Erika Nascimben Santos1,2,3,*, Gábor Veréb1,*, Szabolcs Kertész1, Cecilia Hodúr1,3, Zsuzsanna László1
1 Institute of Process Engineering, Faculty of Engineering, University of Szeged, HU-6725, Moszkvai Blvd. 9., Szeged, Hungary
2 Doctoral School of Environmental Sciences, University of Szeged, H-6701, P.O.B. 440, Szeged, Hungary
3 Institute of Environmental Science and Technology, University of Szeged, H-6720, Tisza Lajos Blvd. 103, Szeged, Hungary
* e-mail address: erikans123@gmail.com, verebg@mk.u-szeged.hu
Introduction
It is important to treat effectively the oil-contaminated waters, since they are produced in high amounts by several industrial activities [1], and their toxics compounds can significantly affect negatively the environment [2, 3]. To achieve excellent efficiency, the conventional techniques (such as flotation, centrifugation, skimming, etc.) are not enough because of the small emulsified oil droplets that cannot be removed by these methods [4]. The complementation of these techniques with membrane filtration can be a good solution to this problem, since, over the high achievable efficiency, it has other additional advantages, like the easy operation and integration. However, the generation of a hydrophobic cake layer – and the fouling of the pores – that reduce quickly and significantly the flux can make the utilization of this technology not feasible [5]. Thinking about this, many studies target to fix this problem by developing different promising solutions. One of them is the membrane modification, which can be achieved, for example, by using hydrophilic and photocatalytic nanomaterials.
The present work shows a brief overview about the utilization of membrane filtration for treating oily wastewaters – explains the difficulties, the main problems and discusses promising solutions to improve this treatment method and to find feasible technologies, focusing on membrane modifications, mainly with hydrophilic and photocatalytic nanomaterials that can results in self-cleaning and antifouling properties.
Main pollutants of oil-contaminated waters and their harmful effects
Oils contain several harmful compounds: saturated straight and branched-chain hydrocarbons, cyclic hydrocarbons, olefins, aromatic hydrocarbons and others, such as sulfur compounds, nitrogen-oxygen compounds, and heavy metals. The harmfulness of the oil-contaminated waters depends on the type, volume, and quality of the polluting oil, but also on the place and conditions of the discharge. The oily wastewaters can cause harmful effects on organisms by coating, asphyxiation, poisoning or causing sublethal and stress effects, reducing the abundance and diversity of the fauna and flora [2]. The soils also can be affected by oil contaminations, reducing the bacteria activity, the life of earthworms and plant growth, by affecting the root elongation and germination [6]. In relation to animals and human beings, oil contaminations can be accumulated in the food chain, can damage the DNA, and can produce genotoxic, carcinogenic, mutagenic effects, and immune-suppression as well [3, 7].
Membrane technology to treat oil-contaminated waters
Membrane filtration technique became a promising purification method to treat oily wastewaters due to its’ several advantages, i.e. no chemical addition, easy handling, low energy requirement, and high efficiency. The separation method consists of using a physical
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barrier (membrane) that allows the water to flow by the action of a driving force while the contaminants are retained by the barrier [8]. Both micro- and ultrafiltration can be used to remove efficiently the oils, however, ultrafiltration shows higher efficiency to remove smaller droplets and to reduce the total organic carbon (TOC) content and chemical organic demand (COD) [9, 10]. The technology faces several challenges e.g. the reduction of fouling, which is the major limitation in several cases [5]. During the filtration, various compounds can be deposited or adsorbed on the membrane surface, such as salts, hydroxides, surfactants and oil droplets [11], causing the fouling of the pores and the formation of hydrophobic cake layer.
These problems cause significantly reduced flux, permeability, productivity, decreased life span, and increased energy consumption and treatment costs. The fouling layer can be affected by different reasons [5]:
i. characteristics of the feed water, e.g. concentrations and physicochemical properties;
ii. characteristics of the membrane, e.g., surface roughness, charge properties, hydrophobicity;
iii. operational conditions, e.g. cross-flow velocity, applied pressure difference, recovery and temperature.
It is necessary to solve the major limitation and make the use of this technology feasible for treating oil-in-water emulsions.
