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AOX removal from industrial wastewaters using advanced oxidation processes: assessment of a combined chemical–biological oxidation J. Luyten, K. Sniegowski, K. Van Eyck, D. Maertens, S. Timmermans, Sven Liers and L. Braeken
ABSTRACT In this paper, the abatement of adsorbable halogenated organic compounds (AOX) from an industrial wastewater containing relatively high chloride concentrations by a combined chemical and biological oxidation is assessed. For chemical oxidation, the O3/UV, H2O2/UV and photo-Fenton processes are evaluated on pilot scale. Biological oxidation is simulated in a 4 h respirometry experiment with periodic aeration. The results show that a selective degradation of AOX with respect to the matrix compounds (expressed as chemical oxygen demand) could be achieved. For O3/UV, lowering the ratio of O3 dosage to UV intensity leads to a better selectivity for AOX. During O3-based experiments, the AOX removal is generally less than during the H2O2-based experiments. However, after biological oxidation, the AOX levels are comparable. For H2O2/UV, optimal operating parameters for UV and H2O2 dosage are next determined in a second run with another wastewater sample. Key words
| AOX removal, chemical–biological oxidation, industrial wastewater
J. Luyten K. Van Eyck D. Maertens S. Timmermans Sven Liers Chemical and Biochemical Process Technology and Control, Katholieke Universiteit Leuven, Department of Chemical Engineering, W. de Croylaan 46, 3001 Heverlee, Belgium J. Luyten K. Van Eyck D. Maertens S. Timmermans Sven Liers Process and environmental technology, Campus De Nayer, J.P. De Nayerlaan 5, 2860 Sint-Katelijne-Waver, Belgium K. Sniegowski L. Braeken (corresponding author) Lab4U, Katholieke Hogeschool Limburg, Agoralaan gebouw B, 3590 Diepenbeek, Belgium E-mail: [email protected] L. Braeken Laboratory for Applied Physical Chemistry and Environmental Technology, Katholieke Universiteit Leuven, Department of Chemical Engineering, W. de Croylaan 46, 3001 Heverlee, Belgium
INTRODUCTION Growing environmental awareness as well as ever decreasing norms drive industry towards an advanced water purification. The ultimate goal of the European Water Directive is indeed to achieve a ‘close-to-zero’ emission for synthetic man-made substances (European Commission ). To this end, strict regulations are or will be implemented for primary hazardous compounds. One class of components are halogenated organic substances adsorbable on activated carbon (AOX). As a result of industrial activity, halogenated compounds may be present in the wastewater. The discharge limit for AOX in Germany is 500 μg L1 Cl (German Sewage Water Administration Regulation ). Controlling doi: 10.2166/wst.2013.459
the level of AOX in industrial wastewater is especially an issue for industries such as the paper, pulp and paperboard industry and pharmaceutical industry and hospitals. Performing a standard biologic treatment on these highly contaminated and toxic wastewaters is often ineffective in lowering the AOX concentrations to the legislative level. Another technique to remove the excessive amount of AOX is by sorption on activated carbon; however, this is only recommended for wastewaters containing a significantly low amount of organic matter or chemical oxygen demand (COD). Furthermore, the hazardous components are not destroyed but transferred from the liquid phase to
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the solid phase. The (saturated) activated carbon therefore still needs further handling. An alternative method for the removal of AOX is by chemical oxidation using advanced oxidation processes (AOPs). Various AOPs already proved successful in lowering the AOX concentration in industrial wastewater from the pulp mill and paper industry (Parilti & Akten ; Perez et al. ; Catalkaya & Kargi ; Zhou & Smith ; Mobius & Cordes-Talle ; Hostachy et al. ), pharmaceutical industry (Hofl et al. ) and in colored synthetic wastewater (Kusic et al. ). On the other hand, Baycan et al. (, a, b) reported elevated AOX concentrations after UV/H2O2 treatment of synthetic wastewaters (EDTA, phenol, methanol and acetone) with chloride concentrations of 1,000 mg L1 and 10,000 mg L1. In addition, the study performed by Seiss et al. () observed an increase of AOX concentration during the UV/ozone treatment of wastewater originating from a landfill. The increase was related to the concentration of chloride ions in the water. The initial AOX concentration tripled when concentrations of chloride ions of 55.6 g L1 were present in the wastewater, but only doubled with chloride concentrations of 5.6 g L1 . So it seems that the use of AOPs for the elimination of AOX is not obvious when high concentrations of chloride ions are present and this is for different reasons. First, chloride ions can react with hydroxyl radicals to form chlorine radicals (Klaening & Wolff ). When these radicals react with organic matter, a net AOX formation could be observed. Second, with ozone-based treatments the reaction of molecular ozone with present chloride ions results in hypochlorite ion and its conjugated acid, which may subsequently react with organic matter to form AOX. Furthermore, because of the scavenging effect of the chloride ions, one might increase the oxidant dosage (Liao et al. ). Because both the matrix compounds and halogenated compounds compete for the oxidant present, the formation of halogenated byproducts will be accelerated, resulting in elevated concentrations of AOX. Finally, the pH affects the AOX concentration when applying AOPs in water containing high chloride concentrations. Mineralization at elevated pH values results in the formation of 2 HCO 3 and CO3 ions, which are reported as Cl-radical scavengers (Mertens & von Sonntag ). So, less AOX formation is expected at higher pH values. This could, on the other hand, slow the degradation of the organic matter, as the formed HCO3 and CO3 radicals are also known scavengers of hydroxyl radicals.
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Furthermore, the problem of AOX formation during the oxidation treatment might be less severe when the degradability of AOX is improved by AOPs. Indeed, in that case an oxidation process combined with a post-biological treatment might lead to an overall better removal efficiency. A limited amount of studies regarding AOPs focused on the combined process of chemical and subsequent biological treatment of wastewater. The recent study of Van Aken et al. () showed that an UV/ozone treatment increased the biochemical oxygen demand to COD ratio by 13%. Also other studies evaluated AOP treatments such as UV/ H2O2 (Koh et al. ), O3 or O3/UV (Pires & Momenti ) combined with biological treatment for various toxic wastewaters and concluded that the resulting wastewater is suitable for further biological treatment. Whether or not the AOX becomes more biodegradable after an AOP treatment seems to be only tested by Drewes & Jekel (), who observed after the successive ozonation and soil-aquifer treatment, an increased degradation rate of AOX from 0.6 μg L1 d1 Cl to 2.73 μg L1 d1 Cl. Additional tests with other AOPs are required to compare the effect of different AOPs on the degradability of AOX. In conclusion, the appropriate AOP, pH and oxidant dosage for wastewaters containing relative high concentrations of halogen ions are crucial to achieve a significant reduction of both COD and AOX. With the current knowledge, however, it is difficult to formulate recommendations to this end. This is mainly due to the complexity of the chemical reactions during oxidation, the limited amount of studies and high variety of tests regarding AOX degradation/formation during AOPs. When evaluating different AOPs, it is necessary to take into account the effect on both concentration and biodegradability of AOX. In addition, since the aim of an oxidation treatment is to decrease both COD and AOX levels, the selectivity of the process must be taken into account when the most suitable oxidation technique is selected. This study aims to evaluate several combined chemical and biological treatments of industrial wastewater for the selective removal of AOX from the total matrix COD. For chemical oxidation, ozone, ozone/UV, H2O2/UV and photo-Fenton (H2O2/UV/Fe(II)) have been applied with varying oxidant dosages and pH. In a first series of tests, special attention is paid to the biodegradability of AOX and the selectivity of the AOP in relation to the type of oxidant and oxidant dosage. A second series of experiments is performed in order to explore the effect of UV intensity and H2O2 dosage on both the chemical and biological AOX removal.
