LEE- Çevre Bilimleri Mühendisliği ve Yönetimi- Yüksek Lisans

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http://hdl.handle.net/11527/19237

Gözat

Yazar "Alaton Arslan, İdil" ile LEE- Çevre Bilimleri Mühendisliği ve Yönetimi- Yüksek Lisans'a göz atma
  • Öge
    The effect of peroxides on the ozonation of reactive dyebath effluent
    (Graduate School, 2023-01-18) Farasat, Shima ; Alaton Arslan, İdil ; 501171756 ; Environmental Sciences, Engineering and Management
    The world's population, industry, and urbanization are all expanding at a rapid rate, which is leading to increased water consumption. Additionally, the quality of water is endangered by the effluent discharge from anthropogenic activities into natural water sources. Particularly in the aquatic system, industrial pollutants such as textile dyes pose a serious risk in the aquatic environment. The production of more than 100,000 dyestuffs has led to the release of significant volumes of colored effluent into wastewater by a variety of industrial processes, including textile, tannery, paint, pigments, pulp, and paper manufacturing. Around 15% of the total amount of dyes being used by different industries is discharged without proper treatment. Dyes are once released into aquatic environments, they might reduce light penetration, alter photosynthetic activity, and, once subjected to anoxic/anaerobic conditions, may be converted into more toxic/carcinogenic dye metabolites. Consequently, there is an urgent need to efficiently tackle the problem of color in dyehouse effluent. Among the textile dyes, fiber reactive dyes are used to dye cotton, regenerated cellulose, cellulose acetate, and wool fibers. They constitute up to 50 % of the total textile dye market and are intentionally designed to resist biodegradation as well as photochemical/thermal decomposition. Further, reactive dyes cannot be reused after the dyeing process and remain in their spent, hydrolyzed form. Hence, their removal becomes a major challenge for the textile dyer and finisher. Several treatment options, including adsorption, membrane operations, fungal treatment, and ozonation have already been investigated. However, these have shown rather limited success or are economically not feasible/costly and hence the search for more effective and, at the same time, sustainable / ecotoxicologically safe treatment alternatives remains a challenge and unsolved treatment problem. So-called Advanced Oxidation Processes (AOP) are applied to remove biologically resistant and/or toxic pollutants through the generation of highly reactive oxidizing species-free radicals. AOP involve conventional oxidants such as O3 or H2O2 (HP), UV light, (photo)catalysts, power ultrasound (sonolysis) and thermal energy to produce mainly hydroxyl radicals (HO) to improve oxidation, reduce toxicity and increase biodegradability. More recently, sulfate radicals (SO4- )-based AOP have attracted considerable attention. Originally introduced for soil and groundwater remediation in the late 1990s - early 2000s to overcome some technical limitations of H2O2 (HP), persulfates (PS) has been activated to initiate SO4- - based AOP. These are regarded as alternatives to the more traditional HO - based AOP in water/wastewater treatment. The advantages of PS-initiated AOP over HP-initiated AOP are a higher free radical formation yield, higher reduction potential but also inherent selectivity, and reduced storage and transportation costs. Moreover, SO4- - based AOP are less sensitive towards reaction conditions (pH, water/wastewater properties). PS can be activated by several direct/indirect methods such as coupling with metals/metal oxides, UV-C light, sonolysis (power ultrasound), thermally, or with strong oxidants such as ozone. In this way, it is expected to increase the removal efficiency of difficult-to-treat industrial pollutants. In particular, green oxidants such as peroxides (persulfate, hydrogen peroxide, peracetic acid, and percarbonate) have recently been used in combination with activators for the treatment of water and wastewater. Considering these facts, in the present study a commercially important and frequently used reactive dye, namely Reactive Red 21, was used as the model industrial pollutant and subjected to ozonation to study the effects of the peroxides like hydrogen peroxide HP, PS, PAA, and PC on ozone treatment in terms of color (peak absorbance) and total organic carbon (TOC) removal rates and efficiencies. The investigations on O3, O3/PS, O3/PC, and O3/PAA were carried out in the semi-batch reactors. Different amounts of