During challenging treatment problems such as algal blooms and pond turnover events, the strained water is pre-treated to improve removal of impurities and maintain the production of the high-quality water. The amount or need for “pretreatment” varies significantly and therefore pretreatment chemicals are added to the process only where needed.
The entire Direct Filtration treatment process utilizes only those chemicals which are approved for use in drinking water by NSF International. The two pretreatment techniques periodically used are; chemical oxidation and adsorption. Potassium Permanganate chemical is sometimes added to break down (oxidize) tough to remove impurities so that they might be transformed to less problematic ones or those that might be removed in the remaining treatment processes.
Powdered Activated Carbon (PAC), specific types of wood ash treated to very high temperature, may be added during algal blooms to remove (adsorb) tastes and odors that can produce unpleasant water quality. Adding PAC is one of the most common techniques used to remove taste and odors because it is non-specific in adsorbing a broad range compounds that produce taste and odors. These pretreatment processes either destroy the problematic compounds or greatly improve the ability to remove them in the next steps of the treatment process.