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Petroleum refinery wastewater treatment: A pilot scale study
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Petroleum refinery wastewater treatment: A pilot scale study Muftah H. El-Naas a,∗ , Riham Surkatti b , Sulaiman Al-Zuhair b a b
Gas Processing Center, College of Engineering, Qatar University, P.O. Box 2713, Doha, Qatar Chemical and Petroleum Engineering Department, UAE University, P.O. Box 15551, Al-Ain, United Arab Emirates
a r t i c l e
i n f o
Article history: Received 14 May 2016 Received in revised form 10 September 2016 Accepted 23 October 2016 Available online xxx Keywords: Pilot plant Refinery wastewater Electrocoagulation Biodegradation Adsorption
a b s t r a c t A three-step pilot plant was designed, fabricated and tested for the treatment of highly contaminated petroleum refinery wastewater. The three-step process consisted of an electrocoagulation (EC) unit, a biological treatment in a spouted bed bioreactor (SBBR) using immobilized Pseudomonas putida in PVA particles, and an adsorption process using granular activated carbon in a packed column. The pilot plant was operated for a period of ten months at a flow rate of 1 m3 /h, with continuous runs lasting up to 12 h. Different arrangements of the three units were tested to determine the most effective sequence. Placing the EC unit as the pretreatment step resulted in the best performance, since it reduced the COD and suspended solids, and consequently enhanced the performance of the succeeding biodegradation and adsorption units. At the optimum conditions and unit arrangement, the pilot plant was able to reduce the COD by 96% and the concentrations of phenol and cresols by nearly 100%. © 2016 Elsevier Ltd. All rights reserved.
1. Introduction Petroleum refineries consume large amounts of water in the refining processes, such as in cooling, cleaning, steam generation, distillation and hydro-treating [1]. The quality and quantity of wastewater, generated from refineries, are highly affected by the refinery configuration. Generally, the amount of wastewater produced from refineries is almost 0.4–1.6 times the volume of refined oil [2]. Refinery wastewater is characterized by high chemical oxygen demand (COD) and high concentrations of phenol and phenolic derivatives [3–5]. The concentrations of these contaminants must be reduced to acceptable limits before discharging the water into the environment. Over the past few years, several water treatment techniques have been developed [6–8] to achieve this objective, which include biodegradation [9], adsorption [10], ion exchange [11], electrochemical separation [12], flotation and oxidation [13,14]. Most of these techniques, however, may not be effective for the treatment of all types of wastewater and may not be able to deal with all types of contaminants. A combination of these approaches is often needed to handle heavily contaminated industrial wastewater such as refinery wastewater, which is usually characterized by high concentrations of organic compounds. Even though biological treatment methods have been proven very effec-
∗ Corresponding author. E-mail address: [email protected] (M.H. El-Naas).
tive in completely removing phenolic compounds from wastewater [15–18], bio-treatment of heavily contaminated wastewater, with high COD values above 2000 mg/L, cannot be effectively achieved using a single unit on its own. Therefore, to achieve effective complete removal of contaminants, treatment methods are usually based on combining mechanical or physicochemical methods, such as oil–water separation and coagulation, with the biological treatment [19]. The effectiveness of the biological treatment was shown to be enhanced by pretreating the wastewater, using electrocoagulation process, which would result in a more suitable conditions for the biological treatment [20]. Adsorption has often been used as a post-treatment or polishing step to remove non-biodegradable components from the refinery wastewater. Activated carbon has been commonly used, due to its large specific surface area and predominant proportion of microspores [21]. In a previous study, the authors evaluated the effectiveness of a laboratory scale combination of three processes, namely electrocoagulation, biodegradation and adsorption, for treating refinery wastewater [22]. A high removal efficiency of most toxic contaminants was achieved. Although laboratory-scale experimental data are essential to evaluate the technical feasibility of the three-step process, they cannot be used for designing a large-scale plant and hence pilot scale data are needed for such purpose. In the current study, therefore, a three-step pilot plant has been designed based on the laboratory scale data, connected to the wastewater treatment plant of a petroleum refinery and then evaluated, using direct wastewater feed stream from the petroleum refinery.
http://dx.doi.org/10.1016/j.jwpe.2016.10.005 2214-7144/© 2016 Elsevier Ltd. All rights reserved.
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Table 1 Characteristics of Pre-treatment and Post-treatment refinery wastewater as ranges of values. Parameter
Pre-treatment
Post-treatment
pH Conductivity(mS/cm) TSS(g/l) TDS(g/l) SO4 (mg/l) COD(mg/l) Phenol(mg/l) o-Cresol(mg/l) m,p-cresol(mg/l) N-hexane(mg/l) Color
8.3–8.7 5.2–6.8 0.03–0.04 3.8–6.2 14.5–16 3970–4745 8–10 55–68 44–61 1.8–1.85 Dark Green
8.5–8.9 6–8 0.01–0.03 4–4.9 8–12 25–292 ND ND ND ND Clear
ND: Not detected.
