Research On The Degradation Efficiency And Products Of Microcystins In Water By UV/O₃

With the increasing problem of eutrophication, the harm that algal blooms outbreak brings has become a global concerns. Algal bloom can produce a series of toxins, including hepatotoxins that the most common in freshwater algae blooms. Microcystis is the main algae produces hepatotoxins in the various microcystin variants, and MC-LR variant is more common and the most toxic. In this paper, UV, O3 and UV-O3 three processes on the removal efficiency of MC-LR and their degradation products were analyzed.MC-LR used in removal experiment was extracted from microcystis aeruginosa cultured in laboratory, mainly including dry algae powder preparation, crude extraction and purification process. MC-LR is detected by high performance liquid chromatography, and mobile phase is water (0.05% TFA): acetonitrile = 67: 33 (V: V); flow rate is 1.0mL/min; test temperature is 30℃; the injection volume is 100μL.MC-LR removal experiment investigated UV, O3, UV-O3 three processes on the MC-LR extract degradation. The results showed degradation efficiency of UV, O3 and UV-O3 on MC-LR in deionized water could reach 90%; while it is different in the filtered Water: UV, UV-O3 technology is better that degradation efficiency is 85% and 90%; but ozone is ineffective in the late reaction that degradation efficiency is about 70%. Investigating the influencing factors can be found that initial concentration of MC-LR had no significant effect on degradation efficiency; ozone concentrations greatly impact on the reaction, the higher ozone concentration, the better degradation efficiency; DOC concentration could significantly inhibit the degradation efficiency of MC-LR.Product analysis is detected by high performance liquid chromatography/mass spectrometry, with Finnigan LCQ DECA XPMAX capillary HPLC ion trap mass spectrometry system, ESI + mode; the scan range is 100 ~ 2000 full-scan; mobile phase is water (0.05% acetic acid): methanol = 30:70 (V: V); flow rate is 1.0mL/min; injection volume is 25 L.The degradation products of microcystin MC-LR using UV, O3 and UV-O3 processes are significantly different. In the analysis of degradation products of UV, O3 and UV-O3 three processes we can find that degradation products of UV technology mainly is m/z = 995 molecular ion , which is the isomers of MC-LR; most degradation products of O3 is m/z=835 and m/z=795 molecular ion, the ketone and aldehydes; UV-O3 degradation of MC-LR can produce m/z = 497,m/z = 520,m/z = 570,m/z = 637,m/z = 683,m/z = 750,m/z = 792,m/z = 877molecular ion.These products were created mainly for the way that the aromatic ring undergun hydroxyl substitution of an or two aromatic hydrogen; the methoxy group of the Adda chain changed; conjugated double bonds of Adda side chain changed and heptapeptide ring structure is destroyed.