Phsicochemical Treatment of Hazardous Wastes - Chapter 14 (end) pps

14 Combinations of Advanced Oxidation Processes 14.1 Introduction As advanced oxidation processes (AOPs) continue to enter the commercial market, treatment efficiency becomes an important factor for selecting a process with better cost efficiency. To analyze the cost efficiency, comparisons between selected AOPs have been reported in recent years. A number of variables, including initial conditions, pH, oxidant, and catalyst concentrations, have been analyzed in combination with kinetic parameters of the process. The kinetics of each process are described by the rate constants and/ or the reaction half times. These investigations have been conducted under identical experimental conditions so that treatment efficiency can be compared under the same conditions. In addition, combinations of various AOPs have also been analyzed with respect to cost efficiency. This comparison was carried out by combining various oxidants such as oxygen, ozone, and hydrogen peroxide (H 2 O 2 ) with catalysts such as ultraviolet (UV), Fe 2+ , and TiO 2 . In general, synergic effects exist when two oxidation systems were combined. This synergy was reflected in a marked increase in the free-radical reaction pathway. The effect was also observed to increase with the com- plexity of the oxidation systems used. The only exception arose in the comparison of Fenton’s reagent system with a combined Fenton’s reagent/ozone system, in which case there seems to be interference of ozone with Fenton’s reagent through oxidation of Fe 2+ , which reduces the amount of Fe 2+ to decompose H 2 O 2 into hydroxyl radicals. 14.2 Fundamental Theory The destruction kinetics of organic pollutants may be inhibited in wastewaters containing complex compounds. Under such conditions, the combination TX69272_C14.fm Page 533 Friday, November 14, 2003 2:13 PM © 2004 by CRC Press LLC 534 Physicochemical Treatment of Hazardous Wastes of UV, O 3 , and H 2 O 2 systems could be a better process because hydroxyl radicals are generated by several mechanisms. As a result, UV/O 3 /H 2 O 2 is less affected by color and turbidity in wastewater than UV/O 3 or UV/H 2 O 2 system. They are also applicable over a wider pH range when compared to UV/H 2 O 2 systems. Figure 14.1 shows a proposed mechanistic pathway that exhibits a network of free-radical chain reactions involving HO 2 • /O 2 , HO 3 • / O 3 •– , and OH • /O •– in the generation and consumption of OH • as proposed by Hong et al. (1996). This reaction network was a revised version based upon the reaction pathways formulated by Staehelin and Hoigne (1985) and Peyton and Glaze (1988). Kinetic rate constants of various reactions in the reaction pathways are listed in Table 14.1. The model includes (1) dark reactions such as the decomposition of O 3 in water and the interaction of O 3 and H 2 O 2 • , and (2) UV-assisted actions such as the photolysis of O 3 and H 2 O 2 . In aqueous media, the free-radical chain reactions are initiated either by the k 1 step or by the k 7 followed by the k 6 step. When H 2 O 2 is added to ozonated water (i.e., peroxone), the k 7 step that produces HO 2 – becomes inconse- quential, and a large amount of H 2 O 2 is available through the addition of the peroxone system. Next, the k 6 step