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Enhanced Primary Treatment of Bypass Wastewater Using Potassium Ferrate(VI) and Iron Electrocoagulation

  • Author / Creator
    Elnakar, Haitham Y.E.

  • In-plant wastewater treatment strategies to deal with bypass wastewater in excess of plant capacity are critical in securing sustainable wastewater management. The overall goal of this research was to test potassium ferrate(VI), iron electrocoagulation, and their combination for the enhancement of primary wastewater treatment as a sustainable process retrofit capable of attenuating the magnitude of untreated bypass wastewater discharge into water bodies.
    The first part of the study investigated the dual capacity of potassium ferrate(VI) as disinfectant / oxidant and coagulant to provide adequate treatment to bypass wastewaters. The effect of rapid mixing speed was investigated for the first time along with potassium ferrate(VI) dosage considering Escherichia coli (E. Coli), Fecal Coliform (FC), Total Suspended Solids (TSS), and Orthophosphates (PO₄³⁻) as the process responses. All responses other than PO₄³⁻ showed good agreement between the observed and modeled values. E. Coli and FC removals were found to increase with the increase of both the mixing intensity and potassium ferrate(VI) dosages. TSS removal exhibited optimal responses. The effluent quality achieved by potassium ferrate(VI), as an independent treatment, can be sufficient for certain types of unrestricted and restricted irrigation reuse purposes suggested by World Health Organisation (WHO) guidelines. Furthermore, this study investigated, for the first time, the role of rapid mixing on the rate of potassium ferrate(VI) decay and disinfection in bypass wastewaters from extreme wet weather flow events. The double exponential model was able to represent the potassium ferrate(VI) decay in all conditions with a high coefficient of determination and low mean square error. There was no significant increase in the potassium ferrate(VI) dissociation and disinfection rates with the increase of the rapid mixing speeds from 500 to 1000 rpm which revealed that the reactions were kinetically controlled. The coagulation capability of potassium ferrate(VI) enhanced the sedimentation ability and contributed almost the same as the chemical disinfection capability to the overall E. Coli removal.
    The second part of the research investigated the effectiveness of enhancing primary treatment of domestic sewage by iron electrocoagulation for the removal of soluble chemical oxygen demand (sCOD) at neutral pH conditions. The experimental results showed that sCOD removal efficiencies increased with increasing electrolysis time, current density, and temperature. The temperature effect was notably demonstrated in this study, for the first time, for the treatment of domestic wastewater using iron electrocoagulation. Using a 15 mA/cm² current density, an average 52% sCOD removal efficiency was achieved after 15 minutes at 23°C while approximately 40 minutes were needed to attain comparable removal efficiency at 8°C. Experimental results and theory showed that adsorption equilibrium was not reached in an electrocoagulation cell; consequently, applying adsorption isotherms to describe the process is not appropriate. An alternative approach using variable-order-kinetic (VOK) models derived from Langmuir and Langmuir-Freundlich adsorption expressions was employed in this study. These models require de facto estimation of ferric hydroxide (adsorbent) mass that accounts for the conversion of ferrous ion (Fe²⁺) to particulate end products. The Langmuir-based VOK model was found to be the better model to describe sCOD removal at 8oC and 23oC under all the operating conditions tested. The mechanism of sCOD removal is proposed to be chemisorption.
    The third and final part of the study introduced a novel enhancement technique of primary wastewater treatment by hybrid potassium ferrate(VI) – iron electrocoagulation system. Oxidation contribution and pH increase resulted from potassium ferrate(VI) incorporation were found to be the most significant factors that significantly enhanced the iron electrocoagulation process in tackling sCOD. Oxidation can help increase the sCOD removal by about 10% while pH increase promoted favourable conditions to quickly oxidize Fe²⁺ to form Fe(OH)₃ precipitates. By using response surface methodology – Box Behnken design, current density and potassium ferrate(VI) and their interaction were significant in achieving higher sCOD removal and faster Fe²⁺ oxidation. It was not possible to correlate zeta potential measurements to sCOD reduction although an isoelectric point was achieved for both iron the electrocoagulation and hybrid potassium ferrate(VI) and iron electrocoagulation systems which indicated that the sCOD removal mechanisms were not entirely related to charge neutralization.

  • Subjects / Keywords
  • Graduation date
    Fall 2018
  • Type of Item
    Thesis
  • Degree
    Doctor of Philosophy
  • DOI
    https://doi.org/10.7939/R3F18SX0W
  • License
    Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.