Wr

PVRa

b

cc

M

a

ARRAA

KMAFA

1

am

aot(FoottPmSp

0h

Catalysis Today 220– 222 (2014) 39– 48

Contents lists available at ScienceDirect

Catalysis Today

jou rn al hom epage: www.elsev ier .com/ locate /ca t tod

astewater treatment of methyl methacrylate (MMA) by Fenton’seagent and adsorption

erla Tatiana Almazán-Sáncheza, Ivonne Linares-Hernándezb,∗,erónica Martínez-Mirandab, Violeta Lugo-Lugoc,.M. Guadalupe Fonseca-Montes de Ocab

Facultad de Química de la Universidad Autónoma del Estado de México, Paseo Colón esq. Paseo Tollocan, S/N, C.P. 50120 Toluca, Estado de México, MexicoCentro Interamericano de Recursos del Agua (CIRA), Universidad Autónoma del Estado de México, Facultad de Ingeniería, Unidad San Cayetano, km. 14.5,arretera, Toluca-Atlacomulco, C.P. 50200 Toluca, Estado de México, MexicoUniversidad Tecnológica del Valle de Toluca, Dirección de Mecatrónica y Sistemas Productivos, Carretera del Departamento del D.F., km 7.5, Ejido de Santaaría Atarasquillo, Lerma, Estado de México, Mexico

r t i c l e i n f o

rticle history:eceived 28 March 2013eceived in revised form 3 September 2013ccepted 6 September 2013vailable online 11 October 2013

eywords:ethyl methacrylate (MMA)

crylic resins

a b s t r a c t

Oxidation-adsorption treatments were applied to improve the biodegradability of wastewater from themanufacture of acrylic resins with methyl methacrylate (MMA). MMA wastewater has an extremely com-plex composition, with a chemical oxygen demand (COD) concentration of 651.25-g O2/L, total organiccarbon (TOC) concentration of 227.86 g/L, N-NH3 concentration of 48.80 g/L, and 352,500-PtCo units. Inthis study, the effects of operating parameters that include the Fenton reagent dosage, the initial pH,and the reaction time of the treatment efficiencies of the Fenton oxidation process were observed. Theimprovement in the biodegradability was attributed to the removal of ammonium and organic pollutantsfrom the wastewater, which was confirmed using infrared spectroscopy. After this process, adsorption

entondsorption

of organic matter from wastewater was also studied; kinetic and equilibrium adsorption studies wereperformed to evaluate the effect of the contact time and pH. Pseudo-second-order kinetics representedthe experimental data well, and Langmuir and Freundlich isotherm models were tested to represent thedata. The maximum adsorption capacity obtained was qm = 1.15 g/g for TOC and 11.65 g/g for COD at opti-mum conditions. The removal efficiencies of the Fenton adsorption treatment were 96% of color, 58% of

TOC, and 60% COD.

. Introduction

Industrial and economic development has been accompanied byn increase in environmental pollution; in particular, water is theost affected resource, and water pollution generally comes from

Abbreviations: a, Elovich constant, initial-adsorption rate (mg/g min); AOPs,dvanced oxidation process; bL , constant of Langmuir isotherm related to the energyr net enthalpy of sorption (L/mg); Ce , concentration of the adsorbate in the solu-ion at equilibrium; bE , Elovich constant, the number of sites available for adsorptiong/mg); COD, chemical oxygen demand; EDS, energy-dispersive X-ray spectroscopy;TIR, Fourier transform infrared; K1, first-order rate constant (1/min); K2, second-rder rate constant (g/mg min); KF , equilibrium constant of Freundlich indicativef adsorption capacity ((mg/g)(L/g AC)1/n); MMA, methyl methacrylate; n, adsorp-ion equilibrium constant whose reciprocal is indicative of the heterogeneity ofhe surface sorbent.; N-NH3, ammonia nitrogen; PAC, powdered-activated carbon;ow, octanol–water partition; qe , adsorption capacity at equilibrium (mg/g); qm ,aximum-adsorption capacity (mg/g); qt , adsorption capacity at time t (mg/g);

EM, scanning electron microscopy; t, time (min); TOC, total organic carbon; U PtCo,latinum and cobalt units; UV, ultraviolet.∗ Corresponding author. Tel.: +52 722 296 5550.

E-mail address: ivonnelinares1978@yahoo.com.mx (I. Linares-Hernández).

920-5861/$ – see front matter © 2013 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.cattod.2013.09.006

© 2013 Elsevier B.V. All rights reserved.

the discharge of industrial, agricultural, or municipal untreatedeffluents into rivers and lakes, resulting in severe ecological dis-equilibrium.

