Competitive Adsorption Between Atrazine and Humic Acid onto NYEX 1000 and its Electrochemical Regeneration
Creators: name: Jambakhsh, Kayvan
Publisher: name: Université d'Ottawa / University of Ottawa
Year: 2020
Subjects: NYEX 1000
Atrazine
Humic Acid
Adsorption
Electrochemical Regeneration

description: Activated carbon (AC) has been extensively used as an adsorbent for the removal of target contaminants from water. However, it has a number of limitations. First, through competition with background organic compounds the ACs capacity to remove the target compounds can be decreased by up 70%. This is attributed to competitive adsorption and pore blockage by the background organics. Second, AC have a finite adsorption capacity so granular activated carbon (GAC) in adsorbers needs to be periodically regenerated or replaced. Third, the conventional thermal GAC regeneration technique results in the loss of 10 to 12% of the carbon mass in each regeneration cycle. As a result, there has been significant lab-scale research on alternative GAC methods that avoid such a significant carbon mass loss. Unfortunately, they have not been as effective as thermal regeneration. NYEX® is a newly-developed graphitic intercalated compound adsorbent capable of removing different types of contaminants and which can be completely regenerated electrochemically without a loss of adsorbent mass. The objectives of this thesis are to determine, if like with activated carbon, the adsorption of trace target contaminants on NYEX® is impacted by the presence of background organic compounds, and to quantify the impact of competitive adsorption has on the electrochemical regeneration. Experiments were conducted using atrazine, as a model toxic target contaminant, and humic acid as a model background organic matter. Bottle-point batch isotherm tests of single solute solutions were performed using two different approaches. The constant adsorbate solution-varying adsorbent dose isotherms for humic acid yielded unreasonable data for the high equilibrium liquid phase concentrations data points, it is speculated this was caused by competition with compounds leaching from the adsorbent. The varying adsorbate solution concentration-constant adsorbent dose humic acid isotherms yielded reasonable results and was adopted for all the remaining experiments. The humic acid isotherm yielded Freundlich model coefficient values that were statistically the same as those of an earlier study. A NYEX® bi-solute (atrazine and humic) isotherm experiment showed that the humic acid decreased the atrazine adsorption capacity by an average of 37%, which is of the same order of magnitude one would expect for the same experiment using activated carbon. Given that NYEX® lacks the large network of internal pores of AC, pore blockage by the humic acid should not be significant yet there still was a significant decrease in the atrazine adsorption. The literature on activated carbon adsorption isotherms involving target contaminants and background organic matter generally does not report on the adsorption of humic acid within these experiments, however two studies indicate that the adsorption capacity of the background acids in only slightly impacted by the competition. So, it was surprising that the bi-solute loading of NYEX® yielded 98% lower humic adsorption capacities. The dominance of atrazine in the competitive adsorption tests is attributed to its higher molar concentration in the test solutions and the higher diffusivity of atrazine. Batch regeneration tests were performed using a reactor with similar construction to the reactor used by Brown et al. (2004a). Electrochemical regeneration yielded regeneration efficiencies of up to 170% indicating the NYEX® 1000 was improved by the electrochemical processing. Hydrogen ions could have bonded to the NYEX® and improved the adsorption capacity of atrazine, which is a weak base, and decreased the adsorption capacity of humic acid. Multiple regeneration cycles of the atrazine-humic acid loaded NYEX® 1000 and atrazine-only loaded NYEX® 1000 were performed, they showed that the presence of the humic acids did not decrease the long-term atrazine adsorption capacities. Thus, the long-term atrazine adsorption on NYEX® followed by the NYEX® electrochemical regeneration is not impacted by the presence of humic acid, i.e., the improvements in the NYEX® compensate for the competitive adsorption decrease in adsorption capacity. This phenomenon should be investigated further in future research.