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DAF-Treated Lube Oil Wastewater (DTLOWW) Treatment: Performance of Bench Scale and Pilot Scale Fenton Process | OMICS International
ISSN: 2165-784X
Journal of Civil & Environmental Engineering
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DAF-Treated Lube Oil Wastewater (DTLOWW) Treatment: Performance of Bench Scale and Pilot Scale Fenton Process

Elmolla ES*
Department of Civil Engineering, Faculty of Engineering, Al-Azhar University, Cairo, Egypt
Corresponding Author : Elmolla ES
Department of Civil Engineering, Faculty of Engineering
Al-Azhar University, Cairo, Egypt
Tel: +20 1113301981
E-mail: [email protected]
Received February 14, 2015; Accepted March 20, 2015; Published April 02, 2015
Citation: Elmolla ES (2015) DAF-Treated Lube Oil Wastewater (DTLOWW) Treatment: Performance of Bench Scale and Pilot Scale Fenton Process . J Civil Environ Eng 5:169. doi:10.4172/2165-784X.1000169
Copyright: © 2015 Elmolla ES. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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Abstract

The lube oil wastewater is produced from Lube Oil Bending Facilities (LOBF) located in Egypt. Currently the lube oil wastewater is treated by oil separator followed by Dissolved Air Flotation (DAF) system. Unfortunately, DAFTreated Lube Oil Wastewater (DTLOWW) contains high concentration of the soluble COD. The first part of this work examined the treatability of DAF-Treated Lube Oil Wastewater (DTLOWW) using bench-scale Fenton process. Effects of H2O2, Fe2+ doses at different reaction time and wastewater strength have been studied. Optimum H2O2 dose was 0.8 g/l for normal DTLOWW strength (sCOD<2000 mg/l) and 1.2 g/l for high DTLOWW strength (sCOD>2000 mg/l). Optimum H2O2/FeSO4 ratio of 3 was achieved for the normal and high strength DTLOWW at pH 3.5. The Second part of this work studied the performance of Pilot-scale Fenton process. Pilot scale Fenton reactor was installed in the field and conducted under the optimum H2O2/FeSO4 ratio that achieved from the bench scale work. The reactor was operating in batch basis at 8 hour cycle period divided in six phases. The results showed that residual sCOD was 788 ± 56 mg/l with sCOD removal of 53.6% which amply met with the local discharge Standards for discharging the industrial wastewater to the municipal sewage network. The Fenton process could be used for treatment of the DTLOWW with daily chemicals cost of 1.25-1.50 $/m3.

Keywords
Bench scale Fenton process; DAF-treated lube oil wastewater; DTLOWW; Pilot scale Fenton process
Introduction
Oily wastewaters is generated during production process of the Petrochemical industries [1,2]. Problems that may be created by the presence of oily wastewater in the Environment are endangering aquatic resources; endangering human health; atmospheric pollution, affecting crop production, destructing the natural landscape [1]. Therefore oily wastewater treatment is an interested area of research.
Different technologies have been reported in the literature for oily wastewater treatment. Some of these technologies are based on separation process such as Flotation [3,4], membrane with different types and materials [5,6]. Other technologies are based on oil degradation either by biological process [7,8], or by chemical oxidation processes [9-12].
Advanced Oxidation Processes (AOPs) have been reported as an emerged technologies in industrial wastewater treatment [13]. Oxidation with Fenton’s reagent is based on hydrogen peroxide, ferrous ion and hydroxyl radicals generated by the catalytic decomposition of hydrogen peroxide in acidic solution [14]. Fenton’s reagent has been reported to be effective in the treatment of refractory industrial wastewaters − 60% COD removal was achieved for oily wastewater [1].
In our previous work, application of AOPs in degradation of antibiotics in aqueous solution using Fenton [15], photo-Fenton [16], TiO2 photocatalysis [17], ZnO photocatalysis [18] were studied. In addition, technical and economic comparisons among different AOPs as well as simulation of Fenton process for treatment of an antibiotic aqueous solution were made [19,20]. However, limited number of pilot Fenton process has been reported; BarbusiƄski applied the Pilot Fenton scale in textile wastewater treatment [21].
