Complete Removal of Organic Contaminants from Hypersaline ...

Article pubs.acs.org/IECR

Complete Removal of Organic Contaminants from Hypersaline Wastewater by the Integrated Process of Powdered Activated Carbon Adsorption and Thermal Fenton Oxidation Weijun Zhang, Xiaoyin Yang, and Dongsheng Wang* Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China S Supporting Information *

ABSTRACT: The feasibility of reusing hypersaline wastewater containing a high concentration of organic contaminants by a combined process of powdered activated carbon (PAC) adsorption and Fenton oxidation was investigated in this study. Operating conditions of the integrated process were optimized by jar tests. According to the results of molecular weight (MW) and full wavelength scanning analysis, most of the aromatic compounds with high MW (>1000 Da) were removed after adsorption pretreatment, but the effects of PAC adsorption on hydrophilic organic pollutants of low MW were rather limited. The adsorption followed a pseudo-second-order kinetic equation. Additionally, the strategy for maximizing the efficiency of both H2O2 and organic removal in saline wastewater was proposed. The Fenton efficiency was strongly dependent on both reaction conditions and feeding modes of reagents. Organic removal was significantly enhanced by slowing down the feeding rate of Fenton’s reagents. Moreover, rapid acidification of the wastewater was observed after adding a small amount of Fenton’s reagents, and the H2O2 dosage required for achieving a sufficient organic removal (effluent total organic carbon (TOC) < 200 mg/L) decreased by 22.2% with pH 3.0 maintained throughout oxidation process. Under the optimal oxidation conditions (reaction temperature = 80−90 °C, pH = 3, Fe2+/H2O2 molar ratio = 0.03), overall TOC removal efficiency of the integrated process was more than 95% of which 30% corresponds to the adsorption of PAC and 65% to the Fenton oxidation process. Furthermore, a pilot test indicated that the final effluent of the integrated process could conform to the standard for saline water recycle, confirming that this process provided a more economical and feasible alternative for reusing the hypersaline water contaminated with a high concentration of organic compounds.

1. INTRODUCTION Hypersaline wastewaters (salt content >20% (w/v)) from different industrial sources, such as those from epoxy resin, organochlorine pesticide, or epoxy chloropropane manufacturing are particularly problematic to treat. In most cases, these wastewaters cannot be discharged into biological treatment systems without prior dilution due to salt-induced plasmolysis of cells and/or the loss of cell functions. Generally, salt is recycled by using multiple effect evaporation (MEE) and crystallization, but this technology is considerably expensive (approximately 31.8−39.7 $/ton wastewater) due to high energy consumption. Therefore, it is very imperative to develop the alternatives to reduce the operating cost of salt recovery process. The combination of adsorption and Fenton oxidation has been successfully used for the pretreatment of highly contaminated dye wastewater containing high sulfate. 1 Activated carbon is the most commonly used adsorbent in the treatment of water, municipal wastewater, and organic industrial wastewaters containing dyes2 and landfill leachate,3 because of its ability to absorb a wide variety of organic compounds, as well as the economic feasibility of use. Organic matter of high molecular weight (MW) refractory to chemical oxidation is more easily removed by adsorption onto activated carbon (AC) from aqueous solutions, while a hydrophilic low MW organic compound is resistant to AC adsorption.4 The Fenton process is one of the most promising advanced oxidation technologies due to the advantages of high © 2013 American Chemical Society

performance and simplicity of process, low cost, and low toxicity of the reagents.5 The Fenton efficiency on organic removal is affected by feeding mode of reagents,6 reaction conditions and properties of wastewater and so on,7 especially the presence of inorganic anions (chloride ions and sulfate ions) may decrease the efficiency of the oxidation processes based on the hydroxyl radicals.8 The influence of chloride ions on the Fenton mechanism is due to complexation of Fe2+/Fe3+ with Cl− and the scavenging of hydroxyl radicals and may further generate less reactive chloride radicals than the hydroxyl radicals.8,9 The inhibition of the photo-Fenton degradation of the organic material in the presence of chloride ion was strongly dependent on reaction conditions. For instance, A. Machulek et al. abated the influence of the chloride ion on the photo-Fenton for organic removal by maintaining the pH of the medium at or slightly above 3 throughout the process, even in the presence of significant amounts chloride ions.10 However, J. Bacardit reported that the global total organic carbon (TOC) removal is not affected by the presence of chloride ions, but the process becomes much slower.11 Thus, it is possible to minimize the inhibitory effect of chloride anions on the efficiency of the Fenton process by controlling the operating Received: Revised: Accepted: Published: 5765

