Correspondence pubs.acs.org/IECR
Reply to “Comments on ‘Reuse of Semiconductor Wastewater Using Reverse Osmosis and Metal-Immobilized Catalyst-Based Advanced Oxidation Process’” Jeongyun Choi and Jinwook Chung* R&D Center, Samsung Engineering Co., Ltd., Woncheon-Dong, Youngtong-Gu, Suwon, Gyeonggi-Do, 443-823, Korea
Ind. Eng. Chem. Res. 2014, 53, 11167−11175 (DOI: 10.1021/ie500805x) In their Comment,1 Kopinke and Georgi have presented comments regarding our previously published manuscript, entitled “Reuse of Semiconductor Wastewater Using Reverse Osmosis and Metal-Immobilized Catalyst-Based Advanced Oxidation Process”. Their explanation can be summarized by the following two points: (1) The H2O2 concentration used in the pilot-scale experiment was assumed to be insufficient to remove 100 ppb of the total organic carbon (TOC) in the organic compounds. (2) The removal of organic compounds was assumed to be achieved by not only the oxidation mechanism associated with heterogeneous Fenton’s reaction but also the adsorption on activated carbon (AC). They also provided some evidence to support the comments that they issued. The following is our response to their comments.
Table A. Consumed H2O2 per Removed TOC in Each Step of Catalytic Reactor Amount of TOC (μg/L) amount of H2O2 (μg/L)
1. INSUFFICIENT H2O2 CONCENTRATION The commenters (Kopinke and Georgi) mentioned the oxidation mechanism of the advanced oxidation process (AOP) and indicated that 14.2 g of H2O2 was theoretically needed to oxidize 1 g of carbon in acetaldehyde to CO2. This stoichiometric calculation might be correct if all of the carbon in the organic compound was transferred to CO2. In addition, they were referring to one paper in which a significantly greater amount of H2O2 (3−4 orders of magnitude) was needed to decompose the methyl tert-butyl ether (MTBE) adsorbed on the AC, compared to our results. If we know the chemical composition of organic compounds in the influent of the catalytic reactor, we can validate whether the amount of H2O2 was (or was not) sufficient to remove the organic compounds. However, we do not report any information about that. Therefore, we recalculate the amount of H2O2 necessary to remove 1 g of TOC, using the data presented in Table 1 in our original manuscript,2 and the result is presented here in Table A. In the calculation, we used the removed TOC concentration instead of influent TOC concentration to verify the exact ratio of H2O2 to TOC in the reaction of organic compounds degradation. The result shows that the amount of H2O2 needed to remove 1 g of TOC was in the range of 5.3−8.1 g in first step and 4.5−5.9 g in second step. If we consider that 5.6 g H2O2 is need to oxidize 1 g of formic acid to CO2, we think that our results are somewhat acceptable. In addition, these values are analogous to the results reported in refs 3−5, in which 5−7 g/L H2O2 that was reacted with a carbon-Fe catalyst degraded 1 g of TOC of phenol and dye (Orange II). © 2014 American Chemical Society
influent effluent
200 300 400 500
95 90 92 104
57 45 36 42
100 100 100 100
57 45 36 42
39 28 14 22
amount of TOC removed (μg/L) 1st Step 38 45 56 62 2nd Step 18 17 22 20
TOC removal efficiency (%)
ratio of H2O2 to TOC
40 50 61 60
5.3 6.7 7.1 8.1
32 38 61 48
5.6 5.9 4.5 5.0
We also want to emphasize that a comparison of the work of Huling in the Comment (ref 6 in this Reply) to our results in the original paper2 is not appropriate. The big difference between the two studies (Huling’s study and our work) is the status of the contaminant. In Huling’s study, Fenton-driven oxidation was applied to degrade MTBE adsorbed on AC, while heterogeneous Fenton oxidation in the our laboratory (as reported in our original study2) was used to remove organic compounds in the permeate solution of the RO system.7