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MATERIALS AND METHODS Oxidation tests are performed with two different wastewater samples originating from the effluent of a biological wastewater treatment plant from a chemical production company. Table 1 lists two different batches from the same plant, showing the typical variability in wastewater characteristics. The wastewater is treated in a pilot-scale reactor, as shown in Figure 1, by recirculating the water over a thinfilm UV-reactor. The internal volume of the recirculation tank (A) is approximately 50 L whereas the internal volume of the UV reactor (B) is only 7 L. The radial distance between the reactor vessel and the UV lamp (a medium pressure Hg lamp, Philips, 2014.1 W) is approximately 2.5 cm. Ozone is generated from a Pacific Ozone Model SGC-21, Aqua Purification System, Inc. and introduced into the wastewater by a venturi (C) at a gas flow rate of 6 L min1. Further dissolution of ozone in water is carried out in a static mixer (D). The dosage into the reactor was set constant. In order to unravel the effect of the oxidant concentration, O3/UV experiments are conducted at three different combinations of ozone feeding rate and UV intensity. An ozone flow rate of 100% refers to 16 g O3 h1 and a UV intensity of 100% corresponds to 2,000 W. H2O2 is continuously fed to the reactor in order to minimize the inhibiting reaction of hydroxyl radicals with hydrogen peroxide. The amount of H2O2 was calculated relative to the amount of COD in the water. A H2O2 dosage of 100% Table 1
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corresponds to a dosage of 2 mg L1 H2O2 per mg COD. The effective percentage was recalculated after the experiment based on the initial COD of the wastewater and the dosed amount of H2O2 during the experiment. For the photo-Fenton experiments (H2O2/Fe2þ), FeSO4 is added in a [Fe2þ]/[H2O2] ratio of 1/100 ww. During all experiments, the pH of the water was adjusted to 9 or 7 and kept constant during the process by adding NaOH or H2SO4, except for the photo-Fenton experiments which were carried out at pH 3. An overview of the details of the oxidation tests is given in Table 1. Samples were taken after 60 min of reaction time to determine the AOX and COD concentration and to start a biological treatment. Biological oxidation is simulated in respirometry experiments in which wastewater samples (500 mL) are mixed with activated sludge (300 mL) from a municipal wastewater treatment plant and periodically aerated. To make sure no biologically degradable components are present in the sludge sample, the sludge is aerated for 24 h prior to the respirometry experiments. The sludge concentration in the respiration reactor is 2.2 g L1. The aeration pumps are controlled using Hamilton VisiFerm optical dissolved oxygen (DO) sensors (type DO 225). Aeration starts when the DO concentration is beneath 2 mg L1 and stops at a DO concentration of 5 mg L1. After 4 h AOX and COD are measured again and corrected by the dilution factor of 500 over 800. Inert COD, which was already present in the sludge sample, is taken into account by subtracting the COD in the sludge supernatant before and after the respirometry experiment.
Composition of used wastewaters and overview of the performed oxidation tests
Wastewater characteristics
Name
UV intensity (kW)
pH
Oxidant
Oxidant dose (g h1)
Sample 1
Ozone/UV pH 9
2.0
9
O3
16
COD ¼ 200 mg L O2 AOX ¼ 1,500 μg L1 Cl Cl ¼ 750 mg L1 pH ¼ 7.8
Ozone/UV Ozone/UV50% Ozone 50%/UV H2O2 42%/UV H2O2 31%/UV H2O2 56%/Fe2þ/UV UV
2.0 1.0 2.0 2.0 2.0 2.0 2.0
7 7 7 7 9 3 7
O3 O3 O3 H2O2 H2O2 H2O2 –-
16 16 8 12.8 9.36 16.2 –-
Sample 2
30% H2O2/12.5% UV
0.25
7
H2O2
6.79
30% H2O2/25% UV
0.5
7
H2O2
6.79
COD ¼ 140 mg L1 O2 AOX ¼ 5,000 μg L1 Cl Cl ¼ 650 mg L1 pH ¼ 7.9
15% H2O2/25% UV 30% H2O2/100% UV 20% H2O2/100% UV 10% H2O2/100% UV 30% H2O2/50% UV UV/O3
0.5 2.0 2.0 2.0 1.0 2.0
7 7 7 7 7 7
H2O2 H2O2 H2O2 H2O2 H2O2 O3
3.4 6.79 4.53 2.5 6.79 16
1
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A standard curve made with 4-chlorophenol is used to calculate the amount of halogen ions (μg L1 Cl) in the water sample. The limit of detection is 10 μg L1 Cl and the relative standard deviation is 11%. The COD determinations, based on the silver-catalysed oxidation of the pollutants with potassium dichromate in acidic environment, are carried out by using 0–1,500 mg L1 range vials. Samples of 2 mL are required for those analyses. A Nanocolor® COD reactor and a Nanocolor® 500 D colorimeter from Machery-Nagel were used during the analysis.
RESULTS AND DISCUSSION
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Figure 1
Scheme of the pilot-scale reactor with feed tank (A), UV reactor (B), venturi for introduction of ozone (C) and static mixer (D). H2O2 is dosed continuously in the piping before the venturi.