becomes the predominant super- oxide- and ozonide-producing pathway, an important chain-initiation reaction. This is evident when the reaction rates of the k 1 and k 6 steps are compared with a typical batch dose of H 2 O 2 (e.g., 10 to 200 mg/L). For applied [O 3 ] = 2 × 10 –5 M (1 mg/L) and [H 2 O 2 ] T = 1.5 × 10 –3 M (50 mg/L) at pH 7 (Hong et al., 1996): k 1 [O 3 ] [OH – ] = 70(2 × 10 –5 )(10 –7 ) = 1.4 × 10 –10 M –1 s –1 (14.1) k 6 [O 3 ] [HO 2 – ] = k 6 [O 3 ] [H 2 O 2 ] T ([H+]/ K [H 2 O 2 ] + 1 + K [H 2 O 2 ]/[H + ]) –1 = (2.8 × 10 6 )(2 × 10 –5 )(1.5 × 10 –3 )(2.5 × 10 –5 ) = 2.1 × 10 –6 M –1 s –1 (14.2) Therefore, the enhancement of the peroxone system is due to faster chain initiation. In addition, when a large amount of H 2 O 2 is added, the scavenging of OH • by H 2 O 2 ( k 5 step) may overtake the O 3 ( k 4 step). For example, [O 3 ] = 1 mg/L and [H 2 O 2 ] T = 50 mg/L at pH 7: k 4 [O 3 ][OH • ] = (1.1 × 10 8 )(2 × 10 –5 )[OH • ] = (2.2 × 10 3 )[OH • ] M –1 s –1 (14.3) k 5 [H 2 O 2 ][OH • ] ≈ k 5 [H 2 O 2 ] T [OH • ] = (2.7 × 10 7 )(1.5 × 10 –3 )[OH • ] = (4.0 × 10 4 )[OH • ] M –1 s –1 (14.4) The model shows that UV illumination introduces additional and more productive OH • generation pathways through three different mechanisms: (1) direct photolysis of O 3 , (2) photolysis of O 3 to produce H 2 O 2 , and (3) photolysis of the formed H 2 O 2 . The contribution of each process to the TX69272_C14.fm Page 534 Friday, November 14, 2003 2:13 PM © 2004 by CRC Press LLC Combinations of Advanced Oxidation Processes 535 generation of hydroxyl radical will be presented in detail in Section 14.4. The reaction mechanism in Figure 14.1 demonstrates that pH is an important parameter. Due to the fact that some anions such as HO 2 – react faster than their conjugate acids, pH will influence the reaction kinetics and thus the steady-state concentrations of various intermediates. As a result, the treatment efficiency can be greatly impacted by pH. The acid–base equilibria of various reacting species must be considered, as shown in Table 14.1 (Hong et al., 1996). The relative amounts of UV illumination, O 3 , H 2 O 2 , and scav- engers (S i ) such as HCO 3 – are critical in determining the level of active OH • radical in the system. In UV-illuminated reactions, contaminant degradation rates are typically observed to be much faster than dark reactions (Zappi et al., 1993). 14.3 Process Description From the late 1980s to the early 1990s, Ultrox International, a commercial manufacturer, has demonstrated the efficacy of ultraviolet-light-enhanced oxidation at sites belonging to the Department of Defense (DOD) and the Superfund sites (Zeff and Barich, 1992). Figure 14.2 illustrates a flow diagram of the Ultrox UV/oxidation treatment system. It shows that two different oxidants are used in the process. Ozone is generated from air and hydrogen FIGURE 14.1 Free-radical chain reaction of UV/O 3 /H 2 O 2 system. (From Hong, A. et al., J. Environ. Eng., 122(1), 58–62, 1996. With permission.) TX69272_C14.fm Page 535 Friday, November 14, 2003 2:13 PM © 2004 by CRC Press LLC 536 Physicochemical Treatment of Hazardous Wastes peroxide from the feed tank; therefore, the process can be operated in any combinations, such as UV/O 3 , UV/H 2 O 2 , and UV/O 3 /H 2 O 2. Figure 14.3 presents an