AND L ITERATURE R EVIEW
1.2.5 Persulfate Oxidation Process
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18
US
H O OH 2 + H (1.48)
2 2
OH + OH H O
(1.49)
2 2
OH + O HO + O
(1.50)
pH of the solution is an important parameter affecting chemistry sono–photolysis. At low pH, H2O2 reacts with proton to generate oxonium ion (H O3 +2) (Daud et al. 2012):
2 2 3 2
H O H H O; while at high pH (> pKa), it undergoes dissociation to generate H+ and HO2 species (Chang et al., 2010): H O 2 2 H + HO+ 2. However, the influence of pH in photolysis process is not much significant and it has been found the optimum pH for photolysis or sono–photolysis reactions is to be neutral (pH = 7). Table 1.3 presents the summary of literature on degradation of variety of pollutants employing sono–photolysis.
heated to moderate temperatures during transient collapse. The H• and •OH radicals produced during transient cavitation can also activate the persulfate anion. The relevant activation reactions are given below (Wang et al., 2015, Roshani and vel Leitner, 2011; Kusic et al., 2011):
US 2
2 8 4
S O 2 SO (1.54)
US
H O OH 2 + H (1.55)
2 + 2
2 8 4 4
S O + H SO + H + SO (1.56)
2
2 8 4 4 2
S O + OH SO + HSO + 0.5O (1.57) Some other reactions that can occur in the persulfate reaction system are as follows:
+ 2
2 4 4
H O + SO H + SO + OH (1.58)
2
2 8 2 8
S O + OH OH + S O (1.59)
2 2
2 8 4 4 2 8
S O + SO SO + S O (1.60)
2
4 4 2 8
SO + SO S O (1.61)
2+ 3+ 2
4 4
Fe + SOFe + SO (1.62)
The last two reactions (either recombination of the sulfate radicals or scavenging of the sulfate radicals by Fe2+ ions) result in loss of oxidation potential. Table 1.4 presents summary of previous studies in degradation of different pollutants with persulfate based oxidation system.
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20
Table 1.3: Summary of published literature on sono-photolysis (US/UV/H2O2) process for wastewater treatment
Hybrid-AOP Pollutants Process parameters Results/ Max. degradation (%) Reference US/UV/H2O2 Phthalate acid esters
(PAEs)
f = 400 kHz (bath), PAEs. = 0.01 mM (mix. of DMP, DEP, DBP, MMP), H2O2 = in-situ generated, UV sources
= 6 nos (254 nm), pH = 6.5, T = 28oC, t = 90 min
Degradation: ~82% for MMP (0.0238 min-1) and ~100% for DMP (0.0293 min-1, DEP (0.0387 min-1) & DBP (0.0712 min-1).
TOC removal of PAEs was 17%
Xu et al. (2015)
US/UV/H2O2 Synthetic pharmaceutical wastewater (SPWW)
f = 20 kHz (bath), P = 140W, TOC = 12 mg/L, H2O2 = 1200 mg/L, UV sources = 1 13W (254 nm), pH = 3.9, T = ND, t = 120 min, Air = 2 L/min
Max. TOC removal was 98% Ghafoori et al.
(2015)
US/UV/H2O2 Atrazine (ATZ) f = 20 (P = 375W) and 400 kHz (P = 120W) (bath), ATZ = 0.02 mM, H2O2
= 5.0 10-4 mM/min (in-situ), UV sources = 1 nos (254 nm), pH = 6.5, T
= 28oC, t = 60 min
~100% degradation was achieved with 60% of TOC removal
Xu et al. (2014)
TH-1390_11610705
Table 1.3 (continued…): Summary of published literature on sono-photolysis (US/UV/H2O2) process for wastewater treatment
Hybrid-AOP Pollutants Process parameters Results/ Max. degradation (%) Reference US/UV/H2O2 Synthetic
pharmaceutical wastewater (SPWW)
f = 20 kHz (horn type), P = 140W, Composition of SPWW (mg/L) = 4AMP (6.25), PCM (2.5), Ph (12.5), CLP (7.5), BA (6.25), SA (28.75), DCF (0.5), NB (7.5), H2O2 = 1750 mg/L, UV sources = 1 13 W (254 nm), pH = 2, T = 33.1oC, t = 90 min, Air = 3 L/min
90% TOC after 180 min Mowla et al.
