Recent improvements in oily wastewater treatment: Progress, challenges, and future opportunities

JES-00407; No of Pages 16 J O U RN A L OF E N V I RO N ME N TA L S CI EN CE S X X (2 0 1 5 ) XX X–XXX

Available online at www.sciencedirect.com

ScienceDirect www.journals.elsevier.com/journal-of-environmental-sciences

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Sanaa Jamaly, Adewale Giwa, Shadi Wajih Hasan⁎

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Institute Center for Water and Environment, Department of Chemical and Environmental Engineering, Masdar Institute of Science and Technology, Abu Dhabi, United Arab Emirates

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Recent improvements in oily wastewater treatment: Progress, challenges, and future opportunities

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AR TIC LE I NFO

ABSTR ACT

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Article history:

Oily wastewater poses significant threats to the soil, water, air and human beings because 15

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Received 29 January 2015

of the hazardous nature of its oil contents. The objective of this review paper is to highlight 16

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Revised 3 April 2015

the current and recently developed methods for oily wastewater treatment through which 17

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Accepted 8 April 2015

contaminants such as oil, fats, grease, and inorganics can be removed for safe applications. 18

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Available online xxxx

These include electrochemical treatment, membrane filtration, biological treatment, 19

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Keywords:

and destabilization of emulsions through the use of zeolites and other natural minerals. 21

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Oily wastewater

This review encompasses innovative and novel approaches to oily wastewater treatment 22

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Electrochemical

and provides scientific background for future work that will be aimed at reducing the 23

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Biological

adverse impact of the discharge of oily wastewater into the environment. The current 24

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Membrane

challenges affecting the optimal performance of oily wastewater treatment methods and 25

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Treatment

opportunities for future research development in this field are also discussed.

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hybrid technologies, use of biosurfactants, treatment via vacuum ultraviolet radiation, 20

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Published by Elsevier B.V. 28

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Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 1. Recent treatment approaches of oily wastewater . . . . . 1.1. Electrochemical treatment . . . . . . . . . . . . . 1.2. Treatment via membrane filtration . . . . . . . . 1.3. Biological treatment . . . . . . . . . . . . . . . . . 1.4. Treatment via hybrid technologies . . . . . . . . . 1.5. Treatment via adsorption and ultraviolet radiation 2. Comparative assessment of oily wastewater methods . . 3. Challenges and opportunities for the future . . . . . . . . 4. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Contents

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© 2015 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. 27

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⁎ Corresponding author. E-mail: [email protected] (Shadi Wajih Hasan).

http://dx.doi.org/10.1016/j.jes.2015.04.011 1001-0742/© 2015 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V.

Please cite this article as: Jamaly, S., et al., Recent improvements in oily wastewater treatment: Progress, challenges, and future opportunities, J. Environ. Sci. (2015), http://dx.doi.org/10.1016/j.jes.2015.04.011

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1. Recent treatment approaches of oily wastewater

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1.1. Electrochemical treatment

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Electrochemical method is one of the most effective oily wastewater treatment techniques recently. Several electrochemical

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Oily wastewater is wastewater mixed with oil under a wide range of concentrations. The oil mixed in water can be fats, hydrocarbons, and petroleum fractions such as diesel oil, gasoline, and kerosene. Nowadays, many industries generate a large amount of oily wastewaters, which have various adverse impacts on the surrounding environment, such as air pollution caused by the evaporation of oil and hydrocarbon contents to the atmosphere. In addition, they can affect groundwater, seawater, or drinking water as a result of the percolation of contaminants in produced water into the water resources beneath the soil. A variety of treatment methods geared toward the removal of the oil impurities can be used to minimize or avoid the adverse effects of oily wastewater. Examples are electrochemical treatment, membrane filtration, use of biological media, adsorption, flotation and chemical coagulation, treatment using ultrasound-dispersed nanoscale zero-valent iron particles, titanium dioxide, vacuum ultraviolet and natural minerals, and hybrid technologies, among others. Electrochemical methods can be used to destabilize the emulsion of oil in wastewater through an electrical current. The most-used electrochemical methods in the treatment of oily wastewater are electrocoagulation and electroflotation. Membrane filtration involves the physical separation of the liquid content from a suspension via a membrane and through the application of pressure. The commonly used membranes are ultrafiltration (UF) and microfiltration (MF) membranes made of ceramic and polymeric materials. In addition, reverse osmosis (RO) membranes have been used in the treatment of oily wastewater. Biological treatment involves the use of microorganisms that produce the lipase enzyme, which breaks down the biodegradable organic substances in oily wastewater. In the treatment of oily wastewater by adsorption, the oil is removed using adsorbents such as polypropylene, activated carbon, chitosan-based polyacrylamide. Furthermore, flotation and coagulation are two conventional methods applied for the treatment of oily wastewater. In the flotation method, the oil (having lower density than water) is removed by allowing it to float on the surface of water. In coagulation, the suspended solids, colloids, and oil particles are destabilized, so they begin to aggregate. As they aggregate to form bigger flocs, the density of the flocs becomes higher than the density of water and hence, the flocs settle down and are removed by sedimentation. It is noteworthy that the treatment of oily wastewater may be difficult and complex to accomplish with only one treatment method. The below sections highlight several contributions made by many scientists applying different treatment approaches.

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technologies have been applied to treat oily wastewater from different sources. These electrochemical technologies include electrochemical oxidation processes and electroFenton achieved using several electrodes. Electrode materials such as iron, aluminum, boron doped diamond, platinum–iridium, and titanium–rubidium have been tested. A summary of the treatment efficiencies of electrochemical technologies obtained in some works aimed at removing pollutants from different sources of oily wastewater is presented in Table 1. Yavuz et al. (2010) investigated the treatment of petroleum refinery wastewater using three electrochemical methods: direct and indirect electrochemical oxidation using a borondoped diamond anode; direct electrochemical oxidation using a ruthenium mixed metal oxide electrode; and electro-Fenton and electrocoagulation using iron electrodes. Their results showed that the electro-Fenton and electrocoagulation process using iron electrodes was the most efficient method, reporting 98.74% and 75.71% removal of phenol and chemical oxygen demand (COD) at 6 and 9 min respectively. Also, in direct electrochemical oxidation operating at 5 mA/cm2, 99.53% and 96.04% removal of phenol and COD were reported respectively. Körbahti and Artut (2010) studied the influence of operating conditions (current density and reaction temperature) on the treatment and purification of bilge water using platinum–iridium electrodes in a batch electrochemical reactor. Their results demonstrated that a current density of 12.8 mA/cm2 and 32°C reaction temperature removed 99.2%, 93.2%, and 91.1% of COD, oil and grease, and turbidity respectively with an average energy consumption of 33.25 kWh/kg COD removed. Also, Yan et al. (2011) investigated the effect of initial pH, cell voltage and applicability of using fine iron (Fe) particles in the treatment of petroleum refinery wastewater. Their results indicated that an electrochemical cell with a three-dimensional multi-phase electrode, which introduced Fe particles and air into a traditional two-dimensional reactor (Fig. 1), was very efficient in the treatment of petroleum refinery wastewater, as 92.8% COD removal and low salinity of 84 μS/cm were reported at initial pH of 6.5, cell voltage of 12 V, and addition of some fine particles of Fe. Ngamlerdpokin et al. (2011) have compared chemical coagulation with electrocoagulation for the treatment of biodiesel wastewater, which was initially treated by acid protonation using three mineral acids, H2SO4, HNO3, and HCl at different pH ranging between 1 and 8. The results showed that H2SO4 was very efficient for the removal of fatty acid methyl esters (FAME) and free fatty acids (FFA) at pH of 2.5 for 7 min. 24.5 mL/L of FAME/FFA was removed using H2SO4 while 15.1 and 21.2 mL/L removal was reported using HNO3 and HCL respectively. Both chemical coagulation and electrocoagulation were effective in oil and grease removal, reducing the concentration from 105 to 80 mg/L. Moreover, the operating cost of chemical coagulation was 1.11 USD/m3 compared to 1.78 USD/m3 for electrocoagulation. Jaruwat et al. (2010) studied the management of biodiesel wastewater by chemical recovery using H2SO4 as a proton donor, with subsequent natural phase separation and electrochemical oxidation using a Ti/RuO2 electrode. Their results indicated that biodiesel was recovered at 6%–7% (W/W) by a protonation reaction with H2SO4 at pH ranging between 2 and 6. Also, 87%–98%, 13%–

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Please cite this article as: Jamaly, S., et al., Recent improvements in oily wastewater treatment: Progress, challenges, and future opportunities, J. Environ. Sci. (2015), http://dx.doi.org/10.1016/j.jes.2015.04.011

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Table 1 – Removal efficiencies of pollutants from oily wastewater by electrochemical treatment.

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24%, and 40%–74% removal of oil and grease, COD and BOD respectively were reported at low pH values. Sekman et al. (2011) investigated the capability of electrocoagulation in the treatment of oily wastewater generated from port waste reception facilities using aluminum electrodes. They indicated that 98.8% removal of suspended solids was obtained at current density of 16 mA/cm2 and electrolysis time of 5 min. In addition, 90% removal of COD was reported at current density of 12 mA/cm2 and electrolysis time of 20 min. However, 80% removal of oil and grease was observed at all tested current densities after an electrolysis time of 10 min. Giwa et al. (2012) analyzed the treatment of petrochemical wastewater as affected by changing the values

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1. Beaker 2. Graphite anode 3. Graphite cathode 4. Gas tube 5. Electric stirrer 6. Metal particle 7. D.C. power

Fig. 1 – Fe particle and air-assisted electrochemical apparatus (Yan et al., 2011).