Methyl methacrylate (MMA) is widely used in the manufac-ture of acrylic resins produced in Mexico (Fig. 1), where thisindustry generates approximately 300 tons/day of wastewater con-sisting primarily of sulfuric acid, ammonium ion, and solubleorganic compounds (acetone cyanohydrin, methyl methacrylate,methanol, acetone) [1] with a solubility of 16 g/L in water, vaporpressure of 4.2 kPa, and log Pow value (octanol–water partition)of 1.83 at 20 ◦C. In addition, MMA can be rapidly absorbed orallyor by inhalation by humans, which irritates the eyes and mucousmembranes [2]. The aquatic toxicity of MMA is clear, and therisk of bioaccumulation is limited because its low log Pow valueindicates a high mobility within an aquatic system. MMA has,in vitro, the potential for inducing mutagenic effects, particularlyclastogenicity [2,3]. MMA wastewater has an extremely complex

composition, with a chemical oxygen demand (COD) concentrationof 651.25 g/L, total organic carbon (TOC) concentration of227.86 g/L, N-NH3 concentration of 48.8 g/L, and 352,500-PtCounits that provide color to the wastewater; if this wastewater is

40 P.T. Almazán-Sánchez et al. / Catalysis Today 220– 222 (2014) 39– 48

echa

downt

aw

wnpdc[wbt

blbiFccdoprat•

as

ta

Fig. 1. General synthesis and m

ischarged into field cultures, lakes, and rivers in a region with-ut pretreatment, severe damage to the ecosystems of the regionould occur, primarily due to the toxic and dangerous nature of theonbiodegradable organic compounds contained in the effluent ofhis industry [4].

Considering the above discussion, it is necessary to implementn optimal treatment to improve the biodegradability of MMAastewater and minimize environmental and health concerns.

There are a wide variety of processes used to treatastewater containing biodegradable organic compounds and/oronbiodegradable (refractory/xenobiotics) [5], such as biologicalrocesses (aerobic, anoxic, and anaerobic) [4], which are preferredue to their low cost, environmental impact, high removal effi-iency of BOD (biochemical oxygen demand), and suspended solids6]. However, these processes do not produce satisfactory resultshen used on industrial wastewater with large amounts of non-

iodegradable organic compounds that are resistant to biologicalreatment [7,8].

Nevertheless, advanced oxidation processes (AOPs), which haveeen used for partial or complete removal of wastewater pol-

ution and for processing products into less-toxic and readilyiodegradable products [5], have shown high efficiencies in remov-

ng organic compounds [6,9]; among these processes are theenton, photo-Fenton, electro-Fenton, ozonation, electrochemi-al oxidation, photocatalysis, UV oxidation O3/UV, etc. [6,10]. Thelassical Fenton treatment is an extremely attractive option toegrade organic compounds present in wastewater due to the low-perating cost and low toxicity of the reagents [11]. The oxidationrocess involves the reaction of Fe2+ salts with H2O2 to produce theadical •OH [10], considered the second strongest oxidizing agentfter fluorine, with a standard reduction potential of 2.8 V [12]. Inhis case, Fe2+ ions act as a catalyst for the formation of the radicalOH [13]. Fenton’s reaction occurs at pH values between 2 and 4,nd the reaction products are carbon dioxide, water, and inorganic

alts [14].

Moreover, adsorption processes provide an attractive alterna-ive for wastewater treatment. The use of activated carbon as andsorbent has shown its effectiveness in removing color, inorganic

nism of methyl methacrylate.

pollutants, and dissolved organic pollutants [15,16], primarilydue to the versatility of its high surface area (1000–1300 m2/g),its structure, large pore volume, and surface-adsorption capacity[17,18].

Therefore, the objective of the present work is to evaluate theoxidation and adsorption processes of wastewater generated by themanufacture of acrylic resins from methyl methacrylate (MMA) topartially fragment the organic matter using a Fenton treatment at apH of 2 and 5.3 and subsequently, adsorb pollutants with activatedcarbon at a pH of 2 and 4.

2. Materials and methods

2.1. Wastewater sample

The wastewater sample used in this work was obtained fromprocess effluents from a Mexican chemical plant that producesacrylic sheets from methyl methacrylate. The sample was collectedin a plastic container and subsequently characterized.

2.2. Methods of analysis

2.2.1. Sample characterizationThe parameters evaluated in this work were the chemical oxy-

gen demand (COD) concentration and color determined using aHach DR 2800 spectrophotometer, total organic carbon (TOC) con-centration determined using a Total Organic Carbon analyzer (O.I. Analytical 1020A), and sulfates and ammonia-ion concentrationsdetermined using Standard Methods Procedures [19].

