Investigation of Hydrophobic Organic Carbon (HOC) Partitioning to 1 kDa Fractionated Municipal Wastewater Colloids

Natural organic matter from the aquatic environment passing a 1 kDa filter has been hypothesized to not contribute appreciably to hydrophobic organic compound (HOC) partitioning; however, to our knowledge this limit has not been verified experimentally for any sorbate/sorbent system. Presently, colloidal organic carbon (COC) < 1 kDa approached 70% of the total COC (<1.5 μm) mass in primary effluent (PE) from a municipal wastewater treatment plant. Partitioning of HOCs 1,2,4,5-tetrachlorobenzene, pentachlorobenzene, and hexachlorobenzene to COC for both 1.5 μm and 1 kDa filtrates of PE was investigated using the gas-stripping technique. Contrary to the hypothesis, significant HOC–COC partitioning to the 1 kDa filtrate was observed with organic carbon-normalized partitioning coefficients (log<i>K</i>_COC) of 4.30, 4.36, and 3.74 for 1,2,4,5-TeCB, PeCB, and HCB, respectively. Further, partitioning to COC < 1 kDa dominated the overall partitioning of the three chlorobenzenes in the 1.5 μm filtrate, and the partitioning behavior did not follow the trend based on hydrophobicity (<i>K</i>_OW). The results show that significant partitioning of HOC may occur to OC < 1 kDa and highlights the need for further experiments with other HOCs and COC characterization to better understand and explain the observed partitioning

Ultra Performance Liquid Chromatography Ion Mobility Time-of-Flight Mass Spectrometry Characterization of Naphthenic Acids Species from Oil Sands Process-Affected Water

Ultraperformance liquid chromatography ion mobility time-of-flight mass spectrometry (UPLC-IM-TOFMS), integrating traveling wave ion mobility spectrometry (TWIMS) with negative electrospray ionization (ESI) mode, was used to achieve two-dimensional (2D) separation (drift vs retention times) of naphthenic acids (NAs). Unprocessed and ozonated commercial NAs were used for method development. Only O₂–NAs were found in unprocessed NAs with ozonation creating O₃–NAs and O₄–NAs. Unprocessed and ozonated oil sands process-affected waters (OSPW) were examined to validate the method for complex matrix NAs. Ozonation increased the <i>x</i> number for O_<i>x</i>–NAs (2 ≤ <i>x</i> ≤ 5) and also impacted the −<i>Z</i> number distribution. OSPW extracted using dichloromethane removed the potential for sample matrix impacts and was used for MS/MS NAs characterization. The O_<i>x</i>–NAs (2 ≤ <i>x</i> ≤ 6) were identified with O₂–NAs separated into three clusters indicating isobaric and isomeric species. MS/MS was used to verify compounds, while also indicating the presence of CH₃CH₂S– NAs groups. This result may be useful for future studies of sulfur-NAs fate, toxicity, and treatment. Overall, the value-added information provided by UPLC-IM-TOFMS makes it a promising analytical technique for analysis of NAs in complex OSPW samples. Moreover, this methodology can be used for other matrices to investigate relative molecular sizes and to separate complex species (e.g., fatty acids, lipids), making it beneficial for environmental and bioanalytical applications

Granular activated carbon for simultaneous adsorption and biodegradation of toxic oil sands process-affected water organic compounds

Naphthenic acids (NAs) released into oil sands process-affected water (OSPW) during bitumen processing in Northern Alberta are problematic for oil sands industries due to their toxicity in the environment and resistance to degradation during conventional wastewater treatment processes. Granular activated carbon (GAC) has shown to be an effective media in removing biopersistent organics from wastewater using a combination of adsorption and biodegradation removal mechanisms. A simultaneous GAC (0.4g GAC/L) adsorption and biodegradation (combined treatment) study was used for the treatment of raw and ozonated OSPW. After 28 days of batch treatment, classical and oxidized NAs removals for raw OSPW were 93.3% and 73.7%, and for ozonated OSPW were 96.2% and 77.1%, respectively. Synergetic effects of the combined treatment process were observed in removals of COD, the acid extractable fraction, and oxidized NAs, which indicated enhanced biodegradation and bioregeneration in GAC biofilms. A bacteria copy number >108 copies/g GAC on GAC surfaces was found using quantitative real time polymerase chain reaction after treatment for both raw and ozonated OSPW. A Microtox® acute toxicity test (Vibrio fischeri) showed effective toxicity removal (>95.3%) for the combined treatments. Therefore, the simultaneous GAC adsorption and biodegradation treatment process is a promising technology for the elimination of toxic OSPW NAs.</p

