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Performance evaluation of the main units of a refinery wastewater treatment plant – A case study
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JECE 714 1–9 Journal of Environmental Chemical Engineering xxx (2015) xxx–xxx
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Journal of Environmental Chemical Engineering journal homepage: www.elsevier.com/locate/jece
Performance evaluation of the main units of a refinery wastewater treatment plant – A case study
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Carlos E. Santo1, André Fonseca1, Eva Kumar, Amit Bhatnagar, Vítor J.P. Vilar* , Cidália M.S. Botelho, Rui A.R. Boaventura* LSRE - Laboratory of Separation and Reaction Engineering, Departamento de Engenharia Química, Faculdade de Engenharia da Universidade do Porto, Rua Dr. Roberto Frias, Porto 4200-465, Portugal
A R T I C L E I N F O
A B S T R A C T
Article history: Received 7 April 2015 Accepted 11 July 2015
Petroleum refineries generate great amounts of wastewaters which require proper treatment before being discharged into coastal waters or other aquatic systems. The main pollutants present in these industrial wastewaters include suspended particles, biodegradable and refractory organics, hydrocarbons, sulfides, phenols and nitrogen compounds. The performance of the Porto Refinery wastewater treatment plant (WWTP) was evaluated in this study. Five sampling campaigns were carried out at six sampling points of the (WWTP), with the purpose of analyzing the most relevant physicochemical parameters and determining the removal efficiencies in each treatment step and the WWTP overall efficiency. The obtained results show that the Porto Refinery WWTP operates with removal efficiencies higher than 90% for TSS, VSS, TPH, O&G, sulfides and phenols, between 80 and 90% for COD, BOD5 and total nitrogen and around 60% for chlorides. The final effluent meets the discharge limits imposed by the Portuguese legislation. A correlation analysis between the most relevant parameters under study was performed, which contributes to define a reliable monitoring plan based on a limited number of parameters, and provides valuable information regarding the process efficiency, at low cost, to the WWTP managers. ã 2015 Published by Elsevier Ltd.
Keywords: Petroleum refinery wastewater Physicochemical parameters Removal efficiency TPH COD
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Introduction
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Petroleum refineries use a lot of complex refining processes to convert crude oil into a large number of refined products, which include gasoline, liquefied petroleum gas, aviation fuel, and kerosene [1]. These processes require large quantities of water and also generate a significant amount of wastewaters (0.4– 1.6 times the volume of processed oil) [2]. Although the contaminants present in the refinery wastewaters depend on the process configuration [3], high concentrations of emulsified oil, phenols, sulfides, mercaptans, cyanides, ammoniacal nitrogen, hydrogen sulfide and some micropollutants are typically present in oil refinery wastewaters [4]. Thus, these industrial wastewaters are often toxic and a major source of environmental health hazard, requiring an adequate treatment before being discharged into water bodies.
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* Corresponding author. Fax: +351 225081674. E-mail addresses: [email protected] (V.J.P. Vilar), [email protected] (R.A.R. Boaventura). 1 The first two authors made equal contribution in this work and are both equally considered as first author.
Nowadays, wastewater treatment plants are facing new challenges to comply with tighter wastewater discharge limits [5]. New regulations to ensure water resources protection originate an increasing complexity of WWTPs through the integration of new and more efficient technologies [6]. The conventional treatment of oil refinery wastewaters involves a sequence of mechanical and physicochemical operations (gravity separators for oil removal, dissolved air flotation (DAF)) followed by a biological treatment. To achieve the discharge limits imposed by legislation, several other treatment processes, namely, Fenton oxidation [7], photocatalytic oxidation [8], ozonation [9] and electrochemical methods [10] have been strongly explored in refinery WWTPs throughout the world. Porto oil refinery (Galp Energia) produces a large variety of derivatives or aromatic products, and important raw materials for the chemical and petrochemical Portuguese industry. It processes two types of crude oil: SOUR (low sulfur content <0.5%) and SWEET (high sulfur content >1.5%). In the present work, the performance of the different treatment units of the Porto oil refinery WWTP (Galp Energia) was evaluated, based on the analysis of several physicochemical parameters. Five sampling campaigns were carried out during 2 years (dry and wet
http://dx.doi.org/10.1016/j.jece.2015.07.011 2213-3437/ ã 2015 Published by Elsevier Ltd.
Please cite this article in press as: C.E. Santo, et al., Performance evaluation of the main units of a refinery wastewater treatment plant – A case study, J. Environ. Chem. Eng. (2015), http://dx.doi.org/10.1016/j.jece.2015.07.011
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seasons) at six sampling points of the WWTP, being possible to determine the removal efficiency of TSS, VSS, TPH, O&G, BOD5, COD, sulfides, phenols, total nitrogen and chlorides in each treatment step and the WWTP overall efficiency. A correlation analysis between the most relevant parameters was performed, providing valuable information to achieve a reliable monitoring plan based on a limited number of parameters, and valuable information, at low cost, to the WWTP managers, as regards the process efficiency. Wastewater treatment procedure at Porto refinery WWTP The Porto refinery wastewater is a mixture of all wastewaters generated in the facility network, including domestic sewage. The refinery WWTP (Unit 7000) has a treatment capacity of 450 m3/h and includes preliminary, primary, physicochemical and biological treatment units as well as storm basins with a capacity of 10,000 m3. The final effluent is discharged into the sea after treatment and the sludge produced is removed from the facility by an authorized contractor. A simplified diagram of the wastewater and sludge treatment, including the various units of the WWTP, is shown in Fig. 1. The liquid phase treatment involves four stages: pre-treatment, physicochemical treatment, biological treatment and advanced treatment. In the pre-treatment stage, most of the oil is separated from water in API (American Petroleum Institute) primary oil Q3 water gravity separators and parallel-plates-interceptors (PPIs). Settled sludge is also removed from these pre-separators. The retention of excess flow in the storm basins is also regulated during the pre-treatment. The physicochemical treatment comprises neutralization, coagulation and flotation, for pH correction and elimination of sulfides, suspended solids and residual
hydrocarbons. The biological treatment is the conventional activated sludge process, which takes place in two separate units working in parallel, for the removal of biodegradable organics. The advanced treatment, for water re-use in the refinery, involves clarification, chlorination, mechanical aeration and filtration. The sludge treatment involves two stages: thickening and clarification. The sludge produced at the facility is elevated to a gravity thickener. After thickening, the sludge is dewatered and then stored in containers before final disposal. The water resulting from the dewatering process is forwarded to the inlet of the WWTP. In the clarification process, the oil collected at different treatment stages is stored, after proper conditioning, or forwarded to the oil recovery slops.
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Sampling points and sampling periods
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Six sampling points from Porto refinery WWTP were selected for collecting wastewater samples: (1) outlet of parallel-platesinterceptors (PPIs); (2) outlet of the sulfide oxidation and coagulation chamber (SOCC); (3) outlet of the dissolved air flotation tank (DAF); (4) outlet of the activated sludge reactor (ASR); (5) outlet of the secondary settling tank (SSR); (6) outlet of the mechanical aeration basin (MAB) (Fig. 1). The typical operation parameters of the main treatment process are shown in Table 1. The WWTP operates at a flow-rate of approximately 300 and 450 m3/h for dry and wet season, respectively. Therefore, five sampling campaigns were carried out in different times of the year (Campaigns A–C in the dry season and Campaigns D and E in the wet season): Campaign A: 18/7/2006; Campaign B: 25/6/2007; Campaign C: 14/8/2007; Campaign D: 10/10/2007; Campaign E: 3/ 12/2007.
