Can You Filter Microplastics? Methods and Effectiveness

Microplastics can be filtered from water, and many existing treatment systems already do it surprisingly well. Municipal wastewater plants routinely remove upward of 95% of microplastic particles before discharge, and advanced drinking water facilities push that figure even higher. But the picture gets more complicated once you consider what sizes of plastic slip through, what happens to the captured particles, and whether your home faucet filter actually does anything useful. The answer depends on which water stream you care about, how small the particles are, and what technology is doing the work.

How Wastewater Treatment Plants Handle Microplastics

Most conventional wastewater treatment plants were never designed with microplastics in mind. They were built to handle sewage solids and dissolved pollutants. Yet the physical processes they already use, especially settling tanks and biological treatment stages, turn out to be quite effective at trapping plastic particles almost by accident. A study examining microplastics between 10 and 5,000 micrometers across multiple treatment stages found that primary treatment alone removed roughly 41–55% of particles, and the full treatment train achieved 96–99% removal efficiency.¹ Most of the captured microplastics end up concentrated in sewage sludge, which is the thick residual material separated during treatment.

That high removal percentage sounds reassuring until you consider volume. A mid-size treatment plant processes tens of millions of liters per day. Even if only 1–2% of microplastics escape, the absolute number of particles discharged into rivers or coastal waters can still be enormous. And fibers, the threadlike microplastics shed from synthetic clothing, are harder to catch than chunky fragments or beads. Research comparing membrane bioreactors with rapid sand filtration found both technologies removed over 95% of particulate-shaped microplastics, but only about 54–58% of fibers.² Fibers are long, thin, and flexible enough to snake through filter media that would easily block a similarly sized sphere or fragment.

Drinking Water Treatment and What Reaches Your Tap

Drinking water plants face a different challenge from wastewater plants. Their source water typically carries fewer microplastics to begin with, but the stakes are higher because everything that passes through ends up in someone’s glass. Fortunately, the combination of coagulation, sedimentation, and granular media filtration that most municipal water plants use is effective here too. A study across ten drinking water treatment facilities found removal rates above 97.5%, driven primarily by chemically assisted granular media filtration or ultrafiltration.³

Not every step in the treatment process pulls its weight equally, though. Coagulation and flocculation, where chemicals are added to clump small particles together, performs poorly against microplastics on its own. In one controlled study, the sedimentation rate for clean plastic particles after coagulation was below 2% across all sizes tested, and even with a chemical coagulant aid, the best result was only about 14% for mid-sized particles.⁴ The real workhorse is granular filtration, which caught between 87% and nearly 100% of particles depending on size. Particles larger than 100 micrometers were almost completely removed, but a dip in performance appeared around 10–20 micrometers, where removal dropped to about 87%.⁴ That gap matters because the smallest particles are the ones researchers worry about most in terms of potential health effects.

Activated carbon filters, which many plants use as a polishing step, add another layer of removal. The effectiveness of activated carbon depends heavily on particle size: larger microplastics get trapped more reliably, while the smallest ones can pass through at rates of up to about 50%.⁵ The surface condition of the plastic also matters. Microplastics that have been weathered or colonized by biofilms behave differently in filter beds than pristine particles straight from a laboratory.

Home Filters and Point-of-Use Devices

Even after municipal treatment, microplastics remain in finished drinking water at low concentrations. This has fueled a growing market in home filtration products marketed specifically for microplastic removal. Conventional drinking water treatment plants achieve roughly 70 to over 90% removal.⁶ Point-of-use devices like under-sink reverse osmosis units, countertop filters with activated carbon blocks, and pitcher-style filters can add an extra layer of protection.

The performance of these devices varies dramatically. Reverse osmosis systems are the most effective home option because their membranes have pore sizes small enough to block most microplastics, including many sub-micrometer particles. Carbon block filters tend to catch larger microplastics but let smaller ones pass. Standard pitcher filters using loose granular carbon are the least effective for this purpose; their primary design targets dissolved chemicals and taste, not solid particles. If you are specifically shopping for microplastic reduction at home, look for reverse osmosis or tight carbon block systems rather than basic pour-through pitchers. Third-party testing certifications like NSF/ANSI standards exist for contaminant reduction, though microplastic-specific standards are still catching up to the science.

Catching Microfibers at the Washing Machine

A large share of the microplastics entering wastewater in the first place comes from laundry. Every wash cycle sheds synthetic fibers from polyester, nylon, and acrylic clothing. One citizen-science project had volunteers use washing machine filters under normal laundry conditions over six months and found an average of about 4.6 milligrams of microfibers per liter of washing water, or about 61 milligrams per kilogram of washed garments.⁷ Those numbers might sound small, but over hundreds of loads a year, a single household can send a substantial mass of microfibers down the drain.

