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Original Article
10 (
2_suppl
); S1674-S1679
doi:
10.1016/j.arabjc.2013.06.012

Removal of organic pollutants from industrial wastewater by applying photo-Fenton oxidation technology

, ,
a Chemical Engineering Department, Faculty of Engineering, Jazan University, Saudi Arabia
b Faculty of Engineering, King Abdul-Aziz University, Jedddah, Saudi Arabia

⁎Corresponding author. Tel.: +966 542552349. ebr_esmail_2004@yahoo.com (Ebrahiem E. Ebrahiem)

Received: , Accepted: ,
© The Author(s) 2013
Disclaimer:
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.

Peer review under responsibility of King Saud University.

Abstract

The general strategy of this study was based on evaluation of the possibility of applying advanced photo-oxidation technique (Fenton oxidation process) for removal of the residuals organic pollutants present in cosmetic wastewater. The different parameters that affect the chemical oxidation process for dyes in their aqueous solutions were studied by using Fenton’s reaction. These parameters are pH, hydrogen peroxide (H2O2) dose, ferrous sulfate (FeSO4·7H2O) dose, Initial dye concentration, and time. The optimum conditions were found to be: pH 3, the dose of 1 ml/l H2O2 and 0.75 g/l for Fe(II) and Fe(III) and reaction time 40 min. Finally, chemical oxygen demands (COD), before and after oxidation process was measured to ensure the entire destruction of organic dyes during their removal from wastewater. The experimental results show that Fenton’s oxidation process successfully achieved very good removal efficiency over 95%.

Keywords

Fenton
Advanced oxidation
Wastewater treatment and chemical oxygen demand (COD)
1

1 Introduction

Advances in technology have resulted in greater water demands for industry. The volume of wastewater from the industries has increased, and needs treatment. This wastewater contains a variety of suspended solids, oils, metals, and organics. The successful cleaning of these new wastewaters prior to discharge, using existing treatments, has yet to be improved comparatively. Advanced oxidation processes (AOPs) generally means application of either advanced oxidation technologies using UV/O3, O3/H2O2, UV/H2O2 or the photo Fenton reaction (UV/H2O2/Fe2+ or Fe3+). Peyton gave a detailed overview and description of AOPs (Jian, 1997; Glaze et al., 1987; Gomez, 1993). The Fenton’s reagent was discovered by Fenton in 1894, (Fenton, 1894). Fenton’s reagent is a mixture of H2O2 and ferrous iron, which generates hydroxyl radicals. The ferrous iron (Fe++) initiates and catalyzes the decomposition of H2O2, resulting in the generation of hydroxyl radicals. The generation of these radicals involves a complex reaction sequence in an aqueous solution (Pingatello, 1992). H2O2 can act as an OH scavenger as well as an initiator (Venkatadri and Peters, 1993). Generally Fenton’s oxidation process is pH adjustment, oxidation reaction, neutralization and coagulation for precipitation. So, the organic substances are removed at two stages of the oxidation and the coagulation (Kange and Hwang, 2000). A continuous photo-Fenton process for the degradation of gaseous dichloromethalane (DCM) can be used Feitz et al., 2002. Solar photocatalytic degradation of the azo dye acid orange 24 by means of a photo-Fenton reaction promoted by solar energy was used (Juan et al., 2006). The degradation of different commercial reactive dyes by using solar light assisted Fenton and photo-Fenton reaction was investigated (Francesc et al., 2004). Photocatalytic organic content reduction of two selected synthetic wastewaters from the textile dyeing industry was studied by the use of heterogeneous and homogeneous photocatalytic methods under solar irradiation, at a pilot plant scale at the Plata forma Solar de Almeria (Kositzi et al., 2004). The scavenging effect of phosphate and bicarbonate anions on the degradation of organic pollutants by means of the Fenton process may be somewhat reduced by the necessity of the application of this technique at moderately low pH (Nogueria et al., 2005). Photo-Fenton processes could be applied in treating many industrial wastewaters, i.e. wastewater from plastic industry, landfill leachate, dye house industry (Bauer and Fallmann, 1997; Feng et al., 2003; Lin and Lo, 1997; Keiichi et al., 2000), quinoline (aromatic compound) Sundstorm et al., 1989; Malato et al., 2000; Faust and Hoigne, 1990 pesticides (Chiron et al., 2000; Mujeebur et al., 2000; Fallmann et al., 1999; Safarzadeh-Amiri et al., 1996; Eisenhauer, 1994), organic compounds and phenolic wastes (Zahng et al., 1980; Ilisz and Dombi, 1999; Rashed et al., 2004), trichloroethylene trihalomethanes (Amy et al., 2001), and wastewater from paper industry. The use of Fenton reaction in the decomposition of phenol and formaldehyde (Rashed et al., 2004), from their aqueous solutions and from industrial wastewater containing them was studied which achieved a very good efficiency of removal over 90%. The removal of color and COD from a mixture of four reactive azo dyes using Fenton oxidation process was investigated which achieved a high efficiency more than 90% (Sureyya et al., 2003). The color and COD removal from textile effluent by coagulation and advanced oxidation processes was studied. FeSO4 and FeCl3 were used as coagulants at varying doses (Solmaz et al., 2006). Wastewater from the Afyon Alkaloids factory was subjected to low-pressure catalytic wet-air oxidation using Fenton’s reagent, and the optimal reaction conditions were investigated (Bıçaksız et al., 2008). The treatment of wastewater coming from painting processes by application of conventional and advanced oxidation technologies was discovered (Consejo et al., 2005), The reduction of organic pollutants in landfill leachate and the effecting factors on the degradation of methyl tert-butyl ether, with Fenton’s Reagent was reported (Ma and Zhou, 2009).