November 13, 2012 March 27, 2013 March 28, 2013 March 28, 2013 dx.doi.org/10.1021/ie3030888 | Ind. Eng. Chem. Res. 2013, 52, 5765−5771

Industrial & Engineering Chemistry Research

Article

filtered to remove the carbon and determine the TOC concentration remaining in solution. 2.3.2. Fenton Oxidation Procedure. The pH of wastewater after PAC adsorption was adjusted to 3 with concentrated hydrochloric acid (HCl) before the Fenton oxidation experiments. An amount of 200 mL of water was added in a 500 mL beaker. The beaker was placed in thermostatic bath (80 °C). Then, to investigate the effect of feeding rate of reagents on organic removal, both ferrous iron (0.5 mol/L) and hydrogen peroxide (30%, w/w) were added simultaneously in multiple steps at different time intervals. When the addition of reagents was finished, the reaction was stopped after 1 h stirring by raising the pH of the solution to 8−9. For analysis, cellulose acetate (CA) membranes with a pore size of 0.45 mm were used to remove the particulates present in the liquor, and then the TOC of the filtrate was determined. 2.4. Analytic Methods. A torch TOC analyzer (Teledyne Tekmar, USA) was used for TOC determination. pH was measured by pH meter (pHS-3C, Shanghai, China). Glycerin was determined according to potassium periodate oxidation followed by iodometric titration.13 High performance size exclusion chromatography (HPSEC) was used to characterize the molecular weight distribution of organic contaminants.14 MW was measured by a Waters liquid chromatography system which consisted of Waters 2487 Dual λ Absorbance Detector, Waters 1525 pump system. A Shodex KW 802.5 column (Shoko, Japan) was used for separation. The mobile phase, Milli Q water buffered with 5 mmol/L phosphate to pH 6.8, and 0.01 mol/L NaCl, was filtered through a 0.22 μm membrane, and then degassed for 30 min by means of ultrasonication before being used to the column. A sample amount of 600 μL was injected at a flow rate of 0.8 mL·min−1. Polystyrene sulfonate standards (Sigma-Aldrich, USA) of MWs 1.8−32 kDa were used for apparent molecular weight (AMW) calibration. UV254 absorbance and full wavelength scanning were measured by UV/vis spectrophotometer (U-2910, Hitachi, Japan).

conditions (reaction conditions and addition mode of reagents). The wastewater flow is approximately 450 ton/day in a bisphenol A epoxy resin manufacturer of Jiangsu province, China. The reuse of saline wastewater in a diaphragm electrolysis process is restricted due to the presence of a high concentration of organic contaminants, since the TOC tolerance limit of electrolysis equipment is 200 mg/L. To reduce the operating cost of high salinity water reuse, the feasibility and effect of combined powdered activated carbon (PAC) and Fenton oxidation on the removal of organics was investigated in this study. First, PAC adsorption was used to remove the organic matter of high MW resistant to chemical oxidation, and then complete mineralization of the residual hydrophilic organic matter with low MW was achieved by Fenton oxidation. The aims of this study were to (1) analyze composition and properties of organic contaminants in wastewater, and then propose the wastewater treatment process according to water quality; (2) investigate the effect of PAC adsorption pretreatment on organic removal and composition in wastewater; (3) maximize the efficiency of Fenton’s reagents for organic removal by controlling and regulating the operating conditions (feeding mode of reagents and reactions conditions).

2. MATERIAL AND METHODS 2.1. Materials. Hydrogen peroxide (30%, w/w) and ferrous sulfate (FeSO4·7H2O) were analytical grade reagents. Concentrated hydrochloric acid (HCl) and 1 mol/L sodium hydroxide (NaOH) were used for pH adjustment. The coal activated carbon was a gift from Shanxi Xinhua activated carbon manufacturer, and the properties of PAC were given in Table 1. Table 1. Basic Information on Activated Carbon

value

T-plot pore volume (cm3/g)

BET surface area (m2/g)

zeta potential (mV)

d50 (μm)

pore diameter (nm)

