Otimização do tratamento das águas do Açude Grande (Cajazeiras-PB)

Abstract

Açude Grande is located in the interior of the state of Paraíba, where reduced water availability and long periods of drought are prevalent. Furthermore, this water body is part of the urbanization process of the city of Cajazeiras and was built with the purpose of supplying the local population. However, over the years, the intensification of human interference promoted the deterioration of the environmental quality. In light of this, the present research aimed to optimize two treatment technologies for Açude Grande's waters using the Central Composite Rotatable Design (CCRD) coupled with the Response Surface Methodology (RSM). Firstly, the efficiency of the adsorption process using powdered activated carbon (PAC) in the removal of Chemical Oxygen Demand (COD) and true color was analyzed, with the independent variables being the adsorbent concentration and pH. Subsequently, the conventional treatment was simulated using aluminum sulfate as a coagulant. In the clarification stages of the conventional treatment (coagulation, flocculation, and sedimentation), the variables concentration of aluminum sulfate and pH were optimized based on the removal of turbidity and apparent color. The simulation of the filtration stage of the conventional treatment was conducted on two prototypes of filters: the single-layer filter composed of sand and the double-layer filter composed of sand, and PAC, in both cases gravel was used as a support. The results showed that in the adsorption technique, the solubilization of CAP occurred, resulting in increase in COD in the samples. Additionally, the generated statistical models were not satisfactory. Regarding the efficiency of the clarification steps in conventional treatment, it was found that, within the study range, the best result was obtained at a coagulant concentration of 60 mg.L-1 and pH of 6 (test 3). This resulted in a turbidity removal of 67,30% and apparent color of 78,13%, meeting the turbidity parameter within the limits set by GM Ordinance of the Ministry of Health Nº. 888/2021. Concerning the filtration process, the single-layer filter proved to be the best proposal from a sanitary and economic perspective, resulting in a faster filtration rate, and good efficiency in removing turbidity parameters (>77%), apparent color (>70%), and BOD (>61%). In conclusion, the conventional full-cycle process is an appropriate technique for treating the waters of Açude Grande.