Ayfer Yediler

Ozonation of hydrolyzed azo dye reactive yellow 84 (CI).

The combination of chemical and biological water treatment processes is a promising technique to reduce recalcitrant wastewater loads. The key to the efficiency of such a system is a better understanding of the mechanisms involved during the degradation processes. Ozonation has been applied to many fields in water and wastewater treatment. Especially for textile mill effluents ozonation can achieve high color removal, enhance biodegradability, destroy phenols and reduce the chemical oxygen demand (COD). However, little is known about the reaction intermediates and products formed during ozonation. This work deals with the degradation of hydrolyzed Reactive Yellow 84 (Color Index), a widely used azo dye in textile finishing processes with two monochlorotriazine anchor groups. Ozonation of the hydrolyzed dye in ultra pure water was performed in a laboratory scale cylindric batch reactor. Decolorization, determined by measuring the light absorbance at the maximum wavelength in the visible range (400 nm), was almost complete after 60 and 90 min with an ozone concentration of 18.5 and 9.1 mg/l, respectively. The TOC/TOC0 ratio after ozonation was about 30%, the COD was diminished to 50% of the initial value. The BOD5/COD ratio increased from 0.01 to about 0.8. Oxidation and cleavage of the azo group yield nitrate. Cleavage of the sulfonic acid groups of aromatic rings caused increases in the amount of sulfate. Formic acid and oxalic acid were identified as main oxidation products by high performance ion chromatography (HPIC). The concentrations of these major products were monitored at defined time intervals during ozonation.

Kinetics of decolorization and mineralization of reactive azo dyes in aqueous solution by the UV/H2O2 oxidation

The photodegradation of three non hydrolysed reactive azo dyes (Reactive red 120, Reactive black 5, Reactive yellow 84) in aqueous solution was investigated in a laboratory-scale batch photoreactor equipped with an immersed low-pressure mercury lamp. Six different doses of hydrogen peroxide, at constant initial concentration of the substrate (100 mg/l) were used. The pseudo-first order rate constants have been calculated from the experimental kinetic curves, for the three azo dyes. These rate constants have extreme values of the order of 0.1 min−1 at a H2O2 dose of 24.5 mmol/l. The effectiveness of the UV/H2O2 process has been evaluated by the degree mineralization of the total organic carbon (TOC), as a complementary indicator of the treatment efficiencies. Our results confirm the suitability of the UV/H2O2 process as a textile wastewater pre-treatment step, once optimum operating conditions and cost effectiveness of the method are established.

DECOLORIZATION OF DISPERSE RED 354 AZO DYE IN WATER BY SEVERAL OXIDATION PROCESSES-A COMPARATIVE STUDY

The degradation of the Disperse Red 354 azo dye in water was investigated in laboratory-scale experiments, using four advanced oxidation processes (AOPs): ozonation, Fenton, UV/H2O2, and photo-Fenton. The photodegradation experiments were carried out in a stirred batch photoreactor equipped with an immersed low-pressure mercury lamp as UV source. Besides the conventional parameters, on acute toxicity test with a LUMIStox 300 instrument was conducted and the results were expressed as the percentage inhibition of the luminescence of the bacteria Vibrio fisheri. The results obtained showed that the decolorization rate was quite different for each oxidation process. After 30 min reaction time the relative order established was: UV/H2O2/Fe(II) > Dark/H2O2/Fe(II) > UV/H2O2=O3 > UV/H2O2/Lyocol. During the same reaction period the relative order for COD removal rate was slightly different: UV/H2O2/Fe(II) > Dark/H2O2/Fe(II) > UV/H2O2 > UV/H2O2/Lyocol > O3. A color removal of 85% and COD of more than 90% were already achieved after 10 min of reaction time for the photo-Fenton process. Therefore, the photo- Fenton process seems to be more appropriate as the pre-treatment method for decolorization and detoxification of effluents from textile dyeing and finishing processes. Sulphate, nitrate, chloride, formate and oxalate were identified as main oxidation products.

