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Disinfection by Pulsed Power Discharges


Ching, Weng Ki (2001) Disinfection by Pulsed Power Discharges. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/RV3M-0849.


We study the disinfection of Escherichia coli in a pulsed power discharge reactor. The pulsed power discharge process is an electrohydraulic phenomenon characterized by a rapid release of electrical energy across a submerged electrode pair.

The survival kinetics of pure strains of E. coli suspensions exposed to 5.5 kV, 90 kA electrohydraulic discharges (EHD) is investigated. The probability of survival Pn of a 2 x 10⁷ E. coli CFU mL⁻¹ population after 50 consecutive EHD's follows a logit distribution that corresponds to lethal doses of LD₅₀ = 2.2 and L:D₉₀ = 10.8 EHDs. Variation of the initial cell concentration produced nearly constant values of LD₅₀ = 0.9±0.1 in the range 2 x 10³ ≤ E. coli/CFU mL⁻¹ ≤ 2 x 10⁶. Beyond 10⁶ CFU mL⁻¹, the LD₅₀ values increase exponentially due to nonlinear light absorbance with increasing E. coli concentrations. Qualitatively similar initial cell concentration dependence is observed for survival under low intensity 254 nm irradiation, in contrast with lower values of LD₅₀ obtained in denser colonies to 20 kHz power ultrasound exposure.

The high intensity (3.3 x 10¹⁰ W m⁻²) ultraviolet radiation emitted by the electrohydraulic discharge is completely suppressed in the presence of less than 100 mg L⁻¹ 2,2'-dihydroxy-4,4'-dimethoxybenzophenone-5,5'-disulfonic acid (BP9), a well-known sunscreen agent. Concentrations of BP9, in the range (0 - 100) mg L⁻¹, are varied to measure the sterilization kinetics of ~3 x 10⁷ CFU mL⁻¹ suspensions to varying degrees of high intensity UV exposure. The slope of the logit plots of E. coli as function of BP9 concentration is consistent with the screening of radiation as the sole lethal agent. Computed values of biologically available light fluences are 5.0 x 10¹¹ photons CFU⁻¹ for high intensity, high power, pulsed EHD experiments and 6.6 x 10⁸ photons CFU⁻¹ for separate low power continuous UV experiments. The net availability of 3 orders of magnitude more photons during high intensity UV exposure suggests the possibility of a multiphotonic disinfection mechanism at play in the EHD process relative to low intensity case.

The overall resistance to long term exposure to EHD is also investigated. Selective pressure experiments with E. coli exposed to 11 cycles of 50 consecutive EHDs each show a weak kinetic change in the dose-response curves reflected in the nearly constant values of LD₅₀ - 0.24 ± 0.03. A greater than 98% metabolic similarity in carbon source consumption between initial and final E. coli populations are enzymatically related. In addition, the results indicate that no bacterial contaminants are propagated throughout the experiment.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Disinfection Kinetics; Electrohydraulic Discharges; Electrohydraulic Discharges; Pulsed Power; Sunscreen Agents
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Environmental Science and Engineering
Minor Option:Aeronautics
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Hoffmann, Michael R.
Thesis Committee:
  • Hoffmann, Michael R. (chair)
  • Nealson, Kenneth H.
  • Newman, Dianne K.
  • Leadbetter, Jared R.
Defense Date:3 May 2001
Record Number:CaltechETD:etd-07252005-142630
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:2980
Deposited By: Imported from ETD-db
Deposited On:25 Jul 2005
Last Modified:02 Dec 2022 00:48

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