Avaliação de técnicas de tratamento na remoção de saxitoxinas em águas de consumo humano

Abstract

This work conducted in batch scale, evaluated the saxitoxin removal by mean of two water treatment processes, namely, adsorption and oxidation. The toxins were produced through extraction of viable cells of cyanobacteria Cylindrospermopsis raciborskii. Five powdered activated carbons (PAC) made available by three Brazilian manufacturers were selected, and three of them were actually used adsorption tests. The characterization of each carbon was done by sweep microscopic in terms of volume of pores, surface area, grain size distribution, and iodine number. The cyanobacteria species cultivated during the study period were collected in a water source in Lagoa Santa. The synthetic water was prepared by means of destilled water and equivalent concentration of saxitoxin set up by Elisa test. The oxidation and adsorption tests were carried out in jar test equipment, using mineral, bond and wood activated carbons and calcium hypochlorite. The detention times were two hoursfor adsorption, and 30 and 60 min for oxidation tests. The results pointed out that the type and the dosage of PAC are strongly related. For all tests,the final saxitoxin concentration was higher than the limit established by The Brazilian drinking water legislation 518 (3,0 g/L). The information concerning the characterization the activated carbons provided by the manufacturers differed from that obtained in the tests, and these parameters were not in agreement with the standards set differed by ABNT (EB-2133). The oxidation efficiency was approximately 80 % for both detention times and distinct dosages, keeping practically constant for all tests according to the limit established by The Brazilian drinking water legislation 518.