Potential solutions for fouling problems
It is necessary to minimize the interaction between the wastewater’s contaminants and the membrane surface to reduce fouling and, for this, there are some possible solutions, i.e.:
i. utilization of backflushing with air, water or permeate, to increase the efficiency and hydrophilicity [12];
ii. application of biological, physical or chemical pre-treatment for example, degasification, chemical softening, media filtration, ion-exchange softening, ozonation, etc. [13]–[15];
iii. Utilization of membrane modification by blending [16], by coating or by the deposition of nanomaterials onto the membrane surface [17].
The use of nanomaterials to modify the membrane has a huge potential to improve membrane efficiency due to its high surface area and high surface-active groups [8].
Membrane modification with photocatalytic nanomaterials
Photocatalytic nanomaterials can also be used to modify the membrane, since they have the ability to decompose several organic pollutants via their light-induced activation [18]. These UV and/or solar-light activated semiconductor materials can generate electron/hole pairs that can oxidize directly or indirectly the organic contaminants. Therefore, these photocatalytic nanoparticles can be used to prepare self-cleaning membrane, that can be activated and purified by photons regaining the permeability without shutdown the filtration, increasing costs or reducing the membrane life [19]. There are several well-known photocatalytic materials such as zinc oxide (ZnO), zinc sulfide (ZnS), tin oxide (SnO2), copper oxide (CuO2), cadmium sulfide (CdS), tungsten trioxide (WO3), and the most investigated, titanium dioxide (TiO2) due to its low cost, high chemical stability and photocatalytic activity, availability, etc. [18]. TiO2 can improve hydrophilicity, stability and anti-fouling properties of membranes, however, it can be activated mostly with ultraviolet light, which is a small fraction of the solar spectrum – 3 to 8%. Therefore, efforts have to be done to develop visible-light sensitive photocatalytic material [20], [21], to form solar-visible-light activable photocatalytic membrane. The addition of other nanomaterials to TiO2 to modify the membrane has gaining attention because of the enhanced properties of the coupled materials. The use of WO3, ZnO, BiVO4 and noble metals such as Ag, Au, Pt, and Pd are showing good results in relation with
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important, and not well investigated until now. It is possible to recognize the effort on research to find efficient photocatalytic composites that can be used to modify membrane used to the treatment of oily wastewater with higher efficiency and better anti-fouling properties, however, further investigations are necessary to be carried out for industrial utilization.
Conclusions
It is difficult, but necessary to find an excellent purification technology to treat oily wastewaters with high efficiency and economically friendly. Membrane filtration has been developed intensely in the last years, nevertheless, membrane fouling and flux reduction are still serious limiting factors in the case of oily contaminants. Membrane modification methods show good potential to further enhances because they can improve the hydrophilicity and anti-fouling properties of the membranes. Photocatalytic nanocomposites can be used to reduce the adhesion of these kinds of pollutants on the membrane surface and to decompose photocatalytically the yet adhered organic pollutants. TiO2 has been widely investigated for membrane modification, but further investigations are necessary to be done in order to find photocatalytic nanocomposites that are able to combine the good filtration properties and high visible-light and solar-light activities to make the system more economical and efficient.
Acknowledgments
The authors are grateful for the financial support provided by the Hungarian Science and Research Foundation (2017-2.3.7-TÉT-IN-2017-00016) and by the Hungarian State and the European Union (EFOP-3.6.2-16-2017-00010 – RING 2017). E.N.S thanks for the support of the Stipendium Hungaricum Scholarship Program.
References
[1] S. G. Poulopoulos, E. C. Voutsas, H. P. Grigoropoulou, and C. J. Philippopoulos,
“Stripping as a pretreatment process of industrial oily wastewater,” J. Hazard. Mater., vol. 117, no. 2–3, pp. 135–139, 2005.
[2] R. P. Cote, “The effects of petroleum refinery liquid wastes on aquatic life, with special emphasis on the Canadian environment,” Natl. Res. Counc. Canada, vol. K1A 0R6, no.
NRC Associate Committee on Scientific Criteria for Environmental Quality, p. 77, 1976.
[3] H. I. Abdel-Shafy and M. S. M. Mansour, “A review on polycyclic aromatic hydrocarbons: Source, environmental impact, effect on human health and remediation,”
Egypt. J. Pet., vol. 25, no. 1, pp. 107–123, 2016.
