Ferrates Synthesis, Properties, and Applications in ... - ACS Publications

Chapter 24

Oxidation of Nonylphenol Using Ferrate

Downloaded by PENNSYLVANIA STATE UNIV on March 16, 2013 | http://pubs.acs.org Publication Date: July 25, 2008 | doi: 10.1021/bk-2008-0985.ch024

Myongjin Yu, Guisu Park, and Hyunook Kim

*

The University of Seoul, Department of Environmental Engineering, 90 Jeonnong-dong, Dongdaemun-gu, Seoul 130-743, Korea Corresponding author: [email protected] *

Public concerns on nonylphenol (NP) and nonylphenol ethoxylates (NPEOs) are growing because they are frequently detected in the aquatic environment and proven endocrine disrupter compounds (EDCs). Since these compounds cannot be biologically completely degraded, chemical oxidation has been frequently applied to degrade NP and NPEOs. In this study, ferrate(VI) (Fe(VI)) was used to oxidize NP and its oxidation kinetics was evaluated. It should, however, be noted that the first order rate was evaluated using data collected only after the initial degradation phase, in which 50-70 % Np was degraded. In fact, the NP and Fe(VI) concentrations during the ID phase could not be quantified since the oxidation was too fast. The effect of hydrogen peroxide (H O ) presence on the NP oxidation by Fe(VI) was also evaluated. In general, the initial destruction of NP by Fe(VI) at lower pH was more significant than higher pH (i.e., 26% at pH 9.0 and 71% at pH 6.0). H O addition did not have much impact on the NP oxidation. When applied to oxidation of NP in natural water, Fe(VI) showed less removal efficiency possibly due to the presence of dissolved organics in the water. 2

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© 2008 American Chemical Society

In Ferrates; Sharma, V.; ACS Symposium Series; American Chemical Society: Washington, DC, 2008.

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Introduction Currently, a large number of chemicals have been emitted into the environment through human activities. Some of these chemicals can cause serious effects on wildlife species and human health. Among the chemicals, nonylphenol (NP) and its ethoxylates (NPEOs) are of more interest due to their anti-androgenic potential in the environment and their possible adverse effects on human health (1-3). For these reasons, utilization of NPEOs is under strict regulation in some countries in Europe and North America (4). In addition, NP is on the second priority list of substances drawn up under the European Union's Existing Substances Regulations (793/93/EEC). Since thefirstsynthesis of these chemicals in the 1940s, their production has been increased yearly due to their wide range of application as an ingredient of detergents, emulsifiers, wetting and dispersing agents. The world production of NPEOs in 1995 was about 520,000 tones (5). Several researchers have pointed out that the effluent from sewage treatment plants (STPs) is one of the major sources of the NPEOs metabolites detected in the aquatic environment (6-8). Incomplete biodegradation of commonly used NPnEO (usually n = 8-12) in STPs results in the production of NPEOs with shorter ethoxylate chains (1-3 ethoxylate units) and NP, which exhibit higher toxicity than their parent compounds (9,10). Therefore, it is necessity to decompose or remove the metabolites in the STPs before treated water is discharged into a stream or a river, which can be a drinking water source in downstream. Table I shows level of NP and its ethoxylates in the effluentfromSTPs in Canada. 1

Table I. Concentration of Nonylphenol and Its Ethoxylates in Sewage Treatment Plant Effluents STP level of treatment Primary Secondary Tertiary SOURCE:

NP

NP1EO

NP2EO

< 0.02-62.1 0.12-4.8 < 0.02-3.2

0.07-56.1 < 0.02 -43.4 0.30 - 26.4

0.34-36.3 < 0.02 - 32.6 0.25 - 12.5

Reproduced with permission from Reference 11, Copyright 2000 CEPA

Advanced oxidation processes seem promising for breakdown of the NPEOs' metabolites as the post-treatment of biological processes in STPs since a variety of aromatic compounds can be efficiently decomposed by these treatments. In fact, the ozone (0 ) has been successfully applied to oxidize various endocrine disrupter compounds (EDCs) (e.g., 17 p-estradiol (12), NP and bisphenol-A (13), and NPEOs (13,14)). 3