2.2.2. Infrared spectroscopy (FTIR)FTIR spectroscopy has been widely used to characterize organic

compounds and ammonium in wastewater. To gain a better insightinto the transformation characteristics of organic pollutants inthe Fenton and adsorption processes, FTIR spectroscopy was usedto analyze the general functional groups. The wastewater was

P.T. Almazán-Sánchez et al. / Catalysis Today 220– 222 (2014) 39– 48 41

Table 1Characterization of active carbon.

Parameter Value Unit

Iodine number 1070 (mg/g)Molasses number 400 (mg/g)Ash 23 (%)Humidity 2 (%)H2O 130 (wt%)DOPa 165 (wt%)Specific area (BET) 1703.2 m2/gPore diameter 2.7538 nmPore volume (p/p0) 1.726 cm3/gMonolayer volume (Vm) 391.33 cm3/g (STPb)

a Dispersed oil particle.b Standard temperature and pressure.

Table 2Molar concentration of Fe2+:H2O2 for different treatments.

Treatment Dosage Fe2+ (M):H2O2 (M)

Fe2+ (M) H2O2 (M)

1 0.0183 1.22 0.0183 3.43 0.0183 5.74 0.0183 85 0.0183 11.56 0.0191 13.8

as

2

STdaw1

2

atimi

2

ts

2

upewF(

Table 3Characteristics of wastewater.

Parameter Units Value

pH – 5.3TOC g/L 227.86Color PtCo units 352,500

7 0.0191 17.28 0.0191 19.59 0.0191 22.9

nalyzed by infrared spectroscopy using the Fourier Transform IRpectroscopy HART mode (IR Prestige-2).

.3. Adsorbent characterization

The adsorbent used was a commercial-activated carbon ofIGMA de México, S.A. de C.V.; the characterization is shown inable 1. The specific area and pore volume of the carbon wereetermined by the Brunauer–Emmett–Teller (BET) method using

Micrometrics equipment model Gemini 2360 after the samplesere kept at 200 ◦C for 2 h; the specific area was determined to be

700 m2/g.

.4. Scanning electron microscopy (SEM)

The samples were analyzed by SEM and X-ray microanalysis. Thenalysis was performed on a Phillips XL-30 microscope to observehe composition and configuration of the structure. SEM providesmages of rough material with a resolution down to fractions of a

icrometer, whereas energy-dispersive X-ray spectroscopy offersn situ elemental analysis.

.5. Thermodynamic analysis

The existence of ammonia and sulfates species in aqueous solu-ion was calculated using the distribution diagrams of chemicalpecies using the MEDUSA program [20].

.6. Oxidation treatment by Fenton’s reaction

Partial oxidation of organic matter and ammonium was donesing Fenton’s reagent at a pH of 2 and 5.3 (initial pH of sam-le), which was adjusted using concentrated sulfuric acid. The

ffects of operating conditions, such as the Fe2+:H2O2 molar ratio,ere evaluated according to the experiments described in Table 2.

enton’s reagent was prepared using ferrous sulfate heptahydrateFeSO4·7H2O) and hydrogen peroxide (H2O2 30%, v/v, J.T. Baker,

COD g/L 651.25N-NH3 g/L 48.80SO4

2− g/L 104.00

USA). Pre- and posttreatment aliquots were collected and analyzedusing the TOC, COD, and color parameters.

2.7. Adsorption kinetics

After the Fenton process, the effluent was treated by batchadsorption studies to obtain rate and equilibrium data; a batch cellwith an effective volume of 50 mL was used as the reactor vessel. Aknown amount of adsorbent (0.80 g of activated carbon) was addedinto the reactor vessel at room temperature with constant stirringat a pH of 2 and 4. Aliquots of the sample were collected at differenttimes and filtered for TOC and color analysis. The adsorbent mate-rial was dried and characterized before and after adsorption usingSEM and FTIR. All experiments were done in triplicate.

2.8. Adsorption Isotherms

100-mg samples of carbon adsorbent were put in contact with10 mL of a solution with different concentrations of TOC, COD, andcolor (raw sample was diluted). The mixtures were shaken for 1 hat room temperature at a pH of 2 and 4. Samples were then filteredand analyzed. Data of the kinetic and adsorption isotherms weremodeled and analyzed using the Origin 8.6 program software.

