Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Chemical and Biochemical Engineering

Supervisor

Dr. Ajay K. Ray

Abstract

Modern consumer demands for tasty, safe and healthier liquid foods and beverages. Chemical preservatives are usually added to foods to extend their shelf life and to protect against food borne pathogens. Application of ultraviolet (UV) light is gaining more attention as an alternative technology to disinfect fluids with low UV transmittance replacing classical chemical or thermal procedures due to growing negative public reaction over chemicals added. UV light irradiation has a positive consumer image as it is a physical non-thermal method efficient against microbial hazards, chemicals free cost effective and energy efficient methods and has been approved by regulatory agencies. While the use of UV light is well established for air and water treatment, its use for treating opaque fluids is limited due to low UV transmittance that restricts dose delivery, and consequently, efficient microbial inactivation. Appropriate UV reactor design that addresses effective mixing can reduce the interference of high UV absorbance and viscosity associated with liquid food products and therefore improves the inactivation efficiency. The flow pattern inside the reactor significantly influences the total applied UV dose distribution.

In this thesis, systematic study has been carried out with different size reactors (static petri dish, Taylor-Couette and impinging jet) to understand the influence of mixing and exposure of UV light for disinfection using two UV sensitive microorganisms, Super-Hume and para hydroxybenzoic acid (pHBA). Dimensional analysis was used to reduce the number of parameters by studying the effects of dimensionless groups on UV treatment process. The limitation of mixing effect in Petri dish was overcome through introduction flow instability and vortices in Taylor-Couette reactor by determining penetration depth of UV light in classical as well as wavy-wall Taylor-Couette reactor. Simulation results were validated with the experimental data for the disinfection of milk and pHBA solution. The effect of mixing on disinfection of low transmittance fluids was quantified and established. Finally, an Impinging Jet reactor was used for large scale treatment of blood water disinfection. It was found that alternation between an irradiation period and dark mixing is the best approach for disinfection of opaque fluids.


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