[4] L. Yu, M. Han, and F. He, “A review of treating oily wastewater,” Arab. J. Chem., vol.
10, pp. S1913–S1922, 2017.
[5] C. Y. Tang, T. H. Chong, and A. G. Fane, “Colloidal interactions and fouling of NF and RO membranes: A review,” Adv. Colloid Interface Sci., vol. 164, no. 1–2, pp. 126–
143, 2011.
[6] J. Tang, M. Wang, F. Wang, Q. Sun, and Q. Zhou, “Eco-toxicity of petroleum hydrocarbon contaminated soil,” J. Environ. Sci., vol. 23, no. 5, pp. 845–851, 2011.
[7] T. L. Tasker et al., “Environmental and Human Health Impacts of Spreading Oil and Gas Wastewater on Roads,” Environ. Sci. Technol., vol. 52, no. 12, pp. 7081–7091,
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TiO2 photocatalysis process,” J. Memb. Sci., vol. 275, no. 1–2, pp. 202–211, 2006.
[10] S. Nazirah, W. Ikhsan, N. Yusof, and F. Aziz, “a Review of Oilfield Wastewater Treatment Using Membrane Filtration Over Conventional Technology,” Malaysian J.
Anal. Sci., vol. 21, no. 3, 2018.
[11] S. Alzahrani and A. W. Mohammad, “Challenges and trends in membrane technology implementation for produced water treatment: A review,” J. Water Process Eng., vol.
4, no. C, pp. 107–133, 2014.
[12] P. Srijaroonrat, E. Julien, and Y. Aurelle, “Unstable secondary oil/water emulsion treatment using ultrafiltration: Fouling control by backflushing,” J. Memb. Sci., vol.
159, no. 1–2, pp. 11–20, 1999.
[13] I. Kovács, G. Veréb, S. Kertész, C. Hodúr, and Z. László, “Fouling mitigation and cleanability of TiO2 photocatalyst-modified PVDF membranes during ultrafiltration of model oily wastewater with different salt contents,” Environ. Sci. Pollut. Res., vol. 25, no. 35, pp. 34912–34921, 2018.
[14] G. Doran, F. Carini, and D. Fruth, “Evaluation of Technologies to Treat oil Field Produced Water or Reuse Quality.” 1997.
[15] R. J. W. Brooijmans, M. I. Pastink, and R. J. Siezen, “Hydrocarbon-degrading bacteria:
the oil-spill clean-up crew,” Microb. Biotechnol., vol. 2, no. 6, pp. 587–594, 2009.
[16] G. Arthanareeswaran, T. K. Sriyamuna Devi, and M. Raajenthiren, “Effect of silica particles on cellulose acetate blend ultrafiltration membranes: Part I,” Sep. Purif.
Technol., vol. 64, no. 1, pp. 38–47, 2008.
[17] W. Chan, H. Chen, A. Surapathi, and M. Taylor, “Zwitterion Functionalized Carbon Nanotube / Polyamide Nanocomposite Membranes for Water Desalination,” ACS Nano, no. Xx, 2013.
[18] J. Saien and H. Nejati, “Enhanced photocatalytic degradation of pollutants in petroleum refinery wastewater under mild conditions,” J. Hazard. Mater., vol. 148, no. 1–2, pp.
491–495, 2007.
[19] S. S. Madaeni and N. Ghaemi, “Characterization of self-cleaning RO membranes coated with TiO2 particles under UV irradiation,” J. Memb. Sci., vol. 303, no. 1–2, pp.
221–233, 2007.
[20] H. Jiang et al., “Hydrothermal fabrication and visible-light-driven photocatalytic properties of bismuth vanadate with multiple morphologies and/or porous structures for Methyl Orange degradation,” J. Environ. Sci., vol. 24, no. 3, pp. 449–457, 2012.
[21] R. Molinari, C. Lavorato, and P. Argurio, “Recent progress of photocatalytic membrane reactors in water treatment and in synthesis of organic compounds. A review,” Catal. Today, vol. 281, pp. 144–164, 2017.
[22] L. Baia et al., “Preparation of TiO2/WO3 composite photocatalysts by the adjustment of the semiconductors’ surface charge,” Mater. Sci. Semicond. Process., vol. 42, pp.