Yavuz et al. (2010)

99.2% COD, 93.2% oil, and 91.1% turbidity 92.8% COD and 94.1% salinity

Körbahti and Artut (2010)

38.94%, COD and 99.36% oil /grease

Ngamlerdpokin et al. (2011) Jaruwat et al. (2010)

Yan et al. (2011)

40%–74% COD and 87%–98% oil/grease 98.8% suspended solids, 90% COD, and 80% oil/grease 97.43% turbidity 100% phenolic compounds 100% oil/grease

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99.53% phenol and 96.04% COD

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Petroleum refinery wastewater in Turkey with phenol concentration of 192.9 mg/L and a COD of 590 mg/L Synthetic bilge water prepared in synthetic 50/50% seawater/fresh water with 3,080 mg/L COD and 2,000 mg/L Oil/grease Petroleum refinery wastewater in China with 1,021 mg/L COD and 1,423 μS/cm conductivity Raw biodiesel wastewater in Thailand with COD 312,000–588,800 mg/L and 18,000–22,000 mg/L oil/grease Raw biodiesel wastewater in Thailand with COD 312,000–588,800 mg/L and 18,000–22,000 mg/L oil/grease Oily wastewater port waste reception facilities in Turkey with 13.3–660 mg/L suspended solids, 240–2,783 mg/L COD, 6.5–736 mg/L oil/grease Real petrochemical wastewater with 313.75 FTU turbidity Real refinery wastewater in Egypt with 3 mg/L phenol Biodiesel solutions from a biodiesel factory in Iran with 6,412 mg/L oil/grease Synthetic oil–water emulsions with 1,800 FAU turbidity Refectory oily wastewater from a student canteen in China with 500–1,500 mg/L COD and 100–250 oil/grease Oily wastewater from Petrobras/UN-SEAL plant in Brazil with 4,980 mg/L COD Petroleum refinery wastewater in UAE with 887–1,222 mg/L sulfate and 595–4,050 mg/L COD Petroleum refinery wastewater in Egypt with 13 mg/L phenol

Reference

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Sekman et al. (2011) Giwa et al. (2012) El-Ashtoukhy et al. (2013) Ahmadi et al. (2012)

99.22% turbidity 95% oil/grease and 75% (COD)

Yang (2007) Xu and Zhu (2004)

57% COD

Santos et al. (2006)

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Source of oily wastewater

93% sulfate and 63% COD 97% phenol removal

El-Naas et al. (2009) Abdelwahab et al. (2009)

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of current densities (7.55–21.64 mA/cm2), the concentration of sodium chloride, NaCl (0.5–2 g/L), and electrolysis time (5–30 min). Their results showed that the ideal operating conditions that removed the maximum turbidity of 97.43% were 21.64 mA/cm2, 2 g/L, and 30 min. El-Ashtoukhy et al. (2013) investigated the removal of phenolic compounds from petrochemical wastewater using electrocoagulation with a fixed bed electrochemical reactor. Their results determined a maximum removal of phenol (80%) at pH 7, NaCl concentration of 1 g/L, current density of 8.59 mA/cm2, and at 25°C. Moreover, 100% removal of phenolic compounds was achieved after 2 hr with initial phenol concentration of 3 mg/L at the later obtained optimum operating conditions. Ahmadi et al. (2012) have tried the addition of H2O2 and polyaluminum chloride in an electrocoagulation cell at different concentrations and doses. Their results showed that the oil and grease content was decreased from 11,781 to 4238 mg/L when the concentration of H2O2 and applied current density were at 2% and 10 mA/cm2 respectively. On the other hand, the oil and grease content was reduced to 1323 mg/L when the concentrations of H2O2 and polyaluminum chloride were at 2% and 0.5 g/L respectively. Yang (2007) investigated the treatment of oily water using electrocoagulation with ferrous ions in the electrodes with the addition of 100 mg/L of NaCl. The turbidity of the inlet water was 1800 FAU. The results showed that after 4 min of the treatment with a current of 2 A, the addition of more iron (165.8 mg/L) resulted in low turbidity of less than 14 FAU. According to Xu and Zhu (2004), the optimum current density to treat the refectory oily wastewater was 10 to 14 A/m2 during 30 min; moreover, the optimal distance of electrode was demonstrated to be 10 mm. The removal efficiency of oil and COD was 95% and 75% respectively. The impact of pH was not significant in the range of 3 to 10.

Please cite this article as: Jamaly, S., et al., Recent improvements in oily wastewater treatment: Progress, challenges, and future opportunities, J. Environ. Sci. (2015), http://dx.doi.org/10.1016/j.jes.2015.04.011

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Recently, membrane filtration has been widely applied for oily wastewater treatment. The performance of several membrane technologies for the removal of pollutants from oily wastewater has been investigated. Some of the tested membrane materials include polyvinylidene fluoride (PVDF), polysulfone (PS), polyacrylonitrile (PAN), ceramic materials, mullite, mullite-alumina ceramic material, TiO2/carbon, and ceramic–polymeric composites. Table 2 shows the treatment efficiencies obtained in some works involving the use of membrane technologies for the removal of pollutants from different sources of oily wastewater. Sun et al. (2010) studied the treatment of shipboard wastewater including gray water, black water, and bilge water using a biofilm membrane bioreactor and flat sheet ceramic membrane (supplied by KeraNor) under dead-end and recycle side stream configurations. Their results demonstrated that a good permeate quality was obtained in both configurations with oil content of 5 mg/L. Soltani et al. (2010) also investigated the treatment of oily water using a membrane bioreactor (MBR). They showed that the bacteria consortium could

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Table 2 – Removal efficiencies of pollutants from oily wastewater by membrane filtration.

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1.2. Treatment via membrane filtration

Source of oily wastewater

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Shipboard wastewater including gray water, black water, and bilge water with 80 mg/L oil Produced water and sea sediment in Iran with 10–22 mg/L oil/grease Industrial oily wastewater in Iran with 78 mg/L oil/grease, 53 NTU turbidity, 68 total suspended solids (TSS), and 2,228 total dissolved solids (TDS) Synthetic oil-in-water (o/w) emulsions with 125–250 mg/L oil/grease Synthetic oily wastewater with 1,000 mg/L total organic carbon (TOC) and real oily wastewater in Iran with 1,060 mg/L TOC Synthetic oily water emulsion Outlet of the API unit of Tehran refinery, Iran with 26 mg/L oil/grease, 92 mg/L TSS, 21 mg/L turbidity and 141 mg/L TOC Raw oily wastewater from gasoline reserving tanks with 3,280 mg/L COD and 89 μS/cm electrical conductivity (EC)

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Santos et al. (2006) studied the effect of a dimensionally stable anode of nominal composition Ti/Ru0.34Ti0.66O2 on the removal of organic components from oily wastewater. Their results indicated that the optimum removal of COD at a current density of 100 mA/cm2 and a temperature of 50°C reached 40% after 12 hr and 57% after 70 hr. El-Naas et al. (2009) worked on batch electrocoagulation experiments in the treatment of petroleum refinery wastewater. They assessed the removal of COD and sulfate by using different types of electrodes: aluminum, stainless steel, and iron at 25°C and different current densities in the range of 2–13 mA/cm2. Their results showed that the aluminum electrode was the most effective, with the removal of 93% of sulfate, more than 2.5 times more than the other electrodes. Also, they showed that as the current density increases, the sulfate removal increases. In addition, 63% removal of COD was reported using aluminum electrodes. Abdelwahab et al. (2009) investigated the removal of oily wastewater containing 13 mg/L of phenols. Their results revealed that the concentration of phenols was reduced to 1 mg/L (92.3% removal) after applying current density of 19.3 mA/cm2 over 2 hr of treatment time at 2 g/L concentration of NaCl and pH 8.

Synthetic hypersaline oily wastewater with 2,250.1 mg/L COD Oil–water emulsion prepared from refinery crude oil in India with 50–200 mg/L oil Synthetic petroleum wastewater with 58–61 mg/L hydrocarbons (toluene, ethylbenzene and nonane) Synthetic hypersaline oily wastewater with 562.5–6,750 mg/L COD, 137–1,650 mg/L TOC, and 87.5–1,050 mg/L oil/grease Raw hypersaline oily wastewater from Malaysia Petronas oilfields with 1,240 ± 119 mg/L COD, 540 ± 27 mg/L TOC, 15 ± 1.8 mg/L oil/grease Synthetic oily wastewater with 555 mg/L COD Synthetic oily wastewater with 0.3% oil and real oily wastewater from the American Petroleum Institute in Tehran refinery with 99 mg/L oil. 200 mg/L oily water Disposed wastewater from Tehran refinery, Iran, with 78 mg/L oil/grease, 60 mg/L TSS, 53 NTU turbidity, and 2,028 mg/L TDS Effluents from ships in France with 20–200 mg/L hydrocarbons Oily waste effluent from copper cable factory, Poland, with 147–257 mg/L oil and lubricants, 988–1,587 mg/L copper, 57–64 mg/L suspended solids (SS), 1173–1,832 mg/L TOC.