2. Pilot plant operation The three-step system was investigated on a laboratory-scale for the treatment of refinery wastewater at a small capacity of 600 mL/h [22]. The laboratory-scale experimental results were used to scale up and design a three-step pilot plant (PP) to treat a direct stream of a highly contaminated wastewater from the wastewater treatment plant of a local petroleum refinery. The wastewater stream is characterized by high COD and high phenols concentrations as shown in Table 1. The pilot plant data can be used by petroleum refinery to design a new water treatment plant based on the three-step process that is more efficient and more compact than the current plant. The aim of the water treatment is to comply with the national discharge limits (COD of 150 mg/L and phenols of 0.1 mg/L). The scaling up was carried out by maintaining the similarity of the main design parameters between the two scales. The three-step PP was fabricated and installed at a local petroleum refinery, near an existing wastewater treatment plant. The PP was designed to treat 1 m3 /h of highly contaminated petroleum refinery wastewater. The main units of the PP are the same as those used in the lab scale, namely electrocoagulation cell (EC), a spouted bed bioreactor (SBBR) and an adsorption column (AD). A detailed process flow diagram of the PP is shown in Fig. 1. The feed stream was introduced to the EC using the first pump (P1) with flow rate of 1m3 /h. The effluent of the EC unit was collected in the first settling tank (ST1) to remove the suspension solids produced by the coagulation process. The EC pretreated water was then fed to the SBBR by the second pump (P2) at the same flow rate of 1 m3 /h. The effluent of the SBBR was collected in the second settling tank (ST2) to remove the fine debris and escaped bacteria resulted from the biodegradation process. The stream was then fed to the AD at the same flow rate and then sent to ST3 to settle the carried out fine particles of activated carbon, before discharging. 3. Scaling up the laboratory scale The operational performance of the PP was compared to that of the three-step treatment in a laboratory scale that showed a high performance in the removal of COD, phenol and cresols [22]. Scaling up the three-step process to a real plant size has to pass first through a PP scale analysis, in order to improve the knowledge required to design an effective plant capable of treating larger amounts of wastewater, which are produced every day in petroleum refineries. The EC in the PP was a ready-made unit, and hence there was limited design consideration involved in the scaling up. In the laboratory scale, a 1.5 L cylindrical EC unit was used with total flow rate of 0.6 L/h. The unit housed two Al or Iron electrodes (40mm × 60mm × 1 mm) that were connected to 17 V DC power supply. In the PP however, an EC unit with maximum capacity of 1.48 m3 /h EC unit was used, housing 73 electrodes
(500mm × 200mm × 3 mm) that were connected to 240 V DC power supply. In both laboratory and pilot scale, the operating temperature was kept at 30–35 ◦ C. On the other hand, the SBBR was scaled up keeping similar operating parameters in PP and laboratory scale. These similar parameters include: residence times of around 60 min and volume percentage of immobilized bacteria of 30%. Temperature of 30 ◦ C and pH of 7 were also kept the same in both scales. The adsorption column in the PP was designed using on a preliminary breakthrough curve found using the laboratory scale unit. Considering high initial COD ranging from 2000 to 3000 mg/L, as the wastewater stream was fed directly to the adsorption column. The laboratory unit operated at a flow rate, QLS , of 600 mL/h, initial COD, Cin , of 2726 mg/L, mass of GAC, mLS , of 130 g with 368.3 g/L bulk density. From the breakthrough curve, the breakthrough volume, VBreakthrough (volume of wastewater passed through the column before the pollutants start to be detected in the output stream), and exhaustion volume, VExhaustion (volume of wastewater passed through the column before the pollutants concentration in output stream equals that in the input) were determined to be 2.7L and 6.6L, respectively. Total capacity of the bed, qe , was determined to be 126 mg/gGAC , using Eq. (1) qe = (Cin · Vexhaustion ) /mLS
(1)
Capacity before breakthrough, qb , was determined to be 57 mg/gGAC , using Eq. (2)
qb = Cin, · VBrakthrough /mLS
(2)
The fraction of unused bed, Xu , was then determined to be 0.55, using Eq. (3) Xu = (qe − qb ) /qe
(3)
The GAC consumption rate, YGAC , in the PP was determined to be 22.8 kgGAC /h, from the wastewater flowrate in the PP, QPP , which was 1m3 /h and considering the bed capacity (qe ) to be the same in both scales, as shown in Eq. (4)
YGAC = Cin, · QPP /qe
(4)
The mass of the GAC in the PP, mPP , needed to provide a breakthrough duration larger than 5 h, was determined to be 250 kg, as shown in Eq. (5)
mPP = 5YGAC, / (1 − Xu )
(5)
3.1. Electrocoagulation (EC) unit The concept behind the EC process is destabilizing suspended, emulsified, or dissolved contaminants in an aqueous medium by introducing an electrical current. The electrical current provides the electromotive force to drive several chemical reactions that drive the dissolved or suspended contaminants to approach more stable states, which are less colloidal, less emulsifiable, or less soluble. As this occurs, the contaminants can be easily removed or settled. A schematic diagram of EC unit, which was acquired from Powell Water Systems, USA, is shown in Fig. S1. The unit was designed to have a maximum capacity of 1.48 m3 /h (6.5 GPM).The refinery wastewater was pumped from the feed tank (FT1) to the EC and entered the unit through WW inlet (N1). The EC Teflon chamber contained a series of metallic electrodes, made of either Aluminum or Iron (500 mm × 200 mm × 3 mm) that were arranged in parallel. The unit was connected to a 240 V single phase AC to DC power supply, with a logic controller introducing a constant current of 65A. To enhance the mixing of the water inside the unit, air was injected to the system from (N3) by a supply pump. Prior to oper-
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Fig. 1. A schematic flow diagram of the pilot plant treatment operation: FT: Feed tank. EC: Electrocoagulation unit. ST: Settling tank. SBBR: Spouted bed bioreactor. AC: Adsorption column.
ation, the electrodes were cleaned using H2 SO4 (9–15%) solution that was injected to the EC unit from (N2). 3.2. Biological reactor (SBBR) The SBBR is a moving bed bioreactor, which is known for its high mixing performance. It is characterized by a systematic intense mixing due to the cyclic motion of particles within the bed, which is generated by air jet injected from the bottom of the reactor. The SBBR contained Pseudomonas putida immobilized inside matrices of polyvinyl alcohol (PVA) gel particles. The preparation of the immobilized bacteria is discussed in a previous publication [23]. After the preparation of the PVA with immobilized bacteria, pellets were cut into cubes with 1 cm3 volume. The reactor was filled with PVA pellets that occupied 30% of the total operating reactor volume. The effluent from the EC unit was sent to settling tank (ST1), before being pumped to the SBBR, which has a total volume of 1.7 m3 , as shown in Fig. S2. Air was injected into the bioreactor through an orifice (N5) at a flow rate of 5 m3 /min, to maintain the aerobic conditions and enhance mixing inside the bioreactor. The total working volume was 1 m3 , which allowed residence time of one hour. Mineral nutrients needed for bacteria growth were continuously supplied (N2) from a feed tank that was installed near the SBBR. The temperature of the biological reactor was in the range of 30–35 ◦ C, which was shown to be the optimum range for the bacterial growth [23]. The pH was maintained constant at 7–7.5 by adding HCl. 3.3. Adsorption column (AD) The final treatment step in the process was carried out in the AD packed with granular activated carbon (GAC), with an average particle size of 1.5 mm, obtained from Lobachemie Company, India. The AD step consisted of two parallel columns; each is packed with 250 kg of GAC, providing a total bed volume of 0.5 m3 . The effluent wastewater from the SBBR was send to second settling tank (ST2) as shown in Fig. 1, from which it was pumped to one of the adsorption columns with flow rate of 1 m3 /h. Fig. S3 shows the adsorption column with 1.8 m in length and 0.6 internal diameter (L/D = 3). Once the activated carbon is saturated in the first column, the adsorption process can be directly shifted to the second one. At the same time, steam at 131 ◦ C and 1.5 bar, which is supplied by a steam generator, can be used for regenerating the activated carbon. The treated wastewater is then sent to the final settling tank (ST3) before discharging. 3.4. Settling and collecting tanks As shown in Fig. 1, the settling tank ST1 was placed after the EC unit, to settle the solids and store the resulted treated water before
