Bridging Filtration

Bridging filtration is a surface‑capture mechanism in which particles form self‑supporting bridges across pore openings, rapidly establishing a separation layer even when the largest particles are close to the pore size. Bridging is promoted by angular particle shape, narrow PSD near the cut‑off and surface finishes that favour initial adhesion. In practice it is the basis of precoat strategies (e.g., using diatomite or perlite) and explains why certain feeds reach specification quickly despite fine tails. Well‑managed bridging yields thin, permeable cakes with stable clarity; poorly controlled bridging transitions into standard or complete blocking as near‑cut particles lodge within pores. Engineers influence bridging by selecting mean‑flow pore size just below the modal feed size, conditioning the slurry to form rigid flocs, and operating with gentle ramps that avoid tearing early bridges. Monitoring the initial ∆p rise and filtrate clarity provides early confirmation that bridging—not deep blocking—is in control.