UV treatment

Ultraviolet radiation (UV) represents an effective method for the inactivation of organisms or the alteration or destruction of specific organic molecules. UV radiation is electromagnetic radiation with a wavelength range of 100–380 nanometers (nm), which is beyond the range of human perception. The UV radiation range can be subdivided into three distinct categories: UV-A (380-315 nm), UV-B (315-280 nm), and UV-C (280-100 nm). UV radiation is more energetic than visible light radiation and has an ionizing effect at wavelengths below 250 nanometers. [1, 2].

Aromatic amino acids, which constitute the fundamental units of proteins, exhibit absorption at approximately 280 nm. When aromatic systems absorb this energy, electrons are excited, resulting in alterations to the molecular properties of the biomolecules. In proteins, this can result in the reduction of disulfide bonds, the formation of radical functional groups, and the formation of new bonds, which in turn give rise to alterations in the spatial molecular structure. Such effects may be observed in the unfolding, misfolding, or aggregation of biomolecules, as well as in the formation of cross-links between proteins and DNA [3].

DNA damage occurs, for example, when thymine bases of the DNA absorb the energy and two adjacent thymine bases form a covalent bond with each other. Such UV-induced DNA damage results in disruptions to the subsequent replication of the DNA, ultimately leading to replication cessation. To repair radiation-induced DNA damage, almost all microorganisms have effective repair systems (termed photolyases) that are activated by low-energy light (within the blue spectral range, 380-500 nm) [4]. Consequently, relatively high doses of radiation are required to inactivate microorganisms, thereby overwhelming their cellular repair mechanisms are preventing the recovery of all radiation-induced damage.

In addition to the direct impact of high-energy UV radiation on biomolecules, other molecular processes resulting from radical or photo-assisted catalytic reactions exert a denaturing influence on organisms or organic structures and biomolecules. UV radiation gives rise to the formation of diverse radicals, such as OH- and O2-, which promptly interact with oxidizable molecules in their immediate vicinity.

Ultraviolet (UV) radiation is employed on a large scale for the disinfection of surfaces and fluids, including in the treatment of drinking water. In the context of drinking water treatment, for example, a dose of 400 J/m² of UV-C (254 nm) irradiation is typically employed [5]. The efficacy of the disinfection process is significantly diminished when cloudy fluids and organic substances are present, as is the case in the treatment of process or waste water.

[1] Federal Office for Radiation Protection, accessed 28.08.2024. https://www.bfs.de/DE/themen/opt/uv/einfuehrung/einfuehrung_node.html

[2] European Commission, Scientific Commitees Glossar, accessed 28.08.2024., https://ec.europa.eu/health/scientific_committees/opinions_layman/de/glossar/tuv/uv-strahlung.htm

[3] M.T. Neves-Petersen, S. Petersen & G.P. Gajula (2012). UV Light Effects on Proteins: From Photochemistry to Nanomedicine, Molecular Photochemistry – Various Aspects, Dr. Satyen Saha (Ed.), ISBN: 978-953-51-0446-9, InTech,

[4] R.P. Rastogi, et al. (2010). Molecular Mechanisms of Ultraviolet Radiation – Induced DNA Damage and Repair. Journal of Nucleic Acid. Volume 2012(592980). DOI: 10.4061/2010/592980.

[5] DVGW regulations, worksheet W 294 “UV disinfection systems for drinking water supply – requirements and testing” Austrian Standards Institute, ÖNORM M 5873 “Requirements for systems for the disinfection of water using ultraviolet rays” (latest edition)