being pumped into the SBBR. Similar two tanks, ST2 and ST3, were placed after the other two steps to collect the treated water from their respective preceding units. The three tanks were made of PVC, but the maximum capacity of settling tank (ST1) was 3 m3 , which was larger than the other two settling tanks (ST2, ST3), which was 2 m3 . The larger volume of ST1 was required to allow enough residence time for the solids generated at the EC unit to settle, whereas in the other two settling tanks, the amount of particles generated in the proceeding units is much less and hence less settling is needed. Fig. S4 shows a schematic diagram of one of the settling tanks. The effluent was introduced to each tank at a flow rate of 1 m3 /h through the WW inlet (N1), and leaves the tank from the other side (N3). To minimize the level disturbances in the tank and facilitate settling, the input stream was injected into the bottom of the tank through a pipe immersed deep inside the liquid, and the effluent is pumped from the top of the tank as shown in the figure. To control the level of the liquid in tank, the tank is provided with an overflow opening. Therefore, the actual volume in the tank did not exceed the 2 m3 capacity. All tanks were frequently cleaned and water was drained by the drainage (N7). 4. Sampling and analysis At regular time intervals, wastewater samples were collected at the outlets of each treatment unit and analyzed for COD and phenol(s) concentrations. The COD was measured using UV–vis spectrophotometer (DR-5000, Germany), more details about COD analysis can be found elsewhere [24]. Phenols including phenol, o, p- and m-cresol were analyzed using GC-FID (Shemadzu, 2010). Further details about the analytical procedure of the phenol and cresols concentrations are found in previous publications [9,23]. 5. Results and discussions 5.1. Pilot scale performance 5.1.1. COD reduction The reduction in COD was determined at the outlet of each main unit in the PP. Refinery wastewater feed was characterized by its dark greenish color, strong pungent odor and high COD ranging from 3900 to 4800 mg/L. Due to the variation in the feed compositions, the COD was determined in the feed at the beginning of each treatment process. The values of COD after each unit in the treatment process at different time intervals are shown in Fig. 2. The results illustrate that at steady state, an overall cumulative reduction of about 96% was reached during continuous operation of up to 8 h. The pilot plant results showed that EC performance was almost consistent throughout the 8 h of operation, with around 35% reduction in the COD. This is considered a relatively good performance,
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12 2 hrs 4 hrs 6 hrs 8 hrs
4000
3000
2000
1000
Phenol Concentration (mg/l)
COD Concentration (mg/l)
5000
0
EC
SBBR
Fig. 2. The reduction of COD after each treatment step in the pilot plant at different durations of operation.
as EC has been shown to be a good pre-treatment step for removing TDS, TSS and metals, but not for COD [25]. The removal increased by another 20% in the effluents of SBBR unit. It was obvious though that the performance of the SBBR reduced with the operation duration. The COD further dropped by 96% in the effluents of the AD column, which shown more consistent performance than the SBBR. Compared to EC, adsorption process is highly recommended for the reduction of COD in wastewater, and activated carbon was shown to have high capability in this regard [24]. Although applying adsorption as single stage in wastewater treatment may have a high performance in COD reduction, a combination of adsorption with other treatment processes, such as electrocoagulation or biological techniques, was shown to enhance the performance of the former process. Papic´ et al. (2004) tested a two-steps process consisting of Al (III) electocoagulation followed by activated carbon adsorption for wastewater treatment. The process achieved a very high removal of COD from wastewater, reaching up to 90%. Similar results were also obtained using a combination of adsorption and biological treatment, with more than 90% COD reduction, from the treatment of recycled paper wastewater, with initial COD ranging from 4000 to 5000 mg/L [26]. Another study on using GAC adsorption followed by a biological treatment for the reduction of COD in wastewater showed that up to 94.5% reduction was achieved [27]. A more recent investigation applied biological treatment before the adsorption for the treatment of dyeing wastewater and 96% COD reduction was achieved [28]. 5.1.2. Reduction in phenols The wastewater generated from the refinery usually has different types of phenols, namely phenol, and o-, and p- and m-cresols. Cresols are the phenolic compounds which are commonly encountered in refinery wastewater streams. The concentrations of these phenols have been analyzed in the feed stream before the treatment process, and at the output of each main treatment unit. As shown in Figs. 3–5, a complete removal of phenol and -cresols was achieved during 8 h of operation. The main reduction in phenolic pollutants occurred in the SBBR step. Phenol and o-cresol were completely removed within this step, whereas m- and p- cresols were dropped significantly, but were completely removed only in the following AD unit. This agrees with previously reported results, confirming that o-and p-substituted phenols are more degradable than m-substituted phenols [29]. The complete removal by the biological treatment step was achieved by the immobilized P. putida, which have been shown to have a good efficiency in degrading phenol and cresols [9,23]. It is well known that activated carbon has an acceptable performance as a polishing step [30]. However, in the
10
8
6
4
2
0
Ac
Feed
EC
SBBR
AC
Fig. 3. The reduction of phenol after each treatment step at different durations of operation.
80
o-cresol Concentration (mg/l)
Feed
2 hrs 4 hrs 6 hrs 8 hrs
2 hrs 4 hrs 6 hrs 8 hrs
60
40
20
0
Feed
EC
SBBR
AC
Fig. 4. The reduction of o-cresol after each treatment step at different durations of operation.
PP, the AD was not required for the removal of phenols during 8 h of operation. 5.2. Comparison between lab and pilot scale To demonstrate the efficiency of the scaling up process, the cumulative reduction of COD, phenol and cresols after each treatment step in the PP was compared to the laboratory scale results as shown in Figs. 5–8 . It is clearly seen that both, lab-scale and PP, show high performance, with similar overall reduction of contaminants. Phenol and cresols were completely removed and the COD removal percentage was higher than 96%. In addition, the odor was completely removed and the color of the treated water converted from dark green to clear (Table 1). The EC unit in the PP showed slightly lower performance in COD removal compared to that in the lab-scale. However, a much lower performance was observed in removing phenol and cresols. The superior performance of EC in the lab-scale for phenols removal, compared to the PP, was due to the variation in the design of the EC unit in both scales, which have been shown to strongly affect the efficiency of EC process [31]. It is worth noting here that these experimental data were collected near the end of the 10 month operation period when the three step process was optimized. However, the EC unit was disadvantaged due the erosion of
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60 50 40 30 20 10
EC
SBBR
Lab-Scale Pilot-Scale
80 60 40 20
AC
Fig. 5. The reduction of m, p-cresol after each treatment step at different durations of operation.
120 100
COD % Reduction
100
0
0
Feed
Lab-Scale Pilot-Scale
80 60 40 20 0
EC
SBBR
AD
Fig. 6. A comparison of cumulative COD reduction after each treatment step in laboratory and Pilot Plant scale.
