• PDMS demonstrated notable biodegradation under anaerobic sludge conditions through microbially mediated hydrolysis. • Structural analysis confirmed Si–O–Si bond cleavage and formation of silanol terminal groups during degradation. • Degradation led to a marked reduction in the thermal stability of PDMS. • Key degradation products identified were low-molecular-weight cyclic and linear siloxanes. • Degradation altered functional properties: dielectric constant decreased, viscosity dropped, and interfacial tension with water reduced. • Metagenomic analysis revealed an anaerobic consortium (e.g., Usitatibacter) enriched with genes for xenobiotics biodegradation. Polydimethylsiloxane (PDMS) is a widely used silicon-based polymer known for its excellent chemical and thermal stability, with broad applications in the power industry and consumer products. Due to its recalcitrance to degradation and persistence in the environment, PDMS has emerged as a potential organic pollutant. Therefore, developing effective environmental degradation methods is urgently needed, among which microbial degradation represents a promising solution. In this study, a laboratory-simulated anaerobic sludge environment was used to conduct an 18-day degradation experiment on PDMS. During this period, the PDMS samples exhibited a mass loss of approximately 28.50%. Structural changes during degradation were systematically analyzed using techniques such as gel permeation chromatography (GPC), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The results indicated significant molecular chain scission of PDMS under anaerobic conditions. After 18 days of degradation, the molecular weight of the samples decreased by 24%. DSC and TGA showed a decline in the thermal properties of the degraded samples, with the initial decomposition temperature and glass transition temperature decreasing by 43.7°C and 3.1°C, respectively. Concurrently, the dielectric constant decreased across the measured frequency range, rheological properties decayed, and the interfacial tension between PDMS and water significantly dropped, indicating alterations in material polarity, flow behavior, and surface hydrophobicity. Additionally, nuclear magnetic resonance (NMR) spectroscopy, and Fourier-transform infrared (FTIR) spectroscopy revealed cleavage of Si–O–Si bonds, accompanied by enhanced –OH signals, indicating hydrolysis of the PDMS backbone and the formation of silanol terminals. Gas chromatography–mass spectrometry (GC–MS) analysis detected degradation products containing cyclic and linear low-molecular-weight siloxanes (D4, hydroxyl-terminated L4, etc.). Metagenomic analysis of the microbial community revealed an anaerobic consortium dominated by genera such as Usitatibacter, Aquihabitans , and Pseudomonas , whose functional gene profile demonstrated a strong potential for xenobiotics biodegradation and metabolism. Finally, from a microscopic perspective, this study elucidated the microbial-mediated hydrolysis mechanism of PDMS in anaerobic sludge, providing new insights for the development of biodegradation technologies for silicon-based polymers.
Yang et al. (Sun,) studied this question.