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Removal efficiencies of pollutants

Reference

95.96%–98.9% oil

Sun et al. (2010)

100% oil removal 97.2% oil and grease content, 96.4% turbidity, 94.1% TSS, and 31.6% TDS 98.8% oil/grease 81.3%–93.8% (for synthetic feed), 70.8%–84% for real feed 99% oil removal 85% of oil/grease, 100% TSS, 98.6% turbidity, and 95% TOC 84% COD and 88% EC by NF-2 membrane. 79% COD and 93% EC by NF-5 membrane removal rate of COD was 98% 93% oil

Soltani et al. (2010) Salahi et al. (2010)

Yang et al. (2011a,b) Abadi et al. (2011)

97% hydrocarbons

Shariati et al. (2011)

97.5% COD, 97.2% TOC, and 98.9% oil/grease 86.2% COD, 90.8%, TOC, and 90% oil/grease 90.28% of COD removal 95% oil from synthetic feed. Around 80% oil from real feed 100% COD 97% oil/grease, 100% TSS, 99% turbidity, and 23% TDS 97% removal of hydrocarbons 98% oil and lubricants, 99% copper, and 100% SS by UF membrane 100% oil and lubricants and 90% TOC by NF membranes.

Pendashteh et al. (2012)

Nandi et al. (2010) Abbasi et al. (2010)

Rahimpour et al. (2011)

Pendashteh et al. (2011) Mittal et al. (2011)

Pendashteh et al. (2012) Yuliwati et al. (2012) Madaeni et al. (2013) Yang et al. (2012a,b) Noshadi et al., 2013 Ghidossi et al. (2009) Karakulski and Morawski (2011)

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NF-5 removed 79% and 93% of COD and EC respectively. Also, they concluded that the optimum pressure and temperature for the COD and EC removals were in the range of 15–20 bar and 20–30°C. Pendashteh et al. (2011) characterized the membrane foulants in a MBR in the treatment of hypersaline oily wastewater. Their results demonstrated that the Fourier Transform Infrared spectra showed the deposition of organic and inorganic substances composed of extracellular polymeric substances and hydrocarbon matters. Atomic Force Microscopy showed surface coverage of the membrane as a fouling mechanism. Scanning Electron Microscopy indicated that the bacteria were major contributors to the formation of the cake layer on the membrane surface. In addition, the energy dispersive X-ray results demonstrated some major metal components in foulants such as Mg, Al, Ca, Na, K, and Fe. The treatment performance of a membrane sequencing batch reactor was modeled using ANN (Pendashteh et al., 2011). A set of 193 operational data were analyzed. Their results demonstrated that the average removal rate of COD was 98%, with an average effluent concentration less than 100 mg/L. Mittal et al. (2011) examined a low-cost hydrophilic ceramic– polymeric composite membrane for the treatment of oily wastewater. The pore size of the membrane ranged between 0.56 and 28 nm while separating oil concentrations of less than 250 mg/L. Their results demonstrated that 93% removal of oil was achieved during 41 min for an initial oil concentration of 200 mg/L at 138 kPa. Shariati et al. (2011) analyzed the effect of the HRT of membrane sequencing batch reactors in the treatment of synthetic petroleum wastewater. They concluded that biodegradation and air stripping contributed to the 97% reduction of hydrocarbons observed at all HRTs (8, 16, and 24 hr). Pendashteh et al. (2012) evaluated the performance of a MBR in the treatment of hypersaline oily wastewater. Several operating conditions were investigated, such as organic loading rates or OLR (0.281, 0.563, 1.124, 2.248, and 3.372 kg COD/(m3·day)), cycle time (12, 24, and 48 hr), and total dissolved solids (TDS) (35,000; 50,000; 100,000; 150,000; 200,000; and 250,000 mg/L). Their results proved that at OLR of 1.124 kg COD/(m3·day), HRT of 48 hr, and TDS of 35,000 mg/L, the removal efficiencies of COD, total organic carbon, and oil and grease from the synthetic oily wastewater were 97.5%, 97.2%, and 98.9% respectively. However, 86.2%, 90.8%, and 90% were obtained respectively for the raw produced water. In addition, at the highest TDS (250,000 mg/L), the COD removal for the synthetic and real produced water were reduced to 90.4% and 17.7% respectively. Yuliwati et al. (2012) investigated the effects of air bubble flow rate (ABFR) (1.2– 3 mL/min), HRT (120–300 min), mixed liquor suspended solids concentration and pH, which were controlled at 4.5 g/L and 6.5 respectively, on the performance of modified PVDF in a submerged UF membrane. Their results indicated that 90.28% of COD removal was observed at 2.25 mL/min ABFR and 276.93 min HRT while improving water flux reaching 145.7 L/(m2·hr). Madaeni et al. (2013) used microfiltration (MF-GRM) and ultrafiltration (UF-GRM) membranes for the treatment of synthetic oily wastewater having 0.3% oil concentration obtained from the American Petroleum Institute in Tehran

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degrade hydrocarbons, hexadecane, and phenanthrene, in the presence of salts. In addition, their results showed that the hydraulic retention time (HRT) to biodegrade oil was about 10 to 15 hr, reporting 100% removal efficiency. Salahi et al. (2010) evaluated and compared the efficiency of five types of polymeric membranes to treat industrial oily wastewater, two microfiltration membranes: PS (0.1 μm) and PS (0.2 μm) and three ultrafiltration membranes: PAN (20 kDa), PAN (30 kDa), and PAN (100 kDa). They concluded that PAN (100 kDa) performed better than other membranes by removing 97.2% oil and grease content, 96.4% turbidity, 94.1% total suspended solids, and 31.6% total dissolved solids with a high permeation flux of 96.2 L/(m2·hr) and with 60% reduction in fouling resistance. Nandi et al. (2010) used low-cost ceramic MF membranes to treat synthetic oily wastewater that were fabricated from inorganic precursors (kaolin, quartz, feldspar, sodium bicarbonate, boric acid, and sodium meta-silicate). They used a comparative assessment of pore blocking and artificial neural network (ANN) model to estimate the permeate flux of oil and water emulsions. Two different feed oil concentrations (125 and 250 mg/L) and transmembrane pressures (68.95 and 275.8 kPa) were investigated. Their results indicated that the membrane removed 98.8% of oil and grease, and the permeate flux was 5.36 × 10−6 m3/(m2·sec) after 60 min at 68.95 kPa of transmembrane pressure. The treatment of synthetic oily wastewater with mullite and mullite-alumina ceramic MF membranes has been investigated (Abbasi et al., 2010). The effects of different operating conditions such as pressure (0.5– 4 bar), cross flow velocity (0–2 m/sec), temperature (15–55°C), oil concentration (250–3000 mg/L), and salt concentration (up to 200 g/L) on permeation flux, fouling resistance, and rejection of mullite and mullite-alumina ceramic MF membranes were studied (Abbasi et al., 2010). The results showed that at the optimum operating conditions of 3 bar, 1.5 m/sec, and 35°C, the mullite ceramic membrane had the highest fouling and rejection rate of 93.8%, and the lowest fouling resistance of 28.97%. However, the mullite-alumina ceramic membrane with 75% of alumina had high permeation flux of 244 L/(m2·hr) and low fouling and rejection rate of 81.3%. Yang et al. (2011a) coated the surface of membranes to treat oily wastewater. They found that a kaolin/MnO2 bi-layer composite dynamic membrane was very effective in the treatment of oily wastewater, with 99% removal when the concentrations of kaolin and KMnO2 were 0.4 and 0.1 g/L respectively. In addition, they observed an increase in permeate flux from 120.1 to 153.2 L/(m2·hr) as the temperature increased from 283 to 313 K. Abadi et al. (2011) investigated the treatment of oily wastewater of a Tehran refinery using a ceramic membrane MF (α-Al2O3). They found that the system removed 85% of oil and grease content, 100% total suspended solids, 98.6% turbidity, and 95% total organic carbon while operating at 1.25 bar, 2.25 m/sec, and 32.5°C of transmembrane pressure, cross flow velocity, and temperature respectively. Rahimpour et al. (2011) evaluated self-made nanofiltration (NF-5) and commercial (NF-2) membranes for the treatment of oily wastewater from gasoline reserving tanks. An MF membrane was used for the pretreatment of the oily wastewater. They found that the NF-2 removed 84% and 88% of COD and electrical conductivity (EC) respectively while

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copper cable factory with a small size of oil droplets (0.1 and 0.4 μm for WIROL 5000 and DRAWLUB emulsions respectively) using integrated UF and nanofiltration (NF) membranes. The UF membranes were a tubular module B1 equipped with PVDF (100 kDa), and the NF membrane was a type of spiral module (Karakulski and Morawski, 2011). Their results showed that UF membranes removed 98%, 99%, and 100% of oil and lubricant, copper, and suspended solids respectively with < 5 SDI and an average permeate flux of 45 L/(m2·hr), whereas 100% and 90% removal of oil and lubricants, and total organic carbon was removed using NF membranes.

