Aplicação do extrato salino de Moringa oleifera e policloreto de alumínio para remoção de cianobactérias em água de abastecimento

Abstract

Cyanobacterial bloom in water supply sources may, among other aspects, implyincreasing the dosages of chemical coagulants to the treated water achieve the quality established in the current Legislation. This increase in the dosage of metallic coagulants may results in health problems due to the presence of aluminum residuals, besides increase the treatment costs. Thus, it was tried to evaluate the applicability of the natural coagulant of Moringa oleifera Lam as a pure solution or when associated to the aluminum polychloride in the removal of cells of Microcystis aeruginosa and Cylindrospermopsis raciborskii by dissolved air flotation. The samples consisted of water from a source of supply located in the MetropolitanRegion of Curitiba plus cyanobacteria cells, aiming to have a initial turbidity value of 40 NTU and cellular density of 5.0 x 105 cells mL-1. The study was developed in three stages: in the first one it was evaluated the efficiency of the natural coagulant for the removal of turbidity, color and cell density of each species of cyanobacteria studied; in the second stage, proportions of Moringa oleifera and aluminum polychloride coagulants were evaluated for turbidity, color and cell density removal of each cyanobacteria species; and finally, experiments were carried out evaluating the influence of a variation of cyanobacteria populations on the treatment when applied to the better proportion of coagulants. In the first step it was found that the better dosage of the natural coagulant for the removal of turbidity, color and cell density was 20 mg L-1 (removal efficiency of 81% for turbidity, 67 - 76% for color and 89 - 97% for cells). For the second stage, the proportion of 75% Moringa oleifera and 25% aluminum polychloride was established as the better for cell removal (95%) and the lowest aluminum residual in the treated water (0.030 mg L-1). In the third step, the proportion of 50% M. aeruginosa and 50% C. raciborskii cells resulted in the better removal of turbidity (94%), color (80%) and cell density (approximately 99%); however, according to statistical tests, no significant difference was observed between the cellular proportions evaluated. Due to the results obtained for all the steps, it is possible to consider that the saline extract of Moringa oleifera proved to be an efficient coagulant for the removal of the studied cyanobacteria species, with an increase in efficiency when associated to the chemical coagulant. In relation to the association of cyanobacteria, it can be suggested that there was no interference of cell density or different cellular morphologies evaluated in the treatment efficiency.