engineering drawing of the process. Standard equipment designs is used in all of these installations. Reactor size varies from 300 to 4800 gal, and reactors are fabricated from stainless steel. Ozone generators range from 21 to 140 lb/day. The ozone is dispersed through porous, stainless-steel diffusers. The number of diffusers required depends on the organic compound being oxidized and the degree of removal required. The UV lamps are enclosed within quartz tubes for easy replace- ment and are mounted vertically within the reactor (Zeff and Barich, 1992). By utilizing a combined UV/O 3 /H 2 O 2 process, the Ultrox oxidation systems proved to be efficient in removing volatile organic compounds (VOCs), benzene, toluene, xylene, hydrazines, phenols, chlorophenols, TABLE 14.1 Rate and Equilibrium Constants for Various Reactions in the UV/O 3 /H 2 O 2 Process Reaction Constant Ref. O 3 + OH – = O 3 . + HO 2 • k 1 = 70 M –1 s –1 Buhler et al. (1984) O 2 •– + O 3 = O 3 • + O 2 k 2 = 1.6 × 10 9 M –1 s –1 Buhler et al. (1984) HO 3 = H • + O 2 k 3 = 1.1 × 10 5 M –1 s –1 Buhler et al. (1984) OH • + O 3 = HO 2 • + O 2 k 4 = 1.1 × 10 8 M –1 s –1 Sehested et al. (1984) OH • + H 2 O 2 = HO 2 • + H 2 O 2 k 5 = 2.7 × 10 7 M –1 s –1 Christensen et al. (1982) HO 2 – + O 3 • = HO 2 • + O 3 • k 6 = 2.8 × 10 6 M –1 s –1 Staehelin and Hoigne (1982) O 3 + OH – = HO 2 • + O 2 k 7 = 48 M –1 s –1 Bahnemann and Hart (1982) OH • + A i = A′ i + OH ; A i = contaminant I — OH • + HCO 3 = HCO 3 • + OH = 1.5 × 10 7 M –1 s –1 Staehelin and Hoigne (1982) OH • + CO 3 2– = CO 3 •– + OH – = 4.2 × 10 8 M –1 s –1 Staehelin and Hoigne (1982) O 2 •– + HO 3 • = O 3 + HO 2 – k t = 10 10 M –1 s –1 Staehelin and Hoigne (1982) O 3 + H 2 O + hν = 2 • OH + O 2 — O 3 + H 2 O + hν = H 2 O 2 + O 2 — H 2 O 2 + hν = 2 • OH — H 2 O 2 = H + + HO 2 – = 11.6 Saucre et al. (1984) HO 2 • = H + + HO 2 •– pK = 4.8 Bielski et al. (1985) HO 3 • = H + + HO 3 •– pK = 6.2 Buhler et al. (1984) OH • = H + + O •– pK = 11.8 Weeks and Rabani (1966) Source: From Hong, A. et al., J. Environ. Eng. 122(1), 58–62, 1966. With permission. k A i ′ k 1 ′ k 2 ναφ λ1 I 0 O 3 ναφ λ ′ 1 I 0 O 3 ναφ λ22 I 0 HO 22 pK HO 22 TX69272_C14.fm Page 536 Friday, November 14, 2003 2:13 PM © 2004 by CRC Press LLC Combinations of Advanced Oxidation Processes 537 dioxanes, polychlorinated biphenyls (PCBs), and pesticides present in wastewaters and groundwaters. Figure 14.4 is the three-dimensional view of the process. The figure illustrates the relative water head at different stages. Because of flexible design, Ultrox UV/oxidation treatment systems have a number of advantages: (1) very few moving parts; (2) operation at low pressure; (3) minimum maintenance; (4) full-time or intermittent operation in either a continuous or batch treatment mode; (5) use of efficient, low-temperature, and long-life UV lamps; and (6) use of a microprocessor to control and automate the treatment process (Zeff and Barich, 1992). 