The pretreatment process aims to improve the quality of the raw water prior to the main treatment process. Pre-treatment chemicals seek to reduce the natural variations or extremes in water quality. Pre-treatment chemicals prepare the water for the main treatment process by changing the form of the hard to remove naturally occurring contaminants into easier to remove compounds. Chlorine Dioxide is added to aid removal of naturally occurring iron and manganese, which can color the water and stain fixtures like toilets.
Chemical coagulants like aluminum sulfate (or alum) are added to react with small clay and organic particles in the water to form larger particles heavy enough to settle out (“floc”). The alum has a charge opposite of the organic particles. When added to the water, it neutralizes the negative charge of the organic particles which allows them to stick together. After pre-treatment chemicals are added, the water flows into a splitter box which divides the water between sedimentation basins.
