05-Asgari

JRHS 2014; 14(1): 29-35

Copyright© Journal of Research in Health Sciences

Microwave/H2O2 Efficiency in Pentachlorophenol Removal from Aqueous Solutions

Ghorban Asgari (PhD)a, AbdolMotaleb Seidmohammadi (PhD)b, Afsane Chavoshani (MSc)c*, Ali Reza Rahmani (PhD)b

a Social Determinants of  Health Research Center (SDHRC), Department of Environmental Health Engineering, School of Public Health, Hamadan University of Medical Sciences, Hamadan, Iran 

b Research Center for Health Sciences, Department of Environmental Health Engineering, School of Public Health, Hamadan University of Medical Sciences, Hamadan, Iran

c Department of Environmental Health Engineering, School of Public Health, Hamadan University of Medical Sciences, Hamadan, Iran

* Correspondence: Afsane Chavoshani (MSc), E-mail: chavoshani.afsane@yahoo.com

Received: 29 August 2013, Revised: 14 October 2013, Accepted: 25 November 2013, Available online: 09 December 2013

Abstract

Background: Pentachlorophenol (PCP) is one of the most fungicides and pesticides. Acute and chronic poisoning from PCP may be occurred by dermal absorption, and respiration or ingestion. With respect to health and environmental effects of PCP, many methods were considered regarding its removal. Microwave assisted other methods are environmental friendly, safety, and economical method, consequently, in this study; microwave assisted with hydrogen peroxide (MW/H2O2) was used for PCP removal from aquatic solutions.

Methods: The possible of PCP removal was considered by application of a modified domestic microwave. PCP removal rate was considered under different factors such as H2O2 dose (0.01, 0.02, 0.1, 0.2, 0.3 mol/L), PCP concentration (100,200, 300, 400, 500, 750, 1000 mg/L), pH­ (3, 7, 11), energy intensity (180,450, 600W), COD (344mg/L), and scavenger testes (0.02 mol/L from each of Tert- butyl alcohol (TBA), NaCl, NaHCO3, and Na2CO3). The concentration changes of PCP were determined­ using spectrophotometer and HPLC spectra, respectively.

Results: The best PCP removal was obtained in condition of pH­ 11, 0.2 mol/L H2O2, and 600­ W energy intensity. Moreover, COD removal in this condition was 83%. Results obtained from radical scavengers indicated that OH° had only an initiator role, and had not a dominant role, and order reaction was in first order.

Conclusion: The results of microwave/H2O2 application showed that this process is suitable for removal of PCP and other chlorinated organic compounds in alkaline pH.

Keywords: Microwave, H2O2, PCP, Alkaline pH

Introduction

Pentachlorophenol (PCP) is widely used in the wood preserving industry and agriculture as a fungicide, pesticide and herbicide. The poisoning  of PCP may be occurred by dermal absorption, respiration­, ingestion, peripheral neuropathy and other problems related to nerve damage (neurotoxicity)­1. PCP is a significant contaminant of soil, surface, and groundwater especially around sawmills and wood preserving facilities2-5. Researchers using a mathematical model calculated that 96.5% of PCP is in soil, 2.5% in water, 1% in air, and less than 1% in suspended sediments and organisms in aquatic environments1. Therefore, PCP removal from aquatic solution is necessary, especially from alkaline wastewater.

Nowadays, environmental researchers have considered the sustainable methods for refractory contaminants removal. Aqueous H2O2 is an ecologically sustainable oxidant with high oxidation potential and water as the only by-product. However, oxidation with H2O2 requires prior activation for radical production­7. Recently, the application of microwave heating in combination with hydrogen peroxide (MW/H2O2) for pollutants treatment has shown to be an efficient oxidation technology­6.­ MW/H2O2 process has showed high degradation efficiency, because it generates active species of hydroxyl and other radicals with a redox potential. Usually, MW/H2O2­ has no need of catalyst separation and no potential risk of environmental pollution, compared to some hybrid MW systems 6,8,9 .

In this study, due to an environmental-friendly as well as highly efficient method and low existence of specific work in this condition, analysis of the PCP removal was performed by MW/H2O2 technology.