14.4 Degradation of Organic Pollutants 14.4.1 Phenol Phenol is degraded faster by ozone processes under basic pH than acidic pH because the contribution of hydroxyl radicals increases with pH. Table 14.2 lists the degradation efficiency of phenol under various experimental FIGURE 14.2 Flow diagram of Ultrox system. (From USEPA, Ultrox International Ultraviolet Radiation/ Oxidation Technology—Applications Analysis Report, EPA/540/A5-89/012, September 1990.) TX69272_C14.fm Page 537 Friday, November 14, 2003 2:13 PM © 2004 by CRC Press LLC 538 Physicochemical Treatment of Hazardous Wastes FIGURE 14.3 Flow diagram of Ultrox system. (From USEPA, Ultrox International Ultraviolet Radiation/ Oxidation Technology—Applications Analysis Report, EPA/540/A5-89/012, September 1990.) FIGURE 14.4 Isometric view of Ultrox system. (From USEPA, Ultrox International Ultraviolet Radiation/ Oxidation Technology—Applications Analysis Report, EPA/540/A5-89/012, September 1990.) Hydrogen Peroxide Feed Tank Contaminated Water Feed Tank From Shallow Groundwater Monitoring Wells Ozone Diffuser (typical) Stainless Steel Reactor UV Lamp (typical) Headspace Overflow Weir (typical) Treated Effluent Storage Tank Effluent Sample Tap Sight Glass Ozone from Ozone Generator Needle Valve (typical) Rotameter (typical) Ozone Manifold Catalytic Ozone Decomposer TX69272_C14.fm Page 538 Friday, November 14, 2003 2:13 PM © 2004 by CRC Press LLC Combinations of Advanced Oxidation Processes 539 variable conditions. At neutral pH and at low H 2 O 2 concentrations, H 2 O 2 improved ozonation slightly but showed an inhibitory effect at concentrations higher than 6.2 mM. The same effect was observed for the combination of UV/O 3 /H 2 O 2 , and the limiting H 2 O 2 concentration was found to be 0.07 mM. Under UV illumination alone, the best conditions were found at pH 5 without any buffer. The degradation rate increased considerably when H 2 O 2 was used; nevertheless, the initial H 2 O 2 concentration exerted little influence on the range used. In photocatalysis, the degradation rate increased with the catalyst concentration up to a value of 0.5 g/L. From that point, the rate was almost constant. In Fenton’s reaction, the limiting factor was the amount of hydrogen peroxide. The higher the amount of H 2 O 2 , the faster the degradation will be. Also, as the concentration of Fe(II) ion is increased, the degradation rate is improved. TABLE 14.2 Phenol Degradation in H 2 O 2 Oxidation Systems as a Function of Time, pH, and Initial Reactant Concentrations AOPs pH (mM) C Fe(II) (mM) (g/L) Time of Treat- ment (min) Phenol Degradation (%) O 3 O 3 O 3 5.7–3 7.2 buffered 9.4 buffered 0 0 0 0 0 0 0 0 0 80 80 80 85.4 90.0 100 O 3 /H 2 O 2 O 3 /H 2 O 2 O 3 /H 2 O 2 O 3 /H 2 O 2 O 3 /H 2 O 2 O 3 /H 2 O 2 O 3 /H 2 O 2 O 3 /H 2 O 2 O 3 /H 2 O 2 5–3.4 5–3.4 6.8 buffered 6.8 buffered 6.8 buffered 6.8 buffered 6.8 buffered 9.3 buffered 9.3 buffered 6.8 534 0.62 6.2 31 78 155 6.2 31 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 80 80 80 80 80 80 80 80 80 80.6 58.3 90.4 93.4 86.9 86.5 77.7 92.5 88.8 UV UV UV 4.4 – 4 6.8 buffered 11.5 buffered 0 0 0 0 0 0 0 0 0 30 30 30 24.2 14.0 5.0 UV/H 2 O 2 UV/H 2 O 2 UV/H 2 O 2 UV/C 5–3.8 (3.5–2.5) (3.2–2.3) (3.1–2.3) —0 0 0 0 0 0 0 0 30 30 30 30 24.2 87.1 90.6 89.8 UV/O 3 UV/O 3 UV/O 3 5.2–3 6.9 buffered 9.4 buffered 0 0 0 0 0 0 0 0 0 80 80 80 80.9 92.6 91.9 Source: Esplugas, S. et al., Water Res., 36, 1034–1042, 2002. With permission. C HO 22 C TiO 2 TX69272_C14.fm Page 539 Friday, November 14, 2003 2:13 PM © 2004 by CRC Press LLC 540 Physicochemical Treatment of Hazardous Wastes 14.4.1.1 Comparison of Pseudo First-Order Kinetic Constant The kinetic parameters