Dissolved Oxygen Model and Passive Samplers for the Athabasca River

• Author / Creator

  Martin, Nancy

• This thesis documents the research undertaken to develop and assess modeling and monitoring tools to improve the water quality management in the Athabasca River, Alberta. The Upper Athabasca River (UAR) has experienced dissolved oxygen (DO) sags, which may affect the aquatic ecosystem. A water quality model for an 800 km reach of this river was customized, calibrated, and validated for DO and the factors that determine its concentration. The model showed that the sediment oxygen demand (SOD) represents about 50% of the DO sink in winter. The DO calibration was improved by implementing an annual SOD based on the biochemical oxygen demand (BOD) load. The model was used to estimate the assimilative capacity of the river based on a trigger DO concentration of 7 mg/L. The results revealed a maximum assimilative BOD load of 8.9 ton/d at average flow conditions, which is lower than the maximum permitted load. In addition, the model predicted a minimum assimilative flow at average BOD load of 52 m3/s. A three-level warning-system is proposed to manage the BOD load proactively at different river discharges. Other mitigation options were explored such as upgrading the wastewater treatment from the major BOD point source, and oxygen injection into the effluents. The model can be used as a management tool to forecast the DO in low flow years and evaluate mitigation measures. After improving the modeling tools for the UAR, monitoring tools for the Lower Athabasca River (LAR) were assessed. Naphthenic acids (NAs) have been identified as a main toxic component in the oil sands process affected water. However, it is desired to improve the current monitoring methods for NAs. Having a state-of-the-art monitoring system to quantify NAs in the LAR and its tributaries will allow calibrating robust models for this reach of the Athabasca River in the future. Passive samplers and the application of fluorescence spectroscopy using organic solvents were explored as a cost-effective alternative to quantify mass loading of NAs. Nine organic solvents, polar protic (methanol, ethanol, and propanol), polar aprotic (dichloromethane, acetone, and acetonitrile) and non-polar (hexane, toluene, and diethyl ether) were evaluated for quantification of NAs using fluorescence. The calibration curves of the polar protic solvents performed the best with lower light scattering and higher method sensitivity. Methanol was selected for further experiments having a strong linearity for concentrations lower than 250 mg/L (R2 > 0.99), and a low relative standard deviation (< 10%). The synchronous fluorescence mode with a reduced offset value of = 10 nm demonstrated potential for fingerprinting. Two passive samplers, the polar organic chemical integrative sampler (POCIS) and the Chemcatcher, were assessed for naphthenic acid monitoring. POCIS presented high partitioning of NAs to the polyether-sulphone (PES) membrane in combination with low diffusion to the resin. The Chemcatcher sampler with PTFE (Teflon ®) membrane and C18 disk presented a high mass transfer, and it was further evaluated using commercial NAs. The sampler was integrative for a 30-day experiment having a reduced lag time, allowing the sampler to satisfactorily account for changes of NAs concentration in water. The temperature and turbulence had a high effect on the uptake rate with a 4-fold increase from 4 to 20 oC, and a 2-fold increase from 60 to 300 rpm. Furthermore, the uptake rate of commercial NAs was lower using river water, likely due to partitioning to colloids. The uptake rate of NAs from the oil sands process water was one order of magnitude lower than that obtained for commercial NAs, which may be due to the selective adsorption of acyclic (Z = 0) compounds with high number of carbons (n). These compounds were more abundant in the commercial NAs. Uptake rates may be required for each compound or group of compounds in the NA mixture depending on the n and Z distribution. Due to the complexity of the NAs mixture (> 3000 different compounds at isomer level), it is recommended to target the compounds with greater toxicity and abundance for further uptake rate evaluation and sampler optimization.

• Subjects / Keywords

  • Naphthenic acids
  • Models
  • Dissolved oxygen
  • Passive samplers
  • Athabasca river

• Graduation date

  Spring 2014

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R31G0J08G

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.