Microplastic Degradation through Thermal Hydrolysis in Sewage Sludge and Its Impact on the Anaerobic Process

In the present study, the abundance of microplastics (MPs) in sewage sludge (SS) and their fate during thermal hydrolysis (TH) pretreatment were investigated. The initial MP concentration in 50 mL of SS sample (dry solids = 1 g) was 206 particles/g SS, of which around 54% were in solid phase while the rest were in the liquid phase. The TH runs were conducted in a high-pressure reactor at temperatures of 140–180 °C for 60 min. To study the degradation of MPs during the TH process, a few runs were performed with distilled water containing mixtures of different combinations of MPs at 160 °C. Subsequently, biogas generation from synthetic wastewater before and after the TH runs was also determined. The destruction of MPs increased with TH pretreatment. In this study, a detailed examination of the changes in shape, counts, particle size, surface composition, and morphology of MPs was performed. Various MP degradation mechanisms and indications of the aging of MPs were identified. Moreover, a significantly higher methane production was observed from the TH pretreated synthetic wastewater containing a mixture of MPs. TH pretreatment was found to be very effective for the destruction of MPs, which reduced their adverse impact on anaerobic treatment.