Coming out in the wash

摘要

Drinking water treatment typically includes the stages of pre-treatment, flocculation, sedimentation, filtration, adsorption and disinfection. The key stage of filtration is a final step to remove the remaining suspended solids and any unsettled flocculants after the sedimentation stage. The standard filtration process is based on rapid sand filtration. Also now widely used is the newer membrane filtration process, which has the capability of removing virtually all particles larger than 0.2μ. Sometimes they are used in tandem, with sand filters removing coarser particles and membrane filtration for the final removal.