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The use of microorganisms for oily wastewater treatment has yielded some impressive results recently. In many cases, a consortium of microbes has been used to remove hazardous pollutants in oily wastewater. Although biological treatment of oily wastewater is not well developed due to the diverse nature and behaviors of microbes under different environmental conditions, recent research activities in this area have yielded notable removal percentages of contaminants from oily wastewater. Table 3 provides some of the results obtained from the application of biological technologies in the treatment of oily wastewater from different sources. Song et al. (2011) combined a whole-cell lipase with Yarrowia lipolytica and a fungal lipase for the treatment of oily wastewater. Their results showed that during 72 hr of whole-cell treatment, 96.9% of oil and 97.6% of COD were removed. However, when only Y. lipolytica was added, 87.1% of oil and 91.8% of COD were removed. In addition, in the control system where no cells were added, 45.1% of oil and 67.5% of COD were removed in 72 hr. Dumore and Mukhopadhyay (2012) used immobilized triacylglycerin lipase in the removal of oil and grease from synthetic oily wastewater, with a concentration of 0.1–0.3 g/L. Their results demonstrated that around 48% of oil and grease and 47% of COD were removed by using 0.3 g/L of immobilized triacylglycerin lipase. Tang et al. (2012) used Bio-Amp to treat a grease trap wastewater that contained fat, oil, and grease (FOG). Their results demonstrated a removal of 40% of FOG after the addition of the commercial bio-additive. Also, COD, total nitrogen, total phosphorous and total fatty acids were reduced by 39%, 33%, 56%, and 59% respectively. Nopcharoenkul et al. (2013) used the Pseudixanthomonas sp. RN402 to degrade diesel oil, crude oil, n-tetradecane, and n-hexadecane. Their results showed that RN402 were efficient at degrading approximately 89%, 83%, 92%, and 65% of diesel oil, crude oil, n-tetradecane, and n-hexadecane respectively. Chanthamalee et al. (2013) examined polyurethane foam (PUF)-immobilized Gordonia sp. JC11 for the treatment of bilge water. PUF-immobilized bacteria performed more efficiently at removing oil than indigenous bacteria and were able to remove 40%–50% of boat lubricant. Hidalgo et al. (2013) studied the co-digestion of residues and pig manure for the pretreatment of waste vegetable oil. They found that the oily vegetable waste could be treated without the addition of chemicals, by co-digestion of substrates that contained high levels of ammonium-nitrogen and alkalinity. Shokrollahzadeh et al. (2008) analyzed the treatment of petrochemical wastewater in Iran using an activated

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refinery. Their results showed that the flux of MF-GRM for the synthetic feed during 2 hr was high compared to the real 383 feed, which contained solid particles and colloids. In addition, 384 both MF-GRM and UF-GRM removed around 95% of oil and 385 grease from the synthetic feed, which was higher than the oil 386 Q14 removal from the real feed (around 80%). Yang et al. (2012a,b) 387 studied the characteristics of a novel electrocatalytic TiO2/ 388 carbon membrane for the treatment of oily wastewater. One 389 parameter used to describe the relationship between electro390 catalytic residence time in the electrocatalytic membrane 391 reactor and COD removal was liquid hourly space velocity 392 (LHSV). The results demonstrated that as the LHSV decreased, 393 the oil removal increased. During the treatment of 200 mg/L 394 oily wastewater, the COD removal was 100% with a LHSV of 395 7.2 L/hr. However, 87.4% of COD removal was achieved when 396 LHSV was 21.6 L/hr. The fouling mechanisms in the treatment 397 of oily wastewater of a refinery using UF have also been 398 investigated (Noshadi et al., 2013). It was shown that the 399 transmembrane pressure, cross flow velocity, and tempera400 ture are some factors affecting UF membrane fouling (Noshadi 401 et al., 2013). Also, it was concluded that UF showed high 402 removal of oil and grease (97%), total suspended solids (100%), 403 turbidity (99%), and TDS (23%). 404 Duong et al. (2014) examined a novel double-skinned 405 forward osmosis membrane for the treatment of emulsified 406 oil–water in order to reduce fouling. The double-skinned 407 membrane showed a high water flux of 17.2 L/(m2·hr) when 408 they used 0.5 mol/L of NaCl, thus, showing less fouling for 409 emulsified oil–water separation (Duong et al., 2014). Novel 410 hollow fiber PVDF membranes with hydrophilic and 411 oleophobic surface properties have also been developed for 412 oil/water emulsion filtration (Zhang et al., 2013; Zhu et al., 413 2013, 2014). A modified phase-inversion process for producing 414 a superhydrophobic–superoleophilic PVDF membrane is 415 shown in Fig. 2. Less fouling was observed with efficient 416 backwashing, resulting in the scouring of any oil droplets that 417 might deposit on the surface of the membrane (Zhu et al., 418 2013). 419 Ghidossi et al. (2009) studied different membranes (0.1 μm 420 and 300 kDa) with the ability to separate hydrocarbons. Their 421 results showed that the 300 kDa membrane was very efficient, 422 with permeate flux more than 100 L/(hr·m2·bar) having less 423 than 1 mg/L of hydrocarbon concentration (97% removal). 424 Karakulski and Morawski (2011) treated waste emulsions in a

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Fig. 2 – Formation of a superhydrophobic-superoleophilic PVDF membrane via a modified phase-inversion process for oil removal (Zhang et al., 2013). PVDF: polyvinylidene fluoride.

Please cite this article as: Jamaly, S., et al., Recent improvements in oily wastewater treatment: Progress, challenges, and future opportunities, J. Environ. Sci. (2015), http://dx.doi.org/10.1016/j.jes.2015.04.011

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Table 3 – Oily wastewater pollutant removal efficiencies by biological treatment.

t3:4

Source of oily wastewater

t3:5 t3:6

Synthetic oily wastewater with 5,000 mg/L oil and 15,000 mg/L COD Synthetic oily wastewater with 827.5–2,455.5 mg/L COD and 100 mg/L oil/grease Grease trap wastewater from student restaurant in USA with 2,570 ± 500 mg/L COD, and 281 ± 36 mg/L Synthetic oily wastewater with diesel oil, crude oil and n-alkanes at concentrations of 450 mg/L Bilge water from fishing boats in Thailand with 58–976 mg/L total petroleum hydrocarbon (TPH) Waste vegetable oil in Spain with 0.25–3.1 mg/L volatile solids (VS)

t3:17

t3:18 t3:19

483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513

89% diesel oil, 83% crude oil, 92% n-tetradecane, and 65% n-hexadecane 40%–50% of boat lubricant

sludge treatment that contained 67 aerobic bacteria such as Pseudomonas, Comamonas, Acidovorax, Flovobacterium, Cytophaga, Sphingomonas, and Acinetobacter genera. Their results demonstrated that the activated sludge treatment removed 89% of COD, 99% of ethylene dichloride, 92% of vinyl chloride, and 80% of total hydrocarbons. Zhao et al. (2006) investigated a pretreatment method for oily wastewater using a group of immobilized microorganisms, B350M and B350, in a pair of biological aerated filter (BAF) reactors. The biodegradation was operated for 142 days with 4 hr HRT. Their results indicated that B350 and B350M are effective in treating oily wastewater that is low in N and P (C:N:P is 100:2.58:0.044) and with lower concentrations of organic substances (COD ranging from 300 to 400 mg/L). They demonstrated that the reactor with immobilized B350M showed a mean degradation efficiency of 78% for total organic carbon and 95% for oil. In addition, B350 degraded 64% and 86% of total organic carbon and oil respectively. Da Cruz et al. (2008) compared crude oil biodegradation by aerobic microbiota from the Pampo Sul Oil Field (sample P1) to natural biodegraded oil (sample P2). Ion chromatograms were used to monitor the biodegradation of sample P1 for 60 days. Their results showed that there was a degradation of C8–C12 n-alkanes and isoprenoids, including pristine and phytane, by the day 60. Khondee et al. (2012) used an internal loop airlift bioreactor (Fig. 3) that contained chitosan immobilizedSphingobium sp. P2 for the treatment of lubricants in wastewater. The chitosan-immobilized bacteria showed high efficiency in removing automotive lubricants from synthetic and carwash wastewater. In semi-continuous batch experiments, they removed 80%–90% of the 200 mg/L total hydrocarbons from both synthetic and carwash wastewater.

Nopcharoenkul et al. (2013)

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Chanthamalee et al. (2013)

100% n-alkanes 80%–90% TPH

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63%–71% VS in single phase system and 69%–72% VS in two-phase system 99% ethylene dichloride, 92% vinyl chloride, and 80% of TPH 78% TOC and 95% oil

84.5% COD, 94% oil, and 83.4% SS

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t3:16

Song et al. (2011) Dumore and Mukhopadhyay (2012) Tang et al. (2012)

40% FOG, and 39% COD

94%–95% COD, 85%–87% TOC, and 98%–99% TSS 80%–99% oil

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Reference

96.9% oil and 97.6% COD 48% oil/grease and 47% COD

81% COD More than 90% oil

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t3:13 t3:14

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t3:12

Petrochemical wastewater in Iran with solvent-extractable 13–43 mg/L TPH Wastewater from an oil field in North China with 38 mg/L TOC and 20 mg/L oil Crude oil from a deep water reservoir in Brazil Synthetic and carwash wastewater in Thailand with up to 200 mg/L TPH Refinery wastewater in South China with 20–140 mg/L COD, 1–10 mg/L oil, and 20–160 mg/L SS Oil refinery wastewaters in Portugal with 400–440 mg/L COD, 84.2–85.6 mg/L TOC, 812–890 mg/L TSS Emulsified oily wastewater in Canada with 50–350 mg/L oil consisting of standard mineral oil (SMO), canola oil (CO), and bright-edge 80 Petroleum refinery effluent in Iran with 450 mg/L COD Synthetic emulsified oily wastewater with 1,680 and 4,315 mg/L oil

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Removal efficiencies of pollutants