Mechanistic investigation of industrial wastewater naphthenic acids removal using granular activated carbon (GAC) biofilm based processes

Naphthenic acids (NAs) found in oil sands process-affected waters (OSPW) have known environmental toxicity and are resistant to conventional wastewater treatments. The granular activated carbon (GAC) biofilm treatment process has been shown to effectively treat OSPW NAs via combined adsorption/biodegradation processes despite the lack of research investigating their individual contributions. Presently, the NAs removals due to the individual processes of adsorption and biodegradation in OSPW bioreactors were determined using sodium azide to inhibit biodegradation. For raw OSPW, after 28 days biodegradation and adsorption contributed 14% and 63% of NA removal, respectively. For ozonated OSPW, biodegradation removed 18% of NAs while adsorption reduced NAs by 73%. Microbial community 454-pyrosequencing of bioreactor matrices indicated the importance of biodegradation given the diverse carbon degrading families including Acidobacteriaceae, Ectothiorhodospiraceae, and Comamonadaceae. Overall, results highlight the ability to determine specific processes of NAs removals in the combined treatment process in the presence of diverse bacteria metabolic groups found in GAC bioreactors.</p

Isotherm and kinetic studies on adsorption of oil sands process-affected water organic compounds using granular activated carbon

The production of oil from oil sands in northern Alberta has led to the generation of large volumes of oil sands process-affected water (OSPW) that was reported to be toxic to aquatic and other living organisms. The toxicity of OSPW has been attributed to the complex nature of OSPW matrix including the inorganic and organic compounds primarily naphthenic acids (NAs: CnH2n+ZOx). In the present study, granular activated carbon (GAC) adsorption was investigated for its potential use to treat raw and ozonated OSPW. The results indicated that NA species removal increased with carbon number (n) for a fixed Z number; however, the NA species removal decreased with Z number for a fixed carbon number. The maximum adsorption capacities obtained from Langmuir adsorption isotherm based on acid-extractable fraction (AEF) and NAs were 98.5 mg and 60.9 mg AEF/g GAC and 60 mg and 37 mg NA/g GAC for raw and ozonated OSPW, respectively. It was found that the Freundlich isotherm model best fits the AEF and NA equilibrium data (r2 ≥ 0.88). The adsorption kinetics showed that the pseudo-second order and intraparticle diffusion models were both appropriate in modeling the adsorption kinetics of AEF and NAs to GAC (r2 ≥ 0.97). Although pore diffusion was the rate limiting step, film diffusion was still significant for assessing the rate of diffusion of NAs. This study could be helpful to model, design and optimize the adsorption treatment technologies of OSPW and to assess the performance of other adsorbents.</p

Investigation of Mono/Competitive Adsorption of Environmentally Relevant Ionized Weak Acids on Graphite: Impact of Molecular Properties and Thermodynamics

The thermodynamics of adsorption and competitive interactions of five weak acids on a graphite surface was assessed in alkaline solutions. Adsorption of the acids in mono- and multicompound solutions followed their Freundlich isotherms which suggest a diversity of graphite adsorption sites as confirmed by the presence of carboxylic and phenolic groups observed on graphite surfaces. Thermodynamic calculations assigned the formation of the negatively charged assisted hydrogen bond (−CAHB) between ionized solutes and adsorbent surface groups as the possible adsorption mechanism. However, the similar p<i>K</i>_a values of current acids resulted in comparable free energies for −CAHB formation (Δ<i>G</i>^–CAHB) being less than solvation free energies (Δ<i>G</i>_Solv). Thus, additional Δ<i>G</i> is supplemented by increased hydrophobicity due to proton exchange of ionized acids with water (ΔΔ<i>G</i>_{Hydrophobicity}). Adsorption capacities and competition coefficients indicated that ΔΔ<i>G</i>_{Hydrophobicity} values depend on the neutral and ionized acid <i>K</i>_ow. Competitive adsorption implies that multilayer adsorption may occur via hydrophobic bonding with the CH₃ ends of the self-assembled layer which affects the acid adsorption capacities in mixtures as compared to monocompound solutions. The determination of adsorption mechanisms will assist in understanding of the fate and bioavailability of emerging and classical weak acids released into natural waters