120
Phenol % Reduction
5
120
70
p,m-cresol % Reduction
m-, p-cresol Concentration (mg/l)
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100
Lab-Scale Pilot-Scale
80
SBBR
AD
Fig. 8. A comparison of cumulative p,m-cresol reduction after each treatment step in laboratory and Pilot Plant scale.
volumetric flow rate over working volume of around 0.0028 min−1 . Also, temperature of 30 ◦ C and pH of 7 were kept the same in both scales. As compared to the laboratory scale, the SBBR in the PP showed a higher performance in the removal of phenols, where complete removal of phenol and cresols was achieved as shown in Figs. 7. This could be attributed to the major difference in the ratio between PVA particle diameter and bed diameter, which was 0.2 and 0.01 for the lab scale and the pilot scale, respectively; the PVA particle size was the same for both scales (1 cm3 ). The much lower particle-to-bed ratio for the pilot scale reactor led to much better mixing and much less wall-effect. As previously reported [32], the lower PVA particle size seemed to reduce mass transfer limitations and enhance the accessibility of the substrate to the bacteria, which in turn enhanced the biodegradability of the phenolic compounds. The PP adsorption process showed similar performance in removing phenolic compounds and COD as the lab scale. This was expected as the amount of GAC in the AD units PP was scaled up from that of the laboratory scale and operated under similar operating conditions. Similar comparison between PP and laboratory scales was reported in the literature [33]. However, the study was carried out on a single wastewater treatment unit, namely anaerobic digestion process for treatment of swine wastewater and compared a lab-scale of 6 L and a pilot scale of 20 m3 . Similar COD removal percentage was obtained in both scales. 6. Conclusions
60 40 20 0
EC
EC
SBBR
AD
Fig. 7. A comparison of cumulative phenol reduction after each treatment step in laboratory and Pilot Plant scale.
An integrated, three-step wastewater treatment process has been scaled-up to a Pilot Plant (PP) scale, by maintaining the same residence times in each unit as used in the lab scale. The PP was found to be effective in the treatment of highly contaminated refinery wastewater. Similar overall efficiency of the PP, compared to the lab-scale, was achieved. Almost a complete removal of COD and phenols was consistently achieved at the effluent of the last step of the process after up to 8 h of continuous operation. The EC unit was found to be an effective pretreatment step, whereas AD was an effective polishing step. Acknowledgements
the electrodes with time and thus reducing its efficiently by about 20–30% compared to that with new electrodes. The SBBR was scaled up keeping similar operating parameters in PP and laboratory scale. These similar parameters include, residence times of around 1 h, volume percentage of immobilized bacteria of 30%, same specific interfacial area of 180 m2 /m3 and air
The authors would like to acknowledge the financial support provided by the Japan Cooperation Centre, Petroleum (JCCP) and the technical support of the JX Nippon Research Institute Co., Ltd .(JX-NRI). They would also like to thank Koike Tech of Japan for fabrication of the Pilot Plant. Special thanks are due to Abdul Rasheed
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Kadiri, Manal Abu Alhaija and Munaver Jaman Basheer for their help with the PP operation. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.jwpe.2016.10. 005. References [1] L. Yan, Y. Wang, J. Li, H. Ma, H. Liu, T. Li, et al., Comparative study of different electrochemical methods for petroleum refinery wastewater treatment, Desalination 341 (2014) 87–93. [2] N.S. Mizzouri, M.G. Shaaban, Kinetic and hydrodynamic assessment of an aerobic purification system for petroleum refinery wastewater treatment in a continuous regime, Int. Biodeterior. Biodegrad. 83 (2013) 1–9. [3] B. Santos, C.F. Galinha, J.G. Crespo, M.A. Santos, S. Velizarov, Prediction of polar oil and grease contamination levels in refinery wastewater through multivariate statistical modeling, Sep. Purif. Technol. 119 (2013) 51–57. [4] A.M. Mansouri, F. Shahrezaei, A.A.L. Zinatizadeh, A.H. Azandaryani, M. Pirsaheb, K. Sharafi, Preparation of poly ethyleneimine (PEI))/nano titania (TiO2) multilayer film on quartz tube by layer-by-layer self-assembly and its applications for petroleum refinery wastewater treatment, J. Taiwan Inst. Chem. Eng. 45 (2014) 2501–2510. [5] L. Yan, H. Ma, B. Wang, W. Mao, Y. Chen, Advanced purification of petroleum refinery wastewater by catalytic vacuum distillation, J. Hazard. Mater. 178 (2010) 1120–1124. [6] L. Altas¸, H. Büyükgüngör, Sulfide removal in petroleum refinery wastewater by chemical precipitation, J. Hazard. Mater. 153 (2008) 462–469. [7] C.-J.G. Jou, G.-C. Huang, A pilot study for oil refinery wastewater treatment using a fixed-film bioreactor, Adv. Environ. Res. 7 (2003) 463–469. [8] G. Hu, J. Li, H. Hou, A combination of solvent extraction and freeze thaw for oil recovery from petroleum refinery wastewater treatment pond sludge, J. Hazard. Mater. 283 (2015) 832–840. [9] R. Surkatti, M.H. El-Naas, Biological treatment of wastewater contaminated with p-cresol using Pseudomonas putida immobilized in polyvinyl alcohol (PVA) gel, J. Water Process Eng. 1 (2014) 84–90. [10] C. Chen, L. Wei, X. Guo, S. Guo, G. Yan, Investigation of heavy oil refinery wastewater treatment by integrated ozone and activated carbon – supported manganese oxides, Fuel Process. Technol. 124 (2014) 165–173. [11] D. Xie, C. Li, R. Tang, Z. Lv, Y. Ren, C. Wei, et al., Ion-exchange membrane bioelectrochemical reactor for removal of nitrate in the biological effluent from a coking wastewater treatment plant, Electrochem. Commun. 46 (2014) 99–102. [12] L. Wei, S. Guo, G. Yan, C. Chen, X. Jiang, Electrochemical pretreatment of heavy oil refinery wastewater using a three-dimensional electrode reactor, Electrochim. Acta 55 (2010) 8615–8620. [13] R.F. de Sena, J.L. Tambosi, A.K. Genena, R.d.F.P.M. Moreira, H.F. Schröder, H.J. José, Treatment of meat industry wastewater using dissolved air flotation and advanced oxidation processes monitored by GC–MS and LC–MS, Chem. Eng. J. 152 (2009) 151–157. [14] H.G. Yang, H.Y. Chun, D. Pak, Improvement of sludge anaerobic degradability by combined electro-flotation and electro-oxidation treatment, Biochem. Eng. J. 90 (2014) 44–48.