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Hidalgo et al. (2013) Shokrollahzadeh et al. (2008) Zhao et al. (2006) da Cruz et al. (2008) Khondee et al. (2012)

Xie et al. (2007) Santo et al. (2013) Srinivasan and Viraraghavan (2010) Rastegar et al. (2011) Ibrahim et al. (2012)

Furthermore, in an internal loop airlift bioreactor containing 4 g/L immobilized bacteria operated at 2 hr HRT for 70 days, the airlift bioreactor removed 85% ± 5% of total petroleum hydrocarbons and 73% ± 11% of COD from the carwash wastewater containing 25–200 mg/L of lubricant at steady state. Xie et al. (2007) used the BAF process to treat polluted oily wastewater under the optimal conditions of 1 hr HRT, 5:1 volume flow ratio of air/water, and with a backwashing cycle of 4 to 7 days. Their results demonstrated that the average removal efficiency of COD, oil pollutants, and suspended solids was 84.5%, 94%, and 83.4%, respectively. Santo et al. (2013) treated petroleum refinery wastewaters using biological treatment by activated sludge. Their results indicated 94%–95%, 85%–87%, and 98%–99% removal of COD, total organic carbon, and total suspended solids respectively. The pseudo first-order kinetic model was also used to describe the rate of degradation with and without sludge recycling, and they achieved rate constant values of 0.055 and 0.959 mg/(L·day) with and without sludge recycling respectively (Santo et al., 2013). In addition, the consumption of oxygen in the biological reactor while operating it with and without sludge recycling behaved according to model parameters a′ (0.071/0.069 mg O2/mg COD) and b′ (0.012/ 0.024 mg O/(mg VSS·day)). Also, the parameters related to production and destruction of biomass for the system were found to be a = 0.33/0.32 mg VSS/mg COD; b = 0.07/0.03 mg VSS/(mg VSS·day) respectively. Srinivasan and Viraraghavan (2010) used a fractional factorial design to monitor the factors affecting removal of three emulsified oils from water: standard mineral oil (SMO), canola oil (CO), and Bright-Edge 80, using a Mucor rouxii fungal biomass rich with chitosan in its cell

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15 cm

percentage of oil removal reached its maximum removal of 571 more than 90% at pH of 6 to 8. 572

Air inlet

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The integration of different oily wastewater treatment technologies, with the purpose of observing the overall impact of the combined technologies on the removal efficiencies of pollutants, has also been investigated. The performance data recorded by authors who have worked on the application of hybridized methods and systems to remove contaminants from different sources of oily wastewater are provided in Table 4. Otadi et al. (2011) analyzed the oily compound removal of Pars Oil Refinery wastewater using a dissolved air flotation (DAF) system and active sludge reactor and clarifier (ASR). They concluded that the physical treatment, DAF, removed 29.7%, 49%, and 27.8% of oil, COD, and BOD respectively. In addition, the biological treatment, ASR, removed 73.4% and 84.7% of COD, and BOD respectively suggesting that the biological treatment had great efficiency in the removal of COD and BOD. Rattanapan et al. (2011) enhanced the DAF treatment by applying acidification and coagulation to the treatment of biodiesel wastewater. They found that DAF alone or DAF with acidification were not efficient in the treatment of biodiesel wastewater; yet DAF with acidification and coagulation achieved additional removal of oil and grease by 10%, giving total removal of 85%–95%. Siles et al. (2011) proved that the combination of acidification, electrocoagulation, and biomethanization were more efficient than acidification, coagulation, flocculation, and biomethanization for the treatment of biodiesel wastewater. Their results determined that acidification, electrocoagulation, and biomethanization removed 99% of COD; however, acidification, coagulation, flocculation, and biomethanization removed 94% of COD. Santo et al. (2012) optimized the coagulation–flocculation and flotation processes in order to reduce the organic matter and oil and grease content. PAX-18 (17% Al2O3), aluminum sulfate, and ferric sulfate were chosen for the primary treatment of coagulation-flocculation. NALCO 71408 was used as flocculant. Their results indicated that a combination of 28.6 mg/L of PAX-18 and 4.5 mg/L of NALCO 71408 removed more than 80% of COD, total organic carbon, and turbidity in a continuous mode of operation. In addition, a flotation test showed a removal of 95% of total petroleum hydrocarbons at a 0.6 kg air/kg of air/solid ratio, suggesting the potential implementation of coagulation– flocculation and flotation for the removal of hydrocarbons from oily wastewater at optimal design and operating parameters. Furthermore, Yang et al. (2012ab) used two parallel submerged MBRs in combination with electrocoagulation and electroflotation for the treatment of restaurant wastewater. When the influent contained 5 and 100 mg/L of oil, the COD removal was 98.3% and 99.1% respectively. The biological treatment in this study showed high performance in the removal of COD. Jing et al. (2014) modeled UV irradiation removal of polycyclic aromatic hydrocarbons (PAHs) from marine oily wastewater using ANN. The ANN model was found to fit the experimental results with a slope of 0.97 and correlation of determination of 0.943. They showed that the initial concentration, salinity, reaction time, and temperature had an effect on PAH photodegradation.

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wall. The factors investigated were: pH (3–9), temperature (5– 30°C), adsorbent dose (0.05–0.5 g), oil concentration (50– 350 mg/L), and rotational speed of the shaker (100–200 r/ min). Their results demonstrated that at pH 3, 80%–99% removal of oil was observed for all types of oil. Temperature had effects on SMO and Bright-Edge 80, while adsorbent dose had an effect on SMO. For instance, at 30°C, the average removal of SMO and Bright-Edge 80 was 13% higher than at 5°C. In addition, oil concentration variations had an effect on CO removal. The average removal of CO was found to be approximately 15% higher at an initial concentration of 50 mg/L than at 350 mg/L. Rastegar et al. (2011) used an upflow anaerobic sludge blanket bioreactor for the optimization of petroleum refinery effluent treatment. Their results indicated that when the system was operating at HRT of 48 hr, the COD removal was 81%. The rate of biogas production increased with the increase of HRT, with a rate of 559 mL/hr at HRT of 40 hr and an influent COD of 1000 mg/L. Furthermore, the optimum region was found to be influent COD of 630 mg/L, upflow velocity of 0.27 m/hr, and HRT of 21.4 hr because the percent removal of COD was 76.3% and the biogas production rate was 0.25 L biogas/L feed. Ibrahim et al. (2012) performed batch adsorption tests on oily wastewater using biosorbents. They investigated the effect of contact time and pH on the removal of emulsified oil in wastewater. Their results showed that the

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Fig. 3 – Internal loop airlift bioreactor for the treatment of lubricants in wastewater (Khondee et al., 2012).

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Air sparger

Please cite this article as: Jamaly, S., et al., Recent improvements in oily wastewater treatment: Progress, challenges, and future opportunities, J. Environ. Sci. (2015), http://dx.doi.org/10.1016/j.jes.2015.04.011

575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 Q15 618 619 620 621 622 623 624 625 626 627 628

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Removal efficiencies of pollutants

Refinery wastewater in Iran with 13.3–58.3 mg/L oil, 256–1,800 mg/L COD, 27–400 mg/L BOD

t4:6

Biodiesel wastewater in Thailand with 60,000–150,000 mg/L COD and 7,000–15,000 mg/L oil/grease Biodiesel wastewater in Spain with 428,000 mg/L COD Refinery wastewater in Portugal with COD up to 580 ± 4 mg/L Simulated restaurant wastewater with 5 and 100 mg/L oil

t4:17

t4:18 t4:19 t4:20 Q12 t4:21

Diesel oil Synthetic oil-in-water emulsion with 3,000 mg/L p-Xylene and 3,817 mg/L TOC

629

97% oil 80%–85% oil removal 99% COD and 99% turbidity

99% COD 1.8 g crude oil per g of seawater 100% oil/grease, 98% TOC, 98% COD, 95% TDS and 100% turbidity 99.9% COD and 99.9% oil/grease

>90% oil 36.7 g/g diesel oil, 50.8 g/g used engine oil, and 47.4 g/g new engine oil 70.6 g/g 96% p-xylene and TOC

In addition, they observed that when the initial concentration of naphthalene was low (2.88 mW/cm2), the reactive 631 radicals produced from UV irradiation were enough to start the 632 photoreaction. 633 McLaughlin et al. (2014) characterized shipboard bilge 634 water before and after treatment for 20 systems using 635 land-based approval data and three systems onboard ships. 636 They showed that the onboard systems passed the 15 mg/L oil 637 discharge compliance limit with oil analysis methods. After 638 the treatment, both the land-based and onboard systems met 639 the 5 mg/L oil discharge compliance level. Santander et al. 640 (2011) worked on emulsified oil removal from water by 641 flocculation and flotation in a modified jet cell. The removal 642 of oil at a concentration of 50 to 600 mg/L and volume mean 643 diameter of oil droplets of 20 μm was effective in both the 644 conventional jet cell (CJC) and the modified jet cell (MJC). The 645 results indicated that the MJC removed 5% more oil than the 646 CJC (85% in MJC and 80% in CJC). In addition, the MJC (5 m3/hr) 647 was tested on a maritime platform, and it showed a high 648 removal of oil of 81% at 24.7 m3/(hr · m2) throughput. Thus, 649 the study concluded that the MJC has a great capacity for the 650 treatment of oily wastewater at high rates. Peng et al. (2014) 651 studied the effect of a biological-physicochemical pretreat652 ment for the degradation of oily wastewater. They investigat653 Q16 ed the effects of premixing Bascillus at 9 wt.% with ultrasonic 654 treatment combined with citric acid addition on methane 655 production. They found that the digestibility of oil wastewater 656 improved by 280% as the oil degradation bacteria, Bascillus, 657 improved the oil degradation.

