Microplastics Mitigation in Sewage Sludge through Pyrolysis: The Role of Pyrolysis Temperature

Abstract

Sewage sludge is an important source of introducing microplastics into the environment, and thus, effective mitigation of microplastics in the sludge is in urgent need. Herein, the effect of pyrolysis on microplastics reduction in sewage sludge was investigated through a lab-scale study. The micro-Raman analysis showed that the microplastics concentrations in sludge residues decreased significantly from 550.8 to 960.9 particles/g to 1.4–2.3 particles/g with the pyrolysis temperature increasing to 500 °C, and no tiny (10–50 μm) microplastics remained. Polyethylene and polypropylene, the two most abundant microplastics in sewage sludge, were entirely degraded when the pyrolysis temperature reached 450 °C. However, during the pyrolysis process, new plastic polymers could be produced through the reaction between original microplastics with organics in sludge, and heavy metals in sludge can also be combined. Moreover, scanning electron microscopy analysis of spiked microplastics showed that incomplete pyrolysis at low temperatures could result in rough surface morphology of microplastics, making it more readily to adsorb contaminants. Overall, the results of this study provide the first insight into the effectiveness of microplastics control in sewage sludge through pyrolysis, but to avoid potential environmental risks induced by incomplete pyrolysis, a pyrolysis temperature of 450 °C should be reached at least.

Enhancing Microplastics Removal from Wastewater Using Electro-Coagulation and Granule-Activated Carbon with Thermal Regeneration

“…Here, the condensate was water discharged from the GAC after thermal regeneration, such as pyrolysis. Previous studies on the pyrolysis of plastics contained in STP sludge reported that many polymers, such as PE, PP, PS, and PA, started to decompose at 375-500 • C [11,34]. However, it should be noted that there is no other study in the literature using GAC thermal regeneration for the removal of MPs.…”

“…The results indicate that the GAC thermal regeneration system could efficiently reduce MPs from the STP retrofitted with the GAC treatment process. Although existing studies on the removal of MPs from the GAC thermal regeneration system are rare, pyrolysis similar to GAC thermal regeneration systems is recognized as a promising sludge treatment technology for removing MPs in an STP [11]. For the removal of MPs in an STP, the major advantages of the GAC thermal regeneration system include the mechanism of filtering and pyrolysis.…”

“…Bing et al (2020) reported that the sludge produced from pyrolysis showed significantly decreased MP concentrations. In addition, pyrolysis resulted in a rough surface morphology of the MPs, making it easier to adsorb contaminants [11].…”

Editorial Overview: Emissions of Microplastics and Their Control in the Environment

“…Additionally, effective plastic waste management and recycling should be promoted at community and jurisdictional levels. Mismanagement of plastic waste is considered a major cause of microplastic pollution (Ni et al 2020). It was estimated that only 9% of waste plastics were recycled by 2015 (Lambert and Wagner 2017).…”

“…Microplastics (MPs) (particle size <5 mm) have been found in almost all environments on Earth, including urban centers, terrestrial areas, and freshwater environments as well as in remote uninhabited islands, deep seafloor, and polar regions (Liu et al 2019;Ni et al 2020;Yin et al 2021). They are released to the environment directly from primary sources (such as cosmetic and cleansing commodities, and personal care and pharmaceutical products), or indirectly from secondary sources through the fragmentation and degradation of meso and macroplastics (Schernewski et al 2020).…”