In the present study, we are interested in studying the possibility of application of Fenton oxidation process, as an advanced chemical technology technique, for removal of residual colors of dyes from wastewater of an artificial dying bath, as a preliminary treatment prior to biological oxidation.

2

2 Materials and methods

2.1

2.1 Wastewater characterization

Wastewater of an Egyptian Cosmetic factory, 6th October Governorate, has been used in this study. This factory has many production lines, such as lip moisturizer, compact powder, creamy powder, hand gel, dettol and foundation cream. In our investigation, the effluent from the line of the production of foundation cream sector is taken as a case of study This wastewater contain silicons, tri-ethanol amin, glycerol mono stearate, Di-sodium EDTA, methyl paraben, probyl paraben, and some dyes, such as yellow iron oxide and red iron oxide. This wastewater is characterized with a high organic load and a low biodegradability index (BOD5/COD) which means that this wastewater is difficult to be degraded by the traditional treatment such as the biological treatment. This wastewater has a turbid color and oily touch. A representative analysis of the wastewater as received in the laboratory is given in Table 1.

Table 1 Characterization of wastewater compared with Egyptian limit values.
Analyzer parameter Average value Limit valuea
Oils and fats (mg/l) 75 100
Conductivity (μS/cm) 4000 5000
BOD5 (mg/l) 1986 1000
COD (mg/l) 6968 1100
Biodegradability (BOD5/COD) 0.28 –
pH 5.5–6 6–9
TSS (mg/l) 38 1000
a Emission limit value for Egyptian industrial wastewater discharges into the municipal sewer system according to the Law 4/year 94 and its follows modification for 2009.

2.2

2.2 Materials

For Fenton and photo Fenton processes, the materials used in this study are: Ferrous sulfate heptahydrate (FeSO4·7H2O) and ferric chloride (FeCl3) used as sources of Fe(II) and Fe(III), were all analytical grade from Merck company for chemicals, Hydrogen peroxide solution (30% w/w) in stable form was provided also from Merck. Distilled water was used throughout. Sulfuric acid 98% purity, 1.84 g/cm3, sodium chloride, sodium hydroxide 99% from Merk company .

