CIV342H1 Lecture Notes - Lecture 3: Sodium Carbonate, Hydraulic Head, Terminal Velocity
Document Summary
Conventional filtration: water passes through filter media by gravity. Filtration bed cleaned by backwash: reverse direction of flow, surface wash rotating jets, air scour. Need to decrease backwash flow over 3-4 steps to allow for restratification of filter media. Top = large media, bottom = small, dense media - large media (anthracite) has low density so that it stays at the top but also prevents smaller media from being washed out. Filter media needs to be sufficiently fine to prevent the passage of susp. solids, deep enough for long filter runs (don"t need to backwash so often), graded - coarse enough to allow space to retain floc. Need to track head loss through filter to determine when backwash needed (prevent air binding) Affected by: media size, filtration rate, temperature, density and size of susp. solids. Attachment mechanisms: electrostatic interactions, chemical bridging, specific adsorption. Affected by coagulant, water quality, filter media.