AOX measurements are performed according to the WAC/IV/B/011 protocol with a ThermoFischer Scientific 3,000 systems TN/TS/TX (SphiNCX). Granular activated carbon (50 mg) is added to 100 mL of water sample and put on a horizontal shaker for 1 h. When necessary, the water samples were first diluted with ultrapure water to remain under the maximum concentration of 250 μg L1 Cl. After 1 h, the active carbon is collected and burned at 1,000 C in the oven of the apparatus. The combustion gas containing the halogen ions is passed over a scrubber into a titration cel for a coulometric titration with silver. W
Table 2
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Table 2 shows the AOX and COD removal efficiencies after the various AOP treatments and after subsequent biological oxidation from wastewater sample 1. Biological oxidation of the original wastewater sample led to a low AOX removal efficiency of approximately 20%. This is not surprising as the wastewater has already undergone a biological oxidation. Most AOP treatment methods reach 50% of AOX removal after 60 minutes of reaction time. Ozone-based techniques show generally less pronounced removal efficiencies (removal between 44 and 62%) than photo-Fenton (removal between 66 and 80%). This might indicate that the ozone is partially used for the formation of AOX, resulting in an overall lower degradation of AOX. The fact that the highest AOX-reduction is achieved with 50% less ozone input seems to confirm this hypotheses. Similar observations can be made for the H2O2based processes, which were studied in more detail for a
AOX and COD concentration after chemical oxidation (60 min) and subsequent biological post-treatment (4 h) for wastewater sample 1 AOX (μg L1 Cl)
COD (mg L1 O2)
Amount removed by AOP
Amount removed by
Amount removed by
subsequent biological oxidationa
AOP þ biological oxidation
Amount Initial
removed by AOP
S(AOX/COD)b
Test
Initial
Ozone/UV pH 9
1,647
843
(51%)
375
(47%)
1,218
(74%)
206
22
(11%)
4.8
Ozone/UV
1,700
806
(47%)
353
(39%)
1,159
(68%)
184
82
(45%)
1.1
Ozone/UV 50%
1,517
670
(44%)
379
(45%)
1,049
(69%)
177
83
(47%)
0.9
Ozone 50%/UV
1,660
1,029
(62%)
294
(47%)
1,323
(80%)
170
77
(45%)
1.4
H2O2 42%/UV
1,588
1,213
(76%)
192
(51%)
1,405
(88%)
ND
ND
ND
ND
H2O2 31%/UV
1,509
1,205
(80%)
41
(13%)
1,246
(83%)
ND
ND
ND
ND
H2O2 56%/Fe /UV
1,429
938
(66%)
64
(13%)
1,002
(70%)
ND
ND
ND
ND
UV
1,156
606
(52%)
66
(12%)
672
(58%)
ND
ND
ND
ND
2þ
a
The removal percentage is calculated as the amount of AOX removed from the residual AOX concentration after the AOP treatment. Δ[AOX]=AOXi The overall selectivity parameter S(AOX/COD) is calculated by: S(AOX=COD) ¼ . A relative standard deviation of 11% on the AOX concentration needs to be taken into account. Δ[COD]=CODi
b
ND stands for not determined.
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different batch of the same wastewater and presented in Table 3. The highest H2O2 (30%) doses resulted in no significant AOX removal, especially at low UV power. Increasing the power of the UV lamp using 30% H2O2 increased the AOX removal but remained significantly lower than at a 10 or 20% H2O2. This can be explained by the fact that H2O2 acts as a scavenger at higher concentration or by the hypothesis that high oxidant doses can lead to the activation of halogen ion which in turn will form halogenated organic compounds. In contrast to photo-Fenton and UV/H2O2, a significantly higher amount is biologically degraded with the ozone-based techniques (between 39–47% removal). Similar effects have been observed in the drinking water industry with total organic carbon (TOC). Cipparone et al. () observed that the biodegradability of the dissolved organic compounds in surface water increased six times upon ozonation. Higher effects on the degradability were observed with a combined H2O2/O3 treatment, but only when sufficiently high ozone concentrations (>0.7 mg mg1 TOC) were used (Speitel ). In general, less enhancement on the biodegradability was observed with UV/H2O2. The higher biodegradability of the compounds with the ozone-based techniques can be explained by the high reactivity of ozone towards unsaturated bindings and aromatic rings, which are also the most recalcitrant compounds for microorganisms. Nevertheless, the chemical oxidation technique reduces most of the AOX concentration. Therefore more of the total AOX is removed with photo-Fenton, i.e. between 66 and 80% of AOX has been degraded. The lowest AOX reduction is achieved with photo-Fenton at higher concentrations of H2O2 (16.2 g h1). In the last column of Table 2 the overall selectivity coefficient S for the ozone-based AOP treatments (without Table 3
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biological oxidation) is shown. From a comparison of the ozone-based experiments at pH 7, it becomes clear that the selectivity towards AOX removal is O3(50%)/UV > O3/UV > O3/UV(50%). It can therefore be concluded that a lower ozone concentration with respect to UV intensity results in a better selectivity for AOX removal. Increasing the pH to 9 further enhances the selectivity for AOX removal. For H2O2-based experiments, no selectivity parameter is reported as no corrections for the COD contribution of residual H2O2 could be made. Residual H2O2 will lead to an increase in COD, and as the H2O2 concentration was changed during the experiment, the contribution of residual H2O2 to the final COD is different over the experiments. This complicates the calculation of the exact amount of removed COD. In order to determine the relative selectivity, a better parameter to monitor might be the TOC removal, which also represents the removal of organic compounds but is not affected by the presence of H2O2. Finally, the results for UV alone confirm the findings of Hofl et al. (), as an AOX removal of approximately 50% is observed without appreciable COD degradation. The medium-pressure lamp is thus able to destroy carbon-halogen bonds; however, the addition of a small amount of oxidant (O3 or H2O2) significantly improves the oxidation of the matrix compounds. A second series of experiments (Table 3) has been performed in order to explore the effect of UV intensity and H2O2 dosage on the chemical and biological AOX removal. The composition of wastewater sample 2 differs significantly from sample 1 (see Table 1). Sample 2 contains three times more AOX and a lower COD level, which means that a higher fraction of the COD is halogenated than in sample 1. Compared to sample 1, the most efficient AOP treatment (H2O2 30%/UV) removes four times more
AOX concentration after chemical oxidation (60 min) and subsequent biological post-treatment (4 h) for wastewater sample 2 AOX (μg L1 Cl)
Test
Amount removed by subsequent biological
Amount removed by AOP þ biological
oxidation*
oxidation
Initial
Amount removed by AOP
30% H2O2/12.5% UV
4,130
271
(7%)
1,019
(23%)
748
(18%)
30% H2O2/25% UV
4,110
275
(7%)
1,000
(26%)
1,275
(31%)
15% H2O2/25% UV
4,908
802
(16%)
718
(17%)
1,520
(31%)
30% H2O2/100% UV
5,493
921
(17%)
1,214
(27%)
2,135
(39%)
20% H2O2/100% UV
4,640
2,933
(63%)
49
(3%)
2,982
(64%)
10% H2O2/100% UV
5,355
2,849
(53%)
626
(25%)
3,475
(65%)
30% H2O2/50% UV
5,283
1,926
(36%)
999
(30%)
2,925
(55%)
UV/O3
4,438
310
(7%)
2,543
(54%)
2,233
(50%)
*The removal percentage is calculated as the amount of AOX removed from the residual AOX concentration after the AOP treatment.