0.1027

882.31

−17.6

14.077

2.104

3. RESULTS AND DISCUSSION 3.1. PAC Adsorption Pretreatment. 3.1.1. Determination of Adsorption Time. Wastewater discharged from the resin manufacturing process had a temperature of 80−90 °C. It was reported that beyond the temperature of 90 °C, no significant improvement of mineralization was observed, although the rate of the process was considerably enhanced.15 Again, the effect of temperature on PAC adsorption of organic matter in aqueous solutions is always negligible,12 so other values of temperature were not considered in this study. The organic removal efficiency of PAC adsorption was not significantly affected by water pH (data not shown). Figure 1 showed the effect of PAC dose on TOC removal at varying contact times. Obviously, the adsorption process was rapid and TOC concentration reached equilibrium within 20 min. To get further understanding to the adsorption process, the kinetic data were analyzed with the pseudo-first-order, pseudosecond-order kinetic and intraparticle diffusion equations (see eqs 1, 2, 3 of Supporting Information). As depicted in Table 3, the fitting results of the adsorption kinetic models indicated that adsorption of organic matter from aqueous solution on PAC could be well described by the pseudo-second-order kinetic model according to R2 (0.99). The calculated value qe (196.5 mg/L) agreed very well with the experimental qe (196.1 mg/L), and the apparent rate constant (k2) was 0.0024 min−1.

2.2. Raw Water Quality. The water quality was given in Table 2. Table 2. Characteristics of raw wastewater

value

pH

TOC (mg/L)

glycerin (g/L)

salinity (%)

UV254 (cm−1)

SUVA254

12.8

2900

3.3

19.2

0.759

0.02

2.3. Experimental Procedure. 2.3.1. PAC Adsorption. 2.3.1.1. Adsorption Kinetics. Batch tests are commonly used to measure the equilibrium adsorption capacity for organic contaminant.12 An amount of 400 mL of wastewater was added to a each flask, and the flasks were placed in a thermostatic bath (80 °C) with a magnetic stirrer, then 1, 3, and 6 g/L PAC was added respectively to each flask. After the stirrer was started, duplicate samples (5 mL each) were withdrawn at appropriate time intervals for TOC analysis during the course of the adsorption (30 min overall). 2.3.1.2. Adsorption Isotherm. An amount of 100 mL of wastewater was added to each flask, and the flasks were placed in a thermostatic bath (80 °C) with a magnetic stirrer. PAC of different dosages was added to each flask. The samples were stirred for a period of 2 h. After being stirred, the samples were 5766

dx.doi.org/10.1021/ie3030888 | Ind. Eng. Chem. Res. 2013, 52, 5765−5771


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Figure 2. Effect of PAC dose on TOC removal and SUVA. Figure 1. Effect of PAC dose on TOC removal at varying contact times.

removed after treatment. Finally, the hydrophilic organics with low MW were resistant to PAC adsorption, hence subsequent chemical oxidation step was required to get a more sufficient organic removal. 3.2. Optimization of Fenton Process for Organic Removal from Wastewater with High Salinity. 3.2.1. Basic Theory and Strategy for Maximization of H2O2 Efficiency. The major operating cost for the Fenton process is the H2O2, hence maximization of H2O2 efficiency is very critical for full-scale application of this process. Basically, the Fenton system can be divided into two steps: reactions associated with production of ·OH and degradation reactions of organic matter (Figure 4). Maximization of both organic removal and H2O2 efficiency can be achieved by enhancing production of ·OH and abating the scavenging effect for ·OH. 3.2.1.1. Maximization of H2O2 Efficiency by Controlling Operating Conditions. 3.2.1.1.1. Control of Reaction Conditions. It is well-known that the efficiency of an advanced process is generally related to the amount of hydroxyl radicals produced during the treatment.18 ·OH production was mainly dependent on the ferric system, since it is the rate-limiting step in the whole Fenton process.19 The Fenton (reaction 1) and Fenton-like (reaction 2 and 3) reactions for ·OH generation are strongly dependent on water pH. Oxidative degradation of organic contaminants by Fenton reactions usually gives optimal results at a pH around 3.19 The Fe3+ catalyst begins to precipitate above pH 3 in the form of relatively inactive hydrous oxyhydroxides, while at pH values lower than 3, the inhibition of ·OH production is inhibited due to the formation of the complex [Fe(H2O)6]2+, which reacts more slowly with H2O2 than does [Fe(OH)(H2O)5]+.6,19

