Microplastics are tiny plastic particles, generally less than 5 millimeters in length, found ubiquitously in natural environments. They originate from the breakdown of larger plastic items or are manufactured as small beads. Their widespread presence raises questions about filtering these particles from water and air.
Understanding Microplastics and Filtration Difficulties
Microplastics encompass a diverse range of plastic particles, typically ranging in size from 1 micrometer to 5 millimeters. They can appear as fragments from degraded plastic products, fibers shed from textiles, or pellets used in industrial manufacturing. This variability in size and form presents a significant challenge for filtration systems.
The irregular shapes and diverse chemical compositions of microplastics further complicate their removal. Unlike uniform particles, microplastics can be jagged, fibrous, or spherical, affecting how they interact with filter media. Their wide array of polymer types, such as polyethylene, polypropylene, and PET, means they have differing densities and surface properties. These characteristics influence their behavior in water and air, making a single, universally effective filtration method difficult to achieve.
Microplastics are present across many environments, including water sources, air, and even soil. Their pervasive nature means filtration solutions must be adaptable to different mediums and concentrations. The continuous introduction of new microplastics into the environment also contributes to the ongoing challenge of their removal.
Filtering Microplastics in Drinking Water
Filtering microplastics from drinking water at home involves several common systems, each with varying degrees of effectiveness. Activated carbon filters, often found in pitcher filters, faucet attachments, and whole-house systems, work by adsorbing contaminants onto their porous surface. While effective at removing chlorine and some organic chemicals, their ability to capture microplastics depends heavily on the particle size and the filter’s pore structure. Most activated carbon filters can remove larger microplastic particles, but very small ones may pass through.
Reverse osmosis (RO) systems offer a more thorough filtration method by forcing water through a semi-permeable membrane. This membrane has extremely small pores, typically around 0.0001 microns, which are capable of rejecting a high percentage of dissolved solids and particles, including most microplastics. RO systems are highly effective at removing microplastics across a broad size range. However, these systems are slower, produce wastewater, and require regular membrane replacement.
Ultrafiltration (UF) systems use membranes with slightly larger pores than RO, usually between 0.01 and 0.1 microns. These systems can effectively remove suspended solids, bacteria, viruses, and most microplastics from water. UF systems are generally more efficient than activated carbon filters for microplastic removal and do not produce wastewater like RO systems. The effectiveness of UF depends on the specific pore size of the membrane, with smaller pores offering better microplastic retention.
Filtering Microplastics in Air
Airborne microplastics, particularly fibers shed from clothing and textiles, are a growing concern in indoor environments. High-Efficiency Particulate Air (HEPA) filters are widely used in air purifiers and vacuum cleaners to capture these particles. HEPA filters are designed to capture at least 99.97% of particles that are 0.3 micrometers in diameter. This efficiency means HEPA filters are highly effective at trapping microplastic fibers and fragments that typically range from a few micrometers to several millimeters in size.
HEPA filters employ a dense mat of fibers to trap particles through a combination of impaction, interception, and diffusion. Regular replacement of HEPA filters is necessary to maintain their efficiency and prevent the re-release of captured particles.
Heating, ventilation, and air conditioning (HVAC) systems also incorporate filters that can capture airborne microplastics. These filters are rated using the Minimum Efficiency Reporting Value (MERV) system, with higher MERV ratings indicating greater filtration efficiency. Filters with a MERV rating of 13 or higher are recommended for improved removal of smaller particles, including many microplastics.
Large-Scale and Developing Filtration Technologies
Wastewater treatment plants play a significant role in attempting to remove microplastics before water is discharged into natural bodies. Conventional primary and secondary treatment processes, which involve physical separation and biological degradation, can remove a substantial portion of microplastics, often between 70% and 90%. However, a considerable amount of smaller particles still pass through these stages, contributing to environmental contamination.
Tertiary treatment methods significantly enhance microplastic removal efficiency in municipal wastewater. Technologies such as membrane bioreactors (MBRs) combine biological treatment with membrane filtration, offering high removal rates for microplastics due to their fine pore sizes. Sand filtration, another tertiary treatment, can also capture a significant percentage of microplastics by trapping them within the granular media. These advanced treatments are not universally implemented but are gaining traction for their improved contaminant removal capabilities.
Beyond established methods, researchers are exploring innovative technologies for microplastic filtration. Advanced oxidation processes (AOPs), which use highly reactive hydroxyl radicals to break down contaminants, show promise in degrading plastic polymers into less harmful substances. Magnetic separation involves using magnetic materials to bind to microplastics, allowing them to be easily removed with magnetic fields. These cutting-edge approaches are currently in various stages of research and development, aiming to provide more comprehensive solutions for microplastic removal from large volumes of water.