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AOX in sample 2. However, relative to the initial concentration, less AOX is removed than sample 1. The higher initial AOX concentration and lower H2O2 dose might explain the difference. For the H2O2-based techniques, the largest AOX degradation is observed when the UV power is high and with an intermediate H2O2 dosage, which was also observed with wastewater sample 2. After the AOP treatment, still a significant amount of AOX (between 17 and 30%) is removed by biological oxidation. However, as with the chemical oxidation the absolute amount of AOX is higher than in sample 1, while the relative amount of AOX is lower than in sample 1, because of the high initial AOX concentration. O3/UV at pH 7 does not significantly change the AOX concentration; however, after respiration, the AOX level is reduced to a similar level as the other treatments. This shows again the potential of AOPs in combination with biological oxidation to (partially) degrade AOX compounds in wastewater. Despite the high efficiency of the combined technique, the discharge limit of 500 μg L1 Cl is not achieved during the experiments, which is due to the higher initial AOX concentration. Figure 2 shows a contour plot for AOX removal by UV/ H2O2 at pH 7 as a function of reaction time and UV intensity (kW) (a) and H2O2 dosage (b). From both graphs, it becomes clear that the best AOX removal is obtained at UV power of 1–2 kW in combination with a H2O2 dosage of 3–4.5 g H2O2 over a reaction time of 50–60 minutes. It can also be seen that within a large area of this plot, a net AOX formation is observed. From all results it can be concluded that a 50% AOX reduction can be achieved with H2O2 dosages of approximately 90 mg L1 H2O2 and a UV energy requirement of 0.02–0.04 kWh L1.
Figure 2
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Contour plot for AOX removal (DAOX in μg Cl/L) by UV/H2O2 at pH 7 as a function of reaction time and UV intensity (kW) (a) and H2O2 dosage (b).
results show that a selective degradation of AOX with respect to the matrix compounds (expressed as COD) could be achieved. For O3/UV, lowering the ratio of O3 dosage to UV intensity leads to a better selectivity for AOX. Finally, the sensitivity of the operating parameters UV and H2O2 dosage towards the AOX removal was determined during a second run with another wastewater sample.
CONCLUSIONS REFERENCES This paper shows that AOX can be significantly reduced in industrial wastewater by a combined chemical–biological treatment. Despite the high chloride concentration in the water, no significant increase in AOX concentration was observed. In general, less AOX is removed during O3-based experiments than during the H2O2-based experiments. Nevertheless, high removal percentages can be achieved when combining AOPs with a post-biological treatment, indicating that AOX are not only degraded but also transformed to components that are more accessible for biological oxidation. The concentration of the oxidant turned out to be the key parameter for the selectivity towards AOX degradation. The
Baycan, N., Sengül, F. & Thomanetz, E. AOX formation and elimination in the oxidative treatment of synthetic wastewaters in a UV-free surface reactor. Environ. Sci. Pollut. Res. 12, 153–158. Baycan, N., Thomanetz, E. & Sengül, F. a Effect of chloride concentration on the oxidation of EDTA in UV-FSR oxidative system. J. Photochem. Photobiol. A 189, 349–354. Baycan, N., Thomanetz, E. & Sengül, F. b Influence of chloride concentration on the formation of AOX in UV oxidative system. J. Hazard. Mater. 143, 171–176. Catalkaya, E. C. & Kargi, F. Color, TOC and AOX removal from pulp mill effluent by Advanced Oxidation Processes: A comparative study. J. Hazard. Mater. B 139, 244–253.
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Cipparone, L. A., Diehl, A. C. & Speitel, G. E. Ozonation and BDOC removal: effect on water quality. J. Am. Water Works Assoc. 89, 84–97. Drewes, J. E. & Jekel, M. Behavior of DOC and AOX using advanced treated wastewater for groundwater recharge. Water Res. 32, 3125–3133. European Commission Roadmap to a Resource Efficient Efficient Europe. http://ec.europa.eu/environment/ resource_efficiency/about/roadmap/index_en.htm (accessed 8 October 2013). German Sewage Water Administration Regulation, appendix 51, Part I No. 86 published December 29, 1998 (Anhang 51 der Rahmenabwasserverordnung 1998 Teil I Nr. 86, ausgegeben zu Bonn, 29. December 1998). Hofl, C., Sigl, G., Specht, O., Wurdack, I. & Wabner, D. Oxidative degradation of AOX and COD by different advanced oxidation processes: A comparative study with two samples of a pharmaceutical wastewater. Water Sci. Tech. 35 (4), 257–264. Hostachy, J. C., Lenon, G., Pisicchio, J. L., Coste, C. & Legay, C. Reduction of pulp and paper mill pollution by ozone treatment. Water Sci. Tech. 35 (2–3), 261–268. Klaening, U. K. & Wolff, T. Laser flash photolysis of HClO, ClO, HBrO, and BrO in aqueous solution. Reaction of Cl- and Br-atoms. Ber. Bunsenges. Phys. Chem. 89, 243–245. Koh, I., Chen-Hamacher, X., Hicke, K. & Thiemann, W. Leachate treatment by the combination of photochemical oxidation with biological process. J. Photochem. Photobiol. A: Chem. 162, 261–271. Kusic, H., Bozic, A. L. & Koprivanac, N. Fenton type processes for minimization of organic content in coloured wastewaters: Part I: Processes optimization. Dyes Pigments 74, 380–387.
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Liao, C. H., Kang, S. F. & Wu, F. A. Hydroxy radical scavenging role of chloride and bicarbonate ions in the H2O2/UV process. Chemosphere 44, 1193–1200. Mertens, R. & von Sonntag, C. Photolysis (¼254 nm) of Tetrachloroethene in Aqueous Solutions. J. Photochem. Photobiol. A: Chem. 85, 1–9. Mobius, C. H. & Cordes-Talle, M. Enhanced biodegradability by oxidative and radioactive wastewater treatment. In Proceedings of the Fifth IAWQ Symposium on Forest Industry Wastewaters Vancouver, Canada, pp. 259–265. Parilti, N. B. & Akten, D. Optimization of TiO2/Fe(III)/solar UV conditions for the removal of organic contaminants in pulp mill effluents. Desalination 265 (1–3), 37–42. Perez, M., Torrades, F., Domenech, X. & Peral, J. Photocatalytic treatment of paper pulp bleach effluents. Quimica Analytica 16 (3), 211–214. Pires, E. C. & Momenti, T. J. Combination of an anaerobic process with O-3, UV and O-3/UV for cellulose pulp bleaching effluent treatment. Desalination Wastewater Treat. 5 (1–3), 213–222. Seiss, M., Gahr, R. & Niessner, R. Improved AOX degradation in UV oxidative wastewater treatment by dialysis with nanofiltration membrane. Water Res. 35, 3242–3248. Speitel, G. E. Advanced Oxidation and Biodegradation Processes for the Destruction of TOC and DBP Precursors. AWWA Research Foundation and American Water Works Association, USA, 139 pp. Van Aken, P., Van Eyck, K., Degrève, J., Liers, S. & Luyten, J. COD and AOX removal and biodegradability assessment for Fenton and O3/UV oxidation processes: a case study from a graphical industry wastewater. Ozone Sci. Eng. 35 (1), 16–21. Zhou, H. & Smith, D. W. Effects of chemical reactions on ozone mass transfer in treating pulp mill effluent. Water Sci. Tech. 32 (2/3), 249–260.