The first part of this study examined the treatability of the DTLOWW using bench scale Fenton process. Effects of H2O2, Fe2+ doses at different reaction time and wastewater strength have been studied. In the Second part of this study, performance of pilot Fenton scale under specific operating conditions was studied.
Materials and Methods
Chemicals
Hydrogen peroxide (50% w/w) and ferrous sulphate (FeSO4·7H2O) were purchased from local supplier.
DAF-Treated Lube Oil Wastewater (DTLOWW)
The lube oil wastewater is produced from a local Lube Oil Bending Facilities (LOBF). Currently the wastewater is treated by CPI oil separator followed by Dissolved Air Flotation (DAF) system. Unfortunately, DAF-Treated Lube Oil Wastewater (DTLOWW) contains high concentration of the soluble COD.
For the purpose of treatability study, two composite samples at different days have been collected from the DAF outlet. The sample collection started from 11 am to 5 pm which covered the working day of the lube oil bending facilities. The sampling bottle of 2 l was filled every one hour throughout the working day. The collected sampling bottles were mixed together in a big container and kept in icebox. Thereafter, big container was sent to the National Research Center laboratory for analysis. The wastewater sample has been kept at 4°C throughout the treatability study period. The DTLOWW wastewater characteristics are summarized in Table 1.
Analytical methods
Physico-chemical analysis of the samples and the treated effluent were carried out. The wastewater samples were analyzed for pH, soluble Chemical Oxygen Demand (sCOD), Biological Oxygen Demand (BOD), Total Suspended Solids (TSS), Total Phosphate (T.P), unless otherwise specified, were conducted according to the Standard Methods for water and wastewater [22].
Experimental setup and procedure
The experimental setup and procedures of Bench scale Fenton process and on-site pilot scale Fenton process are detailed as the followings sub-sections.
Stage 1: Lab scale Fenton process: Batch bench scale Fenton process experiments were conducted in a 600 ml Pyrex reactor with 500 ml of the DTLOWW. The pH of the solution was adjusted to the required value using H2SO4. The required amount of iron in the form of FeSO4.7H2O was added to the DTLOWW and mixed by a magnetic stirrer. Thereafter, necessary amount of hydrogen peroxide was added gradually to the mixture and the time of the hydrogen peroxide addition was considered the beginning of the experiment. Samples were taken at pre-selected time intervals for studying the effect of reaction time. Thereafter, pH of the withdrawn samples was raised above 9 for iron precipitation and decomposing residual H2O2 [23]. Precipitated iron was separated from the reactor and the supernatant was used for measurement of soluble Chemical Oxygen Demand (sCOD).
On-site pilot scale Fenton process: On-Site pilot scale Fenton process reactor with volume of 1.0 m3 was installed in the field. The pilot was equipped with suitable mixer. The mixer paddle was located at the three quarters of the reactor depth. The pilot was equipped with hydrogen peroxide, acid and alkaline dosing pumps. Figure 1 shows photo and schematic of the on-Site pilot scale Fenton process reactor. The DTLOWW feeding pumps was used to fill the reactor. The pH of the solution was adjusted to the required value using H2SO4. The required amount of iron in the form of FeSO4.7H2O was added in solid form to the DTLOWW and the mixer was switched-on. Thereafter, the necessary amount of hydrogen peroxide was added to the mixture and the time of the hydrogen peroxide addition was considered the beginning of the reaction. The reaction continued for the predetermined time. At the end of the reaction time, pH of the solution was raised above 9 by operating the sodium hydroxide dosing pump. For achieving mixer neutralization, mixing continued for 30 min. Thereafter, mixing was stopped for iron precipitation and decomposing residual H2O2 [23]. The supernatant was used for the measurement of soluble Chemical Oxygen Demand (sCOD).