3. Results and discussion

3.1. Wastewater characteristics

Table 3 shows the characteristics of MMA wastewater used forthis work. The wastewater sample presents an acidic pH value of5.3, which contained both sulfates and ammonium ions in the solu-tion. The wastewater consisted of 54.5% organic matter; the CODconcentration was twice as high as the TOC concentration, where45.5% was inorganic matter (obtained from the difference of CODand TOC).

The physicochemical characteristics in Table 3 show high sulfateconcentrations, indicating a strong ionic character of the wastewa-ter; inorganic salts could enhance the adsorption of organic matteron an activated carbon surface [21].

3.2. Fenton treatment and dose H2O2 effect

During a Fenton process, hydrogen peroxide plays an importantrole as a source of hydroxyl radical generation. Figs. 2–4 show theeffects of the hydrogen peroxide dosage on the overall removal ofcolor, TOC, and COD, respectively. The results show a direct corre-lation between an increase in H2O2 dose and a decrease in color,TOC, and COD levels in the sample (Fe2+ and H2O2 doses are shownin Table 2).

A maximum of 94% color-removal efficiency was obtained at anFe2+:H2O2 molar ratio dosage of 0.0198 M:22.9 M (Treatment 9). Itis interesting to note that the color behavior was similar when the

pHs were 2 and 5.3.

The maximum TOC removal obtained was 73.30% at a pH of 2and 68.44% at a pH of 5.3 with an Fe2+:H2O2 molar ratio dosageof 0.0198 M:22.9 M (Treatment 9, Fig. 3). In general, the removal

42 P.T. Almazán-Sánchez et al. / Catalysi

25

35

45

55

65

75

85

95

987654321

Col

or r

emov

al (

%)

Treatments

pH 2

pH 5.3

Fig. 2. Removal percentages of color at pHs of 2 and 5.3.

25

30

35

40

45

50

55

60

65

70

75

987654321

TO

C r

emov

al (

%)

Treatments

pH2

pH 5.3

Fig. 3. Removal percentages of TOC at pHs of 2 and 5.3.

25

30

35

40

45

50

55

60

65

70

75

1 2 3 4 5 6 7 8 9

CO

D r

emov

al (

%)

Treatm ents

pH 2

pH 5.3

Fig. 4. Removal percentages of COD at pHs of 2 and 5.3.

Fig. 5. Scheme of possible decomposit

s Today 220– 222 (2014) 39– 48

efficiencies increased as the dosage increased due to the increasein hydroxyl radicals, which were produced through the decompo-sition of the increased amount of hydrogen peroxide. The increasein the TOC removal efficiency at a pH of 2 could be attributed tothe increase in the ionic strength by the pH adjustment done withsulfuric acid.

Fig. 4 shows that COD removal was almost constant since theFe2+:H2O2 molar ratio dosage was 0.0191 M:17.2 M (Treatment 7),obtaining a maximum-COD removal of 73.6% at a pH of 2 and 57.6%at a pH of 5.3. According to Ince and Tezcanh [22], 0.031 mole ofO2 (0.063 mole of H2O2) per gram of removed COD is necessary. Ifthese conditions are applied to wastewater at a 1:5 molar ratio ofFe2+:H2O2, it would take 1.237 kg of FeSO4·7H2O and 3.5 L of H2O2per liter of wastewater, which would require an excessive amountof reagents, and the production of iron-hydroxide sludge would bea disadvantage in the Fenton process.

The results show that there is a higher oxidation of organic mat-ter with more acidic pH values (pH of 2) and higher H2O2 doses;however, because the goal of the Fenton process in this work is onlythe partial oxidation of organic compounds, Treatment 3 (Table 2)was used for subsequent experiments with a removal efficiency of67% for color, 42% for COD, and 41% for TOC.

The oxidation process of organic matter by the Fenton processthrough hydroxyl radical generation can be described by Eq. (1).Eqs. (2) and (3) show the oxidation reaction, where R representsthe organic matter [23,24].

Fe2+ + H2O2 → Fe3+ + OH− + •OH (1)

R H + •OH → H2O + •R (2)

•R + H2O2 → R OH + •OH (3)

According to the molecular structure of MMA, the first attackof •OH radicals on MMA is primarily at the carbon double bonds(C C), which has an activating effect due to the electron den-sity because an •OH radical could be added to double bonds andcould cause double substitution by water presence [25]. The 2,2-dihydroxypropanoic acid and formaldehyde are expected to beformed and then oxidized to become formic and acetic acids [2].Accordingly, a possible decomposition pathway of MMA to carbondioxide and water under the oxidation processes is shown in Fig. 5.