First received 13 March 2013; accepted in revised form 4 July 2013. Available online 19 October 2013
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AOX removal from industrial wastewaters using advanced oxidation processes: assessment of a combined chemical–biological oxidation J. Luyten, K. Sniegowski, K. Van Eyck, D. Maertens, S. Timmermans, Sven Liers and L. Braeken
ABSTRACT In this paper, the abatement of adsorbable halogenated organic compounds (AOX) from an industrial wastewater containing relatively high chloride concentrations by a combined chemical and biological oxidation is assessed. For chemical oxidation, the O3/UV, H2O2/UV and photo-Fenton processes are evaluated on pilot scale. Biological oxidation is simulated in a 4 h respirometry experiment with periodic aeration. The results show that a selective degradation of AOX with respect to the matrix compounds (expressed as chemical oxygen demand) could be achieved. For O3/UV, lowering the ratio of O3 dosage to UV intensity leads to a better selectivity for AOX. During O3-based experiments, the AOX removal is generally less than during the H2O2-based experiments. However, after biological oxidation, the AOX levels are comparable. For H2O2/UV, optimal operating parameters for UV and H2O2 dosage are next determined in a second run with another wastewater sample. Key words
| AOX removal, chemical–biological oxidation, industrial wastewater
J. Luyten K. Van Eyck D. Maertens S. Timmermans Sven Liers Chemical and Biochemical Process Technology and Control, Katholieke Universiteit Leuven, Department of Chemical Engineering, W. de Croylaan 46, 3001 Heverlee, Belgium J. Luyten K. Van Eyck D. Maertens S. Timmermans Sven Liers Process and environmental technology, Campus De Nayer, J.P. De Nayerlaan 5, 2860 Sint-Katelijne-Waver, Belgium K. Sniegowski L. Braeken (corresponding author) Lab4U, Katholieke Hogeschool Limburg, Agoralaan gebouw B, 3590 Diepenbeek, Belgium E-mail: [email protected] L. Braeken Laboratory for Applied Physical Chemistry and Environmental Technology, Katholieke Universiteit Leuven, Department of Chemical Engineering, W. de Croylaan 46, 3001 Heverlee, Belgium
INTRODUCTION Growing environmental awareness as well as ever decreasing norms drive industry towards an advanced water purification. The ultimate goal of the European Water Directive is indeed to achieve a ‘close-to-zero’ emission for synthetic man-made substances (European Commission ). To this end, strict regulations are or will be implemented for primary hazardous compounds. One class of components are halogenated organic substances adsorbable on activated carbon (AOX). As a result of industrial activity, halogenated compounds may be present in the wastewater. The discharge limit for AOX in Germany is 500 μg L1 Cl (German Sewage Water Administration Regulation ). Controlling doi: 10.2166/wst.2013.459
the level of AOX in industrial wastewater is especially an issue for industries such as the paper, pulp and paperboard industry and pharmaceutical industry and hospitals. Performing a standard biologic treatment on these highly contaminated and toxic wastewaters is often ineffective in lowering the AOX concentrations to the legislative level. Another technique to remove the excessive amount of AOX is by sorption on activated carbon; however, this is only recommended for wastewaters containing a significantly low amount of organic matter or chemical oxygen demand (COD). Furthermore, the hazardous components are not destroyed but transferred from the liquid phase to
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the solid phase. The (saturated) activated carbon therefore still needs further handling. An alternative method for the removal of AOX is by chemical oxidation using advanced oxidation processes (AOPs). Various AOPs already proved successful in lowering the AOX concentration in industrial wastewater from the pulp mill and paper industry (Parilti & Akten ; Perez et al. ; Catalkaya & Kargi ; Zhou & Smith ; Mobius & Cordes-Talle ; Hostachy et al. ), pharmaceutical industry (Hofl et al. ) and in colored synthetic wastewater (Kusic et al. ). On the other hand, Baycan et al. (, a, b) reported elevated AOX concentrations after UV/H2O2 treatment of synthetic wastewaters (EDTA, phenol, methanol and acetone) with chloride concentrations of 1,000 mg L1 and 10,000 mg L1. In addition, the study performed by Seiss et al. () observed an increase of AOX concentration during the UV/ozone treatment of wastewater originating from a landfill. The increase was related to the concentration of chloride ions in the water. The initial AOX concentration tripled when concentrations of chloride ions of 55.6 g L1 were present in the wastewater, but only doubled with chloride concentrations of 5.6 g L1 . So it seems that the use of AOPs for the elimination of AOX is not obvious when high concentrations of chloride ions are present and this is for different reasons. First, chloride ions can react with hydroxyl radicals to form chlorine radicals (Klaening & Wolff ). When these radicals react with organic matter, a net AOX formation could be observed. Second, with ozone-based treatments the reaction of molecular ozone with present chloride ions results in hypochlorite ion and its conjugated acid, which may subsequently react with organic matter to form AOX. Furthermore, because of the scavenging effect of the chloride ions, one might increase the oxidant dosage (Liao et al. ). Because both the matrix compounds and halogenated compounds compete for the oxidant present, the formation of halogenated byproducts will be accelerated, resulting in elevated concentrations of AOX. Finally, the pH affects the AOX concentration when applying AOPs in water containing high chloride concentrations. Mineralization at elevated pH values results in the formation of 2 HCO 3 and CO3 ions, which are reported as Cl-radical scavengers (Mertens & von Sonntag ). So, less AOX formation is expected at higher pH values. This could, on the other hand, slow the degradation of the organic matter, as the formed HCO3 and CO3 radicals are also known scavengers of hydroxyl radicals.
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Furthermore, the problem of AOX formation during the oxidation treatment might be less severe when the degradability of AOX is improved by AOPs. Indeed, in that case an oxidation process combined with a post-biological treatment might lead to an overall better removal efficiency. A limited amount of studies regarding AOPs focused on the combined process of chemical and subsequent biological treatment of wastewater. The recent study of Van Aken et al. () showed that an UV/ozone treatment increased the biochemical oxygen demand to COD ratio by 13%. Also other studies evaluated AOP treatments such as UV/ H2O2 (Koh et al. ), O3 or O3/UV (Pires & Momenti ) combined with biological treatment for various toxic wastewaters and concluded that the resulting wastewater is suitable for further biological treatment. Whether or not the AOX becomes more biodegradable after an AOP treatment seems to be only tested by Drewes & Jekel (), who observed after the successive ozonation and soil-aquifer treatment, an increased degradation rate of AOX from 0.6 μg L1 d1 Cl to 2.73 μg L1 d1 Cl. Additional tests with other AOPs are required to compare the effect of different AOPs on the degradability of AOX. In conclusion, the appropriate AOP, pH and oxidant dosage for wastewaters containing relative high concentrations of halogen ions are crucial to achieve a significant reduction of both COD and AOX. With the current knowledge, however, it is difficult to formulate recommendations to this end. This is mainly due to the complexity of the chemical reactions during oxidation, the limited amount of studies and high variety of tests regarding AOX degradation/formation during AOPs. When evaluating different AOPs, it is necessary to take into account the effect on both concentration and biodegradability of AOX. In addition, since the aim of an oxidation treatment is to decrease both COD and AOX levels, the selectivity of the process must be taken into account when the most suitable oxidation technique is selected. This study aims to evaluate several combined chemical and biological treatments of industrial wastewater for the selective removal of AOX from the total matrix COD. For chemical oxidation, ozone, ozone/UV, H2O2/UV and photo-Fenton (H2O2/UV/Fe(II)) have been applied with varying oxidant dosages and pH. In a first series of tests, special attention is paid to the biodegradability of AOX and the selectivity of the AOP in relation to the type of oxidant and oxidant dosage. A second series of experiments is performed in order to explore the effect of UV intensity and H2O2 dosage on both the chemical and biological AOX removal.
