Research on the use of sewage sludge in the co-gasification process with tire char

The work aimed to assess the feasibility of managing hazardous sewage sludges in steam co-gasification with tire char. Characteristics of sludges from fat (FSS), coke (CSS), and refinery (RSS) wastewater treatment plants indicated a high environmental threat posed by heavy metals (especially cadmium) during their traditional management, and that these are reactive materials (high content of volatile matter, functional groups, and ash with catalytically active components). In turn, tire char was rich in carbon but had an unfavorable ash composition and surface properties. Steam gasification/co-gasification measurements of materials and their blends (ratios: 9:1 and 2:1) were performed using a thermovolumetric method at 800-950 °C under 1 MPa. The formation rates of gas components showed that the gasification of individual materials differed significantly (for tire char, the pyrolysis stage was negligible, while for sludges it dominated). The co-gasification measurements indicated that the addition and increase of: FSS accelerated the process and increased conversion (up to nearly 100% conversion while reducing the process time by more than 40% in the most favourable case); CSS accelerated the process; RSS generally worsened the process. Moreover, the presence of sludges decreased the activation energy and pre-exponential factor of the conversion reaction, while increasing the reaction order, particularly for RSS blends, suggesting that transport phenomena affected the kinetics. Finally, sludges generally harmed the resulting gas (decreased H 2 , increased CO 2 ). However, at 950 °C, all sludges improved conversion, and their effect on gas quality was negligible. Therefore, properly conducted co-gasification may be used to manage sewage sludges.