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Fig. 1. Schematic diagram of the refinery wastewater treatment plant.
Please cite this article in press as: C.E. Santo, et al., Performance evaluation of the main units of a refinery wastewater treatment plant – A case study, J. Environ. Chem. Eng. (2015), http://dx.doi.org/10.1016/j.jece.2015.07.011
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Table 1 Typical operation parameters of the main treatment process. Main treatment units—parameters Oil pre-separators (CB 7031 A/B) Maximum flow rate in rainy days Residence time Hydraulic loading rate
450 m h 33 min 18 m h-1
Oil Separators (CB 7004 A 1/2/3 e CB 7004 1/2/4) Total flow rate for both separators (PPIs and APIs)
453 m3 h-1
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Sulfide Oxidation and Coagulation Chamber (SOCC) (CB 7035/7036) Flow rate 453 m3 h-1 Residence time 4 min Dissolved air flotation tank (DAF) (CB 7037) Maximum hydraulic loading rate, with recirculation Recirculation rate Residence time Maximum saturation pressure
4.2 m h 40% of Max. effluente 62 min 4.5 atm
Floculator-clarifier (CB 7071) Flow rate Residence time
453 m3 h-1 16 min
Activated sludge reactor (ASR) (CB 7041) Volume Flow rate Recycle BOD5loading rate BOD5removal BOD5specific loading rate MLSS concentration MLVSS concentration Residence time Oxygen uptake rate
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1606 m 350 m3 h-1 0.5 m3 h-1 1176 kg d-1 82.20% 0.245 kg/kg MLSS d-1 3 kg m-3 2.1 kg m-3 4.6 h 62 kg h-1
Secondary sludge reactor (SSR) (CB 7042) Flow rate with recirculation Hydraulic loading rate Residence time
550 m h 0.88 m h-1 2.5 h
Sludge thickener (CB 7011) Flow rate Water percentage in sludge (inlet) Specific mass loading rate Residence time
4.22 m3 h-1 98.75% 22.5 kg/kg MLSS d m2 47 h
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The main physicochemical characteristics of the wastewater samples were determined according to Standard Methods for the Examination of Water and Wastewater [11] (Table 2). Due to the high oil content in the wastewater samples, it was necessary to centrifuge the samples for 15 min prior to the analysis of total nitrogen. Two samples were withdrawn from each sampling point and the mean values for each parameter are presented.
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Results and discussion
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Wastewater physicochemical characteristics
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The pH of the wastewater is a critical parameter that needs to be controlled within a specific range depending on each treatment unit, in order to achieve the maximum removal efficiency of the target pollutants. The highest pH values (7.93 and 8.29) were found at the outlet of PPIs in campaigns B and C (Fig. 2(a)). A low pH value (ca. 5.0) was found in the effluent from ASR and SSR units, in campaign E, which slightly reduced the BOD5 and COD removal efficiency in the activated sludge reactor. At WWTP outlet the pH was always within the discharge limit range (6–9). The concentration of total suspended solids (TSS) (Fig. 2(b)) at the outlet of PPIs unit was different in campaigns A, D and E, but very similar concentrations were found in campaigns B and C. The reported variation in TSS concentration might be due to the flow rate and/or pollutant load associated with the rainfall run-off, as sampling campaigns undertaken in winter season (campaigns D and E) showed much higher concentrations of TSS. The VSS exhibited a similar concentration pattern (Fig. 2(c)). Although, there was a considerable variation in VSS concentration among the different campaigns, in the initial treatment stages, the variation decreased throughout the treatment process, reaching a final average value below 15 mg/L. The TPH concentration (Fig. 2(d)) varied considerably at the outlets of PPIs and sulfide oxidation and coagulation chamber (SOCC). High TPH concentrations were found in the samples from campaigns D and E, even at the outlet of the mechanical aeration basin (MAB), where 14.2 and 16.1 mg/L of TPH, respectively, were measured. Nevertheless, these concentrations are below the daily maximum discharge limits (20 mg/L). Oil and grease (O&G) concentration showed a pattern similar to TPH in campaigns D and
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Table 2 Analytical methods and equipments used in the present study. Parameter
Method
Apparatus
Range
Make/model
Reference bibliographic
pH TSS VSS TPH
Electrometry Gravimetry Gravimetry Partition-infrared spectrometry Partition-infrared spectrometry Partition-gravimetry K2Cr2O7; open reflux Dilutions Catalytic oxidation
pH Meter Balance Balance Spectrophotometer
– 0.5 mg/L 0.5 mg/L 0.1 mg/L
Hanna instruments – – Bomem Arid-zone 540
Standard methods [17] APHA 4500-H Standard methods (1998) APHA 2540-D Standard Methods (1998) APHA 2540-E Standard Methods [17] APHA 5520-F
Spectrophotometer balance
0.1 mg/L 0.5 mg/L
–
10 mg O2/L <1.0 mg O2/L 0–25 mg/L 25–100 mg/L 0.01 mg/L 1 mg NO3 /L
G. VITTADINI ORION 97-08-00 Shimadzu 5000 A
Oil & grease
Sulfide Total nitrogen Phenols
Iodometry Persulfate/brucine
Digester DO electrode Total organic carbon analyzer – Spectrophotometer
Extraction with chloroform
Spectrophotometer
0.5 mg/L
Chlorides
Argentometry
–
0.5 mg Cl /L
Electrical conductivity
Conductimetry
Conductivimeter
0.1 ms/cm
COD BOD5 TOC
Standard methods [17] APHA 5520-B Standard methods (1998) APHA 5210-B Standard methods [17] APHA 5310-A
– Standard methods (1998) APHA 4520-F PYE UNICAM PU 8600 Standard methods (1998) APHA 4500-N UV/VIS PYE UNICAM PU 8600 UV/ [18] VIS – Standard methods (1998) APHA 4500Cl B Hanna instruments Standard methods (1998) APHA 2510-A
Please cite this article in press as: C.E. Santo, et al., Performance evaluation of the main units of a refinery wastewater treatment plant – A case study, J. Environ. Chem. Eng. (2015), http://dx.doi.org/10.1016/j.jece.2015.07.011
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Fig. 2. Level of contaminants at the outlet of the different unit operations within the plant. Outlet of PPI’s (1), outlet of SOCC (2), outlet of DAF tank (3), outlet of ASR (4), outlet of SSR tank (5), outlet of MAB (6).
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E, exhibiting slightly higher values than in the other campaigns (Fig. 2(e)). The results showed that the concentration of O&G was high at the outlet of the separators (API and PPIs), which can negatively affect the removal of some pollutants downstream, such as sulfides and phenols.
The chemical oxygen demand (COD) in the effluents from the different units also increased in campaigns D and E (Fig. 2(f)). However, even in these campaigns, the COD of the final effluent (MAB effluent) was below the maximum daily discharge limit (300 mg/L). The biochemical oxygen demand (BOD5) was also higher in
Please cite this article in press as: C.E. Santo, et al., Performance evaluation of the main units of a refinery wastewater treatment plant – A case study, J. Environ. Chem. Eng. (2015), http://dx.doi.org/10.1016/j.jece.2015.07.011
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Fig. 2. (Continued) 150 151 152 153 154
campaigns D and E at the outlet of all units (Fig. 2(g)), but the maximum values at the WWTP outlet (MAB effluent) were 42.4 and 52.7 mg/L, which are below the daily discharge limit value (80 mg/L). The highest sulfide (S2 ) concentrations were observed at the outlet of PPIs in campaigns D and E (140.6 and 147.3 mg/L,
respectively). However, the sulfide concentration in the final effluent was always below the daily discharge limit (2.0 mg/L) (Fig. 2(h)). Lower removal efficiency in the sulfide oxidation and coagulation chamber (SOCC) and/or dis-functioning of some equipment in the WWTP units might be the probable cause for
Please cite this article in press as: C.E. Santo, et al., Performance evaluation of the main units of a refinery wastewater treatment plant – A case study, J. Environ. Chem. Eng. (2015), http://dx.doi.org/10.1016/j.jece.2015.07.011
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Fig. 3. Removal efficiency of different constituents along the treatment process: SOCC-DAF-ASR-SSR-MAB.
