Enhanced separation of microplastics using silanized sand
摘要
Sand filtration is one of the important unit operations at water and wastewater treatment plants contributing to the separation of microplastic contaminants. However, its performance against especially the smaller-sized microplastic particles is not satisfactory. In this study, this problem was addressed by developing an improved sand filtration media via silanization of quartz sand surface, using triethoxy(octyl)silane (CH3(CH2)7Si(OCH2CH3)3). This modification turns the sand surface hydrophobic and thus enhances the attachment of hydrophobic microplastic particles. The successful silanization of the sand surface was confirmed by infrared, nuclear magnetic resonance, and X-ray Photoelectron spectroscopy techniques as well as qualitative water contact angle assessment. Silanized sand was compared against regular sand as a filtration media in microplastics (polyethylene, size 53–63 μm) separation from water. Sand silanization enhanced the separation performance significantly: for 388 bed volumes of treated water (with an empty bed contact time of 15 min), microplastics removal performance remained at ⁓99% with modified sand whereas regular sand lost more than half of its separation efficiency after treating just 10 bed volumes of water. It was possible to eliminate the attached microplastics from the silanized sand with thermal treatment (500 °C for 3 h), after which the silanization can be reapplied to sand enabling repeated use. Partial detachment of the attached microplastics from the silanized sand was achieved by sonication. This study establishes proof of concept for the use of silanized sand as an effective filtration material for microplastics separation which would be easy to apply at any water or wastewater treatment plants already using sand filters.