How microplastics affect sludge pyrolysis behavior: Thermogravimetry-mass spectrum analysis and biochar characteristics

The concentration of microplastics (MPs) in sewage sludge (SS) ranged from 1600 to 56400 particles per kilogram of dried SS (MPs: dried SS = 0.14-5.09), so its effect on SS pyrolysis performance should not be negligible. This study attempted to investigate the effect of typical MPs, including polypropylene (PP), polyethylene (PE), and polyvinyl chloride (PVC), on the pyrolysis performance (pyrolysis characteristics and major gaseous product evolution) of SS and their biochar characteristics via thermogravimetry-mass spectrometry (TG-MS) and physicochemical property analysis of biochar. The results showed that the PVC MPs enhanced the pyrolysis of SS, while the PP and PE MPs had an inhibitory effect. The total amounts of gas products tended to decrease with all MPs addition. However, the proportions of combustible components (H2, CH4, and C2H2) increased. Among the biochar products, the presence of PVC MPs during the pyrolysis of SS resulted in a more porous, stable and aromatic biochar.