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some slight increase in sulfide concentration at the final treatment stage (MAB unit). Moreover, the pre-treatment step (PPIs and APIs) is critical for the removal of heterogeneous components from the wastewater, since a low performance of that treatment step can strongly impair the subsequent biological operation [12,13]. Total nitrogen was also measured in the effluents from the different units. The results showed a gradual reduction in the total nitrogen concentration as the treatment progressed (Fig. 2(i)). However, TN concentration increased in the effluents from ASR, SSR and MAB units, which is attributed to the introduction of domestic sewage in the activated sludge biological reactor, to ensure that the biodegradation of organic matter is not limited by the lack of nutrients. Industrial wastewaters are normally deficient in nitrogen and phosphorus. Therefore, these nutrients need to be added to attain the correct ratio C/N/P for microbial growth. The addition of biodegradable soluble organic matter improves the removal of hard COD as also provides sufficient carbon source for denitrification. The domestic sewage is introduced at this stage since normal refinery operation does not always generate constant and predictable flow-rates or waste streams of the same quality. The phenol concentration (Fig. 2(j)) gradually decreased throughout the process and its content in the effluent from the MAB unit is in the range 0.03–0.2 mg/L, below the daily discharge limit (1.0 mg/L). Alike the behavior of TN concentration in the entire treatment, chloride concentration also slightly increased in the effluent downstream from ASR in all campaigns (Fig. 2(k)), which is also
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related to the introduction of domestic sewage in the ASR. In the subsequent treatment units, the chloride concentration was relatively constant. Similarly, electrical conductivity results also exhibit an increase in the effluent from the ASR unit and subsequent units in all sampling campaigns (Fig. 2(l)). This is the result of the addition of ferric sulfate, sodium hydroxide and sodium triphosphate, as well as domestic sewage, to the biological reactor. The storm basins receive the excess effluent in order to operate the plant at approximately constant conditions. The addition to the industrial effluent is done automatically and the quality of the storm-water is assumed to be the same as the effluent.
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Performance of individual processes for the removal of various contaminants
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Fig. 3(a) shows TSS removal efficiencies of 20–63% in the dissolved air flotation tank, secondary sedimentation tank and mechanical aeration basin, during the five sampling campaigns. The TSS removal efficiency in DAF unit was lower than in SSR and MAB units. Increased efficiency can be achieved by using parallel plate clarifiers, which increase the effective settling area while reducing the distance solids must travel before reaching the collection surface, therefore enhancing the separation efficiency of the DAF process [14]. Fig. 3(b) shows that higher removal efficiency of TPH was obtained in the dissolved air flotation unit (DAF), secondary
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Fig. 4. Relation between the parameters during the treatment process.
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sedimentation tank (SSR) and mechanical aeration basin (MAB). The MAB unit exhibited the highest removal of TPH, due to the degradation of hydrocarbons by the oxygenase-catalyzed reactions in the presence of molecular oxygen [15]. Fig. 3(c) showed that a high O&G removal was achieved in MAB unit after the pre-treatment stage (APIs and PPIs). Proper operation of the downstream treatment processes, requires that API units achieve effluent oil concentrations in the range 50–200 mg/L [16]. The COD and BOD5 removal efficiencies for the individual processes are presented in Fig. 3(d) and (e). The performance of DAF unit, where the wastewater is clarified by the removal of suspended matter such as oils and solids, is lower than that of SSR and MAB units as regards BOD5 and COD removal. The presence of hydrocarbons in relatively high concentrations (ca. 100 mg/L) in the activated sludge reactor (ASR), negatively affects the COD and BOD5 removal efficiency (average removals of 25% and 23% for BOD5 and COD, respectively). The estimated BOD5 and COD (around 200–300 mg/L and 400–600 mg/L, respectively) of the domestic sewage introduced into the activated sludge reactor are close to the ones associated with the flow coming from the DAF (average values of 165 and 373 mg/L, respectively). Thus the low COD and BOD5 removal efficiencies in the ASR are not probably due to not accounting for the induced raw sewage in the reactor, in the calculation of the removal efficiencies in this treatment unit. A likely reason for the low efficiency of the ASR in removing BOD5 and COD is the low recirculation rate of sludge (0.5 m3/h). The typical return activated sludge recycle (RAS) ratio is between 0.25 and 1.00 whereas in the present situation is only 0.0014 (0.5 m3/h/350 m3/h). With this RAS ratio it is almost impossible to attain the required MLSS content in the reactor (3 kg/m3, as indicated in Table 1). In fact, the average value of TSS and VSS out of the ASR are 241 and 106 mg/L, respectively, as shown in Fig. 2(b) and (c). Assuming good mixing conditions, the TSS and VSS concentrations inside the reactor will be the same. So, the bad performance of the ASR is due to the low concentration of biomass (VSS) in the reactor. Nonetheless the concentrations of COD and
BOD5 at the outlet of the WWTP are below the discharge limits and the major contribution to the observed reduction (above 50%) is given by ASR, SSR and MAB units. As expected, a high sulfide removal efficiency (74–80%) was achieved in the SOCC unit, in all sampling campaigns (Fig. 3(f)). In the downstream DAF unit a significant removal of sulfide (60–72%) was also attained. The overall removal efficiency of phenol varied in the range 32– 50% considering all the campaigns (Fig. 3(g)). Fig. 4 shows the correlations between several wastewater constituents. The VSS concentration throughout the treatment process presents a linear relationship with TSS content and VSS contributes by nearly 74% to TSS (Fig. 4(a)). A strong correlation between TPH and VSS was found, indicating that about 70% of VSS correspond to hydrocarbons particles (Fig. 4(b)). Fig. 4(c) shows that TPH and O&G are also strongly correlated. The concentration of TPH is about 60% of O&G content, which was expected since TPH contributes to the O&G concentration. The presence of TPH gives an indication about the risk of oil refinery wastewaters to humans and the environment. The difference between O&G and TPH represents the polar fraction. Comparing the initial O&G and TPH values, the polar fraction is in the range 25–44%. It is worthy to mention that a high O&G content affects negatively some wastewater treatment processes, namely the biological aerobic processes. Fig. 4(d) shows a strong correlation between BOD5 and COD. In this study, BOD5 represents about 44% of COD (COD/BOD5 2.3), which indicates a moderate biodegradability of the wastewater.
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WWTP efficiency
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Fig. 5 shows overall removal efficiencies in the range 87–99% for most constituents (TSS, VSS, TPH, O&G, COD, BOD5, sulfides and phenols), along the five campaigns. The values did not vary much from one campaign to another. Chloride and total nitrogen were eliminated at a lesser extent, corresponding to removal rates of 56– 68% and 68–86%, respectively. Table 3 shows that along the five
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Fig. 5. WWTP removal efficiency of the studied parameters for all five campaigns.
