The detection of plastic contamination in both tap and bottled water has prompted many to consider home filtration for cleaner drinking water. Tiny fragments of plastic, shed from various sources including clothing and the breakdown of larger waste, are now widely distributed in water sources globally. The fundamental challenge in filtering these particles is their extremely small size, which requires specific technologies to successfully capture them. This article explores the efficacy of current water filtration technologies in removing these microscopic contaminants.
Defining the Plastic Contaminants in Water
The plastic particles found in water are primarily categorized by their size, presenting different challenges for removal. Microplastics are defined as any plastic fragment less than 5 millimeters in length, down to 1 micrometer. These larger fragments originate from sources like the breakdown of plastic bottles and synthetic fibers from washing machines.
Nanoplastics are even smaller, with diameters less than 1 micrometer, and in some definitions, down to 100 nanometers or less. These minute particles are particularly concerning because their extremely small size allows them to behave differently in water and potentially cross biological barriers in the body. Nanoplastics are often the result of microplastics degrading further, making them harder to capture with conventional filtration.
Effectiveness of Standard Home Filters
Many consumers rely on standard home filtration systems, such as pitcher filters and faucet-mounted units, which typically use activated carbon. These filters are effective at improving water taste and odor by removing chlorine and larger suspended solids through adsorption and mechanical straining. However, their physical pore size is often too large to reliably capture the smallest plastic contaminants.
Most granular activated carbon filters can only strain particles down to about 5 micrometers, meaning they will only remove the larger range of microplastics. Carbon block filters, which are more compressed, may achieve filtration down to 0.5 micrometers, but still often allow nanoplastics to pass through. While these filters can remove a substantial portion of microplastics, they are not engineered to consistently handle the smallest fraction of plastic particles.
Boiling water cannot remove plastic contaminants. Boiling only causes water to evaporate, which concentrates any non-volatile contaminants like plastics, heavy metals, or pesticides left behind in the remaining water. Therefore, boiling water should not be considered a viable method for reducing plastic particle exposure.
Reverse Osmosis and Advanced Techniques
For the most effective removal of plastic contaminants, high-performance membrane filtration is required. Reverse Osmosis (RO) systems are considered the most effective home solution, forcing water through a semipermeable membrane that acts as an ultra-fine barrier. The pores of an RO membrane are incredibly small, often measuring around 0.0001 micrometers (or 0.1 nanometers).
This pore size is small enough to physically block the vast majority of both microplastics and nanoplastics, achieving removal rates that can exceed 99%. RO is a comprehensive purification method that also removes dissolved solids, heavy metals, and chemicals. It is often installed under the sink and paired with pre-filters, like sediment and carbon blocks, to protect the delicate membrane from clogging.
Other advanced techniques include Ultrafiltration (UF) and Nanofiltration (NF), which also utilize membrane technology. Ultrafiltration membranes typically have pore sizes ranging from 0.01 to 0.1 micrometers, effectively removing microplastics and some of the larger nanoplastics. Nanofiltration uses even tighter membranes, approaching the performance of RO, and is effective at removing contaminants in the lower nanometer range.
Large-Scale Water Treatment Strategies
Municipal water treatment plants are the first line of defense against contaminants, but they were not originally designed to target microscopic plastic fragments. The conventional treatment process relies on coagulation, flocculation, and sedimentation to remove suspended particles. Chemicals are added to clump small particles together, which then settle out or are caught by subsequent sand filters.
These conventional steps are effective at removing larger microplastics, often achieving removal rates of over 90%. However, the systems are less efficient at capturing the smallest plastic particles, particularly nanoplastics, which can remain suspended in the water. To improve efficacy, many municipal plants are exploring the adoption of advanced membrane technologies or tertiary treatments.
Advanced methods like membrane bioreactors or specialized high-rate filtration systems are being considered to improve the removal of the smallest contaminants. Incorporating these technologies would require significant infrastructure upgrades, but they represent the future of municipal water purification for comprehensive plastic contaminant removal.