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Siles et al. (2011) Santo et al. (2012) Yang et al. (2012a,b)

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99% of COD More than 80% COD 98.3 and 99.1% COD when initial concentration was 5 and 100 mg/L respectively 100% naphthalene

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Synthetic marine oily wastewater with 10–500 μg/L naphthalene Shipboard bilge water in USA with up to 129.56 ± 55.53 mg/L oil Simulated offshore petroleum effluents with 50–600 mg/L oil Synthetic oil-in-water emulsion with 62,300 mg/L COD and 29,700 NTU turbidity Petroleum refinery wastewater in China with 4,238 mg/L COD Aqueous solution of 500–30,000 mg/L crude oil in Egypt Refinery wastewater, Iran, with 78 mg/L oil/grease, 81 mg/L TOC, 124 mg/L COD, 2,028 mg/L TDS, 53 NTU turbidity Synthetic oily emulsion with 3,000 mg/L oil and industrial oily wastewater in Iran with 3,591 mg/L oil/grease and 2,698 mg/L COD Synthetic oily wastewater with 250–10,000 mg/L oil Diesel oil, new engine oil, and used engine oil in Malaysia

Otadi et al. (2011)

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29.7% oil, 49% COD, and 27.8% BOD by dissolved air flotation (DAF). 73.4% COD and 84.7% BOD by activated sludge reactor (ASR) 85%–95% oil/grease and up to 50% COD

Rattanapan et al. (2011)

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Table 4 – Oily wastewater pollutant removal efficiencies by hybrid technologies.

Jing et al. (2014) McLaughlin et al. (2014) Santander et al. (2011) Mostefa and Tir (2004) Yan et al. (2010) Sokker et al. (2011) Salahi et al. (2012) Masoudnia et al. (2014)

Ong et al. (2014) Abdullah et al. (2010) Zhao et al. (2011) Yang et al. (2011a,b)

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Mostefa and Tir (2004) coupled electroflotation with flocculation for the treatment of oily wastewater. Three flocculant agents were used in the experiment (iron sulfate, aluminum sulfate, and polyacrylamide). In addition, the concentration of cutting oil was varied between 1% and 4% where the distance of two steel electrodes was 2 cm. Their results demonstrated that the optimal value for maximum percentage removal of COD (97%) and turbidity (99%) was 11.15 mA/cm2. Moreover, the percentage of oil removal reached 99% for an emulsion concentration of 4% for concentrations of iron and aluminum of 200 mg/L. Yan et al. (2010) employed catalytic vacuum distillation (CVD) with various promoters such as FeCl3, kaolin, H2SO4 and NaOH for removal of high COD and salinity from petroleum refinery wastewater. CVD promoted with NaOH showed higher purification efficiency than other systems, and effluents with low salinity and high COD removal efficiency of 99% were obtained after treatment. Advances in membrane hybrid processes for oily wastewater treatment have been recorded recently, especially when the oily wastewater contains very low concentrations of finely-distributed oil droplets. Membrane hybrid treatment systems combine a membrane separation process with a conventional process such as adsorption, solvent extraction, and distillation or with a mechanical process, biological treatment or chemical reaction. Salahi et al. (2012) studied a hybrid UF/RO system using PAN and polyamide (PA) membranes as the UF and RO membranes, respectively, for oily wastewater treatment. The effects of temperature (25, 37.5 and 5°C), transmembrane

Please cite this article as: Jamaly, S., et al., Recent improvements in oily wastewater treatment: Progress, challenges, and future opportunities, J. Environ. Sci. (2015), http://dx.doi.org/10.1016/j.jes.2015.04.011

658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686

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Recently, more innovative methods have been directed toward the treatment of oily wastewater. For example, Sokker et al. (2011) investigated the adsorption of crude oil with an initial concentration of 0.5–30 g/L by a hydrogel of chitosan-based polyacrylamide prepared by radiation-induced graft polymerization. Their results showed that the hydrogel, which was prepared at a concentration of 40% acrylamide and at a radiation dose of 5 kGy, showed high efficiency in removal of crude oil of 2.3 g/g at pH 3. A new cotton-based hydrogel nanocomposite was successfully prepared by free-radical graft copolymerization of acrylamide and acrylonitrile onto fabric followed by insertion of Ag nanoparticles, by Hosseinzadeh and Mohammadi (2014). The resulting nanocomposite exhibited superhydrophilic and superhydrophobic properties, and the pH of zero point charge of the hydrogel nanocomposite was 6.5. Li et al. (2012) studied the use of biosurfactants in controlling bubble behavior in the flotation method instead of chemosynthetic surfactants. They verified that the addition of 0.04 mmol/L of tea saponin as a biosurfactant decreased the ratio of bubbles by 33%, and it reduced the terminal velocity of the bubbles by 35% and constricted the bubble trajectory by 27%. Therefore, biosurfactants had the effect of a flotation method by increasing the density and specific surface area of

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Abdullah et al. (2010) used a Kapok filter to evaluate oil removal via sorption–filtration. Diesel oil, new engine oil, and used engine oil were used as the experimental oils. It was reported that 1 g of Kapok filter removed up to 36.7 g diesel oil, 50.8 g used engine oil, and 47.4 g new engine oil, and the filter remained stable after 15 cycles of reuse. More than 90% of diesel and used engine oil were retained. Zhao et al. (2011) prepared sponge-like exfoliated vermiculite (EV)/carbon nanotube (CNT) hybrids for oil adsorption. Intercalation of CNT arrays in EV layers resulted into the formation of large amounts of pores and improved oil adsorption capacities. A peak adsorption capacity of 26.7 g/g for diesel oil was recorded, and this was increased to 70.6 g/g through the transformation of EV/CNT hybrids into fluffy EV/CNT cotton by high-speed shearing. As a result of its large surface area and abundant quantities of micropores, activated carbon has been broadly applied for advanced oily wastewater treatment (Coca-Prados et al., 2013). The integration of ceramic MF membranes with powdered activated carbon (PAC) has been investigated for the treatment of oil-in-water emulsion (Yang et al., 2011b). The removal efficiency of TOC and p-xylene was not enhanced by the addition of PAC, as 96% removal was achieved with or without PAC. However, PAC addition improved membrane flux due to its membrane scouring action, and reduced membrane fouling. The membrane flux decreased from 810 to 490 L/(m2·h) in 5 h when no PAC particles were used. Magnetic processes can also be hybridized with membrane separation for oily wastewater treatment. Functionalized magnetic particles such as iron (Fe) or iron oxide (Fe3O4) can be rendered hydrophobic, which makes them able to remain in the oil phase. The separation of the magnetic particle-oil mixture can then be effected by using a permanent magnet or electromagnet (De Vicente et al., 2011).

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pressure (1.5, 3 and 4.5 bar), cross-flow velocity or CFV (0.25, 0.75 and 1.25 m/sec) and pH (4, 7 and 10) on treatment efficiency and membrane fouling were investigated. Optimum operating conditions of TMP (3 bar), CFV (1 m/sec), operating temperature (40°C) and pH (9) were recorded. Also, removal efficiencies of 100%, 98%, 98%, 95% and 100% of oil/grease, TOC (total organic carbon), COD, TDS and turbidity were obtained respectively. Masoudnia et al. (2014) used a hybrid PVDF MF/polyethersulfone UF membrane to treat oily wastewater. 99.9% COD and 99.9% oil/ grease removal was obtained from the hybrid system. Ong et al. (2014) evaluated the performance of a submerged membrane photocatalytic reactor (sMPR) consisting of PVDFTiO2 hollow fiber membranes for the degradation of synthetic oily wastewater under UV irradiation (Fig. 4). It was evident that TOC degradation using a PVDF-TiO2 membrane under UV irradiation was greater compared to that obtained using a neat PVDF membrane. Using a PVDF membrane embedded with 2 wt.% TiO2 at 250 mg/L oil, average membrane flux, TOC and oil removal efficiencies of 73.04 L/(m2·hr), 80% and > 90%, were obtained, respectively. Some attempts have been made to combine sorption processes with membrane filtration for oily wastewater treatment. Sorption–filtration processes remove waste matter from wastewater streams via a sorption material such as a filter bed of granular material that adsorbs and filters out oil droplets. Filtering materials such as graphite, vermiculite, zeolites, wood fiber, cotton fiber, kapok fiber, rice husk, vermiculite, sand, polyester, PVDF, and carbon nanotubes have been tested as oil sorbents (Abdullah et al., 2010; Zhao et al., 2011).

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Fig. 4 – Schematic diagram of the submerged membrane photocatalytic reactor (sMPR) system (Ong et al., 2014). (a) connection to UV lamp control panel, (b) feed solution tank, (c) UV-A lamp, (d1, d2) membrane modules of different packing density, (e) connection to peristaltic pump and permeate collection tank, (f) air diffuser, (g) air flow meter and (h) air compressor.