chosen for comparison are rate constants and t 1/2 . Radiation influences and the effect of reactor design are usually identical when these kinetic data are compared between the various AOPs tested. The values for pseudo first-order kinetics and half-lives for various processes are given in Table 14.3. In most cases, the values of t 3/4 are equal to two times those of t 1/2 ; therefore, the reactions obey a first-order kinetics. Figure 14.5. shows that Fenton’s reagent has the largest rate constant, e.g., approximately 40 times higher than UV alone, followed by UV/H 2 O 2 and O 3 in terms of the pseudo first-order kinetic constants. Clearly, UV alone has the lowest kinetic rate constant of 0.528 hr –1 . 14.4.1.2 Cost Estimation The economic evaluation of treatment processes is very important in selecting an AOP from different available systems. The overall costs are repre- sented by the sum of the capital, operating, and maintenance costs (Table TABLE 14.3 First-Order Rate Constants t 1/2 and t 3/4 for Phenol Degradation under Various AOPs Process k (hr –1 ) t 1/2 (hr) t 3/4 (hr) O 3 /H 2 O 2 2.13 0.325 0.63 UV/O 3 3.14 0.221 0.417 O 3 4.42 0.157 0.317 UV/O 3 /H 2 O 2 4.17 0.166 0.333 UV/H 2 O 2 6.26 0.111 0.383 UV 0.528 1.31 3.33 Photo catalysis 0.582 1.19 2.47 Fenton 22.2 0.0312 0.067 Source: Esplugas, S. et al., Water Res., 36, 1034–1042, 2002. With permission. FIGURE 14.5 Comparison of the rate constants for selected AOPs. All processes have been approximately first-order with respect to substrate concentration. (Data from Esplugas, S. et al., Water Res., 36, 1034–1042, 2002. With permission.) Processes k(per hr) TX69272_C14.fm Page 540 Friday, November 14, 2003 2:13 PM © 2004 by CRC Press LLC Combinations of Advanced Oxidation Processes 541 14.4). An estimation of costs has been made in this section; however, it should be pointed out that costs could considerably decrease for photocatalytic treatments when solar light is used. Figure 14.6 indicates that UV alone has the maximum cost because it has the lowest kinetic rate constant. Fenton’s reagent has reasonably lower costs and the highest rate constant. Different AOPs (ozone and its combinations, photocatalysis and UV/H 2 O 2 , photocatalysis and Fenton’s reagent) have been compared in terms of the degradation of phenol in aqueous solution. In UV processes (UV, UV/H 2 O 2 , and photocatalysis), the degradation rate produced by the UV/H 2 O 2 process was almost five times higher than photocatalysis and UV alone. Fenton’s reagent showed the fastest degradation rate, 40 times higher than the UV process and photocatalysis and five times higher than ozonation. Nevertheless, the degradation rates and lower costs obtained with ozonation make it the most appealing choice for phenol degradation. 14.4.2 para-Hydroxybenzoic Acid para-Hydroxybenzoic acid is a very common pollutant in a variety of industrial wastewaters (olive oil and distillation industries). Because it is TABLE 14.4 Analysis of Costs Associated with Various AOPs Process k (hr –1 ) Cost ($/kg) UV 0.528 172.2 O 3 /H 2 O 2 2.13 2.71 UV/O 3 / 3.14 9.28 UV/O 3 /H 2 O 2 4.17 7.12 O 3 4.42 0.81 Fenton 22.2 3.92 Source: Esplugas, S. et al., Water Res., 36, 1034–1042, 2002. With permission. FIGURE 14.6 Cost analysis of selected AOPs. (Data from Esplugas, S. et al., Water Res., 36, 1034–1042, 2002. With permission.) 