After Fenton’s process, the pH of the wastewater was adjustedto 8 by 6 M of NaOH to precipitate Fe3+, and a temperature increaseand foam were observed. This behavior may be attributed to nitro-gen matter or ammonia ions that are oxidized at the basic pH values.Fig. 6 shows a distribution diagram, where, for a pH range of 0–5,ammonia ions remain in the solution; however, the presence ofnitrite ions were observed in a pH range of 5–6.5, and nitrate ionsare present at pH values greater than 8. Based on the above informa-tion, it is possible that ammonia ions present in wastewater could

be oxidized to nitrate ions, as described by Eq. (4) [26]. This pro-cess results in wastewater mineralization and a concentration ofnitrates above 2.5 mg/L in groundwater that can be damaging tochildren and elderly people. It is necessary to consider that this

ion of MMA under •OH radicals.

P.T. Almazán-Sánchez et al. / Catalysis Today 220– 222 (2014) 39– 48 43

Fig. 6. Distribution diagra

0

2

4

6

8

10

12

14

16

18

140120100806040200

qe (

U P

tCo/

g A

C)

X 1

000

pH 2

pH 4

ih

N

3

oaat

t (min)

Fig. 7. Adsorption kinetics of color.

ncrease in the concentrations of nitrate ions can be dangerous toealth [27,28].

H3 + 9OH− → NO3− + 6H2O + 8e− (4)

.3. Adsorption kinetics

The adsorption kinetics, as expressed in terms of the rate

f uptake of the solute, which governs the residence time, isn important consideration for economical wastewater-treatmentpplications. Figs. 7 and 8 show the relationship between con-act time and the sorption capacities of the sorbent. According to

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

140120100806040200

qt (

g T

OC

/ g A

C)

t (min)

pH 2

pH 4

Fig. 8. Adsorption kinetics of TOC.

m of ammonia ions.

the figures, the time reached for equilibrium was approximately80 min for color and 60 min for TOC. To investigate the mechanismof adsorption, the following kinetic models were applied to theexperimental sorption data. The feature constants of sorption wereobtained using a pseudo-first-order model, pseudo-second-ordermodel, and an Elovich model.

3.3.1. Pseudo-first-order model (Lagergren’s model)This model is commonly used for homogeneous sorbents and

physical sorption, where the sorption rate is proportional to thesolute concentration if the sorption behavior exhibits first-orderbehavior [29]; then, the experimental results could be adjusted toLagergren’s equation, where K1 is the sorption constant of Lager-gren (1/min), and qe and qt (mg/g) are the amounts of the adsorbedpollutants at equilibrium and at time t (min), respectively.

qt = qe(1 − eK1t) (5)

The linear form is

log(qe − qt) = log(qe) −(

K1t

2.303

)(6)

3.3.2. Pseudo-second-order modelThe pseudo-second-order model proposed by Ho and McKay

[30] is based on the assumption that the rate-limiting step maybe chemisorption, which involves valence forces via the sharing orexchange of electrons between adsorbent and adsorbate.

The pseudo-second-order equation is

qt = 1

(1/K2q2e )

+(

t

qe

)(7)

The linear form is

t

qt= 1

K2q2e

+(

1qe

)t (8)

where K2 is the pseudo-second-order rate constant for the adsorp-tion process (g/mg min), and qe and qt are the amounts adsorbed atequilibrium and at time t (mg/g), respectively.

3.3.3. Elovich modelThe Elovich equation is a rate equation also based on the adsorp-

tion capacity [31] and is given by Eq. (9), which is

q = 1ln(1 + (ab t)) (9)

t

bEE

The linear form is

qt = 1bE

ln(abE) + 1bE

ln(t) (10)

44 P.T. Almazán-Sánchez et al. / Catalysis Today 220– 222 (2014) 39– 48

Table 4Kinetics constants for pseudo-first-order, pseudo-second-order, and Elovich models for color and TOC.

Color

Pseudo first-order Pseudo second-order Elovich

qe (U PtCo/g AC) K1 (1/min) R2 qe (U PtCo/g AC) K2 (g AC/U PtCo min) R2 a (U PtCo/g AC min) b (g AC/UPtCo) R2

pH 2 14.492 0.193 0.967 15.649 0.022 0.999 227.693 0.615 0.995pH 4 12.078 0.179 0.951 13.297 0.018 0.999 106.305 0.685 0.997

TOC

Pseudo first-order Pseudo second-order Elovich

qe (g TOC/g AC) K1 (1/min) R2 qe (g TOC/g AC) K2 (g AC/g TOC min) R2 a (g TOC/g AC min) b (g AC/g TOC) R2

pH 2 1.649 0.108 0.993 1.8154 0.087 0.985 1.457 3.549 0.947pH 4 1.366 0.255 0.973 1.438 0.351 0.991 477.863 8.989 0.983

Table 5Constants of the Freundlich and Langmuir models for color, TOC and COD.

