Inactivation and subsequent reactivation of Aspergillus species by the combination of UV and monochloramine: Comparisons with UV/chlorine.

Ultraviolet (UV)/monochloramine (NHCl) as an advanced oxidation process was firstly applied for Aspergillus spores inactivation. This study aims to: i) clarify the inactivation and photoreactivation characteristics of UV/NHCl process, ii) compared with UV/Cl in inactivation efficiency, photoreactivation and energy consumption. The results illustrated that UV/NHCl showed better inactivation efficiency than that of UV alone and UV/Cl, and could effectively control the photoreactivation. For instance, the inactivation rates for Aspergillus flavus, Aspergillus niger and Aspergillus fumigatus in the processes of UV/NHCl (2.0 mg/L) was 0.034, 0.030 and 0.061 cm/mJ, respectively, which were higher than that of UV alone (0.027, 0.026 and 0.024 cm/mJ) and UV/Cl (0.023, 0.026 and 0.031 cm/mJ). However, there was no synergistic effect for Aspergillus flavus and Aspergillus fumigatus. As for Aspergillus niger, the best synergistic effect can reach 1.86-log. This may be due to their different resistance to disinfectants, which were related to the size, an outer layer of rodlets (hydrophobins) and pigments. After UV/NHCl inactivation, the degree of cell membrane damage and intracellular reactive oxygen species were higher than that of UV alone. UV/NHCl had the advantages of high inactivation efficiency and inhibition of photoreactivation, which provides a new entry point for the disinfection of waterborne fungi.