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Ma Q.,Key Laboratory of Fisheries Ecology Environment | Ren J.,Key Laboratory of Fisheries Ecology Environment | Huang H.,Wuhan Naval University of Engineering | Wang X.,Key Laboratory of Fisheries Ecology Environment | And 3 more authors.
Fresenius Environmental Bulletin | Year: 2011

Microcystin-LR (MC-LR) is a hepotoxin produced by toxic algae species in waterblooms. For the first time, the degradation of MC-LR by nitrous acid was investigated, and several parameters including initial sodium nitrite concentrations, initial pH value and initial MC-LR concentrations affect the degradation were investigated respectively. Degradation of MC-LR was obvious in the present of sodium nitrite under acidic conditions and no degradation was observed under neutral and alkaline conditions. The reaction processes showed preferable relevance between the concentrations of residual MC-LR and time, and they could fit well with the pseudo-first-order kinetics. The degradation rate increased when the pH value decreased, but was not positive correlated with the initial NaNO2 concentration and the initial concentration of MC-LR in this order of magnitude had little influence on its degradation. It is clear that 94.89% of MC-LR was removed at 5 h under optimum initial condition of 5 mM sodium nitrite, pH 1.73, and 9.78 mg/L MC-LR. © by PSP. Source

Ren J.,Fudan University | Ma Q.-W.,Fudan University | Huang H.-H.,Key Laboratory of Fisheries Ecology Environment | Wang X.-R.,Fudan University | And 2 more authors.
Fresenius Environmental Bulletin | Year: 2010

In this study, the degradation of microcystin-LR (MCLR) in aqueous solutions by UV only, H2O2 only and combined UV/H 2O2 processes was investigated. The application of H 2O2 alone had little effect on MCLR decomposition. On the contrary, the combination of UV and H2O2 was shown to be a very effective process since the pseudo-first-order kinetic constant (k) of MCLR degradation by UV/H2O2 treatment was almost two times that of UV treatment alone, suggesting a synergetic effect between UV radiation and H2O2 oxidation. We further studied in detail the degradation characteristic of MCLR (pseudo-first-order kinetics) in aqueous solutions by the UV/H2O2 process with different concentrations of H2O2, different UV intensities, different concentrations of MCLR, and different solution pH values. Our results showed that H2O2 and UV indeed facilitated MCLR decomposition in a dose and intensity dependent manner respectively. In addition, the reaction rate constant of MCLR decomposition was found to be negatively correlated with the concentration of MCLR and the half-life of MCLR in solution was prolonged by increasing MCLR concentration. Moreover, pH value also played a very important role in the MCLR degradation mediated by the application of UV/H2O2, and the optimum range of pH was found to be between 7 and 8. In sum, this study will help in the design of feasible and efficient water treatment strategies for removing microcystins (MCs) in water contaminated with cyanobacteria. © by PSP. Source

Ma Q.,Fudan University | Ren J.,Fudan University | Huang H.,Key Laboratory of Fisheries Ecology Environment | Wang S.,Fudan University | And 2 more authors.
Journal of Hazardous Materials | Year: 2012

Degradation of microcystin-LR (MC-LR) in the presence of nitrous acid (HNO 2) under irradiation of 365nm ultraviolet (UV) was studied for the first time. The influence of initial conditions including pH value, NaNO 2 concentration, MC-LR concentration and UV intensity were studied. MC-LR was degraded in the presence of HNO 2; enhanced degradation of MC-LR was observed with 365nm UV irradiation, caused by the generation of hydroxyl radicals through the photolysis of HNO 2. The degradation processes of MC-LR could well fit the pseudo-first-order kinetics. Mass spectrometry was applied for identification of the byproducts and the analysis of degradation mechanisms. Major degradation pathways were proposed according to the results of LC-MS analysis. The degradation of MC-LR was initiated via three major pathways: attack of hydroxyl radicals on the conjugated carbon double bonds of Adda, attack of hydroxyl radicals on the benzene ring of Adda, and attack of nitrosonium ion on the benzene ring of Adda. © 2012 Elsevier B.V. Source

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