Efeito da idade celular da cianobactéria Microcystis aeruginosa na eficácia do processo oxidativo UV/H2O2 para o tratamento de água

Abstract

Cyanobacteria are unicellular microorganisms relevant in nature, as they present benefits to the environment, and have specific characteristics such as ease of adaptation to different environments and rapid reproduction. However, these characteristics associated with the presence of nutrients in the water bodies make the water quality become increasingly common, generating an intensified growth, causing changes in the water quality, affecting, color, odor, and that are not defined as handling processes, eg by easy handling. The advanced oxidation process via UV/H2O2 is an alternative to be used in treatment plants. Therefore, this study aimed to evaluate whether the bacterial cell would work with the participation of UV/oxidative process performance considering the water treatment of these organisms. The experiments were carried out with a species Microcystis aeruginosa, and the experimental procedure was divided into two moments, in which the growth curvature of the species M.aeruginosa and the photo-oxidative assays were evaluated. The study water solution consists of a sample cell concentrated to obtain a density of 5 x 105 cel mL1. The growth curve was analyzed for 64 days, with analyzes of dissolved organic carbon (DOC), optical density at 730 nm, cell density and pH. The photo-oxidative assays were carried out from the eighth day of growth of the culture, with intervals of 7 days, therefore, the experiments were carried out on days 8, 15, 22, 29, 36, 43, 50, 57 and 64. oxidative process was carried out in a photochemical reactor composed of a source of ultraviolet radiation from a high-pressure lamp, using two doses of H2O2, 20 mg L- 1 and 50 mg L-1. The exposure time to radiation was 60 minutes, where aliquots were taken for analysis of cell density and DOC, at times 0, 5, 10, 20 and 60 minutes, and for residual H2O2 and optical density at 730 nm, at times 0, 2.5, 5, 10, 20, 30, 45 and 60 minutes. As a result, in relation to the tests, one can observe the decay of the hydrogen peroxide concentration over time, regardless of cell age, in a similar way in both concentrations used. The same behavior was observed for optical density and cell density, where no cells were found at the end of the process. The DOC values found during the process obtained an increase, when compared to time zero, for all cell ages, justified by cell lysis. Cell density and optical analyzes indicate the possibility that DOC values involve intra and extracellular fractions of the cells. For the results of the growth curve, there was a gradual increase in all the analyzes performed, being possible to obtain good correlations between the analyzes performed. It was concluded that the cellular age of the species Microcystis aeruginosa did not change the effectiveness of the advanced oxidative process UV/ H2O2 under the conditions used.