Knowledge Bank

Microcystin-LR (MC-LR), a cyanotoxin produced by harmful algal blooms (HABs), negatively impacts water ecosystems and forces water treatment facilities to optimize or change processes for impacted sources. UV-C treatment can degrade cyanotoxins without producing additional waste in the process. We compared the degradation of ~50 ppb MC-LR spiked in deionized water and surface waters by UV-C light emitted from a krypton-chlorine excimer lamp (UV222) versus a low-pressure Hg lamp (UV254). Quantitative analyses by ELISA, UPLC-PDA, and LC-HRMS of MC-LR exposed to UV doses from 0 - 320 mJ/cm2 demonstrated that the degradation rate constant was 2 - 7 times greater for UV222 than UV254 across all waters (7.60 ± 0.99x10-3 and 2.11 ± 0.52x10-3 cm2/mJ). In DI, the molar absorption (ε) was ~2 times greater at 222 nm than at 254 nm (41222 ± 6354 and 24059 ± 3744 M-1cm-1), and quantum yield (Φ) was ~3 times greater for UV222 than UV254 (0.441 and 0.137 mol/Einstein, respectively). Qualitative analyses conducted with mass spectrometry demonstrated that samples treated by UV254 had higher occurrences of isomers than UV222 at given UV doses from 20 - 320 mJ/cm2. UV254 produced more polar photoisomers than UV222, and the polar isomers increased with dose, while non-polar isomers generally decreased with dose. Bimodal trends in non-polar isomers after treatment with UV222 suggest that they absorb UV222 and degrade after they are produced. This may also suggest a more complete pathway towards non-toxic degradants, which means that UV222 shows promise as an improvement over UV254 for drinking water treatment technology. Electrical Energy per Order (EEO) was similar between UV222 and UV254 across all water matrices and for UPLC-PDA, ELISA, and LC-HRMS, demonstrating that UV222, although currently less efficient, still in preliminary development, and having a lower UVT, has the potential to surpass the overall efficiency of the standard UV sources used in disinfection today.