(2014)
US/UV/H2O2 Trihalomethanes (THMs)
f = 500 kHz (PZT transducer), P = 52.55 W, THMs = 10 mg/L, in-situ generated H2O2, UV sources = 4 10.5 W (254 nm), pH = 4.5, T = 25oC, t = 60 min
100% degradation and 50% TOC were achieved at optimum conditions
Park et al.
(2014)
US/UV/H2O2 Pharmaceutical wastewater (PW)
f = 24 kHz (horn), P = 200W, PW = 125 mg/L (TOC), H2O2 = 6500 mg/L, UV sources = 1 150 W (190-280 nm), pH = 7, T = 30oC, t = 120 min
100% TOC reduction was achieved Monteagudo et al. (2014a)
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Table 1.3 (continued…): Summary of published literature on sono-photolysis (US/UV/H2O2) process for wastewater treatment
Hybrid-AOP Pollutants Process parameters Results/ Max. degradation (%) Reference US/UV/H2O2 Food industry
wastewater
f = 24 kHz (horn type), P = 200W, H2O2 = 11750 ppm, UV sources = 1 150 W (190-280 nm), pH = 8, T = 30oC, t = 180 min
TOC removal 60% after 60 min and 98% after 180 min
Duran et al.
(2013b)
US/UV/H2O2 Dimethyl phthalate (DMP)
f = 400 kHz (bath), P = 120W, DMP = 0.05 mM, H2O2 = 9.75 10-4 mM/min (in-situ), UV sources = 6nos (254 nm), pH = 6.5, T = 28oC, t = 120 min
~100% degradation Xu et al. (2013)
US alone UV alone US/UV/H2O2
Diethyl phthalate (DEP)
f = 283 kHz (horn type), DEP = 45
M, H2O2 = 0.32 M/min (in-situ), UV sources = 4 10 W (254 nm, UVC) or {(2 10 W, 254 nm, UVC) + (2 10 W, 185 nm, VUV)(185 nm + 254 nm)}, pH = 6.2-6.7, T = 15- 18oC, t = 120 min
~92% (1.7 × 10-2 min-1) degradation in US/UVC and ~90% (1.7 × 10-1 min-1) in US/UVC/VUV.
TOC removal: ~30% in US/UVC and
~90% in US/UVC/VUV.
Positive synergy in sono-photolysis with UVC (SF=1.68) and UVC/VUV (SF=1.23)
Na et al.
(2012a)
TH-1390_11610705
Table 1.3 (continued…): Summary of published literature on sono-photolysis (US/UV/H2O2) process for wastewater treatment Hybrid-AOP Pollutants Process parameters Results/ Max. Degradation (%) Reference
US/UV/H2O2 Diethyl phthalate (DEP)
f = 283 kHz (bath), DEP = 45 M, H2O2 = 0.32 M/min (in-situ), TiO2 = 450 mg/L, UV sources = 4 10.5 W (254 nm), pH = 6.2, T = 15-18oC, t = 120 min
Sonophotolysis: ~85% (1.56 10-2 min-1) degradation with synergy effect 1.95. Sonophotocatalysis: ~100% (9:2
10-2 min-1) degradation with synergy effect 1.29. TOC removal: ~18% in sonophotolysis and ~60% in sono- photocatalysis
Na et al.
(2012b)
US alone UV alone US/UV/H2O2
(in-situ generated)
2,4,6-trichlorophenol (TCP)
f = 20 kHz (horn type), P = 750W, UV source = 1 8 W (365 nm), TCP = 50 mg/L, in-situ generated H2O2, pH = ND, T = 10 – 50oC, t = 300 min
Positive synergistic effect was seen between 10-30oC and an antagonistic effect between 40-50oC
Degradation: ~76% (7.99 10-5 s-1) in (US+UV), ~72% (6.5210-5 s-1) with UV only, and ~68% (6.6610-5 s-1) with US alone
Joseph et al.