2.3

2.3 Methods

All experiments concerning the application of the ultraviolet radiation were performed in a batch reactor. The schematic diagram of the experimental set-up used for these processes is shown in Fig. 1. The reactor was cylindrical filled with 0.85 l volume of wastewater and was made from quartz glass which was available for the transfer of the radiation. Irradiation was achieved by using UV lamp (high pressure mercury lamp TQ 150 W, radiation flux used for only degradation of 221 W/h of 200:600 nm, from Heraeus Noblelight Company in Germany) which was immersed in the glass tube. The UV lamp was equipped with a cooling water jacket system which was placed in the reactor vessel. The reaction chamber was filled with the reaction mixture, which was placed between the reactor walls and UV lamp system. For the experiments concerning the application of Fenton reactions the runs were done in dark by using a simple magnetic stirrer without providing the UV lamp.

Set up of photo-Fenton and photo Fenton like experiments. A-Ultraviolet medium pressure mercury lamp, B-UV lamp housing, C-Cooling water in, D-Cooling water out, E-Cooling water chamber, F-Hot plate with magnetic stirrer.
Figure 1 Set up of photo-Fenton and photo Fenton like experiments. A-Ultraviolet medium pressure mercury lamp, B-UV lamp housing, C-Cooling water in, D-Cooling water out, E-Cooling water chamber, F-Hot plate with magnetic stirrer.

For the advanced oxidation processes, the laboratory unit was filled separately with 0.85 l of the wastewater. The desired pH value was adjusted with sulfuric acid before start-up, and then a given weight of iron salt was added. The iron salt was mixed very well with the wastewater before the addition of a given volume of hydrogen peroxide. For the dark processes (Fenton reaction), the reaction time starts when the solution is injected by hydrogen peroxide. For photo-Fenton the time at which the UV lamp was turned on was considered the zero time, or the beginning of the experiment that was taking place simultaneously with injection of hydrogen peroxide and adding the dose of iron salt. The amount of reagent FeSO4·7H2O or FeCl3 and H2O2 designed for the experiment was added and homogenized by the magnetic stirrer.

As reported in the literature (Pignatello, 1992), Fenton and photo-Fenton reactions cannot proceed at pH > 10. Therefore, the reaction was arrested instantly by adding NaOH to the reaction samples before COD analysis. Chemical oxygen demand (COD) was determined via a HACH-2000 spectrophotometer using a dichromate solution as the oxidant in strong acid media (Kolthof et al., 1969). The solution after treatment was decanted into a settling beaker, then filtered to separate the sludge precipitated. A sample was diluted 30 times by addition of distilled water, 2.5 ml of sample was taken into a glass test tube (HACH, company for sales instruments), then two reagents of potassium dichromate (1.5 ml) and sulfuric acid (3.5 ml) were added, the sample was digested into COD reactor (HACH, USA) for 2 h at 150 °C, Then, it was cooled for 30 min and measured by COD meter to detect the removal efficiency of organic materials, (Badawy, 2006).

3

3 Results and discussion

The formation of the hydroxyl radicals by using the photo-Fenton and photo-Fenton processes under application of Fe(II) or Fe(III) occurs according to the following reaction.

(1)
Fe 2 + + H 2 O 2 → Fe 3 + + OH - + OH • Reaction (1), already known as the Fenton reaction, possesses a high oxidation potential, but its revival in the application to wastewater treatment began only recently. UV irradiation leads not only to the formation of additional hydroxyl radicals but also to a recycling of the ferrous catalyst by reduction of Fe(III). Illumination of the system by UV was suggested to overcome the limitations of the Fenton system. The photoreduction of various ferric species contributes to the production of ferrous ions and radical species. For the development of effective wastewater treatment methods, complete degradation of the contaminants to harmless end products (CO2) and mineral salts is important. By this the concentration of Fe(II) increases and therefore the reaction is accelerated. The reaction time needed for the photo-Fenton reaction is extremely low and depends on the operating pH value and the concentrations of H2O2 and iron added.

