Avaliação da degradação de microcistina-LR por processo foto-fenton solar

Abstract

The water bodies eutrophication has as one of its steps excessive growth of cyanobacteria. As a result, there is an increases in the concentration of cyanotoxins in water, such as microcystins. This characterizes an environmental and public health risk, since this contaminant has high hepatotoxicity, which is why the brazilian legislation limits its concentration in drinking water at 1 µg L-1. Aiming to overcome the deficiency of the conventional water treatment in removing microcystins, alternative treatment technologies were developed, among which the advanced oxidation processes (AOPs). AOPs come up with the purpose of organic compounds oxidation by hydroxyl radicals formed in the medium, highlighting the photo-Fenton process assisted by solar radiation. This study evaluated the efficiency of the solar photo-Fenton process in degradation of microcystin-LR dissolved in crude extract, in compound parabolic collector (CPC) reactor, as well as the phytotoxicity to Sinapis alba before, during and after treatment.The factorial 22 design experiments were carried out in a bench scale solar reactor (400 mL) and aimed at evaluating Fe2+ and H2O2 effects on the process. This experiments showed significant effect of Fe2+ in microcystin removal. Using as reference the Chemical Oxygen dDemand (COD) of the samples, it was found that the best conditions for the dosages of H2O2 and Fe2+ were these rates: H2O2/COD=3,18 e Fe+2/COD=0,318. From matrix effect assays, it was conclused that scavengers radicals present in matrix composition (ASM-1) are responsible for a decrease on the reaction rate and mineralization of analyte. Despite that, the solar foto-Fenton process in CPC reactor (2,1 L) was satisfactory for COD (75%) and microcystin-LR (70%) removals from ASM-1 crude extract, after 120 minutes of treatment. For the natural water crude extract, the treatment achieve 77% mineralization of organic compounds, and up to 99% of microcystin-LR removal in only 45 minutes of reaction. The bioassays with Sinapis alba doesn’t show increase in phytotoxicity for treated samples. After 120 minutes of solar photo-Fenton process, no significant effect in roots growth was observed. From this study, it was concluded that solar photo-Fenton process have potential for a future step in treatment of waters contamined which microcystin-LR.