Estudo da viabilidade da recuperação do coagulante sulfato de alumínio em lodo de estação de tratamento de água (LETA)

Abstract

The Sludge of Water Treatment Station (SWTP) is generated in the coagulation step of the conventional water treatment system. The disposal of SWTP in rivers is a reality and this practice can cause negative environmental and social impacts. The acidification of SWTP with sulfuric acid (H2SO4), called the Fulton method, is a recovery option under study, which consists of the solubilization of aluminum hydroxides (Al(OH)ᴈ) and pH adjustment, separating the acidified sludge residue (ASW) and the Recovered Coagulant (RC). The present study aims to assess the viability of recovering the Al2(SO2) and the coagulant and characterizing the ASW for proper disposal. The methodology applied was the collection of samples in a water treatment plant, which uses Al2(SO4)ᴈ, characterization of SWTP application of the acidification method in SWTP in natura, evaluation of the performance of the RC in relation to the Commercial Coagulant ( CC) and ASW characterization. The characterization of SWTP via XRF identified the presence of Si, Fe, Al, Ca, Ba, S, Mn, P, Zr, Br, Zn, Cu, Cr and Mr. In the XRD analysis, it presented three crystalline phases, being quartz, kaolinite and muscovite. In the thermal analysis, 2 endothermic peaks and 2 exothermic peaks were obtained. In the performance analysis, CR1 presented a more favorable result for the removal of turbidity with a dosage of 8 mL, obtaining 0.72 NTU in raw water 1 and 0.64 NTU in raw water 2. The ASW obtained a loss on fire of 20.15 % and in the XRF analysis presented S, Ti, K, Ba, Ca, Mn, Zr, P, Cu, Zn, Br, Sr, Tm. The ASW showed pH in the range of 2.56 - 0.94, being classified as Class I - Hazardous waste, according to NBR 10.004. From the data provided by the WTP under study, it was possible to analyze the possibility of reducing the generation of 7,500 m³ / month of SWTP to 1,500 m³ / month of ASW. However, the acidification method is not environmentally viable because it generates an acid ASW and the application of the method on an industrial scale may be impracticable due to the use in large volumes of H2SO4.