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MATERIALS AND METHODS Oxidation tests are performed with two different wastewater samples originating from the effluent of a biological wastewater treatment plant from a chemical production company. Table 1 lists two different batches from the same plant, showing the typical variability in wastewater characteristics. The wastewater is treated in a pilot-scale reactor, as shown in Figure 1, by recirculating the water over a thinfilm UV-reactor. The internal volume of the recirculation tank (A) is approximately 50 L whereas the internal volume of the UV reactor (B) is only 7 L. The radial distance between the reactor vessel and the UV lamp (a medium pressure Hg lamp, Philips, 2014.1 W) is approximately 2.5 cm. Ozone is generated from a Pacific Ozone Model SGC-21, Aqua Purification System, Inc. and introduced into the wastewater by a venturi (C) at a gas flow rate of 6 L min1. Further dissolution of ozone in water is carried out in a static mixer (D). The dosage into the reactor was set constant. In order to unravel the effect of the oxidant concentration, O3/UV experiments are conducted at three different combinations of ozone feeding rate and UV intensity. An ozone flow rate of 100% refers to 16 g O3 h1 and a UV intensity of 100% corresponds to 2,000 W. H2O2 is continuously fed to the reactor in order to minimize the inhibiting reaction of hydroxyl radicals with hydrogen peroxide. The amount of H2O2 was calculated relative to the amount of COD in the water. A H2O2 dosage of 100% Table 1
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corresponds to a dosage of 2 mg L1 H2O2 per mg COD. The effective percentage was recalculated after the experiment based on the initial COD of the wastewater and the dosed amount of H2O2 during the experiment. For the photo-Fenton experiments (H2O2/Fe2þ), FeSO4 is added in a [Fe2þ]/[H2O2] ratio of 1/100 ww. During all experiments, the pH of the water was adjusted to 9 or 7 and kept constant during the process by adding NaOH or H2SO4, except for the photo-Fenton experiments which were carried out at pH 3. An overview of the details of the oxidation tests is given in Table 1. Samples were taken after 60 min of reaction time to determine the AOX and COD concentration and to start a biological treatment. Biological oxidation is simulated in respirometry experiments in which wastewater samples (500 mL) are mixed with activated sludge (300 mL) from a municipal wastewater treatment plant and periodically aerated. To make sure no biologically degradable components are present in the sludge sample, the sludge is aerated for 24 h prior to the respirometry experiments. The sludge concentration in the respiration reactor is 2.2 g L1. The aeration pumps are controlled using Hamilton VisiFerm optical dissolved oxygen (DO) sensors (type DO 225). Aeration starts when the DO concentration is beneath 2 mg L1 and stops at a DO concentration of 5 mg L1. After 4 h AOX and COD are measured again and corrected by the dilution factor of 500 over 800. Inert COD, which was already present in the sludge sample, is taken into account by subtracting the COD in the sludge supernatant before and after the respirometry experiment.
Composition of used wastewaters and overview of the performed oxidation tests
Wastewater characteristics
Name
UV intensity (kW)
pH
Oxidant
Oxidant dose (g h1)
Sample 1
Ozone/UV pH 9
2.0
9
O3
16
COD ¼ 200 mg L O2 AOX ¼ 1,500 μg L1 Cl Cl ¼ 750 mg L1 pH ¼ 7.8
Ozone/UV Ozone/UV50% Ozone 50%/UV H2O2 42%/UV H2O2 31%/UV H2O2 56%/Fe2þ/UV UV
2.0 1.0 2.0 2.0 2.0 2.0 2.0
7 7 7 7 9 3 7
O3 O3 O3 H2O2 H2O2 H2O2 –-
16 16 8 12.8 9.36 16.2 –-
Sample 2
30% H2O2/12.5% UV
0.25
7
H2O2
6.79
30% H2O2/25% UV
0.5
7
H2O2
6.79
COD ¼ 140 mg L1 O2 AOX ¼ 5,000 μg L1 Cl Cl ¼ 650 mg L1 pH ¼ 7.9
15% H2O2/25% UV 30% H2O2/100% UV 20% H2O2/100% UV 10% H2O2/100% UV 30% H2O2/50% UV UV/O3
0.5 2.0 2.0 2.0 1.0 2.0
7 7 7 7 7 7
H2O2 H2O2 H2O2 H2O2 H2O2 O3
3.4 6.79 4.53 2.5 6.79 16
1
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A standard curve made with 4-chlorophenol is used to calculate the amount of halogen ions (μg L1 Cl) in the water sample. The limit of detection is 10 μg L1 Cl and the relative standard deviation is 11%. The COD determinations, based on the silver-catalysed oxidation of the pollutants with potassium dichromate in acidic environment, are carried out by using 0–1,500 mg L1 range vials. Samples of 2 mL are required for those analyses. A Nanocolor® COD reactor and a Nanocolor® 500 D colorimeter from Machery-Nagel were used during the analysis.
RESULTS AND DISCUSSION
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Figure 1
Scheme of the pilot-scale reactor with feed tank (A), UV reactor (B), venturi for introduction of ozone (C) and static mixer (D). H2O2 is dosed continuously in the piping before the venturi.