External lint filters and in-drum filtration bags intercept fibers before they reach the sewer system. France has already mandated that new washing machines include microfiber filters starting in 2025, and similar proposals are under discussion in other countries. The practical benefit is straightforward: capturing fibers at the source is cheaper and simpler than upgrading every wastewater plant. The filters themselves require periodic cleaning and eventual replacement, but the maintenance is minimal compared to the downstream benefit.

Stormwater Runoff, an Overlooked Pathway

Wastewater and drinking water get most of the attention, but stormwater runoff is another major route by which microplastics reach rivers, lakes, and the ocean. Rain washes tire-wear particles, road-marking fragments, and litter-derived plastics off streets and highways. This water usually flows directly into storm drains with little or no treatment.

Bioretention cells, sometimes called rain gardens, are one of the more promising low-tech solutions. These are shallow planted areas designed to absorb and filter stormwater as it percolates through layers of soil and gravel. A pilot study using 13 bioretention filters irrigated with highway stormwater found that all filters effectively removed microplastics larger than 10 micrometers, along with organic pollutants and most metals.⁸ A separate field study of a bioretention cell receiving urban stormwater measured an 84% drop in microparticle concentrations in the 106–5,000 micrometer range.⁹ These systems double as green infrastructure, managing flood risk and improving water quality at the same time, and they require no energy input beyond the force of gravity.

Chemical Coagulation as a Pretreatment Step

On its own, coagulation is not a great microplastic filter, as the drinking water research shows. But when used as a pretreatment step ahead of physical filtration or membrane separation, it can boost overall removal. The mechanism is relatively simple: a metal-salt coagulant like ferric chloride or polyaluminum chloride neutralizes the surface charge on plastic particles and bridges them together into larger clumps, or flocs, that are easier to settle or filter out.¹⁰

In wastewater applications where coagulation is used as a tertiary polishing step after biological treatment, the results are more impressive. One study testing several coagulants on secondary wastewater effluent achieved up to 99.4% microplastic removal, with ferric chloride and polyaluminum chloride outperforming polyamine-based chemicals.¹¹ The difference between coagulation’s poor standalone performance in clean source water and its strong results in wastewater likely comes down to the organic matter present in wastewater, which helps form denser, stickier flocs. The takeaway is that coagulation works best as part of a multi-step treatment chain, not as a standalone fix.

The Membrane Fouling Problem

Membrane filtration, including ultrafiltration, nanofiltration, and reverse osmosis, offers some of the tightest barriers against microplastics. Membranes with pore sizes smaller than the target particles should, in theory, block them completely. And in practice, they generally do. But membranes have an operational headache that gets worse when microplastics are involved: fouling.

Fouling happens when particles and organic matter accumulate on or within a membrane, reducing its flow rate and increasing the energy needed to push water through. Microplastics, because of their size and surface properties, can contribute to this buildup.¹² However, the picture is more nuanced than “plastics clog membranes.” One study comparing a membrane bioreactor receiving microplastic-laden water with a control found that the microplastic-exposed reactor actually had higher flux and lower fouling resistance. The microplastics were retained effectively by the membrane without worsening the fouling problem, likely because they changed the physical properties of the sludge cake on the membrane surface.¹³ So membrane fouling from microplastics is a real concern for system designers, but it does not appear to be a dealbreaker, and the interactions may even be favorable under some conditions.

Emerging Technologies Still in the Lab

Current filtration methods work reasonably well for microplastics, the particles larger than about one micrometer. Nanoplastics, the sub-micrometer fragments that are harder to detect and potentially more biologically active, are a different story. Most conventional filters simply cannot catch them. This has spurred research into novel materials and approaches.

One promising direction is biobased composite aerogels. Researchers designed a material combining cellulose nanofiber, chitosan, and graphene oxide into an aerogel with large, vertically aligned pores. In laboratory testing, this material captured polystyrene nanoplastics at close to 100% efficiency during seven hours of continuous flow, with an adsorption capacity of about 601 milligrams per gram of material, all while requiring extremely low pressure to operate.¹⁴ The “biobased” label matters here because it means the filter material itself is not adding to the plastic problem.

Electrospun nanofibrous membranes are another active area. These are ultra-thin mats of polymer nanofibers produced by an electrical spinning process. A recent design using poly(ethylene furanoate) and graphene oxide spontaneously forms a multilayer structure during fabrication, which simplifies manufacturing while providing tight filtration.¹⁵ These materials are still at the lab bench, but they point toward a future where nanoplastic removal becomes practical at scale.

