Impacts of poly(lactic acid) microplastics on organic compound leaching and heavy metal distribution during hydrothermal treatment of sludge

Yang Yu; Bingxing Zhu; Yindi Ding; Cailing Zhou; Shifu Ge

doi:10.1016/j.scitotenv.2023.166012

Impacts of poly(lactic acid) microplastics on organic compound leaching and heavy metal distribution during hydrothermal treatment of sludge

Sci Total Environ. 2023 Nov 25:901:166012. doi: 10.1016/j.scitotenv.2023.166012. Epub 2023 Aug 2.

Authors

Yang Yu¹, Bingxing Zhu², Yindi Ding², Cailing Zhou², Shifu Ge²

Affiliations

¹ School of Energy and Environment, MOE Key Laboratory of Environmental Medicine Engineering, Southeast University, Nanjing 210096, PR China. Electronic address: 101012539@seu.edu.cn.
² School of Energy and Environment, MOE Key Laboratory of Environmental Medicine Engineering, Southeast University, Nanjing 210096, PR China.

PMID: 37541517
DOI: 10.1016/j.scitotenv.2023.166012

Abstract

This study provides an in-depth examination of the role of poly(lactic acid) microplastics (PLA-MPs) during sludge treatment, particularly in relation to organic compound leaching and heavy metal distribution. Through the application of advanced analytical techniques such as Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), thermal analysis, and gas chromatography-mass spectrometry (GC-MS), the release of degradation byproducts was quantified, and the effects on organic compound leaching and heavy metal distribution were assessed. Specifically, the results demonstrated that PLA-MPs significantly impacted the hydrolysis reaction, with the pH value descending in pure water as the hydrothermal temperature escalated. At 140 °C, the hydrolysate contained 20.66 % propylene ester and 16.57 % lactic acid. Furthermore, an increase in total organic carbon (TOC) was observed with increasing temperature, with TOC content at 140 °C in water almost doubling from that at 120 °C and 130 °C. With respect to heavy metals, the presence of PLA-MPs influenced the migration of Cr(VI) between solid and liquid phases in sludge. Notably, after 180 °C hydrothermal treatment, the content of Cr(VI) in the liquid phase of sludge with PLA-MPs was 9.72 %, which is higher than that of sludge without PLA-MPs at 5.80 %. These findings underline the need to consider PLA-MPs' influence on organic compound leaching and heavy metal distribution during sludge treatment.

Keywords: Heavy metals; Hydrothermal treatment; Microplastics; Organic compound; Waste activated sludge.