AOX measurements are performed according to the WAC/IV/B/011 protocol with a ThermoFischer Scientific 3,000 systems TN/TS/TX (SphiNCX). Granular activated carbon (50 mg) is added to 100 mL of water sample and put on a horizontal shaker for 1 h. When necessary, the water samples were first diluted with ultrapure water to remain under the maximum concentration of 250 μg L1 Cl. After 1 h, the active carbon is collected and burned at 1,000 C in the oven of the apparatus. The combustion gas containing the halogen ions is passed over a scrubber into a titration cel for a coulometric titration with silver. W
Table 2
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Table 2 shows the AOX and COD removal efficiencies after the various AOP treatments and after subsequent biological oxidation from wastewater sample 1. Biological oxidation of the original wastewater sample led to a low AOX removal efficiency of approximately 20%. This is not surprising as the wastewater has already undergone a biological oxidation. Most AOP treatment methods reach 50% of AOX removal after 60 minutes of reaction time. Ozone-based techniques show generally less pronounced removal efficiencies (removal between 44 and 62%) than photo-Fenton (removal between 66 and 80%). This might indicate that the ozone is partially used for the formation of AOX, resulting in an overall lower degradation of AOX. The fact that the highest AOX-reduction is achieved with 50% less ozone input seems to confirm this hypotheses. Similar observations can be made for the H2O2based processes, which were studied in more detail for a
AOX and COD concentration after chemical oxidation (60 min) and subsequent biological post-treatment (4 h) for wastewater sample 1 AOX (μg L1 Cl)
COD (mg L1 O2)
Amount removed by AOP
Amount removed by
Amount removed by
subsequent biological oxidationa
AOP þ biological oxidation
Amount Initial
removed by AOP
S(AOX/COD)b
Test
Initial
Ozone/UV pH 9
1,647
843
(51%)
375
(47%)
1,218
(74%)
206
22
(11%)
4.8
Ozone/UV
1,700
806
(47%)
353
(39%)
1,159
(68%)
184
82
(45%)
1.1
Ozone/UV 50%
1,517
670
(44%)
379
(45%)
1,049
(69%)
177
83
(47%)
0.9
Ozone 50%/UV
1,660
1,029
(62%)
294
(47%)
1,323
(80%)
170
77
(45%)
1.4
H2O2 42%/UV
1,588
1,213
(76%)
192
(51%)
1,405
(88%)
ND
ND
ND
ND
H2O2 31%/UV
1,509
1,205
(80%)
41
(13%)
1,246
(83%)
ND
ND
ND
ND
H2O2 56%/Fe /UV
1,429
938
(66%)
64
(13%)
1,002
(70%)
ND
ND
ND
ND
UV
1,156
606
(52%)
66
(12%)
672
(58%)
ND
ND
ND
ND
2þ
a
The removal percentage is calculated as the amount of AOX removed from the residual AOX concentration after the AOP treatment. Δ[AOX]=AOXi The overall selectivity parameter S(AOX/COD) is calculated by: S(AOX=COD) ¼ . A relative standard deviation of 11% on the AOX concentration needs to be taken into account. Δ[COD]=CODi
b
ND stands for not determined.
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different batch of the same wastewater and presented in Table 3. The highest H2O2 (30%) doses resulted in no significant AOX removal, especially at low UV power. Increasing the power of the UV lamp using 30% H2O2 increased the AOX removal but remained significantly lower than at a 10 or 20% H2O2. This can be explained by the fact that H2O2 acts as a scavenger at higher concentration or by the hypothesis that high oxidant doses can lead to the activation of halogen ion which in turn will form halogenated organic compounds. In contrast to photo-Fenton and UV/H2O2, a significantly higher amount is biologically degraded with the ozone-based techniques (between 39–47% removal). Similar effects have been observed in the drinking water industry with total organic carbon (TOC). Cipparone et al. () observed that the biodegradability of the dissolved organic compounds in surface water increased six times upon ozonation. Higher effects on the degradability were observed with a combined H2O2/O3 treatment, but only when sufficiently high ozone concentrations (>0.7 mg mg1 TOC) were used (Speitel ). In general, less enhancement on the biodegradability was observed with UV/H2O2. The higher biodegradability of the compounds with the ozone-based techniques can be explained by the high reactivity of ozone towards unsaturated bindings and aromatic rings, which are also the most recalcitrant compounds for microorganisms. Nevertheless, the chemical oxidation technique reduces most of the AOX concentration. Therefore more of the total AOX is removed with photo-Fenton, i.e. between 66 and 80% of AOX has been degraded. The lowest AOX reduction is achieved with photo-Fenton at higher concentrations of H2O2 (16.2 g h1). In the last column of Table 2 the overall selectivity coefficient S for the ozone-based AOP treatments (without Table 3
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biological oxidation) is shown. From a comparison of the ozone-based experiments at pH 7, it becomes clear that the selectivity towards AOX removal is O3(50%)/UV > O3/UV > O3/UV(50%). It can therefore be concluded that a lower ozone concentration with respect to UV intensity results in a better selectivity for AOX removal. Increasing the pH to 9 further enhances the selectivity for AOX removal. For H2O2-based experiments, no selectivity parameter is reported as no corrections for the COD contribution of residual H2O2 could be made. Residual H2O2 will lead to an increase in COD, and as the H2O2 concentration was changed during the experiment, the contribution of residual H2O2 to the final COD is different over the experiments. This complicates the calculation of the exact amount of removed COD. In order to determine the relative selectivity, a better parameter to monitor might be the TOC removal, which also represents the removal of organic compounds but is not affected by the presence of H2O2. Finally, the results for UV alone confirm the findings of Hofl et al. (), as an AOX removal of approximately 50% is observed without appreciable COD degradation. The medium-pressure lamp is thus able to destroy carbon-halogen bonds; however, the addition of a small amount of oxidant (O3 or H2O2) significantly improves the oxidation of the matrix compounds. A second series of experiments (Table 3) has been performed in order to explore the effect of UV intensity and H2O2 dosage on the chemical and biological AOX removal. The composition of wastewater sample 2 differs significantly from sample 1 (see Table 1). Sample 2 contains three times more AOX and a lower COD level, which means that a higher fraction of the COD is halogenated than in sample 1. Compared to sample 1, the most efficient AOP treatment (H2O2 30%/UV) removes four times more
AOX concentration after chemical oxidation (60 min) and subsequent biological post-treatment (4 h) for wastewater sample 2 AOX (μg L1 Cl)
Test
Amount removed by subsequent biological
Amount removed by AOP þ biological
oxidation*
oxidation
Initial
Amount removed by AOP
30% H2O2/12.5% UV
4,130
271
(7%)
1,019
(23%)
748
(18%)
30% H2O2/25% UV
4,110
275
(7%)
1,000
(26%)
1,275
(31%)
15% H2O2/25% UV
4,908
802
(16%)
718
(17%)
1,520
(31%)
30% H2O2/100% UV
5,493
921
(17%)
1,214
(27%)
2,135
(39%)
20% H2O2/100% UV
4,640
2,933
(63%)
49
(3%)
2,982
(64%)
10% H2O2/100% UV
5,355
2,849
(53%)
626
(25%)
3,475
(65%)
30% H2O2/50% UV
5,283
1,926
(36%)
999
(30%)
2,925
(55%)
UV/O3
4,438
310
(7%)
2,543
(54%)
2,233
(50%)
*The removal percentage is calculated as the amount of AOX removed from the residual AOX concentration after the AOP treatment.