3.1

3.1 Effect of irradiation time

The photo-treatment time must be as short as possible to avoid a high electricity consumption, which represents about 60% of the total operational cost when using electric light sources. However, if the fixed pretreatment time is too short, the intermediates remaining in solution could still be structurally similar to initial biorecalcitrant compounds and therefore, nonbiodegradable. Furthermore, at short phototreatment times, the residual H2O2 concentration may be high enough to inhibit the biological stage of the coupled reactor. This oxidant is not required for all the photochemical processes but, whenever utilized it has to be eliminated before the biological stage if it will be applied after the photochemical oxidation step. Figs. 2 and 3 indicate that the optimum irradiation time was 40 min for both photo Fenton and photo Fenton-like systems at pH equals 3, initial amount of hydrogen peroxide equals 1 ml/l and initial amounts of Fe(II) and Fe(III) equal 0.75 g/l for the both photo Fenton and photo Fenton-like systems.

Effect of irradiation time on the treatment of the wastewater. [pH = 3, Fe(II) = 0.75 g/l, H2O2 = 1 ml/l].
Figure 2 Effect of irradiation time on the treatment of the wastewater. [pH = 3, Fe(II) = 0.75 g/l, H2O2 = 1 ml/l].
Effect of irradiation time on the treatment of the wastewater. [pH = 3, Fe(III) = 0.75 g/l, H2O2 = 1 ml/l].
Figure 3 Effect of irradiation time on the treatment of the wastewater. [pH = 3, Fe(III) = 0.75 g/l, H2O2 = 1 ml/l].

3.2

3.2 The effect of the pH value

The pH value has a decisive effect on the oxidation potential of OH• radicals because of the reciprocal relation of the oxidation potential to the pH value. Furthermore, the concentration of inorganic carbon and the hydrolytic speciation of Fe(III) species are strongly affected by the pH value. Therefore, the role of pH in the photo-assisted Fenton reaction must be determined. The same as in Fenton and Fenton-like reactions, the photo-Fenton and photo Fenton-like systems have a maximum catalytic activity at pH of about 2.8–3. The pH value influences the generation of OH• radicals and thus the oxidation efficiency. For pH values above 6 the degradation strongly decreases since iron precipitates as hydroxide derivate, reducing the Fe(II) availability and the radiation transmission. Another reason for the inefficient removal at pH > 3 is due to the dissociation and auto-decomposition of H2O2.

Fig. 4 shows the effect of the pH value during the use of the photo-Fenton and photo Fenton-like process. A maximum COD removal of 95.5 and 91.4% was obtained with the systems UV/H2O2/Fe(II) and UV/H2O2/Fe(III) respectively at a pH = 3 and within irradiation time of 40 min. For pH value of 6 the COD removals strongly decrease to 75.2 and 69.7% for both photo Fenton and photo Fenton–like processes respectively, because at higher pH values iron precipitates as hydroxide and that reduces the transmission of the radiation.

Effect of pH values on the treatment of the wastewater. [H2O2 = 1 ml/l, Fe(II) = 0.75 g/l].
Figure 4 Effect of pH values on the treatment of the wastewater. [H2O2 = 1 ml/l, Fe(II) = 0.75 g/l].

3.3

3.3 The effect of initial hydrogen peroxide concentration

To elucidate the role of H2O2 concentration on the photo-catalytic degradation of cosmetic wastewater taken in this investigation in the photo Fenton and photo Fenton-like systems, some experiments were carried out by varying the initial H2O2 concentrations at constant initial pH (3), initial Fe(II) and Fe(III) of 0.75 g/l for the photo Fenton and photo Fenton-like and within irradiation time of 40 min. As shown in Fig. 5, the degradation efficiency represented by % COD removals is demonstrated when H2O2 concentration increases from 0 to 3 ml/L which is explained by the effect of the additionally produced OH• radicals. However, above this H2O2 concentration, the reaction rate levels off and sometimes is negatively affected, by the progressive increase of the hydrogen peroxide. This may be due to auto decomposition of H2O2 to oxygen and water and recombination of OH• radicals (Reactions (2) and (3)).

