Roughing Filtration.
https://www.emergency-wash.org/water/en/technologies/technology/roughing-filtration
👉🏼 PDF: https://app.box.com/s/24bsq9g7cfqapraje6loq929wjk3q12q ___ A Roughing Filter is used to remove suspended solids from very turbid (or muddy) water using differently sized filtration media ranging from coarse to fine gravel. It is a pre-treatment step prior to a final disinfection process, such as Chlorination T.6 , Slow Sand Filtration T.9 or Ultrafiltration T.10 . It can be used in the stabilisation and recovery phases of an emergency.