Please cite this article in press as: C.E. Santo, et al., Performance evaluation of the main units of a refinery wastewater treatment plant – A case study, J. Environ. Chem. Eng. (2015), http://dx.doi.org/10.1016/j.jece.2015.07.011
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Table 3 Concentration of pollutants at the outlet of the WWTP and daily discharge limits (DDL). Parameter
pH TSS O&G TPH COD BOD5 Sulfide Total nitrogen Phenols a
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– mg/L mg/L mg/L mg/L mg/L mg/L mg/L mg/L
1 7.2 49.7 10.2 7.6 86 24.4 0.8 12.1 0.04
2 7.11 40.5 8.7 3.9 95 26.8 1 10.8 0.03
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Conclusions
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The performance evaluation of the main units of the Porto Refinery WWTP is addressed in the present study. The sulfide removal efficiencies in the sulfide oxidation unit were high but below 80%. Relatively low COD and BOD5 removal efficiencies were achieved in the biological treatment process (activated sludge reactor), when compared to the other units. The entire treatment process is effective for the removal of main pollutants present in the refinery wastewater with the exception of total nitrogen and chlorides. The average removal efficiencies in the WWTP were as follows: 96.7% for TSS, 99.1% for TPH, 99.1% for O&G, 87.3% for COD, 90.5% for BOD5, 99% for sulfides, 68% for total nitrogen, 94.6% for phenols and 62.8% for chlorides. The linear correlations between some of the analyzed parameters showed that: 70% of the VSS correspond to hydrocarbons particles; TPH contributes to O&G by 60% and BOD5 represents about 44% of COD, which indicates a moderate biodegradability of the wastewater. TSS content can be used as a good indicator for VSS, TPH and O&G contents, using the linear relationships obtained in this study, then avoiding unnecessary costs for chemical analysis. TSS can also selected as an operational parameter to control the removal of TPH and O&G along the WWTP.
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Acknowledgements
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This work was co-financed by FCT/MEC,FEDER under Programe PT2020 (Project UID/EQU/50020/2013). C. Santos and André Fonseca acknowledge their PhD scholarship awarded by FCT (SFRH/BD/15342/2005 and SFRH/BD/69654/2010, respectively). Amit Bhatnagar also acknowledges his Post-Doc scholarship awarded by FCT (SFRH/BPD/62889/2009). V.J.P. Vilar acknowledges the FCT Investigator 2013 Programme (IF/01501/2013).
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References
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292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309
313 314 315 316 317
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3 7.37 45.4 6.4 2.7 105.5 38.5 1.4 9.3 0.09
4 7.02 50.5 21.3 14.2 112.5 42.4 1.6 16.3 0.08
5 6.95 58 22 16.1 145 52.7 1.8 20.5 0.2
6.0–9.0 120 30 30 300 80 2 30 1
DDL— daily discharge limits.
campaigns all parameters met the daily discharge limits allowed by the Portuguese legislation. It must be emphasized that, according to the legislation, the discharge limit is to be applied to the average monthly value, i.e., the arithmetic mean of the average daily values. The daily value, based on a representative sample of the wastewater discharged during a period of 24 h, must not exceed the double the average monthly value. This means that the daily discharge limits can be, at most, twice the discharge limits established by the legislation.
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DDLa decree-law no. 236/98
WWTP outlet (campaigns)
[2] A. Coelho, A.V. Castro, M. Dezotti, G.L. Sant’Anna Jr, Treatment of petroleum 322 refinery sourwater by advanced oxidation processes, J. Hazard. Mater. 137 (1) 323 (2006) 178–184, doi:http://dx.doi.org/10.1016/j.jhazmat.2006.01.051. 324 16530949. [3] Q.J. Rasheed, K. Pandian, K. Muthukumar, Treatment of petroleum refinery 325 wastewater by ultrasound-dispersed nanoscale zero-valent iron particles, 326 Ultrason. Sonochem. 18 (5) (2011) 1138–1142, doi:http://dx.doi.org/10.1016/j. 327 ultsonch.2011.03.015. 21507703. [4] Q.J. Rasheed, Effect of additive agents on sono-degradation petroleum refinery 328 wastewater, Hydrol. Curr. Res. 02 (01) (2011) , doi:http://dx.doi.org/10.4172/ 329 2157-7587.1000109. [5] F. Corona, M. Mulas, H. Haimi, L. Sundell, M. Heinonen, R. Vahala, Monitoring 330 nitrate concentrations in the denitrifying post-filtration unit of a municipal 331 wastewater treatment plant, J. Proc. Contr. 23 (2) (2013) 158–170, doi:http:// 332 dx.doi.org/10.1016/j.jprocont.2012.09.011. [6] A.M. Nagy-Kiss, G. Schutz, Estimation and diagnosis using multi-models with 333 application to a wastewater treatment plant, J. Proc. Contr. 23 (10) (2013) 334 1528–1544, doi:http://dx.doi.org/10.1016/j.jprocont.2013.09.027. [7] A.L. Barros, T.M. Pizzolato, E. Carissimi, I.A.H. Schneider, Decolorizing dye 335 wastewater from the agate industry with Fenton oxidation process, Miner. 336 Eng. 19 (1) (2006) 87–90, doi:http://dx.doi.org/10.1016/j.mineng.2005.04.004. [8] M.L. Brooks, J.S. Meyer, D.M. McKnight, Photooxidation of wetland and riverine 337 dissolved organic matter: altered copper complexation and organic compo338 sition, Hydrobiologia 579 (1) (2007) 95–113, doi:http://dx.doi.org/10.1007/ 339 s10750-006-0387-6. [9] S. Esplugas, D.M. Bila, L.G.T. Krause, M. Dezotti, Ozonation and advanced 340 oxidation technologies to remove endocrine disrupting chemicals (EDCs) and 341 pharmaceuticals and personal care products (PPCPs) in water effluents, J. 342 Hazard. Mater. 149 (3) (2007) 631–642, doi:http://dx.doi.org/10.1016/j.jhaz343 mat.2007.07.073. 17826898. [10] C. Carlesi Jara, D. Fino, V. Specchia, G. Saracco, P. Spinelli, Electrochemical 344 removal of antibiotics from wastewaters, Appl. Catal. B Environ. 70 (1–4) 345 (2007) 479–487, doi:http://dx.doi.org/10.1016/j.apcatb.2005.11.035. [11] APHA, American water works association and water pollution control federation, Standard Methods for the Examination of Water and Wastewater, 20th Q6 346 347 edition, APHA, AWWA, WEF, Washington, D.C, 1998. an, R. Özcımder, Wastewater treatment at the petroleum [12] Ş. Demırcı, B. Erdog 348 refinery, Kirikkale, Turkey using some coagulants and Turkish clays as co349 agulant aids, Water Res. 32 (11) (1998) 3495–3499, doi:http://dx.doi.org/ 350 10.1016/S0043-1354(98)00111-0. [13] L. Altaş, H. Büyükgüngör, Sulfide removal in petroleum refinery wastewater by 351 chemical precipitation, J. Hazard. Mater. 153 (1–2) (2008) 462–469, doi:http:// 352 dx.doi.org/10.1016/j.jhazmat.2007.08.076. 17913353. [14] J.P. Guyer, Introduction to Preliminary Wastewater Treatment, (2011) . [15] E.Y. Hwang, J.S. Park, J.D. Kim, W. Namkoong, Effects of aeration mode on the 353 composting of diesel-contaminated soil, J. Ind. Eng. Chem. 12 (2006) 694–701. [16] S.C. Nayar, N.D. Sylvester, Control of phenol in biological reactors by addition of 354 powdered activated carbon, Water Res. 13 (2) (1979) 201–205, doi:http://dx. 355 doi.org/10.1016/0043-1354(79)90093-9. [17] L.S. Clesceri, A.E. Greenberg, A.D. Eaton, Standard Methods for Examination of 356 Water & Wastewater, 21th edition, (2005) American Public Health Association 357 (APHA), American Water Works Association (A.W.W.A.) & Water Environment 358 Federation (WEF). [18] AFNOR, 1976. Norme Experimentale, Essais des Eaux, Détermination de l 359 ’indice phénol.