(2)
2 H 2 O 2 → H 2 O + O 2
(3)
OH • + 2 H 2 O 2 → HO 2 • + H 2 O Excess of H2O2 will react with OH• competing with organic pollutants and consequently reducing the efficiency of the treatment, the H2O2 itself contributes to the OH• radical scavenging capacity. Nevertheless, a higher dose of H2O2 means a higher production of hydroxyl radicals and this dose increases because the higher the H2O2 concentration the more favored the occurrence of auto-scavenging reactions. Therefore, H2O2 should be added at an optimal concentration to achieve the best degradation.
Effect of initial amount of H2O2 on the treatment of the wastewater. [pH = 3, Fe(II) = 0.75 g/l].
Figure 5 Effect of initial amount of H2O2 on the treatment of the wastewater. [pH = 3, Fe(II) = 0.75 g/l].

Since there is a very slight increase of % COD removals at initial amounts of hydrogen peroxide of 1 and 3 ml/L, the dose of 1 ml/L H2O2 considers the optimum dose from the economic point of view. It is found that, the optimal H2O2 concentration is 1 ml/L for the treatment of the wastewater under study with 95.5 and 91.4% COD removals for photo Fenton and photo Fenton-like processes respectively after 40 min irradiation time.

3.4

3.4 The effect of initial amount of Fe ion

Iron in its ferrous and ferric form acts as photo-catalyst and requires a working pH below 4. To obtain the optimal Fe(II) or Fe(III) amounts, the investigation was carried out with various amounts of the iron salt at different constant initial amounts of hydrogen peroxide. Figs. 6–8 show the percent removal of COD as a function of irradiation time at different amounts of the added Fe(II) and Fe(III). The figure shows that the addition of either Fe(II) or Fe(III) at the all constant initial amounts of H2O2 enhanced the efficiency of UV/H2O2 for COD degradation. The degradation rate of organic pollutants distinctly increased with increasing amounts of iron salt till a limit value of either Fe(II) or Fe(III). A higher addition of iron salt resulted in brown turbidity that hindered the absorption of the UV light required for photolysis and caused the recombination of OH radicals. In this case, Fe2+ reacted with OH radicals as a scavenger.

Effect of initial amount of Fe(II) on the treatment of the wastewater [H2O2 = 1 ml/l, pH = 3].
Figure 6 Effect of initial amount of Fe(II) on the treatment of the wastewater [H2O2 = 1 ml/l, pH = 3].
Effect of initial amount of Fe(II) on the treatment of the wastewater [H2O2 = 3 ml/l, pH = 3].
Figure 7 Effect of initial amount of Fe(II) on the treatment of the wastewater [H2O2 = 3 ml/l, pH = 3].
Effect of initial amount of Fe(II) on the treatment of the wastewater [H2O2 = 1 ml/l, pH = 3].
Figure 8 Effect of initial amount of Fe(II) on the treatment of the wastewater [H2O2 = 1 ml/l, pH = 3].

By increasing either Fe(II) or Fe(III) dose up to 0.75 g/l, the COD removals decrease at the adjustable conditions. It is desirable that the ratio of H2O2 to Fe(II) or Fe(III) should be as small as possible, so that the recombination of OH radicals can be avoided and the sludge production from iron complex is also reduced.

4

4 Conclusion

The following conclusions might be drawn as a result of application of an photo-Fenton reaction which indicate that

  • The optimum irradiation time was 40 min. at pH 3, the dose of 1 ml/l H2O2 and 0.75 g/l for Fe(II) and Fe(III).

  • Under these conditions, 95.5% COD removal was obtained.

  • Finally, it is highly recommended to apply the used technique (Fenton’s oxidation process) as treatment of wastewater containing organic compound.

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