Color

Langmuir Freundlich

qm (U PtCo/g AC) b (L/U PtCo) R2 KF (UPtCo/g AC) (L/g AC)1/n 1/n R2

pH 2 12.382 0.255 0.974 3.448 0.382 0.990pH 4 30.652 0.033 0.992 1.429 0.713 0.992

TOC

Langmuir Freundlich

qm (g TOC/g AC) b (L/g TOC) R2 KF (g TOC/g AC) (L/g AC)1/n 1/n R2

pH 2 1.151 0.053 0.981 0.197 0.356 0.966pH 4 5.503 0.025 0.988 0.409 0.499 0.971

COD

Langmuir Freundlich

qm (g COD/g AC) b (L/g COD) R2 KF (g COD/g AC) (L/g AC)1/n 1/n R2

58

93

wpaa

3

vtoalws19

3

ppTatp

p

kinetics, the pseudo-second-order rate constant for a pH of 4was slightly lower than that obtained for a pH of 2 (0.022 g/UPtCo min); in contrast, for TOC, the highest rate occurred at a pHof 4 (0.351 g/g min).

0

2

4

6

8

10

12

14

16

qe (

U P

tCo/

g A

C)

pH 2

pH 4

pH 2 11.655 0.003 0.9pH 4 28.570 0.003 0.9

here a is the initial adsorption rate (mg/g min), bE (g/mg) is aarameter related to the number of sites available for adsorption,nd qt is the amount of adsorbate on the surface of the adsorbentt time t (min).

.3.4. Effect of contact timeFigs. 7 and 8 show the adsorption behavior of color and TOC

ersus contact time, after Fenton’s reaction. A rapid increase inhe percentage removal within the first 11 min of contact timeccurred and attained a maximum adsorption at 80 min for colornd 60 min for TOC, where there was no significant change in equi-ibrium concentration after this time. Based on these results, 60 min

as selected as the equilibrium time and used in the subsequenttudies. For TOC, the maximum percentage removal obtained was6.41%, whereas the maximum percentage removal for color was1.24% at a pH of 2.

.3.5. Effect of pHDue to the ionization of surface functional groups and the com-

osition of solutions, pH is an important parameter in sorptionrocedures. Figs. 7 and 8 show the adsorption kinetics of color andOC at a pH of 2 and 4 with an equilibrium time of 80 min for colornd 60 min for TOC. Based on the graphs, it is clear that the adsorp-

ion is slightly favored at more acidic pH values, obtaining higherercentages of adsorption at a pH of 2.

Table 4 shows the kinetics constants for pseudo-first-order,seudo-second-order, and Elovich models with the correlation

0.145 0.654 0.9770.248 0.709 0.989

coefficients, and to quantify the applicability of each model, cor-relation coefficients R2 were calculated. It can be seen fromTable 4 that the pseudo-second-order model fits the experimentaldata extremely well (R2 > 0.990), which indicates a chemisorptionmechanism could prevail for adsorption systems. For the color

302520151050

Ce (U PtCo/L)

Fig. 9. Adsorption isotherm of color according to the Freundlich model.

P.T. Almazán-Sánchez et al. / Catalysis Today 220– 222 (2014) 39– 48 45

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

1101009080706050403020100

q e(g

TO

C/g

AC

)

Ce (g TOC/L)

pH 2

pH 4

3

fwm

3

c

0

2

4

6

8

10

12

14

300250200150100500

qe (

g C

OD

/g A

C)

pH 2

pH 4

Fig. 10. Adsorption isotherm of TOC according to the Langmuir model.

.4. Sorption isotherms

The maximum sorption capacity of the sorbent was obtainedrom analyzing the sorption isotherms. The experimental resultsere analyzed by nonlinear Langmuir and Freundlich sorptionodels using Origin 8.6 program software.

.4.1. Langmuir modelThe Langmuir model assumes that the maximum adsorption

orresponds to a monolayer saturated with pollutant molecules on

Fig. 12. EDS and SEM of (a) activated carbon and (b)

Ce (g COD /L)

Fig. 11. Adsorption isotherm of COD according to the Freundlich model.

the sorbent homogeneous surface [32]. The Langmuir isotherm isexpressed by Eq. (11), which is

qe = qmbLCe

1 + bLCe(11)

The linear form is

Ce

qe=

(1

qmbL

)+

((1

qm

)Ce

)(12)

where qm is the amount of adsorbate adsorbed per unit weight ofadsorbent in forming a complete monolayer on the surface (mg/g),qe is the amount of adsorbate (mg/g), Ce is the concentration of

activated carbon in contact with wastewater.

