Microplastics are a pervasive environmental concern. Their widespread presence has prompted investigations into removal methods. This article explores current capabilities and approaches for filtering microplastics.
Understanding the Microplastic Challenge
Microplastics are tiny plastic particles, less than 5 millimeters. They originate from sources like breakdown of larger plastic debris, microbeads, and synthetic fibers. Common forms include fibers, fragments, beads, and pellets.
Filtering microplastics is challenging due to several factors. Their variable size, from millimeters to nanometers, means no single method captures all. Varying densities, buoyancy, and shapes also influence their interaction with filtration systems.
Their presence in diverse environments like drinking water, oceans, and wastewater requires distinct capture approaches. They are non-degradable and persist for centuries. This complicates removal, requiring tailored solutions.
Filtration Technologies and Approaches
Methods are employed or under development to filter microplastics from water. Technologies range from household to large-scale municipal systems. Effectiveness varies by microplastic characteristics and application.
Household-Level Solutions
Several household products reduce microplastic exposure in drinking water. Activated carbon filters, in pitcher and refrigerator filters, trap microplastics due to porosity and adsorption. While effective for many contaminants, their microplastic removal depends on the micron rating; a 5-micron filter removes some, but not all.
Reverse osmosis (RO) systems efficiently reduce microplastic levels. They force water through a semi-permeable membrane with tiny pores (0.0001-0.001 microns), blocking most microplastics and many nanoplastics. Some pitcher filters use membrane microfilters (0.2 microns), removing 99.999% of microplastics. Washing machine filters capture microfibers from synthetic clothing, preventing discharge into wastewater.
Wastewater Treatment Plants
Conventional wastewater treatment plants (WWTPs) use primary, secondary, and tertiary stages, removing 57% to over 99% of microplastics. Primary treatment, a physical separation, removes microplastics by density. Secondary biological treatment does not degrade microplastics.
Advanced treatment technologies achieve higher removal rates. Membrane filtration (MF, UF, NF, RO) is effective due to physical size separation. MF membranes (0.1-10 micrometers) and UF (0.01-0.1 micrometers) remove smaller microplastics, bacteria, and some viruses. NF and RO provide finer filtration, removing the smallest microplastics and dissolved compounds. Other methods include sand filtration for larger microplastics, and dissolved air flotation (DAF) where microbubbles float microplastics to the surface.
Emerging Technologies
Innovative methods improve microplastic removal. Acoustic separation uses sound waves to aggregate microplastics into larger, easier-to-filter clumps or separate them by size. Prototypes show potential for significant removal. Magnetic separation uses functionalized magnetic nanoparticles to bind to microplastics for magnetic retrieval. This achieves high separation efficiency for various sizes and polymer types. Advanced coagulation, using plant-based flocculants like okra and fenugreek, shows promise by clumping microplastic particles for easier removal.
Effectiveness and Limitations of Filtration
Filtration methods vary in success; complete elimination remains challenging, especially for the smallest particles. Advanced wastewater treatment (membrane bioreactors, rapid sand filtration, dissolved air flotation) achieves high removal, often exceeding 90%. Membrane bioreactors show removal rates up to 99.9%. Household RO systems also remove a broad range of microplastics, some certified to reduce them by 99.6%.
Despite advancements, removing ultra-fine and nanoplastic particles remains challenging. Nanoplastics, thousands of times smaller, can pass through cellular membranes and accumulate in tissues. While NF and RO capture many nanoplastics, complete removal is hard to verify due to testing limitations.
Widespread implementation of advanced filtration involves significant financial and logistical hurdles. Operational costs and maintenance, especially for fouling-prone membrane systems, can be substantial. Beyond removal, managing concentrated microplastic waste from filtration is a secondary problem. This waste needs proper disposal to prevent re-entry, highlighting the need for comprehensive waste management alongside filtration.