Pulse UV light effect on microbial biomolecules and organic pollutants degradation in aqueous solutions

This study present assessed the effect of UV pulsed light (PL) on microbial and organic pollutants using two spiral lamps were used, i.e., PL1 and PL2 lamps, with wavelength cut-offs of 190 and 240 nm, respectively. Overall, our study demonstrated that pulsed UV light impacts several microbial biomolecules and degrades polycyclic aromatic hydrocarbons (PAHs) in aqueous solution. In microbial inactivation by PL2, temporary changes of bacterial cellular components, specifically proteins, were observed, but the compositional changes of bacteria that were exposed to PL1 were permanent due to ozonolysis. PL1 irradiation caused greater deactivation of the bacteria than PL2 irradiation due to the generation of ozone. The higher efficacy of PL1 in terms of membrane disruption, reduction of respiration rate, and reduction of growth rate was due to the production of ozone during the irradiation period. The bacteria that were irradiated with both PL lamps regrew due to photoreactivation, such as an enzymatic DNA-repair mechanism. The PAH degradation kinetics indicate that higher molecular weights degraded faster than those with lower molecular weights. For both lamps, the degradation of naphthalene and fluorene was first order, whereas second order for pyrene and anthracene. Any effect of ozonolysis on the PAH degradation rates was not apparent, which indicated that photolysis was the primary degradation pathway. PAH solutions treated with both pulsed UV lamps did not result in a toxicity effect on the bacteria.