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

Waste Management 2023 9 citations ? Citation count from OpenAlex, updated daily. May differ slightly from the publisher's own count.
Qiao Xiong, Yinqiu Li, Chaohua Hou, Jie Yang, Xiangjun Zhou, Xiangjun Zhou, Xiao Ma, Xiao Ma, Xiangru Zuo, Xiang Wu

Summary

Microplastics in sewage sludge alter how the sludge burns during pyrolysis: PVC microplastics sped up decomposition while polyethylene and polypropylene slowed it down. This matters because sewage sludge from wastewater plants contains thousands of microplastic particles per kilogram, and understanding how they change the energy recovery and byproduct quality of sludge treatment helps improve the management of this widespread microplastic sink.

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 (H, CH, and CH) increased. Among the biochar products, the presence of PVC MPs during the pyrolysis of SS resulted in a more porous, stable and aromatic biochar.

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