Methods

Sodium salt PCP, which is the sodium salt of PCP (C6Cl5ONa) ­with 98% purity­­­,­ was used without further purification. The characteristics of the PCP included of boiling point: 309-310C°, mass molar: 288.32g/mol. The PCP solution was prepared by dissolving PCP in NaOH solution to accelerate its dissolution1. And hydrogen peroxide (30% w/w).­Under atmospheric pressure, all of the experiments were performed and triplicated in modified domestic microwave oven. Detail modifications of MW were performed­ as follows: drilled a hole in the upper oven wall and then attached an aluminum tube of the same diameter to the hole. The possible of PCP removal was considered by a reactor placed to domestic microwave. PCP removal rate was considered under different factors such as H2O2 dose (0.01, 0.02, 0.1, 0.2, 0.3 mol/L), PCP dose ­ (100,­­ 200, 300, 400, 500, 750, 1000 mg/L), pH (3,­ 7,­ 11), energy intensity (180,­ 450,­ 600W), COD­ (344 mg/L), and scavenger testes­ (0.02 mol/L from each of Tert- butyl alcohol (TBA), NaCl, Na2CO3 and NaHCO3). A Thermometer GENWAY Medal 2003 was utilized to detect variation of solution temperature during degradation process. The leakage of MW oven was measured at 20 cm distance from the aperture. Concentration changes of PCP were determined­ using spectrophotometer according to (APHA, 2005)11, and HPLC spectra. HPLC (Part Number.WATO54275 with dimension of 4.6 mm×250 mm and column of symmetry C18-50 µm ) method was performed with an acetonitrile/water 60:40 (v/v) as mobile phase at a flow rate of 1 ml/min and detection wavelengths of UV was 254 nm12. COD was determined using potassium dichromate solution as oxidizer in a strong acid medium, then by titration step using ferrous ammonium sulfate as the reducing agent and Ferroin as the indicator6.

Results

Removal of PCP in MW/H2O2 in pHs of­ 3, 7 and 11 and reaction time 60 min was obtained 46, 56 and 64%, respectively (Figure 1). The results shown that alkaline pH could sharply accelerate PCP degradation in MW/H2O2 system. Therefore, alkaline pH could slightly speeds up PCP degradation in MW/H2O2 process.

To scavenge all possible OH°, H2O2 and O2, scavengers test was performed by 0.02mol/L from each of TBA, NaCl, Na2CO3, and NaHCO3. Results from experiments indicated that the degradation percentage in MW/H2O2/NaCl­, MW/H2O2/TBA, MW/H2O2/NaHCO3, and MW/H2O2/Na2CO3 was obtained 96, 90,­ 15, and  0% respectively, whereas in MW/H2O2 degradation percentage was attained 93.82%­ (Figure 2).­ Thus, in the MW/H2O2/NaCl process the PCP removal rate was increased.

PCP removal efficiency for 0.01, 0.02, 0.1, 0.2, and 0.3 mol/L of hydrogen peroxide was 23.82, 63.82, 81.82, 90.82, and 90.82% at ­ 60 min respectively (Figure 3). PCP removal was stabled in doses of 0.2 and 0.3 mol/L. Therefore, H2O2 dose of 0.2 mol/L was selected and used as optimal dose.

The test results shown in Figure 4 indicated that degradation rate of PCP gradually increased by increasing the microwave power from 180 to 600W.   Amount of PCP removal in MW/H2O2 with energy intensity of 180, 450, and 600 W was 32, 86 and 93%, respectively (Figure 4). Subsequently, the microwave irradiation of 600 W was chosen for further experiments.

Amount of PCP removal for 100, 200, 300, 400, 500, 750 and 1000 mg/L by MW/H2O2 was obtained 93.82, 92, 91, 90, 89, 88 and 87%, respectively (data was not shown). Increasing PCP concentration had a negligible role in decreasing­ efficiency of process (approximately 7%), consequently, selection of 1000 mg/l as optimal dose was not economic and PCP concentration of 100 mg/l used for further experiments.

In addition, COD removal was 83% (data was not shown). The de-chlorination of PCP by the MW/H2O2 process follows first-order kinetic (Figure 5). According to -lnC/C0=kt equation (where; C0 and C=PCP concentration (mg/l) at 0 and t time, t = reaction time (min) and k= reaction constant (min-1) respectively), k H2O2 only and k MW/H2O2 in 60 min was 0.0035 and 0.044min-1 respectively (P=0.002).

Figure 1: Effect of pH on PCP removal­ ­(C0=100mg/L,­ H2O2=0.02mol/l, E=450W)

Figure 2: Effect of radical scavengers on PCP removal (C0=100mg/L, pH=11, H2O2=0.02mol/L, E=600W, 0.02mol/L from each of radical scavengers)

Figure 3: Effect of H2O2 dose on PCP removal­ (C0=100mg/L, pH=11, E=600W)

Figure 4: Effect of energy on PCP removal (C0=100mg/L, pH=11, H2O2=0. 2mol/L, E=180,450, 600W)

 

Figure 5: Reaction kinetics ­­(C0=100mg/L, H2O2=0.2mol/L, E=600W, pH=11)

Discussion

Wastewater pH is one of the factors that effects on organic degradation. Degradation of PCP by MW/H2O2 system in a broad pH range, from acidic to alkaline conditions, was initially studied. According to previous studies phenolic compounds, in alkaline pH, are in­ anionic state and absorb microwave more than other pHs, also under alkaline pH activated oxygen decomposed from hydrogen peroxide has a significant role for PCP removal6,13.

