Novel Plasma Based Technology for Treatment of Emerging Contaminants in Water: Understanding Physiochemical Processes and Applications

• Author / Creator

  Sohrabi, Amirreza

• Indiscriminate and widespread disposal of pharmaceutical compounds, dye molecules, and pesticides in to water resources pose a serious threat to the quality of drinking water. A critical need exists for developing novel practical, efficient, and cost effective water treatments for remediation of these emerging contaminants since conventional water treatment techniques are ineffective in treating these contaminants. In this research, a new class of water treatment technologies is proposed based on the application of non-thermal plasma. Creation of plasma by means of a helical resonator allows the use of low power for plasma generation (10-15 W, comparable to LED light bulbs). Furthermore, producing plasma by a single electrode significantly increases the flexibility of the method for real life applications. The most important feature that distinguishes this technology from other emerging methods is the presence of a post treatment stage in decontamination. Therefore, not only do the contaminants degrade in the presence of plasma (treatment stage), but decontamination also continues for a long period of time even after the plasma is switched off (post treatment stage). To gain deeper understanding of various physiochemical processes involved in the treatment mechanism, we have systematically investigated the effect of physical and chemical parameters such as the distance between the electrode and water surface (air gap distance), the input voltage to the helical resonator, pH and ion concentration of water. The results indicate that there is an optimum air gap distance (6 mm) at which maximum removal of contaminations can be achieved. Moreover, increasing the input voltage can enhance the removal of the contaminations. However, energy consumptions at higher input voltages render the method inefficient. Presence of various ionic species in water (chloride, phosphate, carbonate, etc.) and the initial pH of the solution can significantly alter the chemistry of the process. Special attention has been paid to the role of chloride ions (Cl-) in the solution. The reason was while some report that the presence of Cl- deteriorates the efficiency, others suggest the enhancing role of these ions in removing contaminants. In this research, for the first time, we showed that during the treatment stage (presence of plasma) the scavenging behavior of Cl- towards OH. decreases the removal%. On the other hand, due to the formation of singlet oxygen (1O2) from reaction of hypochlorous acid (HOCl) and hydrogen peroxide (H2O2) the removal% improves significantly during the post treatment stage (absence of plasma). The initial pH of the solution also affects the decontamination process. While highest removal% in the treatment stage was achieved with initial acidic conditions, both initial acidic and alkaline conditions deteriorate the post treatment stage. Furthermore, almost equal contributions from treatment and post treatment stages can be achieved for solutions with initial near neutral pH values. Finally, the application of the proposed system for degradation of four pharmaceutical contaminants (ampicillin, ibuprofen, fluoxetine and propranolol) has been investigated. We showed that after 3 hr of treatment, 100% of ampicillin, fluoxetine and propranolol and 90% of ibuprofen were removed from water. Moreover, the energy yield of the process (the amount of contaminant degraded for 1 kWh of energy consumption) was calculated to be in the range of 0.12-0.13 g/kWh. For each contaminant, degradation by-products were identified and a degradation pathway was suggested. For all contaminants, the degradation mechanism was mostly dominated by the action of hydroxyl radicals. However, formation of oxygenated by-products suggested the possible role of ozone in the process. Finally, for the first time, this research proposed the application of Excitation-Emission Matrix (EEM) analysis to track the degradation of each contaminant. Possible connections between the EEM analysis and identified degradation by-products were outlined. Not only can the results of this research enhance the understanding of the physiochemical processes involved, but also open up new opportunities for the development of more advanced and efficient water treatment technologies.

• Subjects / Keywords

  • Hydroxyl radicals
  • Pharmaceutical contaminants
  • Singlet oxygen
  • Plasma water treatment
  • Physiochemical processes
  • Ozone

• Graduation date

  Spring 2017

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3N29PK17

• 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.