2. THE POSSIBILITY OF ADSORPTION INSTEAD OF OXIDATION The commenters also mentioned that organic compounds were possibly adsorbed on AC, while the contaminant was oxidized by OH radicals produced in the reaction between H2O2 and metal-immobilized catalysts and the removal efficiency of contaminants by oxidation was somewhat overcalculated. We agree with the commenters’ opinion and, unfortunately, do not have any direct evidence that only oxidation occurred in our system. However, there are several indirect facts in the manuscript which indicate that the main mechanism of TOC removal was oxidation rather than adsorption. First, in our study, the oxidation efficiency was strongly dependent on the H2O2 concentration (60% TOC removal at 200 mg H2O2/L and 85% TOC removal at 400 mg/L). Especially, the scavenger effect of the OH radical was also observed, in which an Published: November 19, 2014 18587
dx.doi.org/10.1021/ie504392k | Ind. Eng. Chem. Res. 2014, 53, 18587−18588
Industrial & Engineering Chemistry Research
Correspondence
injection of more than 400 mg/L of H2O2 caused a decrease in the overall TOC removal (see Table 2 in the original paper2). In addition, our previous study2 showed that the TOC removal efficiency was also dependent on pH, type of anion, which is known to be an important fact of Fenton’s oxidation. Additional evidence is given in a study that we also reported,7 in which the removal efficiency of acetone on AC itself was 20%, while 70% of acetone was removed in the reaction of H2O2 and Fe and Al immobilized catalyst. Finally, we have many other evidence of oxidation that was not provided in the manuscript. More data will be presented in our next paper (which has been submitted to the journal Chemosphere).8 Whenever we synthesize the catalyst, we use a transformation efficiency of isopropyl alcohol to acetone of 100% in the evaluation procedure of the catalyst capability. The reason for lower H2O2 addition was to reduce the operational costs in the real plant. In our real system, we do not need to oxidize all organic compounds to CO2, because there are more 5 units in the following ultrapure water production system to decrease the amount of organic compounds in solution, as shown in Figure 1 in the original paper. The main purpose of this study was to remove particular compounds in wastewater discharged from electronic industry that were known to make the water quality worse than that of ultrapure water produced using treated wastewater.
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AUTHOR INFORMATION
Corresponding Author
*Tel.: +82-31-260-6053. Fax: +82-31-260-3800. E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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REFERENCES
(1) Kopinke, F. D.; Georgi, A. Comments on “Reuse of Semiconductor Wastewater Using Reverse Osmosis and Metal Immobilized Catalyst-Based Advanced Oxidation Process”. Ind. Eng. Chem. Res. 2014, DOI: 10.1021/ie504255n. (2) Choi, J.; Chung, J. Reuse of semiconductor wastewater using reverse osmosis and metal-immobilized catalyst-based advanced oxidation process. Ind. Eng. Chem. Res. 2014, 53, 11167−11175. (3) Ramirez, J. H.; Maldonado-Hódar, F. J.; Pérez-Cadenas, A. F.; Moreno-Castilla, C.; Costa, C. A.; Madeira, L. M. Azo-dye Orange II degradation by heterogeneous Fenton-like reaction using carbon-Fe catalysts. Appl. Catal., B 2007, 74, 312−323. (4) Zazo, J. A.; Casas, J. A.; Mohedano, A. F.; Rodríguez, J. J. Catalytic wet peroxide oxidation of phenol with a Fe/active carbon catalyst. Appl. Catal., B 2006, 65, 261−268. (5) Messele, S. A.; Stüber, F.; Bengoa, C.; Fortuny, A.; Fabregat, A.; Font, J. Phenol degradation by heterogeneous Fenton-like reaction using Fe supported over activated carbon. Procedia Eng. 2012, 42, 1373−1377. (6) Huling, S. G.; Jones, P. K.; Ela, W. P.; Arnold, R. G. Fentondriven chemical regeneration of MTBE-spent GAC. Water Res. 2005, 39, 2145−2153. (7) Choi, J.; Jeong, J. H.; Chung, J. Degradation of acetone and isopropyl alcohol in electronic wastewater using Fe- and Alimmobilized catalysts. Chem. Eng. J. 2013, 218, 260−266. (8) Choi, J.; Chung, J. Evaluation of potential for reuse of industrial wastewater using metal-immobilized catalysts and reverse osmosis. Chemosphere, submitted.
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