ütveren, Treatment of petroleum refinery [1] Y. Yavuz, A.S. Koparal, Ü.B. Ög wastewater by electrochemical methods, Desalination 258 (1–3) (2010) 201– 205, doi:http://dx.doi.org/10.1016/j.desal.2010.03.013.
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Contents lists available at ScienceDirect
Journal of Environmental Chemical Engineering journal homepage: www.elsevier.com/locate/jece
Performance evaluation of the main units of a refinery wastewater treatment plant – A case study
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Carlos E. Santo1, André Fonseca1, Eva Kumar, Amit Bhatnagar, Vítor J.P. Vilar* , Cidália M.S. Botelho, Rui A.R. Boaventura* LSRE - Laboratory of Separation and Reaction Engineering, Departamento de Engenharia Química, Faculdade de Engenharia da Universidade do Porto, Rua Dr. Roberto Frias, Porto 4200-465, Portugal
A R T I C L E I N F O
A B S T R A C T
Article history: Received 7 April 2015 Accepted 11 July 2015
Petroleum refineries generate great amounts of wastewaters which require proper treatment before being discharged into coastal waters or other aquatic systems. The main pollutants present in these industrial wastewaters include suspended particles, biodegradable and refractory organics, hydrocarbons, sulfides, phenols and nitrogen compounds. The performance of the Porto Refinery wastewater treatment plant (WWTP) was evaluated in this study. Five sampling campaigns were carried out at six sampling points of the (WWTP), with the purpose of analyzing the most relevant physicochemical parameters and determining the removal efficiencies in each treatment step and the WWTP overall efficiency. The obtained results show that the Porto Refinery WWTP operates with removal efficiencies higher than 90% for TSS, VSS, TPH, O&G, sulfides and phenols, between 80 and 90% for COD, BOD5 and total nitrogen and around 60% for chlorides. The final effluent meets the discharge limits imposed by the Portuguese legislation. A correlation analysis between the most relevant parameters under study was performed, which contributes to define a reliable monitoring plan based on a limited number of parameters, and provides valuable information regarding the process efficiency, at low cost, to the WWTP managers. ã 2015 Published by Elsevier Ltd.
Keywords: Petroleum refinery wastewater Physicochemical parameters Removal efficiency TPH COD
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Introduction
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Petroleum refineries use a lot of complex refining processes to convert crude oil into a large number of refined products, which include gasoline, liquefied petroleum gas, aviation fuel, and kerosene [1]. These processes require large quantities of water and also generate a significant amount of wastewaters (0.4– 1.6 times the volume of processed oil) [2]. Although the contaminants present in the refinery wastewaters depend on the process configuration [3], high concentrations of emulsified oil, phenols, sulfides, mercaptans, cyanides, ammoniacal nitrogen, hydrogen sulfide and some micropollutants are typically present in oil refinery wastewaters [4]. Thus, these industrial wastewaters are often toxic and a major source of environmental health hazard, requiring an adequate treatment before being discharged into water bodies.
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* Corresponding author. Fax: +351 225081674. E-mail addresses: [email protected] (V.J.P. Vilar), [email protected] (R.A.R. Boaventura). 1 The first two authors made equal contribution in this work and are both equally considered as first author.
Nowadays, wastewater treatment plants are facing new challenges to comply with tighter wastewater discharge limits [5]. New regulations to ensure water resources protection originate an increasing complexity of WWTPs through the integration of new and more efficient technologies [6]. The conventional treatment of oil refinery wastewaters involves a sequence of mechanical and physicochemical operations (gravity separators for oil removal, dissolved air flotation (DAF)) followed by a biological treatment. To achieve the discharge limits imposed by legislation, several other treatment processes, namely, Fenton oxidation [7], photocatalytic oxidation [8], ozonation [9] and electrochemical methods [10] have been strongly explored in refinery WWTPs throughout the world. Porto oil refinery (Galp Energia) produces a large variety of derivatives or aromatic products, and important raw materials for the chemical and petrochemical Portuguese industry. It processes two types of crude oil: SOUR (low sulfur content <0.5%) and SWEET (high sulfur content >1.5%). In the present work, the performance of the different treatment units of the Porto oil refinery WWTP (Galp Energia) was evaluated, based on the analysis of several physicochemical parameters. Five sampling campaigns were carried out during 2 years (dry and wet
http://dx.doi.org/10.1016/j.jece.2015.07.011 2213-3437/ ã 2015 Published by Elsevier Ltd.
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seasons) at six sampling points of the WWTP, being possible to determine the removal efficiency of TSS, VSS, TPH, O&G, BOD5, COD, sulfides, phenols, total nitrogen and chlorides in each treatment step and the WWTP overall efficiency. A correlation analysis between the most relevant parameters was performed, providing valuable information to achieve a reliable monitoring plan based on a limited number of parameters, and valuable information, at low cost, to the WWTP managers, as regards the process efficiency. Wastewater treatment procedure at Porto refinery WWTP The Porto refinery wastewater is a mixture of all wastewaters generated in the facility network, including domestic sewage. The refinery WWTP (Unit 7000) has a treatment capacity of 450 m3/h and includes preliminary, primary, physicochemical and biological treatment units as well as storm basins with a capacity of 10,000 m3. The final effluent is discharged into the sea after treatment and the sludge produced is removed from the facility by an authorized contractor. A simplified diagram of the wastewater and sludge treatment, including the various units of the WWTP, is shown in Fig. 1. The liquid phase treatment involves four stages: pre-treatment, physicochemical treatment, biological treatment and advanced treatment. In the pre-treatment stage, most of the oil is separated from water in API (American Petroleum Institute) primary oil Q3 water gravity separators and parallel-plates-interceptors (PPIs). Settled sludge is also removed from these pre-separators. The retention of excess flow in the storm basins is also regulated during the pre-treatment. The physicochemical treatment comprises neutralization, coagulation and flotation, for pH correction and elimination of sulfides, suspended solids and residual
hydrocarbons. The biological treatment is the conventional activated sludge process, which takes place in two separate units working in parallel, for the removal of biodegradable organics. The advanced treatment, for water re-use in the refinery, involves clarification, chlorination, mechanical aeration and filtration. The sludge treatment involves two stages: thickening and clarification. The sludge produced at the facility is elevated to a gravity thickener. After thickening, the sludge is dewatered and then stored in containers before final disposal. The water resulting from the dewatering process is forwarded to the inlet of the WWTP. In the clarification process, the oil collected at different treatment stages is stored, after proper conditioning, or forwarded to the oil recovery slops.
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Sampling points and sampling periods
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Six sampling points from Porto refinery WWTP were selected for collecting wastewater samples: (1) outlet of parallel-platesinterceptors (PPIs); (2) outlet of the sulfide oxidation and coagulation chamber (SOCC); (3) outlet of the dissolved air flotation tank (DAF); (4) outlet of the activated sludge reactor (ASR); (5) outlet of the secondary settling tank (SSR); (6) outlet of the mechanical aeration basin (MAB) (Fig. 1). The typical operation parameters of the main treatment process are shown in Table 1. The WWTP operates at a flow-rate of approximately 300 and 450 m3/h for dry and wet season, respectively. Therefore, five sampling campaigns were carried out in different times of the year (Campaigns A–C in the dry season and Campaigns D and E in the wet season): Campaign A: 18/7/2006; Campaign B: 25/6/2007; Campaign C: 14/8/2007; Campaign D: 10/10/2007; Campaign E: 3/ 12/2007.