Perhaps the most unconventional approach is acoustic focusing. Rather than passing water through any physical barrier, this technique uses sound waves to push microplastic particles toward the center of a flow channel, where they can be siphoned off. The system requires no filters, no chemicals, and no consumables. Early prototypes use stainless steel tubes and have demonstrated continuous, high-throughput separation in laundry effluent.¹⁶ Because there is nothing to clog, acoustic focusing could sidestep the fouling problem entirely, though it remains to be seen whether the approach can scale to the flow rates needed for municipal treatment.

Biological Filtration by Marine Organisms

Nature has its own microplastic filters: filter-feeding animals. Mussels, ascidians (sea squirts), oysters, and other organisms pump large volumes of water through their bodies to extract food, and microplastics come along for the ride. Mediterranean mussels, for example, rapidly clear microplastics from the water column regardless of particle size, ingesting and then excreting them in fecal pellets.¹⁷ Ascidians efficiently removed particles in the 2–5 micrometer range within just two hours of filtration in a laboratory setting.¹⁸

This is not a practical treatment method for your drinking water, obviously, but it has two important implications. First, dense populations of filter-feeders in harbors, estuaries, and aquaculture sites may already be acting as natural sinks for microplastics, shifting particles from the water column into sediment via fecal pellets. The ascidian research showed that egested pellets sank faster because of the plastic cargo, effectively pulling microplastics out of circulation in the water column.¹⁸ Second, it raises questions about eating shellfish from polluted waters, since the same organisms concentrating microplastics in their guts are the ones landing on dinner plates.

Why Measurement Is Part of the Filtration Problem

One underappreciated wrinkle in all of this: how you count microplastics changes the answer you get about how well filtration works. Different analytical techniques, such as infrared spectroscopy, laser-based detection, and thermal decomposition methods, can produce wildly different counts from the same sample. The wastewater study mentioned earlier found that its plant’s effluent contained either 1 particle per liter, 93 particles per liter, or 2 micrograms per liter of mass, depending on which analytical method was used.¹ That is not a rounding error; it is a difference of nearly two orders of magnitude in particle count.

The discrepancy arises because some techniques only detect particles above a certain size threshold, while others catch smaller particles but miss certain polymer types. Infrared spectroscopy, for instance, requires appropriate filter substrates to work across its full spectral range, and conventional filter materials can interfere with the measurements.¹⁹ This means that when one study reports 90% removal and another reports 99%, they may not be disagreeing about what the filter did. They may simply be measuring different things. Until analytical methods are standardized, comparing filtration performance across studies is a bit like comparing marathon times where every runner’s course is a different length.

Airborne Microplastics and Indoor Filtration

Most of the filtration conversation focuses on water, but microplastics are also suspended in the air you breathe. Synthetic textile fibers, tire dust, and degraded plastic packaging all contribute to airborne microplastic loads, both outdoors and inside buildings. Indoor concentrations tend to be higher than outdoor levels because of clothing, carpets, and upholstered furniture constantly shedding fibers in enclosed spaces.

HEPA filters, the same ones used to trap dust and allergens, are effective at capturing airborne microplastic particles. Their design targets particles down to 0.3 micrometers, which comfortably covers most airborne microplastics and even some nanoplastic-sized fragments. Portable air purifiers with HEPA filters are a straightforward way to reduce indoor airborne microplastic exposure, particularly in bedrooms and home offices where people spend long hours. The limitation, as with all physical filtration, is that HEPA filters do nothing about gaseous pollutants or the very smallest nanoscale particles. Research into nano-engineered and bio-engineered air filters is exploring whether next-generation materials can close that gap while maintaining acceptable airflow.

If you are trying to reduce your overall microplastic exposure, tackling both water and air pathways makes sense. A reverse osmosis system under the kitchen sink handles drinking water. A HEPA purifier in the bedroom handles airborne fibers while you sleep. Neither is perfect, and neither eliminates exposure entirely, but together they meaningfully reduce two of the largest routes of daily intake.

Where Captured Microplastics End Up

Every filtration system that successfully catches microplastics creates a secondary waste problem. Wastewater treatment plants concentrate captured plastics in sewage sludge, and when that sludge is applied to agricultural land as fertilizer, which is common practice in many countries, the microplastics go right back into the environment, just redistributed from waterways to soil. Washing machine lint filters accumulate a compressed wad of microfibers that typically goes into household trash and eventually a landfill. Membrane and granular filter systems require backwashing, which produces a concentrated waste stream of its own.

This is not a reason to stop filtering. Even imperfect capture and disposal is better than letting microplastics flow freely into aquatic ecosystems where they fragment further and become harder to manage. But it does mean that filtration alone is only part of the answer. Reducing the amount of plastic that sheds, wears, and fragments in the first place, through material design, product standards, and reduced use of single-use plastics, is the other half of the equation. A filter is a net, not a cure.