Impact of ozonation pre-treatment of oil sands process-affected water on the operational performance of a GAC-fluidized bed biofilm reactor

Treatment of oil sands process-affected water (OSPW) using biodegradation has the potential to be an environmentally sound approach for tailings water reclamation. This process is both economical and efficient, however, the recalcitrance of some OSPW constituents, such as naphthenic acids (NAs), require the pre-treatment of raw OSPW to improve its biodegradability. This study evaluated the treatment of OSPW using ozonation followed by fluidized bed biofilm reactor (FBBR) using granular activated carbon (GAC). Different organic and hydraulic loading rates were applied to investigate the performance of the bioreactor over 120 days. It was shown that ozonation improved the adsorption capacity of GAC for OSPW and improved biodegradation by reducing NAs cyclicity. Bioreactor treatment efficiencies were dependent on the organic loading rate (OLR), and to a lesser degree, the hydraulic loading rate (HLR). The combined ozonation, GAC adsorption, and biodegradation process removed 62 % of chemical oxygen demand (COD), 88 % of acid-extractable fraction (AEF) and 99.9 % of NAs under optimized operational conditions. Compared with a planktonic bacterial community in raw and ozonated OSPW, more diverse microbial communities were found in biofilms colonized on the surface of GAC after 120 days, with various carbon degraders found in the bioreactor including Burkholderia multivorans, Polaromonas jejuensis and Roseomonas sp.</p

Probing the Adsorption of Weak Acids on Graphite Using Amplitude Modulation–Frequency Modulation Atomic Force Microscopy

Recent thermodynamics calculations and adsorption isotherms showed that the adsorption of a self-assembled layer (SAL) of ionized weak acids to carbon was attributed to the negatively charged hydrogen bonding (−CAHB), yet the direct visualization and characterization of this adsorption behavior have not been reported. Here, an amplitude modulation–frequency modulation atomic force microscopy (AM–FM AFM) technique was applied to discriminate the adsorption of decanoic acids (DA) on highly ordered pyrolytic graphite (HOPG). Thermodynamics calculations revealed that the adsorption of SAL was driven by the formation of −CAHB with negatively charged functional groups of HOPG. Multilayer adsorption could occur over the adsorbed ionized SAL, leading to the development of aggregates. AM–FM AFM imaging showed that the adsorption of the DA molecules forming aggregates occurred only for the HOPG-functionalized steps, while DA molecules were found to adsorb over the entire functionalized HOPG surface after water-plasma treatment, as evident from the frequency shifts identified in AFM images

A wastewater-based risk index for SARS-CoV-2 infections among three cities on the Canadian Prairie

Wastewater surveillance (WWS) is useful to better understand the spreading of coronavirus disease 2019 (COVID-19) in communities, which can help design and implement suitable mitigation measures. The main objective of this study was to develop the Wastewater Viral Load Risk Index (WWVLRI) for three Saskatchewan cities to offer a simple metric to interpret WWS. The index was developed by considering relationships between reproduction number, clinical data, daily per capita concentrations of virus particles in wastewater, and weekly viral load change rate. Trends of daily per capita concentrations of SARS-CoV-2 in wastewater for Saskatoon, Prince Albert, and North Battleford were similar during the pandemic, suggesting that per capita viral load can be useful to quantitatively compare wastewater signals among cities and develop an effective and comprehensible WWVLRI. The effective reproduction number (Rt) and the daily per capita efficiency adjusted viral load thresholds of 85 × 106 and 200 × 106 N2 gene counts (gc)/population day (pd) were determined. These values with rates of change were used to categorize the potential for COVID-19 outbreaks and subsequent declines. The weekly average was considered ‘low risk’ when the per capita viral load was 85 × 106 N2 gc/pd. A ‘medium risk’ occurs when the per capita copies were between 85 × 106 and 200 × 106 N2 gc/pd. with a rate of change &lt;100 %. The start of an outbreak is indicated by a ‘medium-high’ risk classification when the week-over-week rate of change was &gt;100 %, and the absolute magnitude of concentrations of viral particles was &gt;85 × 106 N2 gc/pd. Lastly, a ‘high risk’ occurs when the viral load exceeds 200 × 106 N2 gc/pd. This methodology provides a valuable resource for decision-makers and health authorities, specifically given the limitation of COVID-19 surveillance based on clinical data.</p