391 Ferrate(VI) is the oxidant which recently attracts more attention from researchers with its versatility as a multi-purpose water and wastewater treatment agent for disinfection, oxidation, and coagulation (15,16). Fe(VI) has very strong oxidizing power in the entire pH range (77). Under acidic conditions, the redox potential of ferrate ion is higher than that of any other oxidants, such as Cl , 0 , H 0 , and KMn0 . Due to its strong oxidizing nature, Fe(VI) has been applied to decompose various organic and inorganic compounds; for examples, hydrogen sulfide (75), 1,4-thioxane (19), thioacetamide (20), phenol and chlorophenols (27). Nearly all reactions of Fe(VI), with a variety of compounds, were reported to be first-order for each reactant. Table II shows second-order reaction rate constants of Fe(VI) with selected organic and inorganic compounds. The reported second-order reaction rate constants of Fe(VI) range from about 10~ to 10 M ' V in the pH range of 8.0-9.0. The reactivity of Fe(VI) is highly dependent on the type of compound involved, indicating that Fe(VI) is a very selective oxidant. High reactivity of Fe(VI) was found for reduced sulfur- and nitrogen compounds (i.e., hydrogen sulfide and hydroxylamine) and aromatic compounds (i.e., phenol). On the other hand, Fe(VI) showed low reactivity toward tertiary alkylamine, ammonia, carboxylic acid, aldehydes and alcohols. 2


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Table II. Second-order Rate Constants of Ferrate with Various Compounds at 25°C Compounds

Sulfur compounds Hydrogen sulfide Cysteine Thiourea Thiosulfate 1,4-Thioxane Nitrogen compounds Hydrazine Hydroxylamine Aniline Ammonia Aldehydes, carboxylic acid, and alcohols Formaldehyde Formic acid Methyl alcohol Other compounds Superoxide ion Phenol Hydrogen peroxide

pH

k

(M's')

9.0 9.0 9.0 9.0 9.0

1A 1.0 3.4 7.2 5.8

x 10

9.0 9.0 9.0 9.0

5.6 4.8 3.9 1.7

8.0 8.0 8.0

5.0 x 10-' 4.0 x 10"' 3.0 x 10"

9.0 9.0 9.0

3.0 x 10 1.0 x 10 3.0 x 10'

Ref.

5

18

5

22

x 10 x 10

3

23

2

x 10 x 10'

24 19

3

25 26 27 28

x x x x

10 10 10 10

3

2

1

2

29 29 29

5

30

2

31 32


3

392 In this study, NP oxidation by Fe(VI) was performed in organic-free water and in natural water. The oxidation efficiency was evaluated at different Fe0 " doses, solution pHs or molar ratios of H 0 /Fe0 ". 2

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Material and Methods


Reagents NP (>85% purity) was obtained from Aldrich (USA) and diluted with methanol before use as necessary. The chemical structures of NP and NPEOs are shown in Figure 1. Methanol was chosen as solvent because it was miscible with water and has a low reactivity with Fe(VI) (k = 3.0* 10" M'V , pH 8.0) (29). H 0 solution (35%) was purchased from Junsei (Japan) and diluted to the desirable concentration with the Milli-Q water as necessary. High-performance liquid chromatography (HPLC) grade solvents were used for all the HPLC works. Potassium ferrate (K Fe0 ) (>94% purity) was prepared by modifying the method proposed by Thompson et al. (33). Fe(VI) solution with desirable concentration prepared by adding appropriate amount of K Fe0 to 0.005 M Na HPO /0.001 M borate water buffered at pH 9.0. Fe(VI) is known the most stable at pH 9.0 (34). 2

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Figure 1. Chemical structure of nonylphenol.

Experimental Procedures NP oxidation with Fe(VI) was performed in a 5 L Pyrex glass reactor in which buffered sample was agitated with a magnetic stirrer. Oxidation experiments were conducted with three different Fe0 " doses (i.e., 2, 5 and 10 mg/L) and at four different pHs (i.e., pH 6.0, 7.0, 8.0 and 9.0). In addition, H 0 was injected at different H 0 /Fe0 ' molar ratios (i.e., 0, 0.15 and 0.30) in order to investigate the effect of H 0 presence on the NP oxidation by Fe(VI). Rate constant for Fe(VI) decomposition was estimated using a UV/VIS spectro-photometer (at 510 nm) with a flow cell attached. Once an aqueous sample was taken for NP analysis during an oxidation study, it was immediately 2

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quenched with sodium sulfite (1.25* 10" M) to remove the residual Fe(VI). Subsequently, the sample was centrifuged to remove particle at 2,500 rpm for 30 min. In our study, the first order rate was evaluated with data collected only after the initial decomposition (ID) phase in which 50-70% NP were removed, since decomposition rates of Fe[VI] and NP were too fast to measure.


