Effectiveness and intermediates of microcystin-LR degradation by UV/H2O2 via 265 nm ultraviolet light-emitting diodes

Abstract

Although the degradation of cyanotoxins by 254 nm UV/HO has been well elucidated, the efficiency and mechanism involved are not necessarily true for other UV wavelengths. The degradation of microcystin-LR (MC-LR), a representative cyanotoxin, was explored by UV/HO using 265 nm ultraviolet light-emitting diode (UV-LED). The results indicated that 265 nm UV/HO treatment had a high removal efficiency of MC-LR ([MC-LR] = 0.1 μM, apparent rate constants reached 0.2077 min, half-time at 3.3 min). The qualitative analyses demonstrated that three novel intermediates, CHNO (molecular weight = 1030.5335), CHNO (854.4134), and CHNO (814.3821), were generated in 265 nm UV/HO. Five published intermediates were also confirmed. The generative pathway of these products mainly involved free hydroxyl radical oxidation, resulting in consecutive hydroxyl substitutions and hydroxyl additions of unsaturated bonds in MC-LR. The toxicity of MC-LR was weaken with a relative low mineralization. The electrical energy per order values were calculated to be in the range of 0.00447 to 0.00612 kWh m order for 100-5000 μg L MC-LR. Overall, 265 nm UV-LED/HO can be used as an alternative effective technology to improve the removal efficiency of MC-LR in water.

Kinetics of Microcystin-LR Removal in a Real Lake Water by UV/H2O2 Treatment and Analysis of Specific Energy Consumption

“…The half-life time (HLT) of the MC-LR was reduced from 64.2 (UV alone) H 2 O 2 alone did not allow us to remove the toxin even with high contact time. This result is confirmed by Liu et al [40] who observed an almost absent removal of dissolved MC-LR (0.1 µM) using H 2 O 2 (0.1 mM) at pH nearly 7. On the contrary, the photolysis treatment with UV-C was found to be weakly effective in removing MC-LR (about 50%), with UV fluence equal to or lower than 1000 mJ cm −2 .…”

“…In literature, several examples of application of this process for the removal of MC-LR are reported. UV lamps are used that emit at 254 nm of wavelength [38], close to the wavelength of maximum absorption of the MC-LR (235-238 nm [38,39]) or at 268 nm of wavelength [40]. However, most of the experiments involved the use of synthetic waters, thus only partially evaluating the combined effect of the presence of scavenger substances in the process such as the carbonates.…”

Advanced oxidation processes for the removal of cyanobacterial toxins from drinking water

“…E EO values for cyanotoxin removal by AOPs have only rarely been reported. For UV/H 2 O 2 treatment of MC-LR and CYN, E EO values were 4.5 ×10 -3 -6.1 ×10 -3 and 1.6 ×10 -3 kWh m -3 , respectively [43,154].…”

Advanced oxidation processes for the removal of cyanobacterial toxins from drinking water

“…E EO values for cyanotoxin removal by AOPs have only rarely been reported. For UV/H 2 O 2 treatment of MC-LR and CYN, E EO values were 4.5 × 10 −3 -6.1 × 10 −3 and 1.6 × 10 −3 kWh m −3 , respectively [40,148]. For UV/PMS and UV/PS treatment, E EO values were estimated to range from 10 −4 to 10 −5 kWh m −3 , respectively, for CYN, and 0.7 and 0.2 kWh m −3 , respectively, for MC-LR [40,126].…”