Toxicity evaluation of reactive dyestuffs, auxiliaries and selected effluents in textile finishing industry to luminescent bacteria Vibrio fischeri

The toxicity of 17 selected process effluents, 11 reactive dyestuffs and 8 auxiliaries from a textile dyeing and finishing mill in Ayazaga, Istanbul, Turkey was evaluated by bioluminescence test using bacteria Vibrio fischeri in LUMIStox 300. The EC20 and EC50 for auxiliaries, the EC20 for dyestuffs were determined. For selected process effluents GL-values, the dilution level at which a wastewater sample causes less than 20% inhibition, were examined. Our results demonstrate that the toxicity assessment with luminescent bacteria is effective and of practical use for chemicals applied in textile finishing industry with the limitation of the deep dark-colored dye bath samples and for the related effluents. Inhibition effects of numerous dyestuffs as well as auxiliaries to luminescent bacteria differed considerably with a range 5-600 mg l(-1) for EC20 and 9-6930 mg l(-1) for EC50, respectively. Among 17 effluents, I sample exhibited high toxicity (GL = 100), 7 showed moderate toxicity (GL = 12-32), and 9 had a GL-value <10 indicating a low or no toxicity.

Ozonation of an azo dye C.I. Remazol Black 5 and toxicological assessment of its oxidation products

The effect of ozonation (20.5 mgl(-1)) on the degradation processes of an azo dye, Remazol Black 5 (RB5; CI) was studied. Conventional parameters such as chemical oxygen demand (COD), total organic carbon (TOC), pH, conductivity, colour removal, biodegradability (BOD(5/28)), and toxic potential of the dye and its degradation products were monitored during the process. The results obtained indicated that ozonation is a highly effective way to remove the colour of a corresponding dye solution. However, a considerable organic load still remained as indicated by high COD and TOC residues. The COD, TOC reductions were about 40% and 25% for 6 h ozonation of 2 gl(-1) RB5 aqueous solution. During the ozonation process the rapid decrease of pH and the sharp increase of conductivity indicated the formation of acidic by-products and small fragments and ions which were identified by high performance ion chromatography. The BOD28 data revealed that first by-products after partial ozonation (10-150 min) of RB5 were more biodegradable than the parent compound and ozonation can enhance the biodegradability of azo dyes. During the first 150 min of total 360 min of oxidation, the formation of first by-products with high toxic potential took place as it could be confirmed by two acute toxicity-screening tests, the bioluminescence test (Vibrio fischerii) and the neutral red cytotoxicity assay (rat hepatoma cells). The significant enhancement of microbial biodegradability after long-term ozonation could also be seen as a decrease of toxic intermediates in correlation with the ozonation time as indicated in BOD28 biological degradation test results.

Effects of dye additives on the ozonation process and oxidation by-products: a comparative study using hydrolyzed C.I. Reactive Red 120

Decolorization of azo reactive dyes by ozone has been described by several authors. However, the efficiency of ozonation and the by-products produced by dye additives/impurities such as synthetic precursors, by-products, salts and dispersing agents in commercial azo dyes during the oxidative treatment have not been reported. To investigate the effects of such impurities on the ozonation process and on the formation of oxidation by-products, a commercially available azo reactive dye C.I. Reactive Red 120 was chosen as a model compound. Experiments were conducted in aqueous solutions of hydrolyzed C.I. Reactive Red 120 (200 mg/l) either with or without purification. Treatment efficiencies of purified and unpurified dye were evaluated in terms of COD, BOD28, absorbance and initial decolorization rates. Additionally, organic and inorganic anions were analyzed by HPIC. After 28 days of incubation the BOD28/COD ratio increased from 0.22 to 0.48 and from 0.05 to 0.26 for purified and unpurified C.I. Reactive Red 120, respectively, indicating an enhancement of biodegradable compounds in the ozonated solutions. The results also illustrate that the dye additives/impurities in commercial dyes affect the microbial activity as well as the biodegradability. It is therefore recommended that dyes should be purified before ozonation, if detailed information on the degradation processes and the resulting oxidation by-products are required.

