Avaliação da filtração direta descendente no tratamento de água de manancial com baixa turbidez e cor elevada

Abstract

The treatment of water is carried out by means of an association of chemical and physical processes aimed at transforming raw water into drinking water. The adoption of the most appropriate treatment should be made according to the physical-chemical and biological characteristics of the raw water. Located in Rio Grande do Norte, ETA Extremoz is a conventional type station that treats 750 l / s of water from the lagoon of Extremoz. Although it was designed as a conventional ETA, the history of the last 24 years of the variables apparent color and turbidity of the raw water does not comply with the recommended parameters for the adopted treatment technology and as a consequence the ETA started to operate as a direct descending filtration from the beginning of 2001. The need for ETA adjustments similar to ETA Extremoz indicates the need for studies to evaluate the ideal treatment conditions for water with these characteristics. This work aimed to evaluate to what extent direct downward filtration can be indicated for the treatment of water with low turbidity and high color. For this, the research compared the results of the treatment of the water in a simple sand filter bed and a sand filter and anthracite charcoal followed by adsorption with granulated activated carbon. The experiments were carried out in a Pilot Installation of Water Treatment by Oxidation, Adsorption and Double Filtration, installed in the premises of ETA Extremoz. The treated water quality was evaluated for four filtration rates, 253, 280, 310 and 340 m³ / m².day. For the simple sand filter bed, experiments were carried out on filters with a 700 mm thick filter layer and effective grain diameter (D10) of 0.50, 0.57 and 0.87 mm. For the double bed of sand and anthracite charcoal, the thickness of the sand filter layer was reduced to 450 mm, including anthracite coal layer with 250 mm thickness and D10 = 1,00 mm. For the adsorption in granulated activated carbon, experiments were performed with layer of 650 mm and D10 of 0.23, 0.60 and 0.90 mm. It is concluded that for the double bed of sand and anthracite coal all three grades and four filtration rates studied complied with Ordinance No. 5/2017, the filter F3, for the filtration rate of 340 m³ / m².day, the best condition to be adopted in real scale.