Transport characteristics of polystyrene microplastics in saturated porous media with biochar/Fe3O4-biochar under various chemical conditions

Xiaoxia Wang; Yitong Dan; Yinzhu Diao; Feihong Liu; Huan Wang; Wenjing Sang; Yalei Zhang

doi:10.1016/j.scitotenv.2022.157576

Transport characteristics of polystyrene microplastics in saturated porous media with biochar/Fe₃O₄-biochar under various chemical conditions

Sci Total Environ. 2022 Nov 15:847:157576. doi: 10.1016/j.scitotenv.2022.157576. Epub 2022 Jul 23.

Authors

Xiaoxia Wang¹, Yitong Dan¹, Yinzhu Diao¹, Feihong Liu¹, Huan Wang¹, Wenjing Sang², Yalei Zhang³

Affiliations

¹ Textile Pollution Controlling Engineering Center of Ministry of Environmental Protection, College of Environmental Science and Engineering, Donghua University, Shanghai 201620, China.
² Textile Pollution Controlling Engineering Center of Ministry of Environmental Protection, College of Environmental Science and Engineering, Donghua University, Shanghai 201620, China. Electronic address: wjsang@dhu.edu.cn.
³ College of Environmental Science and Engineering, Tongji University, Shanghai 200092, China.

PMID: 35882331
DOI: 10.1016/j.scitotenv.2022.157576

Abstract

Magnetically modified biochar, with a rougher surface and more positive surface charge, may interact with microplastics (MPs) after being applied to soil, potentially altering the fate and transport of MPs in porous media. In this study, the transport and retention behavior of polystyrene microplastics (PSMPs) in a sandy porous media mixed with biochar/Fe₃O₄ modified biochar (Fe₃O₄-biochar) was investigated under various chemical conditions (humic acid (HA), ionic strength (IS) and cationic types (Na⁺/Ca²⁺)). The results showed that the addition of biochar and Fe₃O₄-biochar can hinder the transport of PSMPs in porous media without HA, and that Fe₃O₄-biochar was more effective in inhibiting the transport of PSMPs through electrostatic adsorption and complexation, with an optimum retention efficiency of 92.36 %. HA significantly attenuated the retention of PSMPs in both porous media through electrostatic repulsion, steric resistance and competitive adsorption under 1 mM Na⁺ solutions, and the mobility of PSMPs in Fe₃O₄-biochar/sand was enhanced more significantly than in biochar/sand with the increase of HA concentration. IS significantly inhibited the transport of PSMPs in both porous media in the absence of HA, but there was an antagonistic effect of HA and IS on the transport of PSMPs in the presence of HA, with the facilitative effect of HA being stronger than the inhibitory effect of IS. Ca²⁺ was consistently more effective in inhibiting the transport of PSMPs than Na⁺ under all test conditions, and HA promoted the transport of PSMPs in all Na⁺ solutions, while it inhibited the transport of PSMPs in high IS (10 mM) with Ca²⁺ solutions. In addition, HA, Fe₃O₄-biochar and PSMPs tend to form larger aggregates under the complex interactions of Ca²⁺, leading to increased retention of PSMPs in porous media. The two-site kinetic retention models suggested that the retention of PSMPs in porous media with biochar was predominantly reversible attachment effect, while retention in porous media with Fe₃O₄-biochar was predominantly an irreversible straining effect.

Keywords: Cations; Fe(3)O(4)-biochar; Humic acid; Microplastics; Transport.

MeSH terms

Charcoal
Humic Substances / analysis
Microplastics*
Plastics
Polystyrenes*
Porosity
Sand
Soil

Substances

Humic Substances
Microplastics
Plastics
Polystyrenes
Sand
Soil
biochar
Charcoal