Formation of hydroxyl radicals, in advanced oxidation process (AOPs) such as MW/H2O2, was always considered to be the main agent in organic removal­. “AOPs have considerable similarities due to the participation of hydroxyl radicals in most mechanisms that are operative during the reaction, but hydroxyl radicals are extremely unstable and reactive because of their high reactivity”14. It seems that in MW/H2O2 and at alkaline pH, OH° is activation initiator and is not dominant radical. According to Hong et al. results activated O2 is  dominant 6

In this study, results of ­ OH° scavenger indicated that at least the main attack toward PCP was not OH° and NaCl had a catalytic role for extra H2O2 and producing O26,15.  However, TBA test had a negligible role for decreasing PCP removal. Decreasing effect of chloride and TBA on degradation has been observed in AOPs systems which are mainly based on OH° radicals16. Because decreasing PCP removal under application of Na2CO3 and NaHCO3 for quenching H2O2 and O2 was significant, according to other studies the main attack toward PCP was done by H2O2 and activated O2 from it and OH° was  only an initiator radical 17. Decomposition rate of PCP can express as an indirect reaction with OH°, because OH° is unstable and immediately able to converted to other radicals8. It seems that H2O2 can be activated by MW to initiate other radicals at high pH under the effect of hydroxyl radical. But application of Na2CO3­ (as H2O2­ scavenger) showed that MW alone was not suitable for PCP removal and addition of H2O2 dose during MW process enhances the rate of PCP degradation, except when the radical scavenging effect of H2O2 is dominant17. However, at high concentrations of H2O2 the increase in PCP removal started decreasing. This is because at high concentrations, the solution has a self-quenching of OH° radicals by extra amounts of H2O2 to produce HO2° radicals. The existences of  extra H2O2 as an scavenger of OH° radicals have also an effect in the removal efficiency 18.

According to our results increasing PCP concentration had a negligible role in decreasing­ efficiency of process and MW/H2O2 process was able to remove high PCP concentrations. Study of Chang et al. has shown that MW/Fenton was able to remove 99% of 500, 1000, 1500, and 2000 mg/l of isopropyl alcohol19. Besides, pollutants such as phenol, aromatic hydrocarbons and PCP with 1000, 5000, and 10000 concentrations can be removed in amount of 98, 96 and 92%, respectively2°. These amounts are much higher than commonly adopted in attractive AOPs 21. It is because of high efficiency of processes integrated with MW and non-thermal effects in these processes. The HPLC spectra indicated that major PCP informed to CO2 and HCl. The HPLC spectra and COD results showed a similar trend in mineralization and the lack of toxic intermediates and by products8,22.

Energy intensity was very important for PCP removal. In this study, with increasing energy, the amount of final temperature increased. These results revealed that H2O2 could be converted to OH° and other radicals by microwave energy resulting in a considerable enhancement in the reaction rates. Thus, the microwave irradiation of 600W was chosen throughout the experiments. Therefore, a high energy power input (and a high electrical field strength) with microwave is more efficient than a low energy input. However, efficiency can only increase to a limited value, and sometimes no further increase of the efficiency and absorption of microwave energy is observed23. Degradation of organic materials is not always increased with increasing microwave power, because characteristic of organic compounds and oxidants is effective for absorption of microwave energy24,25. Reaction kinetic allows the overall comparison between the different AOPs tested14. In our study the reaction kinetics of MW/H2O2 was 12.57 times higher than H2O2 only. Conclusively MW radiation was suitable for H2O2 reaction and increasing PCP removal.

Conclusions

MW/H2O2 process could efficiently degrade refractory substrates at strong alkaline pH, via radical production. The microwave degradation has many advantages such as convenience, safety, economy and high efficiency, and provides a simple and rapid method for H2O2 activation to generate radicals in aqueous solution using microwave energy. MW/H2O2 process was able to remove high PCP concentrations. Addition of H2O2 dose during MW process enhances the rate of PCP degradation, except when the radical scavenging effect of H2O2. Results obtained from radical scavengers showed that OH° had only an initiator role, and had not a dominant role, and order reaction was in first order. Accordingly this method has a better prospect in future for removal of other chlorinated organic compounds in alkaline pH.

Acknowledgments

The authors would like to thank Hamadan University of Medical Sciences for technical and financial support of this study.

Conflict of interest statement

The authors have no conflict of interests to declare.

Funding

Hamadan University of Medical Sciences supported this work (9010274023).

