Banca de QUALIFICAÇÃO: IVAN XAVIER LINS

EXTRACTION OF ELEMENTAL SULFUR FROM PLASTER WASTE USING SANITARY SEWAGE AS A SOURCE OF CARBON

Gypsum waste, Biological sulfate reduction, Sanitary sewage, DCCR, Ultrasound (US), Catalytic Oxidation of H2S.

This thesis presents an innovative study that combines the application of ultrasound (US) with biotechnology to optimize gypsum waste treatment and sulfur recovery. The main objective was to develop an efficient process that involves the enhanced release of sulfates present in gypsum waste, followed by the biological reduction of these sulfates to hydrogen sulfide (H₂S) and the subsequent catalytic oxidation of H₂S to elemental sulfur. For the biological sulfate reduction process, a consortium of sulfate-reducing bacteria (BRS) was used, collected from the soil of gypsum mines located in the Araripe Gypsum Complex, in the Alto Sertão of Pernambuco. The release of sulfates from gypsum residues was facilitated by the use of ultrasonic waves at 40 kHz, optimizing the action of the BRS. Biological sulfate reduction was performed in a UASB (Upflow Anaerobic Sludge Blanket) bioreactor, using synthetic sanitary sewage as a carbon source. To maximize the efficiency of the process, a central rotational composite design (DCCR) was applied to the experiments, with the independent variables being temperature, pH of the medium, sulfate feed concentration and COD ratio [COD/SO42-]. The response variable, the biological efficiency of sulfate removal, reached a mean value of 96.5%. Sulfur recovery was performed using a catalytic solution of Fe/EDTA, which was atomized with the aid of ultrasonic waves ranging between 800 kHz and 10 MHz. The condensation of the resulting mist produced elemental sulfur, which was recovered by centrifugation or decantation, with an efficiency of more than 95%. The catalytic solution was continuously regenerated and recirculated between the sulfur recovery centrifuge and the Fe/EDTA-H2S mixture sonication reactor, ensuring the sustainability and efficiency of the process. The results obtained demonstrate the effectiveness of the proposed process and highlight the importance of ultrasonic techniques in the optimization of biotechnological processes for gypsum waste treatment and sulfur recovery, contributing significantly to environmental sustainability and industrial innovation.