However, the adsorption process could not be fitted with other two models. 3.1.2. Effect of PAC Dosage on Organic Removal. As depicted in Figure 2, TOC removal was enhanced by increasing PAC dosages; 35% of TOC was removed by adding 7 g/L PAC, and no significant improvement of organic removal efficiency was observed with further increase in PAC dosages. Since specific ultraviolet absorption (SUVA) correlated well with the aromaticity and hydrophobicity of the organic carbon, the significant reduction of SUVA revealed that most of the aromatic organic matter was removed after adsorption treatment. The Freundlich and Langmuir models16 (see eqs 4 and 5 of Supporting Information) were applied for the evaluation of experimental results. As showed in Table 4, the fitting results of adsorption isotherms indicated that the adsorption data of organic contaminants onto the PAC could be fitted well with the Langmuir isotherm model but not Freundlich isotherm model. The results also demonstrated the formation of monolayer coverage of organic molecules with high MW at the outer surface of PAC. 3.1.3. Effect of PAC Adsorption on Organic Composition in Wastewater. The raw wastewater contained organic compounds of MW in the range of 100 to 100 000 Da (Figure 3a). It can be seen the high MW organic matter (>1000 Da) disappeared after PAC adsorption, but organics with low MW were not removed completely. Since the organic compound containing no conjugated double bond could not be detected by UV (254 nm), full wavelength scanning analysis was also performed to understand the effects of PAC adsorption on other organcis. Wavelength of maximum absorbance for glycerin-like compounds was found to be from 200 to 210 nm.17 A sharp decline of absorbance in this range revealed that some by-produced polyglycerols from resin synthesis were also

Fe 2 + + H 2O2 → Fe3 + + ·OH + OH−

(1)

Fe3 + + H 2O2 ↔ Fe − OOH2 + + H+

(2)

Fe − OOH2 + → HO2 · + Fe 2 +

(3)

Table 3. Fitting Results of Adsorption Process with Three Kinetic Modelsa first order results a

2nd order

intra-particle

R2

k1 (min−1)

qe (mg/g)

R2

k2 (min−1)

qe (mg/g)

calculated qe(mg/g)

R2

ki (mg/g·min−1/2)

qe (mg/g)

c

0.44

0.115

196.5

0.99

0.0024

196.5

196.1

0.65

8.15

196.5

151.87

The dosage of PAC was 6 g/L. 5767



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Table 4. Fitting Results of Isotherm Constants and Correlation Coefficients Langmuir results

Freundlich

equation

Qm (mg/g)

KL (L/mg)

R2

equation

KF

1/n

R2

Ce/Qe = 0.002Ce+ 0.0308

500

0.0065

0.95

Qe = 229.2Ce0.4572

229.2

0.4572

0.82

Fe2+/Fe3+ with Cl− (reactions 4−7), subsequently resulting in accumulation of H2O2 in the reaction medium. It was reported that increasing the temperature would lead to enhancement of the ferric system to generate radicals and more efficient consumption of H2O2.15,20 On the other hand, chloride ions can act as scavengers of hydroxyl radicals through reactions 8−10, but the capture of HO· by chloride ion was important only at pH < 2.5.8,10,21 Fe2 + + Cl− ↔ FeCl+

(4)

FeCl+ + Cl− ↔ FeCl 2 0

(5)

Fe3 + + Cl− ↔ FeCl2 +

(6)

Fe3 + + 2Cl− ↔ FeCl 2+

(7)

·OH + Cl− → ClOH·− −

−

−

Cl + ClOH· → Cl 2· + OH

(8) −

ClOH·− + H+ → Cl· + H 2O

(9) (10)

Note that the pH of reaction medium was always reduced and deviated from the optimal level because of the transformation of organic compounds (formation of organic acids) and hydrolysis of ferric ions in the Fenton process.10 Therefore, a pH of 3 should be maintained in the whole Fenton process to enhance the generation of ·OH and minimize the scavenging effect of chloride ions. 3.2.1.1.2. Feeding Modes of Reagents. Ferrous can react with H2O2 to generate ·OH. However, both of them can also act as scavengers of ·OH through reaction 11 and 12, especially in the presence of a high concentration of chloride ions. Therefore, organic removal could be enhanced by maintaining a relatively low concentration of Fenton’s reagents in the reaction medium, which can be achieved by feeding Fenton reagents in multiple steps or at a slow flow rate.6

Figure 3. Influence of PAC adsorption on organic composition of wastewater: (a) molecular weight distribution, (b) wavelength scanning spectrum.

