Hydrophobic interaction between nanoplastics and surfactant antagonistically shielding the toxicity of surfactant to syntrophic methanogenesis

Mengyuan Zhang; Gaojun Wang; Bo Zhang; Geli Chen; Qian Li; Rong Chen

doi:10.1016/j.jenvman.2025.126504

Hydrophobic interaction between nanoplastics and surfactant antagonistically shielding the toxicity of surfactant to syntrophic methanogenesis

J Environ Manage. 2025 Jul 11:391:126504. doi: 10.1016/j.jenvman.2025.126504. Online ahead of print.

Authors

Mengyuan Zhang¹, Gaojun Wang², Bo Zhang¹, Geli Chen³, Qian Li⁴, Rong Chen⁴

Affiliations

¹ Key Lab of Environmental Engineering (Shaanxi Province), School of Environmental and Municipal Engineering, Xi'an University of Architecture and Technology, No.13 Yanta Road, Xi'an, 710055, PR China.
² Key Lab of Environmental Engineering (Shaanxi Province), School of Environmental and Municipal Engineering, Xi'an University of Architecture and Technology, No.13 Yanta Road, Xi'an, 710055, PR China; International S&T Cooperation Center for Urban Alternative Water Resources Development, Key Laboratory of Northwest Water Resource, Environment and Ecology (Ministry of Education), Xi'an University of Architecture and Technology, No.13 Yanta Road, Xi'an, 710055, PR China. Electronic address: gjwang@xauat.edu.cn.
³ China Design Group (Shaanxi Branch), No.34, Gaoxing six Road, Xi'an, 710075, PR China.
⁴ Key Lab of Environmental Engineering (Shaanxi Province), School of Environmental and Municipal Engineering, Xi'an University of Architecture and Technology, No.13 Yanta Road, Xi'an, 710055, PR China; International S&T Cooperation Center for Urban Alternative Water Resources Development, Key Laboratory of Northwest Water Resource, Environment and Ecology (Ministry of Education), Xi'an University of Architecture and Technology, No.13 Yanta Road, Xi'an, 710055, PR China.

PMID: 40651412
DOI: 10.1016/j.jenvman.2025.126504

Abstract

Surfactants and nanoplastics are emerging contaminants in organic wastewater. Although the influences of surfactants on the anaerobic digestion of organic wastewater were widely investigated and confirmed, the regulation of co-existed surfactants and nanoplastics on syntrophic methanogenesis was not clear. This study explored the inhibitory mechanism of sodium dodecyl sulfate (SDS) surfactant on syntrophic methanogenesis and deciphered how polypropylene (PP) nanoplastics regulating this inhibition. The results showed that individual 200 mg/L SDS dramatically decreased methane yield (P₀) by 31.7 % and prolonged the lag time (t₀) from 5.2 d to 12.1 d by damaging the cell membrane, disordering extracellular matrix structure, and decreasing cell viability. Meanwhile, the relative abundance of major hydrogenotrophic Methanoculleus decreased by 43.6 %. However, the addition of PP at concentrations between 0.5 and 200 mg/L effectively mitigated the release of intracellular lactate dehydrogenase and enhanced cell viability. Consequently, key parameters P₀ and t₀ recovered to 6.0-20.6 % and 5.0-8.4 d, respectively. This demonstrated an antagonistic effect of PP and SDS co-existence. The physical analysis further suggested that the hydrophobicity of PP acted as carriers for the aggregation of hydrophobic end structure of SDS, which formed surfactant-coated particles. Meanwhile, the exposed hydrophilic head structure of SDS with negative charges had less chance to attach to the cell membrane due to electrostatic repulsion effects, thereby shielded the toxicity of SDS to microbes. These outcomes provided new insights into understanding the role of surfactants and nanoplastics regulating syntrophic methanogenic process.

Keywords: Antagonistic effect; Hydrophobic interaction; Nanoplastics; Surfactant; Syntrophic methanogenesis.