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Fig. 1. Schematic diagram of the refinery wastewater treatment plant.
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Table 1 Typical operation parameters of the main treatment process. Main treatment units—parameters Oil pre-separators (CB 7031 A/B) Maximum flow rate in rainy days Residence time Hydraulic loading rate
450 m h 33 min 18 m h-1
Oil Separators (CB 7004 A 1/2/3 e CB 7004 1/2/4) Total flow rate for both separators (PPIs and APIs)
453 m3 h-1
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-1
Sulfide Oxidation and Coagulation Chamber (SOCC) (CB 7035/7036) Flow rate 453 m3 h-1 Residence time 4 min Dissolved air flotation tank (DAF) (CB 7037) Maximum hydraulic loading rate, with recirculation Recirculation rate Residence time Maximum saturation pressure
4.2 m h 40% of Max. effluente 62 min 4.5 atm
Floculator-clarifier (CB 7071) Flow rate Residence time
453 m3 h-1 16 min
Activated sludge reactor (ASR) (CB 7041) Volume Flow rate Recycle BOD5loading rate BOD5removal BOD5specific loading rate MLSS concentration MLVSS concentration Residence time Oxygen uptake rate
-1
3
1606 m 350 m3 h-1 0.5 m3 h-1 1176 kg d-1 82.20% 0.245 kg/kg MLSS d-1 3 kg m-3 2.1 kg m-3 4.6 h 62 kg h-1
Secondary sludge reactor (SSR) (CB 7042) Flow rate with recirculation Hydraulic loading rate Residence time
550 m h 0.88 m h-1 2.5 h
Sludge thickener (CB 7011) Flow rate Water percentage in sludge (inlet) Specific mass loading rate Residence time
4.22 m3 h-1 98.75% 22.5 kg/kg MLSS d m2 47 h
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3
The main physicochemical characteristics of the wastewater samples were determined according to Standard Methods for the Examination of Water and Wastewater [11] (Table 2). Due to the high oil content in the wastewater samples, it was necessary to centrifuge the samples for 15 min prior to the analysis of total nitrogen. Two samples were withdrawn from each sampling point and the mean values for each parameter are presented.
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Results and discussion
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Wastewater physicochemical characteristics
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The pH of the wastewater is a critical parameter that needs to be controlled within a specific range depending on each treatment unit, in order to achieve the maximum removal efficiency of the target pollutants. The highest pH values (7.93 and 8.29) were found at the outlet of PPIs in campaigns B and C (Fig. 2(a)). A low pH value (ca. 5.0) was found in the effluent from ASR and SSR units, in campaign E, which slightly reduced the BOD5 and COD removal efficiency in the activated sludge reactor. At WWTP outlet the pH was always within the discharge limit range (6–9). The concentration of total suspended solids (TSS) (Fig. 2(b)) at the outlet of PPIs unit was different in campaigns A, D and E, but very similar concentrations were found in campaigns B and C. The reported variation in TSS concentration might be due to the flow rate and/or pollutant load associated with the rainfall run-off, as sampling campaigns undertaken in winter season (campaigns D and E) showed much higher concentrations of TSS. The VSS exhibited a similar concentration pattern (Fig. 2(c)). Although, there was a considerable variation in VSS concentration among the different campaigns, in the initial treatment stages, the variation decreased throughout the treatment process, reaching a final average value below 15 mg/L. The TPH concentration (Fig. 2(d)) varied considerably at the outlets of PPIs and sulfide oxidation and coagulation chamber (SOCC). High TPH concentrations were found in the samples from campaigns D and E, even at the outlet of the mechanical aeration basin (MAB), where 14.2 and 16.1 mg/L of TPH, respectively, were measured. Nevertheless, these concentrations are below the daily maximum discharge limits (20 mg/L). Oil and grease (O&G) concentration showed a pattern similar to TPH in campaigns D and
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Table 2 Analytical methods and equipments used in the present study. Parameter
Method
Apparatus
Range
Make/model
Reference bibliographic
pH TSS VSS TPH
Electrometry Gravimetry Gravimetry Partition-infrared spectrometry Partition-infrared spectrometry Partition-gravimetry K2Cr2O7; open reflux Dilutions Catalytic oxidation
pH Meter Balance Balance Spectrophotometer
– 0.5 mg/L 0.5 mg/L 0.1 mg/L
Hanna instruments – – Bomem Arid-zone 540
Standard methods [17] APHA 4500-H Standard methods (1998) APHA 2540-D Standard Methods (1998) APHA 2540-E Standard Methods [17] APHA 5520-F
Spectrophotometer balance
0.1 mg/L 0.5 mg/L
–
10 mg O2/L <1.0 mg O2/L 0–25 mg/L 25–100 mg/L 0.01 mg/L 1 mg NO3 /L
G. VITTADINI ORION 97-08-00 Shimadzu 5000 A
Oil & grease
Sulfide Total nitrogen Phenols
Iodometry Persulfate/brucine
Digester DO electrode Total organic carbon analyzer – Spectrophotometer
Extraction with chloroform
Spectrophotometer
0.5 mg/L
Chlorides
Argentometry
–
0.5 mg Cl /L
Electrical conductivity
Conductimetry
Conductivimeter
0.1 ms/cm
COD BOD5 TOC
Standard methods [17] APHA 5520-B Standard methods (1998) APHA 5210-B Standard methods [17] APHA 5310-A
– Standard methods (1998) APHA 4520-F PYE UNICAM PU 8600 Standard methods (1998) APHA 4500-N UV/VIS PYE UNICAM PU 8600 UV/ [18] VIS – Standard methods (1998) APHA 4500Cl B Hanna instruments Standard methods (1998) APHA 2510-A
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Fig. 2. Level of contaminants at the outlet of the different unit operations within the plant. Outlet of PPI’s (1), outlet of SOCC (2), outlet of DAF tank (3), outlet of ASR (4), outlet of SSR tank (5), outlet of MAB (6).
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E, exhibiting slightly higher values than in the other campaigns (Fig. 2(e)). The results showed that the concentration of O&G was high at the outlet of the separators (API and PPIs), which can negatively affect the removal of some pollutants downstream, such as sulfides and phenols.
The chemical oxygen demand (COD) in the effluents from the different units also increased in campaigns D and E (Fig. 2(f)). However, even in these campaigns, the COD of the final effluent (MAB effluent) was below the maximum daily discharge limit (300 mg/L). The biochemical oxygen demand (BOD5) was also higher in
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Fig. 2. (Continued) 150 151 152 153 154
campaigns D and E at the outlet of all units (Fig. 2(g)), but the maximum values at the WWTP outlet (MAB effluent) were 42.4 and 52.7 mg/L, which are below the daily discharge limit value (80 mg/L). The highest sulfide (S2 ) concentrations were observed at the outlet of PPIs in campaigns D and E (140.6 and 147.3 mg/L,
respectively). However, the sulfide concentration in the final effluent was always below the daily discharge limit (2.0 mg/L) (Fig. 2(h)). Lower removal efficiency in the sulfide oxidation and coagulation chamber (SOCC) and/or dis-functioning of some equipment in the WWTP units might be the probable cause for
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Fig. 3. Removal efficiency of different constituents along the treatment process: SOCC-DAF-ASR-SSR-MAB.
