The roles of pH and draw solute on forward osmosis process treating aqueous naphthenic acids
Introduction
The Clark hot water extraction method is widely applied by the Canadian oil sands industry, in which large amounts of water are used to separate the bitumen from the oil sands. As a result, both organic and inorganic compounds are dissolved into the process water creating oil sands process-affected water (OSPW). The organic content of OSPW is made up of naphthenic acids (NAs), polycyclic aromatic hydrocarbons (PAHs), benzene, toluene, ethylbenzene, xylene (BTEX) and phenols [1], [2]. Nearly 50% of the extractable organic fraction in OSPW is NAs which are considered to be one of the primary sources of OSPW toxicity towards aquatic species [3]. NAs have an empirical structure formula of CnH2n+ZO2, where n represents the number of carbon atoms and Z is the deficiency of hydrogen atoms [4]. Typically, the NAs found in OSPW have n number varying from 7 to 30 and the Z number ranging from −12 to 0 [3], [5]. The concentrations of these complex ringed compounds range from 40 to 120 mg/L in the various tailing ponds, depending on the mining process and the pond age [6]. Various treatment processes, including physical, chemical, and biological approaches have been conducted to explore the NA removal in OSPW. For membrane process, the reported rejection efficiency for NAs in OSPW varies from 12.4% to 95%, depending on the membrane types and pre-treatment methods [7], [8], [9].
Forward osmosis (FO) is a membrane-based process that employs osmotic pressure difference between draw and feed solution as driving force [10]. In FO process, ideally, only water molecules can be drawn from the less concentrated feed solution to the concentrated draw solution and those undesirable contaminants can be retained in the feed side. Along with high rejection efficiency, FO owns a few advantages over pressure-driven membrane process including less membrane fouling, reduced energy cost, and simplified operating system [10]. Therefore, applying FO to treat oil and gas wastewater is attracting more research interests [11], [12], [13]. FO has been incorporated in the reclamation of oil and gas drilling wastewater [14], [15], separation of emulsified oil–water [12], and recovery water from petroleum/water emulsions [16], among others. Desirable organic rejections and high water recovery can be achieved with the help of FO process in the treatment of oil and gas wastewater [13], [14].
Rejections of organic compounds can be affected by several factors including properties of target compounds, membrane characteristics, and feed/draw solution chemistry [17]. For instance, Jin et al. [18] investigated the rejection of pharmaceuticals including diclofenac, carbamazepine, ibuprofen, and naproxen by commercial cellulose triacetate (CTA) and thin film composite (TFC) FO membranes. The authors found that TFC exhibited a stable performance in terms of contaminant rejection under various pH conditions. They also suggested that, for CTA membranes, size and hydrophobicity of compounds were two important factors affecting the rejection of tested pharmaceuticals at low pH level. Moreover, Cui et al. [19] studied the removal of phenol, aniline, and nitrobenzene via laboratory fabricated FO membrane using feed/draw solutions with different concentration level. It was reported that the rejection efficiencies were barely affected by the rejection of organic micro-pollutant at concentration lower than 2000 ppm. The authors also observed that, increasing the draw solution concentration, in other words, increasing water flux, can benefit the organic contaminant removal. Besides the influence of pH values and membrane types, membrane fouling also needs to be mentioned. Linares et al. [20] evaluated the rejection of organic micro-pollutants using clean and fouled FO membranes. The experimental results illustrated that the hydrophilic ionic compounds showed a higher rejection in both clean and fouled membranes and the fouling layering improved the rejection of all the micro-pollutants due to the increased hydrophilicity and membrane surface charge.
In this study, the effects of feed solution pH and draw solutes were examined as two important factors affecting the NA rejection and OSPW filtration performance. The rejections of NA model compounds, including cyclohexane carboxylic acid (CHA), 1-adamantaneacetic acid (AAA) and the refined Merichem mixture of NAs, were evaluated at different pH conditions. Also, four draw solution (i.e., NaCl, NH4Cl, CaCl2 and Na2SO4) were studies in order to evaluate their influence on NA removal in terms of reverse salt diffusion and permeate water flux.
Section snippets
Bench-scale FO system
A schematic experimental set-up is shown in Fig. 1. The cellulose triacetate (CTA) membrane was purchased from HTI (Hydration Technologies Innovations, Inc., Albany, OR, USA). The commercial CTA membrane was fabricated asymmetrically with a smooth active layer and an embedded polyester mesh support. Detailed membrane characteristics were described elsewhere [21], [22], [23]. The FO membrane was placed in a SEPA FO membrane cell provided by Sterlitech Corporation (Kent, WA, USA) with the feed
Water flux
Fig. 2 presents the baseline corrected water flux in the rejection experiments at various pH values using CHA, AAA and Merichem NAs as feed solution and 1 M NaCl as draw solution, respectively. As a reference, water flux of pH adjusted OSPW (NA concentration = 25.4 mg/L) is also shown in Fig. 2(d). No significant changes on water flux were observed with respect of pH when applying CHA and AAA aqueous solution as the feed. Decreasing the initial CHA and AAA concentrations from 100 to 25 mg/L did
Conclusions
The current study presented the effect of pH and four draw solutes – NaCl, NH4Cl, Na2 SO4 and CaCl2 – on the rejection of selected NA model compounds including CHA, AAA and Merichem NAs in 7 h. The results indicated that from pH 3 to 9, electrostatic repulsion mechanism dominated CHA and AAA rejection. From pH 6 to 9, the rejection of Merichem NAs was stable (> 92%) likely due to its larger size and electrostatic repulsion force of membrane. At pH 9, the overall rejection of three NA model
Acknowledgements
This research was supported by a research grant from a Natural Sciences and Engineering Research Council of Canada (NSERC) Senior Industrial Research Chair (IRC) Program in Oil Sands Tailings Water Treatment through the support by Syncrude Canada Ltd., Suncor Energy Inc., Shell Canada, Canadian Natural Resources Ltd., Total E&P Canada Ltd., EPCOR Water Services, IOWC Technologies Inc., Alberta Innovates – Energy and Environment Solution, and Alberta Environment and Parks. The financial supports
References (43)
- et al.
