• English
  • Português

Data of Thesis

Author: Monica Hatsue Toledo Nassu
Title: Use of SODIS in the disinfection of coliforms and reduction of the concentration of microcystin-LR
Year: 2018                                         Full text (in Portuguese)
The quality of water used for human consumption is a worldwide concern, as not only pathogenic microorganisms but also toxins can be carried by this water resource. One of these toxins is microcystin, produced by several genera of cyanobacteria. In places where conventional water treatment is not available, there is a need for an alternative methodology for the treatment of this water resource, such as SODIS (Solar Water Disinfection). The SODIS methodology consists of filling transparent pet bottles with untreated water put them in the sunlight for 6 hours and let them cool for one night. After this period this water will be free of pathogens and may be consumed. To improve this technique, we can add the water to be treated, additives. The objective of the present study was to evaluate whether SODIS added or not with methylene blue (MB) and hydrogen peroxide (H2O2), could reduce the concentration of microcystin-LR and inactivate two bacterial strains, Escherichia coli (ATCC 25922) and Klebsiella pneumoniae (ATCC 13883). Our results demonstrated that none of the tested concentrations of MB, with or without the use of the chlorine tablet, exposed the SODIS methodology, were able to degrade the microcystin-LR and the blue color of the dye remained in the samples, which would make it difficult to use people. It was observed that the E. coli strain was inactivated using the SODIS methodology and with any of the H2O2 concentrations tested, whether chlorine was used or not, but the K. pneumoniae strain was only inactivated when the SODIS methodology was combined of 6 g/L of H2O2, with no use of the chlorine pellet. In relation to the concentration of microcystin-LR, in the experiments with SODIS added with H2O2, it was observed that the concentration of this toxin decreased significantly in relation to the control, being statistically equal among all tested concentrations, and close to the maximum limit allowed by the consolidation number 5/2017 Ministry of Health of Brazil. The chlorophyll-a concentration decreased significantly in all samples in relation to the control, and with SODIS use, this decrease was to below the limit of detection of the method in all samples added or not with H2O2. The results of this study are not a final solution for reducing the concentration of microcystin-LR in water for human consumption in places where conventional water treatment does not exist, but rather an initial study aiming to reduce the concentration of this cyanotoxin, using methodologies of easy handling and lower cost.