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some slight increase in sulfide concentration at the final treatment stage (MAB unit). Moreover, the pre-treatment step (PPIs and APIs) is critical for the removal of heterogeneous components from the wastewater, since a low performance of that treatment step can strongly impair the subsequent biological operation [12,13]. Total nitrogen was also measured in the effluents from the different units. The results showed a gradual reduction in the total nitrogen concentration as the treatment progressed (Fig. 2(i)). However, TN concentration increased in the effluents from ASR, SSR and MAB units, which is attributed to the introduction of domestic sewage in the activated sludge biological reactor, to ensure that the biodegradation of organic matter is not limited by the lack of nutrients. Industrial wastewaters are normally deficient in nitrogen and phosphorus. Therefore, these nutrients need to be added to attain the correct ratio C/N/P for microbial growth. The addition of biodegradable soluble organic matter improves the removal of hard COD as also provides sufficient carbon source for denitrification. The domestic sewage is introduced at this stage since normal refinery operation does not always generate constant and predictable flow-rates or waste streams of the same quality. The phenol concentration (Fig. 2(j)) gradually decreased throughout the process and its content in the effluent from the MAB unit is in the range 0.03–0.2 mg/L, below the daily discharge limit (1.0 mg/L). Alike the behavior of TN concentration in the entire treatment, chloride concentration also slightly increased in the effluent downstream from ASR in all campaigns (Fig. 2(k)), which is also
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related to the introduction of domestic sewage in the ASR. In the subsequent treatment units, the chloride concentration was relatively constant. Similarly, electrical conductivity results also exhibit an increase in the effluent from the ASR unit and subsequent units in all sampling campaigns (Fig. 2(l)). This is the result of the addition of ferric sulfate, sodium hydroxide and sodium triphosphate, as well as domestic sewage, to the biological reactor. The storm basins receive the excess effluent in order to operate the plant at approximately constant conditions. The addition to the industrial effluent is done automatically and the quality of the storm-water is assumed to be the same as the effluent.
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Performance of individual processes for the removal of various contaminants
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Fig. 3(a) shows TSS removal efficiencies of 20–63% in the dissolved air flotation tank, secondary sedimentation tank and mechanical aeration basin, during the five sampling campaigns. The TSS removal efficiency in DAF unit was lower than in SSR and MAB units. Increased efficiency can be achieved by using parallel plate clarifiers, which increase the effective settling area while reducing the distance solids must travel before reaching the collection surface, therefore enhancing the separation efficiency of the DAF process [14]. Fig. 3(b) shows that higher removal efficiency of TPH was obtained in the dissolved air flotation unit (DAF), secondary
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Fig. 4. Relation between the parameters during the treatment process.
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sedimentation tank (SSR) and mechanical aeration basin (MAB). The MAB unit exhibited the highest removal of TPH, due to the degradation of hydrocarbons by the oxygenase-catalyzed reactions in the presence of molecular oxygen [15]. Fig. 3(c) showed that a high O&G removal was achieved in MAB unit after the pre-treatment stage (APIs and PPIs). Proper operation of the downstream treatment processes, requires that API units achieve effluent oil concentrations in the range 50–200 mg/L [16]. The COD and BOD5 removal efficiencies for the individual processes are presented in Fig. 3(d) and (e). The performance of DAF unit, where the wastewater is clarified by the removal of suspended matter such as oils and solids, is lower than that of SSR and MAB units as regards BOD5 and COD removal. The presence of hydrocarbons in relatively high concentrations (ca. 100 mg/L) in the activated sludge reactor (ASR), negatively affects the COD and BOD5 removal efficiency (average removals of 25% and 23% for BOD5 and COD, respectively). The estimated BOD5 and COD (around 200–300 mg/L and 400–600 mg/L, respectively) of the domestic sewage introduced into the activated sludge reactor are close to the ones associated with the flow coming from the DAF (average values of 165 and 373 mg/L, respectively). Thus the low COD and BOD5 removal efficiencies in the ASR are not probably due to not accounting for the induced raw sewage in the reactor, in the calculation of the removal efficiencies in this treatment unit. A likely reason for the low efficiency of the ASR in removing BOD5 and COD is the low recirculation rate of sludge (0.5 m3/h). The typical return activated sludge recycle (RAS) ratio is between 0.25 and 1.00 whereas in the present situation is only 0.0014 (0.5 m3/h/350 m3/h). With this RAS ratio it is almost impossible to attain the required MLSS content in the reactor (3 kg/m3, as indicated in Table 1). In fact, the average value of TSS and VSS out of the ASR are 241 and 106 mg/L, respectively, as shown in Fig. 2(b) and (c). Assuming good mixing conditions, the TSS and VSS concentrations inside the reactor will be the same. So, the bad performance of the ASR is due to the low concentration of biomass (VSS) in the reactor. Nonetheless the concentrations of COD and
BOD5 at the outlet of the WWTP are below the discharge limits and the major contribution to the observed reduction (above 50%) is given by ASR, SSR and MAB units. As expected, a high sulfide removal efficiency (74–80%) was achieved in the SOCC unit, in all sampling campaigns (Fig. 3(f)). In the downstream DAF unit a significant removal of sulfide (60–72%) was also attained. The overall removal efficiency of phenol varied in the range 32– 50% considering all the campaigns (Fig. 3(g)). Fig. 4 shows the correlations between several wastewater constituents. The VSS concentration throughout the treatment process presents a linear relationship with TSS content and VSS contributes by nearly 74% to TSS (Fig. 4(a)). A strong correlation between TPH and VSS was found, indicating that about 70% of VSS correspond to hydrocarbons particles (Fig. 4(b)). Fig. 4(c) shows that TPH and O&G are also strongly correlated. The concentration of TPH is about 60% of O&G content, which was expected since TPH contributes to the O&G concentration. The presence of TPH gives an indication about the risk of oil refinery wastewaters to humans and the environment. The difference between O&G and TPH represents the polar fraction. Comparing the initial O&G and TPH values, the polar fraction is in the range 25–44%. It is worthy to mention that a high O&G content affects negatively some wastewater treatment processes, namely the biological aerobic processes. Fig. 4(d) shows a strong correlation between BOD5 and COD. In this study, BOD5 represents about 44% of COD (COD/BOD5 2.3), which indicates a moderate biodegradability of the wastewater.
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WWTP efficiency
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Fig. 5 shows overall removal efficiencies in the range 87–99% for most constituents (TSS, VSS, TPH, O&G, COD, BOD5, sulfides and phenols), along the five campaigns. The values did not vary much from one campaign to another. Chloride and total nitrogen were eliminated at a lesser extent, corresponding to removal rates of 56– 68% and 68–86%, respectively. Table 3 shows that along the five
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Fig. 5. WWTP removal efficiency of the studied parameters for all five campaigns.
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Table 3 Concentration of pollutants at the outlet of the WWTP and daily discharge limits (DDL). Parameter
pH TSS O&G TPH COD BOD5 Sulfide Total nitrogen Phenols a
282
– mg/L mg/L mg/L mg/L mg/L mg/L mg/L mg/L
1 7.2 49.7 10.2 7.6 86 24.4 0.8 12.1 0.04
2 7.11 40.5 8.7 3.9 95 26.8 1 10.8 0.03
289 290
Conclusions
291
310
The performance evaluation of the main units of the Porto Refinery WWTP is addressed in the present study. The sulfide removal efficiencies in the sulfide oxidation unit were high but below 80%. Relatively low COD and BOD5 removal efficiencies were achieved in the biological treatment process (activated sludge reactor), when compared to the other units. The entire treatment process is effective for the removal of main pollutants present in the refinery wastewater with the exception of total nitrogen and chlorides. The average removal efficiencies in the WWTP were as follows: 96.7% for TSS, 99.1% for TPH, 99.1% for O&G, 87.3% for COD, 90.5% for BOD5, 99% for sulfides, 68% for total nitrogen, 94.6% for phenols and 62.8% for chlorides. The linear correlations between some of the analyzed parameters showed that: 70% of the VSS correspond to hydrocarbons particles; TPH contributes to O&G by 60% and BOD5 represents about 44% of COD, which indicates a moderate biodegradability of the wastewater. TSS content can be used as a good indicator for VSS, TPH and O&G contents, using the linear relationships obtained in this study, then avoiding unnecessary costs for chemical analysis. TSS can also selected as an operational parameter to control the removal of TPH and O&G along the WWTP.