[15] S. Kumar, D. Arya, A. Malhotra, S. Kumar, B. Kumar, Biodegradation of dual phenolic substrates in simulated wastewater by Gliomastix indicus MTCC 3869, J. Environ. Chem. Eng. 1 (2013) 865–874. [16] Y. Jiang, X. Cai, D. Wu, N. Ren, Biodegradation of phenol and m-cresol by mutated Candida tropicalis, J. Environ. Sci. 22 (2010) 621–626. [17] S. Vasudevan, An efficient removal of phenol from water by peroxi-electrocoagulation processes, J. Water Process Eng. 2 (2014) 53–57. [18] J. Wang, X. Ma, S. Liu, P. Sun, P. Fan, C. Xia, Biodegradation of phenol and 4-chlorophenol by candida tropicalis W1, Proced. Environ. Sci. 16 (2012) 299–303. [19] I. Ben Hariz, A. Halleb, N. Adhoum, L. Monser, Treatment of petroleum refinery sulfidic spent caustic wastes by electrocoagulation, Sep. Purif. Technol. 107 (2013) 150–157. [20] C. Gong, Z. Zhang, H. Li, D. Li, B. Wu, Y. Sun, et al., Electrocoagulation pretreatment of wet-spun acrylic fibers manufacturing wastewater to improve its biodegradability, J. Hazard. Mater. 274 (2014) 465–472. [21] R.-S. Juang, W.-C. Huang, Y.-H. Hsu, Treatment of phenol in synthetic saline wastewater by solvent extraction and two-phase membrane biodegradation, J. Hazard. Mater. 164 (2009) 46–52. [22] M.H. El-Naas, M.A. Alhaija, S. Al-Zuhair, Evaluation of a three-step process for the treatment of petroleum refinery wastewater, J. Environ. Chem. Eng. 2 (2014) 56–62. [23] M.H. El-Naas, S.A. Al-Muhtaseb, S. Makhlouf, Biodegradation of phenol by Pseudomonas putida immobilized in polyvinyl alcohol (PVA) gel, J. Hazard. Mater. 164 (2009) 720–725. [24] M.H. El-Naas, S. Al-Zuhair, M.A. Alhaija, Reduction of COD in refinery wastewater through adsorption on date-pit activated carbon, J. Hazard. Mater. 173 (2010) 750–757. [25] M.H. El-Naas, S. Al-Zuhair, A. Al-Lobaney, S. Makhlouf, Assessment of electrocoagulation for the treatment of petroleum refinery wastewater, J. Environ. Manag. 91 (2009) 180–185. [26] W.H.W. Osman, S.R.S. Abdullah, A.B. Mohamad, A.A.H. Kadhum, R.A. Rahman, Simultaneous removal of AOX and COD from real recycled paper wastewater using GAC-SBBR, J. Environ. Manag. 121 (2013) 80–86. [27] M.H. Muhamad, S.R. Sheikh Abdullah, A.B. Mohamad, R. Abdul Rahman, A.A. Hasan Kadhum, Application of response surface methodology (RSM) for optimisation of COD, NH3–N and 2,4-DCP removal from recycled paper wastewater in a pilot-scale granular activated carbon sequencing batch biofilm reactor (GAC-SBBR), J. Environ. Manag. 121 (2013) 179–190. [28] S. Sathian, M. Rajasimman, C.S. Rathnasabapathy, C. Karthikeyan, Performance evaluation of SBR for the treatment of dyeing wastewater by simultaneous biological and adsorption processes, J. Water Process Eng. 4 (2014) 82–90. [29] T. Al-Khalid, M.H. El-Naas, Aerobic biodegradation of phenols: a comprehensive review, Crit. Rev. Environ. Sci. Technol. 42 (2012) 1631–1690. ˜ [30] I. Vázquez, J. Rodríguez-Iglesias, E. Maranón, L. Castrillón, M. Álvarez, Removal of residual phenols from coke wastewater by adsorption, J. Hazard. Mater. 147 (2007) 395–400. [31] V. Khandegar, A.K. Saroha, Electrocoagulation for the treatment of textile industry effluent – a review, J. Environ. Manag. 128 (2013) 949–963. [32] M.H. El-Naas, S. Al-Zuhair, S. Makhlouf, Continuous biodegradation of phenol in a spouted bed bioreactor (SBBR), Chem. Eng. J. 160 (2010) 565–570. [33] W. Kim, K. Cho, S. Lee, S. Hwang, Comparison of methanogenic community structure and anaerobic process performance treating swine wastewater between pilot and optimized lab scale bioreactors, Bioresour. Technol. 145 (2013) 48–56.
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Petroleum refinery wastewater treatment: A pilot scale study Muftah H. El-Naas a,∗ , Riham Surkatti b , Sulaiman Al-Zuhair b a b
Gas Processing Center, College of Engineering, Qatar University, P.O. Box 2713, Doha, Qatar Chemical and Petroleum Engineering Department, UAE University, P.O. Box 15551, Al-Ain, United Arab Emirates
a r t i c l e
i n f o
Article history: Received 14 May 2016 Received in revised form 10 September 2016 Accepted 23 October 2016 Available online xxx Keywords: Pilot plant Refinery wastewater Electrocoagulation Biodegradation Adsorption
a b s t r a c t A three-step pilot plant was designed, fabricated and tested for the treatment of highly contaminated petroleum refinery wastewater. The three-step process consisted of an electrocoagulation (EC) unit, a biological treatment in a spouted bed bioreactor (SBBR) using immobilized Pseudomonas putida in PVA particles, and an adsorption process using granular activated carbon in a packed column. The pilot plant was operated for a period of ten months at a flow rate of 1 m3 /h, with continuous runs lasting up to 12 h. Different arrangements of the three units were tested to determine the most effective sequence. Placing the EC unit as the pretreatment step resulted in the best performance, since it reduced the COD and suspended solids, and consequently enhanced the performance of the succeeding biodegradation and adsorption units. At the optimum conditions and unit arrangement, the pilot plant was able to reduce the COD by 96% and the concentrations of phenol and cresols by nearly 100%. © 2016 Elsevier Ltd. All rights reserved.
1. Introduction Petroleum refineries consume large amounts of water in the refining processes, such as in cooling, cleaning, steam generation, distillation and hydro-treating [1]. The quality and quantity of wastewater, generated from refineries, are highly affected by the refinery configuration. Generally, the amount of wastewater produced from refineries is almost 0.4–1.6 times the volume of refined oil [2]. Refinery wastewater is characterized by high chemical oxygen demand (COD) and high concentrations of phenol and phenolic derivatives [3–5]. The concentrations of these contaminants must be reduced to acceptable limits before discharging the water into the environment. Over the past few years, several water treatment techniques have been developed [6–8] to achieve this objective, which include biodegradation [9], adsorption [10], ion exchange [11], electrochemical separation [12], flotation and oxidation [13,14]. Most of these techniques, however, may not be effective for the treatment of all types of wastewater and may not be able to deal with all types of contaminants. A combination of these approaches is often needed to handle heavily contaminated industrial wastewater such as refinery wastewater, which is usually characterized by high concentrations of organic compounds. Even though biological treatment methods have been proven very effec-
∗ Corresponding author. E-mail address: [email protected] (M.H. El-Naas).
