Reator de Leito Fixo Bi-fluxo (RLF-BF) aplicado a potabilização de água subterrânea do meio rural

Abstract

Water is part of the basic needs of human beings, but because of its pollution and contamination there is a need for treatment for public supply. However, in Brazil the conventional water purification system is a reality in urban areas, while rural communities and isolated properties have been affected by the lack of water treatment for human consumption. In view of the difficulty of supplying treated water in rural areas in Brazil, the present work aimed to analyze the construction of a Bi-flow Fixed Bed Reactor (RLF-BF) and the evaluation of its efficiency for water purification. The RLF-BF was made with 25, 100 and 200 mm pipes, containing two beds, a filtering bed (descending) and an adsorbing bed (ascending), operated, therefore, in a bi-flow direction. The filtering bed has a volume of 0.0012 m³, consisting of medium sand (0,25 mm) and the adsorbent bed has a volume of 0,00039 m³, consisting of granular activated carbon (CAG) from babassu (Orbignya phalerata) epicarp, with particle sizes (0,0075 to 2,36 mm), both placed above a 15 cm pebble support layer. In the RLF-BF were used surface application rates of 120 and 32 m³ m-2 d-1 for the filter bed and adsorbent bed, respectively, being allocated upstream a 200 L water reservoir, which supplied the RLF-BF. The efficiency of the RLF-BF was evaluated through raw water samples at the outlet of the reservoir and treated by filtration (ATF), as well as water treated by filtration and adsorption (ATF-A), both sampled every 10 min of treatment, for the following parameters: apparent color, free chlorine, pH, turbidity, total and thermotolerant coliforms, considering maximum permitted values (VMP) Consolidation Ordinance GM/MS nº 5, of September 28, 2017 and its amendments in Ordinance nº 888, of May 4, 2021 of the MS, and the parameters not recommended in the Ordinances, absorbance (λ - 254 nm), alkalinity, electrical conductivity, calcium hardness and head loss of the filter bed and adsorbent bed. The analyses were performed in the Water and Ecotoxicology Laboratory of the Federal University of the Southern Frontier (UFFS), Campus Cerro Largo - RS. The operation of the RLF-BF of preliminary tests corresponded to 11 filtering rows and the tests were terminated due to the removal efficiency of turbidity and apparent color, as well as the pressure drop. The parameters turbidity, apparent color and head loss were decisive for the closure of the process, because they are directly linked to filter clogging when the values increase during operation. After the treatment considering 11 filtering rows the maximum loss of load in the filter and adsorbent bed was reached (21 and 15 cm) and an average removal efficiency was identified in relation to the parameters analyzed in the sampling water treated by filtration and adsorption (ATF-A): apparent color (33,2 %), pH (7,2 to 9), turbidity (22 %), absorbance (λ - 254 nm) (16,6 %), alkalinity (33,3 %), electrical conductivity (3,2 %). The parameters free residual chlorine and total and thermotolerant coliforms, recommended in Ordinance nº 888/21 of the MS, were in disagreement with those established in the Ordinance, and calcium hardness, which is not recommended in the Ordinance, had no variation. Regarding efficiency, the installation of the RLF-BF improved the quality of the rural water supply in the ATF-A samples. The head loss of the beds was reached after (2h20min). Finally, as future prospects, it is suggested: (i) perform backwashing tests of the filter bed and the adsorbent bed when they reach the maximum head loss; (ii) replacement of the sand filter after clogging and replicate treatment; (iii) evaluate parameters such as pesticides in raw and treated water, because this is a common pollutant in aqueous matrix in the study region.