacillus firmus under batch anaerobic condition

A new dye decolourising bacterial strain was isolated from textile wastewater and identified as Bacillus firmus. The study indicated that the bacterium could efficiently decolourise different azo dyes under static culture conditions. Characterisation of the efficiency of azo dye reduction by this isolate using both spectral and HPLC analysis was found to be a function of process parameters which include dye concentration, culture broth pH, incubation temperature, aeration as well as nitrogen source. For decolourisation, the optimal pH and temperature were 7–8 and 20–35°C respectively, while remarkable dye degradation was obtained within 18 h for dye concentrations below 100 mg L^?1. With the addition of yeast extract and under optimal conditions, dye reduction was enhanced and complete colour removal was achieved within 12 h. Colour removal was shown to be due to biodegradation rather than adsorption of dyes on bacterial cells. This study confirms the ability of the new dye‐degrading strain, Bacillus firmus, to decolourise and degrade different azo dyes and highlights its high biotechnology potential for the eco‐friendly treatment of textile wastewater when optimal conditions are applied.     

Optimal decolorization and kinetic modeling of synthetic dyes by Pseudomonas strains

Pseudomonas spp were isolated from an anaerobic-aerobic dyeing house wastewater treatment facility as the most active azo-dye degraders. Decolorization of azo dyes and non-azo dyes including anthraquinone, metal complex and indigo was compared with individual strains and a bacterial consortium consisting of the individual strain and municipal sludge (50 50wt). The consortium showed a significant improvement on decolorization of two recalcitrant non-azo dyes, but little effect on the dyes that the individual strains could degrade to a great or moderate extent. Decolorization of Acid violet 7 (monoazo) by a Pseudomonas strain GM3 was studied in detail under various conditions. The optimum decolorization activity was observed in a narrow pH range (7-8), a narrow temperature range (35-40 degrees C), and at the presence of organic and ammonium nitrogen. Nitrate had a severe inhibitory effect on azo dye decolorization: 10 mg/L led to 50% drop in decolorization activity and 1000 mg/L to complete activity depression. A kinetic model is established giving the dependence of decolorization rate on cell mass concentration (first-order) and dye concentration (half order). The rate increased with temperature from 10 to 35 C, which can be predicted by Arrhenius equation with the activation energy of 16.87 kcal/mol and the frequency factor of 1.49 x 10(11) (mg L)1/2/g DCM min.     

TiO2/AC光催化剂对卡马西平的降解特性

以椰壳粉末活性炭(PAC)为载体,钛酸丁酯和乙醇为原料,采用溶胶凝胶-浸渍法制备负载型光催化剂(TiO2/AC),并研究其降解模拟废水中微量污染物卡马西平的效果.结果表明:TiO2/AC对卡马西平的处理效果明显优于粉末二氧化钛(TiO2)和活性炭,TiO2/AC对卡马西平的去除率是TiO2的1.7倍.当卡马西平初始浓度为10 mg/L时,TiO2/AC的投加量为500 mg/L、TiO2的负载量为11.2％、反应pH值为7时,卡马西平去除率达到90.6％.TiO2/AC对不同初始浓度卡马西平溶液的降解过程符合准二级反应动力学,二级反应常数与浓度成反比.利用Langmuir-Hinshelwood(L-H)模型可得出表观吸附平衡常数Ka=9.215×103 L/mol,表面反应速率常数Kr=3.678×10-6 mol/(L·min),微波辐照是实现催化剂再生的最佳方法.     

溶解氧浓度对A~2/O工艺运行的影响

以城市污水厂中最常采用的A2/O工艺为研究对象,开展了处理实际生活污水的研究,系统探讨了DO浓度对该工艺运行的影响。结果表明,当好氧区的DO平均浓度从4.0 mg/L降低至1.0 mg/L时,对COD的去除基本不受影响;而系统的硝化效果逐渐降低,但是低DO浓度引发的SND等作用,使得对TN的去除率反而逐渐升高。单纯从生物脱氮的角度考虑,A2/O工艺可以在DO为1.0～2.0 mg/L之间运行。不过低DO浓度运行对生物除磷效果的影响很大,在DO为1.0 mg/L时,除磷效率逐渐下降,这是由于供氧不足引发了生物除磷性能的恶性循环。另外,低DO浓度运行还引发系统中的污泥发生了微膨胀现象,在污泥微膨胀期间出水SS<5 mg/L。就总体的运行情况而言,不同于A/O等单纯脱氮工艺,A2/O工艺不宜在DO<2.0 mg/L的条件下运行,否则需要引入化学除磷。     

