SÁ, G. B.; http://lattes.cnpq.br/0287804224111392; SÁ, Gabriela Braga de.
Résumé:
Concerns related to the increasing concentration of cyanobacteria in reservoirs are motivated
by the potential production of cyanotoxin, a secondary metabolite that is released in water
by cell lysis and may bioaccumulate in the food chain, which can result in serious diseases
and even death in the affected population. Saxitoxin (SXT) is a toxin that represents a public
health issue when in water even in concentrations within the limits set by regulations.
Therefore, the system developed and evaluated in this study focuses on raw water treatment
by slow filtration associated with heterogeneous photocatalysis and is proposed to be used
as an alternative to public water supply. In the first stage of the study, two slow filters (FL1
and FL2) with filter medium composed of sand and kaolin were evaluated during 90 days.
Both models were evaluated based on physicochemical and microbiological parameters and
one model was selected after the operation period. In the second stage of the study, balls
were produced using kaolin, clay, and TiO2 and characterized by X-ray diffraction (XRD)
and ultraviolet visible spectroscopy (UV-vis). Next, the balls were inserted inside the
photocatalytic reactor, which was connected to the slow filter. The operation continued for
20 days, and the concentrations of TiO2 used were 15% and 30%. The system was fed in
both stages using Piranhas River water. In the first stage, the results obtained for FL1 met
the potability standard values established in Ordinance GM/MS Nº 888/21 in 92%
(turbidity), 100% (pH), 28% (apparent color), 100% (ammoniacal nitrogen), 16% (E. coli),
and 100% (STX) of the samples. FL2 met the standard values in 94% (turbidity), 100% (pH),
34% (apparent color), 100% (ammoniacal nitrogen), 16% (E. coli), and 100% (STX) of the
samples. No filter met the requirement for fecal coliforms. In the second stage, the XRD
results indicated the main phase as being anatase; from the UV-vis spectroscopy, bandgaps
of 3.14 and 3.09 were obtained for balls with 15 and 30% of TiO2, respectively. The results
during the operation of the system indicated a more efficient removal of STX in the reactor
with balls with 30% TiO2, with maximum removal efficiency of 95% and average efficiency
of 39%. Therefore, the system proposed could reduce STX levels and may be used as an
alternative water treatment system, particularly in isolated communities. Moreover, clay and
kaolin exhibited good capacity in the photocatalytic process mediated by sunlight, increasing
degradation/oxidation when compared to other studies in which high sunlight exposure times
were adopted.