·OH + Fe 2 + → Fe3 + + OH−

(11)

H 2O2 + ·OH → H 2O + O2 + H+

(12)

3.2.2. Experimental Optimization of Fenton Oxidation. 3.2.2.1. Effect of Feeding Rate of Reagents on Organic Removal Efficiency. Actually, the feeding mode of reagents determined the concentration of ferrous and hydrogen peroxide participating in the Fenton reaction. The TOC concentration of wastewater after treatment by PAC was 1838 mg/L. As depicted in Figure 5, the residual TOC concentration reduced from 960 mg/L to 187 mg/L by slowing down the feeding rate of H2O2 from 6.8 g/(L·min) to 0.17 g/(L·min). As mentioned above, the presence of a high concentration of chloride ions would retard the ferric system reactions and subsequently caused the accumulation of H2O2 in the reaction medium. Then, the presence of a high concentration of H2O2 intensified the thermal breakdown of H2O2 into O2 and H2O. This was revealed by the fact that a serious foaming problem caused by decomposition of H2O2 was observed if the adding rate of reagents was too fast. Therefore, the feeding rate of regents was

Figure 4. Reaction scheme for the Fenton oxidation in the presence of chloride ion at acidic pH (RH: organic matter).

Moreover, as mentioned above, the presence of chloride ions would retard the Fenton reaction through complexation of 5768



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Figure 7. Effect of hydrogen peroxide dosage on TOC removal efficiency (Fe/H2O2 (mol/mol): 0.03. Fenton’s reagents were added simultaneously in 20 feedings (at 0, 10, 20, ..., up to 200 min); TOCinitial, 1838 mg/L).

Figure 5. Influence of reagents feeding rate on organic removal (H2O2 dosage, 9% (v/v); Fe/H2O2 (mol/mol), 0.03; TOCinitial, 1838 mg/L).

a very crucial operating parameter in practice and needed to be carefully controlled. 3.2.2.2. Fe/H2O2 Molar Ratio. Figure 6 showed that minimum residual TOC concentrations of 179−197 mg/L

chloride ions could be intensified at a pH level below 2.5. To understand the effect of pH control on organic removal, oxidation experiments were conducted at an initial pH 3.0 with no pH control and with pH 3.0 maintained throughout the reaction by the addition of 0.1 mol/L NaOH solution, respectively. It was found that in comparison with the experimental group without pH control, organic removal efficiency was significantly intensified by maintaining the pH value around 3 throughout the Fenton process, and effluent TOC decreased to 198 mg/L when only 7% H2O2 (v/v) was consumed. Furthermore, since the oxidative byproducts become less and less reactive with hydroxyls in the Fenton oxidation process,19 the efficiency of H2O2 reduced with an increase in dosage of the Fenton reagents.

4. PILOT SCALE TEST The scale-up test of integrated process was carried out on the basis of optimal operating conditions obtained from lab experiments, and the flowchart of the pilot test was depicted in Figure 8. A 1 cubic meter polypropylene tank and a 5 cubic meter enamel tank with heat preservation jacket were used as adsorption and oxidation reactors, respectively. The industrial wastewater treatment in the pilot test consisted of neutralization, adsorption (7g/L PAC for 30 min), carbon separation by filter press, pH (3) adjustment, Fenton oxidation, and neutralization (pH 8−9). After treatment, chemical flocculation with polyacrylamide (PAM) was used for improving the ability to settle of sludge flocs (see Figure S1 of the Supporting Information). Furthermore, to obtain a final effluent free of suspended solids, the treated saline water was delivered for diaphragm electrolysis after the residual particulates were removed by DrM filter. The pilot test was repeated eight times to test the efficiency and stability of combined process. As depicted in figure 9, TOC concentrations of the effluent were typically less than 200 mg/L, representing more than 92% removal in most cases. Both operation of electrolysis and quality of products were not affected by treatment of the integrated process (see Supporting Information, Table S1, Table S2), confirming that it is a feasible way to reuse the hypersaline wastewater. In addition, the detailed information about the operating situation