peroxides (0.75, 1.5, 3, and 6 mM) were added to 100 mg/L dye solution in the reactors. The efficiency of dye discoloration was measured as a function of reaction time. In order to explore their oxidation potential and assess their potential contribution to color removal from the reactive dyebath in the absence of ozone, preliminary control tests were carried out just in the presence of peroxides. These experiments were conducted with 10 mM peroxide for 24 h exposure at the natural, alkaline pH of 11. No color removal was observed for HP and PC, while 75 % and 96 % color removals were obtained for the peroxides PS and PAA, respectively. During all ozonation experiments, color abatements followed first-order kinetics and color removal occurred within 2-4 min corresponding to an ozone dose of 144-288 mg. In this study, first-order color removal rate coefficients - kd values (in min -1) – were calculated for varying peroxide concentrations during ozone/peroxide treatments of the RR21 dyebath effluent. In this section results obtained with ozone/peroxide treatments were compared with ozonation alone (with no-0.00 mM peroxide). The addition of PS appreciably increased the kd values for RR21 effluent. According to the results, a slightly different pattern was obtained for O3/PAA treatment of RR21 effluent compared with O3/PS. 6.00 mM PAA had a strong negative effect on color removal rates and the kd value decreased to 1.5 min -1 for this PAA concentration indicating an overdose of PAA that resulted in a free radical scavenging (competitive inhibitory) effect. TOC removals were followed for ozonation and peroxide-assisted ozonation for 40 min at an ozone feed rate of 72 mg/min in the presence of 1.5 mM peroxide which treatment conditions were selected because they resulted in the highest color removal results and corresponded to a peroxide: ozone stoichiometry (molar ratio) of 0.2 (mM peroxide/mM O3), that is indicated as the theoretical optimum range for peroxide: ozone treatment processes. Results displays % TOC removals obtained for specific ozone dose (in mg O3/mg TOC0) for the above-mentioned reaction conditions. Because the initial TOC of the O3/PAA experiments is appreciably higher, the specific ozone dose is more than four times lower than for mere ozonation and the other ozone/peroxide treatments. The overall TOC removals were obtained in the range of 30-40% for ozonation (in the absence of peroxide; 36%), O3/PS (38%), and O3/PC (31%), whereas the overall percent relative TOC removal decreased to 18% for O3/PAA due to its higher initial organic carbon content. Ozone absorption rates measured for different treatment processes indicated that in the presence of PS and PAA, ozone absorption increased from 49% (ozonation only) to 55% and 59%, respectively. For O3/PC on the other hand, no increase but a decrease in ozone absorption rates to 41% was evident, speculatively due to a different oxidation pathway than the other two ozone combinations. Ozone absorption indicates enhanced ozone decomposition to less stable, free radicals as was expected for PS-and PAA-assisted ozonation. . According to the results, there is an inverse relationship between ozone absorption rates (ozone decomposition) and dissolved, molecular ozone concentrations. The biodegradability of the original and ozonated samples was also measured by using BOD7 tests and acclimated, activated sludge from a local textile wastewater treatment plant. The BOD7 values of the original and treated RR21 dyebath effluent samples were determined as 2.5, 4.6, 3.9, 5.8, and 2.1 mg O2/L for the original, ozonated, O3/PS, O3/PAA, and O3/PC-treated RR21 dyebath effluent samples. These values are very low and not very meaningful for interpretation, however, it is evident that biodegradability changes of the reaction solution are minor and the degradation products are not more biodegradable than the original RR21 dyebath effluent sample. Vibrio fischeri (V. fischeri) marine photobacterium was employed as the test organism to assess changes in acute toxicity during the application of the studied ozonation processes. Percent relative inhibition rates for the original and treated (ozone feed rate = 72 mg/min; ozonation time = time of complete color removal and 40 min; peroxide concentrations = 0.00 and 1.5 mM pH = 11.0) RR21 dyebath effluent samples are studied. Acute toxicity experiments conducted with Vibrio fischeri were performed for contact times of t=15 min and t=30 min. Practically no inhibition was observed at the end of the 60th min-treatment for all O3/HP, O3/PS, O3/PAA and O3/PC processes.