Toxicity assessment of collected fractions from an extracted naphthenic acid mixture
Chemosphere
(2008) - et al.
Characterization and pattern recognition of oil-sand naphthenic acids using comprehensive two-dimensional gas chromatography/time-of-flight mass spectrometry
J. Chromatogr. A
(2005) - et al.
Colloidal properties of single component naphthenic acids and complex naphthenic acid mixtures
J. Colloid Interface Sci.
(2013) - et al.
Treatment of oil sands process-affected water with ceramic ultrafiltration membrane: effects of operating conditions on membrane performance
Sep. Purif. Technol.
(2014) - et al.
Improved MEUF removal of naphthenic acids from produced water
J. Membr. Sci.
(2009) - et al.
Forward osmosis: principles, applications, and recent developments
J. Membr. Sci.
(2006) - et al.
Application of forward osmosis for reducing volume of produced/process water from oil and gas operations
Desalination
(2015) - et al.
Application of thin film composite membranes with forward osmosis technology for the separation of emulsified oil-water
J. Membr. Sci.
(2014) - et al.
Forward osmosis desalination of oil and gas wastewater: Impacts of membrane selection and operating conditions on process performance
J. Membr. Sci.
(2015) - et al.
Forward osmosis treatment of drilling mud and fracturing wastewater from oil and gas operations
Desalination
(2013)
The sweet spot of forward osmosis: treatment of produced water, drilling wastewater, and other complex and difficult liquid streams
Desalination
Sustainable water recovery from oily wastewater via forward osmosis-membrane distillation (FO-MD)
Water Res.
Three dimensionless parameters influencing the optimal membrane orientation for forward osmosis
J. Membr. Sci.
Rejection of pharmaceuticals by forward osmosis membranes
J. Hazard. Mater.
Removal of organic micro-pollutants (phenol, aniline and nitrobenzene) via forward osmosis (FO) process: evaluation of FO as an alternative method to reverse osmosis (RO)
Water Res.
Impact of intrinsic properties of foulants on membrane performance in osmotic desalination applications
Sep. Purif. Technol.
Effects of feed and draw solution temperature and transmembrane temperature difference on the rejection of trace organic contaminants by forward osmosis
J. Membr. Sci.
Comparison of tetracycline rejection in reclaimed water by three kinds of forward osmosis membranes
Desalination
Impact of organic and colloidal fouling on trace organic contaminant rejection by forward osmosis: role of initial permeate flux
Desalination
Evaluation of the transport parameters and physiochemical properties of forward osmosis membranes after treatment of produced water
J. Membr. Sci.
Towards direct potable reuse with forward osmosis: technical assessment of long-term process performance at the pilot scale
J. Membr. Sci.
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2021, Process Safety and Environmental ProtectionCitation Excerpt :The general chemical formula for naphthenic acids is CnH(2n+Z)Ox, where n is the number of carbon atoms, Z is the hydrogen deficiency as a result of the rings formation and/or double bonds, and x refers to the oxygen atoms within the structure. In produced water, it is found to have a n number between 7–30 and the Z number from −12 to 0 (Zhu et al., 2018), and x from 2 (classical NAs) and x≥3 for oxidized NAs, where is contemplated a complex mixture of oxidized organics, containing three or more oxygen-atoms, sulfur and nitrogen heteroatoms (Abdalrhman et al., 2020; Meshref et al., 2020; Miles et al., 2020; Speight, 2014; Miles et al., 2020). As previously discussed, naphthenic compounds are ubiquitous and recalcitrant pollutants in OPW, difficult to be biodegraded naturally, consequently, considered the main contributors to OPW complex properties (Wu et al., 2019; Abdalrhman et al., 2020), particularly O2-NA species, which are the most recalcitrant naphthenic acids present in OPW, considering that cyclic structures are generally more resistant to biodegradation than straight-chain molecules of equivalent molecular weight (Klemz et al., 2020; Speight, 2014).
Enhancing the removal efficiency of osmotic membrane bioreactors: A comprehensive review of influencing parameters and hybrid configurations
2019, ChemosphereCitation Excerpt :Luo et al. (2015) revealed that in the absence of aeration, permeate flux dropped significantly from 8.0 L/m2h to 2.0 L/m2h in the experimental period, compared to lower decreases from 8 L/m2h to approximately 5.7 L/m2h, 6.5 L/m2h, and 7 L/m2h in continuous aeration mode at specific aeration demand (SADm) values of 4 m3/m2h, 8 m3/m2h, and 12 m3/m2h, respectively (Luo et al., 2015). pH has been reported to be a critical factor that can affect the performance of both membrane and biological processes (Ruengruehan et al., 2016; Zhang et al., 2014b; Zhu et al., 2018a). The influence of pH on water flux and salt flux in the FO process was studied by Hau et al. (2014) and Wang et al. (2014a); these authors found that permeate water and RSF increased slightly when the pH value of draw solution increased from 4.5 to 7.0.