Please cite this article as: Jamaly, S., et al., Recent improvements in oily wastewater treatment: Progress, challenges, and future opportunities, J. Environ. Sci. (2015), http://dx.doi.org/10.1016/j.jes.2015.04.011

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removed when the current density (c.d.) increased from 0.0009 to 0.02 A/cm2. Moreover, he showed that the oil removal percent was higher with lower sodium chloride concentration. Removal was 90% with fresh water containing 85 mg/L NaCl, whereas, with seawater containing 3.5% NaCl, the oil removal was 80%. However, higher concentrations of NaCl were preferred as the power consumption was lower for seawater with 3.5% NaCl, 0.017 kW/kg-oil removed compared with fresh water containing 85 mg/L NaCl, 0.022 kW/kg-oil removed. Fig. 5 shows the effect of NaCl concentration on the power consumption (Fouad, 2014). Meinero and Zerbinati (2006) studied the oxidative and energetic efficiency of different electrochemical oxidation processes. The electro-Fenton process was shown to have the best degradation efficiency in terms of energy consumption; the specific energy consumption was 0.3 kWh/g of COD, corresponding to 41.8 kWh/m3 (Meinero and Zerbinati, 2006). Furthermore, Coca-Prados and Gutiérrez-Cervelló (2013) reported that the use of membranes is not a desirable method to carry out the whole treatment process for oily wastewater because of the severe fouling that occurs, which leads to high energy consumption, high costs for chemical cleaning, and a need for pretreatment to maintain a steady flux. The optimal choice for lower energy consumption is to combine the oily wastewater technologies with the use of renewable energy. According to Ho et al. (2014), renewable energy technologies are energy-saving methods that can reduce the energy consumption by 20% in wastewater treatment. In addition, Ho et al. (2014) indicated that solar energy and biogas are usually applicable in wastewater treatment. The solar energy source may cover 40% of electricity consumption and biogas can generate 40% of the electricity required. Renewable energy sources can help reduce the carbon dioxide emission with lower treatment cost. Ho et al. (2014) also mentioned that an annual CO2 emission reduction of 7000 to 9100 tons can be achieved with a flow capacity of 100,000 m3/day, leading to reduction of the adverse impacts on the environment.

2. Comparative assessment of oily wastewater methods Several oily wastewater treatment methods are currently used; however, the percent of oil removal varies among them. The assessment of the most efficient technology depends on numerous considerations including the influent quality, the treatment cost, the environmental footprint, and energy consumption. According to Al-Ani (2012), a combined technology consisting of flotation and filtration-adsorption units was the most effective method in the treatment of oily wastewater from an old processing plant of the North Oil Company. Overall removal efficiencies of oil and grease, TDS, COD, and TSS were found to be 99.9%, 89.4%, 99.2%, and 99.5% respectively. Furthermore, Zhu et al. (2014) proved that the most efficient treatment of oily wastewater is membrane technology, including polymer-dominated membranes, ceramic membranes, and nanomaterial-based advanced membranes, because of their high separation efficiency and simple operation. Fakhru'l-Razi et al. (2009) also advised that the biological pretreatment of oily wastewater can be cost effective and environmentally friendly, and it is appropriate to combine it with a physical treatment, like membrane filtration. Chen et al. (2000) concluded that electrocoagulation is a feasible method to treat oily restaurant wastewater characterized by high oil and grease content, because over 94% of oil and grease were removed effectively. Therefore, there are various diverse opinions on how efficient each treatment method is. Energy consumption is another quality used to evaluate the efficiency of oily wastewater treatment technologies. A study was done to separate cottonseed oil from oil–water emulsions using an electrocoagulation method, where the power consumption was calculated (Fouad, 2014). Fouad (2014) reported that the power consumption increased from 0 to 0.9 kW/kg-oil

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There are opportunities for the reuse of oily wastewater in 872 steam boilers or recycling in injection wells for the enhance- 873 ment of crude oil exploitation. There are also opportunities for 874

0.025 Power consumption (kW.h/kg oil removed)

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the bubbles while reducing the bubble size. Rasheed et al. (2011) treated petroleum refinery wastewater by ultrasounddispersed nanoscale zero-valent iron (NZVI). They studied the influence of NZVI dosage and initial pH on COD removal percentage. The optimum initial pH was found to be 5 and the optimum dosage of NZVI was 0.15 g/L. Moreover, Kang et al. (2011) studied a pretreatment system for the treatment of oily wastewater; this pretreatment was based on TiO2 and vacuum ultraviolet irradiation (185 nm). The best conditions for the system were found to be 10 min irradiation, pH 7, flow rate of air 40 L/hr, initial COD 3981 mg/L, and TiO2 150 mg/L. The systems of vacuum ultraviolet and TiO2/vacuum ultraviolet removed respectively 50% ± 3% of COD, 37% ± 2% of BOD2, 86% ± 3% of oil, and 63% ± 3% of COD, 43% ± 2% of BOD2, 70% ± 3% of oil. In addition, ammonia was removed by 17% ± 1% within 30 min of irradiation. Yuan et al. (2011) used natural minerals to destabilize emulsions. The natural minerals that were used in this study consisted of artificial zeolite, natural zeolite, diatomite, bentonite and natural soil. The authors reported that at pH 1 and 60°C that emulsions of were destabilized to form floating oils after the addition of natural minerals, and could be recycled easily. In addition the removal percent of COD was over 90%.

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Fig. 5 – Effect of NaCl concentration on power consumption by electrocoagulation treatment method (Fouad, 2014).

Please cite this article as: Jamaly, S., et al., Recent improvements in oily wastewater treatment: Progress, challenges, and future opportunities, J. Environ. Sci. (2015), http://dx.doi.org/10.1016/j.jes.2015.04.011

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making the sludge more hazardous and creating another environmental concern. For example, 50.9 kWh was required per kg COD removed via Pt/Ir electrodes for oil/water purification of bilge water in a batch electrochemical reactor (Körbahti and Artut, 2010). Without any doubt, newer electrode materials that will ensure lower energy consumption and more deposition of pollutants are required in the future. To reduce the environmental stress resulting from the high energy requirements of electrochemical treatment, future research can also be directed toward the use of renewable or clean energy sources such as solar and wind energy. Doing this will ensure a reduction of depletion of energy resources and improvement in the carbon footprint of oily wastewater treatment via electrochemical methods. Also, there is wide application of membranes in oily wastewater treatment to obtain good oily waste removal efficiencies, especially when the membranes are used for posttreatment. However, membranes are likely to be used when volumes are less than 190 m3 per day (Zeng et al., 2007). Apart from this, membranes are constantly faced with the challenge of fouling, necessitating the need for membrane replacement over time and contributing to economic losses. Therefore, there is a need to develop materials that can give high separation capacity, resistance to oil fouling, and are easily recyclable (Hosseinzadeh and Mohammadi, 2014). Innovative attempts by recent authors to develop functionalized materials with special wettability such as poly(acrylamide) hydrogel (Xue et al., 2011), activated carbon/iron oxide (Ngarmkam et al., 2011), nanocellulose aerogel (Cervin et al., 2011), and reduced graphene oxide foam (Niu et al., 2012) have been technically successful for oil and water separation. From the study carried out by Xue et al. (2011), nanostructured polyacrylamide hydrogel coatings with microscale porous stainless steel mesh substrates (Fig. 6) can separate water (> 99%) from oil/water mixtures such as vegetable oil, gasoline, diesel, and crude oil/water mixtures without any extra power. Several research scientists have developed special wettability-stimulated materials to treat and separate oil and water mixtures. Recent developments of surface wettability materials investigated the absorption capacity of four materials: superhydrophobic and superoleophilic materials, superhydrophilic and under-water superoleophobic materials, superhydrophilic and superoleophobic materials, and smart oil/water separation materials with switchable wettability, for oil and water mixtures (Wang et al., 2015). Wang et al. (2015) estimated that super-lyophobic and super-lyophilic materials can be applied in oil wastewater industries for oil spill remediation in the future. Chen and Xu (2013) developed superhydrophilic and underwater superoleophobic CaCO3-based mineral coatings on poly(acrylic acid)-grafted polypropylene microfiltration membranes for oil/water separation. They concluded that the mineral-coated membranes showed high flux of > 2000 L/(m2·hr), oil/water separation efficiency of > 99%, high oil breakthrough pressure > 140 kPa, and low fouling. A new development of silica-decorated polypropylene microfiltration membranes mediated by a mussel-inspired polydopamine/polyethylenimine layer has also been demonstrated (Yang et al., 2014). These membranes showed high water flux of >1200 L/(m2·hr) under 0.04 MPa, high oil rejection of 99%, and high oil breakthrough