Effect of Fenton's oxidation on the particle size distribution of organic carbon in olive mill wastewater

The study evaluated the effect of Fenton's oxidation on the particle size distribution (PSD) of significant parameters reflecting the organic carbon content of olive oil mill wastewater (OMW). The organic carbon content of the studied OMW was characterized by a COD level of around 40,000 mg/L, with 13,500 mg/L of TOC and 1670 mg/L of total phenols. The corresponding antioxidant activity (AOA) was determined as 33,400 mg/L. PSD of the selected organic carbon parameters was investigated using a sequential filtration/ultrafiltration procedure. COD fractionation based on PSD revealed two major components, a soluble fraction below 2 nm and a particulate fraction above 1600 nm representing 49% and 20% of the total COD, respectively. The remaining COD was distributed in the colloidal and supracolloidal zones. The PSD of TOC, total phenols and AOA exhibited similar profiles with peaks at the two ends of the studied size range. Overall COD removals achieved via Fenton's oxidation both at pH = 3.0 and pH = 4.6 (the original pH of the OMW) remained in the range of 40-50%. As anticipated, the effect of Fenton's treatment was more pronounced in the soluble size range. Fenton's oxidation at pH = 3.0 resulted in 46% and 63% removals for total phenols and AOA, respectively. The results obtained indicated that Fenton's process could only be useful as an alternative preliminary treatment option of the required full treatment scheme that could involve a sequence of filtration, oxidation and/or biological treatment steps.     

The role of hydroxyl radicals for the decomposition of p-hydroxy phenylacetic acid in aqueous solutions

The chemical decomposition of p-hydroxyphenylacetic acid, a priority phenolic pollutant present in wastewaters from some agro-industrial plants, is studied by means of a single photochemical process produced by a polychromatic UV radiation and by hydroxyl radicals generated by the combination of UV radiation plus hydrogen peroxide and by the Fenton's reagent (hydrogen peroxide plus ferrous salts). Batch experiments were conducted to establish the degradation levels obtained and the quantum yields in the single photodecomposition process. An improvement in the decomposition of the phenolic acid in the combined UV/H2O2 oxidation is observed, due to the generation of OH radicals, and the contribution of the radical reaction to the global process is determined. In the Fenton's reagent oxidation, the effects of the operating variables (H2O2 and Fe2+ initial concentrations, pH, type of buffer used) are established and the rate constant for the reaction of p-hydroxyphenylacetic acid with OH radicals is evaluated from a kinetic model, its value being 7.02 x 10(8) M-1 s-1 at 20 degrees C.     

Fenton-like oxidation of 2,4,6-trinitrotoluene using different iron minerals

Degradation of 2,4,6-trinitrotoluene (TNT) was investigated in presence of different oxidants (Fenton's reagent, sodium persulfate, peroxymonosulfate and potassium permanganate) and different iron minerals (ferrihydrite, hematite, goethite, lepidocrocite, magnetite and pyrite) either in aqueous solution or in soil slurry systems. Fenton's reagent was the only oxidant able to degrade TNT in solution (k(app)=0.0348 min(-1)). When using iron oxide as heterogeneous catalyst at pH 3, specific reaction rate constants per surface area were k(surf)=1.47.10(-3) L min(-1) m(-2) and k(surf)=0.177 L min(-1) m(-2) for magnetite and pyrite, respectively while ferric iron minerals were inefficient for TNT degradation. The major asset of iron mineral catalyzed Fenton-like treatment has been the complete oxidation of the pollutant avoiding the accumulation of possible toxic by-products. In soil slurry systems, 38% abatement of the initial TNT concentration (2 g/kg) was reached after 24 h treatment time at neutral pH. Rate limiting steps were the availability of soluble iron at neutral pH together with desorption of the TNT fraction sorbed on the clay mineral surfaces.