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AOX in sample 2. However, relative to the initial concentration, less AOX is removed than sample 1. The higher initial AOX concentration and lower H2O2 dose might explain the difference. For the H2O2-based techniques, the largest AOX degradation is observed when the UV power is high and with an intermediate H2O2 dosage, which was also observed with wastewater sample 2. After the AOP treatment, still a significant amount of AOX (between 17 and 30%) is removed by biological oxidation. However, as with the chemical oxidation the absolute amount of AOX is higher than in sample 1, while the relative amount of AOX is lower than in sample 1, because of the high initial AOX concentration. O3/UV at pH 7 does not significantly change the AOX concentration; however, after respiration, the AOX level is reduced to a similar level as the other treatments. This shows again the potential of AOPs in combination with biological oxidation to (partially) degrade AOX compounds in wastewater. Despite the high efficiency of the combined technique, the discharge limit of 500 μg L1 Cl is not achieved during the experiments, which is due to the higher initial AOX concentration. Figure 2 shows a contour plot for AOX removal by UV/ H2O2 at pH 7 as a function of reaction time and UV intensity (kW) (a) and H2O2 dosage (b). From both graphs, it becomes clear that the best AOX removal is obtained at UV power of 1–2 kW in combination with a H2O2 dosage of 3–4.5 g H2O2 over a reaction time of 50–60 minutes. It can also be seen that within a large area of this plot, a net AOX formation is observed. From all results it can be concluded that a 50% AOX reduction can be achieved with H2O2 dosages of approximately 90 mg L1 H2O2 and a UV energy requirement of 0.02–0.04 kWh L1.
Figure 2
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Contour plot for AOX removal (DAOX in μg Cl/L) by UV/H2O2 at pH 7 as a function of reaction time and UV intensity (kW) (a) and H2O2 dosage (b).
results show that a selective degradation of AOX with respect to the matrix compounds (expressed as COD) could be achieved. For O3/UV, lowering the ratio of O3 dosage to UV intensity leads to a better selectivity for AOX. Finally, the sensitivity of the operating parameters UV and H2O2 dosage towards the AOX removal was determined during a second run with another wastewater sample.
CONCLUSIONS REFERENCES This paper shows that AOX can be significantly reduced in industrial wastewater by a combined chemical–biological treatment. Despite the high chloride concentration in the water, no significant increase in AOX concentration was observed. In general, less AOX is removed during O3-based experiments than during the H2O2-based experiments. Nevertheless, high removal percentages can be achieved when combining AOPs with a post-biological treatment, indicating that AOX are not only degraded but also transformed to components that are more accessible for biological oxidation. The concentration of the oxidant turned out to be the key parameter for the selectivity towards AOX degradation. The
Baycan, N., Sengül, F. & Thomanetz, E. AOX formation and elimination in the oxidative treatment of synthetic wastewaters in a UV-free surface reactor. Environ. Sci. Pollut. Res. 12, 153–158. Baycan, N., Thomanetz, E. & Sengül, F. a Effect of chloride concentration on the oxidation of EDTA in UV-FSR oxidative system. J. Photochem. Photobiol. A 189, 349–354. Baycan, N., Thomanetz, E. & Sengül, F. b Influence of chloride concentration on the formation of AOX in UV oxidative system. J. Hazard. Mater. 143, 171–176. Catalkaya, E. C. & Kargi, F. Color, TOC and AOX removal from pulp mill effluent by Advanced Oxidation Processes: A comparative study. J. Hazard. Mater. B 139, 244–253.
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Cipparone, L. A., Diehl, A. C. & Speitel, G. E. Ozonation and BDOC removal: effect on water quality. J. Am. Water Works Assoc. 89, 84–97. Drewes, J. E. & Jekel, M. Behavior of DOC and AOX using advanced treated wastewater for groundwater recharge. Water Res. 32, 3125–3133. European Commission Roadmap to a Resource Efficient Efficient Europe. http://ec.europa.eu/environment/ resource_efficiency/about/roadmap/index_en.htm (accessed 8 October 2013). German Sewage Water Administration Regulation, appendix 51, Part I No. 86 published December 29, 1998 (Anhang 51 der Rahmenabwasserverordnung 1998 Teil I Nr. 86, ausgegeben zu Bonn, 29. December 1998). Hofl, C., Sigl, G., Specht, O., Wurdack, I. & Wabner, D. Oxidative degradation of AOX and COD by different advanced oxidation processes: A comparative study with two samples of a pharmaceutical wastewater. Water Sci. Tech. 35 (4), 257–264. Hostachy, J. C., Lenon, G., Pisicchio, J. L., Coste, C. & Legay, C. Reduction of pulp and paper mill pollution by ozone treatment. Water Sci. Tech. 35 (2–3), 261–268. Klaening, U. K. & Wolff, T. Laser flash photolysis of HClO, ClO, HBrO, and BrO in aqueous solution. Reaction of Cl- and Br-atoms. Ber. Bunsenges. Phys. Chem. 89, 243–245. Koh, I., Chen-Hamacher, X., Hicke, K. & Thiemann, W. Leachate treatment by the combination of photochemical oxidation with biological process. J. Photochem. Photobiol. A: Chem. 162, 261–271. Kusic, H., Bozic, A. L. & Koprivanac, N. Fenton type processes for minimization of organic content in coloured wastewaters: Part I: Processes optimization. Dyes Pigments 74, 380–387.
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Liao, C. H., Kang, S. F. & Wu, F. A. Hydroxy radical scavenging role of chloride and bicarbonate ions in the H2O2/UV process. Chemosphere 44, 1193–1200. Mertens, R. & von Sonntag, C. Photolysis (¼254 nm) of Tetrachloroethene in Aqueous Solutions. J. Photochem. Photobiol. A: Chem. 85, 1–9. Mobius, C. H. & Cordes-Talle, M. Enhanced biodegradability by oxidative and radioactive wastewater treatment. In Proceedings of the Fifth IAWQ Symposium on Forest Industry Wastewaters Vancouver, Canada, pp. 259–265. Parilti, N. B. & Akten, D. Optimization of TiO2/Fe(III)/solar UV conditions for the removal of organic contaminants in pulp mill effluents. Desalination 265 (1–3), 37–42. Perez, M., Torrades, F., Domenech, X. & Peral, J. Photocatalytic treatment of paper pulp bleach effluents. Quimica Analytica 16 (3), 211–214. Pires, E. C. & Momenti, T. J. Combination of an anaerobic process with O-3, UV and O-3/UV for cellulose pulp bleaching effluent treatment. Desalination Wastewater Treat. 5 (1–3), 213–222. Seiss, M., Gahr, R. & Niessner, R. Improved AOX degradation in UV oxidative wastewater treatment by dialysis with nanofiltration membrane. Water Res. 35, 3242–3248. Speitel, G. E. Advanced Oxidation and Biodegradation Processes for the Destruction of TOC and DBP Precursors. AWWA Research Foundation and American Water Works Association, USA, 139 pp. Van Aken, P., Van Eyck, K., Degrève, J., Liers, S. & Luyten, J. COD and AOX removal and biodegradability assessment for Fenton and O3/UV oxidation processes: a case study from a graphical industry wastewater. Ozone Sci. Eng. 35 (1), 16–21. Zhou, H. & Smith, D. W. Effects of chemical reactions on ozone mass transfer in treating pulp mill effluent. Water Sci. Tech. 32 (2/3), 249–260.
First received 13 March 2013; accepted in revised form 4 July 2013. Available online 19 October 2013
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