Avaliação da eficiência do tratamento na ETA de Gravatá e estudo químico de abrandamento e de estabilização a 25ºC.

Abstract

This work encompasses not only an evaluation of the treatment applied in the water from Boqueirão's dam (Epitácio Pessoa reservoir) by the Water Treatment Station or ETA of Gravata belonging to the Water and Wastewater Company of Paraiba - CAGEPA, but also a deep study over a chemical softening process for this water. Due to the high hardness concentration of the water it were performed the following types of simulations: ( i ) a theoretical softening according to the theory of Loewenthal et alii (1986) and by using the Modified Caldwell - Lawrence Diagram or MCL Diagram and ( i i ) experimental softening by applying chemical substances to the water (Jar Test equipament). The research was carried out in two stages. In the first one, from the physical-chemical and bactériological data obtained in several treatment reactors of the ETA under investigation it was madean evaluation of the treatment applied to the water. Furthermore, at this stage, it was theoretically simulated the softening process for the water by using the MCL Diagram. In the 2nd stage, with the physical- chemical data obtained at only one point of the ETA it was done the proposed softening by applying theoretical and experimental simulations. The softening simulations of the water showed a very high final pH value. In order to reduce this value to that recomended for the consumer (6,5 < pH < 9,5) it were made (a) theoretical simulations by applying recarbonation and acid addition to the final water and (b) experimental simulation by using only an acid dosing. In both kind of simulations it were adapted for the final water a precipitation potential of 5 mg/£CaC03 and a Langelier Saturation Index- IS o f + 0 , 2, according to Loewenthal et alii (1986). The values of the parameters obtained by means of theoretical simulations were compared to those from the Jar Test simulation according to that, it was proved the accuracity of the theory of Loewenthal et alii (1986) and the use of the MCL Diagram for water conditioning purposes. Furthermore, the final water data were better by applying a post- stabilization with carbon dioxide - CO2 (recarbonation). The poststabilization with sulphuric acid - H2SO4 proved not to be 2+ efficient once it raised the final calcium - Ca content of the water producing a hardness beyond the inicially predicted one. It has been proved the efficiency of the treatment process applied in the ETA of Gravata. This is due to the fact that ( i ) the raw water showed physical-chemical values according to the potability recomended limits and ( i i ) the pathogens killing off was sucessfully achieved by using chlorine desinfection.