4 talysis Today 220– 222 (2014) 39– 48

tc

ofttawr

3

w[

q

T

l

wbiott

Atachi

d6wwbmar

3

XpaFne

sAw

3

ciFa

Fig. 13. Infrared spectrums of (a) raw wastewater, (b) oxidized wastewater, and (c)

6 P.T. Almazán-Sánchez et al. / Ca

he adsorbate in the solution at equilibrium (mg/L), and bL is theonstant related to the energy or net enthalpy of sorption (L/mg).

Table 5 shows the parameters obtained from the applicationf this model to the experimental results; the correlation factorsor COT, COD, and color isotherms were good, and it was foundhat the sorption capacity for all parameters was significantly bet-er at a pH of 4 than those obtained at a pH of 2. The maximumdsorption capacity obtained at a pH of 4 for color, TOC, and CODere 30.65-U PTCo/g AC, 5.50-g TOC/g AC, and 28.57-g COD/g AC,

espectively.

.4.2. Freundlich modelThe Freundlich model, which has been applied to adsorbents

ith heterogeneous surfaces and considers multilayer sorption33], is given by Eqs. (13) and (14).

e = KF (C1/ne ) (13)

he linear form is

og qe = log KF +(

1n

)log Ce (14)

here qe is the amount of adsorbate per unit weight of adsor-ent (mg/g), Ce is the equilibrium concentration of the adsorbate

n the solution (mg/L), KF is the equilibrium constant indicativef the adsorption capacity ((mg/g) (L/g)1/n), and n is the adsorp-ion equilibrium constant whose reciprocal (1/n) is indicative ofhe heterogeneity of the surface sorbent.

In Table 5, isotherm parameters KF, n and qe are summarized.ccording to the correlation coefficient, the results are adjusted to

he Freundlich model, which is applied for heterogeneous surfacesnd multilayer sorption [33]. Also, for this model, the adsorptionapacity KF obtained at a pH of 4 for color, TOC, and COD was muchigher than those at a pH of 2. Figs. 9–11 show the adsorption

sotherms of color, TOC, and COD at pHs of 2 and 4.When the Fenton process was carried out in order to partially

egrade the organic matter, the removal efficiency obtained was7% of color, 41% of TOC, and 42% of COD. Batch adsorption studiesere performed after Fenton’s reaction and the removal efficiencyas obtained with 91.24% of color, just 16.41% of TOC. Separate

atch-adsorption studies were carried out (without Fenton’s treat-ent) and low removal was obtained with 20% TOC, 24% COD,

nd 94% color. Finally, the coupled treatment achieved a maximumemoval of 96% of color, 58% of TOC, and 60% of COD.

.5. SEM and EDS analysis

The scanning electron microscopy (SEM) and energy-dispersive-ray spectroscopy (EDS) indicate a porous and irregular mor-hology, surface texture, porosity, and elemental composition ofctivated carbon (AC) before and after sorption. As can be seen inig. 12(a), before the sorption process the AC presents a heteroge-eous structure with a composition consisting of C, O, Na, and Plements.

After adsorption of the Fenton’s wastewater treatment, brightpots appeared on the AC surface (Fig. 12(b)) from the presence ofl, Si, S, and Ca, due to by-products and minerals present in theastewater.

.6. Fourier transform infrared spectroscopy (FTIR) of wastewater

FTIR spectroscopy has been widely used to characterize organic

ompounds and ammonium in wastewater. To gain a better insightnto the transformation characteristics of organic pollutants in theenton and adsorption processes, FTIR spectroscopy was used tonalyze the general functional groups.

treated water by adsorption.

As can be seen in Fig. 13(a), which shows the FTIR spectrum ofthe raw MMA wastewater, there is a band at 3329.14 cm−1 cor-responding to O H stretching, and the band at 3329.14 cm−1 isattributed to the vibrations of N H bonds and is due to a primaryamide. The band at 2341.58 cm−1 is indicative of N H stretch-ing of ammonium ions. The band at 2086.98 cm−1 is attributedto C N bonds and is due to the nitrile groups. Moreover, theband at 1631.78 cm−1 is due to C O stretching vibrations and isattributed to an ester or a C C vibration due to the presence ofan alkene in the MMA wastewater. At 1442.75 cm−1, the vibrationband could be attributed to methylenes and the antisymmetricaldeformation of methyl. The 1184.29-cm−1 band is due to C-OHvibrations corresponding to a tertiary alcohol and shows a bandof out-of-plane vibrations at 1041.56 cm−1 due to the CH CH2bond.

