RESUMO
Granular activated carbon (GAC) fixed bed adsorption technology was applied to remove carbamates carbaryl, methomyl and carbofuran from public water supply. In order to minimize the effect of clogging and to evaluate adsorbent saturation for carbamates, the microfiltration (MF) was previously used to adsorb and the backwash procedure of the GAC bed was carried out. The determination and quantification of the carbamates were performed by analytical technique in high performance liquid chromatography with post-column derivatization and fluorescence detector. The MF of the water previously adsorbed in the GAC fixed bed allowed the greater removal of 100% of the carbamates pesticides with an initial concentration of 25â µgâ L-1 during the first 48â h of operation. The saturation of the GAC fixed bed occurred in 240â h, due to the partial removal of the natural organic matter by the MF, consequently the competition for adsorptive sites of the GAC was smaller. The backwashing procedure contributed to the partial recovery of the performance of the hydraulic filtration and allowed to identify the saturation of the adsorption column, since the sealing phenomenon preceded the saturation. Finally, the use of public water supply was considered a relevant and positive aspect, since it allowed the identification of the performance of this technology in the removal of carbamates pesticides considering the presence of substances inherent to the public water supply.
Assuntos
Praguicidas , Poluentes Químicos da Água , Purificação da Água , Adsorção , Qualidade da Água , Abastecimento de ÁguaRESUMO
The application of a fixed bed adsorption column of granular activated carbon (FBAC-GAC), in the removal of carbaryl, methomyl and carbofuran at a concentration of 25â µgâ L-1 for each carbamate, from the public water supply was investigated. For the determination of the presence of pesticides in the water supply, the analytical technique of high-performance liquid chromatography with post-column derivatization was used. Under conditions of constant diffusivity, the FBAC-GAC was saturated after 196â h of operation on a pilot scale. The exhaust rate of the granular activated carbon (GAC) in the FBAC-GAC until the point of saturation was 0.02â kgâ GACâ m-3 of treated water. By comparing a rapid small-scale column test and FBAC-GAC, it was confirmed that the predominant intraparticle diffusivity in the adsorption column was constant diffusivity. Based on the results obtained on a pilot scale, it was possible to estimate the values to be applied in the FBAC-GAC (full scale) to remove the pesticides, which are particle size with an average diameter of 1.5â mm GAC; relationship between the internal diameter of the column and the average diameter of GAC ≥50 in order to avoid preferential flow near the adsorption column wall; surface application rate 240â m3â m-2â d-1 and an empty bed contact time of 3â min. ABBREVIATIONS: BV: bed volume; CD: constant diffusivity; EBCT: empty bed contact time; FBAC-GAC: fixed bed adsorption column of granular activated carbon; GAC: granular activated carbon; MPV: maximum permitted values; NOM: natural organic matter; PD: proportional diffusivity; pHPCZ: pH of the zero charge point; SAR: surface application rate; RSSCT: rapid small-scale column test; WTCS: water treated conventional system.