tive in completely removing phenolic compounds from wastewater [15–18], bio-treatment of heavily contaminated wastewater, with high COD values above 2000 mg/L, cannot be effectively achieved using a single unit on its own. Therefore, to achieve effective complete removal of contaminants, treatment methods are usually based on combining mechanical or physicochemical methods, such as oil–water separation and coagulation, with the biological treatment [19]. The effectiveness of the biological treatment was shown to be enhanced by pretreating the wastewater, using electrocoagulation process, which would result in a more suitable conditions for the biological treatment [20]. Adsorption has often been used as a post-treatment or polishing step to remove non-biodegradable components from the refinery wastewater. Activated carbon has been commonly used, due to its large specific surface area and predominant proportion of microspores [21]. In a previous study, the authors evaluated the effectiveness of a laboratory scale combination of three processes, namely electrocoagulation, biodegradation and adsorption, for treating refinery wastewater [22]. A high removal efficiency of most toxic contaminants was achieved. Although laboratory-scale experimental data are essential to evaluate the technical feasibility of the three-step process, they cannot be used for designing a large-scale plant and hence pilot scale data are needed for such purpose. In the current study, therefore, a three-step pilot plant has been designed based on the laboratory scale data, connected to the wastewater treatment plant of a petroleum refinery and then evaluated, using direct wastewater feed stream from the petroleum refinery.
http://dx.doi.org/10.1016/j.jwpe.2016.10.005 2214-7144/© 2016 Elsevier Ltd. All rights reserved.
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Table 1 Characteristics of Pre-treatment and Post-treatment refinery wastewater as ranges of values. Parameter
Pre-treatment
Post-treatment
pH Conductivity(mS/cm) TSS(g/l) TDS(g/l) SO4 (mg/l) COD(mg/l) Phenol(mg/l) o-Cresol(mg/l) m,p-cresol(mg/l) N-hexane(mg/l) Color
8.3–8.7 5.2–6.8 0.03–0.04 3.8–6.2 14.5–16 3970–4745 8–10 55–68 44–61 1.8–1.85 Dark Green
8.5–8.9 6–8 0.01–0.03 4–4.9 8–12 25–292 ND ND ND ND Clear
ND: Not detected.
2. Pilot plant operation The three-step system was investigated on a laboratory-scale for the treatment of refinery wastewater at a small capacity of 600 mL/h [22]. The laboratory-scale experimental results were used to scale up and design a three-step pilot plant (PP) to treat a direct stream of a highly contaminated wastewater from the wastewater treatment plant of a local petroleum refinery. The wastewater stream is characterized by high COD and high phenols concentrations as shown in Table 1. The pilot plant data can be used by petroleum refinery to design a new water treatment plant based on the three-step process that is more efficient and more compact than the current plant. The aim of the water treatment is to comply with the national discharge limits (COD of 150 mg/L and phenols of 0.1 mg/L). The scaling up was carried out by maintaining the similarity of the main design parameters between the two scales. The three-step PP was fabricated and installed at a local petroleum refinery, near an existing wastewater treatment plant. The PP was designed to treat 1 m3 /h of highly contaminated petroleum refinery wastewater. The main units of the PP are the same as those used in the lab scale, namely electrocoagulation cell (EC), a spouted bed bioreactor (SBBR) and an adsorption column (AD). A detailed process flow diagram of the PP is shown in Fig. 1. The feed stream was introduced to the EC using the first pump (P1) with flow rate of 1m3 /h. The effluent of the EC unit was collected in the first settling tank (ST1) to remove the suspension solids produced by the coagulation process. The EC pretreated water was then fed to the SBBR by the second pump (P2) at the same flow rate of 1 m3 /h. The effluent of the SBBR was collected in the second settling tank (ST2) to remove the fine debris and escaped bacteria resulted from the biodegradation process. The stream was then fed to the AD at the same flow rate and then sent to ST3 to settle the carried out fine particles of activated carbon, before discharging. 3. Scaling up the laboratory scale The operational performance of the PP was compared to that of the three-step treatment in a laboratory scale that showed a high performance in the removal of COD, phenol and cresols [22]. Scaling up the three-step process to a real plant size has to pass first through a PP scale analysis, in order to improve the knowledge required to design an effective plant capable of treating larger amounts of wastewater, which are produced every day in petroleum refineries. The EC in the PP was a ready-made unit, and hence there was limited design consideration involved in the scaling up. In the laboratory scale, a 1.5 L cylindrical EC unit was used with total flow rate of 0.6 L/h. The unit housed two Al or Iron electrodes (40mm × 60mm × 1 mm) that were connected to 17 V DC power supply. In the PP however, an EC unit with maximum capacity of 1.48 m3 /h EC unit was used, housing 73 electrodes
(500mm × 200mm × 3 mm) that were connected to 240 V DC power supply. In both laboratory and pilot scale, the operating temperature was kept at 30–35 ◦ C. On the other hand, the SBBR was scaled up keeping similar operating parameters in PP and laboratory scale. These similar parameters include: residence times of around 60 min and volume percentage of immobilized bacteria of 30%. Temperature of 30 ◦ C and pH of 7 were also kept the same in both scales. The adsorption column in the PP was designed using on a preliminary breakthrough curve found using the laboratory scale unit. Considering high initial COD ranging from 2000 to 3000 mg/L, as the wastewater stream was fed directly to the adsorption column. The laboratory unit operated at a flow rate, QLS , of 600 mL/h, initial COD, Cin , of 2726 mg/L, mass of GAC, mLS , of 130 g with 368.3 g/L bulk density. From the breakthrough curve, the breakthrough volume, VBreakthrough (volume of wastewater passed through the column before the pollutants start to be detected in the output stream), and exhaustion volume, VExhaustion (volume of wastewater passed through the column before the pollutants concentration in output stream equals that in the input) were determined to be 2.7L and 6.6L, respectively. Total capacity of the bed, qe , was determined to be 126 mg/gGAC , using Eq. (1) qe = (Cin · Vexhaustion ) /mLS
(1)
Capacity before breakthrough, qb , was determined to be 57 mg/gGAC , using Eq. (2)
qb = Cin, · VBrakthrough /mLS
(2)
The fraction of unused bed, Xu , was then determined to be 0.55, using Eq. (3) Xu = (qe − qb ) /qe
(3)
The GAC consumption rate, YGAC , in the PP was determined to be 22.8 kgGAC /h, from the wastewater flowrate in the PP, QPP , which was 1m3 /h and considering the bed capacity (qe ) to be the same in both scales, as shown in Eq. (4)
YGAC = Cin, · QPP /qe
(4)
The mass of the GAC in the PP, mPP , needed to provide a breakthrough duration larger than 5 h, was determined to be 250 kg, as shown in Eq. (5)
mPP = 5YGAC, / (1 − Xu )
(5)
3.1. Electrocoagulation (EC) unit The concept behind the EC process is destabilizing suspended, emulsified, or dissolved contaminants in an aqueous medium by introducing an electrical current. The electrical current provides the electromotive force to drive several chemical reactions that drive the dissolved or suspended contaminants to approach more stable states, which are less colloidal, less emulsifiable, or less soluble. As this occurs, the contaminants can be easily removed or settled. A schematic diagram of EC unit, which was acquired from Powell Water Systems, USA, is shown in Fig. S1. The unit was designed to have a maximum capacity of 1.48 m3 /h (6.5 GPM).The refinery wastewater was pumped from the feed tank (FT1) to the EC and entered the unit through WW inlet (N1). The EC Teflon chamber contained a series of metallic electrodes, made of either Aluminum or Iron (500 mm × 200 mm × 3 mm) that were arranged in parallel. The unit was connected to a 240 V single phase AC to DC power supply, with a logic controller introducing a constant current of 65A. To enhance the mixing of the water inside the unit, air was injected to the system from (N3) by a supply pump. Prior to oper-
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Fig. 1. A schematic flow diagram of the pilot plant treatment operation: FT: Feed tank. EC: Electrocoagulation unit. ST: Settling tank. SBBR: Spouted bed bioreactor. AC: Adsorption column.
