Potencial bactericida de biocarvões do pseudocaule da bananeira (Musa sp.)

Abstract

The access to quality drinking water is a basic need that represents as a major problem for many people around the world, about 2.1 billion people in 2017 according to the World Health Organization. One of the critical factors for the standards of water quality for human consumption is the control of the concentration of microorganisms present in it, since these living beings cause not only changes in taste and odor, but also pipes and equipment corrosion, contaminate food and spread diseases among human beings. Based on the problems generated by the contamination of microorganisms, mainly in water sources, this work seeks to evaluate the bactericidal potential of activated carbon obtained from the banana pseudostem (CA-PCB in portuguese), to investigate its possible use in filters or other equipment that act on bacterial inhibition. To determine the charcoal inhibition capacities, experiments were carried out with strains of E. coli and P. aeruginosa, comparing different production conditions of CA-PCB by a Box-Behnken (BB) design, with variations in the concentrations of the activating agent ZnCl2 (Cimp), heating rate (R) and activation temperature (Tativ) in the pyrolysis and activation process. In addition, other activated carbons (obtained from açaí and a commercial one impregnated with Ag/Cu) were also evaluated for comparison purposes. Thus, as an indicator of bactericidal potential, the formation of inhibitory halos by coals in Petri dishes expressed by the areas of inhibition halos was evaluated as a variable response of the BB design, for each of the studied bacterial strains. In addition, the stability of the coal was evaluated (by hot washing and by cold running water), the pH of the CA-PCB was determined, as well as the possibility of leaching in terms of pH variations due to contact with carbons, as well as the leaching of elements into the aqueous phase. The coals were also characterized as to their morphology (by microscopy) as well as their elemental composition. In general, different behaviors were observed in the formation of inhibitory halos for each strain, while in plaques with P. aeruginosa the coals with the highest concentrations of impregnating material (Cimp = 2 mol L-1) had the highest bactericidal potential (halo areas above 3 cm2), with E. coli the best results were obtained for coals with production variables at more central values (Cimp = 1 mol L-1; R = 10 °C min-1; Tativ = 600 °C). Additionally, a partial loss of the bactericidal potential of CA-PCB was observed after the leaching experiment (cold wash with running water) and a total loss of inhibitory capacity after the pH determination procedure (hot wash), for strain P. aeruginosa. The pH of the CA-PCB was 4.06 and, therefore, aiming to investigate the inhibitory mechanisms, it was found that the acidic pH (< 4) can be characterized as the cause of inhibition for the CA-PCB, however this factor was not confirmed (at least not as the only cause of the bactericidal capacity). In addition, the experiment to evaluate the possible leaching of elements from CA-PCB indicated an irrelevant release of zinc (Zn) and a remarkable removal of chlorine (>97%) by activated carbon, which is a promising characteristic of this carbon (based on the NBR 10698 – which is a Brazilian regulatory standard that states about the quality standards of water filters). Based on the obtained results, it can be concluded that the use of CA-PCB is very promising for the manufacture of filters, for the removal of organic and inorganic compounds, and also with bactericidal potential. However, further studies are still necessary for a comprehensive understanding of the stability behavior of this activated carbon, in addition to identifying the inhibitory mechanisms provided by the material that promotes the bactericidal activity.