Ozonation of high strength segregated effluents from a woollen textile dyeing and finishing plant

Abstract Effluents from dyeing processes of woollen textile finishing industries are highly polluted with recalcitrant compounds compared to effluents from rinsing and finishing processes. Oxidation of woollen textile dyeing effluent consisting of wastewater generated from spent dye baths and first and second rinses (remaining composite wastewater) were investigated. Ozone oxidation (CO3=18.5 mg/l; input rate) was applied on remaining composite wastewater, before and after the biological treatment, for various time intervals. Treatment efficiency was monitored by decolorization and by COD removal rates. Additionally, toxicity tests (bioluminescence test) were carried out to determine the effect of oxidation process. The results indicated that 40 min ozonation of biologically treated wastewater yielded almost colorless effluent with a decolorization efficiency of around 98–99% and with a corresponding ozone absorption rate of 58.0 mg/l. Biological treatment followed by 10 min ozone oxidation reduced the overall toxicity significantly (92%). However, ozonation was found to have only slight effect on COD removal.

Ozonation of oxytetracycline and toxicological assessment of its oxidation by-products

Antibiotic formulation effluents are well known for their difficult elimination by traditional bio-treatment methods and their important contribution to environmental pollution due to its fluctuating and recalcitrant nature. In the present study the effect of ozonation on the degradation of oxytetracycline (OTC) aqueous solution (100mgl(-1)) at different pH values (3, 7 and 11) was investigated. Ozone (11mgl(-1) corresponds the concentration of ozone in gas phase) was chosen considering its rapid reaction and decomposition rate. The concentration of oxytetracycline, chemical oxygen demand (COD), biochemical oxygen demand (BOD) and BOD5/COD ratio were the parameters to evaluate the efficiency of the ozonation process. In addition, the toxic potential of the OTC degradation was investigated by the bioluminescence test using the LUMIStox 300 instrument and results were expressed as the percentage inhibition of the luminescence of the marine bacteria Vibrio fischeri. The results demonstrate that ozonation as a partial step of a combined treatment concept is a potential technique for biodegradability enhancement of effluents from pharmaceutical industries containing high concentration of oxytetracycline provided that the appropriate ozonation period is selected. At pH 11 and after 60min of ozonation of oxytetracycline aqueous solutions (100 and 200mgl(-1)) the BOD5/COD ratios were 0.69 and 0.52, respectively. It was also shown that COD removal rates increase with increasing pH as a consequence of enhanced ozone decomposition rates at elevated pH values. The results of bioluminescence data indicate that first by-products after partial ozonation (5-30min) of OTC were more toxic than the parent compound.

PCDD/Fs, PCBs, HCHs and HCB in sediments and soils of Ya-Er Lake area in China: Results on residual levels and correlation to the organic carbon and the particle size

Sediments and soils collected from the Ya-Er Lake area in China were analysed for the polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polychlorinated biphenyl (PCBs), hexachlorocyclohexane (HCHs) and hexachlorobenzene (HCB). The results indicated the main pollution problems in the Ya-Er Lake area, which was heavily polluted by HCHs and chlorobenzenes, now is dominantly polluted by PCDD/Fs, PCBs and HCB. The occurrence of PCDD/Fs and PCBs with relatively high levels of HpCDDs, OCDD and low chlorinated-substituted PCBs, is attributed to the discharge of waste water and biodegradation. The vertical distributions of HCH-residues are related with the content of organic carbon and particle size. Copyright (C) 1996 Elsevier Science Ltd

Adsorption of linear alkylbenzene sulfonate (LAS) on soils

Abstract Experimental measurements of the adsorption of linear alkylbenzene sulfonate (LAS) on soils were made at 25°C using a continuous adsorption apparatus. The adsorption of LAS on natural soils could be divided into two stages: linear and exponentially increasing isotherms. At low LAS concentration ( −1 ), the adsorption isotherms were linear and Kd was among 1.2 to 2.0. At high LAS levels (>90 μg ml −1 ), cooperative adsorption was observed and the adsorption amount of LAS increased exponentially with the increasing of LAS concentration in solution. LAS adsorption mechanisms on soil were mainly specific site surface interactions and hydrogen bonding. The LAS adsorption capacity of a soil significantly depended on its physical clay content. Under real soil environments where LAS levels are rather low, the LAS adsorption ability of a soil is very weak.