Ultraviolet-C decontamination of Staphylococcus aureus and MS2 in porous nonwoven structures

Abstract

The growing need for sustainable alternatives for synthetic materials has focused the research towards bio-based high-end products. Synthetic materials are used, for example, in filter applications, where reusing or recycling products could substantially reduce single-use waste. This Master’s thesis studies the effectiveness of ultraviolet-C light (UVC) as a decontamination method for porous nonwoven structures using Staphylococcus aureus and MS2 as model organisms. The research focuses on polypropylene (PP) and cellulose-based filter materials, specifically evaluating the potential of cellulose-based materials as sustainable alternatives to synthetic filters. The study aims to assess the efficacy of UVC decontamination on porous nonwoven structures, analyze the impact of structural differences such as fiber type, porosity, and number of layers, determine the applicability of UVC on cellulose-based materials, and investigate the decontamination of deeper parts of porous structures using UVC. The results showed that both S. aureus and MS2 can be effectively inactivated from PP and cellulose-based materials. Notably, cellulose-based materials exhibited higher decontamination levels at lower UVC irradiation doses than PP in both non-porous and porous structures. A 30 mJ/cm2 dose for S. aureus and 150 mJ/cm2 for MS2 demonstrated log reductions ranging from 3.55 to 6.01 in all cellulosic samples. These minimum required doses were determined for both microorganisms through experiments with one-layer structures, where S. aureus required approximately five times lower doses compared to MS2. UVC penetrates through gaps and pores in the material, allowing transmittance through a maximum of three layers of nonwoven cellulose or PP with a grammage of 25 g/m2. The adherence behavior to cellulose fibers differs, with MS2 exhibiting a higher adherence level compared to S. aureus. Recovering viable microorganisms from cellulose fibers of a contaminated four-layer structure confirms a higher number of MS2 obtained from the upper layers compared to S. aureus. Both microorganisms exhibit higher adherence to cellulose fibers compared to PP fibers. The cellulose-based filter material examined in this study served as an example of an alternative sustainable filter. The filtration efficiency for 3 µm particles was found to be 87 %, reaching a lower range of community face coverings, with potential for improvement using techniques such as electrospinning. Cellulose-based filters hold promise for various filtration applications, offering advantages such as high microbial capturing efficiency and effective UVC decontamination. However, the underlying reason why cellulosic materials decontaminate more effectively requires more research.