Analytical Methods for Nonylphenol For the analysis, NP was separated and concentrated in water by modifying the solid phase extraction (SPE) method proposed by Marinez et al. (35). SPE method for NP analysis is provided in Figure 3. SPE cartridge was obtained from Waters (Oasis, HLB 6 cc, 200 mg), USA). All glassware was washed by 0.1 M HC1 and distilled water and baked at 550°C for at least 4 hours before used for an experiment. The analysis of the NP was performed with a HPLC with fluorescence detection (HPLC/F) and mass spectrometry detection (HPLC/MS). The ring chromophore in NPEO molecules enables direct UV or fluorescence detection possible. The instrument used in the study was a Dionex Summit HPLC System (Dionex, USA) with an Inertsil PH column, 150 mm * 4.6 mm ID (GL Sciences Inc., Japan) at 40°C. A 50 uL sample was chromatographed at a flow rate 1 mL/min. A mobile-phase gradient was made to separate the compounds: solvent A was pure methanol and solvent B was distilled water (36). Initial conditions were 60% A; a gradient was started immediately after injection until 85% A was reached; these conditions were maintained for 25 min and then the percentage of B was gradually increased over 10 min to 40%. Finally, the column was stabilized for 15 min with 60% A; total run time was 60 min. Fluorescence detection (RF 2000, Dionex, USA) was achieved by 275 nm excitation and 300 nm emission wavelengths. Table III shows analytical condition of HPLC/MS for NP analysis.

Results and Discussion Decomposition of Ferrate Figure 3 shows the decomposition of Fe(VI) at different pHs and at different H 0 /Fe0 " molar ratios. In general, the decomposition rate of Fe(VI) strongly depended on the initial ferrate concentration, pH, and solution temperature (37). Under our experimental condition, the Fe(VI) decomposition at < pH 6.0 was too fast to determine, possibly due to instability of Fe(VI) at lower pH. Fe(VI) decomposition rate was significantly increased from 0.5xl0" to 10.7> 0.8 E

7c 0.6

o 0

1 0.4 0.2 0.0 0

60

120

180

240

300

360

420

Time (sec) 10.0 8.0 £ 6.0 u c o _ 4.0 > u. 2.0 0.0 0

60

120 180 Time (sec)

240

300

Figure 6. Time profiles offerrate and nonylphenol concentrations at different pH values. (FeO/' = 10 mg/L, NP = 1.129 mg/L, T = 21±1 °C)


399 Table V. Rate Constant and Removal Efficiency of Nonylphenol Oxidation by Ferrate at Different pHs ID (mg/L)

* (xlO'V) N

Removal

5min

(%)

pH6.0

pH7.0

pH8.0

pH9.0

7.53 3.3 86* (71)

6.46 3.5 88 (68)

3.86 4.9 90 (57)

3.34 5.0 83 (26)


: Removal efficiency at 4 min.

Effect of Hydrogen Peroxide on Nonylphenol Oxidation by Ferrate In our other study, ozone, when used together with H 0 , showed more effective NP oxidation (data not shown). However, Fe(VI) is known to rapidly react with H 0 (30). This may indicate that NP may not be effectively oxidized at all if Fe(VI) is applied with H 0 . In this section, therefore, effect of H 0 addition on the NP oxidation by Fe(VI) is evaluated. In this specific experiment, H 0 at different doses (molar H 0 /Fe0 " of 0, 0.15, and 0.3) were added into the water along with Fe(VI) of 10 mg/L (= 0.0833 mM) was applied at pH 8.0. No pH change was observed after the addition of H 0 in phosphate buffer solution. In fact, we expected H 0 addition would significantly enhance Fe(VI) decomposition. However, its decomposition rate was not significantly enhanced by the H 0 addition (Figure 7); for. all H 0 /Fe0 " ratios of 0-0.3, similar rate constant for NP oxidation was obtained (i.e., 4.7>

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