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the sale of the oil concentrate from oily water treatment to oil recycling companies. Furthermore, opportunities for the recovery of precious metals from oily wastewater, especially from petrochemical industries, present a viable economic opportunity, if implemented. However, turning these opportunities into reality has remained a complicated undertaking. A great amount of oily wastewater is discharged into the environment by industries focusing on mechanics and metals because of the difficulty of efficient treatment to remove the fluctuating compositions of different components in oily wastewater under real operating conditions. As a result of the diverse quantities of the varying compounds in oily wastewater, there is no one-size-fits-all approach for the removal and/or recovery of these components. Nowadays, there has been a continuous review of regulatory limits for oily wastewater discharge into the environment in many countries. In China, for example, with a population of 1.36 billion people, the maximum allowable limit for recycling wastewater, as required by the China Department of Petroleum, is 2 mg/L oil and suspended solids for reuse in boiler inlets, and 10 mg/L oil and 5 mg/L suspended solids for recycling into injection wells (Zeng et al., 2007). Thus, efforts toward achieving optimal treatment in terms of the quality of treated oily wastewater for reuse or recycling remain a challenging task (Tir and Moulai-Mostefa, 2008; Zouboulis and Avranas, 2000). Furthermore, limited research concerning the recovery or removal of heavy metals from oily wastewater has been carried out, as most of the previous and current research efforts have been geared toward the separation of oil from water. The presence of heavy metals is one of the major problems militating against the recycling or reuse of wastewater due to their highly hazardous nature. In addition, the presence of heavy metals together with particularly hazardous chemicals (PHCs) in oily wastewater could even result in more deleterious effects when discharged into the environment. In general, not much has been done toward the removal and recovery of heavy metals from oily wastewater to render it less toxic; and this calls for future concern. High levels of heavy metals including Cd, Cr, Cu, Pb, Hg, Ag, Ni, and Zn may be present in oily wastewater from petroleum refineries (Rocha et al., 2012). For example 0.1–100 mg/L Cr and 0.2–10 mg/L Pb, as well as other hazardous pollutants, are contained in oily wastewater from many refineries and process plants (Yavuz et al., 2010). Electrochemical oxidation seems to be an effective method for heavy metal removal from oily wastewater. While using Pt and boron-doped diamond anodes, at a constant applied current density of 40 mA/cm2 and 25°C, heavy metals including Ba, Cr, Fe, Cd, Mn, Zn, Cu, Ni, Pb, Ag, Al, and Sn were removed from petrochemical wastewater by Dos Santos et al. (2014). These inorganics were deposited on the cathode, as observed at this electrode after electrolysis treatment. Electrocoagulation has been found to be more effective than many other treatment technologies because it requires no addition of chemicals, low capital cost, and enhances the settling of the oily sludge produced. However, electrocoagulation requires high operating cost because of the electrical energy requirement, which is mostly sourced from the consumption of fossil fuels in real plants. Apart from this, there is a release of high quantities of metals into the oily sludge produced, thereby

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The adverse impact of highly toxic generated oily wastewaters as well as scarcity of water resources in many regions around the world has driven many researchers and scientists toward developing useful techniques and approaches to produce treated waters of a quality suitable for reuse and recycling. That being stated, technologies such as electrochemical, membrane-based, adsorption and many others have been

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The Masdar Institute of Science and Technology, Abu Dhabi, United Arab Emirates is hugely appreciated for making this review a success through the provision of a library platform where the articles and works reviewed in this paper were accessed.

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investigated at different design parameters and operating limitations. Promising results were reported, yet continuous improvements and innovative solutions along with the cooperative efforts from local and international governments need to be put together toward on-the-ground implementation. In general, there is increasing need to devise new sustainable approaches for oily wastewater treatment that will be geared toward economic savings and environmental preservation, as most of the previous methods are either too costly to be implemented on a commercial scale or require large environmental footprints. Acids had been used, some decades ago, to break down the oil molecules from water. However, because of the labor-intense nature of acid treatment, many of the recent treatment methods discussed in this paper have been developed to make the treatment of oily wastewater become easier and more efficient. Furthermore, more attention should be focused on extremely toxic contaminants that may be present in oily wastewater such as radionuclides, persistent organic pollutants, and PHCs. The release of these substances to soil, water, or air would pose serious threats to the existence of life and environmental sustainability. A single technology cannot satisfy all of the reuse and disposal requirements for different oily sludge wastes. The use of microbial decomposition to remove pollutants from oily wastewater also has its drawbacks, as most of the biological processes are time-consuming and require highly expensive enzymes. In the future, therefore, an integrated approach seems plausible to remove the many components with dissimilar chemical and biological compositions and properties in oily wastewater. This can ensure that the different regulatory limits in many localities or municipalities are met.

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pressure of 0.16 MPa. Similarly, Liu et al. (2015) developed layered double-hydroxide-functionalized textile for an effective separation of oil and water mixtures. Their results indicated high separation efficiency of >97%. They also suggested that superhydrophobic and superoleophilic textiles may be successful for application in cleanup of marine oil spills, recovery, and fuel purification. The design of novel materials with high performance, especially in porous membranes, and the treatment of oily wastewater with membrane coating by the use of wetting surface materials with selective absorption, are highly promising (Chu et al., 2015). The feasibility of the scale-up of these approaches for commercial purposes and the economics of the processes involved for large-scale application have not been investigated. Many of the recent technologies focusing on the improvement of wettability of surfaces (or reduction of interfacial problems) have been carried out using facile methods and synthetic oily wastewater, and more research efforts still need to be directed toward the development of practical solutions for real-world applications. Innovative techniques for membrane fouling reduction such as the use of sponge balls to wipe the membrane surface and clean the membrane of accumulated debris should be enhanced. Doing this will improve membrane efficiency, prolong membrane life, and reduce operating cost. Guo et al. (2008) achieved a 100% increase in sustainable membrane flux, 95% DOC removal, and 97% COD removal through the addition of sponge with a volume fraction of 10% in a membrane bioreactor.

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Fig. 6 – Oil/water separation of polyacrylamide hydrogel-coated mesh (Xue et al., 2011).

Please cite this article as: Jamaly, S., et al., Recent improvements in oily wastewater treatment: Progress, challenges, and future opportunities, J. Environ. Sci. (2015), http://dx.doi.org/10.1016/j.jes.2015.04.011

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Abadi, S.R.H., Sebzari, M.R., Hemati, M., Rekabdar, F., Mohammadi, T., 2011. Ceramic membrane performance in microfiltration of oily wastewater. Desalination 265 (1-3), 222–228. Abbasi, M., Mirfendereski, M., Nikbakht, M., Golshenas, M., Mohammadi, T., 2010. Performance study of mullite and mullite-alumina ceramic MF membranes for oily wastewaters treatment. Desalination 259 (1-3), 169–178. Abdelwahab, O., Amin, N.K., El-Ashtoukhy, E.S.Z., 2009. Electrochemical removal of phenol from oil refinery wastewater. J. Hazard. Mater. 163 (2-3), 711–716. Abdullah, M.A., Rahmah, A.U., Man, Z., 2010. Physicochemical and sorption characteristics of Malaysian Ceiba pentandra (L.) Gaertn. as a natural oil sorbent. J. Hazard. Mater. 177, 683–691. Ahmadi, S., Sardari, E., Javadian, H.R., Katal, R., Sefti, M.V., 2012. Removal of oil from biodiesel wastewater by electrocoagulation method. Korean J. Chem. Eng. 30 (3), 634–641. Al-Ani, F.H., 2012. Treatment of oily wastewater produced from old processing plant of north oil company. Tikrit J. Eng. Sci. 19 (1), 23–34. Cervin, N.T., Aulin, C., Larsson, P.T., Wågberg, L., 2011. Ultra porous nanocellulose aerogels as separation medium for mixtures of oil/water liquids. Cellulose 19 (2), 401–410. Chanthamalee, J., Wongchitphimon, T., Luepromchai, E., 2013. Treatment of oily bilge water from small fishing vessels by PUF-immobilized Gordonia sp. JC11. Water Air Soil Pollut. 224, 1601. Chen, P.C., Xu, Z.K., 2013. Mineral-coated polymer membranes with superhydrophilicity and underwater superoleophobicity for effective oil/water separation. Sci. Rep. 3, 2776. Chen, X., Chen, G., Yue, P.L., 2000. Separation of pollutants from restaurant wastewater by electrocoagulation. Sep. Purif. Technol. 19 (1-2), 65–76. Chu, Z., Feng, Y., Seeger, S., 2015. Oil/Water separation with selective superantiwetting/superwetting surface materials. Angew. Chem. Int. Ed. 54 (8), 2328–2338. Coca-Prados, J., Gutiérrez-Cervelló, G., 2013. Economic sustainability and environmental protection in Mediterranean countries through clean manufacturing methods. NATO Science for Peace and Security Series C: Environmental SecuritySpringer, Netherlands, Dordrecht. Coca-Prados, J., Gutiérrez, G., Benito, J.M., 2013. Treatment of oily wastewater by membrane hybrid processes. In: Coca-Prados, J., Gutiérrez-Cervelló, G. (Eds.), Economic sustainability and environmental protection in Mediterranean countries through clean manufacturing methodsNATO Science for Peace and Security Series C: Environmental Security. Springer, Netherlands, pp. 35–61. Da Cruz, G.F., dos Santos Neto, E.V., Marsaioli, A.J., 2008. Petroleum degradation by aerobic microbiota from the Pampo Sul Oil Field, Campos Basin, Brazil. Org. Geochem. 39 (8), 1204–1209. De Vicente, J., Klingenberg, D.J., Hidalgo-Alvarez, R., 2011. Magnetorheological fluids: a review. Soft Matter 7 (8), 3701–3710. Dos Santos, E.V., Sena, S.F.M., da Silva, D.R., Ferro, S., De Battisti, A., Martínez-Huitle, C.A., 2014. Scale-up of electrochemical oxidation system for treatment of produced water generated by Brazilian petrochemical industry. Environ. Sci. Pollut. Res. Int. 21 (4), 8466–8475. Dumore, N.S., Mukhopadhyay, M., 2012. Removal of oil and grease using immobilized triacylglycerin lipase. Int. Biodeterior. Biodegradation 68, 65–70. Duong, P.H.H., Chung, T.S., Wei, S., Irish, L., 2014. Highly permeable double-skinned forward osmosis membranes for

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