ation, the electrodes were cleaned using H2 SO4 (9–15%) solution that was injected to the EC unit from (N2). 3.2. Biological reactor (SBBR) The SBBR is a moving bed bioreactor, which is known for its high mixing performance. It is characterized by a systematic intense mixing due to the cyclic motion of particles within the bed, which is generated by air jet injected from the bottom of the reactor. The SBBR contained Pseudomonas putida immobilized inside matrices of polyvinyl alcohol (PVA) gel particles. The preparation of the immobilized bacteria is discussed in a previous publication [23]. After the preparation of the PVA with immobilized bacteria, pellets were cut into cubes with 1 cm3 volume. The reactor was filled with PVA pellets that occupied 30% of the total operating reactor volume. The effluent from the EC unit was sent to settling tank (ST1), before being pumped to the SBBR, which has a total volume of 1.7 m3 , as shown in Fig. S2. Air was injected into the bioreactor through an orifice (N5) at a flow rate of 5 m3 /min, to maintain the aerobic conditions and enhance mixing inside the bioreactor. The total working volume was 1 m3 , which allowed residence time of one hour. Mineral nutrients needed for bacteria growth were continuously supplied (N2) from a feed tank that was installed near the SBBR. The temperature of the biological reactor was in the range of 30–35 ◦ C, which was shown to be the optimum range for the bacterial growth [23]. The pH was maintained constant at 7–7.5 by adding HCl. 3.3. Adsorption column (AD) The final treatment step in the process was carried out in the AD packed with granular activated carbon (GAC), with an average particle size of 1.5 mm, obtained from Lobachemie Company, India. The AD step consisted of two parallel columns; each is packed with 250 kg of GAC, providing a total bed volume of 0.5 m3 . The effluent wastewater from the SBBR was send to second settling tank (ST2) as shown in Fig. 1, from which it was pumped to one of the adsorption columns with flow rate of 1 m3 /h. Fig. S3 shows the adsorption column with 1.8 m in length and 0.6 internal diameter (L/D = 3). Once the activated carbon is saturated in the first column, the adsorption process can be directly shifted to the second one. At the same time, steam at 131 ◦ C and 1.5 bar, which is supplied by a steam generator, can be used for regenerating the activated carbon. The treated wastewater is then sent to the final settling tank (ST3) before discharging. 3.4. Settling and collecting tanks As shown in Fig. 1, the settling tank ST1 was placed after the EC unit, to settle the solids and store the resulted treated water before
being pumped into the SBBR. Similar two tanks, ST2 and ST3, were placed after the other two steps to collect the treated water from their respective preceding units. The three tanks were made of PVC, but the maximum capacity of settling tank (ST1) was 3 m3 , which was larger than the other two settling tanks (ST2, ST3), which was 2 m3 . The larger volume of ST1 was required to allow enough residence time for the solids generated at the EC unit to settle, whereas in the other two settling tanks, the amount of particles generated in the proceeding units is much less and hence less settling is needed. Fig. S4 shows a schematic diagram of one of the settling tanks. The effluent was introduced to each tank at a flow rate of 1 m3 /h through the WW inlet (N1), and leaves the tank from the other side (N3). To minimize the level disturbances in the tank and facilitate settling, the input stream was injected into the bottom of the tank through a pipe immersed deep inside the liquid, and the effluent is pumped from the top of the tank as shown in the figure. To control the level of the liquid in tank, the tank is provided with an overflow opening. Therefore, the actual volume in the tank did not exceed the 2 m3 capacity. All tanks were frequently cleaned and water was drained by the drainage (N7). 4. Sampling and analysis At regular time intervals, wastewater samples were collected at the outlets of each treatment unit and analyzed for COD and phenol(s) concentrations. The COD was measured using UV–vis spectrophotometer (DR-5000, Germany), more details about COD analysis can be found elsewhere [24]. Phenols including phenol, o, p- and m-cresol were analyzed using GC-FID (Shemadzu, 2010). Further details about the analytical procedure of the phenol and cresols concentrations are found in previous publications [9,23]. 5. Results and discussions 5.1. Pilot scale performance 5.1.1. COD reduction The reduction in COD was determined at the outlet of each main unit in the PP. Refinery wastewater feed was characterized by its dark greenish color, strong pungent odor and high COD ranging from 3900 to 4800 mg/L. Due to the variation in the feed compositions, the COD was determined in the feed at the beginning of each treatment process. The values of COD after each unit in the treatment process at different time intervals are shown in Fig. 2. The results illustrate that at steady state, an overall cumulative reduction of about 96% was reached during continuous operation of up to 8 h. The pilot plant results showed that EC performance was almost consistent throughout the 8 h of operation, with around 35% reduction in the COD. This is considered a relatively good performance,
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12 2 hrs 4 hrs 6 hrs 8 hrs
4000
3000
2000
1000
Phenol Concentration (mg/l)
COD Concentration (mg/l)
5000
0
EC
SBBR
Fig. 2. The reduction of COD after each treatment step in the pilot plant at different durations of operation.