Figure 6. Effect of molar ratio of ferrous and H2O2 on organic removal (H2O2 dose, 9% (v/v). Fenton’s reagents were added simultaneously in 18 feedings (at 0, 10, 20, ..., to 180 min), TOCinitial, 1838 mg/L).

were observed when the Fe/H2O2 molar ratio was kept in the range from 0.03 to 0.05. When the Fe/H2O2 molar ratio was less than 0.03, the mineralization of organics was inhibited. The ferric system is the rate-limiting step in the whole Fenton process,19 which was inhibited at low total iron concentration. However, the removal efficiency of TOC decreased as the initial Fe/H2O2 molar ratio was over 0.05, which was attributable to the competing reaction of ferrous ions on OH·.22 Considering both the cost of sludge disposal and catalytic effect, the value of 0.03 was applied in practical application. 3.2.2.3. pH Control in Fenton Process. As depicted in Figure 7, Fenton experiments performed at an initial pH 3 showed a rapid acidification of the reaction mixture during the initial stages of the reaction, approaching a limiting value in the pH range of 1.5−1.8, indicating the formation of the low MW organic acids. As mentioned earlier, the inhibition effect of 5769



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Figure 8. Diagram of pilot test for industrial wastewater treatment by integrated process.

Table 5. Estimated Operating Costs for the Combined Process of PAC Adsorption and Fenton Oxidation items

unit price ($/kg)

PAC* 0.722 total adsorption cost H2O2 (27.5%) 0.161 NaOH (40%) 0.128 HCl (30%) 0.064 FeSO4·7H2O 0.080 iron sludge 0.16 disposal total oxidation cost total main operating cost of integrated process total operating cost of MEE *

Figure 9. Organic removal efficiency of integrated process (T, 80−90 °C; H2O2 dose, 7% (v/v); feeding rate of H2O2, 3L/min; Fe/H2O2 (mol/mol), 0.03).

consumed (kg/ ton)

operating costs ($/ton)

7

5.504 5.50

70 5 30 3.5 2.8

11.27 0.64 1.92 0.28 0.448 14.56 20.06 31.8−39.7

Regeneration of activated carbon was not considered.

of diaphragm electrolysis, quality of products, and sludge dewatering equipment was also given in Supporting Information.

cofuel in the boiler-furnace. The sludge produced from wastewater treatment in the resin industry should be disposed of as hazardous solid waste (160.5 $/ton). This solution represents a considerable improvement with respect to MEE for reusing saline wastewater.

5. ECONOMICAL ANALYSIS Table 5 summarized the estimated main operating costs (chemicals, energy, and sludge disposal) for the treatment of the saline wastewater upon PAC pretreatment followed by high-temperature Fenton oxidation. The estimates were given in the most common approach of per unit volume of wastewater. The coal-based activated carbon used in the pilot test was purchased from Shanxi Xinhua activated carbon Co., Ltd. in China. The industrial grade H2O2 (27.5%), NaOH (40%), HCl (30%), and FeSO4·7H2O were produced by the chemical factory itself (Jiangsu Yangnong Chemical Group Co., Ltd.). Owing to its heating value, the spent PAC can be used as

6. CONCLUSION In this study, the integrated process of PAC adsorption and Fenton oxidation was proposed to minimizing the organic content in saline wastewater, and the optimization of operating conditions was performed. Finally, some conclusions could be drawn as follow: (i) A total of 35% of TOC was removed when the dosage of PAC was 7 g/L, and a further increase of PAC dosages did not result in significant enhancement of organic removal. Most of the complex aromatic compounds were removed after adsorption treatment. The adsorption process could be fitted well with the pseudo-second-order kinetic equation. 5770