0 50 100 150 200 1 Processes Cost $ ( per kg) UV O3/UV O3/UV/ /H2O Fenton O3/H2O2 O3 TX69272_C14.fm Page 541 Friday, November 14, 2003 2:13 PM © 2004 by CRC Press LLC 542 Physicochemical Treatment of Hazardous Wastes highly toxic and refractory to anaerobic biological treatment, it was chosen for the comparison as being representative of phenolic acids, and its degradation efficiency and kinetics are compared for several AOPs. The first stage was to compare the 12 oxidation processes applied to the destruction of p-hydroxy-benzoic acid. Table 14.5 lists the semi-reaction times and the conversions attained at 5 and 10 min of reaction time. The kinetic parameters of different oxidation processes are also shown in Table 14.5. Figure 14.7 demonstrates that Fenton’s reagent has the highest kinetic rates followed by ozonation and then UV irradiation. To study the improvement by different AOPs, the various oxidation systems are divided into three groups corresponding to the three basic oxidation processes from which they derive: UV irradiation, ozonation, and Fenton’s reagent. TABLE 14.5 Oxidation Rate Constants for Various AOPs Oxidation Process k (min –1 ) t 1/2 (min) UV/O 3 /H 2 O 2/ Fe 2+ 0.46510067 1.49 UV/H 2 O 2/ Fe 2+ 0.33157895 2.09 O 3 /H 2 O 2 /Fe 2+ 0.231 3.00 UV/O 3 /H 2 O 2 0.20086957 3.45 H 2 O 2 /Fe 2+ 0.17111111 4.05 UV/H 2 O 2 0.154 4.50 O 3 /H 2 O 2 0.1125 6.16 UV/O 3 0.10862069 6.38 O 3 /Fe 2+ 0.10358744 6.69 O 3 0.08640898 8.02 UV/TiO 2 0.06861386 10.1 UV 0.03705882 18.7 Source: Data from Beltan-Heredia, J. et al. Chemosphere, 42, 351–359, 2001. FIGURE 14.7 Selected destruction rate constants for p-hydroxybenzoic acid. (Data from Beltan-Heredia, J. et al. Chemosphere, 42, 351–359, 2001.) Processes k( per min) TX69272_C14.fm Page 542 Friday, November 14, 2003 2:13 PM © 2004 by CRC Press LLC [...]... FIGURE 14. 18 Rates of formation of 2- and 4-chlorophenol by-products (From Boncz, M.A et al., Water Sci Technol., 35(4), 65–72, 1997 With permission.) rates of para- and ortho-chlorophenols The reactivity of chlorophenolate anion is higher than that of chlorophenol itself, as can be seen from the comparison between the oxidation of 2–CP and 4-CP at increasing pH values 14. 4.4 Reactive Dyes 14. 4.4.1... TX69272_C14.fm Page 551 Friday, November 14, 2003 2:13 PM Combinations of Advanced Oxidation Processes 551 TABLE 14. 12 Rate Constants and t1/2 for Chlorophenols Compound kt × 103 min–1 t1/2 (min) 4-CP 2-4 -DCP 2,4,6-TCP 2,3,4,6-TeCP 644 65 68 71 1.3 15.6 11.8 9.7 Source: Data from Benitez, F.J et al., Chemosphere, 41, 1271–1277, 2000 kt * 1000 (per min) 700 600 500 400 300 200 100 0 4-CP 2-4 -DCP 2,4,6-TCP... PM Combinations of Advanced Oxidation Processes 549 TABLE 14. 10 Oxidation Rate Constants for Various AOPs kt × 103 min–1 Compound 4-CP 2-4 -DCP 2,4,6-TCP 2,3,4,6-TeCP kr × 103 min–1 601 44 33 29 36 6.9 7.2 7.9 Source: Data from Benitez, F.J et al., Chemosphere, 41, 1271–1277, 2000 40 3 Kr * 10 (per min) 35 30 25 20 15 10 5 0 4-CP 2,4-DCP 2,4,6-TCP 2,3,4,6-TeCP Chloro compounds FIGURE 14. 14 Combined process... Table 14. 24 and Figure 14. 25 14. 