as EC has been shown to be a good pre-treatment step for removing TDS, TSS and metals, but not for COD [25]. The removal increased by another 20% in the effluents of SBBR unit. It was obvious though that the performance of the SBBR reduced with the operation duration. The COD further dropped by 96% in the effluents of the AD column, which shown more consistent performance than the SBBR. Compared to EC, adsorption process is highly recommended for the reduction of COD in wastewater, and activated carbon was shown to have high capability in this regard [24]. Although applying adsorption as single stage in wastewater treatment may have a high performance in COD reduction, a combination of adsorption with other treatment processes, such as electrocoagulation or biological techniques, was shown to enhance the performance of the former process. Papic´ et al. (2004) tested a two-steps process consisting of Al (III) electocoagulation followed by activated carbon adsorption for wastewater treatment. The process achieved a very high removal of COD from wastewater, reaching up to 90%. Similar results were also obtained using a combination of adsorption and biological treatment, with more than 90% COD reduction, from the treatment of recycled paper wastewater, with initial COD ranging from 4000 to 5000 mg/L [26]. Another study on using GAC adsorption followed by a biological treatment for the reduction of COD in wastewater showed that up to 94.5% reduction was achieved [27]. A more recent investigation applied biological treatment before the adsorption for the treatment of dyeing wastewater and 96% COD reduction was achieved [28]. 5.1.2. Reduction in phenols The wastewater generated from the refinery usually has different types of phenols, namely phenol, and o-, and p- and m-cresols. Cresols are the phenolic compounds which are commonly encountered in refinery wastewater streams. The concentrations of these phenols have been analyzed in the feed stream before the treatment process, and at the output of each main treatment unit. As shown in Figs. 3–5, a complete removal of phenol and -cresols was achieved during 8 h of operation. The main reduction in phenolic pollutants occurred in the SBBR step. Phenol and o-cresol were completely removed within this step, whereas m- and p- cresols were dropped significantly, but were completely removed only in the following AD unit. This agrees with previously reported results, confirming that o-and p-substituted phenols are more degradable than m-substituted phenols [29]. The complete removal by the biological treatment step was achieved by the immobilized P. putida, which have been shown to have a good efficiency in degrading phenol and cresols [9,23]. It is well known that activated carbon has an acceptable performance as a polishing step [30]. However, in the
10
8
6
4
2
0
Ac
Feed
EC
SBBR
AC
Fig. 3. The reduction of phenol after each treatment step at different durations of operation.
80
o-cresol Concentration (mg/l)
Feed
2 hrs 4 hrs 6 hrs 8 hrs
2 hrs 4 hrs 6 hrs 8 hrs
60
40
20
0
Feed
EC
SBBR
AC
Fig. 4. The reduction of o-cresol after each treatment step at different durations of operation.
PP, the AD was not required for the removal of phenols during 8 h of operation. 5.2. Comparison between lab and pilot scale To demonstrate the efficiency of the scaling up process, the cumulative reduction of COD, phenol and cresols after each treatment step in the PP was compared to the laboratory scale results as shown in Figs. 5–8 . It is clearly seen that both, lab-scale and PP, show high performance, with similar overall reduction of contaminants. Phenol and cresols were completely removed and the COD removal percentage was higher than 96%. In addition, the odor was completely removed and the color of the treated water converted from dark green to clear (Table 1). The EC unit in the PP showed slightly lower performance in COD removal compared to that in the lab-scale. However, a much lower performance was observed in removing phenol and cresols. The superior performance of EC in the lab-scale for phenols removal, compared to the PP, was due to the variation in the design of the EC unit in both scales, which have been shown to strongly affect the efficiency of EC process [31]. It is worth noting here that these experimental data were collected near the end of the 10 month operation period when the three step process was optimized. However, the EC unit was disadvantaged due the erosion of
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EC
SBBR
Lab-Scale Pilot-Scale
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Fig. 5. The reduction of m, p-cresol after each treatment step at different durations of operation.
120 100
COD % Reduction
100
0
0
Feed
Lab-Scale Pilot-Scale
80 60 40 20 0
EC
SBBR
AD
Fig. 6. A comparison of cumulative COD reduction after each treatment step in laboratory and Pilot Plant scale.
120
Phenol % Reduction
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p,m-cresol % Reduction
m-, p-cresol Concentration (mg/l)
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Lab-Scale Pilot-Scale
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SBBR
AD
Fig. 8. A comparison of cumulative p,m-cresol reduction after each treatment step in laboratory and Pilot Plant scale.
volumetric flow rate over working volume of around 0.0028 min−1 . Also, temperature of 30 ◦ C and pH of 7 were kept the same in both scales. As compared to the laboratory scale, the SBBR in the PP showed a higher performance in the removal of phenols, where complete removal of phenol and cresols was achieved as shown in Figs. 7. This could be attributed to the major difference in the ratio between PVA particle diameter and bed diameter, which was 0.2 and 0.01 for the lab scale and the pilot scale, respectively; the PVA particle size was the same for both scales (1 cm3 ). The much lower particle-to-bed ratio for the pilot scale reactor led to much better mixing and much less wall-effect. As previously reported [32], the lower PVA particle size seemed to reduce mass transfer limitations and enhance the accessibility of the substrate to the bacteria, which in turn enhanced the biodegradability of the phenolic compounds. The PP adsorption process showed similar performance in removing phenolic compounds and COD as the lab scale. This was expected as the amount of GAC in the AD units PP was scaled up from that of the laboratory scale and operated under similar operating conditions. Similar comparison between PP and laboratory scales was reported in the literature [33]. However, the study was carried out on a single wastewater treatment unit, namely anaerobic digestion process for treatment of swine wastewater and compared a lab-scale of 6 L and a pilot scale of 20 m3 . Similar COD removal percentage was obtained in both scales. 6. Conclusions
60 40 20 0
EC
EC
SBBR
AD
Fig. 7. A comparison of cumulative phenol reduction after each treatment step in laboratory and Pilot Plant scale.
An integrated, three-step wastewater treatment process has been scaled-up to a Pilot Plant (PP) scale, by maintaining the same residence times in each unit as used in the lab scale. The PP was found to be effective in the treatment of highly contaminated refinery wastewater. Similar overall efficiency of the PP, compared to the lab-scale, was achieved. Almost a complete removal of COD and phenols was consistently achieved at the effluent of the last step of the process after up to 8 h of continuous operation. The EC unit was found to be an effective pretreatment step, whereas AD was an effective polishing step. Acknowledgements
the electrodes with time and thus reducing its efficiently by about 20–30% compared to that with new electrodes. The SBBR was scaled up keeping similar operating parameters in PP and laboratory scale. These similar parameters include, residence times of around 1 h, volume percentage of immobilized bacteria of 30%, same specific interfacial area of 180 m2 /m3 and air
The authors would like to acknowledge the financial support provided by the Japan Cooperation Centre, Petroleum (JCCP) and the technical support of the JX Nippon Research Institute Co., Ltd .(JX-NRI). They would also like to thank Koike Tech of Japan for fabrication of the Pilot Plant. Special thanks are due to Abdul Rasheed
Please cite this article in press as: M.H. El-Naas, et al., Petroleum refinery wastewater treatment: A pilot scale study, J. Water Process Eng. (2016), http://dx.doi.org/10.1016/j.jwpe.2016.10.005
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Please cite this article in press as: M.H. El-Naas, et al., Petroleum refinery wastewater treatment: A pilot scale study, J. Water Process Eng. (2016), http://dx.doi.org/10.1016/j.jwpe.2016.10.005