66–71, 2016.
[23] G. Kovács et al., “TiO2/WO3/Au nanoarchitectures’ photocatalytic activity, ‘from degradation intermediates to catalysts’’ structural peculiarities", Part I: Aeroxide P25 based composites,’” Appl. Catal. B Environ., vol. 147, pp. 508–517, 2014.
[24] A. Mishra, A. Mehta, M. Sharma, and S. Basu, “Impact of Ag nanoparticles on photomineralization of chlorobenzene by TiO2/bentonite nanocomposite,” J. Environ.
Chem. Eng., vol. 5, no. 1, pp. 644–651, 2017.
[25] X. Yu, Q. Ji, J. Zhang, Z. Nie, and H. Yang, “Photocatalytic degradation of diesel pollutants in seawater under visible light,” Reg. Stud. Mar. Sci., vol. 18, pp. 139–144, 2018.
25th International Symposium on Analytical and Environmental Problems
INVESTIGATION OF PRIORITY POLLUTANTS IN THE SEDIMENT PHASE – PROJECT SIMONA
Mária Mörtl1, Zsófia Kovács2, Győző Jordán3, András Székács1
1Department of Environmental Analysis, Agro-Environmental Research Institute, National Agricultural Research and Innovation Centre,
H-1022 Budapest, Herman Ottó u. 15, Hungary.
2Institute of Environmental Engineering, University of Pannonia, H-8200 Veszprém, Egyetem u. 10, Hungary
3Department of Applied Chemistry, Faculty of Food Science, Szent István University, H-1118 Budapest, Villányi út 29-43, Hungary
e-mail: mortl.maria@akk. naik.hu
Abstract
The Framework Directive (WFD) of the European Union (EU) aims to achieve good status for water bodies in EU, but there occurs a delay in its implementation related to priority pollutant substances. A key issue in water protection and management is that priority pollutants should be monitored not only in the water bodies, but also in sediments and the biota. Distribution between the water and sediment phases is strongly affected by numerous factors, including the polarity of the analytes, as well as amorphous organic matter and suspended matter content in the water body, and are often affected by methodological parameters. As a result, certain pollutants will be detected in the water phase, others in the sediment, again others in both, as indicated by reported cases in the scientific literature. This challenge is illustrated in the case of project “Sediment-quality Information, Monitoring and Assessment System” (SIMONA) (2018-2021) within the Danube Transnational Program.
Introduction
Water protection is one of the priorities of the European Commission. The European Water Policy aims to protect clean water in the European Union (EU) by preventing water pollution and to restore clean water from polluted sites. Thus, the EU Water Framework Directive (WFD), as one of the key EU policy measures, aims to reach a good status both chemical and ecological, for water bodies in Europe [1]. Water pollutants that jeopardize such good status represent a threat to the aquatic environment, and the WFD specified the most hazardous substances of these to be phased out. For this purpose, priority substances (PSs) presenting a significant risk to or via the aquatic environment were listed in 2008 [2]. The first watch list for European Union-wide monitoring of water bodies was published in 2015 [3] containing ten substances or groups of components, that was further extended in 2018 [4].
Nonetheless, the original goals of the EU water protection policy have not yet been achieved, and there appears a delay in the implementation of the objectives set in the WFD [5].
Previously monitoring at the point of discharge was typical to control the emission of specific pollutants (end-of-pipe). In turn, regulation has shifted lately towards systematic (integrated) thinking that focuses on sustainability, flexible water governance, determination of indicators, complex understanding of drivers, pressures, state impacts and responses in catchments. In addition to the determination of emissions and maximum limits, environmental quality standards (EQSs) have been set for certain substances, and management actions must account for the effects of multiple stressors. Monitoring and assessment need to better reflect improvement in the ecological status and long-term tendencies [6].
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Affecting factors that influence distribution of pollutants
The current list of 20 PSs, 13 priority hazardous substances (PHSs) [2], 11 substances subject to review for possible identification as PSs or PHSs, and 8 substances on watch list [3]
includes, among other groups of toxic compounds, pesticide active ingredients and their metabolites or contaminants. In addition, chemical intermediates, by-product polyaromatic hydrocarbons (PAHs), polybrominated biphenylethers (PBDEs), biocides, metals, as well as hormones and antibiotics are also found on the lists.