Results and Discussion
Lab scale Fenton process
Effect of H2O2/COD molar ratio: To study the effect of H2O2 dose on soluble COD (sCOD) removal, initial H2O2 dose was varied in the range of 0.8–2.4 g/l. Other operating conditions were; pH 3.5, initial sCOD 1500 mg/l, ferrous sulphate heptahydrate (FeSO4.7H2O) 0.70 mg/l and reaction time 150 min. The effect of H2O2 dose and Fenton reaction time on sCOD removal at initial sCOD of 1500 mg/l and 4800 mg/l in the form of residual sCOD are shown in Figure (2a) and (b), respectively. As shown in the figure, both H2O2 concentration and reaction time significantly affect the sCOD reduction. After 150 min reaction time, the residual sCOD was 300, 266, 391 and 637 mg/l for initial sCOD of 1500 mg/l; and 1641, 1366, 1508 and 2142 mg/l for initial sCOD of 4800 mg/l at H2O2 dose of 0.8, 1.2, 1.6 and 2.4 g/l, respectively. The achieved sCOD removal was 80.0, 82.30, 74.0 and 57.6% for initial sCOD of 1500 mg/l; and 65.3, 71.1, 68.1 and 54.7% for initial sCOD of 4800 mg/l at H2O2 dose of 0.8, 1.2, 1.6 and 2.4 g/l, respectively. The minimum residual sCOD concentration was 1366 mg/l at initial sCOD of 4800 mg/l which did not complying with the required local Standard. However, it was 266 mg/l at initial sCOD of 1500 mg/l which complied with the local Standard.
The achieved sCOD removal percent at initial sCOD of 4800 mg/l is quite lower than that of 1500 mg/l. There is small improvement in sCOD removal due to increase H2O2 dose from 0.80 to 1.2 mg/l; however increasing H2O2 dose more than 1.2 did not improve the sCOD removal. This may be due to scavenging of OH• by H2O2 as in Reaction 1 [24].
OH• + H2O2 → H2O + HO2Reaction 1
Based on the results, it may be considered that optimal H2O2 dose of 0.8 g/l for initial sCOD of 1500 mg/l and 1.2 g/l for initial sCOD of 4800 mg/l. This agrees well with reported study in the literature [21].
Effect of H2O2/FeSO4 ratio: In Fenton process, iron and hydrogen peroxide are two major chemicals determining the operation cost as well as efficiency [16]. As much as we can reduce the required chemicals, the operation cost of the treatment process will be decreased. To study the effect of iron dose on the sCOD removal, experiments were conducted at H2O2 dose of 0.8 mg/l for initial sCOD of 1500 mg/l and 1.2 g/l for initial sCOD of 4800 mg/l; and varying FeSO4 dose in the range 0.2-1.4 g/l. The corresponding H2O2/FeSO4 ratio (w/w) were 0.6, 1.2, 3 and 4 for initial sCOD of 1500 mg/l and 1.2, 2.4, 3 and 4 for initial sCOD of 4800 mg/l. Other operating conditions were pH 3.5 and reaction time up to 150 min.
The effect of FeSO4 dose and Fenton reaction time on sCOD removal at initial sCOD of 1500 mg/l and 4800 mg/l in the form of residual sCOD are shown in Figure (3a) and (b), respectively. As shown in the Figure both FeSO4 dose and reaction time significantly affect the sCOD removal. After 150 min reaction time, residual sCOD was 490, 312, 263 and 290 mg/l for initial sCOD of 1500 mg/l at H2O2/ FeSO4 ratio 0.6, 1.2, 3 and 4; and 1642, 1392, 1050 and 1201 mg/l for initial sCOD of 4800 mg/l at H2O2/FeSO4 ratio 1.2, 2.4, 3 and 4, respectively. The achieved sCOD removal was 67.8, 79.5, 82.7 and 81.0% for initial sCOD of 1500 mg/l at H2O2/FeSO4 ratio 0.6, 1.2, 3 and 4; and 65.5, 70.7, 77.9 and 74.4% for initial sCOD of 4800 mg/l at H2O2/FeSO4 ratio 1.2, 2.4, 3 and 4, respectively.
