Coagulação/floculação e eletrofloculação para o tratamento de efluentes contendo boro e/ou amônia: Um estudo sistemático usando planejamento fatorial

Abstract

Factorial design of experiments (FDE) is a statistical tool that allows to evaluate the effect of a large number of factors from a small number of experiments. Thus, the FDE was applied in order to verify the effect of factors studied for the treatment of Na2B4O7 based from synthetized and real effluents by means of chemical coagulation and for electroflocculation. The two processes of treatment of effluents are physical chemical type and differ as operation results and removal of desired parameters. While conventional treatment requires addition of chemical coagulants, the electroflotation treats effluents without chemical coagulants, which are formed in situ from the anodic oxidation. Therefore, PFE was applied in order to verify the effect of variables studied for the removal of boron or ammonia from synthetic boron based effluents on and real by means of chemical coagulation or electroflocculation. The synthetic, treated by electroflocculation, was studied using FDE 23 for the factors: electrode distance, support electrolyte concentration and electric current. On the other hand, the actual effluent from a locomotive workshop was studied by applying FDE 22 and the factors was: electroflocculation time and electric current. Thus, with high values of removal of turbidity (99.96%), color (93.21%) and COD (90.89%) was observed. In both treatments for electro-flocculation boron removal was also evaluated and iron electrodes were used in the anode. And both results demonstrated low boron removal efficiency and an indication for the current electrical factor as more significant. As for the physico-chemical treatments by coagulation and flocculation, the boron removal was studied for synthetic effluent and effluent from the mechanical workshop and yard of fertilizer handling, for the removal of ammonia. The tests were performed by varying the following variables at two levels: concentration of the aluminum sulfate, time of coagulation, velocity of coagulation, flocculation time, velocity of flocculation and sedimentation time. Boron removal efficiency (maximum of 60.24%) was better observed for the conventional physical chemical treatment in relation to electroflocculation. As for the ammonia removal, the maximum value of 61.34% was reached for the jar test.