These compounds are regularly measured in water bodies, their EQSs are intended also for sediment and biota, yet far less information is available about their substantive concentration in the sediment. Partition of the components depends on their polarity characterized by their octanol/water partition coefficient (Kow). On the other hand, higher organic matter content in the sediment bind more non-polar components compared to those with lower organic content.
Therefore, the equilibrium constant is often given to organic matter content of soils (Koc).
Distribution between the two phases results in different mobilities , which is strongly influenced by other factors e.g., suspended matter content. Worthy of note, that there is no equilibrium in the rivers between water body and the sediment. Based on the Kow, compounds having Kow < 3 are water pollutants, while components characterized by Kow > 5 are sediment pollutants. Other components (3 ≤ Kow ≤ 5) are present in both phases. Partition influences the analytical results and contamination levels determined in water. Analysis of the entire water body often fails as the water sample is filtered prior to sample preparation (solid phase extraction) or instrumental analysis (liquid chromatography) in numerous analytical protocols.
Certain pollutants, however, are partially or completely removed by filtration. Faludi et al. [8]
determined substituted phenols in both the Danube river and its suspended matter. Yet e.g., priority substance pentachlorophenol was detected only in the suspended phase, which is rarely analyzed.
Temporal variation of the analytes is high in the water phase, but less variable in the sediment. If a spot sample is taken, only the concentration currently present in water can be measured. Nowadays, pollutant levels on a longer time-scale can be determined in surface water by the use of passive samplers. These keep collecting pollutants for one or two weeks, but the derived information differ from the results obtained for spot samples. Both information are important as not only the maximum, but also the average concentrations are often regulated for certain pollutants. Grab sampling and collection by polar organic chemical integrative sampler (POCIS) for organic compounds with a 0 ≤ log Kow ≤ 5 were simultaneously applied, and the results were compared [9]. Pollution patterns reflect the land use and loads, but also the presence of persistent components. For example, herbicide active ingredient atrazine is still detected, despite of its ban in the EU in 2004. A partial cause of this water polluting characteristics is accumulation and practically no decomposition of the compound in the anaerobic soil zones, and subsequent leaching to surface water.
Unfortunately, illegal use of this prohibited pesticide active ingredient also occurs: fresh loads of atrazine were confirmed by its high concentration together with its low metabolite levels (desethyl atrazine). Atrazine was detected by us in Hungarian water and soil samples as well at around 2010, after its ban in 2007, but it did not appear any further during monitoring of the Danube river in 2015, indicating that its level decreased below the detection limit of our method [10].
Comparison of pollution patterns and contamination levels of sediment and water samples [11] showed significant spatial variations in water and sediment. Seasonality in concentration was observed in water, but not in sediment, although sediment concentrations varied substantially among different years. Average measured non-equilibrium distribution coefficients exceeded equilibrium hydrophobic partitioning-based predictions for 5 of the 7
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hydrophobicity and persistence. These observations indicate non-equilibrium conditions between water and sediment phases and slow rate of adsorption. Among detected compounds, the distribution of more polar and degradable components showed greater variability, probably due to their degradation. On the other hand, non-sorptive components (based on their log Kow values) were found also in the sediment indicating the importance of other processes (e.g. complex formation).
Inorganic components of the sediment may occasionally be equally important, as it was observed for example in the case of glyphosate and iron-oxide. Gama et al. [12] studied the distribution of different herbicides. Non-polar compounds with high log Kow and Koc values were more likely to be found in the inorganic fraction of the sediment, whereas more polar herbicides with high solubility and low Koc values were dispersed between both the organic and inorganic fractions. The interaction between chemicals and amorphous organic matter (e.g., humic and fulvic acids, proteins, lignin, polysaccharides) might also modify the partition process.
Partition among the water-dissolved phase (DP), suspended particulate matter (SPM) and sediment may also become characteristic. Montuori et al. [13] measured pollution by organophosphate pesticides (OPP) in the Sarno river (Italy), and detected these compounds in
Partition among the water-dissolved phase (DP), suspended particulate matter (SPM) and sediment may also become characteristic. Montuori et al. [13] measured pollution by organophosphate pesticides (OPP) in the Sarno river (Italy), and detected these compounds in