New research from The University of Manchester shows that activated carbon and biochar, widely used in water treatment, can shed tiny particles that bind to contaminants and carry them through sand and membrane filters. In experiments, particle-bound lead made up 84.5% of remaining lead after fine-sand filtration for activated carbon, and up to 90.2% for corn straw biochar. This means standard dissolved-phase measurements may miss a large share of pollutants still moving through the system. The study, published in the journal Biochar, highlights co-transport: contaminants attach to microscopic carbon fragments that slip past filters designed to catch larger particles. Even after 0.45-micrometer membrane filtration, lead remained associated with particles in the 0.02 to 0.45 micrometer range. The authors suggest that water treatment performance should be assessed for both dissolved and particle-bound contaminant fractions. Practical countermeasures like pre-washing adsorbents, granulation, and improved coagulation are proposed for testing. The finding challenges the assumption that adsorption equals permanent removal, urging engineers and regulators to track residual carbon particles as carefully as the water itself.