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(9) Kiwi, J.; Lopez, A.; Nadtochenko, V. Mechanism and Kinetics of the OH-Radical Intervention during Fenton Oxidation in the Presence of a Significant Amount of Radical Scavenger (Cl−). Environ. Sci. Technol. 2000, 34, 2162. (10) Machulek, A.; Moraes, J. E. F.; Vautier-Giongo, C.; Silverio, C. A.; Friedrich, L. C.; Nascimento, C. A. O.; Gonzalez, M. C.; Quina, F. H. Abatement of the Inhibitory Effect of Chloride Anions on the Photo-Fenton Process. Environ. Sci. Technol. 2007, 41, 8459. (11) Bacardit, J.; Stotzner, J.; Chamarro, E.; Esplugas, S. Effect of Salinity on the Photo-Fenton Process. Ind. Eng. Chem. Res. 2007, 46, 7615. (12) Wang, L. K.; Hung, Y. T.; Shammas, N. K. Advanced Physicochemical Treatment Processes; Humana Press Inc.: NJ, 2006. (13) Pohle, W. D.; Mehlenbacher, V. C. A Modification of the Periodic Acid Method for the Determination of Monoglycerides and Free Glycerol in Fats and Oils. J. Am. Oil. Chem. Soc. 1950, 27, 54. (14) Wang, D. S.; Xing, L. N.; Xie, J. K.; Chow, C. W. K.; Xu, Z. Z.; Zhao, Y. M.; Drikas, M. Application of Advanced Characterization Techniques To Assess DOM Treatability of Micro-polluted and Unpolluted Drinking Source Waters in China. Chemosphere 2010, 81, 39. (15) Zazo, J. A.; Pliego, G.; Blasco, S.; Casas, J. A.; Rodriguez, J. J. Intensification of the Fenton Process by Increasing the Temperature. Ind. Eng. Chem. Res. 2011, 50, 866. (16) Halim, A. A.; Aziz, H. A.; Johari, M. A. M.; Ariffin, K. S. Comparison Study of Ammonia and COD Adsorption on Zeolite, Activated Carbon and Composite Materials in Landfill Leachate Treatment. Desalination 2010, 262, 31. (17) Xu, H.; Zhu, T.; Yu, R. Study on the Absorption and Fluorescence Spectra of Ethylene Glycol and Glycerol. Spectrosc. Spectral Anal. 2007, 27, 1381 (In Chinese). (18) Ahmed, B.; Limem, E.; Abdel-Wahab, A.; Nasr, B. Photo-Fenton Treatment of Actual Agro-industrial Wastewaters. Ind. Eng. Chem. Res. 2011, 50, 6673. (19) Pignatello, J. J.; Oliveros, E.; MacKay, A. Advanced Oxidation Processes for Organic Contaminant Destruction Based on the Fenton Reaction and Related Chemistry. Crit. Rev. Environ. Sci. Technol. 2006, 36, 1. (20) Pliego, G.; Zazo, J. A.; Blasco, S.; Casas, J. A.; Rodriguez, J. J. Treatment of Highly Polluted Hazardous Industrial Wastewaters by Combined Coagulation-Adsorption and High-Temperature Fenton Oxidation. Ind. Eng. Chem. Res. 2012, 51, 2888. (21) Grebel, J. E.; Pignatello, J. J.; Mitch, W. A. Effect of Halide Ions and Carbonates on Organic Contaminant Degradation by Hydroxyl Radical-Based Advanced Oxidation Processes in Saline Waters. Environ. Sci. Technol. 2010, 44, 68228. (22) Neyens, E.; Baeyens, J. A Review of Classic Fenton’s Peroxidation as an Advanced Oxidation Technique. J. Hazard. Mater. 2003, 98, 33.

(ii) The MW of organic compounds in wastewater ranged from 100 to 100000 Da. The large molecular organic matter (>1000 Da) disappeared after adsorption treatment, while the residual compounds which were mainly composed by hydrophilic organics of low MW were resistant to PAC adsorption. (iii) The residual organic pollutants were almost completely mineralized by the Fenton oxidation, but the reaction conditions and feeding modes of reagents needed to be carefully controlled to get a satisfactory result. Under the optimal operating conditions (T = 80−90 °C, pH = 3, Fe/ H2O2 molar ratio = 0.03, feeding rate of H2O2 = 0.17 g·L−1·min−1), the effluent TOC reduced to below 200 mg/L when 7% hydrogen peroxide (v/v) was dosed. (iv) The pilot test indicated that both operation of electrolysis equipment and product quality were not influenced by treatment of the integrated process, confirming that this combined process was a feasible and economical way to reuse the hypersaline wastewater.

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ASSOCIATED CONTENT

S Supporting Information *

Additional models, tables, and figures as described in the text. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*Tel.: (86)-10-62849138. Fax: (86)-10-62849138. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This study was financially supported by the Special Coconstruction Project of Beijing Municipal Commission of Education.

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REFERENCES

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