References

  1. Engwall  MA, Pignatello JJ, Grasso D. Degradation and detoxication of the wood preservative creosote and pentachlorophenol in water by the photo-Fenton reaction. Water Res. 1999;33:1151-1158.
  2. Ewers U, Krause C, Schulz C, Wilhelm M. Reference values and human biological monitoring values for environmental toxins. Int Arch Occup Environ Health. 1999;72:255-260.
  3. Stehly GR, Hayton WL. Effect of pH on the accumulation kinetics of­ pentachlorophenol in goldfish. Arch Environ Contam Toxicol. 1990;19:464-470.
  4. Song Z. Effects of Pentachlorophenol on Galba pervia, Tubifex sinicus and Chironomus plumousus Larvae. Bull Environ Contam Toxicol. 2007;79:278-282.
  5. Jorens PG, Schepens PJC. Human pentachlorophenol poisoning. Hum Exp Toxi.1993; 12:479-495.  
  6. Hong J, Yuan N, Wang Y, Qi S. Efficient degradation of Rhodamine B in microwave-H2O2 system, at alkaline pH. Chem Eng J. 2012;191:364-365.
  7. Kumar R, Sharma N, Sharma N, Sharma A, Sinha AK. Metal-free activation of H2O2 by synergic effect of ionic liquid and microwave: chemoselective oxidation of benzylic alcohols to carbonyls and unexpected formation of anthraquinone in aqueous condition. Mol Divers. 2011;15:687-695.
  8. Han DH, Cha SY, Yang HY. Improvement of oxidative decomposition of aqueous phenol by microwave irradiation in UV/H2O2 process and kinetic study. Water Res. 2004;38:2782-2790.
  9. Zhao D, Cheng J, Hoffmann MR. Kinetics of microwave-enhanced oxidation of phenol by hydrogen peroxide. Front Environ Sci Engin China. 2011;5:57-64.
  10. Anotai J, Wuttipong R, Visvanathan C. Oxidation and detoxification of pentachlorophenol in aqueous phase by ozonation. J Environ Manage. 2007;85:345-349.
  11. American Public Health Association. Standard methods for the examination of water and waste water. Washington DC: APHA; 2005.
  12. Al-Momani F. Combination of photo- oxidation process with biological treat­ment, [PhD thesis]. Barcelona: Barcelona University of Environmental Engineering; 2003.
  13. Movahedyan H, Seidmohammadi A­M. Comparison of different advanced oxidation process degradation P-cholorophenol in aqueous solutions. Iran J Environ Health. 2009;6:153-160.
  14. Rodriguez M. Comparison of different advanced oxidation processes for phenol degradation. Water Res. 2002;36:1034-1042.
  15. Lau K, Chu W, Graham NJD. The aqueous degradation of butylated hydroxyanisole by UV/S2O82: study of reaction mechanisms via dimerization and mineralization. Environ Sci Technol. 2007;41:613-619.
  16. Yuan R, Ramjaun SN, Wang Z, Liu J. Effects of chloride ion on degradation of acid orange 7 by sulfate radical-based advanced oxidation process: implications for formation of chlorinated aromatic compounds. J Hazard Mater. 2011;196:173-179.
  17. Wu T, Englehardt JD. A new method for removal of hydrogen peroxide interference in the analysis of chemical oxygen demand. Environ Sci Technol.­ 2012;46:2291-2298.
  18. Oh SY, Kang SG, Chiu PC. Degradation of 2, 4-dinitrotoluene by persulfate activated with zero-valent iron. Sci Total Environ. 2010;408:3464-3468.
  19. Chang YJ, Lin CH, Hwa MY, Hsieh YH. Study on the decomposition of isopropyl alcohol by using microwave/Fe3O4 catalytic system. J Environ Eng Manage. 2010;20:63-68.
  20. Roshani B, Karpel vel Leitner N. The inuence of persulfate addition for the degradation of micropollutants by ionizing radiation. Chem Eng J. 2011;168:784-789.
  21. Yang S, Wang P, Yang X, Wei G, Zhang W, Shan L. A novel advanced oxidation process to degrade organic pollutants in wastewater: Microwave-activated persulfate oxidation. J Environ Sci. 2009;21:1175-1180.
  22. Lee HY, Lee CL, Jou CJG. Comparison degradation of pentachlorophenol using microwave-induced nano scale Fe0 and activated carbon. Water Air Soil Poll. 2010;211(1):17-24.
  23. Zhang  Z,  Xu  Y, Ma  X , Li F, Liu D. Microwave degradation of methyl orange dye in aqueous solution in the presence of nano-TiO2-supported activated carbon (supported-TiO2/AC/MW). J Hazard Mater. 2012;209-210:271-277.
  24. Yang Y, Wang P, Shi S, Liu Y. Microwave enhanced fenton-like process for the treatment of high concentration pharmaceutical wastewater. J Hazard Mater. 2009;168:238-245.
  25. Jou CJ. Degradation of pentachlorophenol with zero valence iron coupled with microwave energy. J Hazard Mater.  2008;152:699-702.


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