In contrast, Fig. 13(b) shows the FTIR spectrum of the oxidizedwastewater and that only the ammonium ion oxidized; no moresignificant change was observed in the remainder of the sam-ple. These results agree with Ji et al. [3], who demonstrated thatthe oxidation of organic pollutants, such as methyl methacrylate,requires extreme-pressure conditions at 2 MPa at a temperatureof 220 ◦C.

Fig. 13 (c) presents the FTIR spectrum of wastewater treatedby AC adsorption. The band at 2993.52–2816 cm−1 is attributed tothe deformation of methyls (C-CH3). The band at 1188.15 cm−1 is

indicative of C-OH vibrations, and the band at 2086.98 cm−1 couldbe associated to the C N stretching of the nitrile group, which isextremely interesting and may indicate the presence of acetone

P.T. Almazán-Sánchez et al. / Catalysis Today 220– 222 (2014) 39– 48 47

F anic cs

cm

3

amcawoprsoime

oMawami

ig. 14. Environmental concerns of (a) ions (NO3− , SO4

2− , and HCO3−) and (b) org

oil and groundwater.

yanohydrin, a raw material required for the synthesis of methylethacrylate.

.7. Environmental concerns of MMA wastewater

Wastewater disposition is a serious problem for industriesround the world and even more so if the wastewater containsany dangerous pollutants or, worse, dangerous pollutants at large

oncentrations. Fig. 14(a) shows a diagram of the layers of soilnd the migration of ions in wastewater to groundwater if MMAastewater is discharged into farming soil. Ammonia ions may be

xidized to nitrite, and nitrate ions may be oxidized due to theresence of O2 and nitrifying bacteria. Also, sulfate ions may beeduced to sulfide ions by H+ ions present in the wastewater andulfate-reducing bacteria. We must also consider that the oxidationf organic matter is done at acidic conditions to produce CO2, which,n contact with water, becomes carbonic acid. Finally, calcium and

agnesium bicarbonates are formed; therefore, groundwater min-ralization is increased [23,34].

Fig. 14(b) shows the migration of organic compounds, severalf which are intermediaries of methyl methacrylate’s synthesis.ethanol and acetone are volatile compounds that are not easily

bsorbed by the soil. Acetone cyanohydrin has a tertiary alcohol,

hich is freely soluble in water [35]. It is not possible to oxidize,

nd also, inorganic ions may migrate to groundwater. However,ethacrylamide and methyl methacrylate can be ionized by H+

ons present in wastewater, which subsequently increases their

ompounds (methyl methacrylate, acetone cyanohydrins, and methacrylamide) on

solubility, decreases the adsorption process in soil, and facilitatestheir dangerous migration to groundwater.

4. Conclusions

Oxidation/adsorption treatments were applied successfully toimprove the biodegradability of wastewater generated by the man-ufacture of acrylic resins from methyl methacrylate (MMA).

The effects of operating parameters, which include the Fenton-reagent dosage, initial pH value, and the reaction time onthe treatment efficiencies of the Fenton-oxidation process wereobserved. Approximately 67% of color, 42% of COD, and 41% of TOCremoval efficiency were reached with an Fe2+:H2O2 molar ratio of0.0183 M:5.7 M.

The maximum adsorption capacity was obtained by the Lang-muir isotherm, where qm = 1.15 g/g of TOC and 11.65 g/g of CODat a pH of 2 at the optimum conditions, and pseudo-second-orderkinetics were found to represent the experimental data well.

The coupled treatment of Fenton adsorption achieved 96% ofcolor, 58%, of TOC and 60% of COD.

It is clear that the removal efficiencies contributed to dimin-ishing the organic and inorganic matter; however, it is necessary

to perform new studies in order to improve the quality of effluentto be discharged to soil or water bodies without causing damageto the environment, especially by subproducts and intermediarieslike cyanohydrin acetone.

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cknowledgements

The authors are thankful for the support of the Universidadutónoma del Estado de Mexico, project 3192/2012U, particularly

he Centro Interamericano de Recursos del Agua (CIRA), Laborato-io de Investigación y Desarrollo de Materiales Avanzados (LIDMA),ONACYT, SNI and PROMEP support.

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