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Typical pretreatment consists of:
- Coarse filtration (~80 micron) to remove large materials - City water has typically been filtered to meet this standard.
- Hypochlorite addition to reduce biofouling potential – City water has typically been treated by chlorine or chloramines for this purpose.
- Fine filtration using multimedia filters or clarification.
- Carbon Filter or Bisulfite addition to reduce remove residual free chlorine.
- Water Softener or Antiscalant to remove hardness and prevent scaling.
- Cartridge 5 Micron Sediment filter upstream of the feed pump and membranes Additional pretreatment considerations: Water with higher particle contents, measured by silt density index (SDI), require a higher degree of pretreatment to achieve acceptable quality. Systems using groundwater as the feed source frequently operate without hypochlorite and bisulfte addition. Waters with high hardness may require softening and/or acid addition. Activated carbon may be needed for water with high organic content.