4.8 Fulvic Acids Volk et al (1997) assessed the effects of ozone, ozone/hydrogen peroxide, and catalytic ozone by changes in the organic constituents of a synthetic solution of fulvic acids Initial dissolved organic carbon (DOC) and © 2004 by CRC Press LLC TX69272_C14.fm Page 562 Friday, November 14, 2003 2:13 PM 562 Physicochemical Treatment of Hazardous Wastes TABLE 14. 23... 300 Time, sec FIGURE 14. 24 Degradation kinetics of phenanthrene with UV/ozone/H2O2 system (From Trapido, M and Veressinina, Y., Environ Technol., 16, 729–740, 1995 With permission.) © 2004 by CRC Press LLC TX69272_C14.fm Page 560 Friday, November 14, 2003 2:13 PM 560 Physicochemical Treatment of Hazardous Wastes TABLE 14. 19 Half-Life of Phenanthrene by Various AOPs System Half-Life (s) O3/H2O2 UV/O3... 2:13 PM 548 Physicochemical Treatment of Hazardous Wastes kp *1000 (per min) 450 400 350 pH 2 pH9 300 250 200 150 100 50 0 4-CP 2-4 -DCP 2,4,6-TCP 2,3,4,6-TeCP CPs FIGURE 14. 13 Effect of pH on chlorophenol oxidation rates at various pH values (Data from Benitez, F.J et al., Chemosphere, 41, 1271–1277, 2000.) hydroxylation is the first elementary step and precedes dissociation of chlorine atoms (Tang and... the degradation rate of chlorophenols by UV/H2O2 Figure 14. 12 suggests that 4-CP was rapidly degraded by Fenton’s reagent, and decreasing rates were obtained for 2,4-DCP, 2,4,6-TCP, and 2,3,4,6-TeCP This suggests that the increase of chlorine atoms in a chlorophenol molecule decreases the susceptibility of aromatic rings to attack by the hydroxyl radicals gen- TABLE 14. 9 Comparison of Rate Constants for... TX69272_C14.fm Page 557 Friday, November 14, 2003 2:13 PM Combinations of Advanced Oxidation Processes 557 Percent of TCB Remaining 16 14 12 Humic Acid 10 Carbonate 8 6 4 2 0 No humic acid added, no carbonate added 1.6 mg/L of humic acid, 2.0 mM carbonate 10 mg/L of humic acid, 10 mM carbonate FIGURE 14. 21 Degradation of TCB under the influence of humic acid and bicarbonate (From Masten, S et al., J Hazardous. .. provided in Table 14. 18 14. 4.6.2 Pyrene The results obtained in AOP -treatment of pyrene in aqueous solutions were quite similar to those of anthracene and phenanthrene For pyrene, ozonation has been more effective at lower pH values than at neutral pH values The half-lives of pyrene at pH 3, 7, and 9 are 17, 24, and 42 s, respectively; however, the half-life of pyrene increased in the series of O3 < UV/O3... the application of ozone are given in Table 14. 7 Figure 14. 9 presents the pseudo first-order rate constants of p-hydroxybenzoic degradation The degradation rates follow the increasing order: O3 < O3/H2O2 < O3/H2O2/Fe2+ < O3/Fe2+ < UV/O3 < UV/O3/H2O2 < UV/ O3/H2O2/Fe2+ 14. 4.2.3 AOPs Using Fenton’s Reagent In regard to the degree of conversion of p-hydroxybenzoic acid at 5 and 10 min of reaction time, . min) TX69272_C14.fm Page 551 Friday, November 14, 2003 2:13 PM © 2004 by CRC Press LLC 552 Physicochemical Treatment of Hazardous Wastes rates of para- and ortho-chlorophenols. The reactivity of chlorophenolate anion. permission. C HO 22 C TiO 2 TX69272_C14.fm Page 539 Friday, November 14, 2003 2:13 PM © 2004 by CRC Press LLC 540 Physicochemical Treatment of Hazardous Wastes 14. 4.1.1 Comparison of Pseudo First-Order Kinetic Constant The. LLC 546 Physicochemical Treatment of Hazardous Wastes 14. 4.3.1 Comparison of Various AOPs The decomposition of all four selected CPs (4-CP, 2,4-DCP, 2,4,6-TCP, 2,3,4, 6- TeCP) was achieved by utilizing