(2011)
4AMP - 4-aminophenol, PCM - paracetamol, Ph - phenol, CLP - chloramphenicol, BA - benzoic acid, SA - salicylic acid, DCF - diclofenac sodium, NB – nitrobenzene, ND – not defined/ not determined, SF – synergy factor, SP – sono-photolysis, THMs = CF - chloroform, DCBM - dichlorobromomethane, CDBMM - chlorodibromomethane, BF – bromoform, PAEs = dimethyl phthalate (DMP), diethyl phtha-late (DEP), di-n-butyl phthalate (DBP) and monomethyl phthalate (MMP)
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Table 1.4: Summary of published literature on sono-persulfate system for wastewater treatment
Hybrid-AOP Pollutants Process parameters Results/ Max. Degradation (%) Reference US/PS
US/EL/PS
Aniline (AN) f = 160 kHz (PZT), P = 320 W, AN = 75 mg/L, PS = 2.5 wt% (1.88 mg/L), EP = 6 V, pH = 3, T = 45oC, t = 7 h, N2 = 150 mL/min
TOC removal was ~25% in sono- persulfate process and ~92% in sonoelectro-persulfate. N2 gas flow helps the TOC removal in sonoelectro- persulfate process nearly 100%
Chen and Huang (2015)
US/PS Phenanthrene (PhN) f = 20 kHz (bath), P = 90 W, PhN = 65, 390 and 816 mg/kg soil, PS = 0- 100 g/L, [Fe(III)–EDTA] = 150 mg Fe/L, NaOH = 2M, pH = 5.8, T = 20oC, t = 30 min
100% degradation in 30 min of treatment in all concentration of PhN
Deng et al.
(2015)
US/PS Humic acid (HA) f = 40 kHz (bath), P = 200 W, HA = 30 mg/L, PS = 100 mM, pH = 3, T = 40oC, t = 120 min
90% humic acid was removed in 2 h of treatment using US/PS
Wang et al.
(2015)
US/PS Ammonium perfluorooctanoate
(APFO)
f = 20 kHz (bath), P = 300 W, APFO = 46.4 mol/L, PS = 10 mM, pH = 6, T
= 25oC, t = 120 min
51.2% APFO was removed after 120 min of treatment in presence of 20 kHz ultrasound frequency
Hao et al.
(2014)
TH-1390_11610705
Table 1.4 (continued…): Summary of published literature on sono-persulfate system for wastewater treatment
Method Pollutants Process parameters Results/ Max. Degradation (%) Reference US/PS
US/Fe0/PS
Acid Orange 7 (AO7) f = 20 kHz (bath), P = 60 W, AO7 = 30 mg/L, PS = 300 mg/L, Fe0 = 500 mg/L, pH = 5.8, T = 22oC, t = 60 min
Maximum decolorization was achieved 10% in US/PS and 96.4% in US/Fe0/PS
Wang et al.
(2014)
US/PS US/Fe0/PS
Sulfadiazine (SD) f = 20 kHz (bath), P = 40 W, SD = 20 mg/L, PS = 1.84 mM, Fe0 = 0.92 mM, pH = 3-7, T = 25oC, t = 60 min
Degradation of SD was13.7% in US/PS and 95.7-98.4% in US/Fe0/PS in the pH range of 3-7
Zou et al.
(2014)
US/PS/H2O2/Fe Pharmaceutical effluent
f = 30 kHz (bath), COD = 10667 mg/L, PS = 5 g/L, H2O2 = 5 g/L, iron
= 4 g/L, pH = 3, T = 30-50oC, t = 30 min
100% COD removal was achieved after 30 min of treatment, degradation increases with in temperature
Nachiappan and
Muthukumar (2013) US/PS NFDOHA
Perfluoroalkylether sulfonates (PFS)
f = 28 kHz (bath), P = 200W,
NFDOHA 50 M, PS = 10 mM, pH
= ND, T = 28oC, t = 24 h
55.7% NFDOHA was decomposed after 24 h
Hori et al.
(2012)
EP – electrode potential, US – ultrasound, PS – persulfate, NFDOHA - Perfluoroether carboxylic acids (CF3OC2F4OCF2COOH, CF3OC2F4OC2F4OCF2COOH, CF3OC3F6COOH, C2F5OC2F4OCF2COOH, C4F9OC2F4OC2F4OCF2COOH)
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