311
Acknowledgements
312 Q5
318
This work was co-financed by FCT/MEC,FEDER under Programe PT2020 (Project UID/EQU/50020/2013). C. Santos and André Fonseca acknowledge their PhD scholarship awarded by FCT (SFRH/BD/15342/2005 and SFRH/BD/69654/2010, respectively). Amit Bhatnagar also acknowledges his Post-Doc scholarship awarded by FCT (SFRH/BPD/62889/2009). V.J.P. Vilar acknowledges the FCT Investigator 2013 Programme (IF/01501/2013).
319
References
284 285 286 287 288
292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309
313 314 315 316 317
320 321
3 7.37 45.4 6.4 2.7 105.5 38.5 1.4 9.3 0.09
4 7.02 50.5 21.3 14.2 112.5 42.4 1.6 16.3 0.08
5 6.95 58 22 16.1 145 52.7 1.8 20.5 0.2
6.0–9.0 120 30 30 300 80 2 30 1
DDL— daily discharge limits.
campaigns all parameters met the daily discharge limits allowed by the Portuguese legislation. It must be emphasized that, according to the legislation, the discharge limit is to be applied to the average monthly value, i.e., the arithmetic mean of the average daily values. The daily value, based on a representative sample of the wastewater discharged during a period of 24 h, must not exceed the double the average monthly value. This means that the daily discharge limits can be, at most, twice the discharge limits established by the legislation.
283
DDLa decree-law no. 236/98
WWTP outlet (campaigns)
[2] A. Coelho, A.V. Castro, M. Dezotti, G.L. Sant’Anna Jr, Treatment of petroleum 322 refinery sourwater by advanced oxidation processes, J. Hazard. Mater. 137 (1) 323 (2006) 178–184, doi:http://dx.doi.org/10.1016/j.jhazmat.2006.01.051. 324 16530949. [3] Q.J. Rasheed, K. Pandian, K. Muthukumar, Treatment of petroleum refinery 325 wastewater by ultrasound-dispersed nanoscale zero-valent iron particles, 326 Ultrason. Sonochem. 18 (5) (2011) 1138–1142, doi:http://dx.doi.org/10.1016/j. 327 ultsonch.2011.03.015. 21507703. [4] Q.J. Rasheed, Effect of additive agents on sono-degradation petroleum refinery 328 wastewater, Hydrol. Curr. Res. 02 (01) (2011) , doi:http://dx.doi.org/10.4172/ 329 2157-7587.1000109. [5] F. Corona, M. Mulas, H. Haimi, L. Sundell, M. Heinonen, R. Vahala, Monitoring 330 nitrate concentrations in the denitrifying post-filtration unit of a municipal 331 wastewater treatment plant, J. Proc. Contr. 23 (2) (2013) 158–170, doi:http:// 332 dx.doi.org/10.1016/j.jprocont.2012.09.011. [6] A.M. Nagy-Kiss, G. Schutz, Estimation and diagnosis using multi-models with 333 application to a wastewater treatment plant, J. Proc. Contr. 23 (10) (2013) 334 1528–1544, doi:http://dx.doi.org/10.1016/j.jprocont.2013.09.027. [7] A.L. Barros, T.M. Pizzolato, E. Carissimi, I.A.H. Schneider, Decolorizing dye 335 wastewater from the agate industry with Fenton oxidation process, Miner. 336 Eng. 19 (1) (2006) 87–90, doi:http://dx.doi.org/10.1016/j.mineng.2005.04.004. [8] M.L. Brooks, J.S. Meyer, D.M. McKnight, Photooxidation of wetland and riverine 337 dissolved organic matter: altered copper complexation and organic compo338 sition, Hydrobiologia 579 (1) (2007) 95–113, doi:http://dx.doi.org/10.1007/ 339 s10750-006-0387-6. [9] S. Esplugas, D.M. Bila, L.G.T. Krause, M. Dezotti, Ozonation and advanced 340 oxidation technologies to remove endocrine disrupting chemicals (EDCs) and 341 pharmaceuticals and personal care products (PPCPs) in water effluents, J. 342 Hazard. Mater. 149 (3) (2007) 631–642, doi:http://dx.doi.org/10.1016/j.jhaz343 mat.2007.07.073. 17826898. [10] C. Carlesi Jara, D. Fino, V. Specchia, G. Saracco, P. Spinelli, Electrochemical 344 removal of antibiotics from wastewaters, Appl. Catal. B Environ. 70 (1–4) 345 (2007) 479–487, doi:http://dx.doi.org/10.1016/j.apcatb.2005.11.035. [11] APHA, American water works association and water pollution control federation, Standard Methods for the Examination of Water and Wastewater, 20th Q6 346 347 edition, APHA, AWWA, WEF, Washington, D.C, 1998. an, R. Özcımder, Wastewater treatment at the petroleum [12] Ş. Demırcı, B. Erdog 348 refinery, Kirikkale, Turkey using some coagulants and Turkish clays as co349 agulant aids, Water Res. 32 (11) (1998) 3495–3499, doi:http://dx.doi.org/ 350 10.1016/S0043-1354(98)00111-0. [13] L. Altaş, H. Büyükgüngör, Sulfide removal in petroleum refinery wastewater by 351 chemical precipitation, J. Hazard. Mater. 153 (1–2) (2008) 462–469, doi:http:// 352 dx.doi.org/10.1016/j.jhazmat.2007.08.076. 17913353. [14] J.P. Guyer, Introduction to Preliminary Wastewater Treatment, (2011) . [15] E.Y. Hwang, J.S. Park, J.D. Kim, W. Namkoong, Effects of aeration mode on the 353 composting of diesel-contaminated soil, J. Ind. Eng. Chem. 12 (2006) 694–701. [16] S.C. Nayar, N.D. Sylvester, Control of phenol in biological reactors by addition of 354 powdered activated carbon, Water Res. 13 (2) (1979) 201–205, doi:http://dx. 355 doi.org/10.1016/0043-1354(79)90093-9. [17] L.S. Clesceri, A.E. Greenberg, A.D. Eaton, Standard Methods for Examination of 356 Water & Wastewater, 21th edition, (2005) American Public Health Association 357 (APHA), American Water Works Association (A.W.W.A.) & Water Environment 358 Federation (WEF). [18] AFNOR, 1976. Norme Experimentale, Essais des Eaux, Détermination de l 359 ’indice phénol.
ütveren, Treatment of petroleum refinery [1] Y. Yavuz, A.S. Koparal, Ü.B. Ög wastewater by electrochemical methods, Desalination 258 (1–3) (2010) 201– 205, doi:http://dx.doi.org/10.1016/j.desal.2010.03.013.
Please cite this article in press as: C.E. Santo, et al., Performance evaluation of the main units of a refinery wastewater treatment plant – A case study, J. Environ. Chem. Eng. (2015), http://dx.doi.org/10.1016/j.jece.2015.07.011