Thesis

Optimisation of ultra-violet and visible light based technologies for disinfection applications in clinical and other environments

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Awarding institution
  • University of Strathclyde
Date of award
  • 2011
Thesis identifier
  • T12950
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Abstract
  • Despite enormous worldwide research efforts and resource commitments, infectious disease problems associated with medical care and with food and water supplies remain as serious public health problems in both developed and developing countries. New infection control technologies are required and this study investigated ultraviolet and visible light-based technologies for microbial inactivation. A major aspect of the work was the modelling optimisation of the High-Intensity Narrow-Spectrum light Environmental Decontamination System (HINS-light EDS), a ceiling-mounted light source developed at the Robertson Trust Laboratory for Electronic Sterilisation Technologies (ROLEST), which provides continuous decontamination of air and surfaces within illuminated environments. This study involved the design and development of a fully integrated and controllable HINS-light EDS. Initial investigations in the study involved the use of pulsed ultraviolet (PUV)-light for microbial inactivation, and results demonstrated the effectiveness of PUV-light for inactivation of the bacterial species Staphylococcus epidermidis and Staphylococcus aureus and the yeast species Saccharomyces cerevisiae in liquid suspension using both a broadband spectrum and 260 (± 10) nm light pulses. To determine the visible-light wavelength sensitivity of a number of significant bacterial species, this study utilized a continuous xenon white-light source in combination with a range of narrow-band optical filters (10 nm FWHM) to expose L. monocytogenes, S. aureus and methicillin-resistant Staphylococcus aureus (MRSA) in liquid suspension. Results demonstrated that the bacteria showed sensitivity to wavelengths of light within the visible region, with the peak wavelength for inactivation being 405 (± 5) nm. The study also investigated the use of 405 nm High Intensity Narrow Spectrum (HINS) light, generated from light-emitting diodes (LEDs). When comparing the inactivation kinetics of MRSA, S. aureus, S. epidermidis and L. monocytogenes using the 405 nm HINS-light with those from the 405 nm filtered light, at an irradiance of 8.6 mWcm-2, similar results are found, indicating that the applied dose is the important factor regardless of the source. The most significant area of this study was the development, testing and modelling of a fully-integrated HINS-light Environmental Decontamination System (EDS). Previous work within ROLEST saw the development of an initial prototype model which has been successfully trialled within an NHS hospital, with results showing significant reductions of environmental contamination levels in isolation rooms. This initial prototype had a number of design and operational limitations which required improving. In this study, a new topology for the HINS-light EDS has been developed and its light distribution has been studied. Optimal parameters for the uniform light distribution have been established including: the Lambertian mode number (m), configuration of the Fresnel lens and diffuser, space distance between light source (LEDs), Fresnel lens and diffusers, and the optimum LED-to-LED array spacing. A mathematical model which allows analysis of the light distribution from different topologies has been successfully developed, with results proving that intensity distribution of the system is in good agreement with experimental data. In addition the system has improved thermal management with integrated power supplies providing a light-weight compact design suitable for ceiling mounting. Analytical study of safety calculations and risk assessment of the new HINS-light EDS prototype have been evaluated and calculated. The results confirm that the HINS-light EDS, at an irradiance level of 0.08 mWcm-2 for each individual 405 nm LED engine, and with a total irradiance level of 0.32 mWcm-2 at a distance of 200 cm below the system, is safe in relation to UV, UV-A and thermal interaction with unprotected skin and eyes and blue light retinal hazard. Bacterial inactivation data using this new prototype HINS-light EDS has been shown to achieve reductions in bacterial levels on agar surfaces of up to 73% for S. aureus, 57% for E. coli and 55% for L. monocytogenes, after 6 hours exposure at a distance of 200 cm below the system. The results demonstrate that the improved prototype system is effective for inactivation of pathogenic bacteria in exposed environments.
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Note
  • This thesis was previously held under moratorium from 27th February 2012 until 27th February 2014.
DOI
Date Created
  • 2011
Former identifier
  • 869747

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