Abstract
The reclamation of oil sands process-affected water (OSPW) is a matter of environmental importance because of the aquatic toxicity to biota. This study describes refinements in advanced analytical methods to assess the performance of biological treatment systems for OSPW, such as constructed wetland treatment systems (CWTSs). Assessment of treatment efficiency by measurement of the degradation of naphthenic acid fraction compounds (NAFCs) in OSPW is challenging in CWTS due to potentially interfering constituents such as humic acids, organic acids, salts, and hydrocarbons. Here we have applied a previous weak anion exchange (WAX) solid-phase extraction (SPE) method and high-resolution Orbitrap-mass spectrometry (MS) to remove major interferences from the NAFC analysis. The refinements in data processing employing principal component analysis (PCA) indicates that the relative abundance of NAFCs decreased with time in the treated OSPW relative to the untreated OSPW. The most saturated NAFCs with higher carbon numbers were relatively more degraded as compared to unsaturated NAFCs. The use of Kendrick plots and van Krevelen plots for assessment of the performance of the CWTS is shown to be well-suited to detailed monitoring of the complex composition of NAFCs as a function of degradation. The developments and application of analytical methods such as the WAX SPE method and high-resolution Orbitrap-MS are demonstrated as tools enabling the advancement of CWTS design and optimization, enabling passive or semi-passive water treatment systems to be a viable opportunity for OSPW treatment.
Highlights
The mining of oil sands in northeastern Alberta, Canada, generates large volumes of petroleum-contaminated water known as oil sands process-affected water (OSPW)
The organic compounds contained in OSPW can be further classified as dissolved organics or water-soluble polar organic acid fraction, including a group of organic acids identified as naphthenic acid fraction compounds (NAFCs) [10,11,12]
This study provides further evidence that the weak anion exchange (WAX) solid-phase extraction (SPE) method combined with high-resolution Orbitrap-mass spectrometry (MS) is viable and robust for measurement of the biodegradation of OSPW-Naphthenic acids (NAs) in constructed wetland treatment systems (CWTSs)
Summary
The mining of oil sands in northeastern Alberta, Canada, generates large volumes of petroleum-contaminated water known as oil sands process-affected water (OSPW). A volume of 720 million m3 of OSPW, held in tailing ponds that cover an area of more than 170 km , awaits remediation [1]. The OSPW is a complex mixture of varying proportions of suspended solids, including extremely fine clays, inorganic constituents (i.e., salts, metals, metalloids), and organic constituents (e.g., naphthenic acids (NAs), polycyclic aromatic hydrocarbons (PAHs), oil, and grease) [9]. The organic compounds contained in OSPW can be further classified as dissolved organics or water-soluble polar organic acid fraction, including a group of organic acids identified as naphthenic acid fraction compounds (NAFCs) [10,11,12]. Naphthenic acids (NAs) are one component of NAFCs that are described by a general formula of Cn H2n+Z Ox, where n indicates the carbon number and Z specifies the hydrogen deficiency due to ring or double bond formation. Since Z is either zero or a negative integer, some researchers prefer the positive values of the double bond equivalent (DBE)
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