The results show that sCOD removal increased with increase of H2O2/FeSO4 ratio up to 3.0. Increasing H2O2/FeSO4 ratio more than 3 did not significantly improve sCOD removal. This may be ascribed to direct reaction of OH• radical with metal ions at high concentration of Fe2+ as in Reaction 2 [24].
Fe2+ + OH• → Fe3+ + HO Reaction 2
Based on the results, it may be considered that optimal H2O2/FeSO4 ratio is 3 for sCOD removal.
On-site pilot scale Fenton process
The On-Site pilot scale Fenton process reactor is operated in batch basis at 8 hour cycles divided in six phases: 0.50 hr filling, 0.25 hr adding reagents, 5 hr reaction, 0.50 hr neutralisation, 1.5 hr chemical sludge settling and 0.25 hr decanting. The reagents doses were: 1000 mg/l for H2O2 and 330 mg/l for Fe2+ in the form of ferrous sulphate (the weight ratio between H2O2 to Fe2+ was 3:1) and pH 3.5. The sCOD of DTLOWW which has been used in the pilot study was 1700 ± 150 mg/l. Fenton reactor is filled with DTLOWW and then pH is adjusted (with H2SO4) to value of 3.5. The next step was addition of ferrous sulphate. Thereafter, hydrogen peroxide was added to the mixture. When addition of the required amount of H2O2 is completed, the pumps are shut off and Fenton reaction started. All the experimental time, the DTLOWW and reagent are mixed by means of mixer. At the end of the reaction time, pH of the solution was raised to above 9 by operating the sodium hydroxide dosing pump and the mixing continued for 30 min for neutralization. The pilot study was repeated three times and the standard deviation is presented in Figure 4. The Figure shows the effect of reaction time on residual sCOD and sCOD removal percent. After 5 hours reaction time with overall cycle period of 8 hours, residual sCOD was 788 ± 56 mg/l with sCOD removal of 53.6% which amply met with the local discharge Standards for discharging the industrial wastewater to the municipal sewage network [25]. Excessive heating was noted during the reaction time this could be ascribed to the exothermic phenomena of the Fenton reaction [21]. It is noted that the mixing is a crucial factor in the performance of the pilot scale Fenton process. In the preliminary works (data not shown), the Fenton process performance was bad when the mixing was conducted using circulation pumps.
Estimated chemical costs for pilot scale Fenton process
The estimated chemical consumption and its cost are based sCOD strength of less than 2000 mg/l. The main cost contributors for Fenton process are hydrogen peroxide (H2O2) and ferrous sulphate (FeSO4.7H2O). The average price in the local market of 1.0 kg of ferrous sulphate is 0.6 $/kg; however, the average price of hydrogen peroxide 1.0 $/kg. Considering that hydrogen peroxide and ferrous sulphate are the main consumed chemicals in the Fenton process so, the daily cost of chemicals is 1.25-1.50 $/m3.
Conclusions
• In bench scale Fenton process, optimum H2O2 dose is 0.8 g/l for normal DTLOWW strength (sCOD<2000 mg/l) and 1.2 g/l for high strength DTLOWW strength (sCOD>2000 mg/l) with optimum H2O2/FeSO4 ratio of 3 for the normal and high strength DTLOWW and pH 3.5.
• The On-Site pilot scale Fenton process achieved residual sCOD of 788 ± 56 mg/l with sCOD removal of 53.6% which amply met with the local discharge Standards for discharging the industrial wastewater to the municipal sewage network.
• The Fenton process could be used for treatment of the DAFTreated lube oil wastewater (DTLOWW) with daily chemicals cost of 1.25-1.50 $/m3.
Acknowledgement
The author is thankful to Mr. M. Ali, and Mr. K.I. Ali; and the management of the LOBF for their Support.
References

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